José Antonio Pérez Agúndez

Sarra Chenouf
email: sarra.chenouf@univ-brest.fr

Pascal Raux
email: pascal.raux@univ-brest.fr

Addressing the Governance of Harmful Algal Bloom Impacts: A Case Study of the Scallop Fishery in the Eastern French Coasts of the English Channel

Keywords: HAB, governance, management, monitoring, bans, toxicity, Giant Scallop, fishing activity

Harmful Algal Blooms (HAB) are phenomena that result from alterations to ecosystems. Due to their potential toxicity, the level of danger depends on the species concerned, their frequency and intensity. They can cause impacts on biodiversity and on the anthropic activities that take place in maritime and coastal areas. Primary industries such as shellfish fisheries are mainly affected. To deal with this issue, the French administration has built a governance system based on two pillars. The first relies on a water quality monitoring system that assesses the risks of HAB contamination of coastal waters. The second is a regulatory system of production and commercial bans of seafood products from the impacted areas. This public action has two objectives. The first is human health-related and aims to protect consumers of seafood. The second is economic-based and aims to minimize the economic impacts associated with the commercial bans suffered by the businesses concerned. These two objectives may appear to be antagonistic. Using the case study of the French scallop fishery in the eastern Channel and based on an analysis of the commercial bans associated with HAB and associated potential economic impacts, this paper analyses the governance scheme dealing with HAB events in France. The authors highlight that this governance is not only a matter of applying administrative closures when toxicity thresholds are exceeded, but is a dynamic decision-making process involving experts and the Administration that attempts to balance acceptable health risks and economic impacts.

Introduction

Harmful algal blooms (HAB) are phenomena that result from imbalances in ecosystems due to natural processes or anthropogenic effects [START_REF] Zingone | The diversity of harmful algal blooms: A challenge for science and management[END_REF]. They are highly complex processes that are difficult to predict. Under certain conditions, these microalgae release toxins that can have negative impacts on aquatic biodiversity [START_REF] Anderson | Approaches to monitoring, control and management of harmful algal blooms (HAB)[END_REF]. Beyond the ecological considerations, these events can also generate economic and social impacts of a different nature. HAB can thus lead to human health issues through the ingestion of contaminated seafood leading to nausea and vomiting to more severe symptoms such as paralysis and amnesia, or by direct exposure to contaminated waters causing respiratory disturbances due to inhalation of aerosols or skin irritations [START_REF] Masó | Harmful microalgae blooms (HAB); problematic and conditions that induce them[END_REF][START_REF] Wiśniewska | The importance of cyanobacteria and microalgae present in aerosols to human health and the environment-Review study[END_REF]. In order to preserve human health and reduce the associated health costs, access bans to affected areas and commercial bans on shellfish production are usually decreed by the Administration. These bans can also lead to economic impacts on marine and coastal regions, and fishing and aquaculture are among the most exposed sectors. These impacts are related to deferred sales, loss of biomass and the additional costs associated with adaptation strategies to limit the consequences of HAB [START_REF] Moore | Harmful Algal Blooms: Identifying Effective Adaptive Actions Used in Fishery-Dependent Communities in Response to a Protracted Event[END_REF]. Other activities may be affected such as recreational fishing [START_REF] Anderson | Recreational Demand for Shellfish Harvesting Under Environmental Closures[END_REF], beach walking or bathing. In addition to the loss of amenity for recreational activities, HAB can also cause economic impacts on local and regional economies [START_REF] Larkin | Harmful Algal Blooms and Coastal Business: Economic Consequences in Florida[END_REF][START_REF] Dyson | Regional economic impacts of razor clam beach closures due to harmful algal blooms (HABs) on the Pacific coast of Washington[END_REF]. Moreover, management and monitoring expenses to prevent or cope with HAB also represent a social cost [START_REF] Hoagland | The economic effects of harmful algal blooms in the United States: Estimates, assessment issues, and information needs[END_REF][START_REF] Sanseverino | eu%2Frepository%2Fbitstream% 2FJRC101253%2Flbna[END_REF].

Assessing the impacts associated with HAB is complex due to the heterogeneity, availability and quality of information related to the impacted activities. The economic impacts of HAB are difficult to compare due to the diversity of these events, their frequency, intensity, spatial distribution, the diversity of activities affected and the socio-cultural and institutional contexts [START_REF] Sanseverino | eu%2Frepository%2Fbitstream% 2FJRC101253%2Flbna[END_REF]. According to Bernard et al. [START_REF] Bernard | Developing global capabilities for the observation and prediction of harmful algal blooms[END_REF], the annual costs associated with HAB events solely in marine areas that are related to research, monitoring and mitigation activities are in the order of USD 55 million in the USA, USD 850 million in Europe and nearly USD one billion in Japan. Although it is interesting for accounting purposes to highlight the importance of these events, the single and aggregated monetary valuation of the impacts associated with HAB is of little interest regarding the decision-making process. How impacts are distributed among stakeholders and within activities tells much more in terms of coping and mitigation strategies.

The mechanisms that are implemented to respond to these phenomena are part of the management or governance of HAB [START_REF] Anderson | Approaches to monitoring, control and management of harmful algal blooms (HAB)[END_REF]. The complexity this governance is related to the lack of accurate models to predict their trends and occurrences and, therefore, to anticipate their effects. In this context, Zingone and Enevoldsen [START_REF] Zingone | The diversity of harmful algal blooms: A challenge for science and management[END_REF] question the practical modes of action to be implemented in terms of marine resource management, protection of dependent economic activities, health protection, and anthropogenic actions likely to engage efficient responses against HAB impacts.

In terms of practical governance actions, there are three main types of possible responses to HAB events [START_REF] Anderson | Approaches to monitoring, control and management of harmful algal blooms (HAB)[END_REF]. The first is mitigation which refers to using all available means to reduce the negative effects associated with HAB. This includes establishing monitoring systems to safeguard human health, avoiding or reducing the impacts, avoiding biomass kills and improving knowledge to enhance the ability to predict these events [START_REF] Heil | Monitoring, management, and mitigation of Karenia blooms in the eastern Gulf of Mexico[END_REF]. In the case of aquaculture, individual mitigation responses may rely on towing of fish cages [START_REF] Zingone | The diversity of harmful algal blooms: A challenge for science and management[END_REF], safeguarding in storage tanks or detoxifying contaminated products [START_REF] Anderson | Monitoring and Management Strategies for Harmful Algal Blooms in Coastal Waters[END_REF][START_REF] Pérez Agúndez | Technological Adaptation to Harmful Algal Blooms: Socioeconomic Consequences for the Shellfish Farming Sector in Bourgneuf Bay (France)[END_REF]. The adoption of these different options depends on the costs associated with their implementation and the capacity of stakeholders to fund them. In the case of fisheries, responses from companies to avoid or to reduce economic impacts rely on moving to other uncontaminated fishing areas, diversifying fishing activity to other species that are not affected by HAB or transferring activity to other businesses. These different responses depend on the capacity of companies to adapt according to the economic gain associated with each option.

The second type of action concerns anticipatory prevention rather than post-crisis adaptation. This type of action involves implementing measures capable of reducing problems at the source in order to reduce the intensity and frequency of HAB. Although modelling of these phenomena is not yet reliable [START_REF] Zhu | Understanding the blob bloom: Warming increases toxicity and abundance of the harmful bloom diatom Pseudo-nitzschia in California coastal waters[END_REF], some works have progressed on identifying factors that can exacerbate the occurrence of HAB [START_REF] Thorel | Nutrient ratios influence variability in Pseudo-nitzschia species diversity and particulate domoic acid production in the Bay of Seine (France)[END_REF]. Prevention via integrated coastal zone management processes to improve water quality is, therefore, a means of combating HAB by reducing anthropogenic pressures on ecosystems from the agricultural sector, coastal economic activities or urban pollution rather than engaging in extensive restoration efforts [START_REF] Brooks | Are harmful algal blooms becoming the greatest inland water quality threat to public health and aquatic ecosystems?[END_REF]. These measures have results only in the long term.

Finally, the third type of measure concerns control. These are curative measures implemented after the impact. They aim to compensate HAB effects by various means, mechanical, biological, chemical, genetic and environmental [START_REF] Anderson | Approaches to monitoring, control and management of harmful algal blooms (HAB)[END_REF][START_REF] Kim | Mitigation and controls of HAB[END_REF]. However, they are controversial due to the consequences they may have for biodiversity in the water column and on the seabed [START_REF] Anderson | Approaches to monitoring, control and management of harmful algal blooms (HAB)[END_REF].

In the case of France, the governance of HAB impacts aims to protect consumers of seafood and refers to the European regulatory framework. The main regulations concern (1) the specific hygiene rules applicable to food products of animal origin [START_REF]Regulation (EC) No 853/2004 of the European parliament and of the council of 29 April 2004 laying down specific hygiene rules for food of animal origin[END_REF], with a specific chapter applicable to live bivalve molluscs which details the toxicity thresholds of marine biotoxins that must not be exceeded and (2) the organization of controls on food products of animal origin intended for human consumption [START_REF]Regulation (EC) No 854/2004 of the European Parliament and of the Council of 29 April 2004 laying down specific rules for the organization of official controls on products of animal origin intended for human consumption[END_REF], including the construction of monitoring systems, the description of sampling to be implemented for sensitive areas and the modalities of the closure of areas contaminated by HAB. Three specific groups of toxic microalgae are monitored through these directives: Dinophysis (which produces diarrethic toxins), Pseudo-nitzschia (amnesia toxins), and Alexandrium (paralytic toxins). While regulations dealing with HAB are built at the national level, the structure of this governance differs according to the species at local or regional levels. The organization of public governance is led by the territorial Administration (Direction Départementale des Territoires et de la Mer-DDTM) with the support of scientific expertise provided by IFREMER (the French Institute for Ocean Science).

More specifically, this paper focus on the French scallop fishery operating in the eastern English Channel area due to the socio-economic importance of this activity and its high potential for exposure to HAB. This maritime area has experienced changing HAB dynamics to which monitoring strategies, management measures and governance structure have had to adapt [START_REF] Chenouf | Caractérisation des Impacts des Efflorescences Algales Nuisibles en Manche. Application au cas de la Pêcherie de Coquilles Saint-Jacques de la Manche Est[END_REF]. Before 2012, management focused on local scales and measures were applied to small areas. In 2012, the scallop production zones (Figure 1), that rely on particular located stocks of scallop were created following the major ASP (Amnesic Shellfish Poisoning) crisis that affected the entire eastern Channel area. In order to reduce the economic impact on the fishing sector, this zoning aimed at dividing the maritime space in order to control the production areas more finely so that only the areas affected by HAB were closed. A balance must, therefore, be found between the effectiveness and the cost of monitoring since applying controls and closures over smaller areas reduces the number of vessels concerned but increases the monitoring costs. After 2012, the monitoring locations and sampling have also been modified to determine the level of toxicity by production area. Since 2016, the measures for closing production areas have evolved, with a particular focus on the expected evolution of blooms and not only on the toxicity levels measured by in situ analyses. This has led to the implementation of precautionary closures in the case of detection of phycotoxins and depending on the phytoplankton biomass observed. Some areas may be thus closed for some concentrations under the regulatory thresholds, and this is known as the half-threshold (80 µg/kg instead of 160 µg/kg for Diarrhetic Shellfish Poisoning toxins (DSP) and 10 mg/kg instead of 20 mg/kg for Amnesic Shellfish Poisoning toxins (ASP)). This measure is implemented after consultation with experts from IFREMER and depending on the particular conditions of each event. The objective of such a measure is to avoid ex post closures when future toxicity is expected, which may result in the sale of batches of shellfish that have been contaminated but whose control result has been obtained late. This is of particular concern to producers because, in the event of a batch being recalled, the company has to take responsibility for the whole operation, i.e., finding the batch already sold, ensuring its destruction and cancelling the sale or even reimbursing the buyer. This operation is costlier for companies, which would prefer to solely suffer a closure than be forced to manage batch recall operations.

Since 2018, each administrative department must therefore organize and manage the phytoplankton and phycotoxins monitoring programs. For the scallop fishery, the Interregional Directorate for the Sea-East Channel, North Sea (DIRM-MEMN) is in charge of the entire monitoring and management procedures in this area, from observation to decision-making. This Administration, therefore, (1) manages the sampling protocols with approved laboratories to carry out the sampling and analysis of phycotoxins, and then (2) determines the appropriate management measures. For other professional activities, DDTMs ensure the monitoring and management of production areas in close collaboration with the regional health agencies (ARS), which are in charge of the monitoring for recreational activities.

This paper discusses the governance of HAB impacts in France as a decision-making process that engages stakeholders in a framework with two potentially contradictory objectives: minimizing health risks and minimizing economic impacts of the affected activities. The analysis conducted is focused on the example of HAB management in the scallop fishery on the eastern French coasts of the English Channel. To analyze this gover-nance, this work focuses on the dynamics of fishing area closures based on the analysis of historical data from the REPHY ("REseau d'observation et de surveillance du PHYtoplancton") and REPHYTOX ("REseaux de surveillance des PHYcoTOXines dans les organismes marins") networks, the two French national monitoring networks for phytoplankton and phycotoxins [START_REF] Belin | Trente Années D'observation des Micro-Algues et des Toxines D'algues Sur le Littoral[END_REF]. The analysis of the structure and organization of the monitoring and management of HAB allowed the identification of the stakes and the strategies that guide the Administration's decision-making processes in the event of a HAB. This analysis of how decisions are made will lead to a better understanding of the governance gaps in achieving public policy goals related to the sustainability of social ecological systems affected by HAB. Since 2018, each administrative department must therefore organize and manage the phytoplankton and phycotoxins monitoring programs. For the scallop fishery, the Interregional Directorate for the Sea-East Channel, North Sea (DIRM-MEMN) is in charge of the entire monitoring and management procedures in this area, from observation to decision-making. This Administration, therefore, (1) manages the sampling protocols with approved laboratories to carry out the sampling and analysis of phycotoxins, and then (2) determines the appropriate management measures. For other professional activities, DDTMs ensure the monitoring and management of production areas in close collaboration with the regional health agencies (ARS), which are in charge of the monitoring for recreational activities.

This paper discusses the governance of HAB impacts in France as a decision-making process that engages stakeholders in a framework with two potentially contradictory objectives: minimizing health risks and minimizing economic impacts of the affected activities. The analysis conducted is focused on the example of HAB management in the scallop fishery on the eastern French coasts of the English Channel. To analyze this governance, this work focuses on the dynamics of fishing area closures based on the analysis of historical data from the REPHY ("REseau d'observation et de surveillance du PHYtoplancton") and REPHYTOX ("REseaux de surveillance des PHYcoTOXines dans les organismes marins") networks, the two French national monitoring networks for phytoplankton and phycotoxins [START_REF] Belin | Trente Années D'observation des Micro-Algues et des Toxines D'algues Sur le Littoral[END_REF]. The analysis of the structure and organization of the monitoring and management of HAB allowed the identification of the stakes and the strategies that guide the Administration's decision-making processes in the event of a HAB. This analysis of

Materials and Methods

This work focuses on the French eastern coasts bordering the English Channel, from the Pas-de-Calais Strait in the east to the Anglo-Norman Gulf in the West, bordering Brittany. This area covers the coasts of two administrative regions: Hauts-de-France and Normandy (See Figure 1). The geographical location of the English Channel and its morphological, hydrological and biological characteristics create the conditions for an area rich in biodiversity and economic activities [START_REF] Carpentier | Atlas des Habitats des Ressources Marines de la Manche Orientale-CHARM II, Channel Habitat Atlas for marine[END_REF][START_REF] Dauvin | The English Channel: La Manche[END_REF]. This area is significantly affected by HAB events with potentially important economic and social impacts [START_REF] Husson | Two decades of Pseudo-nitzschia spp. blooms and king scallop (Pecten maximus) contamination by domoic acid along the French Atlantic and English Channel coasts: Seasonal dynamics, spatial heterogeneity and interannual variability[END_REF]. It has experienced several toxic bloom events over the last thirty years, with toxicity and contamination crises by ASP and DSP affecting several shellfish species, mainly scallops (Pecten maximus). In addition, this area has long been affected by other harmful non-toxic algal blooms, such as Phaeocystis and Karenia mikimotoi, which produce scum that can cause mortality of marine animals by anoxia [START_REF] Napoléon | Dynamics of phytoplankton diversity structure and primary productivity in the English Channel[END_REF][START_REF] Lefebvre | Trajectories of Changes in Phytoplankton Biomass, Phaeocystis globosa and Diatom (incl. Pseudo-nitzschia sp.) Abundances Related to Nutrient Pressures in the Eastern English Channel, Southern North Sea[END_REF].

The analysis of governance of HAB impacts in this paper is based on a quantitative analysis aiming at understanding the basis of administrative decisions regarding commercial bans associated with HAB events in the French eastern English Channel. The management area is divided into 17 zones based on scallop beds, and resource management, monitoring and administrative decisions are based on this zoning.

The analysis is based firstly on a study of the evolution of scallop toxicities in the area in order to translate them into theoretical closures. The theoretical closure of a production area is the administrative decision that should be taken when toxicity concentrations of the water or shellfish flesh analyzed at a control point exceed the regulatory thresholds defined by the European regulation [START_REF] Chenouf | Determination of scallop production areas closures due to phycotoxins along the Eastern English Channel using data from REPHY and REPHYTOX monitoring networks[END_REF]. These theoretical closures are then compared with the actual observed closures that occurred by administrative decree. When the concentration of toxins does not exceed the regulatory thresholds, the area should theoretically remain open.

The comparison between theoretical and observed closures was made on cumulative annual durations of closures per area and per fishing season from 2012 to 2019. More recent years were not considered due to the lack of data about localized closures as there is no centralized management nor data collection of observed closures. A more detailed analysis of closures data (theoretical and observed) was also conducted for weekly data between October 2012 and May 2015 to better understand the observed discrepancies between theoretical and effective closures in production areas 9 and 12. These two production areas were chosen as they are important and frequently used fishing areas, and also because they appear to have a higher risk of blooms and phycotoxin contamination. As a consequence, they support the analysis of the decision-making process regarding closures and illustrate the global functioning of governance. To that purpose, the interpretation of the discrepancy between theoretical and observed closures is used to explain the different governance strategies.

The data used in this analysis are of a varying nature and come from various sources. Data on the actual administrative closures of scallop production areas were collected from the DIRM-MEMN. This database provides details about the date and duration of closures in number of days for each production area and by fishing season from 2012 to 2019.

This period was characterized by numerous HAB events. Table 1 shows the heterogeneity of HAB risk in this marine area, both in space and time. Some fishing areas are not subject to HAB. On the other hand, others such as Areas 9 and 12, had numerous closures during the period observed. While toxic blooms resulting in closures are observed every year, there is no clear trend. A longer data set would be needed to verify a potential trend, but the closures do not appear to follow any particular cycle.

Theoretical closures were simulated using (1) the REPHY-REPHYTOX national monitoring network using data about scallop phycotoxin contamination, (2) the calendar of scallop fishing operations in the eastern Channel, and (3) regulations that define the toxicity thresholds not to be exceeded and the conditions for closing and opening the production areas. Utilizing these information sources made it possible to build a new database on theoretical closures based on the toxicity levels revealed by the in situ analyses [START_REF] Chenouf | Determination of scallop production areas closures due to phycotoxins along the Eastern English Channel using data from REPHY and REPHYTOX monitoring networks[END_REF]. Data processing enabled the creation of a calendar of closures/openings using a binary coding (0 and 1) that compares the results of shellfish toxicity tests to the regulatory thresholds. A "0" represented data below or equal to the thresholds and openings, and "1" represented non-compliant analysis results (results above the thresholds) that led to access bans on fishing areas. This calendar was then used to simulate the number and duration of closures of production areas according to the following rule: if the results of the phycotoxicity tests are non-compliant, the areas concerned are closed. According to the regulations in force, these areas are only reopened after two successive compliant test results, i.e., results below or equal to the regulatory thresholds. The algorithm programmed under the R software analyses the REPHY-REPHYTOX database, line by line [START_REF] Chenouf | R code to simulate closures of scallops fishing areas due to harmful algal blooms (Theoreticalclosures)[END_REF]. This analysis is complemented by indirect qualitative information on HAB management strategies obtained from stakeholders via face-to-face interviews.

Results

Analysis of Scallop Toxicity by Phycotoxins and the Rational of Commercial Bans

Figure 2 provides an overview of phycotoxin concentrations in scallops over the last ten years. This historical view highlights trends over two different time periods. The first is characterized by ASP toxin contamination due to the development of the Pseudo-nitzschia group between January 2012 and May 2014, which resulted in long closures of production areas due to slow natural detoxification of the shellfish. The second period from the beginning of the 2014-2015 fishing season was dominated by contamination by DSP toxins released by the genus Dinophysis. This period is more characterized by shorter periods of toxicity with higher frequencies in contrast to the ASP contaminations.

This shift is likely related to the diversity of phytoplanktonic species, and thus toxin production, which varies annually, and the level of cellular toxicity of each species for which environmental conditions, particularly nutrient ratio, play an important role [START_REF] Thorel | Nutrient ratios influence variability in Pseudo-nitzschia species diversity and particulate domoic acid production in the Bay of Seine (France)[END_REF]. The composition of the Pseudo-nitzschia phytoplanktonic group in 2012-2013, which is characterized by highly toxic species (the broad-celled species such as P. australis), is different from the composition observed since 2014, which is probably characterized by non-toxic species (in general, the group of fine-celled species). There is a succession of species, both toxic and non-toxic, within the Pseudo-nitzschia group but the dynamics of this diversity remain difficult to explain due to the complex nature of algal blooms and the lack of sufficient data sets [START_REF] Thorel | Nutrient ratios influence variability in Pseudo-nitzschia species diversity and particulate domoic acid production in the Bay of Seine (France)[END_REF]. This shift could also be explained by the changes in environmental conditions that seem, on the one hand, not favorable to the development of toxic species of Pseudo-nitzschia or to the production of toxins. On the other hand, these conditions boost the development of the Dinophysis group and the resulting increase in DSP toxicities. Concerning PSP toxins, their concentrations in scallops have never reached the regulatory threshold in the eastern Channel. This shift is likely related to the diversity of phytoplanktonic species, and thus toxin production, which varies annually, and the level of cellular toxicity of each species for which environmental conditions, particularly nutrient ratio, play an important role [START_REF] Thorel | Nutrient ratios influence variability in Pseudo-nitzschia species diversity and particulate domoic acid production in the Bay of Seine (France)[END_REF]. The composition of the Pseudo-nitzschia phytoplanktonic group in 2012-2013, which is characterized by highly toxic species (the broad-celled species such as P. australis), is dif- The diversity of HAB represents a considerable challenge for the management to adapt over time to the dynamics of environmental conditions and blooms. Figure 3 underlines the dependence of the fishery management system on the changes and dynamics of HAB and their toxicities illustrated by the two examples of production areas 9 and 12. The results show some inconsistencies between the degree of toxicity and administrative decisions. Closures (represented by a pink background color) were observed when some toxicity results were below the regulatory thresholds (red line on Figure 3). Conversely, some toxicity results were not compliant with regulatory thresholds but the zones remained open. These results show two scenarios in the management of closures. The first is a situation of "normality" when there is a match between the estimated theoretical closure and the administrative decision. This is often the case when toxin concentrations are not subject to interpretation. Thus, if toxin concentrations are far above regulatory thresholds or persist over time, an area must be closed. This was the case in 2012 and 2013 when episodes of ASP were observed and led to numerous closures in Zone 9 and 12. While toxin concentrations were far below regulatory thresholds, these areas remained open to fishermen.

Commente

The second scenario concerns more questionable situations, where the toxicity levels of the analyses are between the regulatory thresholds and the half-thresholds. As mentioned earlier, these half-sets were established with the agreement of the fishery sector to avoid costly batch recalls. The interpretation of each situation leads to a decision in favor of opening or closing the area. This is the case, for example, of these two areas 9 and 12 for the period between June and November 2013. In Figures 3 and4, red dots are plotted corresponding to analyses of the three toxins that describe a situation of theoretical closure, where concentrations exceed regulatory half-thresholds, but these fishing areas remained open. Conversely, in Area 12, between November and December 2013, the observed toxins concentrations were below regulatory thresholds but the area remained closed. This was also the case for the closures observed in early 2015 in these two areas while concentrations were close to the half threshold but still below the regulatory threshold. The discrepancy between the decision that should have been applied following the toxicity analyses and the final decision to open or close a production zone underlines that decision is, therefore, not always the result of a simple protocol.

Comparison between Theoretical and Observed Closures for the Whole Period and Production Areas

The comparison between the theoretical closures and observed administrative closures was carried out for all the production areas between 2012 and 2019. This comparison again highlighted discrepancies between the durations of the two closures as shown in Figure 5. The results of these analyses provided a complementary vision of management measures in order to better handle economic and social issues associated with HAB.

The retrospective analysis of REPHY-REPHYTOX data and administrative decisions on closures during the period analyzed highlights two cases. The first concerns the underestimation of the duration of theoretical closures compared with observed closures (7% of cases). The production areas can be closed if phycotoxin levels in shellfish are below the regulatory thresholds. As previously explained, these are precautionary closures before the results of the analyses are obtained, or closures at the half-threshold (80 µg/kg for lipophilic toxins (DSP), and between 10 and 16 mg/kg for ASP). Other reasons for the discrepancies between theoretical and observed closures are related to the absence of shellfish samples or the absence of phycotoxin analysis results. These absences are due to difficulties in accessing the sampling areas (e.g., bad weather conditions), problems related to the analysis themselves (transport issues, loss of samples) or disinterest in sampling an area of lower economic importance at some point in the season. A lack of sampling represents 72.34% of the cases of underestimation of theoretical closures compared with the observed closures. Other management strategies including the implementation of a rest periods to protect the scallop stock can also explain the underestimations of theoretical closures. This measure in support of the stock management of scallop was implemented in 2015 based on the results of the IFREMER programs and it consists of identifying an area each year to be closed for the entire season. Therefore, commercial bans due to HAB proved the effectiveness of biological rest and thus facilitated its implementation for resource management objectives. According to the REPHYTOX data, sampling and toxicity analyses are not conducted within these areas, showing that the choice of rest areas is not related to scallop toxicity events.

Comparison between Theoretical and Observed Closures for the Whole Period and Production Areas

The comparison between the theoretical closures and observed administrative closures was carried out for all the production areas between 2012 and 2019. This comparison again highlighted discrepancies between the durations of the two closures as shown in Figure 5. The results of these analyses provided a complementary vision of management measures in order to better handle economic and social issues associated with HAB. again highlighted discrepancies between the durations of the two closures as shown in Figure 5. The results of these analyses provided a complementary vision of management measures in order to better handle economic and social issues associated with HAB. The retrospective analysis of REPHY-REPHYTOX data and administrative decisions on closures during the period analyzed highlights two cases. The first concerns the underestimation of the duration of theoretical closures compared with observed closures (7% of cases). The production areas can be closed if phycotoxin levels in shellfish are below the regulatory thresholds. As previously explained, these are precautionary closures before the results of the analyses are obtained, or closures at the half-threshold (80 µg/kg for lipophilic toxins (DSP), and between 10 and 16 mg/kg for ASP). Other reasons for the discrepancies between theoretical and observed closures are related to the absence of shellfish samples or the absence of phycotoxin analysis results. These absences are due to difficulties in accessing the sampling areas (e.g., bad weather conditions), problems related to the analysis themselves (transport issues, loss of samples) or disinterest in sampling an area of lower economic importance at some point in the season. A lack of sampling represents 72.34% of the cases of underestimation of theoretical closures compared with the observed closures . Other management strategies including the implementation of a rest periods to protect the scallop stock can also explain the underestimations of theoretical The second case, which accounts for 93% of the data, involves overestimations of closures by the algorithm, mainly between the 2012-2013 and 2014-2015 seasons. This is due to the fact that access to production areas may be open during toxicity periods despite regulatory thresholds being exceeded. This case only concerns ASP contaminations and this measure is implemented under several conditions. When the concentrations of amnesic toxins are between 20 and 250 mg/kg (total drained flesh), a second analysis is made on the edible parts (muscle and gonad). If the result is less than 4.6 mg/kg, the fishery is authorized for shucking industries, otherwise fishing activities are prohibited. Toxicity tests on the edible parts are only implemented if the fishing companies have an economic interest in the shucking industry; they are, therefore, not carried out systematically. The absolute error calculated between the theoretical closure values and the observed closures showed that of the total data, 49.58% had results of theoretical closure estimates consistent with the recorded and observed closures. For the rest of the data, 42.86% show discrepancies that were explained by management strategies adapting to the evolution of HAB in order to minimize the associated socio-economic impacts. Some of the differences between the theoretical and observed closures (7.56% of the data) were not explained due to lack of data or errors in the databases used. This comparison approach allowed verification of the quality of the estimates of the theoretical closures by the algorithm and showed that these discrepancies are not related to programming errors but rather to the noise generated by human factors that were not considered in the programming.

Comment

Discussion

The societal issues resulting from HAB are complex to address due to the difficulties in predicting these events. Much of the literature that deals with HAB mainly focuses on biological and ecological dimensions in order to better understand their dynamics [START_REF] Hallegraeff | Harmful algal blooms: A global overview[END_REF][START_REF] Anderson | Progress in understanding harmful algal blooms (HAB): Paradigm shifts and new technologies for research, monitoring and management[END_REF]. This work often aims at identifying the factors that contribute to these blooms and to quantify the way in which they operate [START_REF] Tian | Spatiotemporal variability and environmental factors of harmful algal blooms (HABs) over western Lake Erie[END_REF]. Moreover, most of the works on socio-economic issues related to HAB are devoted to assessing the financial impacts on the affected sectors [START_REF] Hoagland | The economic effects of harmful algal blooms in the United States: Estimates, assessment issues, and information needs[END_REF][START_REF] Sanseverino | eu%2Frepository%2Fbitstream% 2FJRC101253%2Flbna[END_REF]. Although each of the ecological, economic and social dimensions of these phenomena is in itself highly complex, the uncertainty and non-linear nature of the processes involved in HAB increase the level of difficulty in understanding these blooms and managing their impacts. While HAB issues are mainly addressed by the natural sciences and, to a lesser extent, by economists who seek to assess their economic impacts, few works deal with HAB governance at an operational level. The absolute error calculated between the theoretical closure values and the observed closures showed that of the total data, 49.58% had results of theoretical closure estimates consistent with the recorded and observed closures. For the rest of the data, 42.86% show discrepancies that were explained by management strategies adapting to the evolution of HAB in order to minimize the associated socio-economic impacts. Some of the differences between the theoretical and observed closures (7.56% of the data) were not explained due to lack of data or errors in the databases used. This comparison approach allowed verification of the quality of the estimates of the theoretical closures by the algorithm and showed that these discrepancies are not related to programming errors but rather to the noise generated by human factors that were not considered in the programming.

Discussion

The societal issues resulting from HAB are complex to address due to the difficulties in predicting these events. Much of the literature that deals with HAB mainly focuses on biological and ecological dimensions in order to better understand their dynamics [START_REF] Hallegraeff | Harmful algal blooms: A global overview[END_REF][START_REF] Anderson | Progress in understanding harmful algal blooms (HAB): Paradigm shifts and new technologies for research, monitoring and management[END_REF]. This work often aims at identifying the factors that contribute to these blooms and to quantify the way in which they operate [START_REF] Tian | Spatiotemporal variability and environmental factors of harmful algal blooms (HABs) over western Lake Erie[END_REF]. Moreover, most of the works on socioeconomic issues related to HAB are devoted to assessing the financial impacts on the affected sectors [START_REF] Hoagland | The economic effects of harmful algal blooms in the United States: Estimates, assessment issues, and information needs[END_REF][START_REF] Sanseverino | eu%2Frepository%2Fbitstream% 2FJRC101253%2Flbna[END_REF]. Although each of the ecological, economic and social dimensions of these phenomena is in itself highly complex, the uncertainty and non-linear nature of the processes involved in HAB increase the level of difficulty in understanding these blooms and managing their impacts. While HAB issues are mainly addressed by the natural sciences and, to a lesser extent, by economists who seek to assess their economic impacts, few works deal with HAB governance at an operational level.

The results of the analysis in this work show that decision processes regarding HAB are not automatic and are based on the comparisons of observed and allowed toxicity levels. Decisions taken by public authorities are also complex due to their responsibility for economic and health issues. An excessively strict implementation of the rules could lead to increased economic impacts on fisheries. As observed in other fishing areas in Brittany, such as the Bay of Brest, long closure periods have led a majority of the concerned fishing fleet stopping their activity and abandoning the fishery [START_REF] Ragueneau | The Impossible Sustainability of the Bay of Brest? Fifty Years of Ecosystem Changes, Interdisciplinary Knowledge Construction and Key Questions at the Science-Policy-Community Interface[END_REF]. Similarly, the Administration has a responsibility to protect seafood consumers from health risks. Although the main priority is to protect human health, as explained in the previous chapter, under certain conditions the Administration can implement the regulation in a more flexible way. Fishing areas can be closed or opened to minimize economic impacts when toxicity is between the regulatory threshold and the half-threshold. This flexibility does not increase the risk for consumers. The results of monitoring carried out by the Administration did not show any correlation to specific food poisoning events that could be linked to HAB events. For this reason, the flexibility in decision-making to deal with HAB allows for better consideration of the socio-economic impacts associated with these events, which are not considered by the European health-related regulations.

In a context where control systems remain efficient in protecting consumers, decisionmaking processes with the involvement of experts allow interpretation of the conditions of each event to anticipate a closure or postpone it if the risk is considered low. In the first case, the anticipation of a closure makes it possible to prevent the sale of contaminated batches just before the realization of an analysis revealing a HAB contamination.

While decision-makers are doing the best they can with the tools at their disposal, there is still room for progress in achieving the objectives of governance. This is because there are several gaps that need to be addressed in future work. The departments of the Administration in charge of managing fisheries and those in charge of managing HAB impacts are not the same. Those in charge of HAB issues have only a global vision of the sector. Without the integration of these two institutional frameworks, fisheries and health, the initiatives undertaken by decision-makers to minimize the economic impacts are only based on the optimization of the monitoring networks. They do not take into account the complexity and heterogeneity of the fishing sector, i.e., the diversity of spatial and temporal production strategies of the companies, nor their vulnerability to risk, sensitivity or coping capacities. Agreements for self-regulation, carried out at the initiative of the fishermen, to accelerate the reopening of a fishing area if the analyses demonstrate the absence of toxicity before the official tests, also reinforces the measures in favor of reducing economic impacts. Moreover, considering the absence of reliable HAB prediction models, governance of HAB impacts occurs within a framework of action in crisis. Consequently, management procedures are based on reacting to impacts rather than avoiding and anticipating them. There are no active collective plans about how to adapt to HAB; instead, all decisions are adapted to each event.

The discrepancies between the theoretical and observed closures reveal the usefulness of this work. Moreover, this approach also demonstrates the dynamics of the HAB risk management strategies in adapting to the evolution of the blooms and the fishery social ecological systems. The subjectivity inherent in the decision-making processes with respect to the "objective" application of the rules results from the analysis of the conditions of each event by the Administration and experts and leads to a specific decision that is not simple on all occasions. As a result, socio-economic risk analysis based on observed closures (e.g. [START_REF] Guillotreau | The vulnerability of shellfish farmers to HAB events: An optimal matching analysis of closure decrees[END_REF]) may be less suitable for these specific contexts such as scallop fisheries. The use of theoretical closures, as proposed in this work, refers to the consideration of a notion of risk based on toxicity, which is a pertinent proxy to assess ecological risks and socio-economic impacts associated with HAB.

Conclusions

This paper analyzed the dynamic of decision-making processes to address the challenges faced by social-ecological systems affected by HAB. In particular, the analyses conducted, using the example of the scallop fishery in the eastern English Channel, highlighted the ways administrations in charge of managing HAB deal with the occurrences, the toxicities and the socio-economic impacts associated with these events.

The methodology developed in this work, based on the analysis of the management processes and the mechanics of the implementation of measures, has made it possible to better understand the issues and constraints of this governance, which are poorly addressed in the literature. Such a methodology is useful to assess more precisely the impacts associated with this phenomenon, but also to explore the ways to improve management systems through the identification of issues and, therefore, societal needs. The authors also highlight the need for decision makers to build adaptive governance approaches. The current European regulations are based on simple protocols built on automatic actions to be undertaken. This regulation addresses only health issues. However, the growing socio-economic stakes in coastal and marine areas lead the authorities in charge of HAB management to build adaptive mechanisms in response to the dynamics of these events in order to minimize their impacts.

In a way, this functioning of HAB management in France is relatively efficient since the combined objectives of protecting seafood consumers and the reduction of socio-economic impacts are achieved overall. However, as HAB are dynamic, the Administration and governance processes must also constantly adapt to maintain their effectiveness. The assessment of ecological risks and their translation into socio-economic risks is one of the main challenges on which the scientific community should work in order to provide the necessary knowledge to tackle the future challenges of HAB, and particularly to build anticipatory responses such as emergency plans rather than adaptive action after a crisis.

J 18 Figure 1 .

 181 Figure 1. Location map of the study area (zones from 1 to J represent the scallop management areas or production areas).

Figure 1 .

 1 Figure 1. Location map of the study area (zones from 1 to J represent the scallop management areas or production areas).

18 Figure 2 .

 182 Figure 2. Changes in phycotoxin concentrations in scallops (a) [DA(Domoic Acid) -ASP, (b) OA(Okadaic Acid) -DSP and (c) SXT (Saxitoxins) -PSP] in scallops in the eastern Channel by production area (see Figure 1). Red dotted line = regulatory toxicity threshold; orange dotted line = half toxicity threshold.

Figure 2 .

 2 Figure 2. Changes in phycotoxin concentrations in scallops (a) [DA(Domoic Acid) -ASP, (b) OA(Okadaic Acid) -DSP and (c) SXT (Saxitoxins) -PSP] in scallops in the eastern Channel by production area (see Figure 1). Red dotted line = regulatory toxicity threshold; orange dotted line = half toxicity threshold.

18 Figure 3 .

 183 Figure 3. Results of phycotoxin analyses in scallops (a) [DA(Domoic Acid) -ASP, (b) OA(Okadaic Acid) -DSP and (c) SXT (Saxitoxins) -PSP] from production areas 9 from September 2012 to July 2015: Red dots = results > regulatory thresholds; orange dots = results > half regulatory threshold; black dots = results below regulatory threshold; pink background color = closure periods; red dotted line = regulatory toxicity threshold; orange dotted line = half toxicity threshold.

Figure 3 .

 3 Figure 3. Results of phycotoxin analyses in scallops (a) [DA(Domoic Acid) -ASP, (b) OA(Okadaic Acid) -DSP and (c) SXT (Saxitoxins) -PSP] from production areas 9 from September 2012 to July 2015: Red dots = results > regulatory thresholds; orange dots = results > half regulatory threshold; black dots = results below regulatory threshold; pink background color = closure periods; red dotted line = regulatory toxicity threshold; orange dotted line = half toxicity threshold.

Figure 4 .

 4 Figure 4. Results of phycotoxin analyses in scallops (a) [DA(Domoic Acid) -ASP, (b) OA(Okadaic Acid) -DSP and (c) SXT (Saxitoxins) -PSP] from production areas 12 from September 2012 to July 2015: Red dots = results > regulatory thresholds; orange dots = results > half regulatory threshold; black dots = results below regulatory threshold; pink background color = closure periods; red dotted line = regulatory toxicity threshold; orange dotted line = half toxicity threshold.

Figure 4 .

 4 Figure 4. Results of phycotoxin analyses in scallops (a) [DA(Domoic Acid)-ASP, (b) OA(Okadaic Acid)-DSP and (c) SXT (Saxitoxins)-PSP] from production areas 12 from September 2012 to July 2015: Red dots = results > regulatory thresholds; orange dots = results > half regulatory threshold; black dots = results below regulatory threshold; pink background color = closure periods; red dotted line = regulatory toxicity threshold; orange dotted line = half toxicity threshold.

Figure 5 .

 5 Figure 5. Comparison of theoretical and observed closures duration in scallop production areas in the eastern Channel.

Figure 5 .

 5 Figure 5. Comparison of theoretical and observed closures duration in scallop production areas in the eastern Channel.

  Figures 6 and 7 illustrate the concentrations of ASP in the edible parts of scallops and the number of tests conducted per month from January 2012, respectively. They show that related tests for shucking occurred in the first seasons of the analyzed time series (2011-2012, 2012-2013) and in a few months of the 2013-2014 season, with a significant number of tests in 2012-2013 (between 14 and 32 tests per month). After these periods, the number of tests for shucking dropped and no tests were performed after the 2013-2014 season (two tests for ASP concentration in edible parts of scallops were conducted in 2016 (July and September) but this was outside the fishing season).

  number of tests conducted per month from January 2012, respectively. They show that related tests for shucking occurred in the first seasons of the analyzed time series(2011- 2012, 2012-2013) and in a few months of the 2013-2014 season, with a significant number of tests in 2012-2013 (between 14 and 32 tests per month). After these periods, the number of tests for shucking dropped and no tests were performed after the 2013-2014 season (two tests for ASP concentration in edible parts of scallops were conducted in 2016 (July and September) but this was outside the fishing season).

Figure 6 .

 6 Figure 6. Evolution of ASP concentrations in edible parts of scallops in the eastern Channel. Red dotted line = regulatory toxicity threshold.

Figure 6 . 18 Figure 7 .

 6187 Figure 6. Evolution of ASP concentrations in edible parts of scallops in the eastern Channel. Red dotted line = regulatory toxicity threshold. J. Mar. Sci. Eng. 2022, 10, x FOR PEER REVIEW 14 of 18

  figures. If so, please change all of them in Commented [JP9R8]: Done

Figure 7 .

 7 Figure 7. Evolution of the number of ASP tests per month on edible parts of scallops in the eastern Channel. Pink areas correspond to the scallop fishing seasons.

Table 1 .

 1 Closures of scallop fishing areas (duration in days). Source: DIRM-MEMN.

				Scallop Fishing Season
	Zone	2012-2013	2013-2014	2014-2015	2015-2016	2016-2017	2017-2018	2018-2019	Total Zone
	1		0	0	0	0	0	0	0
	2		0	0	0	0	0	0	0
	3		0	0	0	0	0	0	0
	4		0	0	0	0	0	0	0
	5		0	3	0	0	0	0	5
	6		24	16	4	0	0	5	49
	7		24	16	0	12	0	20	76
	8		0	36	0	2	0	24	66
	9	192	139	64	0	3	0	151	549
	10		0	26	0	13	35	5	79
	11	36	0	24	0	15	21	11	107
	12	77	29	98	36	13	0	64	317
	13	21	68	3	61	20	0	49	222
	14	35	0	59	64	16	0	13	187
	15	12	0	54	32	0	0	119	217
	I		0	11	61	0	0	0	74
	J		0	8	50	0	14	9	83
	Total	387	284	418	308	94	70	470	2031

Acknowledgments:

The authors express their gratitude firstly to the S3-EUROHAB project for the financial support in this work and secondly to the people who were consulted to better understand the socio-economic stakes associated with HABs.

This work has been carried out through the S3-EUROHAB project (Sentinel-3 products for detecting EUtROphication and Harmful Algal Bloom events) and funded by the European Regional Development Fund through the INTERREG France-Channel-England (Project Number 106).

Institutional Review Board Statement: Not applicable.

Data on theoretical closures are available in https://doi.org/10.528 1/zenodo.6320765 (accessed on 6 July 2022) and data on observed closures were collected from the DIRM-MEMN Administration.

Comment corner is n provide th

Conflicts of Interest:

The authors declare no conflict of interest.


Coralie Le Maout Alvarez

Anaïs Minne

William Le Saux

Laurent Cantrel

Marie-Odile Simonnot
email: marie-odile.simonnot@univ-lorraine.fr

Characterization of precipitates susceptible to clogging of sump filters after a Loss-of-Coolant-Accident in PWRs

Keywords: LOCA, mineral fibers, calcium-silica precipitates, temperature effect, nuclear power plant, CHESS Highlights

niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Introduction

In the event of a Loss of Coolant Accident (LOCA), involving a break in the primary circuit of a Pressurized Water Reactor (PWR), safety systems are implemented. A boron (in the form of boric acid) water injection safety system is activated to cool the reactor core. If the accident leads to an increase in pressure and temperature in the reactor building, the containment spray system is activated. Spraying alkaline water with soda also reduces the level of molecular iodine gas (especially 131-iodine isotope) in the atmosphere due to droplet capture. Water for both functions is initially taken from the 1 600 m 3 pool treatment and cooling system tank. When the water reaches a low level, the safety injection circuits automatically switch to recirculation mode, during which they suck up the water that has fallen into the sumps located at the bottom of the reactor building. The water collected in the sumps is a mixture of ≈0.2 M boric acid and 0.06 M sodium hydroxide. The target pH is therefore approximately 8.5. The temperature of the water in the sumps may reach 130 °C for a transient time and then slowly cool to 50 °C in the post-LOCA phase.

During a LOCA, debris is produced because of the impact of the steam jet from the primary circuit initially at 155 bars in the area near the rupture. The main debris consists of thermal insulation (mineral fibers) on the piping, degradation of paint covering the inner surfaces or latent debris such as concrete dust. Some of this debris can be transported to the sump filters by water drag and/or settling. Filters are implemented to prevent debris from flowing through fuel core channels and pumps during the recirculation water phase which can last for weeks.

In the early 1990s, several incidents in boiling water reactors (Barsebäck in Sweden, Perry, and Limerick in the United States) highlighted the risk of clogging of sump filters. In particular, during the incident that affected, on July 28, 1992, the reactor #2 of the Barsebäck power plant [START_REF] Pointner | Generic issues on sump clogging[END_REF].

This accident occurred following the untimely opening of a valve, releasing 200 kg of fibrous debris (heat mineral fiber insulation used to insulate piping). Part of this debris was carried into the condensation pool, causing a significant increase in the pressure drop across the filters of the emergency cooling systems after 70 min.

These different incidents have raised questions about the possible clogging of sump filters in LOCA situations for PWRs. Indeed, depending on the characteristics of the debris (size, mass, etc.), some of it may be carried to the filters and create a debris bed, which can cause their clogging by a physical effect coupled with a chemical effect. The speculative chemical contribution may correspond to the formation of precipitates within the fibrous bed [START_REF] Sandrine | Precipitate formation contributing to sump screens clogging of a nuclear power plant during an accident[END_REF][START_REF] Tregoning | Phenomena identification and ranking table evaluation of chemical effects associated with generic safety issue 191[END_REF]. The formation of these precipitates may result from the presence in the solution of elements released by the corrosion/dissolution of debris and metal surfaces due to oversaturation.

For French PWRs, the debris source term is made up of i) mineral fibers composed mainly of silica (SiO2), sodium oxide (Na2O), and calcium oxide (CaO) at 65, 16 and 8 wt.%; ii) concrete dust, in smaller amounts, of variable composition (the composition of the concrete may depend on the reactor). In our study, the concrete powder is made of 4 and 54 wt.% of SiO2 and CaO; iii) galvanized steel metal surfaces potentially releasing zinc (Zn) after hot water leaching. The main elements dissolved from the fibers and concrete particles are silicon (Si) and calcium (Ca). Since the amount of fiber generated in this type of accident is greater than the amount of concrete dust, so a Ca/Si molar ratio of less than unity is expected.

Concerning the galvanized steel surfaces, several thousand square meters are present in the PWR reactor buildings. The corrosion rate of galvanized steels has been widely reported [START_REF] Johns | Small-scale experiments: effects of chemical reactions on debris-bed head loss[END_REF][START_REF] Niyogi | Corrosion of aluminum and zinc in containment following a LOCA and potential for precipitation of corrosion products in the sump[END_REF][START_REF] Piippo | Corrosion behaviour of zinc and aluminum in simulated nuclear accident environments[END_REF]. The closest to our conditions of interest are those of Piippo et al. [START_REF] Piippo | Corrosion behaviour of zinc and aluminum in simulated nuclear accident environments[END_REF]. Indeed, their objectives were to carry out tests under conditions as close as possible of a LOCA to study this phenomenon of corrosion of galvanized steels. According to their results, a corrosion rate of 0.045 g.m -2 .h -1 is to be considered for a pH of 8.0. Under LOCA conditions for a 900 MWe PWR, the sump water is composed of boric acid and sodium hydroxide for a pH between 8.0 and 8.5, which leads to a Zn concentration of ≈10 -4 M after 24 hours of leaching.

Thus, knowing the composition of the debris source term, and considering that the main elements transferred into solution are Ca, Si and Zn, the open question is to status to what extent precipitates are likely to form and may contribute to increase the head loss to sump screens in LOCA conditions.

Therefore, this study focuses on the formation of precipitates in the presence of Si, Ca and Zn in a buffer solution containing boric acid and sodium hydroxide at pH 8.0 to 8.5 at 25 °C. According to the literature review, many precipitates can be formed. Among the potential precipitates, hydrated calcium silicates (C-S-H) are good candidates. These hydrates have already been the subject of important research works, in particular on their formation during cement hydration [START_REF] Fujii | Heterogeneous equilibrium of calcium silicate hydrate in water at 30 °C[END_REF][START_REF] Greenberg | Investigation of colloidal hydrated calcium silicates. I. Solubility products[END_REF][START_REF] Taylor | Proposed structure for calcium silicate hydrate gel[END_REF]. The evolution of the Ca/Si molar ratio of the solid has been investigated, several phases of C-S-H have been identified: C-S-H (α) (0.66 < Ca/Si < 1), C-S-H (β) (1 < Ca/Si < 1.5) and C-S-H (λ) (Ca/Si > 1.5) [START_REF] Fujii | Heterogeneous equilibrium of calcium silicate hydrate in water at 30 °C[END_REF][START_REF] Grangeon | Structure of nanocrystalline calcium silicate hydrates: Insights from X-ray diffraction, synchrotron X-ray absorption and nuclear magnetic resonance[END_REF][START_REF] Greenberg | Investigation of colloidal hydrated calcium silicates. I. Solubility products[END_REF][START_REF] Grutzeck | A new model for the formation of calcium silicate hydrate (CSH)[END_REF][START_REF] Taylor | Proposed structure for calcium silicate hydrate gel[END_REF]. Under our conditions, the Ca/Si molar ratio is less than 1, i.e. in the C-S-H (α) domain. For this molar ratio range, the coexistence of two different phases has been reported: C-S-H (α) and silica gels [START_REF] Fujii | Heterogeneous equilibrium of calcium silicate hydrate in water at 30 °C[END_REF][START_REF] Greenberg | Investigation of colloidal hydrated calcium silicates. I. Solubility products[END_REF][START_REF] Taylor | Proposed structure for calcium silicate hydrate gel[END_REF]. Indeed, once Ca is consumed in solution, the remaining Si will involve polymerization reactions leading to the formation of oxide networks. The polymerization reactions occur in two steps: hydrolysis which creates silanol groups (Si-OH) and condensation which converts the silanol groups to siloxane bridges (Si-O-Si) which is the basic building block of the inorganic polymer chain [START_REF] Aelion | Hydrolysis of ethyl silicate[END_REF][START_REF] Brinker | Sol-gel science: The physics and chemistry of sol-gel processing[END_REF]. Studies have also been conducted on the delay of hydration of cement and thus the formation of C-S-H. Weiler states that the use of borate ions in the cementitious medium delays the hydration process [START_REF] Weiler | Method of and composition for retarding the setting time of portland cement[END_REF]. Bell and Coveney investigated this phenomenon using molecular scale simulation (MOPAC software) and interpreted it as the chemisorption of borate ions on silicates resulting from the dissolution of anhydrous silicates [START_REF] Bell | Molecular modelling of the mechanism of action of borate retarders on hydrating cements at high temperature[END_REF]. This phenomenon would slow down the growth of silicate chains, with the formation of borosilicate species. Other species likely to precipitate are calcium borates. Table 1 lists the different calcium borate mineral species with the reagents used, the synthesis temperatures, and the pH range according to the literature data.

Furthermore, if dissolved zinc is present, a zinc-based silicate can be formed at a relatively low temperature (20 to 104°C). This is mostly an amorphous precursor that crystallizes after calcination at ~1000°C to form willemite (Zn2SiO3) [START_REF] Takesue | Thermal and chemical methods for producing zinc silicate (willemite): A review[END_REF]. Finally, zinc borate precipitates are likely to be formed. Finally, precipitates of zinc borate are likely to form. Their formation is highly temperature dependent: around 25 °C they have low zinc and high boron content, while around 90 °C they are richer in zinc oxides [START_REF] Kryk | Zinc corrosion after loss-ofcoolant accidents in pressurized water reactors -Physicochemical effects[END_REF].

This brief literature review demonstrates that a wide variety of compounds are likely to be formed; under our specific conditions, experimental data are needed to characterize the nature and amount of precipitates.

This paper presents results of analytical tests devoted to study of potential chemical effects relative to sump filter clogging that can occur in a LOCA situation. The experimental results will be compared to the data from the simulations using the CHESS calculation code [START_REF] De Windt | CHESS Tutorial and Cookbook[END_REF]. The objective is to understand and identify the nature of the precipitates and to determine the critical thresholds in terms of species concentration and temperature beyond which the risk of precipitate formation is evidenced. Ca(OH)2 + H3BO3(aq) 100 to 400 °C - [START_REF] Hart | The synthesis of new calcium borate compounds by hydrothermal methods[END_REF][START_REF] Lehmann | Zur Chemie und konstitution borsaurer salze. I. Die hydrogenmonoborate des calciums[END_REF][START_REF] Liu | Synthesis and thermochemistry of 2CaO•B2O3•H2O. Thermochim[END_REF][START_REF] Sun | Hydrothermal synthesis and single-crystal X-Ray structure refinement of three borates: Sibirskite, parasibirskite and priceite[END_REF]) Colemanite (Ca2B6O11.5H2O) Ca(OH)2 + H3BO3(aq) 100 °C - [START_REF] Hart | The synthesis of new calcium borate compounds by hydrothermal methods[END_REF]

Materials and methods

Experimental set-up

A 1-liter solution was prepared by adding 14.3 g of boric acid (H3BO3, Alfa Aesar, 99%) and 60.0 mL of 1 M sodium hydroxide (NaOH, Fisher) in ultrapure water. This solution was divided into three aliquots named S1 and S2 of 490.0 mL each and S3 of 20.0 mL to make the stock solutions. Three stock solutions were prepared by adding 1) calcium chloride (CaCl2, Alfa Aesar, 97%) to S1, 2) sodium silicate (Na2SiO3, Alfa Aesar) to S2 and 3) zinc chloride (ZnCl2, Alfa Aesar, 98%) to S3. The concentration values of calcium (Ca), silicon (Si) and zinc (Zn) for each experiment are shown in Table 2 andTable 3. Three temperatures were used to study the influence of precipitation kinetics as a function of temperature (30, 60, and 90 °C).

The experiments were performed in a thermostated 1-L jacketed glass reactor. Solutions S1, S2, and S3 were successively added to the reactor, which was heated to the target temperature. The mixture was kept homogeneous with stirring (130 rpm) using a propeller stirrer. The temperature was controlled by a thermoregulator associated with a K-type thermocouple immersed directly in the mixture, the temperature accuracy was ±2 °C. Liquid samplings were taken regularly for analysis. After 24 h, the remaining solution was filtered on a Büchner to recover any precipitates that may have formed. The precipitates were washed with a small quantity of ultrapure water (10.0 mL) to remove the species adsorbed on the surface. They were then dried in an oven at 60 °C for 12 h before weighing.

Analysis

For each sample, the pH was measured at 25 °C, then the concentrations of dissolved Ca, Si and Zn cations were measured in a 0.2 M nitric acid (HNO3, VWR, 69%) solution using a Perkin Elmer Optima 800 DV ICP-AES.

The precipitates were characterized by different techniques. Crystallinity was examined by X-ray diffraction (XRD), using a Bruker D8 Advance A25 model XRD instrument with a Bragg-Brentano mode (θ-2θ) geometry, ranging from 3 to 50° (2θ). Morphology and structure were determined using a Zeiss Sigma 500 VP model SEM and chemical (or elemental) analysis was performed using an Oxford Isis 300

EDS system in conjunction with SEM. A Nicolet IS50 FTIR Tri-Detector Gold Spectrometer with an integrated ATR module and a monolithic diamond crystal was used in the 4000-450 cm -1 wave range.

Both elemental and molecular surface analysis was performed using a ToF-SIMS 5 (ION-TOF) spectrometer which has an ion gun generating a beam of primary Bi 3+ (25 KeV; 0.2pA), representing the analysis beam.

Experimental grids

A test matrix was established by varying only the concentrations of Ca (6.2 10 -4 to 1.9 10 -3 M) and Si (1.6 10 -3 to 5.3 10 -3 M). The temperature was set at 60 °C and the test duration at 24 h ( ] (M) Temperature (°C) 1 6.4.10 -4 ± 6.4.10 -6 5.3.10 -3 ± 5.3.10 -5 -2 1.2.10 -3 ± 1.2.10 -5 -3 1.9.10 -3 ± 1.9.10 -5 30, 90 4 6.4.10 -4 ± 6.4.10 -6 1.1.10 -2 ± 1.0.10 -4 -5 1.2.10 -3 ± 1.2.10 -5 30, 45, 75 and 90 6 1.9.10 -3 ± 1.9.10 -5 30, 90 7 6.4.10 -4 ± 6.4.10 -6 1.6.10 -2 ± 1.6.10 -4 -8 1.2.10 -3 ± 1.2.10 -5 30, 90 9 1.9.10 -3 ± 1.9.10 -5 30, 90

Finally, the study was completed by adding Zn between 0.9.10 -4 to 7.7.10 -4 M, this upper range was intended to better highlight some precipitation process and reduce weighing uncertainties. All the tests, where no precipitation had been observed with Ca and Si, were performed in the presence of Zn (Table 3). In addition, as a comparison, test #5 was carried out in the presence of Zn at different temperatures (30, 60, and 90 °C) (Table 3).

) Test # [Ca 2+ ] (M) [Si 4+ ] (M) [Zn 2+ ] (M) Temperature (°C)
1.Zn 6.4.10 -4 ± 6.4.10 -6 5.3.10 -3 ± 5.3.10 -5 Between 8.8.10 -5 ± 8.9.10 -6 to 7.7.10 -4 ± 7.7.10 -5 60 2.Zn 1.2.10 -3 ± 1.2.10 -5 60 4.Zn 6.4.10 -4 ± 6.4.10 -6 1.1.10 -2 ± 1.0.10 -4 60 5.Zn 1.2.10 -3 ± 1.2.10 -5 30, 60, 90 7.Zn 6.4.10 -4 ± 6.4.10 -6 1.6.10 -2 ± 1.6.10 -4 60 8.Zn 1.2.10 -3 ± 1.2.10 -5 30

Software for calculating equilibria in solution

The CHESS software allows simulating the evolution of an initial chemical system towards its thermodynamic equilibrium state [START_REF] De Windt | CHESS Tutorial and Cookbook[END_REF][START_REF] Lartigue | Aqueous inorganic uranium speciation in European stream waters from the FOREGS dataset using geochemical modelling and determination of a U bioavailability baseline[END_REF]. All calculations are based on the formation constants of chemical species given in a thermodynamic database. CHESS calculates the ionic activity products and evolves the system through reactions in solution, precipitation, or dissolution to match the formation constants entered in the database. This equilibrium calculation code does not take into account kinetic limitations. This may lead to uncertainties, as precipitation is a complex process, which may involve non-equilibrium situations.

To ensure good consistency between experimental results and simulation data, it is necessary to verify that the expected species are present in the databases. Moreover, it is important to ensure that the thermodynamic constants (log Ks) are given at the study temperatures, i.e. up to 90 °C. To meet all these requirements, the databases chosen were chess.tdb and tdbvit0.tdb [START_REF] De Windt | CHESS Tutorial and Cookbook[END_REF] which are the most complete for our study.

For each calculation, the input data were sample volume (set to 1 L), pH, temperature and species concentrations. The pH value was not fixed to check the coherence between the experimentally measured value and the one from the simulation. The concentrations of boric acid and sodium hydroxide were set at 0.23 and 0.06 M respectively. The content of carbon dioxide gas was set at a fugacity coefficient at 3.1mol.% which represents the CO2 partial pressure in the atmosphere. The concentrations of Ca, Si and Zn, as well as temperature were input to match the conditions listed in Table 2 andTable 3.

Results

Precipitate masses as a function of concentration and temperature

For the experiments conducted at 60 °C in the absence of Zn (Table 2, grid I), only tests 3, 5, 6, 8, and 9 resulted in precipitate formation. Within this series, the tests differed in their Ca and Si concentrations. It can be noticed that the Ca concentration strongly influences the precipitation: indeed, for Si concentrations of 1.1.10 -2 and 1.6.10 -2 M, the minimal Ca concentrations necessary for precipitation were respectively 1.2.10 -3 and 1.9.10 -3 M. For a Si concentration of 5.3.10 -3 M, the minimum Ca concentration necessary to obtain a precipitate was about the same, 1.9.10 -3 M.

By varying the temperature from 30 to 90 °C (Table 2, grid II) almost all the tests gave rise to a precipitate, except test #5 at 30 and 45 °C and #8 at 30 °C, which highlights the effect of temperature.

Indeed, for fixed concentrations of Ca and Si and varying only the temperature, the precipitate masses obtained were different (Fig. 1).

In the presence of Zn (Table 3), all the experiments led to the formation of precipitates, whereas for most of them this was not the case in the absence of Zn. This clearly shows the involvement of new precipitation reactions. And as before, temperature has a significant influence on precipitation (Fig. 1, trial #5.Zn). In all cases, the highest mass of precipitate was reached around 60 °C (Fig. 1).

Fig. 1 -Mass of precipitate experimentally obtained as a function of temperature for fixed concentrations of Ca, Si and Zn

The addition of Zn led to a greater amount of precipitates but the temperature trend was not affected by the addition of this element. This can be explained as follows: Zn reacted very strongly to form a precipitate which, in turn, acted as a nucleus and favored the precipitation of the other precipitates determined previously.

The pH measured during the test phases was between 8.0 and 8.5 at 25 °C; this stability was due to the buffering capacity of the chemical conditioning of the solution matrix (pKa of the couple B(OH)3/B(OH)4 -of 9.3 at 25 °C).

In Table 4 are reported the masses of Ca, Si and Zn lost in solution for test #3, 5 and 5.Zn at the different temperatures tested. For tests #3 and 5, the highest masses of precipitated Ca and Si were monitored at 60 °C; they were higher in the presence of Zn at 60 °C (Table 4); these results are in good agreement with those shown in Fig. 1. Almost the Zn present in solution was consumed, which may indicate that it was in default with respect to the stoichiometry of the reactions involved.

Characterization of the precipitates

Hereafter, only the characterization of the precipitates obtained in tests #3, 5 at 60 °C and 5.Zn at 60 and 90 °C are detailed, as the species identified are the same for all precipitates obtained in the other tests.

No diffraction peak was recorded by XRD analysis, which means that the species formed were amorphous.

Regarding the morphology of the particles, SEM imaging of precipitate #3 (Fig. 2a) revealed the presence of two different zones: one with a cluster of fine particles (Z1) and a rough zone (Z2). SEM imaging of precipitate #5 (Fig. 2b) did not show well-defined structures. EDX analysis of Z1 indicated the presence of oxygen (O) (41 wt.%), Ca (17 wt.%), and B (8.4 wt.%). The presence of these elements can be explained by the formation of calcium borate. The rough zone (Z2) contained O (55 wt.%s), Si (15 wt.%), B (9.5 wt.%), and a small amount of Ca (3.1wt. %). This same result was obtained for the EDX analysis of precipitate #5 (Fig. 2b). These analyses potentially indicated the formation of silica and/or borosilicate species.

For the tests involving Zn, SEM images of the two precipitates did not show a well-defined structure.

However, the 5.Zn precipitate at 90 °C (Fig. 2d) was more friable than that obtained at 60 °C (Fig. 2c).

EDX analysis of Z4 location (Fig. 2c) indicated the presence of O (54 wt.%), Si (13 wt.%), and B (12 wt.%). The presence of these elements referred to the possible formation of a borosilicate species. Z5 (Fig. 2c), contained mostly O (56 wt.%) and Si (17 wt.%), which revealed the presence of silica (SiO2). Finally, Z6 (Fig. 2d) contained mostly O (47 wt.%)), Si (33 wt.%), and Zn (8 wt.%)) which could be assimilated to zinc silicates. The FTIR/ATR spectra of precipitates (Fig. 3) exhibited the presence of hydroxyl groups (OH) with the elongation band ν(H-O-H) at 1 635 cm -1 ; borate species with the elongation bands ν(B-O) at 1 409 cm -1 and 1 348 cm -1 [START_REF] Kizilca | Thermal dehydration of colemanite: kinetics and mechanism determined using the master plots method[END_REF][START_REF] Vierne | Spectre de réflexion infrarouge de minéraux monocristallins ou en poudre III : Carbonates[END_REF]. These bands were better defined in precipitate #3 (Fig. 3b), indeed, the initial Ca concentration of calcium in this test was higher. The bands could be attributed to the formation of calcium borate; silicate species, with the symmetrical elongation bands ν(Si-O) at 1 180 cm -1 and 1 045 cm -1 [START_REF] Mollah | A Fourier transform infrared spectroscopic investigation of the early hydration of Portland cement and the influence of sodium lignosulfonate[END_REF]; silica (SiO2)

with the elongation band ν(Si-O-Si) at 800 cm -1 and the deformation band δ(Si-O-Si) at 480 cm -1 [START_REF] Mollah | A Fourier transform infrared spectroscopic investigation of the early hydration of Portland cement and the influence of sodium lignosulfonate[END_REF]. The ToF-SIMS analysis was restricted to precipitates #5 and #5.Zn at 60 °C. Table 5 list the analytical results for these two precipitates. Precipitate #5 at 60 °C was characterized by high intensities of silicon ions (Si + ), low mass ions characteristic of silica (SiOx -), high molecular weight ions corresponding to silicon (hydr)oxides or silicates (SixOyHz -), boron (B + ), and a small quantity of calcium (Ca 2+ ) and its hydroxyls (CaxOyHz + ).

Precipitate #5.Zn at 60 °C was characterized by higher intensities of Ca ions (Ca + ), their (hydr)oxides (CaxOyHz + ), and Si ions (Si + ). Moreover, the presence of Zn ions (Zn + ), indicates that this one reacted during the test phase. On the other hand, the intensities of low mass ions characteristic of silica (SiOx -), high molecular weight ions corresponding to silicon (hydr)oxides or silicates (SixOyHz -), and boron ions (B + ) are lower in the presence of zinc.

These analyses confirmed the presence of silica and silicate species in both precipitates. However, the presence of Ca, B and Zn (for #5.Zn) in the precipitate indicated that they have reacted in solution but it was not possible to determine precisely the exact respective amounts of each possible precipitates, borosilicate, zinc borates, calcium borates and zinc silicates (for precipitate #5.Zn).

Simulation results

The tests presented in Tables 2 and3 were simulated with CHESS. In the CHESS database, only one mixed calcium-boron species is present: colemanite (Ca2B6O11.5H2O).

According to the tests simulations in the Table 2, the formation of quartz (SiO2) and colemanite (Ca2B6O11.5H2O) are predicted for each Ca and Si concentrations at temperatures ranging from 30 to 110 °C. Simulations of the tests in Table 3 additionally indicate the formation of a zinc silicate, willemite (Zn2SiO3) for each condition of Si, Ca and Zn concentrations at temperature ranging from 30 to 110 °C.

The influence of temperature on the precipitate mass was investigated between 30 and 110 °C for the tests #5 and #5.Zn. For both tests, the simulation indicated that the formation of quartz was favored at rater low temperature (30 °C), contrary to colemanite, whose mass formed increased from 30 to 60 °C and stabilized beyond 60 °C. In the presence of Zn, the amount of quartz formed was lower, which can be explained by the formation of willemite. On the other hand, the formation of colemanite was not affected by the presence of Zn. However, whatever the temperature, the quantity of willemite formed remained unchanged. From a general point of view, the amount of precipitate was the highest between 37 and 53 °C (Fig. 4).

Discussion

The study of the reactivity between calcium and silicon in a solution of soda and boric acid (Table 2)

showed the formation of a precipitate after 24 h under the following conditions: i) [Ca 2+ ] ≥ 1.2 10 -3 M;

[Si 4+ ] ≥ 1.1 10 -2 M for T ≥ 60 °C; ii) [Ca 2+ ] ≥ 1.9 10 -3 M; [Si 4+ ] ≥ 5.3 10 -2 M for T ≥ 30 °C. The study of the impact of the addition of Zn in the system (Table 3) indicated a higher reactivity. Indeed, the precipitation conditions were different: [Ca 2+ ] ≥ 1.2 10 -3 M; [Si 4+ ] ≥ 1.1 10 -2 M for T ≥ 60 °C; [Zn 2+ ] ≥ 0.9.10 -4 M. The precipitate masses were the highest at approximately 60 °C and the presence of Zn did not affect the temperature dependence observed on the mass of precipitates. However, the total amount of precipitate formed was much greater in the presence of Zn.

The characterizations of the precipitates revealed the presence of amorphous species with and without Zn. Among them, the formation of amorphous silica (SiO2) is s attested by the presence of Si-O and Si-O-Si bonds, revealed by FTIR/ATR analysis. The presence of borate species(s) was shown by FTIR with the two ν(B-O) elongation bands. Among them, the presence of calcium borate was confirmed from SEM-EDX analyses. However, several types of calcium borates exist, and their stability depends on pH.

According to our pH values, the calcium borate likely to be formed is inyoite (Ca2B6O11.13H2O) due to its chemical stability between pH 7.4 and 9.6 (25 °C) [START_REF] Gode | Preparation of calcium borates from aqueous solutions[END_REF][START_REF] Yılmaz | Boron removal by means of chemical precipitation with calcium hydroxide and calcium borate formation[END_REF]. Borosilicate has also been identified by FTIR. Indeed, borate ions can chemically bind to silicates at the end of the chain, thus blocking its propagation and the formation of calcium silicate [START_REF] Bell | Molecular modelling of the mechanism of action of borate retarders on hydrating cements at high temperature[END_REF][START_REF] Weiler | Method of and composition for retarding the setting time of portland cement[END_REF]. In the presence of Zn, silica, borate species and silicates were also identified. In addition, the presence of Zn inside the precipitate was identified (SEM-EDS and ToF-SIMS), but the characterization techniques did not allow to determine with certainty if this element combined with Si to form zinc silicates or boron to form zinc borates. Based on the masses consumed in the solution, the consumption of Si was greater when Zn was present, which was consistent with the assumption of a zinc silicate species. This was not observed for B, present in excess in the mixture. Nevertheless, the formation of zinc borates was strongly dependent on temperature (between 30 and 90 °C) [START_REF] Kryk | Zinc corrosion after loss-ofcoolant accidents in pressurized water reactors -Physicochemical effects[END_REF]. Indeed, at low temperatures (30 °C), the zinc borates formed tended to have lower Zn and higher B content. At higher temperatures (close to 90 °C), this trend was reversed. This information may result in a low formation of this type of compound at low temperatures but was favored at higher temperatures. Experimentally, it has been shown that temperature had no impact on the formation of Zn species, so the formation of zinc borate was questioned in our test conditions.

Simulation with CHESS have indicated the formation of quartz (SiO2), colemanite (Ca2B6O11.5H2O) and willemite (Zn2SiO4) for tests in the presence of Zn at the equilibrium phases. Moreover, the effect of temperature on the mass of precipitate has been demonstrated for quartz and colemanite. Indeed, the formation of quartz is favored at the lowest temperature, and it is the opposite for colemanite. For zinc silicates, no temperature dependance was simulated.

The comparison between the experimental data and the simulations shows a rather good consistency between the identified species, except for borosilicate. Indeed, these species are absent from the database used for the simulations, and to our knowledge, no data is available in the literature to be implemented in the database. The formation of quartz indicates that the amorphous silica identified experimentally can lead to the transition from an amorphous structure to a crystalline structure in the thermodynamic equilibrium state for a more or less long period of time. Finally, for the experimentally identified calcium borate(s), the formation of inyoite can be assumed, based on its stability in the pH range of 7.4 to 9.6 and our experimental data. The simulation indicates that it is a colemanite-type calcium borate, but it is the only calcium borate formula present in the database. The crude formulas of these two species are very similar: they differ only in their degree of hydration: 5 for colemanite and 13 for inyoite thus the solubility constant should not differ a lot from one species to another. This information indicates that the calcium borate species that can be formed at thermodynamic equilibrium will have the crude formula Ca2B6O11.xH2O with x equal to 5 or 13. Regarding the temperature effect, it was observed experimentally and by simulation. After the simulation, temperature range between 37 and 54 °C promotes the formation of a higher mass of precipitates. Experimentally, the maximum is obtained at 60 °C, knowing that the chosen temperatures were 30, 60, and 90 °C. The species formed with Zn were not formally experimentally identified, however, but data suggest the formation of zinc silicate. The simulation confirmed this hypothesis with the presence of willemite.

Conclusion

The objective of this work was to determine/confirm the existence of a potential chemical effect on sump filter clogging resulting from the formation of precipitates due to mineral elements released from concrete/insulation materials dissolution in solution, for different temperatures.

In the presence of Si and Ca only, effects in species concentration and temperature were observed on the reactivity of these elements. The Ca concentration mainly governs the precipitation process. On the other hand, when the system is completed by the addition of zinc under Zn 2+ cation, this favors precipitation whatever the temperature tested. The presence of zinc in the mixture induces new reactions which result in the formation of precipitate. Moreover, the temperature has an influence on the mass of precipitate, which is more important for a temperature close to 60 °C, this temperature where are observed the highest precipitation amounts is not affected by Zn addition. Identifications of the species formed were obtained by experimental data coupled to simulations at thermochemical equilibrium:

• Data from chemical analysis performed at the end of experiments show that the precipitates are formed by a mix of amorphous silica (SiO2); amorphous calcium borate -possibly inyoite (Ca2B6O11.13H2O); amorphous borosilicate (xSiO2.yB2O3); zinc -species formed not identified but potentially attributed to amorphous zinc silicates.

• Data from the simulation indicate the presence of quartz (SiO2), colemanite (Ca2B6O11.5H2O), and willemite (Zn2SiO4). In the databases, borosilicate species are not listed, however, this does not exclude that the formation of this species is experimentally plausible. Moreover, an effect of temperature on mass has been demonstrated for quartz and colemanite. Indeed, the formation of quartz seems more favorable at low temperatures (30 °C); for colemanite, it is the opposite. On the other hand, for willemite, this effect is not observed. From a general point of view, according to the simulation, the quantity of precipitate formed is more important for temperatures between 37 °C and 53 °C.

From these data, chemical effects cannot be excluded and must be considered in the sump clogging issue for PWRs. The concentrations of elements (Ca, Si, Zn), as well as the critical temperatures, were determined by the formation of a precipitate in an aqueous solution containing boric acid and sodium hydroxide at pH 8.5 over 24 hours:

• [Ca 2+ ] ≥ 1.2.10 -3 M; [Si 4+ ] ≥ 1.1.10 -2 M; T ≥ 60 °C

• [Ca 2+ ] ≥ 1.9.10 -3 M; [Si 4+ ] ≥ 5.3.10 -3 M; T ≥ 30 °C

• [Ca 2+ ] ≥ 1.2.10 -3 M; [Si 4+ ] ≥ 1.1.10 -2 M; [Zn 2+ ] ≥ 1.5.10 -4 M ; T ≥ 60 °C Finally, the CHESS simulation tool indicates good consistency with the experimental results, although thermodynamic equilibrium is not reached under the test conditions.

Soon, this study will be completed by tests under dynamic conditions in a circulation loop. In the latter, debris will be injected into an aqueous solution composed of boric acid and sodium hydroxide pH 8.5 (at 22 °C) which can be heated up to 110 °C and circulated through a 2.5 mm steel plate filter.

To evaluate potential effect on filter pressure drop, dynamic tests should be performed to evaluate potential impact of chemical effect in relevant conditions in terms of temperature, flowrate and mass of debris.

Fig

  Fig. 2 -SEM images of precipitates obtained in tests #3 at 60 °C (a), #5 at 60 °C (b), #5.Zn at 60 °C (c) and 90 °C (d) with SEM-EDS analysis area

Fig. 3 -

 3 Fig. 3 -Infrared spectra of precipitates obtained in tests #3 at 60 °C(a), #5 (b) at 60 °C, #5.Zn at 60 °C (c) and 90 °C (d)

Fig. 4 -

 4 Fig. 4 -Simulation of total mass precipitation as a function of temperature for tests #5 and #5.Zn.

Table 1 -

 1 Summary of calcium borate mineral species with reagents used synthesis temperature and pH range

	Mineral species	Reagents	Temperature	pH range References
	of calcium borate
	Inyoite	Ca(OH)2 + H3BO3(aq)	-	7.4 to 9.6 (Gode, 1970;
	(Ca2B6O11.13H2O)			Yılmaz et al., 2012)
	Gowerite
	(CaB6O10.

Table 2

 2

-grid I). To study the impact of temperature on precipitation, additional tests were carried out by varying the temperature (30 to 90°C) for the tests that produced a precipitate at 60 °C (Table 2 -grid II).

Table 2 -

 2 Test performed in H3BO3/NaOH solution -pHi 8.5 (at 25 °C) -24 hours (impact of Ca and Si concentrations and temperature)

		Grid I -Temperature set at 60 °C	Grid II -Temperature variation
	Test #	[Ca 2+ ] (M)	[Si 4+

Table 3 -

 3

Test performed in H3BO3/NaOH solution -pHi 8.5 (at 25 °C) -24 hours (impact of the addition of a metallic additive: zinc

Table 4 -

 4 Mass of Ca, Si and Zn lost in solution for test #3, 5 and 5.Zn at different temperatures tested.

	Test # Temperature	Mass of Ca precipitated	Mass of Si precipitated	Mass of Zn precipitated
		(°C)	(mg)	(mg)	(mg)
	3	30	3.60 ± 0.36	8.37 ± 0.84	-
		60	14.0 ± 1.40	35.3 ± 3.50	-
		90	5.90 ± 0.59	14.2 ± 1.40	-
	5	30	0 84 ± 0.08	2.90 ± 0.29	-
		45	0.54 ± 0.05	1.80 ± 0.18	-
		60	10.6 ± 1.60	81.6 ± 8.16	-
		75	3.21 ± 0.32	70.8 ± 7.08	-
		90	2.60 ± 0.26	45.8 ± 4.58	-
	5.Zn	30	19.6 ± 2.00	113 ± 11.3	48.1 ± 4.8
		60	22.8 ± 2.38	136 ± 13.6	49.1 ± 4.9
		90	14.1 ± 1.41	123 ± 12.3	47.6 ± 4.8

Table 5 -

 5 Most significant positive and negative ions intensities for precipitates #5 and #5.

	Zn at 60°C

Only the values of the same species (same line in the table) are comparable

Acknowledgements

This work was carried out at the Institut de Radioprotection et de Sûreté Nucléaire (IRSN, Cadarache) and the Laboratoire de Réaction et Génie des Procédés (LRGP, Lorraine). The authors thank IRSN for the funding. They also thank Dr Baptiste LAUBIE and Dr Bastien JALLY for the training on the CHESS simulation tool and Dr P. NERISSON for his scientific support to the writing of this article.