Philippe Girones

Vincent Chapurlat

A contribution for dismantling of nuclear facilities: a functional pattern for dismantling operations and indicators design and management

Keywords: Depollution, depollution system, system sciences, system engineering, model, functional architecture, legacy waste retrieval

Optimizing nuclear installation decommissioning and dismantling operations is an ongoing quest. Faced with the complexity of this activity, the Model Based System Engineering promotes relevant principles and modeling techniques. It motivated then the definition of a functional generic pattern model of the waste package production line and the decommissioning of the facility. It proposes a global and generic functional architecture of such system aiming to reduce the level of the pollutant. This pattern is coupled with a process of logistics. Six functions are combined to define this functional pattern. The application of this pattern model to a case of waste recovery in a pit shows the relevance of model-based system engineering approach, reducing the weight of the history in the development of scenarios by optimizing the control means for the nuclear safety and product quality.

Introduction

Nuclear facility dismantling is an industrial activity whose products are waste packages and cleanedup structures [START_REF] Asn | Definitive shutdown and decommissioning operations to the nuclear power industry[END_REF], [START_REF]Preparing for Decommissioning During Operation and After Final Shutdown[END_REF]. The wide diversity of pollutants and of the nuclear facilities themselves (reactors, research laboratories, spent fuel reprocessing factories…) has generally meant that the preparation of depollution scenarios depends on the type of facility involved [START_REF] Cea | Evaluation de l'état radiologique, physique, chimique de l'installation à assainir ou à démanteler. Techniques de caractérisation[END_REF] [START_REF] Cea/Den | L'assainissement démantèlement des installations nucléaires[END_REF]. As a result, there are no or very few systematic approaches for helping the definition of requested dismantling operations and flows (data, material and energy) that are then exchanged between these operations [START_REF] Lafon | Élaboration d'une méthode équipée, basée sur une approche systémique, pour l'organisation et le suivi de chantiers d'assainissement et démantèlement d'installations nucléaires[END_REF]. This situation opens up numerous perspectives for nuclear facility dismantling engineering [START_REF] Lafon | The D\&D of Nuclear Facilities: A Systemic Approach for Project Organization and Monitoring[END_REF]. We consider particularly hereafter principles provided by Model-Based System Engineering [START_REF] Incose | Survey of Model-Based Systems Engineering (MBSE) Methodologies, Model Based Systems Engineering (MBSE) Initiative from International Council on Systems Engineering (INCOSE)[END_REF] approach. Indeed, it offers combined inputs from strong system concepts, from the use of modelling activities, modelling languages and tools as a support for exchanges between different trades, and from confident iteration by promoting models checking and validation then system evaluation by using these models. MBSE advantages have already been recognized in many other fields, including avionics, transport, health… In nuclear field, it is a way we suggest to generalize dismantling scenario definition, modelling and validation prior to examine standard equipment, and to evaluate sources of savings, of performances, and of safety.

The proposition outlined here is based on two hypotheses: Page 2 sur 18 -A so-called "dismantling system" is defined in section I. It allows defining i.e. modelling and checking rigorously, sharing between all stakeholders and validating, then operationalizing and managing dismantling projects (i.e. set operations, resources, means, risks analysis, etc.). -The management of such operations is based on a single indicator as proposed in section II. This paper presents an innovative contribution in nuclear dismantling field. It consists to define and formalize then propose to all stakeholders being involved in such projects what must be the more logical arrangement of such operations and with which main indicators must be managed all along the project. The set of operations represents the functional architecture of the depollution system that must be then as much as possible generic, flexible and adaptable to various kinds of nuclear installations to be dismantled. It is then question here of equivalent of Design Patterns [START_REF] Pfister | A proposed meta-model for formalizing Systems Engineering knowledge, based on functional architectural patterns[END_REF] for Nuclear Decommissioning and Dismantling operations. The result emerged is applied to the retrieval and to the conditioning of waste stored in a pit as presented in Section III.

Last, and before concluding and setting some perspectives, Section IV, the so-called "system model" for dismantling system has been the opportunity to question the role of the facility's industrial history in the definition of functional dismantling scenarios. More specifically, it raises questions as to the alignment of the historical content with the requirements for dismantling operations. The proposed approach eliminates the necessary mastery of industrial history. It complements the work carried out on the engineering of basic model systems (MBSE) by focusing on a functional analysis [START_REF] Lafon | The D\&D of Nuclear Facilities: A Systemic Approach for Project Organization and Monitoring[END_REF], an analysis close to the business lines.

Problematic: nuclear facility dismantling

Dismantling a nuclear facility is a depollution operation [START_REF] Tallec | Démantèlement des installations nucléaires[END_REF]. The French Nuclear Safety Authority (ASN) supports such an approach [START_REF] Asn | Definitive shutdown and decommissioning operations to the nuclear power industry[END_REF] and its Guide 14 [START_REF] Asn | Guide de l'ASN N°14 : Mise à l'arrêt définitif, démantèlement et déclassement des installations nucléaires de base en France[END_REF] specifies the method to be used in reaching the decommissioning objective. The depollution activity must make strategic choices. For example, [START_REF] Tallec | Démantèlement des installations nucléaires[END_REF] describes the advantages of immediate dismantling, which favors profiting from existing knowledge about the facility, a position in line with the ASN doctrine.

Whatever the strategic choice decided on, two types of requirements must be mainly considered in order to manage these operations. The first type concerns nuclear safety. The second type is imposed by budget limitations. A priori, these concerns can oppose each other [START_REF] Petitfrère | Elaboration d'un scénario de démantèlement[END_REF] interpreting a safe operation is assumed to be costly. In France, dismantling is carried out within an extended ecosystem of enterprises [START_REF] Martin | Nuclear decommissiong and organizational reliability, involving subcontractors in collective action[END_REF], and is therefore seen and represented as a system of systems [START_REF] Sage | On the Systems Engineering and Management of Systems of Systems and Federations of Systems[END_REF]. Indeed, each enterprise is and remains autonomous in terms of decision and strategy all along dismantling duration, being then considered as one of the often numerous and heterogeneous Stakeholders of the dismantling. This induces technical, human and economic interactions [START_REF]L'arrêt et le démantèlement des installations nucléaires[END_REF] among all the stakeholders, often sometimes complex [START_REF] Gomez | Le rôle et les motivations d'une firme leader dans l'essai de transformation de son écosystème d'affaires en écosystème de l'innovation -Le cas du site de Marcoule et du démantèlement nucléaire[END_REF].

The depollution of complex older facilities, with the risk of discontinuity in historical knowledge due to the strategic and organizational choices previously made, or yet again the seeming antagonism between the two types of requirements, does not favor establishing common ground among all the different stakeholders. Nevertheless, it is necessary to find an equilibrium in order to design and qualify the depollution operations, in confidence and from harmonious way. This fact has motivated the definition of a set of "simplified requirements law" or "shared temporal observables", to facilitate and make durable the requested cooperation among the stakeholders.

An evolution of the activity through time

The concentrations and the levels of pollutants in the facility are measured using radiation protection or gamma camera instruments (Figure 1) [START_REF] Girones | Methodology for determining the radiological status of a process: Application to decommissioning of fission product storage tanks,» chez AIEA -Enseignements tirés du déclassement des installations nucléaires et cessation sûre des activités nucléaires[END_REF]. These qualify the operational objective, i.e. the target for the depollution actions. [START_REF] Ghiban | L'usine du futur au service de l'assainissement et du démantèlement[END_REF] proposes the concept of "surgical dismantling". In this, the concentration points are identified, then removed, optimizing the decontamination factor. Such operations efficiently reduce the impact on human health, and therefore meet the nuclear safety requirements.

Figure 1 : Left and center: dose rate measurement results following the Z axis. Right: composite image of the sceneoverlap of a visible image and a gamma camera acquisition (blue through to red zones) -Installation in the nuclear fuel cycle [START_REF] Girones | Instrumentation des processus en Assainissement Démantèlement[END_REF] The approach is then to consider that managing the level and the distribution of radioactivity in the facility meets industrial performance criteria in an economic context which is a reasonable as possible, and safe.

This option facilitates exchanges among the stakeholders, because relevant shareable indicators have been identified. The indicators retained come from lessons learned [START_REF] Girones | Instrumentation des processus en Assainissement Démantèlement[END_REF], either during a facility operation phase or during its dismantling.

The health quality of the scene within the limits of the image on the right in Figure 1 is qualified based on three indicators: the contamination ( : activity, Bq, image on the right), the irradiation ( : dose rate in mGy/h, table in the center), and the concentration of fissile matter ( : mass of fissile matter, g).

A facility examined with these indicators is a temporal series with each variable indexed by a spatial ensemble S. The temporal series resembles mining prospection with an ensemble of measurements for each variable in:

.

Each variable is a real random process, for example: . A is a measurable function:

with a real value. The location of the site s Є S is generally associated with a piece of equipment or perhaps waste.

The variables are dependent. The constraints, i.e. the dose rate, contamination, and concentration of the mass of fissile matter, are dependent on the activity: (Bq). More specifically, they are a function of the activity. The depollution is therefore managed based on a state of variable A at a given moment t whose object has been modelled by a minimisation function f. The depollution function: f in is therefore: Equation 1Where, : activity of the source term in Becquerel (Bq)

The depollution becomes an operation for the reduction of the radioactivity level ( , Bq) retained or contained in a facility (Figure 2). . Generally, the solution resembles:

. The variation of activity through time:

, depends on the radioactive half-life (T 1/2 ) and on the results of the depollution operation. These depollution results, or objectives, are indexed by the overall decontamination factor:

. The steps are simulated based on:

, A Є [A 0 , A c ].
, where:

: Total radiological activity (source term) evaluated during the inventory phase. This is the activity present before the dismantling operations begin.

: Activity target for the depollution operation, : Cut-off value, final depollution requirement imposed by the legislator or the regulator.

Decreased radioactivity is also the consequence of radioactive decay. Therefore, two possible strategies can be envisaged. The first consists in starting the depollution process after the radioactive decay of the radionuclides [START_REF] Lecocq | Démantèlement et déconstruction des centrales nucléaires, la stratégie d'EDF[END_REF]. This implies a period of facility mothballing, or a decay period. For the second, in the case of radionuclides with a radioactive half-life longer than 30 years [START_REF] Tallec | Démantèlement des installations nucléaires[END_REF], radioactive decay has little or no influence on the decrease in the source term, and there would be an inevitable loss of the knowledge and know-how accumulated during the facility operation phase [START_REF] Rosini | La mémoire lacunaire du nucléaire[END_REF]. Depollution operations should then be undertaken as quickly as possible after the final shutdown of the facility.

The initialization of the minimization Equation 1 by A 0 and managing the radionuclide quality is therefore a strategic aspect.

These elements are often accepted by all the stakeholders. They group stakeholder interests in the form of single shared, measurable indicators. Even more, they represent a "requirement function" for the industry [START_REF] Faisandier | Notions de système et d'ingénierie de système[END_REF]. The function therefore structures the system engineering approach based on an optimization of industrial performance and of nuclear safety.

These first structuring elements give rise to an operational view, in the form of a logistics chain for the Becquerel. It means emptying the "Becquerel stock" and sending waste packages to a disposal site, or "final customer", and then delivering the decommissioning facility to a future owner.

An amount of Data, Information and Knowledge to be shared and managed

First, lot of Data, Information and Knowledge (DIK) flows could be more or less available, coming from the facility's engineering and construction phases, from operation and maintenance phases (historical DIK) as modelled simply in Figure 3. There is a requested continuity of the exchange modalities used during the facility dismantling operational phase. The facility owner imposes the DIC management rules, and essentially favors an organic view. This is centered on the facility manager during the operation phase, then on the project manager during the dismantling phase. Their positions, roles, and responsibilities impose the quality and the volume of DIC exchanged or required. However, some of these DIK are however discarded a priori for studies of the dismantling phase. This absence of some crucial DIK during this phase impacts for instance the treatment line for the waste, then the decommissioning of the nuclear facility of interest. This problem is classically due to various kinds of interoperability problems when authoring project's stakeholders to select, access, use and reformat, adapt, and share these historical DIK.

Second, stakeholders will have to create new DIK (proper DIK) in coherence and confidence all along the project but also make appear other flows that appear as considered in systemic sciences: material flows (e.g. waste package) and energy flows (e.g. electricity) between operations.

Considering historical DIK exchange, interoperability problems are studied both technically speaking (e.g. in terms of format, etc.) and conceptually speaking (e.g. of syntactic, of semantic, or pragmatic interoperability). Some solutions are today proposed such as [START_REF] Concetta | Formalization of data-driven Invariant modelling Constructs: Contribution of the thesys[END_REF]. We must then consider all the flows (historical and proper DIK, Material, and Energy, Figure 3) having to be modeled during dismantling project preparation (in project design time) and managed during the dismantling operation (in project run time).

Working hypotheses

Prior to describe the contribution of the work that is presented in the next, we must set two main hypotheses of work.

A model of 'depollution system' for MBSE principles

To face these problems, some systemic concepts and principle could help stakeholders for instance to put in light and model from an unambiguous manner the expected flows and their requested treatment, making then appear the so-called functional architecture of the project. In this way, dismantling operation could be defined as functions that exchange flows from both DIK (historical and proper), Material or Energy type. So, a working hypothesis has been set and positioned in a scientific framework. This framework is based on model-based system engineering approach (MBSE) [START_REF] Carroll | Systematic Literature Review: How is Model-Based Systems Engineering Justified?[END_REF]. It favors an approach where the exchange of information among all stakeholders (engineers, contractors, authorities…) is no longer governed by documents written in natural language. The engineering is indeed organized around three main principles: the principle of system applied to depollution system, the place and use of a set of models that are to be built then exchanged by stakeholders, and finally engineering processes that are even standardized [START_REF]ISO15288, Ingénierie des systèmes et du logiciel -Processus du cycle de vie du système[END_REF]. The main advantages of MBSE hereafter considered is to facilitate representation (modelling languages, tools and techniques), discussion (share a common vocabulary and rules by putting in light systemic principles), evaluation (by using models, more or less formal) and to provide proofs and arguments for decision makers by using simulation techniques and analysis mechanisms (e.g., sensibility or dependence analysis).

We call the whole set of models a "depollution system model" on which exchanges among the stakeholders become possible and promising [START_REF]ISO15288, Ingénierie des systèmes et du logiciel -Processus du cycle de vie du système[END_REF]. This model highlights particularly, and at least:

 a requirements repository model that must be established and validated then shared involving all stakeholders and following Requirements Engineering principles;  architectures models: functional model that focus on what the system must do and which flows are to be exchanged between functions, logical model that focus on with which components and links the system must perform its functions [START_REF] Estefan | Survey of model-based systems engineering (MBSE) methodologies[END_REF], and physical i.e. how the system must be then implemented in the reality by choosing all components from both technical, organizational, or human nature.

As an example, the co-design of the functional architecture of the dismantling system (Figure 4) is facilitated needing involvement from all the trades. In the same way, by reducing the dependence on historical DIK, the model becomes transposable (Figure 4). It is not attached to a single facility [START_REF]ISO15288, Ingénierie des systèmes et du logiciel -Processus du cycle de vie du système[END_REF]. Last, it is of course mandatory to deploy and push all project's stakeholders, whatever may be their roles and responsibilities, to use the proposed engineering framework, to map the polluted space, to define applicable solutions, to analyze risks, etc. The first phase in structuring the dismantling system model is a logical sequence of tasks (Figure 5). It addresses classical operations: 1) management of the Data, Information, and Knowledge [START_REF] Meinadier | Le métier d'intégration de systèmes[END_REF], of Material and Energy flows, definition of the Becquerel stock and contaminant mapping or location of the "stocks", 2) simulation of the depollution processes (dismantling) and reduction operations, then finally 3) conditioning and dispatch of the products (Figure 5). This is an iterative process, with given milestones, as depollution can be achieved sequentially and repetitively (Figure 2). In this case, the intermediate activity levels targeted are defined, labelled: A c,i (Figure 2). The last configuration is characterized by a target activity level achieved:

<A s , the contamination level to reach in order to consider the structure or the facility depolluted.

The intermediate level reached: A c,1 , A c,2 , A c,n for which A c,n > A s indicates a notable step, for example a change in the working conditions. This can be the change from needing breathing equipment to protect the workers to being able to work without protection. It can also represent a change in the category of waste packages produced, from Intermediate level to Very Low Level, for example [START_REF] Regnier-Precastaing | Enjeux et méthodes de la gestion des données[END_REF]. These different operational configurations meet the criteria of the same process, as they have the same objective: deliver a depolluted facility gaining both in confidence, performance, safety and security, whatever may be the initial contamination level. So it exists a general process named "Becquerel logistics" that highlights different steps and milestones to be respected. The objectives are initiated and maintained throughout the depollution operation, governed by specific regulatory conditions: those of waste zoning, of radiation protection zoning, and of waste categorization [START_REF] Regnier-Precastaing | Enjeux et méthodes de la gestion des données[END_REF]. Operational constraints depend on the radiation protection zoning. Decommissioning is a change in the waste zoning [START_REF] Asn | Guide de l'ASN N°14 : Mise à l'arrêt définitif, démantèlement et déclassement des installations nucléaires de base en France[END_REF]. The "Becquerel logistics" process has the advantage of clarifying task sequencing. A process is a necessary framework, but does not give a high enough level of definition to structure the activities of the trades involved. To do this, system engineering extends the definition of the requirements into the proposed functional architecture pattern.

Contribution: a functional architecture pattern model for nuclear facility dismantling

Considering these hypotheses, and as detailed in the next, it seems important and innovative to note that, independently of inherent complexity of depollution system, the requested operations and the general process make appear it exists a common and generic set of functions that could be organized, sequenced and synchronized from the same manner to each the depollution system objectives. So, we propose a functional generic architecture model based on a function inventory.

The flows of waste or of contaminated matrices (matter) is transformed via a succession of steps or functions. The result of a function is a concentration of the associated risk: for example, the removal of a pollutant by aspiration concentrates this pollutant in the collection point.

By concentrating the hazardous product, the upstream functions impose ever-increasing constraints on the downstream functions through to the conditioning step.

The function is defined as an activity of transformation An input flux (Input) of matter, energy, or information is transformed into an output flux (Release). The function is characterized in a reference document of time, of space, and of form. It is constrained by the means of control. The activity is ensured by a resource flux [START_REF] Faisandier | Notions de système et d'ingénierie de système[END_REF], and the function is defined by its quality (f(t)). The general depollution function is based on the operational view, the regulatory objectives, and the reduction Equation 1: Radiological (Figure 6).

Radiologic level evolution Mapping equipment, manucfatering equipment, skills Measurable indicator…

Waste package

Inputs Outputs

Industrial data Product data volume of constraints. In merging the details of the operational model (Figure 5) of the general function (Figure 6), a functional decomposition for which the interfaces are characterized and managed is envisaged. The intention is also to break down the details of the depollution system or "Becquerel logistics" until a generalizable set of functions can be obtained [START_REF] Estefan | Survey of model-based systems engineering (MBSE) methodologies[END_REF]. The arrangement of functions then forms an architecture from which the engineering companies can simulate industrial performances and establish the safety laws while respecting cost control.

The breakdown is based on the depollution process (Figure 5). The different steps in the Becquerel logistics chain are approached functionally: managing the distribution of the pollutant within the facility, simulation then physical removal of the pollutant, followed by its conditioning and the transport of the product. This opposes performance law and operational behavior, as they often seem antagonistic.

The proposition means a safe, simple activity because of a dual analysis combining the risks and the performances. The elements of the functional breakdown focus on:

The site/the facility must not leave an industrial "memory" for the future, in the form of residual pollutant. At the end of the operations, "the pollutant warehouse" must be empty.

The waste packages are products compatible with the disposal facility requirements.

Package fabrication and site release are managed using checked, or safe and reproducible functions, with architecture based on the components of the logistics chain: Becquerel logistics.

The major issue is to have vocabulary which is accessible and sufficiently precise to structure the analysis of the interfaces between the functions. A depollution activity is described by six functions (Table 1): identify (ID), treat (TRT), condition (CDT), store (ENT), decommission (DCL) and transport (TRS).

Function definition Symbol Function characteristics

IDentify is a function of knowledge, information, and data collection, management, and supplementing. All these information items are attached to an object, a function, a place The constraints (in): measurement uncertainties, contamination dynamics

The constraints (out): contamination distribution mapping and operational conditions

The TReaT function is an operation for waste radiological and physical resizing. This aspect concentrates the problems related to safety. It must be shown that the process is managed as concerns criticality safety, containment, and radiation protection (holdup). The constraints (out): access to storage zones Table 1: Inventory of the basic functions of the dismantling system Throughout the line, the flux is a coupling of materials and of information. At each step, transformations of material via energy are accompanied by DIC. The quality and the weight of the DIC dominate in the functional view vision. The DIC and "the Becquerel" move from the stock towards the finished product uninterruptedly.

An arrangement of the six functions corresponds to an industrial configuration. Source term accessibility is centered on the product and reduces the weight of the mapping. The functional architecture is independent of the quality of the facility.

At this stage, the depollution model system is defined based on reduced requirements and on a proposition for a modular functional architecture. An evaluation must next be made the ranking of the DIC flux called "legacy" or dimension the weight of these DIC for the system.

A test application: treatment of waste stored in a pit

The arrangement of the six functions describing the system is an architecture, and this favors the definition of the functional interfaces. It reduces the distance between the trades involved, in order to manage the complexity of a depollution system better.

To decrease the complexity of the functional interfaces and evaluate the weight of the operation phase DIC in the depollution model definition, a simple configuration was retained: the retrieval of legacy waste containing all of the pollutant from the part of the facility under consideration.

The case of legacy waste retrieval from storage is a configuration where the source term is limited (managed volume). Moreover, the logistics chain is often compact and located very near the waste concerned. It is a simple case for the application of the depollution system modelling.

Application of an arrangement of the 6 functions for waste reconditioning

In this case, the waste is stored in a pit. The retrieval operation, i.e. taking the waste out, then conditioning it in waste containers, is broken down into three steps. Classically, it begins by identifying the waste, for example by collecting the following information: mass (kg), activity (Bq), and physicalchemical quality (elements). It goes on to a treatment which consists in removing part of the waste from the pit, then carrying out a resizing of the pieces. The operation is finished when the material is put into a waste or conditioning container. By respecting the logistics process and the general equation for pollutant minimization, the functional viability of this architecture is based on its ability to identify the waste in the pit, or more precisely, on the ability to define the terms of the function:

. If the architecture can indeed propose a succession of actions that appear causal, it is cleared of physical constraints. So how to characterize an object located at the bottom of a pit? The tools available and the accessibility conditions generally do not enable this (Empty DIK, Figure 7). The functional sticking point therefore comes from the of source term accessibility, stated to be the decisive parameter for the definition of a scenario. Without knowledge of the contaminant quality and its distribution in space, the depollution operation seems impossible to launch.

Propagation of poorly identified waste within the production line leads to a product of random quality. As in a classical logistics chain, the start point is essential. Moreover, in the case of a depollution operation the results of the IDentify function categorizes the work conditions or safety management.

To ensure correct management of the product, i.e. the waste package, in spite of the poor source term accessibility, a functional alternative must be defined. To do so, new checkpoints are necessary in order to monitor the operating conditions by evaluating the dose rates (mGy/h) and the volumetric level of contamination (Bq/m 3 ), and thus guarantee industrial performances by managing the radiological activity handled (Bq).

Checking waste material as it is retrieved from the pit a priori meets industrial performance criteria and a safety criterion focusing on the worker who handles the waste. When these checks are carried out during the different operations, they give information on the operating conditions but are not aligned with the industrial performance requirements. The radiological activity and the physical-chemical quality are not measured, even though they qualify the raw material going into the final package.

The alternative to the previous architecture (Figure 7) is therefore a functional architecture where identification of the waste while in the pit is discarded. The waste is therefore removed under the terms of another function: transport. This means the retrieved waste is first identified outside the pit using in situ means for radiological characterization, then treated and conditioned (Figure 8). The radiological quality of the waste is managed after its retrieval from the pit and not from a pit mapping. The measurement of the magnitudes of interest associated with the production of waste packages is therefore carried out under conditions where these magnitudes are managed. The background noise and the waste volumes are reduced, and the physical-chemical quality can be assessed. The uncertainty associated with the activity measurement is therefore lower, a guarantee of gains in industrial performance and in safety.

This second architecture, where the initial identification of the pollutant is reduced to the limits of the contaminated space, must be used in such waste retrieval operations. The evaluation of the contamination level and its distribution within the zone considered no longer have any interest. The weight of the industrial history is therefore lower. Only the elements or fractions of waste are mapped, and then carried over in a process of treatment and conditioning. The process is organized taking into the operational constraints, and has the means for differential orientations depending on the waste category. This architecture can be generalized, as the industrial history is not the controlling element for the source term. The operational depollution essentially depends on physical limits and so, as was the case during the operation phase, it depends on the waste zoning and radiation protection zoning. These parameters are deliberately neutral and are applied whatever the type of facility.

Section IV: Comments and discussion on the current limits of the general dismantling model for nuclear combination of views -operational, then functionalundertaken to define a simplified model of a depollution system, contributes to the qualification and then the quantification of stakeholder exchanges.

Organization is not integrated in the approach, and represents a first limitation for the proposition. It can be assumed that it is attenuated by the reduction in the number of performance indicators. The retained hypothesis, or minimization function reduces the number of indicators to simple Becquerel management. This indicator or pollution level is spatialized (function:

, firstly for the pollution assessment or original pollution mapping, then for the depollution method planning.

It can be shown that the convergence point for the stakeholders is a mapping and a depollution objective formalized by a decontamination factor: or . The notion of a weak interaction among the stakeholders can be advanced by weakening the organization view (Figure 9) focusing on a sharing of reduced constraints. The elements taken from the operational view confirm that the mapping is the decisional support for the depollution industry. A map is a shareable decision element, but it can also be acted on through the decontamination factor. For each point on the map, it targets the hoped-for evaluation estimator or indicator. All the stakeholders can converge on this support, as if on the musical score of an orchestra conductor. The of information and of decision must therefore be structured on the basis of contamination maps. This fact is the model's second limitation.

Pollutant mapping is not always accessible. The initial activity: A 0 is nevertheless essential for the definition of the depollution system. It supports the definition of the operating conditions and industrial performance, as it dimensions the decontamination factor and the product quality.

Waste storage configuration is confronted with the impossibility of this mapping, as accurate mapping of buried waste pollution cannot be carried out. Thus, managing the limits imposed by "the storage facility" or zoning is the only available viable mapping element. The retrieval of legacy waste from storage was the configuration retained to augment the operational model by a functional view and overcome this new limit. It is representative of depollution operations, as pollutants are rarely accessible.

This functional limit is approached in the form of a simple question: thirsty hikers are beside a well. Can they trust the reassuring signs displayed, or demand complete checks of the entire well contents, or checks on the contents of the bucket from which they are going to drink the amount of water necessary to survive?

To be sure of the quality of the well water, the hikers must ask the local population who use the water, taking the risk of not having enough energy left to return to the well to drink. This approach is useful if the information can be found and is accurate. The history of the well water consumption is enough to know if it can be drunk, but gathering the information and interpreting it has a cost. What's more, it must be accurate and safe.

We would all agree that the safest way is to checkanalyze -the well water before drinking it. This would not be reasonable in every case of water consumption, but must be imposed for a truly safe approach, particularly in the case of suspect, possibly life-threatening products. This is the situation for operations where hazardous products removed from storage must be handled. It is unnecessary to check or to write the history of the entire storage facility, as it is enough to check the retrieved objects.

This principle is applied to the retrieval of waste from a storage pit. It parallels depolluting a contaminated well. The goal is to remove the pollutant so that the well can refill and be used without restriction on its consumption. Two points follow on from the approach:

 The quality check operations on the products removed can be launched based on just the limits of the zone of interest, without mapping and without a historical record,  Systematic checks on the bucket contents before consumption reduce the weight of history in managing the production of packages. The water is drunk if, and only if, the bucket contents meet health requirements.

The simplifications contributed by analogy with the evaluation of the well water health quality reduces the flux of DIC coming from the facility's construction and operation phases (historical DIC). They can be discarded a priori for studies of the dismantling phase. A new limit appears, that of the impact of the absence of this flow on preparing the functional architecture of the treatment line for the waste, then the decommissioning of the structures.

Conclusion

The dismantling of nuclear facilities is a young industry, still evolving towards maturity. In this context, operational and functional models can accelerate the generalization of safe, efficient means. The approach proposed here, and applied to a case study, is based on two elements: a source term minimization equation, and a logistics process (Becquerel logistics).

The pollutant is extracted, conditioned, and then sent on to a customer. This flow sheet satisfies the need to reduce the pollutant content of a facility. It meets both the necessary criteria: industrial performance and risk reduction. The minimization communicates clearly with and mobilizes all the stakeholders, and reduces the weight of trade ontology without ignoring it.

These perceptions open the way for the definition of functional architectures adapted to industrial configurations: retrieval of legacy waste, removal of solid components, or the clean-up of large surfaces. Each pattern or functional architecture (scenario) is thus the result of the organization of six elemental functions: identify, treat, condition, transport, store, decommission.

The application of the functional model to the treatment of waste stored in a pit shows that the source term definition is reduced to the limits of the polluted space. The functional input (pattern) therefore serves to enhance industrial performance and safety while putting aside "pollutant history" and favoring instrumentation of the production line.

The combination of the six elemental functions of the Becquerel logistics chain must now deal with complex operations: cutting and removal of components, or clean-up operations. These applications will enable the functional vocabulary to be extended to and confirmed in industrial depollution operations. These studies will be carried out with the goal of extracting organic architectures, followed by the identification of equipment that can be generalized to the entire depollution industry.

Figure 2 :

 2 Figure 2: Reducing the source term by depollution operations -radiological contamination case Several conditions are checked:. Generally, the solution resembles:. The variation of activity through time:, depends on the radioactive half-life (T 1/2 ) and on the results of the depollution operation. These depollution results, or objectives, are indexed by the overall

  of the "source term" (Bq) contained in a nuclear if acility as a f unction of time Activity af ter def inite shutdown of the installation, A0

Figure 3 :

 3 Figure 3: A model of exchanges for depollution engineering centered on documents and on the nuclear facility operator (DIK: Data, Information, and Knowledge, MOC: Maintenance in Operational Condition Op.: Operational)

  The next focus on the proposition of six generic functions allowing us to provide functional architecture modelling patterns. The equation for managing the Becquerel qualifies the performances and the risks. These results open the way to a standardization of dismantling methods and means, thus contributing to an optimization of nuclear facility dismantling operations.

Figure 4 :

 4 Figure 4: A model for depollution engineering centred on a simplified model (MBSE)

  model for activity reduction (Bq)

Figure 5 :

 5 Figure 5: Simplified process of activity (Bq) reduction in three stepsnuclear facility dismantling

Figure 6 :

 6 Figure 6: Functional pattern (top) applied to Flows, constraints, monitoring, and resources of the general function f(t) (bottom) By definition, the depollution system mission, i.e. its main function, does not propose a reading of the interface complexities. It does not enable a formalization of the resources or integrate too great a

Flux

  quality: information, data, and knowledge The resources (in): DIC, characterization techniques, information system The resources (out): indicators interpreted to define the work conditions and the result of the operation (DF)

  Flux quality: contaminated matrix or waste The resources (in): the means for cutting, for radiological characterization of the waste, the means for contamination containment The resources (out): the means for monitoring the work environment The constraints (in): the waste dimensions and masses, the radiological characteristics, the mass of fissile matter The constraints (out): the contamination dispersion, the dose rates The Waste packaging or CoNDitioning function groups the resizing and radiological operations on the waste in order to supply the finished object: the process product, i.e. the waste package. Flux quality: resized waste, containers The resources (in): the containers The resources (out): the DIC associated with the waste: physicalchemical and radiological The constraints (in): the package dimensions, the radiological and physical-chemical cutoffs The constraints (out): the health safety quality of the waste package Function definition Symbol Function characteristics The TRanSport function includes all movements of objects within the facility or storage locations, and on the public road network [29]. Flux quality: waste packages The resources (in): means of handling The resources (out): definition of the transport means and modes The constraints (in): Hazardous goods road transport authorisation Accord pour le transport des marchandises Dangereuses par la Route (classe 7) [29]The constraints (out): transportation of hazardous materialThe Decommission DCL function is the operation guaranteeing that the treated facility is in conformity with the rules set by the French Nuclear Safety Authority (ASN).

  Flux quality: matter or civil engineering structure The resources (in): the means for low level mapping, a monitoring station at the site exit The resources (out): a decommissioned building The constraints (in): 0 Bq [10] or 300 µGy/year The constraints (out): none The ENT, or Storage function consists in keeping the waste in safe, accessible conditions. Flux quality: waste packages The resources (in): the storage buildings and locations The resources (out): storage plans The constraints (in): the limits set for each facility

Figure 7 :

 7 Figure 7: Proposition of an architecture for the treatment and conditioning of pit waste, with the data flux

Figure 8 :

 8 Figure 8: Proposition of an architecture for the treatment and conditioning of waste from a pit, inspired by Lessons Learned

Figure 9 :

 9 Figure 9: A general function for site depollution described by a minimization equation of the pollutant content, focalization elements for the stakeholders