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Communication Dans Un Congrès Année : 2017

Severe Accident Research activities at the CEA Methodology and Main Insights Related to Source Term Quantification and Fuel Behavior.

Résumé

Despite the very high level of control and safety in Nuclear Power Plant, they are not exempt from device malfunction, human errors or even natural disasters, which may lead to nuclear incidents or accidents. When consequences involve a high degradation of the reactor core (melting), associated with the release of Fission Products (FPs) and other radioactive materials from the reactor core, it is classified as a Severe Accident (SA, TMI-2, Chernobyl and Fukushima for instance). These released FPs may be transported by air masses or water and thus cover extensive areas and affect all living beings due to their radiological effect and may as well act as poisons. The amount and isotopic composition of the radioactive material released from the core is called Source Term, and its assessment has been the main objective of several international research programs for more than thirty years. These research programs are commonly classified into two main groups, according to their approach (1) Integral programs, such as PHEBUS FP, studying the response of a whole nuclear core during a severe accident, in a reduced scale; (2) On the other hand, analytical programs studying the fuel and FPs when submitted to accidental conditions, by means of Separate-Effect Tests (SET). Examples of the latter are the HI/VI, VEGA, VERCORS and VERDON programs. As result from all the research programs an extensive experimental database has been generated. However, up to now, predicting correctly the FPs release from UO2 and/or MOX fuels in SA conditions is still a significant and very important challenge since there are many remaining uncertainties. In order to improve these estimations, the global fuel and FPs behavior during the accidental sequence must be better understood, and specific emphasis has to be put on mechanisms which promote FPs release and fuel relocation. One of the most useful ways to do that is to perform appropriated annealing treatments with representative thermal transients in order to measure the absolute level and kinetics of the released FPs. To understand the promoting mechanisms, theses FPs release measurements have to be coupled with the corresponding fuel micro-structural changes resulting from these thermal transient.To this end, since the last decade, CEA has set up two complementary research axes, aiming at reproducing conditions representative of nuclear severe accidents, using both high burn-up irradiated fuel samples and model materials. The first axis corresponds to the VERDON program and deals with commercial UO2 and MOX fuels irradiated in French PWR. Model materials (often called SIMFUELS) consist in natural UO2 doped with stable isotopes of FP in concentrations that match a targeted burn-up. Therefore, SIMFUELS are representative of irradiated nuclear fuels but without their radioactivity. The importance of such materials lies in the possibility of using powerful characterization techniques, such as X-ray Absorption Spectroscopy, which today are unavailable for large samples of irradiated nuclear fuels.The present paper, organized in four main parts, presents successively the experimental facilities available at the CEA Cadarache and Marcoule centers together with the corresponding RetD axes SA experimental VERDON laboratory and associated annealing test device as MERARG, Analytical and micro analysis laboratories by which all the pre- and post-test fuels examinations, supported by analytical development on simulated corium samples, are performedUse of SIMFUELS methodology.The last part of the paper focuses on results obtained with this general approach, with special emphasis on VERDON-1 test.
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Dates et versions

hal-02418108 , version 1 (18-12-2019)

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  • HAL Id : hal-02418108 , version 1

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Yves Pontillon, F. Audubert, C. Legall, E. Geiger, V. Basini, et al.. Severe Accident Research activities at the CEA Methodology and Main Insights Related to Source Term Quantification and Fuel Behavior.. HOT LAB 2017, Sep 2017, Mito, Japan. ⟨hal-02418108⟩

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