Progress of ASTEC Topic in SARNET network. Perspectives of code evolution

Titre du congrès :CSARP 2006 Cooperative Severe Accident Research Program Ville du congrès :Albuquerque Date du congrès :25/09/2006

The ASTEC integral code is jointly developed by IRSN and GRS (Germany) for LWR source term Severe Accident (SA) evaluation, PSA level 2 studies and SA management evaluation. ASTEC constitutes now the reference European integral code through its role in the Network SARNET (Severe Accident Network of Excellence) in the EC 6th Framework Program. The models of next version V1.3, soon released in Oct.06, represent the current State of the Art, its validation is very extensive (in particular on Phébus.FP) and, after next implementation of a model for reflooding of degraded cores, it will cover all needs for SA evaluation in PWR-VVER. It will be the reference code for the IRSN PSA level 2 on French PWR 1300 MWe that starts in 2006. In the frame of SARNET, IRSN coordinates the ASTEC Topic gathering 30 partners that assess the code through validation against experiments and benchmarks with mainly MELCOR and MAAP4 codes on plant applications. Besides, the knowledge generated by SARNET Topics (Corium, Source term and containment) will be progressively integrated into the code through improved or new models. The 2nd Users' Club organized by IRSN at Aix-en-Provence in June 06, with 45 participants from 27 organizations, allowed fruitful discussions with the Maintenance Team. After 2 years of work, code validation shows good overall results, often reaching limits of present knowledge (for instance on MCCI and DCH). Benchmarks on plant applications have shown that main trends of results are similar to MELCOR or MAAP4 results but some differences come from differences in current modelling. These benchmarks will focus in the next stage more on fission products results. Concrete action plans and associated teams have been set up for BWR and CANDU model adaptation and future benchmarks. At short term, perspectives of code evolution will focus on feedback from ASTEC V1 PSA2-1300 and SARNET applications, and on a new model of reflooding of a degraded core. The documentation will be largely improved, mainly users manuals and users guidelines. At long term, a 1st version ASTEC V2.0 is planned in 2008, where the ICARE2 IRSN mechanistic code will be the new core degradation module. This ASTEC version will include the EPR applicability, the simulation of external vessel cooling for new reactor designs and a full modelling of Ruthenium behaviour in circuit and containment for air ingress situations. Beyond, future evolutions of ASTEC code will concern first the repository of knowledge created in SARNET (in particular from ISTP experimental program), then the extension of scope of application to BWR and CANDU, also to Gen.IV reactors. Investigations have already started about decrease of calculation time in the perspective of future emergency tools and on the possibility to adapt ASTEC models for ITER safety evaluations.