Progress and perspectives of ASTEC applications in the European Network SARNET

The ASTEC integral code is jointly developed by IRSN (France) 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 6. Framework Program. The models of next version V1.3, released before end of 2006, represent the current State of the Art, its validation is very extensive (in particular on Phebus FP) and, after next implementation of a model for reflooding of degraded cores, it will cover all needs for SA evaluation in PWR and VVER. It will be the reference code for the IRSN PSA level 2 (Probabilistic Safety Analysis) 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 reference codes like CATHARE or RELAP5 for the reactor coolant circuit and COCOSYS for the containment. Plant application calculations are compared with MELCOR and MAAP4 results for a series of different SA sequences. 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 2. Users' Club organized 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 close to results of reference codes. Some results reach the limits of present knowledge, for instance on Molten-Corium-Concrete-Interaction (MCCI) and Direct Containment Heating (DCH). Benchmarks on plant applications have been performed on diverse reactor types: PWR 900, Konvoi 1300, Westinghouse 1000, VVER-1000 and VVER-440. The main trends of results are similar to MELCOR or MAAP4 results. The objective of the quantitative comparisons to be performed more intensively in the next period is to learn whether the differences on results are caused by differences in physical models and/or in safety systems modelling. These benchmarks will also more focus on fission products behaviour and on specific parts of the sequences such as MCCI. Concrete action plans and associated teams have been set up for BWR and CANDU model adaptation and future benchmarks. At short term, the code evolution will focus on feedback from PSA level2 1300 and SARNET ASTEC V1 applications, and on a new model of reflooding of a degraded core. The documentation will be largely improved, mainly users manuals and users guidelines. In parallel, the preparation by IRSN-GRS of a new family V2 of ASTEC versions has started. The general specifications will account for the needs as expressed by the SARNET users. 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 act as repository of knowledge created in SARNET and in the international context. The possible use of ASTEC to analyse severe accident sequences in future reactors (Generation IV, ITER) is under consideration. (authors)