The EVITA (European Validation of the Integral Code ASTEC) project is a shared-cost action of the 5th Framework Programme (FwP) of Euratom. The project, coordinated by GRS (Germany) with a very strong support from IRSN, started in February 2000 and ended in July 2003, involving 20 partners (researchers, universities, utilities, vendors and licensing authorities) from 8 European countries. The main objective was to distribute the severe accident integral code ASTEC (Accident Source Term Evaluation Code), jointly developed by IRSN and GRS, to European partners in order to apply the validation strategy issued from the VASA project within the 4th FwP and achieve a first evaluation of code capabilities by users independent from the code developers. The ultimate aim was to achieve an important step towards a well-validated European integral code for the simulation of severe accidents in European reactors, including severe accident management.
Experiments and severe accident plant sequences have been selected for the ASTEC validation and application process:
- Validation on high-quality experiments such as OECD International Standard Problems (ISP),
- Plant applications on different types of reactors (PWR, VVER) with activation of safety systems (spray, venting, etc....).
Each ASTEC application included a comparison with internationally used codes that should represent the State of the Art in terms of modelling: detailed (or mechanistic) codes for validation, integral codes for plant applications.
Two successive ASTEC versions (V0 and V1) were installed successfully on the partners’ platforms and training courses for code users were organized. The V1 version allowed for the first time a simulation of the front-end phase of the scenario, dealing with two-phase thermalhydraulics of primary and secondary circuits.
The main outcomes of the project were on one hand a first level of validation by partners independent from code development teams, and on the other hand the conclusion that ASTEC models were near or at the State of the Art for most physical phenomena. Of course, like for other codes, some model improvements needed to be yet done on phenomena not fully understood (core reflooding, long-term molten-corium-concrete interaction, iodine behaviour in primary circuit..).
As regards the calculation time, the partners agreed on the target that has been defined in VASA previous project (4th FwP), i.e. less than 12 hours for a complete calculation of a reactor sequence (including automatic post-processing of the results).