The French Institut de Radioprotection et de Sûreté Nucléaire (IRSN) and the German Gesellschaft für Anlagen und Reaktorsicherheit mbH (GRS) have been jointly developing since the mid-90s the system code (also called “integral” code) ASTEC (Accident Source Term Evaluation Code), to simulate the full sequence of events occurring during a severe accident (SA) in a water-cooled nuclear power plant (NPP), from the initial events yielding the loss of reactor core cooling until the possible release of radioactive substances out of the reactor containment, so-called “source term” to the environment. The ASTEC application range covers Severe Accident Management (SAM) measures (i.e., prevention and mitigation measures), estimation of the risks associated with SA various sequences and of the corresponding radioactive releases by an extensive use in level 2 Probabilistic Safety Analysis (PSA2) studies and calculation of the source term to the environment in view of assessing countermeasures for the protection of the population and the environment against radiological hazards. Taking benefit of its modular structure, some ASTEC modules have been optimized for implementation at the IRSN emergency centre.
ASTEC has progressively reached a larger international dimension through projects of the European Commission Research Framework Programmes (FP), first VASA (VAlidation strategy of Severe Accident codes) from 1998 to 2000 and EVITA (European Validation of InTegral code ASTEC) from 2000 to 2004, both coordinated by GRS. Then, in the frame of the SARNET European Network of Excellence in FP6 and FP7, coordinated by IRSN, jointly-executed research activities were performed from 2004 to 2013 with the ultimate objective of providing state-of-the-art models for integration into ASTEC and make the code, in its current family of V2 versions since 2009, the European reference tool for severe accident studies. Almost forty collaboration agreements have been signed with IRSN or GRS on ASTEC development and validation, including partners out of Europe (Russia, Belorussia, Canada, India and China).
The ASTEC models have been developed and validated using the understanding gained from international SA research. They took a great benefit from the detailed interpretation of the Phébus FP integral experiments that were performed by IRSN at Cadarache in the last 20 years. The latest version V2.0 rev3 of the code is applicable to most Generation II and III NPPs (in particular EPR), and the new FP7 project CESAM starting in 2013 aims at improving the modelling concerned with priority SAM measures for all types of European NPPs, in particular in the light of the Fukushima-Daiichi accidents. The scope of application is being extended to BWR and CANDU reactors, particularly for the models of core degradation (while most other models of the current version are already applicable). The code is also being applied by IRSN to accidents in the ITER fusion nuclear facility. Besides the feedback of international SA research, the next major ASTEC version V2.1, to be released end of 2014, will provide in particular a unified vessel-RCS thermal-hydraulics and models of reflooding of a severely degraded core.
This Nuclear Engineering and Design special issue is the opportunity to summarize the code status after very valuable collaborative development, assessment and application during 8 years in and out of SARNET. It presents an overview of the code models and validation, as well as illustrations of diverse scenario calculations in French 1300 MWe, VVER-440 and -1000 NPPs, as well as in the Fukushima-Daiichi plants. It gathers 15 papers written by IRSN, GRS and seven partners (ENEA in Italy, IVS in Slovakia, AREVA NP SAS in France, University of Bochum in Germany, INRNE in Bulgaria, Kurchatov Institute in Russia and BARC in India).
In the future, ASTEC will remain the European repository of knowledge gained from international R&D on SA but due to the number of NPP applications now growing rapidly, efforts will focus too on improvements of user's tools, simplification of input decks and computing time reduction. Other long-term objectives are on one hand the adaptation to accidents in Sodium-cooled Fast Reactors that started in 2011 in the frame of the FP7 project JASMIN, and on the other hand an extended use in support to emergency response tools and for severe accident simulators.
The former and present ASTEC project leaders must be acknowledged, F. Jacq, Jean-Pierre VAN DORSSELAERE and P. Chatelard on IRSN side and H.J. Allelein, B. Schwinges and N. Reinke on GRS side, as well as the whole IRSN-GRS ASTEC team. The European Commission must also be acknowledged for the funding of the SARNET and CESAM projects of the 7th Framework Programme of Research and Development.