ASTEC status and applications

J.P. Van Dorsselaere, F.Jacq (1), H.J. Allelein, B.Schwinges (2).
CSARP meeting, 6-8 mai 2003, Bethesda (USA)

The version ASTEC V1.0, jointly developed by IRSN and GRS, was delivered mid-2002 to 15 European partners (utilities, designers, safety authorities, R&D) in the frame of the EVITA project (EC 5th F.P.) devoted to code validation by independent users. This code version simulates the complete scenario, starting from the front-end thermalhydraulics phase, and includes most core degradation models from the IRSN reference code ICARE2. Most modules are currently used for IRSN PSA2 on 900 MWe reactors. Applications to several scenarios on French 900-1300 and German 1300 PWR, VVER-440 and –1000 are being performed in EVITA project.

Strong continuous efforts are put on validation. The intensive work performed with the previous V0 version is being extended to the RCS thermalhydraulics field (LOFT-LP-FP2, CORA-13…), to the OECD ISPs and to VVER-specific experiments (partly in EVITA and in the frame of collaboration IRSN-Kurchatov Institute). ISP46 application on Phébus FPT1 integral experiment gave overall correct results (except for iodine chemistry) and proof of code consistency. ISP 41 results on CAIMAN and AECL tests showed IODE capability to reasonably evaluate gas iodine concentrations in different conditions (pH, T, dose…). As for VVER field, the application to the EREC T5 experiment on VVER-440 containment thermalhydraulics with bubble condenser towers showed a general agreement with measurements (except on pressure oscillations). In parallel, the ASTEC fission product (FP) modules (release, transport, iodine) are being used as reference tools for detailed interpretation of the integral tests Phébus.FP. As for plant applications, current efforts focus on a detailed analysis of a Loss of Steam Generator Feedwater sequence on French 900 and 1300 MWe PWRs. Preliminary VVER applications cover an integral calculation of SBLOCA on VVER-1000 (RCS results are in general agreement with ICARE/CATHARE ones) and MBLOCA on VVER-440/V213 where the vessel nodalization accounts for bundle shrouds in the core and fuel followers in the vessel lower plenum.
In the next 2 years, the efforts will focus on code consolidation through an extension of validation (TMI-2, LOFT…), plant calculations and benchmarks with other codes in order to increase the code robustness. EVITA outcomes will be taken into account by the development team about code use, SAM capabilities, and guidance for further validation. But some developments will continue: for instance the new MCCI module MEDICIS, core quenching models, FP release from molten pools, complete 800 species thermochemical bank for RCS gas chemistry, improvement of H2 combustion model in containment for fast turbulent deflagrations, ICH3 radiolytic destruction. The progressive implementation of MDB Material Data Bank containing all properties (physical, chemistry reactions, isotopes…) is also important for general consistency and for code quality and robustness. At the end of 2004, the version ASTEC V1.2 should represent most PWR features with models at the state of the art, and be sufficiently reliable and validated for allowing a wide scope of plant applications on present PWR and VVER.
Beyond, the ASTEC V2 developments aim at modeling the remaining risk-relevant key-phenomena such as corium coolability, FP release from MOx fuel, FP retention in complex structures, gaseous iodine chemistry in RCS (including kinetics), and iodine behavior under radiation (including interactions iodine-painted walls). This is mostly consistent with outcomes of the PIRT performed in 2002 in the EURSAFE EC 5th FP project. Validation will have to be performed on further experimental programs such as ARTEMIS (IRSN), OECDMCCI, ARTIST (PSI), CHIP (IRSN), EPICUR (IRSN). Other objectives will be the extension to other types of reactors (BWR, RBMK, future designs…), the merging with more detailed codes ICARE2 and COCOSYS (GRS), the extension of coupling capability with other codes and a broader use for safety studies (PSA2, European countries…).An important step will be in 2004 the new EC 6th FP project Severe Accident Network of Excellence SARNET where ASTEC will be the reference European integral code.

(1) : IRSN
(2) : GRS