Since several years, the French Institut de Radioprotection et de Sûreté Nucléaire (IRSN) and the German Gesellschaft für Anlagen und Reaktorsicherheit mbH (GRS) have been jointly developing a system of calculation codes, so-called “integral” code, ASTEC (Accident Source Term Evaluation Code) to simulate the complete scenario of a hypothetical severe accident in a nuclear water-cooled reactor, from the initial event until the possible radiological release of fission products out of the containment.
The latest ASTEC V1 version (namely the V1.3-rev2 version), which was released by IRSN and GRS in December 2007, was in particular extensively used in 2008 by European partners in the frame of the last year of the SARNET phase-1 project.
This V1.3-rev2 version allowed complete calculations of different severe accident sequences on PWR-900, PWR-1300, KONVOI-1300, VVER-1000 and VVER-440 operating at full power, such as station black-out, loss of steam generator feed-water, steam generator tube rupture, as well as small, medium and large break loss of coolant accidents.
Overview of the WP4.1 work-package (USTI Work-Package)
The WP4.1 activity aims at providing a support to ASTEC code users through delivery of code versions and revisions, assistance in code use, organisation of training courses … as well as at enhancing code use experience through organisation of users’ club meetings.
In that frame, IRSN and GRS have proceeded to the freezing in June 2009 and the delivery in July 2009 of the ASTEC V2.0 version (first version of the new series of ASTEC V2 versions) to any SARNET-WP4 partner.
At the same time (from June 29 up to July 3, 2009), a one-week training course for ASTEC beginners was hosted by IRSN at Aix-en-Provence.
In addition, a dedicated ASTEC web site was built à IRSN and is now operating since end of October 2009. Its objective is to provide users with an easy way to download either any code documentation update or any future code version (new version or patch-version).
Overview of the WP4.2 work-package (ACAS work-package)
The WP4.2 activity aims at covering a broad matrix of ASTEC reactor applications, aiming at the most important accident scenarios for 5 types of reactors (PWR, BWR, VVER, EPR, CANDU), as a direct continuity to the RAB work-package from the SARNET 1st phase.
As concerns in-vessel analyses, one of the main expected improvement lies in the modelling of the core degradation processes, thanks to the use in ASTEC V2 of the new 2D magma model (issued from the best-estimate IRSN ICARE/CATHARE code) instead of the quite simple 1D candling model from ASTEC V1.
In complement to these plant applications, ASTEC assessment will continue as a direct continuity to the PHYMA work-package from the SARNET 1st phase. However, only a part of these validation activities will be carried out in the frame of this WP4.2 work-package, the other part being directly managed within four other dedicated work-packages (for instance, quenching models will be assessed in the frame of the WP5-COOL work-package, MCCI models will be assessed in the frame of the WP6-MCCI work-package, …).
Overview of the WP4.3 work-package (AMEX Work-Package)
The WP4.3 activity aims at extending the current ASTEC applicability (i.e. the applicability to PWRs and VVERs as it was demonstrated during the SARNET 1st phase using the ASTEC V1.3-rev2 version) to BWR and CANDU reactors.
According to the conclusions drawn at the end of the SARNET 1st phase, the main efforts to allow ASTEC simulating severe accidents in BWR and CANDU should be paid to the modelling of the vessel components behaviour (thermal-hydraulics and core degradation).
So, the capabilities of the current ASTEC circuit thermal-hydraulics module will be first evaluated through dedicated benchmark calculations.
In parallel, the main work to be done in priority will consist in the elaboration of the technical specifications concerning either the adaptation of existing ASTEC models or the development of new models, focusing in particular on the in-vessel degradation aspects.
The next step will be to implement in accordance adequate models in future ASTEC versions, to be then intensively used for BWR and CANDU full scale applications in the frame of the WP4.2 work-package.