Last update on April 2016
JASMIN (Joint Advanced Severe accidents Modelling and Integration for Na-cooled fast neutron reactors) is a project of the 7th Research and Development Framework Program (RDFP) of the European Commission. It seeks to extend to sodium-cooled fast neutron reactors (SFR) the use of ASTEC, a computer modelling package
that simulates core-meltdown accidents in water-cooled nuclear reactors. The
JASMIN project will run for four-and-a-half years and started in December 2011.
It subscribes to the general objective of enhancing the resistance of 4th
generation SFRs to severe accidents, a major objective of the Strategic
Research Agenda and Deployment Strategy set by the SNETP (Sustainable Nuclear
Energy Technology Platform).
Background and objectives
The European JASMIN project seeks to adapt ASTEC to sodium-cooled fast neutron reactors (SFR), a Generation IV reactor system, with the more general aim of developing advanced numerical simulation tools for this type of reactor. Current software systems for modelling accidents in SFRs date back to the 80s and are not flexible enough to model innovative reactor designs and possibly new types of fuel.
The JASMIN project focuses on simulating the initial phase of a core meltdown accident in an SFR. Nevertheless, new models that simulate the physical and chemical behavior of sodium aerosols within the containment1 have also been developed and integrated into the software. The resulting application – ASTEC-Na – uses adapted versions of many of the existing ASTEC modules, such as the thermohydraulic module. Other new modules also had to be developed, for instance to simulate the thermomechanical behavior of fuel and the fission gases it contains, and to simulate in a simplified way (with no significant fuel displacement) the evolution of the neutron power generated during an accident.
Development of the project
The project brings together nine partners and is coordinated by IRSN. It involves four main types of activity:
- managing the software system in terms of science and computing (i.e. integrating the models into ASTEC and checking they are correctly installed). Most of this work is carried out by IRSN;
- preparing general specifications for new developments. This involves all the partners;
- developing new models; sharing knowledge of existing physical models; comparing the calculation results with both existing experimental results and the results from existing software. All these tasks involve all the partners;
- disseminating of knowledge and the training of researchers and students.
The first eighteen months were spent specifying what would be developed and defining a matrix of tests to compare the results of the ASTEC-Na calculations either with experimental results, or with the results from other calculation packages. The matrix covered fuel behavior and thermohydraulics in the reactor vessel and included around ten tests using a single rod or a rod assembly, carried out using new fuel with a low, medium or high combustion rate and pellets with and without a central hole, for various types of accident transient (e.g. slow/fast, loss of flow rate or reactivity accidents).
Results and projections
Several versions incorporating successive developments were produced and delivered to the partners. In particular, new models for the physical and chemical behavior of sodium aerosols were developed based on the tests carried out by IRSN in collaboration with the University of Lille. The results from the ASTEC-Na calculations were compared with experimental results, mainly from the CABRI and SCARABEE programs (for the behavior of fuel during accident transients) and the ABCOVE and FAUNA programs (for sodium fires and the behavior of sodium aerosols respectively). All these programs were run by IPSN in the seventies and eighties.
The ASTEC-Na package was also compared with other calculational tools such as SIMMER, SAS-SFR and CONTAIN. Its application might later be extended to SFRs in other phases of a severe accident (transition and long-term phases) and possibly to fast reactors cooled by different molten metals.
The various exercises comparing the results of the ASTEC-Na calculations with experimental results and results from other packages are currently at the final-analysis stage. They will enable us to draw conclusions about the level of development and the quality of the validation achieved by ASTEC-Na, and guide us in planning subsequent developments.
1. This is relevant particularly to accidents in which primary sodium is ejected outside the reactor vessel and burns (a "sodium fire") within the containment.