SARNET

Aims

• Improved coordination of research capabilities on core meltdown accidents

• Helping to reduce the remaining problems in this area by conducting appropriate joint research programs

• Integrating the best state of knowledge in high-performance numerical simulation tools (ASTEC software in priority) for the evaluation of reactor safety, most notably in the context of Level 2 Probabilistic Safety Assessments (PSA2), i.e. probabilistic studies of the consequences of core meltdown accidents

• Disseminating knowledge and training new experts in this field

Activities of the network

Analysis of needs and drawing up of research programs

The main directions to be pursued by European research programs to answer the essential questions in the field of core meltdown accidents are periodically redefined, using the methodology adopted in the EURSAFE project of the 5th PCRD. The preliminary lessons learned from the accident at the Fukushima Daiichi Plant in March 2011 were taken into account in the final report on research priorities issued by SARNET in mid-2013. Program proposals are drawn up by taking existing programs into account and by seeking to take advantage of the complementary features of the various laboratories.

Research work and summary of knowledge

This activity, conducted along the priority lines defined in the first phase of the network, aims to conduct research work and supplying 'state of the art' reports and recommendations in terms of physical modelling.

Four areas are covered:

• The possibility of cooling the core or the corium (mixture of materials resulting from the melting of the core) inside the vessel (flooding of a degraded core, etc.).

• The interaction between the corium and the concrete of the foundation raft on which it may rest after the failure of the vessel bottom head, and the possibility of cooling it.

• The strength of the containment vessel (possibility of hydrogen combustion, steam explosion, etc.)

• The behaviour of the radioactive products released from fuel(in particular impact of oxidising conditions, like air ingress, on release from fuel and transport in circuits, chemistry of iodine in the primary circuit and the containment).

New experimental programs have been conducted within the network, particularly on the first two topics mentioned above. Their joint interpretation by the partners and the comparison of calculations from different computer programs have improved understanding of the phenomena and their physical modeling.

All the experimental results produced and used by the partners have gradually been collected, following the same protocols, in a network of controlled-access databases (based on the STRESA tool developed and maintained by the European Commission's Joint Research Center) for reliable archiving. At the beginning of 2013, the results of 265 tests conducted in 43 installations were stored in the database.

There are close partnerships with the other international projects (e.g., OECD projects).

Development of tools and reference methods 

ASTEC software, developed jointly by the IRSN and the GRS, is supplied to members of the network who contribute to its validation. ASTEC has progressively integrated the physical models developed in the network, and is being adapted to the needs of users for their interpretation work and their application to reactors. It is already applicable to Generation II and III pressurized water reactors (including EPR), and its extension to boiling water reactors and Candu reactors is in progress. Because it capitalizes on acquired knowledge, widely distributed, ASTEC has become the European reference for computation software concerning core meltdown accidents.

All the experimental result produced and used by the partners are gradually collected, according to the same protocols, in a network of databases with controlled access in order to guarantee their continuity.

Work on the harmonization of methods used for PSA2 took place in the first phase of the network. A certain amount of progress was achieved, and since 2008 the efforts have continued in a separate European PCRD, ASAMPSA2, uniting 21 European organizations and coordinated by the IRSN. Close consultation is maintained between the two projects.

Finally, all the experimental results produced and used by the partners are gradually collected, according to the same protocols, in a network of databases with controlled access in order to guarantee their continuity.

Spreading knowledge

The transmission of knowledge is one of the objectives of SARNET.

In addition to training in the use of ASTEC, knowledge transfer takes place in four ways:

• A big conference, ERMSAR (European Review Meeting on Research on Severe Accidents), is periodically organized to present and discuss the progress achieved in the network. This conference is gradually becoming one of the major international events in the field of core meltdown accidents:
• Training courses are organized periodically for students and young researchers or for specialists with a certain amount of experience,
• A book on ‘Core meltdown accidents’, targeting the scientific community, will be published in late 2011, 
• A mobility program allows young scientists or students to be detached to other laboratories in the network for several months in order to familiarize themselves with the research taking place there. Seven conferences have been organized since 2004, and the next will be hosted in Warsaw by NCBJ, a Polish TSO, in the spring of 2017;
• Week-long training courses are regularly organized for students and young researchers, or for specialists with a certain amount of experience. Six courses have been organized since 2004, with the last held in July 2015 at the University of Stockholm;
• A book on core meltdown accidents for readers in the scientific community was published at the end of 2011;
• There have been numerous publications in scientific journals and presentations at national or international conferences: at time of mid-2013, 93 articles in peer-reviewed journals and 262 conference presentations. Two special journal issues have been published: a focus on ASTEC, for Nuclear Engineering and Design (early 2014); and a selection of the best articles of ERMSAR 2013, for Annals of Nuclear Energy (in spring 2014). A third issue of Annals of Nuclear Energy presenting a selection of ERMSAR 2015 articles is scheduled for early 2016.
• A mobility program allowed young researchers and students to be assigned to other laboratories within the network so that they can learn about the research work being conducted there.

Status and outlook of SARNET

SARNET has been a real success. On the one hand, the network has been able to define – as part of a broad consultation process involving industrial groups, research bodies and TSOs – the areas in which European research efforts relating to core meltdown accidents should be prioritized. On the other hand, it has been able to organize research in these priority areas by drawing on the expertise and additional resources of the various members of the network. The network regularly reviews its priorities in light of international developments, particularly in order to take into account safety concerns and progress in international research. The network has strengthened its European leadership in the area of core meltdown accidents, and has consolidated the position of ASTEC software as an international reference. Finally, it has produced numerous summary and status reports, the distribution of which, together with training courses and seminars, has helped increase the knowledge and expertise of new generations of scientists concerned with the safety of the electronuclear industry.

This trend is set to continue, as one of the lessons learned from the Fukushima accident was the need to strengthen the capacity to mitigate the consequences of core meltdown accidents. Accordingly, future programs will be developed in this priority area. Since mid-2013, the network has been integrated into NUGENIA (NUclear GENeration II & III Association), an international body whose mission is to coordinate all European research on generation II and III reactors. NUGENIA has assigned SARNET the task of coordinating one of its eight research topics: this topic ranges from core meltdown accidents to crisis and post-accident situations. The activities of the network expanded by the two latter subjects are coordinated by the IRSN within a new framework, which does not, however, call into question SARNET's internal modus operandi (conferences, technical seminars, courses, development of new projects, etc.). Note that the network is now open to any NUGENIA member, but other organizations may attend certain events, such as the conferences, seminars and courses.

The network's success is now recognized beyond the confines of Europe, several new partners (from Poland, Canada, Japan, and elsewhere) are now contributing to its activities, and still other parties are expressing their interest on a regular basis.