An Overview of Past and Present Activities in the Severe Accident Domain within the Framework of WGAMA
NURETH-14 - 2011 September 25-30

Presented at:
2011 September 25-30
Toronto, Canada
Session Title:
O9-2 OECD NEA Session on Analysis and Management of Accidents (Best-estimate methods and uncertainty

Salih Guentay (Paul Scherrer Institut)


The objectives of the NEA-CSNI’s Working Group on the Analysis and Management of Accidents (WGAMA) are to assess and where necessary strengthen the technical basis needed for the prevention, mitigation, and management of potential accidents in nuclear power plants, and to facilitate international convergence on safety issues and accident management analyses and strategies. In order to fulfill this objective, the working group undertakes:

§   Exchange technical experience and information relevant for resolving current or emerging safety issues,

§   Promote the development of phenomena-based models and codes used for the safety analysis, including the performance of benchmarking exercises,

§   Assess the state of knowledge in areas relevant for the accident analysis and where needed,

§   Promote research activities aimed to improve such understanding, while supporting the maintenance of expertise and infrastructure in nuclear safety research.

Continuing to be active in the severe accident field as the successor of the previous principle working group 4 (PWG4) of CSNI, WGAMA has accumulated an immense consolidated knowledge, which has been created along the years and reflects the improved understanding in very complex severe accident phenomenology, their modeling and  their risk and safety relevance.

WGAMA activities related to severe accidents include exclusively the following technical areas: progression of accident into core damage and associated in-vessel phenomena; coolability of over-heated cores; ex-vessel corium interaction with concrete and coolant; in-containment combustible gas control; physical-chemical behavior of radioactive species in the containment. The activities mainly focus on existing reactors, but will also comprise applications for some advanced reactor designs.


Being established in 2000, WGAMA carried out the activities which had been initiated by the former PWG 4 group for the first few years, and initiated several more afterwards. A more targeted approach was introduced in 2005 to set-up the priorities and timeline of new activities. As a result, selection of the currently running activities was established by a careful review of all relevant severe accident issues and considering the status of research being conducted in 2006-2007. Several severe accident issues that have potential to be tackled by means of the standard OECD tools were identified and grouped under 11 main titles. The appropriate activity type was assigned to each issue under the main title, their risk and regulatory relevance was determined based on responses of WGAMA members and possible activities in the short, mid and long term were defined. Currently (2010-2011), the screening process is repeated since many of the international severe accident projects have been completed or are well advanced.


The present paper will provide a brief overview of the WGAMA activities carried out in the last three decades in the severe accident field. It will highlight the results achieved in fission product release, transport, deposition and retention behavior, in-vessel behavior of degraded cores and in-vessel protection, containment behavior and containment protection, as well as in reaching a common understanding of severe accident management measures and their treatment in risk assessment.

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