OECD Analysis and Management of Nuclear Accidents Integrated Plan


  • Committee on the Safety of Nuclear Installations
  • 15 pages
  • For Official Use
  • September 2009


1. WGAMA Mandate


The Working Group on the Analysis and Management of Accidents (WGAMA) shall be responsible for activities related to potential accidental situations in nuclear power plants, including the following technical areas: reactor coolant system thermal-hydraulics; design-basis accident including ECCS strainer clogging; pre-core melt conditions and progression of accident and in-vessel phenomena; coolability of over-heated cores; ex-vessel corium interaction with concrete and coolant; incontainment combustible gas control; physical-chemical behaviour of radioactive species in the containment; fire safety. The activities will mainly focus on existing reactors, but will also comprise applications for some advanced reactor designs. Priority setting will be based on established CSNI criteria as documented in the CSNI Operating Plan, in particular on safety significance as well as risk and uncertainty considerations.


The WGAMA objective is 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 fulfil this objective, the working group shall:

  • 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

The Working Group shall report to the Committee on the Safety of Nuclear Installations (CSNI) and
assist this Committee with its work. The activities will normally be carried out by small task groups,
each set up for performing a specific task under the WGAMA supervision. The output of the Working
Group will consist of state-of-the-art reports and other technical reports, workshops and related
proceedings, benchmarking exercises and joint research proposals.

The Working Group will aim to provide answers as requested by CSNI and/or CNRA and will coordinate
its work with other working groups, notably with WGRISK for risk related issues and for
priority setting, WGOE for emerging issues and WGIAGE for ageing and structure integrity
evaluation. WGAMA will also work in co-ordination with the NEA-NSC on scientific issues such as
advanced coupled neutronic / thermal-hydraulic methods. Interaction with joint projects will be
strengthened as recommended in the CSNI Operating Plan.

2. WGAMA vision and goals

The Group vision is to make significant contributions in the followings safety related areas:

  • Regulatory decision-making regarding prevention and management of accidents and related high priority safety issues, through the elaboration of existing information or data available in member countries. Where appropriate, missing information should be identified, providing also recommendations on how to obtain it. The input for activities in this sector is expected to come from CSNI, CNRA (through CSNI) or directly from member countries (through their representative in WGAMA). Typically, the duration of each activity should not exceed 1-1½ year. The products would be recommendations on best use of existing knowledge for accident management purposes or on means to acquire more information where needed. Regulators and industry are to be the main users of these WGAMA products.
  • Analyses of relevant operational events, for the purpose of producing an as clear as possible understanding of specific events and for identifying possible preventing measures. The analyses may expand over a broader range of conditions in order to evaluate the extent to which similar events in different circumstances might challenge plant safety. Investigations may also address industry initiatives aimed to increase plant output through e.g. power up-ratings and plant life extension, for which co-operation with other CSNI WGs would be needed. Possible lack of knowledge of the processes involved or limitations in models or computer codes prediction capability might surface from work in this sector. Thus, activities in this area may have varying duration depending on scope and on the obtained results, and may be structured in distinct self-contained phases. Input is expected to come from WGOE, from CSNI or directly from member countries. The product would be assessments based on analyses carried out by one or more parties with one or more analytical tools. Users would be regulators, safety research organisations and industry.
  • Assessment of the state of knowledge and progress in the understanding of phenomena and processes governing the occurrence, progression and mitigation of potential accidents, including improved methodology 1 and performance and use of safety analysis codes. Gradually increasing attention should be given to new or advanced reactor systems, for which there will be a need of substantial knowledge build-up. As this is a broad and not precisely defined area of work, rigorous criteria should be applied in setting priorities, focusing on those areas that have higher safety relevance and/or a more pronounced risk profile, and for which relevant outcome is likely to be produced in a reasonable time frame. The activities in this sector are expected to constitute the “base-load” of the WGAMA group. As they may be long lasting, it is very important that they be well prioritised and structured, such that useful intermediate results are systematically bought forward: interaction with WGRISK is important for priority setting. Input is expected to come from CSNI or from member countries (through their representative in WGAMA and/or in WGRISK). Output is to be used by safety analysts.

Strategy for new WGAMA activities

Most of the present WGAMA programme has dealt or deals with

  • Calculation tools and methods, such as the CFD and BEMUSE tasks
  • Benchmarking exercises such as ISP-41, ISP-47, ISP-49, ISP-50 and CFD benchmark based on customised T-junction experiment or the accident progression exercise
  • Knowledge assessment through state of the art reports, e.g. on iodine or nuclear aerosols
  • Data preservation and knowledge transfer (CCVM and THICKET)

It can be observed that in most cases the programme has been oriented towards generic aspects, without entering into the specifics of well-defined issues or of particular reactor designs or accident management features. An exception has been the SERENA programme, which has focussed on the invessel and vessel steam explosion issue.

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