Nuclear Energy Agency Online Bulletin

September 2000

Nuclear Safety Information


The first meeting of the CSNI Programme Review Group was held at the NEA on 3-4 July. The main points of the meeting are briefly summarised below:

  • The Programme Review Group (PRG) elected Mr. King (US NRC) as its Chairman.
  • It discussed its mandate and its working methods, as well as the main points of its working procedures.
  • It discussed a methodology to compile and prioritise a "CSNI List of Current Safety Issues", and agreed on a preliminary list of high-level safety issues as well as on a procedure to produce descriptions of these issues and obtain comments from CSNI Working Groups and Special Expert Groups.
  • It discussed the current and proposed programme of work of the Working Groups and Special Expert Groups, and made a number of recommendations.
  • It identified several cross-cutting issues. It discussed in some detail the topic of safety margins analysis, recognised a number of problems in this area, and decided to examine the matter in greater depth at its next meeting.
  • It decided to take the lead on the preparation of a Collective Opinion Statement stressing the main outcome and recommendations of the work of the former Senior Group of Experts on Nuclear Safety Research Facilities and Programmes (SESAR/FAP), widening the perspective to include aspects of the need to preserve a critical mass of safety research capabilities as well as the role of safety research in maintaining safety competence.
  • It heard a brief progress report on the establishment of OECD Joint Projects.
  • It discussed how to take over the work undertaken by the SESAR/FAP and decided to continue the proactive attitude of the Senior Group in the area of major facilities, programmes and capabilities at risk while relying more on the input from the Working Groups and Special Expert Groups.
  • It expressed willingness to participate in the Organising Committee preparing the June 2001 CNRA/CSNI Special Meeting on the Role of Safety Research in the Regulatory Context.
  • The second meeting of the PRG will be held at the NEA on 16-17 October 2000. The PRG agreed on the main lines of the agenda of the meeting.

Results of the work of the CSNI/PWG2 Task Force on Fuel Safety Criteria have recently been published in the CSNI report NEA/CSNI/R(99)25 entitled Fuel Safety Criteria Technical Review.

Most current safety criteria were established during the 1960s and early 1970s, and verified against experiments with fuel that were available at that time, mostly with unirradiated specimens. In order to optimise fuel cycle cost, the nuclear industry began work in the mid-1980s on new fuel and core designs with the aim of increasing fuel burnup, for example, for extending the cycle length or upgrading the power level. This again led to a number of basic design changes, e.g. new cladding materials. New demands on fuel and plant performance, however, have reduced the available margins. In addition, optimising fuel utilisation and core performance show a trend towards conditions where less operational and experimental experience exists.

The OECD/CSNI/PWG2 Task Force on Fuel Safety Criteria (TFFSC) was therefore given the mandate to technically review the existing fuel safety criteria, focusing on the "new" design elements (new fuel and core design, cladding materials, manufacturing processes, high burnup, MOX, etc.) introduced by the industry. It should also identify if additional efforts may be required (experimental, analytical) to ensure that the basis for fuel safety criteria is adequate to address the relevant safety issues.

Three separate meetings of TFFSC were held in June 1997, October 1997 and September 1998. Based on some individual members' contributions a draft of the report entitled "Fuel Safety Criteria Technical Review" was prepared for PWG2's consideration and submission to the CSNI for approval. The draft report was approved by the CSNI in December 1999. In the report, 20 different fuel-related criteria are discussed without attempting to categorise them according to event type or risk significance. For each of them, a brief description of the criterion as it is used in several applications along with the rationale for having such a criterion is presented. "New" design elements can affect fuel-related margins and, in some cases, the criteria themselves. Some of the more important effects are mentioned in order to indicate whether the criteria need to be re-evaluated. The discussion may not cover all possible effects, but should be sufficient to identify those criteria that need to be addressed. A summary of these discussions is given in Section 7 of the report.

As part of the assessment of the safety criteria, the Task Force looked at various issues, as they relate to one or more criteria, that have become of special interest. These topics included high burnup, core management, MOX, mixed cores, incomplete control rod insertion, and axial offset anomaly.

As a summary, the Task Force considered the current framework of fuel safety criteria generally applicable, being largely unaffected by the "new" or modern design elements; the levels (numbers) in the individual safety criteria may, however, change in accordance with the particular fuel and core design features. Some of these levels have already been - or are continuously being - adjusted; level adjustments of several other criteria (RIA, LOCA) also appear to be needed, on the basis of experimental data and the analysis thereof.

The report will also be available as an OECD/NEA publication in English and French versions.