Nuclear Energy Agency Online Bulletin

November 2003

Nuclear science news

Working Party on Nuclear Criticality Safety (WPNCS)

The Working Party on Nuclear Criticality Safety and its expert groups held their annual meetings in Tokyo, Japan on 15-17 October 2003. An overview of their recent activities is presented below.

The Expert Group on Burn-Up Credit discussed the final results of the Phase II-C benchmark on the sensitivity to burn-up profile asymmetry. The publication of the associated report is planned for 2004. The group defined a new benchmark (Phase II-D) on the effect of absorbers on burn-up calculations. The final specifications of the Phase II-D benchmark will be published by the end of 2003. A report summarising the findings of the group's work to date and the lessons learnt will be published in 2005.

The Expert Group on Criticality Excursion Analysis is addressing the lack of information on available computer codes for criticality transient simulations by encouraging member countries to fully describe the features of their codes using a standard identification sheet. In parallel, inter-comparison exercises are under way to compare the prediction capabilities of these codes using experiments from the French Commissariat à l'energie atomique (CEA) at Valduc and the Japan Atomic Energy Research Institute (JAERI). A shortened version of the draft format for reporting transient experiments that was proposed last year was adopted for the initial phase of this work. The more complete format may be used in the future if sufficient interest and support for this work is established. Moreover, the scope of the group was broadened by considering simplified evaluation models needed for criticality safety assessment.

The Expert Group on Minimum Critical Values agreed on a timetable for the production and publication of the final report compiling and comparing minimum critical data for a set of homogeneous water-moderated and reflected uranium and plutonium media. In 2004, the expert group will review proposals for the continuation of this work.

The Expert Group on Source Convergence Analyses discussed the final draft reports of four inter-comparison exercises. These reports will be published in early 2004. Further investigations to better understand the effect of Monte Carlo simulation options on the statistical properties of calculated k-eff replicas are planned for 2004. In parallel, work is ongoing at both the French Institut de radioprotection et de sûreté nucléaire (IRSN) and the US Los Alamos National Laboratory to implement statistical methods for the detection and suppression of generations in which the source distribution is unconverged. A detailed programme of work for the validation of these methods will be elaborated in 2004.

The International Criticality Safety Benchmark Evaluation Project has published a new edition of the ICSBEP handbook. The handbook contains 3070 critical and subcritical experimental configurations (189 were added in the new edition). Both the September and the October 2003 issues of the journal Nuclear Science and Engineering feature the ICSBEP project.

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