Reactivity Initiated Accident (RIA) Fuel Codes Benchmark Phase-II – Volume 1: Simplified Cases Results Summary and Analysis

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Reactivity-initiated accident (RIA) fuel rod codes have been developed for a significant period of time and validated against their own available database. However, the high complexity of the scenarios dealt with has resulted in a number of different models and assumptions adopted by code developers; additionally, databases used to develop and validate codes have been different depending on the availability of the results of some experimental programmes. This diversity makes it difficult to find the source of estimate discrepancies, when these occur.

A technical workshop on “Nuclear Fuel Behaviour during Reactivity Initiated Accidents” was organised by the NEA in September 2009. A major highlight from the session devoted to RIA safety criteria was that RIA fuel rod codes are now widely used, within the industry as well as the technical safety organisations (TSOs), in the process of setting up and assessing revised safety criteria for the RIA design basis accident. This turns mastering the use of these codes into an outstanding milestone, particularly in safety analyses. To achieve that, a thorough understanding of the codes predictability is mandatory.

Volume 1 of the report provides a summary and documents the conclusions and recommendations from the first activity.

A detailed and complete RIA benchmark Phase II specification was prepared in order to ensure as much as possible the comparability of the calculation results submitted. The specifications regarding the first activity are compiled in the Volume 2 of the present report.