An Industry Initiative to Facilitate the Criticality Assessment and Subsequent Licensing of Transport Packages

The World Nuclear Transport Institute (WNTI) set up an Industry Task Force in 2005 to explore the possibility of developing an Industry Knowledge Base on Criticality Assessment. The objective of the Knowledge Base is to provide a philosophy and source of technical data to assist applicants in the preparation of criticality safety cases with a view to achieving, where practicable, worthwhile harmonisation. The initial focus has been on new and spent fuel assemblies; the intention is to consider the full range of nuclear fuel cycle materials eventually. Currently, when considering hypothetical accident conditions, the underlying assumptions can differ widely from application to application. One stage of the Task Force process has been to increase understanding of the basis for approaches to identifying and justifying realistic and achievable configurations of nuclear materials following an impact accident. A challenge for industry is to see if it can arrive at a more common understanding of realistic worst cases, i.e. those which have most effect on the approach to criticality, based on sound engineering principles and analysis, coupled with experimental evidence. The importance of reaching a consensus on the content and style of the Knowledge Base was recognised and a way forward has been agreed which successfully addresses the above issues. Good progress has been made. Sections of the Knowledge Base addressing fuel lattice expansion and fuel pin cladding failure have been drafted; abstracts of relevant and supporting information have been prepared in support and areas requiring further substantiation have been identified. At the most recent workshop, earlier this year, sections of the Knowledge Base covering e.g. enrichment mapping, water ingress and burn-up credit were considered and are now in preparation.