Guide for nuclear criticality safety analysis and review - Accounting for neutron irradiation and radioactive decay

The paper and presentation refer to work on a Swedish guide but limits the discussions to differences and news compared with guides published elsewhere. Accounting for irradiation and decay has been considered in criticality safety during transport and storage in Sweden during at least 30 years. Sweden has participated in OECD/NEA studies, IAEA technical meetings as well as in initiations of ANS and ISO standards for irradiation credit. In early 2005, the Swedish industry expressed intentions to prepare for irradiation credit in CLAB, at a reactor site and in transport. There is no time to wait for international standards being completed. A recent revision of a statute related to the Swedish nuclear energy law gives guidance on criticality safety. Defence-in-depth as well as deterministic and probabilistic safety analyses is required. Consideration of irradiation and decay does not change the fundamental criticality safety principles. A primary incentive for irradiation credit in CLAB is reduction of administrative controls. The criticality safety related fuel specifications are based on fuel as well as reactor design and operation. A safety analysis covering routine and normal operation together with human error, incidents and accidents can be made only when these fuel specifications are coupled with the proposed storage or transport designs and operations. Realistic fuel specifications, including fission products, need to be considered during irradiation simulation, keff validation and verification measurements. Integral reactivity effects of irradiation and decay during different conditions need to be evaluated. A licensing process of the expected application for CLAB storage will determine specific criteria and requirements that may be useful in international standards development. (author)