Assessment of dose rates due to a criticality accident - Influence of source and protections

13th International Congress of the International Radiation Protection Association (IRPA 13)

In the event of a criticality accident, exposure to ionizing radiations of workers located close to the accident site can be consequent. Moreover, as in the case of the Tokai-Mura criticality accident (Japan, 1999), significant dose rates can be reported at large distances from the place of the accident (several mSv.h-1 at several hundreds meters). In order to study the radiological consequences of such an accident, the exposure has to be estimated, not only for workers located in the accident vicinity, but also for other on-site workers and for population living in the surrounding area.

As a consequence, operators of nuclear plants dealing with fissile materials must add to their regulatory files, maps of dose rates and doses likely to be received in case of an hypothetical criticality accident, inside and outside of the concerned plant. As a technical support to the French Nuclear Safety Authority (ASN), the Institute for Radiological Protection and Nuclear Safety (IRSN) has developed an expert support tool, allowing to quickly assess the dosimetric consequences in case of a criticality accident.

This tool includes a database of dose rates calculations for numerous configurations of sources of criticality accident and biological protections, for distances up to 1 kilometre from the source. On the basis of dose rates (from neutrons and secondary gamma emissions) comparison, influence of source type (metallic, solution…), of shielding nature and thickness, and of distance from the source has been studied.

The proposed poster presents and analyzes some dose rates due to neutron and secondary gamma radiations obtained with this tool, depending on different parameters of the configuration (nature of the source, nature of the biological protections, and geometry).