Research on the induced radioactivity of HTR-PM's reactor pressure vessel: A comparative study between FLUKA, KORIGEN and QAD-CGA

The reactor pressure vessel (RPV), which is made of steel containing impurities, will be irradiated by a strong neutron field during the long-term operation of the reactor. Induced radioactivity due to neutron irradiation, which may affect the health of staffs during the maintenance and decommissioning, was studied in the case of the High Temperature Reactor - Pebble-bed Module (HTR-PM). The activation products and their corresponding specific activities were calculated by KORIGEN, which is based on deterministic method, and by the Monte Carlo code FLUKA. A comparison of these two programs shows good agreement, and the differences of specific activities are within one order of magnitude for 60% of the nuclides. Furthermore, the remanent dose rates at shutdown time and after 30 days, 1 year, 5 years and 10 years of cooling times were calculated by FLUKA and QAD-CGA, which is based on point-kernel integration technology. The comparison of dose results also shows good agreement. Meanwhile Monte Carlo method can give more accurate results. In the end, the ambient dose equivalent rates at typical points and times caused by the whole RPV were calculated by integration method. A preliminary radiation protection strategy was also concluded from these calculation results for HTR-PM's RPV decommissioning.