Research on Significant Isotopes Selection of Postulated Siting Accident

Fission product inventory in reactor core includes thousands of radioisotopes, it is not feasible to consider such a large number of radioisotopes in the accident source term analysis since the calculation amount is too large. Therefore, selection of significant isotopes from such a large number of radioisotopes for accident source term analysis is a key issue in the design and safety review of nuclear power plant. The selection of significant isotopes should not only be convenient for source term analysis, but also ensure the accuracy of dose results. Energy sector standard of China NB/T 20470-2017RK stipulates the selection of significant isotopes, requiring that the dose contribution of the screened significant isotopes should not be less than 90% of the total dose results. In this paper, a selection method of significant isotopes was proposed along with the postulated siting accident source term analysis for HPR1000. A group of significant isotopes that had indispensable contributions to the dose results were screened out according to their core inventory, half life, release characteristics and contribution to the dose results. The dose contribution of the screened significant isotopes accounted for more than 99% of the total dose results, far exceeding the criterion of 90% in NB/T 20470-2017RK.