Research On Calculation Of Release Source Term In Pressurized Water Reactor Nuclear Power Plant

The emission of gaseous and liquid radioactive releases has always been the focus of safety assessment and environmental impact assessment of nuclear power plant.It is of great significance to carry out the calculation and study of releases source term to ensure the safe operation of nuclear power plant,the optimal management of radioactive waste and the environmental impact assessment.Firstly,the physical processes of radionuclides in different kinds of systems of PWR nuclear power plant are studied and analyzed in this paper.According to the initial source of radionuclides and their radioactive concentration in the primary or secondary coolant,combining with the design characteristics,operational mode and treatment process of the reactor itself,and considering the total removal of radionuclides by various equipment during the migration of the relevant systems.The corresponding calculation models of the gaseous and liquid radioactive releases source term in the nuclear island plant ventilation system,waste gas treatment system,boron recovery system,waste liquid treatment system and secondary circuit system are established,which reflect the specific design and process characteristics,the gaseous and liquid radioactive releases source term is obtained by analytical method.Secondly,based on the theoretical model and solution method of releases source term,the program PWR-RST is developed by using FORTRAN computer programming language and structured programming method.During the design and development of PWR-RST program,different evaluation modes of radionuclides for different systems are considered.The corresponding parameters can be selected,setted and modified to meet the needs of releases source term prediction and evaluation of different kinds of systems during the normal operation.To verify the accuracy of the developed PWR-RST program,The test examples are established based on the design parameters of CPR1000,The calculation results of this program are compared with those of CPGale program developed by CGN.and they are in good agreement.Finally,taking airborne radioactive release source terms from reactor building as the research objective,the calculation platform of uncertainty and sensitivity analysis based on statistical sampling method is established.the input parameters that affect the calculation results of the releases source term are selected.the probability distribution function,uncertainty range and sampling number of the parameters are determined.By using Latin Hypercube Sampling(LHS)method,the input parameters were randomly sampled,and then the input parameter uncertainty is propagated to the release source terms uncertainty by the source term program PWR-RST,Finally,The calculation results of release source term are statistically analyzed.The results show that for the noble gas release source term,it has a strong positive correlation with the primary coolant leakage rate and the uncertainty of the calculation results is 3.34%.For airborne iodine and particulates release source term,there is a strong positive correlation with primary coolant leakage rate and the corresponding partition factor,and a strong negative correlation with the corresponding decontamination factor and the uncertainty of the calculation results is 5.69%and 5.66%respectively.