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

With the rapid development of industrial production in the world,nuclear energy has been paid more and more attention by many countries because of its high efficiency,non-pollution,economy and safety,and nuclear power generation is the most important part of the utilization of nuclear energy.From the first nuclear reactor in human history to the present large power light water reactor,with the continuous increase of reactor power,the accumulation of radionuclides is gradually increasing.In order to meet the radiation safety standards of nuclear power plants,the existing nuclear power plants implement the principle of defense in depth,but kinds of accidents will inevitably occur.And once an accident occurs,radionuclides will leak into the environment from the fuel assemblies,they will even spread to the world,posing a great threat to environmental safety and human health,so it is of great significance to calculate and study the source term after nuclear power plant accidents.There are many initial accidents that cause pressurized water reactor nuclear power plants.in this paper,according to the accident characteristics,the analyzed accidents are divided into design basic accidents(DBA)and severe accidents(SA),according to the frequency of accidents and the seriousness of the consequences of the accidents.Six design basic accidents,DBA loss of coolant accident(DBA LOCA),fuel handling accident(FHA),steam generator tube rupture accident(SGTR),decay box rupture accident,volume control box rupture accident,main steam line break accident(MSLB),and two severe accidents,SA large loss of coolant accident(SA LOCA)and loss of coolant accident in spent fuel pool are selected to analyze.By analyzing the release,migration and distribution characteristics of fission products after the accidents,the calculation models of the source term of gas and liquid after the accidents are established,and the calculation procedure is developed.After the establishment of the model,an example of each accident is calculated and analyzed,and the radioactivity of nobal gas and iodine radionuclide is paid more attention in the process of analysis,in which the calculated results of SGTR,decay box rupture accident and volume control box rupture accident are compared with the reference values,the results show that the calculated results are in good agreement with the reference values.The calculation results of other accidents whose reference solutions are not publicly available are analyzed,and the change rule of source term is also reasonable,so the accuracy of the calculation model is proved.After the accidents,radionuclides will exist in the factory buildings in the form of gas or aerosol,and at the same time,they will migrate between the buildings through the incomplete sealing of the pipes and equipments in the buildings,so this paper studies the generation and removal of the airborne source term in the factory buildings.The calculation models of the airborne source term in the single plant and multi-plant are established,and the calculation program of the airborne source term in the plant is developed.In the program,the GEAR method is used to solve the equation.In the process of analyzing the calculation results,we pay more attention to the radioactivity of noble gas,iodine and alkali metals.Through the verification of the calculation results of single plant and multi-plant,the results show that the equilibrium activity concentration of radionuclide in single plant is consistent with the reference value.The calculated results of multi-plant are in good agreement with the results of analytical method,which proves the accuracy of program calculation.