Research On Reactor Pressure Vessel Fast Neutron Fluence Calculation Technologies Based On The S_N Method

The precise calculation of reactor pressure vessel(RPV)fast neutr on fluence can evaluate the degree of materials irradiation damage during the designed lifetime and support analyses for a potential plant life extension.The discrete ordinates method is one of the main methods to solve such problems for its advantages in handling the deep penetration model.In the RPV fast neutron fluence calculation process that based on method,deviations introduce by alternative algorithms cannot be neglected and the deviation is different for various reactors.A relatively sufficient analysis and conclusion have been done both at home and abroad.However,the systematically research and analysis that combining the developing neutron transport equation numerical methods and advanced reactor is relatively less.Hence,it makes great significance to do comprehensive study on RPV fast neutron fluence calculation method.This study firstly summarizes the calculation process of the main shielding,and analyses the influencing factors that may introduce the deviation during the calculation.The typical pressurized water reactor models are used as the test examples to analyze the bias introduced by influence factors in this study.The effect of the change of the neutron source treatment,the deviation introduces by the SN numerical discrete method(mainly includes the approximation of anisotropic scattering cross section and the different spatial discretization method)are the influence factors discusses in this study.Further,the neutron adjoint theory is introduced to study the response of the detector to the change of the neutron source treatment.According to the study,it is found that various neutron source distribution has a great influecnce on the calculation results.Different treatment on the assembly power distribution generates a bias around 70%.The deviation introduces by the adoption of various fission nuclides and corrsponding fission fraction is relatively small,within 15%.In the process of the numerical discrete,the different order of Legendre expansion,whether to fixup the negative scattering source,the adoption of the transport correction methods and different spatial discretization method introduce the deviation which is around 10% separately.The actual calculation model is sensitive to grid step,the change of the spatial grid spacing will influence the final calculated value to a large extent.The conclusions are given on the basis of the qualitatively and quantitatively analysis of each influence factor faced the typical pressurized water reactor.This discussion provides theoretical support for deviation between calculated results and the measured values,contributes to properly recognize of the weak links in current algorithms,indicates the improvement of relevant calculation model and numerical discrete methods and enhances the degree of confidence in the results.This study can be a theoretical guidance for other practical reactor calculation.Based on the typical pressurized water reactor and TMSR-SF1 experimental reactor,the main shielding calculation and analysis are carried out systematicly.It is of certain significance to improve the reactor neutron fluence calculation precision and develop more reliable shielding design.