Research Of The Method To Process The Multigroup Macroscopic Cross Section Of Fe Considering The Energy Self-shielding Effect

As an important shielding and structural material,iron is widely used in the actual engineering of the nuclear facilities,such as the steel containment vessel,the control rods and the thermal neutron shielding in the reactor,etc.Besides,iron acts as a medium quality nuclide,in the resonance energy region,there are serious energy self-shielding effects,causing a bigger deviation of the multigroup macroscopic cross section data.The shielding devices are fast spectrum devices,having higher neutron energy,neutron penetration is very strong,so the accuracy of the multigroup macroscopic cross section data become more important in the medium and high energy region.In view of the above problem,this thesis adopted three methods to produce the multigroup macroscopic cross section:subdividing resonance energy region,collapsing group calculation and buckling iteration model,separately from the three aspects:the structure of energy group,the weighting function and the method of resonance processing,aim at improving the calculation precision of macroscopic cross section,providing reference for the actual application of shielding design.Considering from the aspect of the energy group structure,adopting the method of subdividing resonance energy region.Based on the general use of VITAMIN-J 175-group structure to perform shielding calculation,considering the energy point of 56Fe special resonance peak,and the resonance energy region of VITAMIN-J 175 was divided into the 692-group energy structure in the same interval,thus reducing the influence of the energy self-shielding effect on the section precision.Based on the previous method,considering from the aspect of the weighting function,adopting the method of collapsing group calculation,the energy spectrum of the 692-group transport calculations is more closely related to the real energy spectrum.So using the flux moment of the 692-group transport calculations as the weighting function,collapsing to the higher precision of 175-group of macroscopic cross section.Considering from the method of resonance calculation,the first two methods are using the Bondarenko method to perform the resonance calculation.For the buckling iteration method,improving the shortcomings of the Bondarenko method when calculating the iron media devices,at the same time,this method also retained the characteristic of the Bondarenko method to calculate the heterogeneous and dense cell,the method further improved the calculation precision and the application scope of the method in the iron media devices.In view of the above three methods,this thesis respectively selected several benchmarks to perform testing and analysis,comparing the parameters such as effective value-added factor keff and neutron leakage rate,suggesting that these three methods could reduce the effect of energy self-shielding on the iron’s cross section to a certain extent,and improve the processing precision of the multigroup macroscopic cross section of iron,especially the result of collapsing group calculation method and buckling iteration method.For the calculation of the leakage rate of fixed source benchmark,compared to the result of the VITAMIN-J 175-group,692-group of calculated results has certain improvement overall,especially the low energy region,the calculated results were reduced by an average of 13.2%,more close to the experimental value,but it is not obvious improvement in the resonance energy region.The calculated results of the collapsing group were reduced by an average of 12.31%in the resonance energy region,which is close to the experimental value.Compared to the first two methods,the calculated results of the buckling iteration method were reduced by an average of 15.03%in the resonance energy region,which is more close to the experimental value.For the keff calculation of the critical benchmark,the maximum calculation deviation of the keff of the buckling iteration method has decreased from-5500pcm to 860pcm.In a word,compared to the traditional processing method,these three methods can reduce the effect of the energy self-shielding effect of iron on the cross section,and can partly improve the processing precision of the iron’s multigroup macroscopic cross section,providing a reference for practical engineering application.