Research On Improvement Of Source Term Model For Activation Corrosion Products In Nuclear Reactors

Today,water-cooled reactors are one of the most widely used types of nuclear reactors.However,as the operating time of a water-cooled reactor increases,the metal materials in the primary circuit undergo corrosion and neutron activation,leading to the production of activated corrosion products.These activated corrosion products migrate and deposit in the primary circuit system with the flow of coolant.Some of the radioactive isotopes emit a large amount of high-energy gamma rays during decay,which can cause radiation damage to the workers of the nuclear reactor.Therefore,it is crucial to accurately calculate and analyze the source term of activated corrosion products in nuclear reactors.This helps to improve the radiation protection level of workers.Since 2013,North China Electric Power University has independently developed the CATE program for analyzing the source term of activated corrosion products in nuclear reactors.After years of development and promotion,the CATE program has been preliminarily applied in source term analysis of multiple water-cooled reactors.However,the current calculation model of the CATE program has shortcomings or simplifications in simulating important physical phenomena,node partitioning,solubility calculations,and other aspects.Therefore,it is necessary to improve and enhance the existing calculation model of the CATE program to increase its modeling capabilities and calculation accuracy.This article presents a systematic improvement of the calculation model of the CATE program.Specifically,the improvements include:adding a calculation model for recoil release phenomenon,establishing a refined node calculation model for the primary circuit,and creating a multi-element solubility calculation model that includes Fe,Ni,and Cr.For water-cooled reactors,recoil release caused by high-energy neutron collisions with target nuclei in the core can lead to the release of some activated corrosion products from the wall surface into the coolant,which then migrates to non-irradiated areas.This article investigates the mechanism of recoil release in the reactor and establishes a calculation model and program module for recoil release.Using the improved CATE program,the study calculates and analyzes the values of the main activated corrosion product isotopes in the core and steam generator before and after considering recoil release,clarifying the extent of the effect of recoil release on the source term of activated corrosion products.In the primary circuit,there are spatial distributions of neutron flux density and coolant temperature for the core and steam generator.This article improves the original CATE program’s regionally homogenized calculation model by increasing the number of node partitions for the core and steam generator regions.The study investigates the impact of the spatial distributions of neutron flux density and coolant temperature on the calculation of the source term of activated corrosion products.The metal materials in the primary circuit are composed of various elemental components such as Fe,Ni,and Cr,and the solubility of corrosion products from different elements in the coolant varies.The original CATE program calculates the solubility of different elements as Fe using the generally accepted international practice.This article accurately calculates the solubility of Fe,Ni,and Cr elements using specialized water chemistry calculation software,improves the calculation model of the CATE program,and analyzes the impact of multi-element solubility on the source term of activated corrosion products.The research work presented in this paper will contribute to further enhancing the analysis capability and computational accuracy of the CATE program for the analysis of activation corrosion products in water-cooled reactors.It has certain theoretical and practical value in engineering applications.