Research On Migration Model Of Multi-phase Multi-region Of Activated Corrosion Products In The Water-Cooled Reactor

In water cooling loop of PWR and fusion reactor,the structure materials will be corroded continuously when the water is in Contact with the structure materials.Some corrosion products will be activated by neutrons when coolant flows through in-flux region,producing activated corrosion products(ACPs).The activated corrosion products are the dominant radioactive source during normal operation and shutdown inspection of nuclear reactor system.Accurate calculation of activated corrosion products is conducive to reasonable selection of structure materials and water chemical parameters which can effectively reduce the radiation dose level of staff.Currently,most calculation models or codes of the activated corrosion products rely on experiment or operation data of the power plant,and they have done a lot of simplification on radionuclides species,physical phases,and spatial regions.In fact,thousands of radionuclides are generated after the activation of corrosion products.The calculation of activated corrosion products source term is subject to factors such as the physical phases,abundance in the material and solubility in the coolant of each radionuclide.Therefore,it is necessary to consider the influence of these factors comprehensively to obtain more accurate results.Under real operating conditions,oversimplified calculation models cannot accurately simulate phase and spatial distribution of activated corrosion products in each equipment or component.And they will adversely affect the accuracy of calculation.Aiming at the transport problem of activated corrosion products of different phases in different regions,the research on the production and migration mechanism of activated corrosion products is carried out in this dissertation.Based on the theory of control body,the coolant circuit can be discretely partitioned according to engineering needs.Each region corresponds to an important part or part of it.In each region,four phases of oxide layer,deposits layer,ions,particles are mainly considered.The physical and chemical phenomena involved in the transformation of different phases and the migration of different regions are accurately described.And a multi-phase multi-region model is proposed.The theoretical calculation methods are established for key parameters of the model such as corrosion rate,mass transfer coefficient,and solubility.Among them,the real-time calculation of solubility enables the model to support analysis of source term under special operating conditions such as oxidation operation,which breaks through the limitation of previous models on operation conditions.With the deposition experiment in the research group,the deposition module is modified successfully by analyzing experiment results,which realizes the influence of pH value on deposition behavior.The refined calculation model involves coupled calculation of multiple nuclides,multiple nuclear reactions,and multiple regions.In terms of mathematical characteristics,it is the large-scale,strong rigid,nonlinear ordinary differential equations.The classical GEAR numerical method is used to directly solve the calculation model,providing a high-precision reference solution of the source term,and clarifying the calculation accuracy and efficiency that can be achieved.The influence of spatial region,physical phase and radionuclide properties attributes on calculation efficiency of the model is comprehensively analyzed.Finally,an accelerated method is proposed,which combined the screening of target nuclides and quantitative discrepancies analysis.Taking the Limiter-Out-Board Baffle(LIM-OBB)loop of ITER as an example,calculation results showed that the efficiency by using the accelerated method is more than 200 times higher than that of the original calculation.So,the precise and efficient calculation of activated corrosion product source term is successfully achieved.Based on the above work,the code CATE-V3.0 for accurate calculation of the activated corrosion products in PWR and water-cooled fusion reactor is developed.CATE-V3.0 realizes the function of any nuclides calculation,which can meet simultaneously the calculation requirements of different materials and different operating conditions for PWR or water-cooled fusion reator.The analysis of each improved/added function through typical examples shows the significant advantages of the improved CATE-V3.0 in terms of phase,spatial region,radionuclide type,solution method and operating Conditions.In order to verify the correctness and reliability of multi-phase multi-region model and the code,the verification is performed from the perspective of experiment and code.In terms of experimental verification,the MIT-PCCL experimental loop is selected for simulation and the results obtained by CATE V3.0 agree reasonably well with experimental results.In terms of code verification,the Qinshan-II NPP primary loop and the water-cooling loop of ITER are simulated.The results present a consistency in quantity with published data calculated by other international codes.In summary,the correctness of the model and the applicability of source term calculation in the water-cooled reactor are verified.Finally,in this dissertation,the code CATE-V3.0 is used to complete detailed analysis of the source term in China Fusion Engineering Test Reactor(CFETR)and the third-generation pressurized water reactor The related suggestions for the optimization of radiation protection work are put forward.The multi-phase multi-region model of activated corrosion products and its efficient solution algorithm established in this dissertation have certain methodological research value.At the same time,the developed CATE-V3.0 and completed examples also have certain engineering application value,which is helpful to comprehensively improve the ability to analyze source term of activated corrosion products and is of great significance to radiation safety of plant personnel and environment.