Evaluation Of Gamma Radiation On PWR Primary Surfaces Based On TRIPOLI-4 Monte Carlo Code

In order to promote the popularization of the third-generation PWR technology worldwide and to compensate for the lack of experience in Monte Carlo simulation of such reactors,this work focuses on the Monte Carlo simulation of gamma radiation from the primary circuit of the third-generation PWR.Three types of PWR including AP1000,EPR and APWR that have applied for design certification from the US NRC are referred.We sequentially analyze the source and distribution of primary gamma rays,model the main components?reactor pressure vessels,steam generators and main pipelines?and proceed on the relevant simulations tasks.The gamma flux and dose equivalent rates on the primary surfaces have been calculated and evaluated.The Monte Carlo simulations tasks are done using the TRIPOLI-4 code.According to other researches'results,the nitrogen-16 is the main source of gamma rays in the primary circuit of PWRs,accounting for more than 94%of all.Therefore,we mainly investigate on the radiation doses induced by nitrogen-16.In this work,the production process of nitrogen-16 is analyzed,the relevant formulae are deduced,and the?n,p?reaction rate of oxygen-16,the specific activity and distribution of nitrogen-16,and the unit responses of nitron-16 to the gamma flux and doses on the primary surfaces are calculated.The results show that the gamma radiation is relatively highest in the vicinity of the junction of RPV and hot-leg pipelines,respectively at 1.09×10⁷?.cm^-2.s^-1-319 mSv/h,1.93×10⁷?.cm^-2.s^-1-569 mSv/h,and 1.31×10⁷?.cm^-2.s^-1-386mSv/h for AP1000,EPR and APWR.From 93 to 99.9%of the contribution comes from the main pipes,not the RPV.The ambient dose equivalent rates per unit thermal power of the reactor are 96?Sv/h/MWth,111?Sv/h/MWth and 71?Sv/h/MWth respectively.However,according to other researchers results on radiation measurement on primary chamber,the corresponding values are within 100–125?Sv/h/MWth.Hence there is no significant improvement on the radiation shielding on the primary circuit of generation III PWRs.Therefore,we suggest that the radiation shielding design of the reactor buildings be enhanced in order to meet the relative criteria on radiation reduction.This work demonstrates the complete process of modeling,neutron activation simulations and photon shielding simulations based on the TRIPOLI-4 Monte Carlo code.The usage of both basic and advance functions provided by TRIPOLI-4 is introduced in chapter 2.The best application strategy and efficiency of the modules is discussed.In addition,mathematical theories are used to analyze the impact of various modeling methods or calculation methods on the results;simple fracture mechanics theories are used to make up for the lack of modelling data of wall thickness of main pipes and steam generators;the sensitivities of design parameters such as density,temperature and fuel enrichment are evaluated by Monte Carlo method;the contribution of bremsstrahlung and annihilation of electron–positron is simulated and discussed.We have generated many sets of simulation results normalized to unit source intensity,which is referable for future studies.The results also reveal that the bremsstrahlung and the annihilation of electron pair are very important on photon shielding calculations.In an ideal situation,these effects could increase the photon flux by about 20.83%.In our study,this number does not exceed 18%for photon flux,and 8%for dose equivalent.