Criticality Safety Analysis For Spent Fuel Pool Of AP1000 Nuclear Power Plant

AP1000 is an advanced pressurized nuclear power plant with Generation?reactor,its passive design concept greatly improves the safety and economy of the system operation,the Sanmen nuclear power plant and the Haiyang nuclear power plant of China are the world's first AP1000 nuclear power plants.AP1000 spent fuel is stored in the corresponding spent fuel pool in the form of dense storage,so it's significant to ensure criticality safety of the pool.In this paper,the SCALE program was used in the criticality safety analysis of AP1000 spent fuel pool.First,this paper built the model of the region 1 area of the spent fuel pool,then calculated,the results show that lager water density,deeper depth of fuel assembly immersed in water within a certain range makes the k_eff of region 1 be bigger,which verifies that the Westinghouse company's related hypothesis is conservative.Based on this,this paper obtains the region 1 safe k_eff value which considered the uncertainty factors is 0.9205,and through the calculation,that the region 1 can meet the criticality safety requirement was verified,also the calculating results agree well with the Westinghouse APP report.Second,this paper used the TRITON module of SCALE to conduct burnup calculation,and built the model of the region 2 area,conducted modeling and calculation by using STARBUCS module,the results were compared with Westinghouse,it shows that they agree well with each other,which verifies effectiveness of the model.Based on this,the four cells model and the whole region 2 model were established,which were compared with the single storage rack model,it shows that the first two models are too conservative and they are not conducive to the sensitivity and uncertainty analysis,finally this paper choosed the single storage rack model to carry on criticality analysis of region 2,obtains the safe k_eff value of region 2 is 0.93084,took the k_eff value as the standard value,established the burnup loading curve of region 2.Again,this paper conducted the calculation and analysis of two typical accident conditions in region 2,accident?is that a new fuel assembly is loaded into the storage rack by error,and accident?is that a spent fuel assembly falls above the storage rack,the results show that the region 2 can only meet the requirements of criticality safety of accident?.After improving,it shows that simply increasing the fuel assembly spacing can't improve the ability of pool to resist the accident,but making all the assemblies be surrounded by absorber in the periphery of them can make the pool to meet the requirements of criticality safety of the two accidents.Finally,sensitivity factors of the burnup credit method were researched,the results show that the higher boric acid concentration inside the reactor and control rod insertion when conducting burnup calculation are conservative,in addition,assembly power density has little effect on k_eff of region 2,when spent fuel was cooled in the pool for 100 hours k_eff reached the maximum value,then the value decreased gradually,actinides and fission products can reduce k_eff.And using reflect boundary in the axial is more reasonable and conservative than white boundary when conducting criticality calculation.