The Research Of The Spent Fuel Container Nuclear Criticality Safety Based On The MCNP Program

The high-level radioactive waste disposal is the key which relates to nuclear power closed-loop in China and China's national economy and people's livelihood,and it is the bottleneck should be break through.It is the most promising method that the deep geological disposal has got more and more attention both at home and abroad.China's high-level radioactive waste disposal starts late,but developing rapidly.Based on the experience of Sweden,which KBS-3 system has been rigorous safety evaluation and is widely adopted.The main physical barrier in its system is spent fuel Zirconium cladding,sealed container,buffer material and bedrock.The main process is as follows:firstly,the spent fuel has been stored by decades,and then put it in the copper-steel container sealed.Afterwards,the spent fuel container through the disposal of drilling hole placed in the hundreds of meters deep underground.Finally,the spent fuel container is coated with bentonite clay.In this paper,the KBS-3 system is used as the research content,and the MCNP5 program is used as the research tool.Supported by the"HLW&MLW&LLW"Waste Disposal Project of the State Administration of Science,Technology and Industry for National Defence,PRC and the CNNC Beijing Research Institute of Uranium Geology,Geological disposal of high-level radioactive waste Project.Researching the different spent fuel container insert material impact on the K_eff value,and under different flooding height of the spent fuel container criticality safety simulation analysis in the KBS-3 vertical disposal and the KBS-3 horizontal disposal.Combining with the neutron spectrum,analyzed the changing of K_eff value.The main research contents and achievements of this paper are as follows:?1?To investigate the geological disposal of high-level radioactive waste related information and development status,to understand the latest developments and relevant data at home and abroad.?2?Based on the MCNP5 program,to simulate calculating the three different insert materials with I24,I25 and I26 in the spent fuel containers,simulating the spent fuel containers'in the condition of laboratory,that in normal circumstances the spent fuel containers'initial K_eff value is 0.13.In the case of extreme accident flooding,the maximum K_eff value is 0.71,failed to reach the K_eff minimum operating margin,without considering the K_eff value of the spent fuel quickly increased in a short time.The nuclear criticality safety of spent fuel container is dependable under the premise of large exothermic damage.?3?Researching the nuclear criticality safety simulation of the KBS-3 vertical disposal,to verify the safety of the scheme,and the results are analyzed.In the case of anhydrous immersion in spent fuel assembly,the initial K_eff value of the three cast iron insert materials is 0.14,which is slightly more than the initial K_eff value in normal circumstances.In the case of groundwater immersion in the spent fuel assembly,with the water level rising,its corresponding K_eff value increases to 0.71 gradually,ensuring the nuclear criticality safety of the spent fuel container.?4?Researching the nuclear criticality safety simulation of the KBS-3 horizontal disposal,to verify the safety of the scheme,and the results are analyzed.In the case of anhydrous immersion in fuel assembly,the initial K_eff value of the three cast iron insert materials is 0.14,which is substantially the same as the KBS-3 vertical disposal.In the case of groundwater immersion in spent fuel assembly,the corresponding K_effff value increases to 0.71 gradually as the water level continues to rise,and the nuclear criticality safety of the spent fuel container is guaranteed.?5?The KBS-3 vertical disposal and the KBS-3 horizontal disposal are analyzed by the neutron spectrum,which explained that the change of K_eff value is due to the various influencing-factors combined action.The major is the neutron moderation effect and the neutron reflection effect,and then the factor of geometry shape,of course the neutron resonance capture in the low-energy region can not be ignored.