The radiation assessment for the maintenance scenarios of CSNS inner reflector plug

China Spallation Neutron Source (CSNS) is a neutron facility with 100 kW beam power, which can be upgraded to 500 kW after several years irradiation. The moderator-reflector plug is divided as Inner Reflector Plug (IRP) and Out Reflector Plug (ORP) for cost saving. The IRP consists two moderators, beryllium (Be) reflectors and upper shielding blocks. It should be periodically replaced due to radiation damage caused by intensity neutrons and other secondary particles. Since the IRP is highly activated after several year irradiation, the intensity residual gamma rays result the severe challenge for its replacements and potential radiation exposure to the personnel. Detailed calculations about the radionuclides, activity, decay gamma rays and dose rate distributions of the IRP are performed. The dose rates to the personnel during the maintenance scenarios are assessed. The shielding casks used to transport these activated components are also designed. Detailed information about the dose rate distributions during the IRP replacement is analyzed. Calculations are performed by Monte Carlo code MCNPX2.5 and the activation code CINDER’90 combined with an Activation Script and a Gamma Source Script.