Radiation shielding design for X-ray of the CFETR NNBI prototype

[Background] China fusion engineering test reactor (CFETR) negative ion based neutral beam injection system (NNBI) prototype was designed for hydrogen beam operation. When the NNBI prototype works, the energetic particles collide with the solid targets of the prototype structural material during production and transmission to produce bremsstrahlung. When the CFETR NNBI prototype is designed to operate with a beam energy of 200 keV and beam current of 20 A, the dose rate outside the vacuum wall is higher than the limit dose rates of general worker radiation (10 μSv · h^-1). [Purpose] This study aims to reduce the radiation dose rate of the CFETR NNBI with hydrogen beam energy of 200 keV. [Methods] The radiation dose of the prototype was simulated by the radiation shielding theory. The shielding design scheme of sinking the prototype with lead plate was put forward and evaluated. [Results] When the CFETR NNBI is placed underground and shielding layer on the top, the outside dose rate at 1 m from vacuum wall (with 2 cm thickness) of ion source (200 keV, 20 A) is below the limit. [Conclusion] The design scheme can meet the radiation safety standards when the CFETR NNBI prototype operated with radiation shielding. (authors)