KAMINI Reactor South Beam Port Shield-Structure Optimization

KAMINI is the Kalpakkam Mini Reactor, and its main purpose is to cater to experimental needs and for neutron radiography. It is a water-cooled reactor with 233U as the fissile material. Using the Monte Carlo nparticle transport code MCNP, shielding optimization calculations are carried out for the south beam port tube, which is meant for neutron radiography of spent-fuel subassemblies of the fast breeder test reactor. The neutron beam port is a graded cylindrical aluminium channel starting from the center of the reactor core; it pierces through the biological shield and is 2 m long. The diameter of the channel at the core center is 54 mm, at the other end it is 25 cm, and it is 0.5 m below the floor level. The latter end serves as the neutron surface source for these calculations. The calculations have been carried out in cylindrical geometry (r,z) of shield structures. From results of the analysis, a movable shield 50 cm thick (25 cm paraffin and 25 cm lead), 75 cm wide, and 172 cm long extending ~95 cm into the demineralizer room (cooling water purification room) is proposed to replace the existing temporary shield structure. In addition, fixed shields of the same thickness and width of 50 cm on either side of the beam is recommended to reduce the dose levels to a few tens of microsieverts per hour in the accessible areas. Further, the leadshielded cylindrical tube meant for insertion of irradiated fuel subassemblies for neutron radiography needs to be covered with 20 cm of paraffin up to a height of 1 m from ground level to avoid streaming of neutrons through the air column.