Neutron shielding effects of spent fuel tank of high temperature reactor

High temperature gas cooled reactor-pebble bed module (HTR-PM) adopts the coated particle spherical fuel elements, during the reactor's running, the constantly discharged spent fuel spheres will be loaded into the spent fuel tank. The spent fuel tank should use proper materials and thicknesses to shield gammas and neutrons effectively, and guarantee the dose limit not to be exceeded outside the tanks. Both relaxation length method and Monte Carlo simulation method were employed to study the neutrons' shielding capabilities of the spent fuel tank. Iron and borated polyethylene were chosen to be the shielding materials. The shielding capabilities of iron and borated polyethylene with different B₄C contents (mass fraction 0, 5%, 10% and 15%) were calculated. The effect of the spent fuel spheres' self-absorption to the dose rate outside the tank was also considered, when the tank was full of the spent fuel spheres. The calculation results of these two methods are in good agreement, and provide important guiding suggestions for the shielding design in the practical engineering. (authors)