Abstract: Boron-containing polyethylene could be selected as the neutron shielding of the spent fuel storage tank outer casing shield tank. Because of it’s sensitive to temperature, if the structural design is unreasonable, the deformation of boron-containing polyethylene could be too large for the structure stability and shielding effect when the ambient temperature difference is large or the tank temperature changes greatly for accident. This may produce gaps and cracks, who scatter the ray to environment and cause pollution. Double layer structure is used for neutron shielding out of the spent fuel storage tank. The inner layer is the main shielding layer, for which expansion joints are reserved to meet large temperature difference of environment and the accident conditions. The outer layer is a supplementary protective layer, which can effectively solve the problem of leakage at the expansion joints. The top of the shielding structure is designed open, filled with boron-containing polyethylene powder. In accident conditions, the powder will melt to fill, and the height of shielding structure could be kept to avoid radiation exposure.