Annular storage vessel for nuclear fuel material and neutron shielding member thereof

Polyethylene blocks are used as neutron shielding members. Since polyethylene has a hydrogen atom content identical with or greater than that of paraffin, it has a sufficient neutron shielding effect. That is, a plurality of polyethylene blocks for neutron shielding are filled densely in the inner cylinder of the annular vessel main body for storing nuclear fuel materials in the form of solution. In this case, each of the blocks has an outer shape corresponding to the cross sectional shape of the inner cylinder and they are stacked in a plurality of stages. With such a constitution, the annular storage vessel can be manufactured in about two days, although two weeks have been required so far by the conventional method of filling molten paraffin. Further, since they can be charged and discharged in the form of blocks, it is not necessary to cut them upon dismantling of the annular storage vessel. (T.M.)