PURPOSE:To obtain a shielding material excellent in heat resistance and processability by forming a mixed molding of calcium silicate powder and powder of a boron compound, and using boron carbonate (B4C) or europium boride (EuB6) as the boron compound. CONSTITUTION:A structure wherein a boron compound serving as a neutron absorbing material and a heat-resisting binder 2 of calcium silicate are uniformly and finely dispersed at a porosity of preferably within 45% is provided. The neutron absorbing material is a boron compound (B4C, EuB6, etc.) and the heat- resisting binder is dopamolite, zenolite, etc. The boron compound is provided by at least 50 parts by weight for 100 parts by weight of calcium silicate. A reinforcing material such as glass fiber is added when needed. Powder of the boron compound is added and mixed in silica powder and lime powder both of which are the synthetic raw material of the calcium silicate. Further, water is added in the range 0 to 50wt% to the mixture and the mixture is hardened through a reaction in steam at high temperatures and high pressures.
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