Neutron absorber, spent fuel assembly storage rack and spent fuel assembly containing vessel

In a matrix of an austenite stainless steel containing boron 10, Gd as an element having greater neutron absorption per unit volume than that of the iron based alloy is contained in an amount of 3wt% or less as a solid-solubilization limit. Since the element having greater neutron absorption per unit volume than that of the boron-containing iron based alloy can be involved in the matrix so far as the addition is up to the solid solubilization limit, the slipping in crystal grains is somewhat lowered compared with that before the addition, but the degradation of workability and the strength is extremely reduced compared with a case where the added element is segregated. In addition, since the austenite stainless steel is excellent in the corrosion resistance, it is suitable as a constitutional material for a storage vessel. Accordingly, neutron absorption of the neutron absorbing material per unit volume can be improved, and a neutron absorbing material having excellent corrosion resistance, workability and strength can be attained. (T.M.)