Fuel assembly

Dissolved oxygen of high temperature water is less scattered at gaps where spacers and a channel box are in contact, as a result, there was a problem that pH is lowered, and generated hydrogen tends to be absorbed to the spacers. Then, before inserting the spacer into the channel box, only the surface of the spacer is heated at a high temperature to modify the surface. Namely, a high temperature oxidized film is formed on the surfaces of the spacers by the heat treatment at high temperature. As a result, the surface of the spacer has corrosion resistance, which provides an effect of suppressing corrosion of gaps between spacers. Then, even in a case where the gaps between the spacers and channel box are exposed to high temperature water at from 200degC to 350degC, the failure, which the spacers made of zirconium and zirconium alloy absorb hydrogen by gap corrosion, can be prevented. (N.H.)