Structural material for fuel assembly of high burnup degree and fuel assembly

In a structural material for a fuel assembly of a high burnup degree prepared by heating a zirconium alloy comprising one or more of iron, nickel and chromium to higher than about 830degC and then quenching, Σ Ai value is determined within a range greater than 2 x 10-19 and smaller than 2 x 1018 as a condition for the heat treatment. Zirconium has a stable α-phase at a low temperature and a stable β-phase at a higher temperature, and the starting temperature for transformation from α-phase to β-phase is lowered by addition of the alloy elements. Further, an intermetallic compound between iron, nickel and chromium as the ingredient and zirconium is melted into a mother material by applying a predetermined heat treatment to the zirconium alloy. Precipitation of the intermetallic compound is prevented by suppressing a subsequent heat treatment to improve characteristics against blistering corrosion. Oxidation of structural materials for the fuel assembly can be minimized over the whole range of to the burnup degree of the fuel assembly up to about 42 GW/t, thereby enabling to maintain the mechanical integrity of fuels. (N.H.)