ESTIMATION OF HYDROGEN REDISTRIBUTION IN ZIRCALOY CLADDING OF SPENT FUEL DURING DRY STORAGE AND ITS INFLUENCE ON MECHANICAL PROPERTIES OF CLADDING

用Charpy冲击试验方法测定了含氢量为100 ppm和400 ppm的Ziraloy-2合金试样（尺寸为5 mm × 10 mm × 50 mm）在室温至250 ℃范围内的冲击韧性。测量结果表明，氢化物非均匀分布试样的韧性大于氢化物均匀分布试样的韧性。从理论上分析了轻水堆燃料干贮存条件下锆合金包壳中氢化物的再分布现象，并通过计算机模拟计算了氢化物再分布的速率。其中燃料的燃耗假定为40- 55 Gwd/t，包壳中吸收的氢量也假定为300- 400 ppm。计算中假设干贮温度条件为150-450 ℃，得出以下结论：（1）在设计的干贮温度条件下，反应器内产生的氢化物在锆合金包壳径向上的不均匀分布不会得到缓和。(2)在锆合金包壳含400 ppm氢的乏燃料干式贮存的情况下，如果锆合金包壳的温度因某些事故而升高到480 ℃以上，则锆合金包壳中氢化物的不均匀分布将被破坏，氢化物的均匀分布将在一小时内建立。氢化物的再分布将导致锆合金包层韧性的显著下降。这些结果在国际原子能机构会议和日本原子能学会秋季会议上提出。

The toughness of Ziraloy-2 specimens (size : 5mm x 10mm x 50mm) containing 100 ppm or 400 ppm hydrogen was measured with the Charpy test in a temperature region from room temperature to 250ﾟC.The hydrogen concentration in the specimens was gradient in one dimension, which was prepared with the thermomigration of hydrogen. The measurement suggested that the toughness of the specimen, in which the hydride is nonuniformly distributed, was larger than that of the specimen in which the hydride was uniformly distributed. The redistribution phenomena of hydride in the Zircaloy cladding of the fuel for the light water cooled reactors under the conditions of the dry storage was analyzed from the thermodynamical aspect and the rate of redistribution of the hydride was calculated with the computer simulation, in which the burn-up of the fuel was assumed as 40-55Gwd/t and the amount of hydrogen absorbed in the cladding was also assumed as 300-400ppm. In the calculation, the temperature conditions of the dry storage was assumed as 150-450ﾟC.Followings were concluded : (1) The nonuniform distribution of the hydride in the radial direction of the Zircaloy claddings, which was brought about in the reactors, would not be relaxd under the designed temperature conditions of the dry storage. (2) In the case of the dry storage of the spent fuel with the Zircaloy cladding containing 400 ppm hydrogen, the nonuniform distribution of the hydride in the Zircaloy cladding would be collapsed and uniform distribution of the hydride would be built up in an hour provided that the temperature of the Zircaloy cladding would be increased over 480ﾟC because of certain accidents. This redistribution of the hydride would bring about the marked decrease of the toughness of the Zircaloy cladding. These results were presented in the meeting of International Atomic Energy Agency and in the Fall Meeting of Nihon Genshiryoku Gakkai.