LMFBR-fuel cladding thermal creep strain under linearly increasing internal pressure

This paper describes an apparatus designed to simulate the continuously increasing internal pressure due to the accumulation of fission product gas. There is also an examination of the effects of increasing pressure on the thermal creep rate of cladding. Test specimens are 20% C.W. type 316 stainless steel tubes with 6.5 mm OD, 5.6 mm ID and 200 mm length. Increasing pressure creep tests were performed at 7000C, the hoop stress was increased in steps with 3 incremental rates of 0.15, 0.075 and 0.0375 kg/mm2h. Constant pressure creep tests were also performed at the same temperature for comparison. The results show that the creep rates obtained from creep curves under increasing pressure are several times as high as the stationary creep rates measured under the same constant pressure. Creep strain rate under increasing pressure, due to the accumulation of gaseous fission products in the actual fuel cladding, is approximately 2 to 5 times that of the constant pressure creep rates, although the creep rate magnification depends on the stress and the stress-increase rate. (Auth.)