Zenichiro Takao

Behavior of Cladding Tube under Coolant-Loss Accident Conditions

The behavior of cladding tubes, both stainless steel and zircaloy under the post-accidental conditions of coolant loss has been discussed, based on the results of three experiments performed this time. The effect of oxidation in post-accidental steam atmosphere up to temperatures where the cladding tube should burst with the pressure of entrapped fission product gas was found to be negligible. The bursting behavior of tubes containing pre-determined amounts of inert gas corresponding to the amounts of released fission product gas that should be present in various states of fuel usage was also examined. No effect of corrosion in zircaloy-2 that should affect its strength could be found up to a weight gain corresponding to several years of use under normal operating conditions, either in the burst strength or creep burst behavior.

Effect of Poorly Uniform Thickness and Surface Defects on Burst Test Results of Fuel Cladding Tubes

A study was undertaken to evaluate and determine “an acceptable defect level” of fuel cladding tubes for light water reactor. The burst strengths of both zircaloy-2 and AISI 304 L stainless steel tube were evaluated by burst testing naturally or artificially defected tube samples. As a result, (1) the burst strength of zircaloy-2 tube with poorly uniform thickness is affected by the minimum thickness of the tube, (2) a deep natural defect on the wall of the tube generally impairs the burst pressure value more them an artificially-made defect of the same extent as determined by non-destructive test; (3) artificial defects of depths up to 30% of the wall thickness do not cause appreciable deterioration of burst strength.