Leakage Rates of High-Temperature Water From Wet-Type Transport Casks of Spent Fuel

In Japan, a program for enhancement of fuel bumup in their cores has been promoted as one of the sophistication programs of light water reactors to reduce fuel cost and to minimize the amount of spent fuel generated. To be consistent with this program, a new wet-type transport cask has been developed to ship the high bumup spent fuels effectively (e.g., Kokaji et al. 1992). A sealing function is essential for transport casks of radioactive materials in transport to prevent radioactive materials from being released into the environment. The evaluation method on the release rate has been standardized by the ISO. For a lack of highly accurate data on high temperature water leakage rates of 10-4 to 0.1cm /s, which are closely related to the sealing performance of wet-type transport casks of spent fuels, the appropriateness of the evaluation method on the leakage rate specified in the standardization has never been verified. In this work, leakage rates of high temperature water from capillary tubes, whose configurations and dimensions were known, were first investigated experimentally to understand the vaporization effect of superheated water on the leakage rate. Next, the leak paths subjected to a preshipment leak test were simulated by a scratch on an 0-ring surface and very thin wires adhering to an 0-ring surface. High temperature water leakage rates from these simulated leak paths were investigated to establish an evaluation method of leakage rates from a noncircular leak path and multiple leak paths.