Measurement of hydriding susceptibility of Zircaloy cladding by the tube-burst technique at high pressure and high temperature

High-pressure hydriding of Zircaloy (Zry) cladding was studied using the tube-burst technique. The aim was to demonstrate a practical laboratory test that reliably predicts the hydriding resistance of cladding. The test consists of pressurizing a section of tubing with hydrogen (wet or dry) and measuring the time to failure. Surviving specimens lasted 140 h, the maximum test time. Duplicate experiments were conducted in the temperature range 300–385°C to investigate the temperature dependence of hydriding as well as reproducibility. In addition, the effects of water vapor content in hydrogen gas and cladding surface condition on the hydriding susceptibility were investigated. The failure time was found to be highly sensitive to temperature. In dry hydrogen and for the particular type of cladding studied, a failure threshold of ≈340°C was observed. Above this temperature the failure time decreased rapidly with increasing temperature. Water vapor in the gas prevented hydriding for H2/H2O ratios less than 5.0×104. Chemical etching rendered the specimen immune from hydriding in the conditions of the test.