Loss of coolant accident testing round robin

A loss of coolant accident (LOCA) round robin test program was conducted to evaluate experimental variations and experimental practices associated with the post quench ductility and breakaway oxidation testing techniques. A common set of high level parameters, consistent with the US Nuclear Regulatory Commission's (NRC) draft guidance, was used by each laboratory. The goals of the program was for each laboratory to generate, for Zircaloy-4, a ductile-to-brittle (DTB) transition curve after oxidation at 1200°C and quenching at 800°C at as-built, 200, 400 and 600 wt. ppm hydrogen concentrations and to determine the onset of breakaway oxidation at 800 and 1000°C within an accuracy of 500 seconds. The post quench ductility (PQD) test results indicate small variations between the laboratories, but overall the trend is consistent with the test results reported by Argonne National Laboratory and the US NRC. However, the effort revealed that, for most laboratories, existing hydrogen charging techniques are not sufficiently robust and cannot consistently produce uniformly distributed hydride samples at targeted hydrogen concentrations, which would have been necessary for a statistical treatment. Therefore, the prescribed procedure, oxidizing multiple samples to different equivalent cladding reacted (ECR) levels at the same hydrogen concentration to bracket the DTB transition, cannot be followed. Also, as a consequence of the hydrogen charging difficulties, many test samples were oxidized to ECRs inconsistent with the target hydrogen content. The lack of test data at consistent hydrogen concentrations makes statistical comparison between laboratories difficult and it also complicates each laboratory's ability to establish a DTB curve since a ductile and a brittle sample at comparable hydrogen concentration are needed to establish the transition per US NRC draft guidance. None of the laboratories detected breakaway oxidation at 800°C up to 7000 seconds of exposure. Four of the laboratories detected breakaway oxidation at 1000°C within the expected time window of 5000-6000 seconds. Two of the laboratories failed to detect breakaway at 1000°C up to 7000 seconds of exposure; however, metallographic examination of the oxide layer suggests the samples are very close to breakaway oxidation. The failure of two of the laboratories to detect breakaway oxidation at 1000°C is under investigation.