Hydride morphology in zirconium cladding tubes after the SPIZWURZ bundle test. Part I: analysis of experimental data

The SPIZWURZ bundle test was carried out at the LICAS facility at Karlsruhe Institute of Technology. The test involved a bundle of 21 unirradiated hydrogenated cladding tubes (Zircaloy-4, opt. ZIRLO™ and Duplex DX-D4) which were subjected to an internal gas pressure and slow cooling for 250 days simulating the dry storage conditions of spent nuclear fuel. The following hydride morphology metrics were measured after the test: radial hydride fraction; hydride continuity coefficient; hydride length (mean and maximum, and their statistical distributions and densities); and number density. Hydrides in Zircaloy-4 have a higher tendency to reorientation, higher connectivity and are 2–3 times shorter (in both maximal and mean length) than those in opt. ZIRLO™. The evolution of hydride morphology in DX-D4 is mainly characterized by diffusional redistribution of hydrides from the substrate to the liner and the liner/substrate interface. Several samples exhibited local anomalies in hydride morphology, which can cause significant local embrittlement. The main experimental results are in good agreement with earlier published data. The supplementary materials include records of all the thermocouples and pressure sensors, which can be used to simulate the SPIZWURZ bundle test in detail.