A Review of Delayed Hydride Cracking of Spent Fuel Rods in Dry Storage

Dry storage of spent fuel rods is being considered as an alternative to the interim storage method until a final decision on their final disposal is made. Most studies on the integrity of spent fuel rods in dry storage have focused on cladding creep, which is known to be the most likely failure mechanism, and reorientation of hydrides to secure their retrievability after dry storage. Little attention has been paid to delayed hydride cracking (DHC) because this phenomenon will not occur due to limited stresses and slow diffusion of hydrogen at low temperatures below 200 .deg. C. However, Simpson and Ells reported a failure of unirradiated Zr-2.5Nb fuel rods after their long-term storage at room temperature, the cause of which was recognized to be DHC. Therefore, it is clear that in contrast to what is believed to be that no DHC occurs in the spent fuel rods in dry storage, they would fail as long as stress raisers such as surface flaws or the weld region are present inside the cladding tube. Especially, high burnup fuel rods may have incipient cracks on the inside cladding surface due to an interaction of the fuel and the cladding during reactor operation