Abstract

Potential damage mechanisms postulated for spent fuel in dry storage include stress corrosion cracking (SCC), delayed hydride cracking (DHC), and accelerated (tertiary) creep leading to creep rupture. The primary conditions that govern the evolution of these damage mechanisms during dry storage are the spent fuel rod’s internal chemical environment and its thermal and mechanical histories. In a recent publication, (see cited references), thorough evaluation of these mechanisms, utilizing conservative estimates of pre-existing thermomechanical and physical conditions of the cladding, show that SCC and DHC are not likely operative mechanisms in dry storage. This leaves creep rupture as the primary mechanism of concern. Evaluation of this mechanism is the subject of the present paper. Results of creep modeling and analysis are presented to show that self-limiting creep deformations govern the behavior of fuel rods in dry storage. This leads us to suggest that a liberal strain limit of several percent, with a side condition on stress evolution to remain below the local yield strength, is an appropriate acceptance criterion for dry storage.

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