Dry Storage Demonstration for High-Burnup Spent Nuclear Fuel-Feasibility Study

Abstract

Initially, casks for dry storage of spent fuel were licensed for assembly-average burnup of about 35 GWd/MTU. Over the last two decades, the discharge burnup of fuel has increased steadily and now exceeds 45 GWd/MTU. With spent fuel burnups approaching the licensing limits (peak rod burnup of 62 GWd/MTU for pressurized water reactor fuel) and some lead test assemblies being burned beyond this limit, the need was identified for a confirmatory dry storage demonstration program after the U.S. Nuclear Regulatory Commission (NRC) published their Interim Staff Guidance 11 (ISG-11) in May 1999. With the publication of the second revision of ISG-11 in July 2002, the desirability for such a program further increased to obtain confirmatory data about the potential changes in cladding mechanical properties induced by dry storage, which would have implications to the transportation, handling, and disposal of high-burnup spent fuel. While dry storage licenses have kept pace with reactor discharge burnups, transportation licenses have not-and are considered on a case by case basis. Therefore, this feasibility study was performed to examine the options available for conducting a confirmatory experimental program supporting the dry storage, transportation, and disposal of spent nuclear fuel with burnups well in excess of 45 GWd/MTU. Summary x has a policy, because of an agreement with the State of Idaho, that prohibits spent fuel being brought into and residing in the state for >5 years, which is not commensurate with the needs of the demonstration program. Estimated costs and schedule for the three options are provided in Table S-1. The options are estimated to run from 5 to 12 years with destructive post-irradiation examinations (PIEs)

Stress and temperature-dependent hydride reorientation of Zircaloy-4 cladding and its effect on the ductility degradation

“…However, tensile stress can be built up in the cladding after the fuel discharging from the reactor. The temperature of spent nuclear cladding in the pool storage is about 50 • C. At this temperature, most of the hydrogen in the cladding can be precipitated; however, the peak cladding temperature can increase up to more than 400 • C during vacuum drying and backfilling the cask with helium for dry storage [5][6][7]. After the drying transfer operations, the cladding temperature slowly cools down during the long-term dry storage.…”