An Overview of Spent Fuel Storage at Commercial Reactors in the United States

Abstract

A legacy of the growth in the use of nuclear power in the USA over 1960–2005 has been the accumulation of large quantities of spent nuclear fuel (SNF) at the reactor sites, a situation initially caused by an embargo on fuel reprocessing and later exacerbated by delays in the opening of a national repository. The nation’s inventory of SNF stands at ~54,000 metric tons of heavy metal (MTHM) in late 2005, and grows at an annual rate of ~1,750 MTHM. Storage pools are becoming full as a result, despite the use of high-density fuel racks. To alleviate the problem older SNF assemblies are being dry stored in casks placed on concrete pads in independent spent fuel storage installations (ISFSIs). There are now 30 ISFSIs in the USA and their number is growing. Experience with both wet and dry storage has been very reassuring. Wetstored SNF derives its stability from an adherent oxide layer on its Zircaloy cladding which resists further corrosion, even in water of poor quality. The destructive examination of SNF that had been vacuum-dried and stored in Hefilled casks for nearly 15 years revealed no increase in the internal fission-gas pressure or increase in the cladding creep of its fuel rods. The terrorist attacks of September 2001 focused attention on the security of reactors and their associated SNF storage. Analysis suggests that dry storage at an ISFSI may be more secure than wet storage at a reactor. However, offloading SNF to dry storage and a return to the use of open-frame racking are measures that could improve security at spent fuel pools.