SPENT FUEL MEASUREMENTS IN SUPPORT OF BURNUP CREDIT

Storage, transportation and disposal of spent nuclear fuel continue to be significant problems faced by the commercial nuclear industry. Agreements made between the nuclear utilities and the Department of Energy regarding spent fuel disposal have yet to be implemented due to the delayed opening of the Yucca Mountain waste repository. This delay has forced utilities to consider alternative spent fuel storage options, the most common being dry storage in casks on the reactor site. A large number of casks have already been loaded and many more will be before a disposal site becomes available. In the longer term it will be necessary to transport fuel casks from the reactor sites to a repository. During this phase of the spent fuel management cycle significant cost savings may be realized if vendors license casks that take advantage of either burnup credit or moderator exclusion. Both methods allow for higher cask packing densities reducing both the number of casks and the number of shipments required. While moderator exclusion and burnup credit are feasible, only burnup credit is in compliance with current U.S. federal regulations for radioactive materials transportation (10 CFR Part 71). Currently, no regulations are in place that define how burnup credit may be applied to cask licensing. However, the Interim Staff Guidance-8 rev2 issued by the Nuclear Regulatory Commission (NRC) Spent Fuel Project Office provides some clear recommendations. One recommendation is that measurements should be used to confirm reactor records for each assembly. The provision is made for this confirmation to be based on measurements of a sample of assemblies rather than each assembly provided that certain conditions are met. For this reason it is recommended that utilities carrying out spent fuel measurement campaigns prior to future cask loading. This would allow the application of burnup credit without having to unload assemblies in the future to make the required measurements. BIL solutions, Inc. have developed and implemented spent fuel measurement services that are consistent with NRC recommendations. This paper presents burnup credit measurements and provides examples of how these measurements have been applied in the past.