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The ANTT Subcommittee of NERAC met February 26th and 27th (S. Pillon absent) to begin a review of the potential role of transmutation technologies in increasing the capacity of the geological repository for spent reactor fuel. This work is in support of the recommendation required from the Secretary of Energy later in this decade on the need for a second repository. Since repository issues were under discussion, representatives of the Office of Civilian Radioactive Waste Management (RW) were in attendance.

The focus of the transmutation program up to now has been on the potential to reduce the required time of isolation of spent fuel from the biosphere from hundreds of thousands of years to on the order of a thousand years. What has evolved from the program is the potential of a system involving a combination of spent-fuel partitioning, recycling of actinides and other long-lived radioactive components in thermal-spectrum reactors, followed finally by a treatment in a fast- spectrum facility (one fast spectrum facility for every five to ten thermal reactors). If such a system were to be developed and deployed not only would the required isolation time be reduced, but the capacity of a geological repository such as Yucca Mountain would be increased by a factor of roughly 50, more than enough to handle all the spent fuels generated in this century from any conceivable nuclear energy deployment scenario. The increase in capacity comes from the destruction of the actinides that generate the heat which limits the capacity of the repository (see Section II).If the issue to be addressed is only the capacity of the repository, the allowable amount of actinides and other long-lived elements in the material going to the repository can be significantly increased above that allowed in the reduced isolation time scenario. The Committee therefore asked that the laboratories review transmutation scenarios looking at the potential only for an increase in capacity. Further, we asked that thermal-spectrum-only systems be studied as well as a combination of thermal- and fast-spectrum systems. For the next several decades, only thermal-spectrum light-water reactors (LWRs) will be available in the U.S. for any such application. This report is mainly devoted to reviewing the results of that study. It should be noted that the analysis is preliminary, as it was only requested about three months prior to the Committee review and, therefore, the scenarios are by no means optimized.

The question posed was what could be done with some number of cycles of spent- fuel partitioning and transmutation where after the last cycle all of the remainder was to be sent to the repository.