Characteristics of a geological disposal system for the increasing burnup of spent nuclear fuel

The characteristics of a geological disposal system to accommodate increasingly higher burnup levels of spent fuel were assessed based on the Korea reference disposal system concept. First, a status investigation that included a projection of spent fuel quantity versus burnup was carried out to demonstrate the trend toward higher burnup levels. Next, main features of the Korea reference disposal system were introduced. Finally, the disposal tunnel length, excavation volume, and the raw materials (e.g., a cast insert, copper, bentonite and backfill) necessary for a disposal system were comprehensively analyzed to define the characteristics and overall effects on geological disposal at increasingly higher burnup levels. Our study determined that it is reasonable to use a canister containing 4 spent fuel assemblies with burnup levels up to 50 GWD/MTU, while a canister containing 3 spent fuel assemblies can accommodate burnup levels beyond 50 GWD/MTU. A remarkable increase of 33 % in disposal tunnel length and 30 % in excavation volume was observed as the burnup increased from 50 to 60 GWD/MTU. However, this was offset by a reduction of 17% in raw materials used in canister fabrication. Therefore, it seems that spent fuel at increasingly higher burnup levels is not a serious concern for deep geological disposal