NNSA converts its 110th research reactor following decade-long effort in Japan

The KUCA conversion project started in the late 2000s and has been an important part of U.S.-Japanese collaboration on nuclear nonproliferation ever since. NNSA and Japan's Ministry of Education, Culture, Sports, Science, and Technology (MEXT) committed to converting KUCA from HEU to HALEU fuel in a joint statement at the 2016 Nuclear Security Summit and as part of the U.S.-Japan Nuclear Security Working Group.

KUCA is a critical assembly facility that contains three different nuclear cores. The newly converted Core C uses light water as a moderator, whereas Cores A and B use solid moderators. A critical assembly is a facility similar to a nuclear research reactor that is distinguished by a flexible fuel loading arrangement. By adjusting the geometry and composition of the fuel assembly, researchers can study various reactor concepts. KUCA had been shut down since 2021 when the irradiated HEU fuel was removed.

The project faced multiple challenges in the intervening years with the design, transportation, and regulatory approval of the HALEU fuel, which were resolved through collaboration between NNSA and its national laboratories, MEXT, Kyoto University, Framatome CERCA, and other partners.