NNSA and Japan converted 110th research reactor and facility together

The National Nuclear Security Administration collaborated with Japan’s Kyoto University to convert a reactor to run on high-assay low enriched uranium, according to an agency press release. 

The National Nuclear Security Administration (NNSA) and Japan’s Ministry of Education, Culture, Sports, Science and Technology first agreed to convert Kyoto University Critical Assembly’s (KUCA) fuel in a joint statement at the 2016 Nuclear Security Summit to help proliferation risks from highly enriched uranium (HEU). NNSA said it was the 110th HEU reactor the agency has either converted or shut down.

The KUCA conversion project began in the late 2000s, the press release said. The most recent conversion was “Core C,” one of three different reactor cores that KUCA uses.

KUCA is a critical assembly, or a facility similar to a research reactor but with a different fuel composition, that consists of three nuclear cores, according to the university’s website. Kyoto University researchers use KUCA to study nuclear physics.

“Through our close cooperation, NNSA and our partners were able to overcome the barriers to success and deliver on our shared commitment to HEU minimization,” Kasia Mendelsohn, principal assistant deputy administrator for defense nuclear nonproliferation, said in the release. “We are grateful to the entire multilateral team for seeing it through.”

Core C can now fulfill its research and development missions “with fuel that presents a substantially lower proliferation risk,” according to the release.

Wednesday’s release said that NNSA and Kyoto University expect to complete converting the other two cores in KUCA in 2025. In August 2022, Kyoto University had intended to convert KUCA to operate with low enriched uranium by the end of 2023. The release said the project faced “multiple challenges” in the intervening years involving design, transportation, and regulatory approval of high-assay, low enriched uranium.