Researchers at U.S. Idaho National Laboratory (INL) have completed initial testing on a newly developed fuel test capsule that is expected to provide crucial performance data for sodium-cooled fast reactors. Fuel testing experiments are underway at INL’s Transient Reactor Test Facility (TREAT) as part of a joint project between the U.S. and Japan.

The Temperature Heat-Sink Overpower Response (THOR) capsule houses fuel experiments designed to mimic the conditions of fast reactors during temperature transients, complete with specialized instrumentation to monitor how fuel pins respond to the conditions in real time. The testing marks the first time in 20 years that irradiated transient experiments on fast reactor fuel have been conducted anywhere in the world.

Fresh fuel pins developed for the decommissioned EBR-II sodium-cooled fast reactor were used to design and test the THOR capsules. Preparations are being made for transient experiments using high-burnup materials from historic irradiation testing in the EBR-II. The tests will include both mixed oxide fuel samples used in Japanese and French fast reactor designs and metallic alloy fuel samples similar to the fuel planned for TerraPower’s Natrium design.

Four irradiated fuel experiments are planned at the TREAT facility, with the first transient test expected to start in February 2023.