Canadian, US regulators publish joint TRISO report

30 June 2023

The joint report by the Canadian Nuclear Safety Commission (CNSC) and the US Nuclear Regulatory Commission (NRC) establishes a common regulatory position on tristructural isotropic (TRISO) fuel qualification, for use in the licensing of advanced reactor and small modular reactor (SMR) technologies.

A TRISO particle (Image: US Department of Energy)

The report is part of the cooperative activities established under a memorandum of cooperation on advanced reactor and SMR technologies signed by the two regulators in 2019. The CNSC and NRC subsequently selected Terrestrial Energy's Integral Molten Salt Reactor for their first joint technical review of an advanced, non-light-water nuclear reactor technology, which they completed in 2022.

The latest joint report provides a common understanding on the evidence fuel vendors need to demonstrate the acceptability of "pebbles" made from TRISO fuel. TRISO fuel comprises spherical kernels of enriched uranium oxycarbide (or uranium dioxide) surrounded by layers of carbon and silicon carbide, giving a containment for fission products which is stable up to very high temperatures.

According to the scope and objectives set out in the report, the two regulators aim to work together "to establish a common regulatory position on TRISO fuel qualification based on existing knowledge and to identify any potential analytical or testing gaps that would need to be addressed to enable TRISO use in advanced reactor licensing applications". The report aims to: provide the evidentiary basis to support regulatory findings for items associated with fuel qualification that are generically applicable to TRISO fuel based on currently available information; identify areas of TRISO fuel qualification that are design dependent; and highlight areas where additional information, testing, or both is still needed to support regulatory approval.

The NRC has worked with two vendors of advanced reactors that are proposing the use of TRISO fuel in their reactor designs, Kairos Power and X-energy. It anticipates that licensing activities with X-energy are likely to increase following that company's 2020 selection by the US Department of Energy to deliver a commercial TRISO fuel fabrication facility and a four-module version of its Xe-100 high-temperature gas-cooled reactor by 2027 as part of the department's Advanced Reactor Demonstration Program. Meanwhile, through its Vendor Design Review process, the CNSC has worked with two vendors - X-energy and Ultra-Safe Nuclear Corporation - that are proposing to use TRISO fuel in their advanced reactor designs.

The report, dated March 2023, was made public by the NRC on 29 June.

Researched and written by World Nuclear News