Terrestrial Energy (IMSR) TD Nuclear Roundtable (Virtual) summary

Reactor design and fuel

• IMSR is a Gen IV, thermal-spectrum, graphite-moderated reactor with a large core; it uses standard LEU enriched to no more than 5%, with actual enrichment significantly lower.

• The LEU choice, made roughly 10 years ago, was intended to avoid HALEU supply bottlenecks and support fleet-scale fuel supply; the focus is commercial viability, not a theoretically perfect molten salt design.

Materials and qualification

• Graphite and nuclear-grade steels are well supplied, but regulatory qualification requires QA-compliant performance data that can support a license application.

• Graphite has been undergoing testing for several years in a powerful Netherlands test reactor; test duration is constrained by reactor power, and alloys and other components also require data collection.

Licensing and pilot programs

• NRC topical reports establish agreement on licensing elements; submissions cover Principal Design Criteria, Postulated Initiating Events, and graphite-qualification methodology, with at least three reports planned for 2026.

• DOE authorization agreements for a pilot reactor and pilot fuel plant overlay an existing testing program; the pathway can accelerate testing by avoiding the standard NRC test-reactor operating-license process.

• Part 53 is under consideration as a potential licensing path; its technology-neutral, risk-informed, phased approach may support efficient first-plant licensing and repeatable fleet approvals.