- Terrestrial Energy submitted a graphite-themed report to advance the IMSR regulatory plan.
- Graphite serves as a neutron moderator in the IMSR design and is critical to the core unit's lifespan.
- The company plans to submit at least three thematic reports in 2026 to support the power plant license application.
- The new report requests the NRC to review the graphite qualification methodology but does not approve construction or operation.
Terrestrial Energy has submitted a graphite-themed report to the U.S. Nuclear Regulatory Commission (NRC) to advance the regulatory plan for its Integral Molten Salt Reactor (IMSR), as the company works toward commercial deployment. The report seeks NRC approval for the company's graphite qualification methodology for the IMSR core unit, a key component in Terrestrial Energy's fourth-generation molten salt reactor design. This submission is the second of at least three IMSR thematic reports the company plans to submit to the NRC in 2026, aimed at addressing key technical and regulatory issues in preparation for Terrestrial Energy's future power plant license application.
Graphite is crucial to the IMSR design, a graphite-moderated molten salt reactor, meaning graphite acts as the reactor's neutron moderator while molten salt serves as the fuel transport and heat transfer medium. Although graphite has been used in commercial nuclear reactors for decades, its behavior in each specific reactor design must be proven. Therefore, Terrestrial Energy has a dedicated qualification program to demonstrate that its selected graphite can withstand the expected operating conditions within the IMSR core unit.
The Role of Graphite in the IMSR Design
The company stated that it has spent years collecting graphite performance data through testing at the NRG Qualcomm reactor in Petten, Netherlands. This program examined multiple nuclear graphite grades from various suppliers. These results will support the qualification methodology described in the newly submitted report.
According to Terrestrial Energy CEO Simon Irish, graphite performance ultimately determines the IMSR core unit's service life. The company stated that the new submission initiates the NRC's review of its intended material qualification methodology for commercial operation.
The graphite-themed report is part of Terrestrial Energy's broader pre-application engagement with the NRC. The company previously received NRC approval for its primary design criteria thematic report in 2025 and for its postulated accident methodology thematic report in 2026. Thematic reports allow the regulator to review specific technical and regulatory issues before a full power plant license application. Terrestrial Energy stated that the approved reports can establish the foundational elements of the IMSR license, which can be referenced in future applications without re-evaluating the same technical issues.
Future Thematic Report Plans
The company expects to submit at least three additional thematic reports in 2026, covering areas it considers critical to the eventual IMSR power plant license. The related regulatory work is proceeding alongside Terrestrial Energy's engineering, testing, supply chain development, and commercial planning for its first commercial IMSR deployment in the early 2030s.
The graphite report also touches on a particular aspect of Terrestrial Energy's proposed business model. The IMSR core unit is designed to be replaceable, and the company plans to replace the core unit approximately every seven years during the operational life of an IMSR power plant. Terrestrial Energy stated that this approach is crucial to its capital-light business model and could create a continuous component supply revenue stream after the power plant is built. An IMSR power plant can provide 822 MWt of net thermal energy or 390 MWe of net electrical power, or a customized combination of both.
While the graphite qualification process remains an important regulatory step, the newly submitted report itself does not approve IMSR construction or operation. Instead, it requests the NRC to review the methodology Terrestrial Energy intends to use to demonstrate that its graphite can meet the reactor's expected operating condition requirements.
Key Steps in the IMSR Regulatory Plan
Terrestrial Energy's submission of the graphite-themed report marks a significant advancement in its nuclear regulatory process. As graphite is a key component of the IMSR core unit, its performance directly affects the reactor's operational lifespan and must undergo rigorous qualification. This process not only helps ensure safety but also paves the way for future commercial deployment. As the company plans to submit multiple thematic reports in 2026, it demonstrates its long-term commitment and strategic planning for success in the nuclear energy market.