US-based Terrestrial Energy Submits IMSR Graphite Topical Report to Advance Molten Salt Reactor Licensing Preparation

US fourth-generation molten salt nuclear power plant developer Terrestrial Energy Inc. (NASDAQ: IMSR) recently announced that it has submitted a graphite topical report to the US Nuclear Regulatory Commission (NRC). The report is intended to provide a regulatory basis for the use of graphite, a key core component of the Integral Molten Salt Reactor (IMSR), in commercial power plant operation.

Terrestrial Energy CEO Simon Irish stated that this is the second of at least three IMSR topical reports the company plans to submit to the NRC in 2026, and is part of its structured regulatory engagement plan, with the ultimate goal of preparing for the submission of an IMSR plant license application. He stated that graphite performance determines the service life of the IMSR core unit, and this submission marks the beginning of the NRC's review of graphite qualification under commercial operating conditions.

The IMSR employs a graphite-moderated molten salt reactor design. Graphite has been used as a reactor moderator in commercial nuclear power operation for decades, but regulators typically require a "qualification" program for specific reactor designs to verify its performance under expected operating conditions. For Terrestrial Energy, this program corresponds to the graphite materials in the IMSR core unit.

Terrestrial Energy stated that its graphite qualification program has made progress. Over the past several years, the company has conducted graphite performance data collection at the NRG high-flux reactor in Petten, the Netherlands, with test subjects including multiple nuclear-grade graphite materials from various suppliers. The relevant test data will be used to support the qualification methodology proposed in the graphite topical report.

The graphite topical report seeks NRC acceptance of Terrestrial Energy's methodology for completing graphite qualification for the IMSR plant. The methodology described in the report includes steps such as graphite selection, identification and resolution of information needs, and scheduling of qualification activities, to demonstrate that graphite can meet the performance requirements under expected operating conditions of the IMSR core unit.

In March 2026, Terrestrial Energy stated that it expected to submit at least three topical reports to the NRC that year, covering key areas in IMSR licensing preparation. Each report is intended to resolve important regulatory issues before formal application and to establish licensing basis elements that can support subsequent license applications.

This graphite topical report submission is part of the company's engineering, licensing, supply chain development, testing, and commercial project development plans. Terrestrial Energy plans to achieve commercial deployment of its first IMSR plants in the early 2030s.

Prior to this, Terrestrial Energy received NRC approval in 2026 for its "Hypothetical Initiating Events Methodology Topical Report," and in 2025 received approval for its "Principal Design Criteria Topical Report." Approved topical reports can be referenced as licensing basis elements in future license applications, thereby reducing duplicative evaluation content in subsequent technical reviews.

Terrestrial Energy stated that the replaceable IMSR core unit is an important part of its business model. According to the plan, IMSR plants will replace the core unit every seven years over their operating lifetime, creating ongoing demand for subsequent component supply. The company expects that related component supply will constitute an important source of lifecycle revenue for each IMSR plant.

The IMSR plant employs a small modular design, with target application scenarios including data centers, petrochemical synthesis, and other industrial sectors, aiming to provide high-temperature heat and electricity. This technology pathway uses standard low-enriched uranium fuel, and Terrestrial Energy is working with regulators, suppliers, and partners to advance preparation for first project deployment.