NRC Completes Safety Evaluation and Approves Terrestrial Energy IMSR Principal Design Criteria Including its Mechanism for Inherent Reactor Power Control

Terrestrial Energy continues to lead molten salt reactor commercialization with first ruling by NRC on IMSR Plant’s inherent safety mechanisms and first such ruling by NRC for a commercial design of molten salt reactor

Terrestrial Energy’s pre-application NRC engagement advanced with the completion of the first NRC Topical Report and ruling on the IMSR plant design, which rules on IMSR’s unique and inherent safety mechanisms including IMSR use of temperature as the inherent control mechanism of reactor power for safe operation

CHARLOTTE, N.C., Sept. 10, 2025 (GLOBE NEWSWIRE) -- Terrestrial Energy Inc., a developer of small modular nuclear power plants using Generation IV reactor technology, today announced that the U.S. Nuclear Regulatory Commission (NRC) has issued its Safety Evaluation on the Principal Design Criteria (PDC) for Integral Molten Salt Reactor (IMSR) Structures, Systems, and Components following the company’s submission of its topical report to the agency. The NRC’s Safety Evaluation of Terrestrial Energy’s IMSR, the first of its kind to be completed for a molten fuel salt reactor designed for commercial use, approved the IMSR’s use of temperature as the inherent control mechanism for power control.

A topical report allows for NRC review of a safety-related topic and leads to a Safety Evaluation, which can be referenced in a future licensing application. This regulatory approval avoids the need for re-adjudication of important topics of reactor safety and increases the efficiency of the licensing process.

Principal Design Criteria of the nuclear reactor are the foundational safety requirements, quality standards, and design requirements of key plant systems, structures and components. These criteria ensure that the reactor is designed to operate safely, effectively, and in manner with nuclear regulations.

This topical report has established the criteria for all major IMSR plant systems including the use of IMSR inherent reactivity control of fission power. The IMSR manages the fission process through its inverse relationship with the molten salt temperature, creating a reactor with inherently stable power dynamics.

“This topical report is a key milestone. It represents NRC regulatory approval of important elements of the IMSR’s safety mechanisms, particularly those relating to IMSR inherent safety and reactor power control,” said Simon Irish, CEO of Terrestrial Energy. “Inherent safety mechanisms play a critical role in the safety of the IMSR and its commercial value. They draw on the natural behavior of molten salt reactors, which include inherent power control, heat dissipation through convective flow of fuel salt and chemical containment of fission products within the fuel salt. The IMSR is designed to be inherently safe, capturing the many unique safety and distinguishing characteristics of the molten salt reactor technology class.”

The significance of this achievement is echoed by Terrestrial Energy Advisor Jeffery Merrifield, who served two terms as a U.S. NRC Commissioner.

“Acceptance of a reactor PDCs is the foundation for future success of operating license applications as it establishes a fundamental design framework for subsequent licensing steps and commercialization of the IMSR Plant,” said Jeffrey Merrifield. “The safety ruling on the IMSR’s Principal Design Criteria is a clear signal of progress in nuclear technology. The NRC’s rigorous review process ensures safety remains paramount, and this step reflects both the maturity of Terrestrial Energy’s approach and the potential of molten salt reactors to contribute to our energy landscape. It’s a meaningful and welcome milestone that sets a precedent for others in the field.”

In April 2023, the Canadian Nuclear Safety Commission's (CNSC) completed its programmatic Vendor Design Review (VDR) of the IMSR Plant and concluded that there was “no fundamental barriers to licensing” the IMSR Plant for commercial use. This is the first advanced, high-temperature fission technology to complete a review of this type. The VDR is a comprehensive pre-licensing regulatory review against Canadian nuclear safety standards, its scope and conclusion provide commercial confidence to proceed to licensing and construction. The April 2023 VDR was the first technology review completed by a major regulator of a nuclear plant design that uses a molten salt reactor technology, a Generation IV technology.

About Terrestrial Energy
Terrestrial Energy is a developer of Generation IV nuclear plants that use its proprietary Integral Molten Salt Reactor (IMSR). The IMSR captures the full transformative operating benefits of molten salt reactor technology in a plant design that represents true innovation in cost reduction, versatility and functionality of nuclear energy supply. IMSR plants are designed to be small and modular for distributed supply of zero-carbon, reliable, dispatchable, low-cost, high-temperature industrial heat and electricity, and for a dual-use energy role relevant to many industrial applications, such as chemical synthesis and data center operation. In so doing, they extend the application of nuclear energy far beyond electric power markets. Their deployment will support the rapid global decarbonization of the primary energy system across a broad spectrum and increase its sustainability. Terrestrial Energy uses an innovative plant design together with proven and demonstrated molten salt reactor technology and standard nuclear fuel for a nuclear plant with a unique set of operating characteristics and compelling commercial potential. Terrestrial Energy is engaged with regulators, suppliers and industrial partners to build, license and commission the first IMSR plants in the early 2030s.

On March 26, 2025, Terrestrial Energy and HCM II Acquisition Corp. (Nasdaq: HOND) announced that they have entered into a definitive Business Combination Agreement for a business combination (the “Business Combination”) that would result in the listing of the combined company (Terrestrial Energy) on the Nasdaq Stock Market under the ticker symbol “IMSR”.

Important Information for Shareholders

This communication does not constitute an offer to sell or the solicitation of an offer to buy any securities or constitute a solicitation of any vote or approval.

The proposed business combination will be submitted to shareholders of HCM II for their consideration. HCM II has filed a registration statement on Form S-4 (as amended, and may be further amended from time to time, the “Registration Statement”) with the SEC, which includes a preliminary proxy statement/prospectus solicitation statement to be distributed to HCM II’s shareholders in connection with HCM II’s solicitation for proxies for the vote by HCM II’s shareholders in connection with the proposed business combination and other matters described in the Registration Statement, as well as the prospectus relating to the offer of the securities to be issued to Terrestrial Energy’s shareholders in connection with the completion of the proposed business combination. After the Registration Statement has been declared effective by the SEC, a definitive proxy statement/prospectus will be mailed to the shareholders of HCM II and Terrestrial Energy. INVESTORS OF HCM II AND TERRESTRIAL ENERGY ARE URGED TO READ THE REGISTRATION STATEMENT, THE PROXY STATEMENT/PROSPECTUS CONTAINED THEREIN (INCLUDING ALL AMENDMENTS AND SUPPLEMENTS THERETO) AND ALL OTHER DOCUMENTS RELATING TO THE BUSINESS COMBINATION THAT WILL BE FILED WITH THE SEC CAREFULLY AND IN THEIR ENTIRETY WHEN THEY BECOME AVAILABLE BECAUSE THEY WILL CONTAIN IMPORTANT INFORMATION ABOUT THE BUSINESS COMBINATION.

Investors will be able to obtain free copies of the proxy statement/prospectus and other documents containing important information about HCM II and Terrestrial Energy once available, through the website maintained by the SEC at http://www.sec.gov. In addition, the documents filed by HCM II may be obtained free of charge from HCM II’s website at https://hcmacquisition.com/ or by written request to HCM II at 100 First Stamford Place, Suite 330 Stamford, CT 06902.

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The forward-looking statements contained in this press release are based on our current expectations and beliefs concerning future developments and their potential effects on HCM II and the Company. There can be no assurance that future developments affecting HCM II and the Company will be those that we have anticipated. These forward-looking statements speak only as of the date this press release is actually delivered and involve a number of risks, uncertainties (some of which are beyond our control) or other assumptions that may cause actual results or performance to be materially different from those expressed or implied by these forward-looking statements. Should one or more of these risks or uncertainties materialize, or should any of our assumptions prove incorrect, actual results may vary in material respects from those projected in these forward-looking statements. Factors that may cause actual results to differ materially from current expectations include, but are not limited to: (1) the occurrence of any event, change or other circumstances that could give rise to the termination of the definitive agreements with respect to the Business Combination; (2) the outcome of any legal proceedings that may be instituted against HCM II, the Company, the combined company or others following the announcement of the Business Combination and any definitive agreements with respect thereto; (3) the inability to complete the Business Combination due to the failure to obtain approval of the shareholders of HCM II or the SEC’s declaration of the effectiveness of the Registration Statement (which will include the proxy statement/prospectus contained therein) to be filed by HCM II and the Company or to satisfy other conditions to closing; (4) changes to the proposed structure of the Business Combination that may be required or appropriate as a result of applicable laws or regulations or as a condition to obtaining regulatory approval of the Business Combination; (5) the ability of HCM II to meet stock exchange listing standards following the consummation of the Business Combination; (6) the risk that the Business Combination disrupts current plans and operations of the Company as a result of the announcement and consummation of the Business Combination; (7) the ability to recognize the anticipated benefits of the Business Combination, which may be affected by, among other things, competition, the ability of the combined company to grow and manage growth profitably, maintain relationships with customers and suppliers and retain its management and key employees; (8) costs related to the Business Combination, including the reorganization described in the business combination agreement; (9) changes in applicable laws or regulations; (10) the possibility that the Company or the combined company may be adversely affected by other economic, business, and/or competitive factors; (11) the amount of redemption requests made by HCM II shareholders; (12) the potential development of U.S. sources of HALEU with government support, and (13) other risk factors described herein as well as the risk factors and uncertainties described in the Registration Statement, that certain prospectus of HCM II dated August 15, 2024 and the HCM II’s other filings with the SEC, as well as any further risks and uncertainties to be contained in the proxy statement/prospectus filed in connection with the Business Combination. In addition, there may be additional risks that neither HCM II or Company presently know, or that HCM II or Company currently believe are immaterial, that could also cause actual results to differ from those contained in the forward-looking statements. Nothing in this communication should be regarded as a representation by any person that the forward-looking statements set forth herein will be achieved or that any of the contemplated results of such forward-looking statements will be achieved. You should not place undue reliance on forward-looking statements, which speak only as of the date they are made.

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Terrestrial Energy Investor Center:

https://www.terrestrialenergy.com/investors

Terrestrial Energy Media & Investor Contact:

TerrestrialEnergy@icrinc.com

HCM II Investor Contact:

HCM II Acquisition Corp.
Steven Bischoff
sbischoff@hondiuscapital.com
(203) 930-2200

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