NRC Completes Safety Evaluation and Approves Terrestrial Energy IMSR Principal Design Criteria Including its Mechanism for Inherent Reactor Power Control
Terrestrial Energy has achieved a significant regulatory milestone as the U.S. Nuclear Regulatory Commission (NRC) completed its Safety Evaluation on the Principal Design Criteria (PDC) for its Integral Molten Salt Reactor (IMSR). This marks the first such ruling for a commercial molten salt reactor design.
The NRC specifically approved the IMSR's innovative use of temperature as an inherent control mechanism for power control. This regulatory approval establishes foundational safety requirements and design standards for key plant systems, notably validating the IMSR's inherent reactivity control of fission power through its relationship with molten salt temperature.
This achievement follows the April 2023 Canadian Nuclear Safety Commission's completion of its Vendor Design Review, which found no fundamental barriers to licensing the IMSR Plant for commercial use, marking another first for advanced, high-temperature fission technology.
Terrestrial Energy ha raggiunto un importante traguardo regolatorio: la U.S. Nuclear Regulatory Commission (NRC) ha completato la sua Valutazione di Sicurezza sui Criteri Principali di Progetto (PDC) per l'Integral Molten Salt Reactor (IMSR). Si tratta della prima decisione di questo tipo per un progetto commerciale di reattore a sali fusi.
L'NRC ha specificamente approvato l'uso innovativo della temperatura nell'IMSR come meccanismo intrinseco per il controllo della potenza. Questo via libera normativo stabilisce requisiti di sicurezza fondamentali e standard di progettazione per i principali sistemi dell'impianto, convalidando in particolare il controllo intrinseco della reattività e della potenza di fissione basato sulla temperatura del sale fuso.
Il risultato segue la conclusione nell'aprile 2023 della Vendor Design Review della Canadian Nuclear Safety Commission, che non ha riscontrato barriere fondamentali alla licenza dell'IMSR per uso commerciale, segnando un altro primato per la tecnologia di fissione avanzata ad alta temperatura.
Terrestrial Energy ha logrado un hito regulatorio importante: la U.S. Nuclear Regulatory Commission (NRC) completó su Evaluación de Seguridad sobre los Criterios Principales de Diseño (PDC) para su Integral Molten Salt Reactor (IMSR). Esto supone la primera resolución de este tipo para un diseño comercial de reactor de sales fundidas.
La NRC aprobó específicamente el uso innovador de la temperatura en el IMSR como mecanismo intrínseco para el control de potencia. Esta aprobación regulatoria establece requisitos de seguridad básicos y estándares de diseño para los sistemas clave de la planta, validando en particular el control intrínseco de la reactividad y la potencia de fisión mediante la relación con la temperatura del sal fundido.
Este logro sigue a la finalización en abril de 2023 de la Vendor Design Review por la Canadian Nuclear Safety Commission, que no encontró barreras fundamentales para la licencia de la planta IMSR para uso comercial, marcando otro primer hito para la tecnología de fisión avanzada de alta temperatura.
Terrestrial Energy는 중요한 규제 성과를 이루었습니다. 미국 원자력규제위원회(NRC)가 자사의 통합 용융염 원자로(IMSR)에 대한 주요 설계 기준(PDC)에 대한 안전성 평가를 완료했습니다. 이는 상업용 용융염 원자로 설계에 대한 첫 번째 판정입니다.
NRC는 IMSR이 온도를 고유한 전력 제어 메커니즘으로 사용하는 혁신적 방식을 특히 승인했습니다. 이 규제 승인으로 핵심 설비에 대한 기초적 안전 요건과 설계 기준이 확립되었으며, 특히 용융염 온도와의 관계를 통해 핵분열 출력의 고유한 반응도 제어가 검증되었습니다.
이번 성과는 2023년 4월 캐나다 원자력안전위원회가 수행한 공급업체 설계검토(Vendor Design Review)를 완료해 IMSR 플랜트의 상업적 허가에 대해 근본적 허가 장벽이 없다고 판단한 데 이은 것으로, 고온 고급 핵분열 기술의 또 다른 첫 사례입니다.
Terrestrial Energy a franchi une étape réglementaire importante : la U.S. Nuclear Regulatory Commission (NRC) a achevé son examen de sécurité des Principal Design Criteria (PDC) pour son Integral Molten Salt Reactor (IMSR). Il s'agit de la première décision de ce type pour une conception commerciale de réacteur à sels fondus.
La NRC a approuvé en particulier l'utilisation innovante de la température dans l'IMSR comme mécanisme intrinsèque de contrôle de la puissance. Cette approbation réglementaire établit des exigences de sécurité fondamentales et des normes de conception pour les systèmes clés de l'usine, validant notamment le contrôle intrinsèque de la réactivité et de la puissance de fission via la relation avec la température du sel fondu.
Cette réussite fait suite à l'achèvement en avril 2023 de la Vendor Design Review par la Canadian Nuclear Safety Commission, qui n'a trouvé aucun obstacle fondamental à l'octroi de licence pour l'exploitation commerciale de l'usine IMSR, marquant un nouveau premier pour la technologie de fission avancée à haute température.
Terrestrial Energy hat einen bedeutenden regulatorischen Meilenstein erreicht: Die U.S. Nuclear Regulatory Commission (NRC) hat ihre Sicherheitsbewertung zu den Principal Design Criteria (PDC) für den Integral Molten Salt Reactor (IMSR) abgeschlossen. Dies ist die erste derartige Entscheidung für ein kommerzielles Design eines Salztopfreaktors.
Die NRC genehmigte insbesondere die innovative Nutzung der Temperatur im IMSR als inhärenten Regelmechanismus zur Leistungssteuerung. Diese regulatorische Zustimmung legt grundlegende Sicherheitsanforderungen und Entwurfsstandards für die wesentlichen Anlagensysteme fest und bestätigt insbesondere die inhärente Reaktivitäts- und Leistungsregelung der Spaltung über die Beziehung zur Temperatur des flüssigen Salzes.
Dieser Erfolg folgt auf den Abschluss der Vendor Design Review durch die Canadian Nuclear Safety Commission im April 2023, die keine grundlegenden Hindernisse für eine Zulassung der IMSR-Anlage für den kommerziellen Betrieb feststellte und damit einen weiteren Meilenstein für die fortschrittliche Hochtemperatur-Spaltungstechnologie darstellt.
- First NRC Safety Evaluation approval for a commercial molten salt reactor design
- NRC approval of IMSR's unique temperature-based inherent power control mechanism
- Previous successful completion of Canadian Nuclear Safety Commission's VDR review
- Regulatory validation of inherent safety mechanisms enhancing commercial viability
- Streamlined future licensing process through pre-approved safety evaluation
- Still requires additional regulatory steps before full commercial deployment
- Complex new technology requiring continued regulatory scrutiny
Insights
Terrestrial Energy achieves significant regulatory milestone with NRC approval of its molten salt reactor safety mechanisms, accelerating commercialization pathway.
This NRC Safety Evaluation for Terrestrial Energy's IMSR Principal Design Criteria represents a significant regulatory breakthrough in advanced nuclear development. As the first such approval for a commercial molten salt reactor design, this milestone validates the inherent safety approach of using temperature as a natural control mechanism for reactor power—a distinctive feature of molten salt technology.
From a regulatory perspective, securing this topical report approval is strategically valuable as it establishes precedent that can be referenced in future licensing applications, eliminating the need to re-adjudicate these safety aspects. This substantially streamlines the licensing pathway for Terrestrial Energy, potentially accelerating their time-to-market compared to competitors.
The approval specifically validates three critical inherent safety mechanisms: power control through temperature feedback, heat dissipation via convective flow, and chemical containment of fission products within the fuel salt. These passive safety features represent a fundamental advantage over conventional reactor designs that require active safety systems.
This development follows the
The NRC approval of Terrestrial Energy's Principal Design Criteria marks a decisive competitive advantage in the crowded advanced nuclear market. By securing regulatory validation for its inherent safety mechanisms—particularly the use of temperature as a passive control mechanism—Terrestrial has established a meaningful first-mover advantage among molten salt reactor developers.
This regulatory milestone enhances Terrestrial's commercial positioning through three tangible benefits: reduced regulatory uncertainty for potential investors and partners, streamlined future licensing processes through the ability to reference this Safety Evaluation, and validated technical differentiation of their inherent safety approach.
Market context is crucial here—this achievement occurs amid intensifying competition in small modular reactor development. The dual regulatory progress in both U.S. (NRC) and Canadian (CNSC) jurisdictions gives Terrestrial Energy a unique cross-border advantage that could accelerate deployment opportunities in both markets.
The inherent safety mechanisms approved by the NRC represent a compelling economic proposition: passive safety systems that require fewer engineered safety features potentially translate to lower construction and operating costs. The reference to "commercial value" in the CEO's statement directly connects these safety features to the business case for the technology.
The endorsement from former NRC Commissioner Jeffrey Merrifield adds credibility, highlighting that this approval establishes "a fundamental design framework for subsequent licensing steps and commercialization." This suggests Terrestrial Energy has cleared a crucial hurdle in translating its technical approach into a viable commercial product.
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.
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Terrestrial Energy Investor Center:
https://www.terrestrialenergy.com/investors
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FAQ
What is the significance of NRC's approval of Terrestrial Energy's IMSR design criteria?
How does Terrestrial Energy's IMSR control nuclear reactions differently from traditional reactors?
What regulatory approvals has Terrestrial Energy's IMSR received so far?
What makes Terrestrial Energy's IMSR inherently safe?
What is the next step for Terrestrial Energy after receiving NRC's Safety Evaluation approval?
