Regulatory Milestones

10 CFR Part 50 is the U.S. Nuclear Regulatory Commission’s established licensing framework for commercial nuclear power plants. It is a well-understood two-step approach consisting of a Construction Permit issued after safety and environmental review, and an Operating License issued after construction completion and final safety inspection.

Part 50 has been used successfully for over 50 years to license more than 100 reactors in the United States. While originally developed for light-water reactors, we believe this approach will likely be cumulatively faster than Part 52 options due to a more flexible change control process during the construction period. The Part 50 pathway also allows X-energy to reference its numerous NRC-approved topical reports – covering fuel qualification, safety analysis, source term methodology, and other foundational safety matters – as regulatory assets that subsequent Xe-100 projects can cite without re-justifying the underlying technical analysis.

The NRC’s 18-month Construction Permit review timeline for Long Mott, announced June 2025, represents one of the most efficient advanced reactor review schedules announced to date. The NRC cited the completeness and quality of X-energy’s and Dow’s application, and the volume of pre-application work conducted as key considerations in determining the review schedule.

As part of its pre-application engagement, X-energy submitted more than 30 technical documents, and secured safety evaluations on 14 topical reports before submitting a Construction Permit Application in March 2025. This front-loaded technical work helps to resolve complex safety questions early, allowing the NRC to conduct focused reviews of site-specific factors rather than fundamental design questions.

Construction Permit approval authorizes X-energy and Dow to begin site preparation, below-grade concrete work, and installation of safety-related structures, systems, and components. While the plant is under construction, an Operating License Application is submitted to the NRC requesting authorization to operate the plant. This application includes final as-built design documentation, operational procedures, emergency planning implementation, and operator training programs.

Throughout construction, NRC inspectors verify quality assurance compliance and adherence to approved designs. The Operating License is issued only after NRC confirms all construction requirements are met and operational readiness is demonstrated.

Yes. Long Mott’s regulatory achievements serve as referenceable regulatory assets for all future Xe-100 projects, with the potential to significantly accelerate subsequent licensing timelines. Specifically:

• NRC-Approved Methodologies: Topical reports with Safety Evaluations apply to the Xe-100 design generically, not just Long Mott. Future projects can cite these approved methodologies without re-demonstrating the underlying technical bases, helping reduce review scope to site-specific factors.
• Design Standardization: Once Long Mott’s Construction Permit is issued, the approved reactor design becomes a “reference plant” that future applications can leverage. Subsequent site-specific reviews are then able to focus on local factors rather than fundamental reactor safety questions.
• Regulatory Precedent: Long Mott is the first advanced high temperature gas reactor Construction Permit Application under Part 50 in over 7 years. The NRC’s review process for Long Mott helps establish precedents that inform how subsequent Xe-100 applications are evaluated, reviewed, and approved.

While both projects are progressing under Part 50, the Cascade Advanced Energy Facility’s licensing process has significant potential for increased efficiency – benefiting both from the regulatory precedents established through Long Mott’s Construction Permit Application review, and co-location with Energy Northwest’s Columbia Generating Station, a boiling water reactor (BWR) licensed until 2043.

Co-location allows Cascade to operate within Columbia’s existing 10-mile emergency planning zone, leverage shared security and emergency response infrastructure, and interconnect with existing transmission assets. Columbia Generating Station’s 40+ years of operational history also provides extensive qualitative site-specific data that can be leveraged as part of the application. These and other co-location factors create opportunities for increased efficiency in the licensing process, further supported by regulatory precedent established during Long Mott’s CPA review.

To ensure safe and reliable operations when co-locating a new nuclear facility, the NRC conducts site-specific reviews of potential interactions between the two facilities. Broadly, the NRC evaluates whether a new nuclear facility can safely share emergency planning zones, security infrastructure, and emergency response resources with an existing facility, or whether independent systems are required. As an example, the Xe-100’s 400-meter emergency planning zone allows Cascade to operate entirely within Columbia’s existing 10-mile EPZ boundary, simplifying emergency planning coordination and reducing regulatory complexity.

Additional NRC evaluation areas include seismic and external event interactions between facilities, spent fuel storage, electrical grid isolation to prevent cross-facility service disruptions, and workforce qualification requirements. Energy Northwest’s 40+ years of nuclear operating experience at Columbia provides extensive site characterization data and operational expertise that inform Cascade’s design and licensing approach.

Yes. NRC regulations under 10 CFR Part 50 allow a single Construction Permit Application to cover multiple identical or similar reactor units at one site, provided the application demonstrates adequate safety analysis for all units and site capacity to support full build-out. This approach has been used successfully throughout the U.S. nuclear fleet, with most large nuclear plants licensed as multi-unit sites in a single proceeding.

Cascade is planned as a 4 – 12-unit deployment with phased construction. Multi-unit approval enables a single environmental assessment covering full site build-out, and common safety analysis for identical reactor designs. Even with multi-unit approval, each reactor undergoes independent NRC construction inspections and receives an operating license only after demonstrating individual unit readiness.

Generic Design Assessment (GDA) is a significant step in the United Kingdom’s reactor design approval process, administered by the Office for Nuclear Regulation (ONR). Unlike U.S. NRC licensing under 10 CFR Part 50 which combines design review and site-specific licensing in one proceeding, the U.K. separates design approval from site licensing into two sequential phases:

• Generic Design Assessment: ONR evaluates reactor design, safety systems, fuel performance, and operational procedures without reference to any specific site. If approved, ONR issues a Design Acceptance Confirmation (DAC) and Statement of Design Acceptability (SDA) valid for any U.K. site meeting specified parameters.
• Site-Specific Licensing: After GDA approval, the reactor vendor and site developer apply for site-specific licenses from ONR. ONR evaluates site suitability, local site characteristics, emergency planning, and environmental factors

Yes. Generic Design Assessment approval is design-specific, not site-specific. Once ONR issues a Design Acceptance Confirmation (DAC) and a Statement of Design Acceptability (SDA) for the Xe-100, that approval applies to any U.K. project that meets the generic design parameters without requiring repeated design reviews for each site. This standardized approach helps to enable fleet-scale deployment, much like the NRC’s licensing process under Part 52.

After GDA completion, each site requires only site-specific licensing evaluating local seismicity, emergency planning zones, grid interconnection, and environmental impacts. All U.K. Xe-100 plants would reference the same approved GDA safety documentation, helping to ensure consistent safety standards while reducing per-site regulatory burden.

The U.S. and the U.K. signed the U.S.-U.K. Civil Nuclear Energy Agreement (renewed 2024) and a Memorandum of Understanding (2025) to foster technical cooperation between the NRC and ONR. The agreements allow regulatory information sharing, joint technical reviews, and mutual recognition of certain safety analyses, helping to reduce duplication and increase the overall efficiency of Xe-100 licensing. X-energy’s NRC-approved topical reports can be shared with ONR, allowing U.K. regulators to leverage NRC’s technical findings rather than conducting entirely independent reviews from scratch.

The agreement also facilitates the export of U.S. reactor and fuel technology and TRISO fuel from TX-1 in Oak Ridge, Tennessee to U.K. sites under streamlined procedures. As Long Mott progresses through NRC Construction Permit review, regulatory precedents and safety analysis approaches can inform ONR’s GDA evaluation, potentially reducing Hartlepool’s total licensing timeline compared to entirely independent reviews.