Phase 1 pre-licensing vendor design review executive summary: Moltex Energy
Moltex Energy is designing a 300 MWe (750 MWth) molten salt reactor, the SSR-W300. The Canadian Nuclear Safety Commission (CNSC), as Canada’s nuclear regulator, under the authority of the Nuclear Safety and Control Act, entered into an agreement with Moltex Energy on November 16, 2017, to conduct a Phase 1 pre-licensing vendor design review (VDR) of the SSR W300 molten salt reactor. The VDR process is described in regulatory document REGDOC 3.5.4, Pre-Licensing Review of a Vendor’s Reactor Design.
The VDR is an optional service that the CNSC provides at the request of a vendor. It is a high-level review of the proposed reactor technology’s design information against Canadian regulatory requirements and guidance. The service does not involve the issuance of a licence under the Nuclear Safety and Control Act and is not part of the licensing process. The conclusions of such a review do not bind or otherwise influence decisions made by the Commission. The CNSC’s licensing processes will require a more detailed review of the design and safety case for a specific licence application at a specific site.
A Phase 1 VDR determines whether, at a general level, the vendor’s reactor design and design processes demonstrate implementation of CNSC regulatory requirements. It is intended to provide early feedback to the vendor on matters relating to CNSC regulatory requirements and expectations. This can allow for early identification and resolution of potential regulatory or technical issues in the design and design process, particularly those that could result in significant changes to the design.
This Phase 1 report outlines the CNSC staff review process, the assessment findings, and the conclusions of the review.
Application of REGDOC-2.5.2
REGDOC-2.5.2, Design of Reactor Facilities: Nuclear Power Plants, was written to be technology-neutral to the extent practicable. However, the document contains requirements and guidance that incorporate extensive operating experience from the use of water-cooled reactors. It is recognized that vendors of specific technologies may present alternative technological approaches and methodologies; however, alternative approaches remain subject to the same safety objectives, high-level safety concepts and safety management principles articulated in CNSC design and safety analysis documents such as REGDOC-2.5.2 and supporting documentation. Technical expertise, professional judgment and adequately documented processes can also be used to ensure that the application of, or departure from, regulatory requirements is objective and consistent so that the required level of safety is achieved.
Phase 1 vendor design review results
The Moltex Phase 1 VDR was carried out at the request of the vendor, over a 42-month period. Moltex Energy submitted 50 documents broken up into 8 work packages to cover the 19 technical review focus areas. Moltex Energy also provided familiarization sessions, responses to requests for additional information, and technical clarifications through letters, emails and meetings. Based on the documentation submitted, CNSC staff concluded the following:
- Overall, Moltex Energy understands and has correctly interpreted the high-level intent of the CNSC’s regulatory requirements for the design of nuclear power plants in Canada within the scope of the Phase 1 VDR.
- In several instances, owing to the unique characteristics of the reactor design, Moltex Energy is proposing alternative approaches and methodologies to address the underlying intent of CNSC regulatory requirements, in accordance with section 11 of REGDOC-2.5.2. Moltex Energy has indicated that it intends to adequately justify the use of these alternative approaches, and understands that it will be expected to provide evidence that these alternative approaches will result in an equivalent or superior level of safety.
- Moltex Energy will be required to do additional work to address the findings raised in this review. These are discussed below.
- The design of the SSR-W300 evolved throughout the Phase 1 VDR and may continue to evolve. Any changes to the design must be documented and described in detail for any future review.
The following points are a summary of clarifications or findings that will require additional follow-up in a future review:
- The management system documentation submitted by Moltex Energy does not yet show sufficient systematic processes to support its ongoing design development activities. It was noted, though, that Moltex Energy is implementing a number of improvements to its management system. As a result, additional information will be needed in Phase 2 to confirm that Moltex Energy’s updated management system processes to control design, safety analysis, and research and development activities meet the intent of requirements and expectations set out in applicable regulatory documents and standards.
- The safety classification of structures, systems and components (SSCs) in the SSR-W300 design has not yet been linked to the quality assurance programs. Similarly, the safety classification methodology submitted has not yet been fully developed to provide information as to how sub-classifications are established. In Phase 2, the vendor will need to establish and demonstrate, using examples, the relationship between the safety classification designation and engineering design rules in order to ensure that SSCs are designed, manufactured, constructed, installed, commissioned, operated, tested, inspected and maintained such that their quality and reliability are commensurate with the classification.
- Moltex Energy takes the position that a secondary control room is not needed in the design. While the proposal of an alternative approach is acceptable, Moltex has not yet justified that such an approach will have at least an equivalent level of safety. Such a justification will be required for any Phase 2 review.
- The SSR-W300 design includes 2 novel means of shutdown. Limited information was provided regarding the reliability of these means for all operating states, their capability to safely reduce the reactor to low power levels, and their ability to put the reactor in a guaranteed shutdown state. Such information is expected for a Phase 2 review.
- The containment structures presented by the vendor are still at a conceptual level. The capability of the structures to respond to accident scenarios, including design-basis and beyond-design-basis threats, are not discussed. Such information is expected for a Phase 2 review.
- Given the novelty of some of the SSR-W300 design and safety features, in Phase 2 additional information will be required to confirm:
- the interface requirements between SSCs of different safety classifications
- the adequacy of the research and development activities to substantiate the fuel qualification program, including the role of a first-of-a-kind reactor
- the validation and verification of the capability of the software tools to model the reactor and to analyze the reactor behaviour under all operating modes
- the functionality, adequacy and reliability of inherent and passive safety systems and components claimed in the safety case for the reactor
Notwithstanding the above, these issues are foreseen to be resolvable and will be followed up on in future phases of the VDR.
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