Executive summary: Phase 2 pre-licensing vendor design review – Terrestrial Energy Inc.

Background

Terrestrial Energy Incorporated (TEI) is designing the IMSR400, a 400-MWth (200-MWe) molten salt reactor. On May 9, 2018, 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 TEI to conduct a Phase 2 pre-licensing vendor design review (VDR) of the IMSR400.

A VDR is an optional service that the CNSC can provide at the request of a vendor. It is a high-level review of the proposed reactor design information and takes place during the design process while the design is still evolving. It is intended to provide timely feedback to the vendor on matters related to CNSC regulatory requirements and expectations. This can allow for early identification and resolution of potential regulatory or technical issues in the design and the design process, particularly those that could result in significant changes to the design.

This service does not certify a reactor design, nor does it involve the issuance of a licence under the Nuclear Safety and Control Act. It is not required as part of the licensing process for a new nuclear reactor facility. The conclusions of a VDR do not bind or otherwise influence decisions made by the Commission, with whom the authority resides to issue licences for nuclear reactor facilities. 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.

The purpose of a Phase 2 VDR is to determine whether TEI understands CNSC regulatory requirements and the extent to which the reactor design meets those requirements as the design is further evolving. This phase focuses on identifying if any potentially fundamental barriers to licensing exist or are emerging. The VDR process is described in more detail in regulatory document REGDOC‑3.5.4, Pre-Licensing Review of a Vendor’s Reactor Design.

The Phase 2 VDR was carried out at the request of TEI and was a pre-project assessment of the IMSR400 design. The design is currently in progress and certain details have yet to be finalized and confirmed. As a result, many of CNSC staff’s findings and technical clarification requests that are documented in the report are related to work that would need to be completed to confirm certain aspects of the design or analysis.

This report outlines the CNSC staff review process, the assessment findings, and the conclusions of the review. Based on the documentation submitted, CNSC staff concluded the following:

• Overall, TEI understands and has correctly interpreted the high-level intent of the CNSC’s regulatory requirements for the design of reactor facilities in Canada.
• No fundamental barriers to licensing were identified within the completed review of the topical areas as part of the phase 2 VDR. The IMSR400 design requires further advancement in some areas for CNSC staff to confirm that it meets all Canadian regulatory expectations. TEI will be required to perform additional work to address the technical clarifications and findings raised in this review, should it or another proponent pursue a licence for the design.

The following is a summary of technical clarifications and findings that will require additional follow-up in any future review:

1. More details are needed on some aspects of the reactor design to confirm the design defence-in-depth and safety functions, as well as to ensure that the design meets all Canadian regulatory expectations.
2. Sensors and monitoring equipment have to be developed for several key plant parameters (e.g., molten salt chemistry). Once this is completed, the instrumentation and control system design will need to be finalized and the details provided.
3. Further testing is required to demonstrate some modes of operation at low power. Details are needed since they may impact the shutdown system and start-up instrumentation design.
4. The capability and effectiveness of the proposed means of reactor control and shutdown needs to be further demonstrated. Particularly, the reliance on the overall negative temperature reactivity coefficient. The negative coefficient will need to be verified for all conditions and circumstances to help support the proposed design for reactor shutdown.
5. More details demonstrating the implementation of the System Engineering Program need to be provided.
6. The knowledge gaps in the reactor chemistry need to be addressed, including:
   1. Operating specifications and potential phase changes
   2. Chemistry changes and monitoring
   3. Fission products retention and effects of impurities
   4. Potential interactions between molten salt and water if such interactions cannot be practicably eliminated
7. Safety analyses demonstrating the effectiveness of passive safety systems, particularly the internal reactor vessel auxiliary cooling system (IRVACS), need to be performed.
8. The validation and verification of the software tools used for the safety analyses need to be provided.

If this design is the subject of future VDR work or licence application reviews, these issues will be followed up by the CNSC.