Executive summary: Combined phases 1 and 2 pre-licensing vendor design review - X-energy

Background

X-energy LLC is designing the Xe-100, an 80 MW_e (200 megawatt thermal) high-temperature gas cooled reactor. 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 X-energy on July 20, 2020, to conduct a combined phases 1 and 2 pre‑licensing vendor design review (VDR) of the Xe-100 reactor. The VDR process is described in REGDOC‑3.5.4, Pre-Licensing Review of a Vendor’s Reactor Design.

The purpose of the combined phases 1 and 2 VDR was to determine whether X-energy understands CNSC regulatory requirements and the extent to which the reactor design meets those requirements. A VDR takes place during the design process, while the design is still evolving, in an effort to provide early feedback. This allows 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.

A VDR 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 the VDR do not bind or otherwise influence decisions made by the Commission.

Results of combined phases 1 and 2 vendor design review

The Xe-100 review was based on information provided by X-energy in over 400 documents. It also included technical presentations, a week-long evaluation, and written responses to CNSC questions across 19 focus areas. CNSC staff concluded from this information that X-energy understands and has correctly interpreted the intent of regulatory requirements for the design of nuclear power plants in Canada. CNSC staff did not identify any fundamental barriers to licensing. However, the review did reveal some technical areas that need further development in order for X-energy to better demonstrate adherence to CNSC requirements:

• More in-depth information supporting human factors, decommissioning, and fire protection is needed for the CNSC to determine how these programs will meet CNSC requirements.
• There is a need for additional information on the reactor pressure vessel construction code approach, to ensure consistency between its safety importance and safety class, design and fabrication and the associated quality assurance requirements.
• Sufficient information has not yet been provided to demonstrate that all requirements in REGDOC-2.5.2 for means of reactor shutdown are fully met. The negative reactivity characteristics are a fundamental safety feature of Xe-100 design and play an important role in the control and shutdown of the reactor. Demonstration of this feature shall include operating experience (OPEX) and experimental data to the extent practicable.
• The safety analysis provided is not sufficiently complete to confirm that all applicable regulatory requirements are met, including derivation of initiating events, analysis methodology and computer code qualification. X-energy intends to further address this topic in a phase 3 VDR of the Xe-100.

The design and safety analysis of the Xe-100 evolved throughout the VDR, and design details have continued to mature since the CNSC’s review. The design was also at different levels of maturity for different focus areas, which limited CNSC staff’s ability to make definitive conclusions for all focus areas. These issues will be re-evaluated by the CNSC in future VDR phases or licence application reviews.