Safety assessments consider two main periods of time:

• Pre-closure is the period when we are constructing and operating the deep geological repository and associated facilities.
• Post-closure is the period after the deep geological repository has been sealed and closed.

Preclosure safety assessments

Preclosure safety assessments demonstrate that the repository and associated facilities can be operated safely under normal circumstances, as well as during abnormal events and accidents. They are conducted as part of the facilities design and development process.

Preclosure safety assessments are conducted for siting, construction and operation of the facility, transportation of used fuel from nuclear generating stations to the facility, and eventual decommissioning and closure of the facility.

They consider factors such as public health, the environment, public and worker safety, and security and safeguards. Preclosure safety assessments will be submitted in support of a licence application once a site is selected.

Postclosure safety assessments

Post-closure safety assessments demonstrate that the deep geological repository for Canada’s used nuclear fuel will continue to protect people and the environment over the very long term, following the decommissioning and closure of the repository.

The assessments evaluate the performance of the repository under expected or “normal” conditions over time, including the effects of potential future events such as earthquakes, glaciation and climate change. The assessments also consider the effects of highly unlikely events, as well as purely hypothetical scenarios, on the performance of the repository.

The post-closure safety assessments test the safety of the repository by looking at the potential impact on a hypothetical family in the future, living and working directly above the repository and obtaining food from local sources and well water. The analysis shows that that for a well-designed repository at an appropriate site, the family would be safe.

A post-closure safety assessment will be submitted in support of a licence application.

Assessments to date

On Nov. 28, 2024, the NWMO selected the Revell site in northwestern Ontario, near the Township of Ignace in the territory of Wabigoon Lake Ojibway Nation, as the site for Canada’s deep geological repository for used nuclear fuel.

Before site selection, detailed designs were completed and generic safety assessments were conducted based on hypothetical sites and conceptual designs. The case study provided below is an example of a generic post-closure safety assessment in crystalline rock.

Pre- and post-closure safety assessments were conducted for the Revell site and it was found to be potentially suitable for a deep geological repository. The key safety arguments and conclusions of the assessments are documented in the Confidence in Safety report for the Revell site.

Following this evaluation process, the Revell site was selected as the location for the deep geological repository for Canada’s used nuclear fuel. The NWMO is currently preparing safety assessments as part of the regulatory decision-making and licensing process.

National and international guidelines

Pre- and post-closure safety assessments are prepared according to the requirements defined by the Canadian Nuclear Safety Commission in REGDOC-2.4.4, Safety Analysis for Class 1B Nuclear Facilities and REGDOC-2.11.1, Waste Management, Volume III: Safety Case for the Disposal of Radioactive Waste, Version 2.

We also consider international guidance on the development and safety of repositories, including the International Atomic Energy Agency’s Specific Safety Guide SSG-23: The Safety Case and Safety Assessment for the Disposal of Radioactive Waste. This guide describes international best practices with respect to achieving and demonstrating safety.