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
Postclosure safety assessments show how the repository will continue to protect people and the environment over the very long term and will be submitted in support of a licence application once a site is selected.
Before potential sites for a repository have been identified and detailed designs completed, generic studies are conducted based on hypothetical sites and conceptual designs. The 6th and 7th Case Studies are examples.
Two sites are being considered by the NWMO for a deep geological repository. The Revell Site in the Wabigoon Lake Ojibway Nation-Ignace area is located in crystalline rock, while the South Bruce Site in the Saugeen Ojibway Nation-South Bruce area is located in sedimentary rock. Both sites are potentially suitable for a deep geological repository. Each has been the subject of a separate pre-project postclosure safety assessment. The reports illustrate the safety assessment models and approaches as applied to these conceptual designs.
These reports build on a series of postclosure safety assessments illustrating the long-term performance and safety of different repository designs within various geological settings.
Postclosure safety assessments will become increasingly specific as field tests provide additional information and potential repository sites are identified.
What the assessments show so far
Postclosure safety assessments test a wide range of scenarios to ensure people and the environment would be protected. In the “Normal Evolution Scenario,” the system behaves as expected. This includes, for example, glaciers forming at the site over long time periods.
“Disruptive scenarios,” by contrast, test a range of hypothetical circumstances in which one or more barriers fails. These might include even very unlikely scenarios such as failure of all containers at 10,000 years or 60,000 years, or the failure of the seals within the repository shafts.
These 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 from a deep well. The analysis so far show that for a well-designed repository at an appropriate site, the family would be safe.
National and international guidelines
Safety assessments are prepared according to the guidance of REGDOC-2.11.1, Waste Management, Volume III: Safety Case for the Disposal of Radioactive Waste, Version 2. This guide describes approaches and factors that the regulator considers important to consider when assessing long-term safety of a deep geological repository.
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.