Frequently Asked Questions - Seismic Events

How have developments in Japan impacted on NWMO’s work on the APM program?

How can Canadians be assured that a used nuclear fuel repository will withstand an earthquake?

How do you know you will be able to identify a safe site?

Has the NWMO considered extreme events like earthquakes?

Can used fuel burn, explode or meltdown in a repository, or during transportation?

Is used fuel susceptible to hydrogen explosion during transportation, or in a repository?

Can heat build up in a repository?

Will heat build-up in the repository create faults in the surrounding rock?

What would happen to used nuclear fuel in the event of an earthquake impacting a Canadian nuclear reactor?

How have developments in Japan impacted on NWMO’s work on the APM program?

Recent developments in Japan must be taken seriously as NWMO looks at all aspects of its program. One of the cornerstones of the APM program is a commitment to continuous learning from new developments, and adapting and refining plans for all aspects of the long-term management plan for Canada’s used nuclear fuel. In this regard, we will also take this opportunity to reflect on whether refinements are needed to our plans. We will take the next several months to conduct a review and report out to Canadians.

With regard to the site selection process, communities are in the early phase of learning about the APM program and the siting process, asking questions and exploring important areas such as safety for people and the environment. Through this period of learning more about the site selection process and APM, we believe it is important to take the time to review developments in Japan, and discuss questions and concerns with communities.

o It is important to provide opportunities for communities to ask questions and explore the important topic of safety to their satisfaction before NWMO and communities proceed to initiate feasibility studies.

o NWMO will only move to the next step of conducting feasibility studies with interested communities after we have paused to review information and new learning from recent events and we have been able to share this information with communities in the site selection process. It is essential that any decision that the NWMO and a community take to proceed to the multi-year feasibility study phase is a fully informed decision that takes into account all available information.

We understand that the developments in Japan have triggered questions and concerns for many and NWMO will be pleased to provide information on Canada’s plan for the safe, secure long-term management of used nuclear fuel.

How can Canadians be assured that a used nuclear fuel repository will withstand an earthquake?

The objective of the Deep Geological Repository is to safely contain and isolate used nuclear fuel in a stable rock formation. The deep repository is designed to protect people and the environment against a wide range of natural events like earthquakes in a passive manner without relying on active maintenance or active safety features such as power backup or cooling systems.

It is well known that deep underground structures are more resilient to earthquakes than surface structures. Used nuclear fuel containers will be sealed in a deep geological formation using a multi-barrier system.

The selection of a safe site is based on a comprehensive set of geoscientific criteria and a thorough site evaluation process which is expected to take seven to 10 years. The impact of seismic events is a key component of the site evaluation process.

Resilience to earthquakes is a critical technical evaluation criterion for selecting a site to safely host Canada’s deep geological repository for used nuclear fuel. To be selected, a site will have to satisfy a comprehensive set of geological criteria which include looking at active faults and seismicity. Any site will be excluded if there are geological conditions that would make it unsafe.

A good predictor of future performance is what has happened in the past. There are many deep geologic formations in Canada that have remained stable for hundreds of millions of years despite numerous past events such as earthquakes and ice ages.

The facility will be designed and built in a manner that will ensure the integrity of the multiple barrier system for containing and isolating the used fuel.

The repository will be subject to an environmental assessment and regulatory process to ensure that it can be implemented safely for humans and the environment.

How do you know you will be able to identify a safe site?

There are many geologic formations in Canada that have been in place for hundreds of millions of years and have not been disturbed by seismic events. A good predictor of future performance is what has happened in the past.

The selection of a safe site will be based on a comprehensive set of geoscientific criteria and a thorough site evaluation process that will last 7 to 10 years. The impact of seismic events is a key component of the site evaluation process. Indicators of seismicity include:

o Seismic history and regional structural geology

o Signs of major faults or fractures that are visible at surface, and their size and age of formation;

o Signs of displacement of rock along old fractures due to historic earthquakes

o Groundwater chemistry and indications for stability over long times

o The strength of the rock

In order to licence a deep geological repository, the NWMO will have to demonstrate its safety to the satisfaction of the host community, the regulator, and to other interested or potentially affected individuals and organizations.

Has the NWMO considered extreme events like earthquakes?

The NWMO and other international waste management organizations have conducted many studies and analyses on the impact of extreme events on a DGR. This includes seismic events and extreme conditions such as the next ice age.

Any potential candidate site would be subject to a thorough site evaluation process. This would include detailed geological investigations and numerical simulations to develop a thorough understanding of past seismicity and predict the magnitude of future seismic events.

A repository would not be sited in the vicinity of active faults that would have an impact on the integrity of the repository containment and isolation system.

In addition to siting in a place with low earthquake risk, the repository will include features to make it robust to earthquakes. These include placing containers at a distance from fractures or faults, mechanically robust containers, and the use of self-sealing clay barriers.

APM requires NWMO to take stock to see if there is anything to learn from the Japanese event and to redirect our plans if appropriate.

Can used fuel burn, explode or meltdown in a repository, or during transportation?

No. Used nuclear fuel is a hard solid material. It not a gas or a liquid. It is resistant to heat, not easily soluble in water, and does not vaporize.

Used fuel intended for a repository can be handled and stored safely in air without active cooling. It requires active cooling for several years after being discharged from a reactor, and would not be transported or placed in a repository during this period. By the time it is transported, it has already been stored dry.

Is used fuel susceptible to hydrogen explosion during transportation, or in a repository?

No. Used fuel intended for a repository is not sufficiently hot to generate significant hydrogen quickly, and it is kept under dry conditions without access to significant amounts of water needed to form hydrogen.

In a closed repository deep underground, there will be no oxygen. Under these conditions, slow anaerobic corrosion of the containers (not the used fuel itself) over thousands of years can generate hydrogen. However, these corrosion processes only occur when there is no oxygen, and therefore no explosion is possible. This gas would be contained in the rock and slowly disperse, similar to naturally occurring methane (natural gas), or be consumed by natural microbial reactions .

Can heat build up in a repository?

A repository would heat up to around 100oC near the containers. The specific temperature is limited by the container spacing and simple heat conduction into the surrounding rock. No active cooling or power is necessary.

A Canadian used fuel container would generate about one kilowatt of heat, decreasing with time. A repository with 10,000 containers would generate about ten megawatts of heat initially. This would be spread over an area of a few square kilometers.

Will heat build-up in the repository create faults in the surrounding rock?

The container spacing would be designed to limit temperatures and thermal stresses in the surrounding rock so that fractures would not be created.

The peak temperatures would occur within the first hundred years or so. Remote monitoring would provide early information if fractures are created.

What would happen to used nuclear fuel in the event of an earthquake impacting a Canadian nuclear reactor?

All of Canada’s used nuclear fuel is safely stored on an interim basis in licensed facilities at the nuclear reactor sites. Nuclear power plants in Canada are located in areas where major earthquakes are not expected. Reactors must be qualified to withstand the level of seismic activity that is expected for each individual reactor location.

Waste management facilities at the plants are designed and built to withstand seismic events.

The interim management of used nuclear fuel at reactor sites is the responsibility of the waste owners. Questions about used fuel at reactor sites should be directed to them.