Feasibility of Using Geoscientific Criteria for Early Screening of Large Geographic Areas that would be Unsuitable for Safely Hosting a Deep Geologic Repository

The Nuclear Waste Management Organization (NWMO) is responsible for implementing Adaptive Phased Management (APM), Canada’s plan for the long-term care of the used nuclear fuel produced by Canada’s nuclear reactors. The end point of APM is long-term containment and isolation of used nuclear fuel in a deep geological repository constructed in a suitable rock formation at a depth of approximately 500 m.<br/>One of the major tasks with regard to implementing APM is to collaboratively develop the process that will be used for seeking an informed and willing community to host the deep geological repository. For fairness, the siting process will be focused in the four provinces directly involved in the nuclear fuel cycle: Saskatchewan, Ontario, Québec and New Brunswick. In order to inform the siting process, the NWMO identified the need to review the available geoscientific information in the four nuclear provinces as well as the scope and application of geoscientific factors at early stages in a siting process for a geological repository, based on international guidance, Canadian regulatory requirements and the experience of other countries.<br/>In this context, NWMO retained AECOM Canada Limited (AECOM) to undertake the following:<br/>i) review geoscientific factors that need to be considered to ensure the safety of a geological<br/>repository; and ii) assess the feasibility and practicality of using proposed geoscientific<br/>exclusion criteria for early identification of large geographic areas within the four nuclear<br/>provinces that would be unsuitable for safely hosting a deep geological repository without the<br/>need for further field investigation.<br/>This report reviewed the geoscientific characteristics of the four nuclear provinces as well as<br/>the geoscientific factors would be considered to ensure the safety of a deep geological<br/>repository. The safety functions considered include the ability of the repository to safely contain<br/>and isolate used nuclear fuel, the long-term stability of the site, the ability to easily characterize<br/>the site, the safe construction, operation and closure of the repository and the potential for<br/>human intrusion in the long term. The geoscientific characteristics and factors reviewed were<br/>grouped under geology, geomechanics, seismicity, hydrogeology, hydrogeochemistry and the<br/>potential for economically exploitable natural resources.<br/>The assessment of whether the geoscientific factors considered could be used to exclude large<br/>areas of the four nuclear provinces early in the siting process highlighted two main challenges.<br/>First, most of the geoscientific factors that need to be considered require site specific<br/>information at depth which is typically lacking at early stages in the siting process. The other<br/>challenge is associated with the large geographic extent of the four nuclear provinces<br/>(3,300,000 km2) compared to the typical repository scale at which site specific geoscientific<br/>information is needed (~6 km2). After reviewing the international literature and the available<br/>geoscientific information from the four provinces, it is concluded that:<br/>It is not practical to exclude large areas of the four nuclear provinces early in the siting process<br/>(pre-screening) based on the geoscientific factors identified herein. However, some of the<br/>geoscientific factors may be used as exclusion factors at later stages of the site evaluation<br/>process as more local scale and site specific information becomes available such as during<br/>screening studies, feasibility studies and detailed field investigations.<br/>The findings of this report are consistent with international experience and the outcome of<br/>general siting studies conducted in other countries.