The Nuclear Waste Management Organization (NWMO) is responsible for implementing Adaptive Phased Management (APM); the approach selected by the Government of Canada for long-term management of Canada’s used nuclear fuel. This paper identifies potential ventilation system enhancements to be incorporated in the repository ventilation design to minimize smoke back layering effects.

A number of scenarios were evaluated in which a variety of typical underground (UG) mining equipment was used to represent different fire size ranges in specific locations within the repository. Data from the simulations were used to evaluate the critical airflow velocity to be supplied by the DGR (Deep Geological Repository) ventilation system to prevent or minimize smoke back layering. Calculations for back layering distance were also examined using empirical equations developed for actual UG fire experiments by Office of Mine Safety and Health Research at the National Institute for Occupational Health and Safety in US. Results have shown that a fire incident in placement rooms will result in back layering of smoke which may last up to the full duration of the fire if not properly ventilated. Moreover, smoke from a fire in the access tunnels can be controlled with the employment of properly sized fans which can match or exceed the smoke’s critical velocity.