[en] The concept for disposal of Canada's nuclear fuel waste is based on a vault located deep in plutonic rock of the Canadian Shield. We document in this report a method to assess the long-term impacts of a disposal facility for nuclear fuel waste. The assessment integrates relevant information from engineering design studies, site investigations, laboratory studies, expert judgment and detailed mathematical analyses to evaluate system performance in terms of safety criteria, guidelines and standards. The method includes the use of quantitative tools such as the Systems Variability Analysis computer Code (SYVAC) to deal with parameter uncertainty and the use of reasoned arguments based on well-established scientific principles. We also document the utility of the method by describing its application to a hypothetical implementation of the concept called the reference disposal system. The reference disposal system generally conforms to the overall characteristics of the concept, except we have made some specific site and design choices so that the assessment would be more realistic. To make the reference system more representative of a real system, we have used the geological observations of the AECL's Whiteshell Research Area located near Lac du Bonnet, Manitoba, to define the characteristics of the geosphere and the groundwater flow system. This research area has been subject to more than a decade of geological and hydrological studies. The analysis of the reference disposal system provides estimates of radiological and chemical toxicity impacts on members of a critical group and estimates of possible impacts on the environment. The latter impacts include estimates of radiation dose to nonhuman organisms. Other quantitative analyses examine the use of derived constraints to improve the margin of safety, the effectiveness of engineered and natural barriers, and the sensitivity of the results to influential features, events, and processes of the reference disposal system. The study results indicate that the reference disposal system would meet the requirements established by the Atomic Energy Control Board and indicate that implementation of the disposal concept can provide safe disposal of nuclear fuel waste using currently available or readily achievable technology and without relying on institutional controls to maintain safety in the long term. (author)