The paper presents a conceptual design for a four unit (850 MWe each) underground CANDU nuclear power station constructed in a series of large caverns excavated in Precambrian rock. Recent results of a geotechnical test program are described and the corresponding in-situ and laboratory measurements are considered in assessing design of rock cavern support systems, cavern liner requirements, and rock cavern stability under both thermal and seismic loads. The overall safety of the underground station design is also discussed. In this context the predictions of a preliminary analysis of the station accident containment capability suggest that post-accident temperatures and pressures in the rock caverns are below acceptable levels. Operational concerns for the underground CANDU design are also briefly considered. Finally, preliminary station capital cost estimates, based on a construction schedule extended by sixteen months, reveal a penalty of 31–36% relative to an equivalent surface facility.
Ontario Hydro, Canada's largest power utility with a total installed capacity of 24,000 MWe of which roughly 22% is nuclear generation, has recently completed a two-year investigation of the feasibility, both technical and economic, of constructing an underground CANDU nuclear power station (Oberth and coworkers, 1979). CANDU is a unique Canadian pressure tube reactor design using natural uranium fuel and heavy water as both the coolant and moderator. The investigation, performed by in-house engineering staff with the aid of geotechnical consultants, concentrated on deep rock siting in which reactor units are constructed in caverns excavated in Precambrian rock. This paper presents a conceptual underground design for the rock-sited 4 × 850 MWe CANDU power station, and evaluates the safety, operational, and economic implications of the design. Previous investigations of underground siting in Europe (Lindbo, 1978; Kröger and coworkers, 1976) and in the USA (Allensworth and coworkers, 1977; California Energy commission, 1978) revealed possible benefits such as improved containment, increased station protection and security, and significant reductions in seismic ground motion experienced in underground rock caverns. This paper examines these potential benefits in the context of the CANDU reactor design and Ontario's unique geological situation. The Ontario Hydro study examined two methods of constructing an underground nuclear power station: rock cavern excavation and cut-and-cover burial. Each method has its own set of siting constraints, technical and economic implications, and environmental and safety factors. This paper concentrates on the first of these two underground siting options in which the reactor components are erected within large underground rock caverns with the rock face serving as both the reactor building superstructure and the containment boundary.
A number of areas in Ontario were examined for local geological conditions and other general siting considerations. While no specific site was selected for the underground nuclear station design study, the economic benefits of siting close to a large urban load centre provided an incentive to focus on areas near Toronto. These economic benefits include reduced transmission costs and the potential use of waste heat for district heating purposes.
