General Interest: Chalk River

On June 4, 1962, the Nuclear Power Demonstration (NPD) Reactor at Rolfton, near Chalk River began to feed power into the Ontario Hydro power grid. On June 1, 2002, the Ontario Heritage Foundation, in conjunction with the Canadian Nuclear Society, unveiled a plaque at the site to recognize the first commercial nuclear electric power generator in Canada.

Back in the early 1950s Ontario Hydro needed more electric power than its famous water power — “white coal” — could produce. Nuclear power, an emerging technology, offered one option. Physics offered two design approaches. Naturally occurring uranium is a mixture of two isotopes, U235 and U238. The former is fissile — when hit by a neutron, it splits and releases high-energy neutrons. But it represents only 0.7% of uranium ore by weight. One way to increase the amount of energy is to use enriched uranium, which contains a higher proportion of U235. But enriched uranium is very expensive.

The other option is to slow down or moderate the neutrons to increase the likelihood of them splitting an atom, releasing more neutrons, and getting a sustained chain reaction. Neutrons can be moderated with ordinary water (H2O), but water captures too many neutrons in the process. Heavy water (D2O) made from deuterium, hydrogen with an extra neutron in its nucleus, captures fewer neutrons. However, only about 1 in 7,000 molecules of naturally occurring water is D2O and separating it from light water is expensive.

Canada’s choice of neutron economy reflects the fact that there is more to engineering and life than physics. Canada had uranium resources, but no enriched uranium fuel plant, and unlike the United States, it had no nuclear weapons program to justify the cost of setting one up. Therefore, when Ontario Hydro, Atomic Energy of Canada Limited and Canadian General Electric started work in 1955 to create the NPD reactor, they chose to explore “the feasibility of producing electric power from a nuclear power plant using heavy water as the moderator and coolant and natural uranium as the fuel.”(AECL 1957-1958 Annual Report)

Ontario was in such a hurry for nuclear power that well before the first Chalk River reactor was finished engineers started designing the next generation of nuclear electric stations, hoping to generate 10 times NPD’s 20MW output. But when the engineers scaled up the pressure vessel housing the reactor core, fuel, moderator, and coolant, they discovered it would be too big, too expensive, and possibly unsafe.

The implication was clear: if the NPD reactor design could not be scaled up, it would be a technological dead-end. It took considerable courage to write off years of expensive work and suspend construction in early 1957, but that’s what the project administrators did. Construction restarted in early 1958 on a new NPD reactor with multiple pressure tubes to contain the pressure system in place of a single pressure vessel. A zirconium alloy unavailable at the start of the NPD-1 project allowed for the radical re-design. Coolant and moderator were separated and, for greater fuel efficiency, a new system was designed to load and unload uranium oxide fuel while the reactor was operating. These design changes, which put NPD back on track, created the reactor that AECL dubbed CANDU (CANadian Deuterium-Uranium).

The NPD reactor commemorated by the Ontario Heritage Foundation this June is actually NPD-2, the CANDU prototype and test bed. Was the abandoned NPD-1 a poor design? Absolutely not. It was a necessary step in the development of commercially produced nuclear energy.

Decommissioned in 1987, the NPD-2 reactor is more than a monument to good engineering. It is a monument to the administrative courage and wisdom that acts honestly on new knowledge, even if it means radical change in mid-project. No matter how you feel about nuclear power, the NPD story holds a lesson about dealing with rapidly changing technology.

Norman S. Ball, Ph.D is director of the Centre for Society Technology and Values, University of Waterloo Faculty of Engineering.