The “SLOWPOKE” or Safe Low-Power Critical Experiment is a low-energy, pool-type nuclear research reactor designed by Atomic Energy of Canada Limited (AECL, now Canadian Nuclear Laboratories)  in the late 1960s. This type of reactor was primarily intended for Canadian universities, providing a higher neutron flux than available from small commercial accelerators, while avoiding the complexity and high operating costs of existing nuclear reactors. The reactor utilized a very small quantity of uranium fuel, and was surrounded by a beryllium reflector that scattered neutrons back into the core, maintaining the fission chain reaction as long as possible. By adding thicker pieces of beryllium to this reflector region it was possible to extend the life the original fuelled core to several decades.

Diagram of a SLOWPOKE reactor.

In 1970 a prototype unit known as SLOWPOKE-1 was designed and built at Chalk River and was moved the next year to the University of Toronto. It had only one irradiation site in its design and initially operated at a power level of 5 kW with a permissible period of unattended operation of four hours. In 1973, the power was increased to 20 kW and the period of unattended operation increased to 18 hours.

The first commercial version of the SLOWPOKE reactor was started up in 1971 at AECL’s Commercial Products Division in Ottawa; and in 1976 a commercial design, named SLOWPOKE-2, was installed at the University of Toronto, replacing the original SLOWPOKE-1 unit. The commercial model has five irradiation sites in the beryllium reflector and five sites stationed outside the reflector.

Between 1976 and 1984, seven SLOWPOKE-2 reactors with Highly Enriched Uranium (HEU) fuel were commissioned in six Canadian cities and in Kingston, Jamaica. In 1985 the first low-enriched Uranium (LEU) fuelled SLOWPOKE-2 reactor was commissioned at the Royal Military College of Canada (RMC) in Kingston, Ontario. Since then several units have been converted to LEU, as part of a U.S.-led program to reduce the amount of HEU in use around the world in civilian reactors.

In the early 1980s AECL also designed and built a scaled-up version (2 — 10 MW) called SLOWPOKE-3 for district heating at its Whiteshell Nuclear Research Establishment in Manitoba. The economics of a district-heating system based on SLOWPOKE-3 technology were initially estimated to be competitive with that of conventional fossil fuels for use in remote communities, however market interest in the SLOWPOKE heating system eventually dwindled due to the low price of natural gas. Currently, the high price of oil and natural gas has sparked renewed interest in the use of nuclear energy for district heating purposes.