| SLOWPOKE reactor | |
| Concept: | Low-energy, tank-in-pool type nuclear research reactor |
| Generation: | Neutron |
| Fuel Type: | Enriched uranium |
| Coolant: | Light-water |
| Use: | Neutron activation analysis |
The SLOWPOKE (acronym for Safe LOW-POwer Kritical Experiment) is a family of low-energy, tank-in-pool type nuclear research reactors designed by Atomic Energy of Canada Limited (AECL) beginning in the late 1960s. John W. Hilborn (born 1926 or 1927[1]) is the scientist most closely associated with their design.[2] They are beryllium-reflected with a very low critical mass, but provide neutron fluxes higher than available from a small particle accelerator or other radioactive sources.
The SLOWPOKE-2 reactors (most numerous of SLOWPOKE-family reactors) originally used 93% highly enriched uranium in the form of 28% uranium-aluminium alloy with aluminium cladding, and then in 1985 a new low enriched uranium design (~19.9 % enriched) was commissioned using ceramic UO2 fuel. The core is an assembly of about 200-300 fuel pins, only diameter and high, surrounded by a fixed beryllium annulus and a bottom beryllium slab. Criticality is maintained as the fuel burns up by adding beryllium plates in a tray on top of the core. The reactor core sits in a pool of regular light-water, diameter by deep, which provides cooling via natural convection. In addition to passive cooling, the reactor has a high degree of inherent safety; that is, it can regulate itself through passive, natural means, such as the chain reaction slowing down if the water heats up or forms bubbles. These characteristics are so dominant, in fact, that the SLOWPOKE-2 reactor is licensed to operate unattended overnight (but monitored remotely). Most SLOWPOKES are rated at a nominal 20 kW, although operation at higher power for shorter durations is possible.
The SLOWPOKE research reactor was conceived in 1967 at the Whiteshell Laboratories of AECL. In 1970 a prototype unit called SLOWPOKE (both the name of the reactor and of the prototype reactor class of 2 reactors it was a member of; especially later when further generations of SLOWPOKE reactors had appeared, these type of reactors were named SLOWPOKE-1), was designed and built at Chalk River Laboratories. It 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 Chalk River prototype went critical in 1970, and was moved to the University of Toronto in 1971. It had one sample site in the beryllium reflector and operated at a power level of 5 kW. In 1973 the power was increased to 20 kW and the period of unattended operation was increased from 4 hours to 18 hours. The reactor was dismantled in 1976 and replaced in University of Toronto by a next generation SLOWPOKE-2 reactor.
The first commercial example started construction in 1970 and was started up 14 May 1971 at AECL's Commercial Products Division in Tunney's Pasture - 20 Goldenrod Driveway, Ottawa, Ontario. It had a power output of 20 kW (thermal) and it was of the SLOWPOKE/SLOWPOKE-1 type. The reactor was a prototype and was shut down 1984.
Two reactors of SLOWPOKE aka SLOWPOKE-1 type were built. Both reactors have been decommissioned.
In 1976 a next generation commercial design, named SLOWPOKE-2 (again both the name of the reactor and reactor class, further members of which were constructed elsewhere), was installed at the University of Toronto, replacing the original SLOWPOKE-1 unit (see above). The commercial model has five sample sites in the beryllium reflector and five sites stationed outside the reflector.
Between 1976 and 1985, further 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 five SLOWPOKE-2 reactors have been decommissioned (Saskatchewan Research Council, University of Toronto, University of Alberta, Dalhousie University, and AECL/MDS Nordion reactor in Kanata), and three converted to LEU (Polytechnique Montreal, University of the West Indies and Royal Military College of Canada).
All in all, eight SLOWPOKE-2 reactors were built, seven in Canada and one in Jamaica.[3] of the eight, three are operational (the ones using/converted for LEU) and five have been decommissioned.
AECL also designed and built (start of construction 1985, start of operation 1987) a scaled-up version (2-10 MWth) called the SLOWPOKE Demonstration Reactor (SDR, SLOWPOKE-3) for district heating at its Whiteshell Nuclear Research Establishment in Manitoba. The economics of a district-heating system based on SDR technology were estimated to be competitive with that of conventional fossil fuels. However, the market for this technology did not materialize, and the proposed SES-10 (SLOWPOKE-4 based on SDR experience) was never built, and the SDR shutdown for decommissioning in 1989.
During the mid-1980s Canada briefly considered converting its s to nuclear power using a SLOWPOKE nuclear reactor to continuously recharge the ship's batteries during submerged operations.[4] A good deal of work had been done on potential marine applications of the reactor at Royal Military College of Canada.[5]
SLOWPOKE reactors are used mainly for neutron activation analysis (NAA), in research and as a commercial service, but also for teaching, training, irradiation studies, neutron radiography (only at the Royal Military College of Canada), and the production of radioactive tracers. The main advantages are the reliability and ease of use of this design of reactor and the reproducibility of the neutron flux. Since the fuel is not modified at all for at least 20 years, the neutron spectrum in the irradiation sites does not change and the neutron flux is reproducible to about 1%.
Three of the original reactors are still in operation. Although all of the technical goals of this reactor were achieved, the lack of foreign sales was disappointing.
Two of the SLOWPOKE/SLOWPOKE-1 reactors (out of 2 built), five of the SLOWPOKE-2 reactors (out of 8 built) and the single SLOWPOKE-3 reactor (out of 1 built) have been decommissioned. No SLOWPOKE-4 reactor was ever built.
Whitlock:Web site: Canadian Nuclear FAQ. The Canadian Nuclear FAQ by Dr. Jeremy Whitlock. March 5, 2005.
G. Kennedy and J. St. Pierre::Web site: LEU-FUELLED SLOWPOKE-2 RESEARCH REACTORS: OPERATIONAL EXPERIENCE AND UTILISATION. 2002 International Meeting on Reduced Enrichment for Research and Test Reactors. October 1, 2005.