Dictionaries describe rabbits several ways. The most appropriate description for the nuclear industry is the one crediting them with being “capable of speeds and very rapid stops and starts”. Fast-moving “rabbits” have been used in several Canadian research reactors. This was the nickname given to the systems used to rapidly insert small amounts of materials in carrier capsules into high-flux areas of the reactors to be irradiated for materials analysis. The initial types were air-driven, while later versions were liquid-propelled.
The first rabbit system was installed in the NRX reactor at Chalk River in 1949. The Pneumatic Rabbit was based on 38 mm long by 14 mm diameter aluminum capsules that were capable of holding about one gram of material. The capsules were air-driven through tubing leading from the Chemistry building, which was about 900 feet from NRX, into a high-flux area of the reactor core. There the capsules were quickly stopped, irradiated as long as desired, and then sped back to the Chemistry building for analysis.
A Hydraulic Rabbit driven by cooling water was added in NRX in 1958. The slightly larger capsules used in this system were mostly used for short-term irradiations of experimental fuels which, after being irradiated, were discharged into shielded flasks for examination in the hot cells.
Similar pneumatic and hydraulic systems were incorporated into the design of NRU and became important experimental tools. The Hydraulic Capsule Facility (HCF) was used throughout the life of NRU, and over the last years of operation of the reactor it was used for experiments aimed at the production of Pu-238, an isotope highly valued in the space industry for use in the Radioisotope Thermoelectric Generators (RTG) used to power deep space probes. Bill Richmond, who participated in these experiments, recently donated one of the capsules of the type used in the HCF to the Society for the Preservation of Canada’s Nuclear Heritage, Inc. (SPCNHI). The hollow aluminum capsule, 70 mm in length and 38 mm in diameter, would have a flat disc cold-welded to it as a seal and to contain any cover gas required for the irradiations.
A Pneumatic Rabbit modeled on the one used in NRX was adapted for the WR-1 reactor at the Whiteshell Laboratories. The Iron Rabbit capsule used there was made of high-purity iron with dimensions identical to the NRX design. Samples were thermo-sealed in plastic containers and then held in the capsule with a screw top. After irradiation, the capsules were sent to their destination several hundred meters from the reactor. The capsules were then opened and the samples removed for analysis away from the background radiation from the iron that had been activated in the reactor.
A Super-Rabbit was later developed at WR-1. It used a slightly larger diameter capsule made of polyethylene to avoid the problem of activation of the carrier and was used for a number of years for neutron activation analysis at the laboratories. Mike Attas, a Whiteshell alumnus, has donated samples of both the Iron Rabbit and Super-Rabbit capsules to the Society.
It is to be hoped that during the decommissioning of NRX and NRU additional capsules may be located at the back of desk drawers or obscure hiding places, and that the Society may be able to assemble a complete set. There may be some debate as to what this “collection of rabbits” should be called. The internet informs us that such an assemblage is now called a fluffle – a somewhat unscientific sounding term. Suggestions for a better name can be sent to the Society via info@nuclearheritage.ca
