The fuel transfer flask in position on the reactor deck plate


The WR-1 reactor at the Whiteshell Nuclear Research Establishment (WNRE), is unique among research reactors in its flexibility and is the world's only operating heavy water-moderated reactor cooled by an organic (oil) fluid.

The story of WR-1 began in the late 1950s when AECL researchers realized that substantial economies could be achieved in large natural uranium heavy water moderated reactors if organic coolants proved operationally feasible. Organics were much less expensive than heavy water and their high boiling points, permitting low pressure primary coolant systems, promised further reductions in capital cost. In addition, a low pressure system suggested less neutron-absorbing structural material in the core.

The organic liquid, called OS-84, selected as a coolant in WR-1 is a mixture of terphenyls treated catalytically with hydrogen to produce 40 percent saturated hydrocarbons. The terphenyls are petrochemical derivatives that are readily available and are already in use as heat transfer media.

Costing $14,500,000, construction of WR-1 began in 1963, at a site cleared of heavy brush on the east bank of the Winnipeg River, 100 km northeast of Winnipeg. Structural steel erection began in 1964 and by June 1965 WR-1 was essentially complete. Criticality was attained on November 1, 1965. Unique among research reactors, WR-1 is designed to be used for a variety of engineering tests with differing fuels, fuel channel materials and configurations as well as a variety of reactor coolants.


The reactor vessel or calandria is a cylindrical stainless steel tank about 5 metres high and nearly 3 metres in diameter, containing tubes with extensions through the top and bottom shields. Calandria tubes separate the heavy water moderator from the pressure tubes which pass through the calandria tubes and contain fuel and circulating coolant. Extensions of the pressure tube beyond the calandria tubes provide connections to coolant circulation above and below radiation shields at each end of the calandria.

The initial fuel charge in WR-1 was uranium dioxide enriched slightly to 2.4 percent by weight U-235. The pressure tube material in the core section was initially stainless steel, with the exception of four zirconium alloy tubes. With the expansion of the core to 54 sites, replacement of all the stainless steel tubes by tubes made of zirconium alloy (Ozhennite 0.5), and the use of uranium monocarbide in place of uranium dioxide in the fuel, the enrichment now ranges between 1.3 and 2.25 weight percent. Because of the small size of the core some enrichment will always be necessary. Some thorium fuel bundles have been irradiated in WR-1 as part of advanced fuel cycle studies at WNRE to obtain physics measurements and to determine the physical stability of the fuel.

The driver fuel is sheathed in zirconium-2.5 niobium alloy, although experimental rods sheathed in sintered aluminum product (SAP), Zircaloy-4 and Ohzennite 0.5 have also been irradiated.

Most of the heat produced in the reactor is dissipated through heat exchangers to the nearby river. No electrical power generation is planned from WR-1, although one of the cooling circuits provides up to 13 MW(t) to a pressurized plant-wide hot water heating system. Standby boilers fired by blended #5 oil provide heating during reactor down-time or supplementary heating when demand exceeds about 13 MW(t) during extreme cold spells.


Following initial criticality on November 1, 1965, the reactor was operated for more than two months at low power for physics and commissioning tests. First significant thermal power was produced on December 5, 1965, and the reactor went to high power in January 1966. Since July 1966 the average availability has been in excess of 85 percent and the average operating efficiency, about 70 percent. These are extremely good results for a reactor committed so heavily to tests and experiments, and reflect a sound concept and design. WR-1 has been operated at coolant temperatures as high as 425oC. At present, operating temperatures are generally 325oC in the 'A' and 'B' circuits, and 345oC in 'C' circuit which provides the plant heating.

WR-1 has been relatively trouble free. Its equipment has performed reliably in a high temperature organic environment; primary cooling circuits and their immediate surroundings remain exceptionally free of radioactive contamination; fuel fouling and fire hazards, at temperatures needed for high-efficiency generating stations, have been controlled with ease.

Revised March 1982

WR-1 Design details

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