Heavy Water Reactor (PHWR)
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ZThe Pickering nuclear power plant with eight CANDU heavy water reactors is located in a town of the same name, on the coast of Lake Ontario in Canada.
There are 44 operating heavy water reactors (PHWR, which stands for “pressurized heavy water reactor”) in the world, of which 35 are CANDU type reactors (CANada Deuterium Uranium). It was developed in Canada and exported to India, Pakistan, Argentina, Korea, and Romania.
It is fueled by natural uranium. The reactor core is a horizontally placed cylindrical vessel (so-called calandria) 7 × 6 meters large. There are horizontal pressure tubes passing through the calandria and the fuel channels housing the nuclear fuel in the form of short fuel bundles. The calandria is flooded with a heavy water moderator that is cooled by a dedicated circuit. The coolant passes through the fuel channels. CANDU reactors may be refueled under power.
The temperature of the heavy water moderator inside a CANDU reactor is just 30 °C.
Heavy water (D2O) is used as both the coolant and the moderator. It exhibits excellent moderation properties and in comparison to ordinary water, it does not absorb almost any neutrons. This enables the use of natural unenriched uranium as the fuel. The water pressure in the primary circuit is 9.3 MPa and the temperature is 300 °C. The moderator must be cooled because with increasing temperatures, its moderation properties worsen. The coolant transfers its energy to ordinary water in a steam generator and the generated steam then drives a turbine.