PHWRtechnologie

PHWRtechnologie, short for pressurized heavy-water reactor technology, is a class of nuclear reactor design that uses heavy water (deuterium oxide, D2O) as both moderator and primary coolant. The core concept centers on a network of horizontal fuel channels housed inside a large tank of heavy-water moderator, the calandria. Each fuel channel contains a pressure tube with the fuel bundles, and the tubes are kept under high pressure to prevent boiling. Heat from the fuel is transferred to a secondary loop via steam generators, where ordinary water is turned into steam to drive turbines.

A distinguishing feature of PHWRs is online refueling, which allows fuel to be added or removed without shutting down the entire reactor. This capability, together with the use of natural uranium fuel, stems from the favorable neutron economy provided by heavy-water moderation. The design typically uses a primary heavy-water coolant within pressure tubes and a separate secondary loop of light water for steam generation.

Fuel and fuel cycle options are a core part of PHWR technology. Natural uranium can be used without enrichment, reducing uranium preprocessing requirements but increasing heavy-water demand and cost. The possibility of employing thorium-based fuels has attracted interest in some countries, notably in India. Spent fuel remains highly radioactive and requires robust containment and cooling facilities; tritium is also produced in the heavy-water environment and requires management.

PHWRs have been deployed primarily in Canada (the CANDU program) and in other countries such as India and Pakistan, with several variants and ongoing developments. The technology supports modular design concepts and on-site refueling strategies, while facing challenges related to the supply and handling of heavy water, maintenance of pressure tubes, and radiation management. Future directions include advanced PHWR designs and potential thorium fuel cycles.