Pressurized Heavy-Water Reactor (PHWR)

The PHWR reactor uses heavy water as coolant and moderator.

The fuel is natural uranium. The fuel elements are located in pressure tubes which are located in a steel vessel (the calandria). The heavy water circulating through the pressure tubes is prevented from boiling. Like in PWRs PHWRs have a secondary cooling circuit with steam generators (called boilers) -using normal water.

The space between the pressure tubes is filled with an insulating gas. Thus the moderator in the calandria is kept cool. The pressure tube design allows on-load refuelling as in GCR and RBMK reactors. Most frequently used is the Canadian designed CANDU reactor.