The Nuclear Pressurized Heavy Water Reactor (PHWR) have been promoted primarily in Canada and India, with additional commercial reactors operating in South Korea, China, Romania, Pakistan, and Argentina. Canadian-designed PHWRs are often called “CANDU” reactors. Siemens, ABB (now part of Westinghouse), and Indian firms have also built commercial PHWR reactors.
Heavy water reactors now in commercial operation use heavy water as moderators and coolants. The Canadian firm, Atomic Energy of Canada Limited (AECL), has also recently proposed a modified PHWR (the ACR series) which would only use heavy water as a moderator. Light water would cool these reactors. No successful effort has been made to license commercial PHWRs in the United States.
PHWRs have been popular in several countries because they use less expensive natural (not enriched) uranium fuels and can be built and operated at competitive costs. The continuous refueling process used in PHWRs has raised some proliferation concerns because it is difficult for international inspectors to monitor. Additionally, the relatively high Pu-239 content of PHWR spent fuel has also raised proliferation concerns. The importance of these claims is challenged by their manufacturers. PHWRs, like most reactors, can use fuels other than uranium and the ACR series of reactors is intended to use slightly enriched fuels. Particular interest has been shown in India in thorium-based fuel cycles.