raskasvesireaktorit

Raskasvesireaktorit, eller heavy-water reactors, are nuclear reactors that use heavy water (deuterium oxide, D2O) as the neutron moderator and, in many designs, as the primary coolant. The low neutron absorption and superior neutron economy of heavy water enable the reactor to sustain a fission chain reaction with natural uranium or with only modest enrichment, giving fuel flexibility and potentially longer fuel cycles. Some designs also allow on‑power refueling, reducing downtime and increasing capacity factor.

The most prominent example is the Canada Deuterium Uranium (CANDU) reactor family. CANDU reactors use pressurized heavy water as moderator and coolant, with the fuel arranged in individual pressure tubes within a calandria. This modular design supports online refueling and allows a variety of fuel options, including natural uranium, slightly enriched uranium, or recovered fuels, and adaptation to thorium cycles.

Global use and variants: heavy-water technology has been exported and adapted in several countries. Major Canadian facilities include the Pickering, Darlington, and Bruce reactors. India operates PHWRs based on CANDU heritage, including several units that use heavy water moderation and natural uranium fuel. Romania has pursued CANDU-derived units at the Cernavodă site. In addition to power reactors, heavy-water systems have historically been employed in research reactors for isotopes production and materials studies.

Advantages and challenges: heavy-water moderation provides high neutron economy and fuel flexibility, including natural uranium and thorium options. Disadvantages include the high cost and complexity of producing and maintaining large quantities of D2O, tritium handling considerations, and specialized materials requirements.