Advanced CANDU reactor

The Advanced CANDU reactor (ACR), or ACR-1000, is a Generation III+ nuclear reactor designed by Atomic Energy of Canada Limited. It combines features of the existing CANDU pressurised heavy water reactors (PHWR) with features of light-water cooled advanced pressurized water reactors (APWR). From CANDU, it takes the heavy water moderator, which gives the design an improved neutron economy that allows it to burn a variety of fuels. However, it replaces the heavy water cooling loop with one containing conventional light water, greatly reducing costs. The name refers to its design power in the 1,000 MWe class, with the baseline around 1,200 MWe. Development of the ACR ended after AECL's reactor division was sold off in 2011.

The ACR-1000 was introduced as a lower-price option compared to a larger version of the CANDU design then being considered, the CANDU-9. ACR was slightly larger but less expensive to build and run. The downside was that it did not have the flexibility of fuels that the original CANDU design offered, and would no longer run on pure unenriched uranium. This was a small price to pay given the low cost of enrichment services and fuel in general. The ACR-1000 was bid on several proposals around the world but won no contests. The last serious proposal was for a two-reactor expansion of the Darlington Nuclear Generating Station, but this project was canceled in 2009. With no other sales prospects, the AECL design division was sold to SNC-Lavalin to provide services to the existing CANDU fleet, and the ACR design effort ended.

The original CANDU design used heavy water as both the neutron moderator and the coolant for the primary cooling loop. It was believed that this design would result in lower overall operating costs due to its ability to use natural uranium for fuel, eliminating the need for enrichment. Further, the design used both pressurized and unpressurized sections, the later known as a "calandria", which it was believed would lower construction costs compared to designs that used highly pressurized cores. This design also allowed it to be refueled while it was running. However, the use of natural uranium also meant the core was much less dense compared to other designs, and much larger overall. It was expected this cost would be offset by lower operational costs.

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