Editing CANDU reactor (section)

===Generation III+ designs===
{{Main|Advanced CANDU reactor}}
Through the 1980s and 1990s the nuclear power market suffered a major crash, with few new plants being constructed in North America or Europe. Design work continued throughout, and new design concepts were introduced that dramatically improved safety, capital costs, economics and overall performance. These [[Generation III reactor|generation III+]] and [[Generation IV reactor|generation IV]] machines became a topic of considerable interest in the early 2000s, as it appeared that a [[nuclear renaissance]] was underway and large numbers of new reactors would be built over the next decade.<ref>[http://www.world-nuclear.org/info/inf104.html "The Nuclear Renaissance"], World Nuclear Association.</ref>

AECL had been working on a design known as the ACR-700, using elements of the latest versions of the CANDU&nbsp;6 and CANDU&nbsp;9, with a design power of 700&nbsp;MW<sub>e</sub>.<ref name="CANDU Evolution"/> During the nuclear renaissance, the upscaling seen in the earlier years re-expressed itself, and the ACR-700 was developed into the 1200&nbsp;MW<sub>e</sub> ACR-1000. ACR-1000 is the next-generation (officially, "generation III+") CANDU technology, which makes some significant modifications to the existing CANDU design.<ref name=acr1000/>

The main change, and the most radical among the CANDU generations, is the use of pressurized light water as the coolant. This significantly reduces the cost of implementing the primary cooling loop, which no longer has to be filled with expensive heavy water. The ACR-1000 uses about 1/3rd the heavy water needed in earlier-generation designs. It also eliminates tritium production in the coolant loop, the major source of tritium leaks in operational CANDU designs. The redesign also allows a slightly negative [[void coefficient|void reactivity]], a major design goal of all Gen III+ machines.<ref name=acr1000>[http://www.aecl.ca/Assets/Publications/ACR1000-Tech-Summary.pdf "ACR-1000 Technical Summary"] {{Webarchive|url=https://web.archive.org/web/20110606062512/http://www.aecl.ca/Assets/Publications/ACR1000-Tech-Summary.pdf |date=6 June 2011 }}, AECL.</ref>

The design also requires the use of [[enriched uranium#slightly enriched uranium|slightly enriched uranium]], enriched by about 1 or 2%. The main reason for this is to increase the burn-up ratio, allowing bundles to remain in the reactor longer, so that only a third as much spent fuel is produced. This also has effects on operational costs and timetables, as the refuelling frequency is reduced. As is the case with earlier CANDU designs, the ACR-1000 also offers online refuelling.<ref name=acr1000/>

Outside of the reactor, the ACR-1000 has a number of design changes that are expected to dramatically lower capital and operational costs. Primary among these changes is the design lifetime of 60 years, which dramatically lowers the price of the electricity generated over the lifetime of the plant. The design also has an expected capacity factor of 90%. Higher-pressure steam generators and turbines improve efficiency downstream of the reactor.<ref name=acr1000/>

Many of the operational design changes were also applied to the existing CANDU&nbsp;6 to produce the Enhanced CANDU&nbsp;6. Also known as CANDU&nbsp;6e or EC&nbsp;6, this was an evolutionary upgrade of the CANDU&nbsp;6 design with a gross output of 740&nbsp;MW<sub>e</sub> per unit. The reactors are designed with a lifetime of over 50 years, with a mid-life program to replace some of the key components e.g. the fuel channels. The projected average annual [[capacity factor]] is more than 90%. Improvements to construction techniques (including modular, open-top assembly) decrease construction costs. The CANDU&nbsp;6e is designed to operate at power settings as low as 50%, allowing them to adjust to load demand much better than the previous designs.<ref>[http://www.aecl.ca/Reactors/EC6.htm "Enhanced CANDU 6"] {{Webarchive|url=https://web.archive.org/web/20110606053133/http://www.aecl.ca/Reactors/EC6.htm |date=6 June 2011 }}, AECL.</ref>