In nuclear power technology, online refuelling is a technique for changing the fuel of a nuclear reactor while the reactor is

critical Critical or Critically may refer to: *Critical, or critical but stable, medical states **Critical, or intensive care medicine * Critical juncture, a discontinuous change studied in the social sciences. *Critical Software, a company specializing ...

. This allows the reactor to continue to generate electricity during routine refuelling, and therefore improve the

availability In reliability engineering, the term availability has the following meanings: * The degree to which a system, subsystem or equipment is in a specified operable and committable state at the start of a mission, when the mission is called for at a ...

and profitability of the plant.

Benefits of online refuelling

Online refuelling allows a nuclear reactor to continue to generate electricity during periods of routine refuelling, and therefore improves the

and therefore the economy of the plant. Additionally, this allows for more flexibility in reactor refuelling schedules, exchanging a small number of fuel elements at a time rather than high-intensity offline refuelling programmes. The ability to refuel a reactor while generating power has the greatest benefits where refuelling is required at high frequency, for example during the production of plutonium suitable for nuclear weapons during which low-

burnup In nuclear power technology, burnup (also known as fuel utilization) is a measure of how much energy is extracted from a primary nuclear fuel source. It is measured as the fraction of fuel atoms that underwent fission in %FIMA (fissions per initi ...

fuel is required from short irradiation periods in a reactor. Conversely, frequent rearrangement of fuel within the core can balance the thermal load and allow higher fuel burnup, therefore reducing both the fuel requirements, and subsequently the amount of high-level nuclear waste for disposal. Although online refuelling is generally desirable, it requires design compromises which means that it is often uneconomical. This includes added complexity to refuelling equipment, and the requirement for these to pressurise during refuelling gas and water-cooled reactors. Online refuelling equipment for

Magnox Magnox is a type of nuclear power/production reactor that was designed to run on natural uranium with graphite as the moderator and carbon dioxide gas as the heat exchange coolant. It belongs to the wider class of gas-cooled reactors. The n ...

reactors proved to be less reliable than the reactor systems, and retrospectively its use was regarded as a mistake. Molten salt reactors and pebble-bed reactors also require online handling and processing equipment to replace the fuel during operation.

Reactor designs with online refuelling

Reactors with online refuelling capability to date have typically been either liquid sodium cooled, gas cooled, or cooled by water in pressurised channels. Water-cooled reactors utilising pressurised vessels, for example PWR and

BWR A boiling water reactor (BWR) is a type of light water nuclear reactor used for the generation of electrical power. It is a design different from a Soviet graphite-moderated RBMK. It is the second most common type of electricity-generating nuc ...

reactors and their Generation III descendants, are unsuitable for online refuelling as the coolant is depressurised to allow for disassembly of the pressure vessel and therefore requires a major reactor shutdown. This is typically carried out every 18–24 months. Notable past and present nuclear power plant designs that have incorporated the ability to refuel online include: *

CANDU The CANDU (Canada Deuterium Uranium) is a Canadian pressurized heavy-water reactor design used to generate electric power. The acronym refers to its deuterium oxide ( heavy water) moderator and its use of (originally, natural) uranium fuel. C ...

reactors: Pressurised heavy-water cooled and moderated, natural uranium fuel reactors of Canadian design. Operated 1947–present. *

reactors: -cooled, graphite-moderated, natural uranium fuel reactors of British design. Operated 1954–2015. * RBMK reactors: Boiling water cooled, graphite-moderated, enriched uranium fuel reactors of Russian design. Operated 1954–present. * UNGG reactors: -cooled, graphite-moderated, natural uranium fuel reactors of French design. Operated 1966 - 1994. *

BN-350 The BN-350 is a sodium-cooled, fast reactor located at the ''Mangyshlak Nuclear Power Plant'', located in Aktau (formerly known as Shevchenko under the control of the USSR in 1964–1992), Kazakhstan, on the shore of the Caspian Sea. Constru ...

;

BN-600 The BN-600 reactor is a sodium-cooled fast breeder reactor, built at the Beloyarsk Nuclear Power Station, in Zarechny, Sverdlovsk Oblast, Russia. Designed to generate electrical power of 600 MW in total, the plant dispatches 560 MW t ...

BN-800 The BN-800 reactor (Russian: реактор БН–800) is a sodium-cooled fast breeder reactor, built at the Beloyarsk Nuclear Power Station, in Zarechny, Sverdlovsk Oblast, Russia. The reactor is designed to generate 880 MW of electrical pow ...

reactors: Sodium cooled fast-breeder reactor of Russian design. Operated 1973–present. * AGR (Advanced gas-cooled) reactors: -cooled, graphite-moderated, enriched uranium fuel reactors of British design. Operated 1976–present. There are a number of planned reactor designs which include provision for online refuelling, including pebble-bed and

molten salt Molten salt is salt which is solid at standard temperature and pressure but enters the liquid phase due to elevated temperature. Regular table salt has a melting point of 801 °C (1474°F) and a heat of fusion of 520 J/g.Journal of Chemical Th ...

Generation IV reactors Generation IV reactors (Gen IV) are six nuclear reactor designs recognized by the Generation IV International Forum. The designs target improved safety, sustainability, efficiency, and cost. The most developed Gen IV reactor design is the sodium ...

References

Nuclear technology {{nuclear-power-stub