nuclear power Nuclear power is the use of nuclear reactions to produce electricity. Nuclear power can be obtained from nuclear fission, nuclear decay and nuclear fusion reactions. Presently, the vast majority of electricity from nuclear power is produced ...

technology, online refuelling is a technique for changing the fuel of a

nuclear reactor A nuclear reactor is a device used to initiate and control a fission nuclear chain reaction or nuclear fusion reactions. Nuclear reactors are used at nuclear power plants for electricity generation and in nuclear marine propulsion. Heat from nu ...

while the reactor is critical. 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 ...

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 Plutonium is a radioactive chemical element with the symbol Pu and atomic number 94. It is an actinide metal of silvery-gray appearance that tarnishes when exposed to air, and forms a dull coating when oxidized. The element normally exhib ...

suitable for

nuclear weapon A nuclear weapon is an explosive device that derives its destructive force from nuclear reactions, either fission (fission bomb) or a combination of fission and fusion reactions ( thermonuclear bomb), producing a nuclear explosion. Both bom ...

s 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 init ...

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 Radioactive waste is a type of hazardous waste that contains radioactive material. Radioactive waste is a result of many activities, including nuclear medicine, nuclear research, nuclear power generation, rare-earth mining, and nuclear weapons ...

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 na ...

reactors proved to be less reliable than the reactor systems, and retrospectively its use was regarded as a mistake.

Molten salt reactor A molten salt reactor (MSR) is a class of nuclear fission reactor in which the primary nuclear reactor coolant and/or the fuel is a molten salt mixture. Only two MSRs have ever operated, both research reactors in the United States. The 1950's ...

s and

pebble-bed reactor The pebble-bed reactor (PBR) is a design for a graphite-moderated, gas-cooled nuclear reactor. It is a type of very-high-temperature reactor (VHTR), one of the six classes of nuclear reactors in the Generation IV initiative. The basic desig ...

s 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 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 The RBMK (russian: реактор большой мощности канальный, РБМК; ''reaktor bolshoy moshchnosti kanalnyy'', "high-power channel-type reactor") is a class of graphite moderated reactor, graphite-moderated nuclear react ...

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; BN-600 & BN-800 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.Proc. Roy. Soc. Bibli ...

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 sodiu ...

References

Nuclear technology {{nuclear-power-stub