RTG pellet glowing red due to the heat generated by the radioactive decay of plutonium-238 dioxide, after a thermal isolation test.
Decay heat is the heat released as a result of radioactive decay. This heat is produced as an effect of radiation on materials: the energy of the alpha, beta or gamma radiation is converted into the thermal movement of atoms.
Decay heat occurs naturally from decay of long-lived radioisotopes that are primordially present from the Earth's formation.
In nuclear reactor engineering, decay heat continues to be generated after the reactor has been shut down (see SCRAM and nuclear chain reactions) and power generation has been suspended. The decay of the short-lived radioisotopes such as iodine-131 created in fission continues at high power for a time after shut down.[1] The major source of heat production in a newly shut down reactor is due to the beta decay of new radioactive elements recently produced from fission fragments in the fission process.
Quantitatively, at the moment of reactor shutdown, decay heat from these radioactive sources is still 6.5% of the previous core power if the reactor has had a long and steady power history. About 1 hour after shutdown, the decay heat will be about 1.5% of the previous core power. After a day, the decay heat falls to 0.4%, and after a week, it will be only 0.2%.[2] Because radioisotopes of all half-life lengths are present in nuclear waste, enough decay heat continues to be produced in spent fuel rods to require them to spend a minimum of one year, and more typically 10 to 20 years, in a spent fuel pool of water before being further processed. However, the heat produced during this time is still only a small fraction (less than 10%) of the heat produced in the first week after shutdown.[1]
If no cooling system is working to remove the decay heat from a crippled and newly shut down reactor, the decay heat may cause the core of the reactor to reach unsafe temperatures within a few hours or days, depending upon the type of core. These extreme temperatures can lead to minor fuel damage (e.g. a few fuel particle failures (0.1 to 0.5%) in a graphite-moderated, gas-cooled design[3]) or even major core structural damage (meltdown) in a light water reactor[4] or liquid metal fast reactor. Chemical species released from the damaged core material may lead to further explosive reactions (steam or hydrogen) which may further damage the reactor.[5]
^ abRagheb, Magdi (15 Oct 2014). "Decay heat generation in fission reactors" (PDF). University of Illinois at Urbana-Champaign. Archived (PDF) from the original on 2022-01-30. Retrieved 24 March 2018.
^"Spent Fuel" (PDF). Argonne National Laboratory. April 2011. Archived from the original (PDF) on 4 March 2016. Retrieved 26 January 2013.
^"IAEA TECDOC 978: Fuel performance and fission product behaviour in gas cooled reactors" (PDF). International Atomic Energy Agency. 1997. Archived (PDF) from the original on 2022-01-30. Retrieved 2019-11-25.
^Lamarsh, John R.; Baratta, Anthony J. (2001). Introduction to Nuclear Engineering (3rd ed.). Prentice-Hall. Section 8.2. ISBN 0-201-82498-1.
^INSAG-7 The Chernobyl Accident: Updating of INSAG-1(PDF). International Atomic Energy Agency. 1992. p. 20. Archived (PDF) from the original on 2021-04-25.
Decayheat is the heat released as a result of radioactive decay. This heat is produced as an effect of radiation on materials: the energy of the alpha...
The power produced by decayheat decreases as the fission products decay, but it is large enough that failure to remove decayheat may cause the reactor...
undergo radioactive decay, which produces decayheat. Different isotopes produce different amounts of heat per mass. The decayheat is usually listed as...
OKBM Critical Test Facility in Russia. Decayheat accidents are where the heat generated by radioactive decay causes harm. In a large nuclear reactor...
nuclear battery that uses an array of thermocouples to convert the heat released by the decay of a suitable radioactive material into electricity by the Seebeck...
see the inside of the reactors." TEPCO estimated for Unit 1 that "the decayheat must have decreased enough, the molten fuel can be assumed to remain in...
even after a reactor is shut down because the fuel continues to produce decayheat. A core damage accident is caused by the loss of sufficient cooling for...
three systems that allow for the efficient transfer of decayheat (created from nuclear decay) from the reactor to pools of water outside containment –...
provides heat through radioactive decay. They are similar to tiny radioisotope thermoelectric generators (RTG) and normally provide about one watt of heat each...
the initial decayheat is a fraction of the reactor operating power the lower operating power of SMRs makes them much safer since less heat needs to be...
continue to generate a significant amount of decayheat even after the fission chain reaction has stopped. If the heat cannot be removed from the reactor, the...
continues to be generated, from the decay of short half-life fission products. In conventional reactors, removing this decayheat passively is challenging because...
Fission product decay also generates heat that continues even after the reactor has been shut down and fission stopped. This decayheat requires removal...
nuclear chain reaction and stopping the heat generated by fission. However, the reactor continued to generate decayheat, initially equivalent to approximately...
fuel rods. This allows short-lived isotopes to decay and thus reduces the ionizing radiation and decayheat emanating from the rods. The water cools the...
A quantity is subject to exponential decay if it decreases at a rate proportional to its current value. Symbolically, this process can be expressed by...
and high-level waste (HLW), which is highly radioactive and hot due to decayheat, thus requiring cooling and shielding. In nuclear reprocessing plants...
Radioactive decay (also known as nuclear decay, radioactivity, radioactive disintegration, or nuclear disintegration) is the process by which an unstable...
required that the decayheat stored in the fuel assemblies at any one time does not overwhelm the ECCS. As such, the measure of decayheat generation known...
to safety and auxiliary non-safety components, as well as remove the decayheat from the reactor when the plant is offline. One natural-draft tower and...
heat continues to be generated at significant levels by the radioactive decay of the fission products for days or months. This is known as decayheat...
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