Decay Heat

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 beginning.

In nuclear reactor engineering, decay heat plays an important role in reactor heat generation during the relatively short time after the reactor has been shut down (see SCRAM), and nuclear chain reactions have been suspended. The decay of the short-lived radiositopes created in fission continues at high power, for a time after shut down. 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%. 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.

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 or even major core structural damage (partial meltdown) in a light water reactor 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

Read more about Decay HeatNatural Occurrence, Power Reactors in Shutdown, Spent Fuel, Radioisotope Thermoelectric Generator

Other articles related to "decay heat, heat, decay":

Decay Heat - Radioisotope Thermoelectric Generator
... The decay heat of a radioisotope is used in an RTG to make electrical power. ...
Light Water Reactor - Reactor Design - Moderator
... moderation of neutrons will cause the chain reaction to slow down, producing less heat ... just a 5% power level for 1 to 3 years called the "decay heat" ... This 5% "decay heat" will continue for 1 to 3 years after shut down, whereupon it finally reaches "full cold shutdown" ...
Liquid Fluoride Thorium Reactor - Advantages - Safety
... operation and low pressure differences through the primary heat exchangers, the potential for large leaks is also greatly reduced ... products, such as Xenon, for processing, thereby these decay products would not be spread in a disaster ... Molten fluorides have high volumetric heat capacity, some such as FLiBe, even higher than water ...
Spent Nuclear Fuel - Spent Fuel Decay Heat
... reaction has ceased, a significant amount of heat will still be produced in the fuel due to the beta decay of fission products ... For this reason, at the moment of reactor shutdown, decay heat will be about 7% 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 ...
Boiling Water Reactors - Technical and Background Information - Thermal Margins - Average Planar Linear Heat Generation Rate (APLHGR)
... APLHGR, being an average of the Linear Heat Generation Rate (LHGR), a measure of the decay heat present in the fuel bundles, is a margin of safety associated with the ... capacity, and there is a possibility that fuel could be designed that produces so much decay heat that the ECCS would be overwhelmed and could not cool ... So as to prevent this from happening, it is required that the decay heat stored in the fuel assemblies at any one time does not overwhelm the ECCS ...

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