en>Rjwilmsi: 10.1016/j.physletb.2004.06.001

2014-09-26T13:05:13Z

10.1016/j.physletb.2004.06.001

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2013-11-23T19:25:03Z

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	~~Bryan~~ is ~~really~~ a ~~superstar inside~~ the ~~generating~~ and ~~also~~ the ~~job advancement initially next~~ to ~~his third theatre record~~, ~~And~~ , will be the ~~resistant~~. ~~He burst on~~ the ~~scene~~ in ~~2001 regarding his best mix~~ of ~~straight down-property accessibility~~, ~~movie superstar excellent appearance~~ and ~~words~~, is ~~defined t within~~ a ~~significant way~~. ~~The brand new album Top~~ in the ~~land chart~~ and ~~#2 in~~ the ~~put maps~~, ~~generating it~~ the ~~second greatest very first during those times~~ of ~~2004 for the region performer~~. <br><br><br><br>The ~~kid~~ of ~~your ,~~ ~~is aware~~ of ~~perseverance~~ and ~~willpower~~ are ~~important elements with regards~~ to ~~an effective profession~~- . ~~His initially record~~, ~~Remain Me~~, ~~made~~ the ~~very best hits “All My Pals tim mcgraw concert (~~[http://~~minioasis~~.~~com http:~~//~~minioasis~~.~~com~~/]) ~~Say”~~ and ~~“Country Gentleman~~,~~” when his~~ ~~energy~~, ~~Doin’~~ ~~Factor~~, ~~found~~ the ~~vocalist-~~a ~~few right No~~. ~~3 men~~ and ~~women: Else Getting~~ in [http://~~lukebryantickets~~.~~pyhgy~~.com ~~luke bryan vip tickets~~ for ~~sale] touch with Is actually a Excellent Factor~~.”<br><br>~~Inside~~ the ~~slip~~ of ~~2013, Concerts~~: ~~Luke~~ ~~And which in fact had~~ a ~~remarkable set~~ of ~~, such as City~~. ~~“It’s almost like you’re acquiring~~ a ~~acceptance~~ to ~~visit~~ to ~~another level~~, ~~claims all those designers that were~~ a ~~part~~ of the ~~Concertsover~~ in a ~~bigger degree~~ of ~~musicians~~.~~” It wrapped among~~ the ~~most successful~~ ~~excursions in their twenty~~-year ~~historical past~~.<br><br>~~Also visit my blog~~: [http://www.~~banburycrossonline~~.com ~~luke bryan live concert~~]		[[Image:Radioisotope thermoelectric generator plutonium pellet.jpg\|thumb\|right\|150px\|[[Radioisotope thermoelectric generator\|RTG]] pellet glowing red because of 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 particle\|alpha]], [[Beta particle\|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 radioisotopes created in fission continues at high power, for a time after [[shutdown (nuclear reactor)\|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%.<ref>{{cite web \|url=http://www.anl.gov/sites/anl.gov/files/spent_fuel_nutt.pdf \|title=Spent Fuel \|publisher=Argonne National Laboratory \|date=April 2011 \|accessdate=26 January 2013}}</ref> 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.<ref>{{cite web \|url=http://www.ewp.rpi.edu/hartford/~ernesto/F2011/EP/MaterialsforStudents/Petty/Ragheb-Ch8-2011.PDF \|title=Decay Heat Generation in Fission Reactors \|author=M. Ragheb \|publisher=University of Illinois at Urbana-Champaign \|date=22 March 2011 \|accessdate=26 January 2013}}</ref>

			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<ref>[http://www.iaea.org/inisnkm/nkm/aws/htgr/abstracts/abst_29009817.html IAEA TECDOC 978: Fuel performance and fission product behaviour in gas cooled reactors]</ref> or even major core structural damage (partial meltdown) in a light water reactor<ref>[[Three Mile Island accident]]</ref><ref>[[Fukushima Daiichi nuclear disaster]]</ref> 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<ref>[http://www-pub.iaea.org/MTCD/publications/PDF/Pub913e_web.pdf The Chernobyl Accident]</ref>

			==Natural occurrence==
			Naturally occurring decay heat is a significant source of the heat in the interior of the [[Earth]]. Radioactive isotopes of [[uranium]], [[thorium]] and [[potassium]] are the primary contributors to this decay heat, and this [[radioactive decay]] is the primary source of heat from which [[geothermal energy]] derives.<ref name=ucsusa>http://www.ucsusa.org/clean_energy/our-energy-choices/renewable-energy/how-geothermal-energy-works.html How Geothermal energy works</ref>

			==Power reactors in shutdown==
			[[Image:Decay heat illustration2.PNG\|thumb\|Decay heat as fraction of full power for a reactor [[SCRAM]]ed from full power at time 0, using two different correlations]]
			In a typical [[nuclear fission]] reaction, 187 [[MeV]] of energy are released instantaneously in the form of [[kinetic energy]] from the fission products, kinetic energy from the fission neutrons, instantaneous [[gamma rays]], or gamma rays from the capture of neutrons.<ref>[http://www.hss.doe.gov/nuclearsafety/ns/techstds/standard/hdbk1019/h1019v1.pdf#page=85.5 DOE fundamentals handbook - Nuclear physics and reactor theory] - volume 1 of 2, module 1, page 61</ref> An additional 23 MeV of energy are released at some time after fission from the [[beta decay]] of [[fission product]]s. About 10 MeV of the energy released from the [[beta decay]] of [[fission products]] is in the form of [[neutrinos]], and since neutrinos are very weakly interacting, this 10 MeV of energy will not be deposited in the reactor core. This results in 13 MeV (6.5% of the total fission energy) being deposited in the reactor core after any given fission reaction has occurred.

			When a nuclear reactor has been [[shutdown (nuclear reactor)\|shut down]], and nuclear fission is not occurring at a large scale, the major source of heat production will be due to the [[beta decay]] of these fission fragments. For this reason, at the moment of reactor shutdown, decay heat will be about 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%. The decay heat production rate will continue to slowly decrease over time; the decay curve depends upon the proportions of the various fission products in the core and upon their respective [[half-lives]].<ref>http://books.google.com/books?id=yugQKddO82IC&pg=PA680&dq=neutron+startup+source&lr=&as_drrb_is=q&as_minm_is=0&as_miny_is=&as_maxm_is=0&as_maxy_is=&num=50&as_brr=3&cd=52#v=onepage&q=neutron%20startup%20source&f=false</ref>  An approximation for the decay heat curve valid from 10 seconds to 100 days after shutdown is
			::<math>\frac{P}{P_0} = 0.066 \left( \left( \tau - \tau_s \right)^{-0.2} - \tau^{-0.2} \right)</math>
			where <math>P</math> is the decay power, <math>P_0</math> is the reactor power before shutdown, <math>\tau</math> is the time since reactor start and <math>\tau_s</math> is the time of reactor shutdown measured from the time of startup (in seconds).<ref>http://www.nuceng.ca/papers/decayhe1b.pdf</ref> For an approach with a more direct physical basis, some models use the fundamental concept of [[radioactive decay]]. Used nuclear fuel contains a large number of different isotopes that contribute to decay heat, which are all subject to the radioactive decay law, so some models consider decay heat to be a sum of exponential functions with different decay constants and initial contribution to the heat rate.<ref>http://www.exitech.com/models/core_neutronics.htm</ref> A more accurate model would consider the effects of precursors, since many isotopes follow several steps in their radioactive [[decay chain]], and the decay of daughter products will have a greater effect longer after shutdown.

			:<math>\frac{P}{P_0} = \sum_{i=1}^{11}P_i e^{-\lambda t}.</math>

			The removal of the decay heat is a significant reactor safety concern, especially shortly after normal shutdown or following a [[loss-of-coolant accident]]. Failure to remove decay heat may cause the reactor core temperature to rise to dangerous levels and has caused [[nuclear accidents]], including the nuclear accidents at [[Three Mile Island]] and [[Fukushima I nuclear accidents\|Fukushima I]]. The heat removal is usually achieved through several redundant and diverse systems, from which heat is removed via heat exchangers. Water is passed through the secondary side of the heat exchanger via the [[Nuclear safety systems#Essential service water system\|essential service water system]]<ref name=pcsr-09-06-29>[http://www.epr-reactor.co.uk/ssmod/liblocal/docs/PCSR/Chapter%20%209%20-%20Auxiliary%20Systems/Sub-Chapter%209.2%20-%20Water%20Systems.pdf Pre-construction safety report - Sub-chapter 9.2 – Water Systems] AREVA NP / EDF, published 2009-06-29, accessed 2011-03-23</ref> which dissipates the heat into the 'ultimate heat sink', often a sea, river or large lake. In locations without a suitable body of water, the heat is dissipated into the air by recirculating the water via a [[cooling tower]]. The failure of ESWS circulating pumps was one of the factors that endangered safety during the [[1999 Blayais Nuclear Power Plant flood]].

			== Spent fuel ==
			After one year, typical [[spent nuclear fuel]] generates about 10 [[kW]] of decay heat per [[tonne]], decreasing to about 1 kW/t after ten years.<ref>[http://www.world-nuclear.org/education/phys.htm world-nuclear.org] - Some physics of uranium</ref> Hence effective active or passive cooling for spent nuclear fuel is required for a number of years.

			== Radioisotope thermoelectric generator ==
			The decay heat of a radioisotope is used in an [[Radioisotope thermoelectric generator\|RTG]] to make electrical power.

			== See also ==

			* [[Decay energy]]
			* [[Spent fuel pool]]
			* [[Dry cask storage]]

			==References==
			{{reflist}}

			==External links==
			*[http://www.hss.doe.gov/nuclearsafety/ns/techstds/standard/hdbk1019/h1019v2.pdf#page=125 DOE fundamentals handbook - Decay heat, Nuclear physics and reactor theory] - volume 2 of 2, module 4, page 61
			*[http://www.nuceng.ca/papers/decayhe1b.pdf Decay Heat Estimates for MNR], page 2.
			*[http://www.energyfromthorium.com/javaws/SpentFuelExplorer.jnlp Spent Nuclear Fuel Explorer] Java applet showing activity and decay heat as a function of time

			[[Category:Nuclear technology]]
			[[Category:Heat transfer]]

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en>Rjwilmsi: 10.1016/j.physletb.2004.06.001

en>Ysyoon: /* Definition */

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