Spent nuclear fuel 4094572 213399757 2008-05-19T04:05:18Z Wwoods 43844 format refs '''Spent nuclear fuel''', occasionally called '''used nuclear fuel''', is [[nuclear fuel]] that has been irradiated in a [[nuclear reactor]] (usually at a [[nuclear power plant]]) to the point where it is no longer useful in sustaining a [[nuclear reaction]]. [[Nuclear reprocessing]] can separate spent fuel into various combinations of [[reprocessed uranium]], [[plutonium]], [[minor actinides]], [[fission products]], remnants of zirconium or steel [[cladding]], [[activation products]], and the reagents or solidifiers introduced in the reprocessing itself. Alternatively, the intact spent fuel can be disposed as [[radioactive waste]]. The US is currently planning disposal in deep geological formations, such as [[Yucca Mountain]], where it has to be shielded and packaged to prevent its migration to mankind's immediate environment for thousands if not millions of years.<ref name="largeassociates"> [http://www.largeassociates.com/3145/3145-a1%20FINAL.pdf] ([[PDF]]) {{dead link|date=May 2008 }} </ref> ==Nature of spent fuel== Large John H ''Radioactive Decay Characteristics of Irradiated Nuclear Fuels, January 2006''.<ref name ="largeassociates"/> ===Nanomaterial properties=== Spent [[enriched uranium|low enriched uranium]] nuclear fuel is an example of a [[nanomaterial]] which existed before the term [[nano]] became fashionable. In the oxide [[fuel]] intense temperature gradients exist which cause [[fission products]] to migrate. The [[zirconium]] tends to move to the centre of the fuel [[pellet]] where the [[temperature]] is highest while the lower boiling fission products move to the edge of the pellet. The pellet is likely to contain lots of small [[bubble]] like pores which form during use, the fission [[xenon]] migrates to these voids. Some of this xenon will then decay to form [[caesium]], hence many of these bubbles contain a lot of <sup>137</sup>Cs. [[Image:SEMofusedMOX.jpg|thumb|340px|A used MOX, which has 63 GW days(thermal) of burnup and has been examined with a [[scanning electron microscope]] using electron microprobe attachment. The lighter the pixel in the right hand side the higher the plutonium content of the material at that spot]] In the case of the MOX the xenon tended to diffuse out of the plutonium rich areas of the fuel, and it was then trapped in the surrounding uranium dioxide. The [[neodymium]] tended to not be mobile. [[Image:SEMofusedMOXshowing Nd and Xe.jpg|thumb|340px|A used MOX, which has 63 GW days(thermal) of burnup and has been examined with a [[scanning electron microscope]] using electron microprobe attachment. The lighter the pixel the higher the neodymium (left) or xenon (right) content of the material at that spot]] Also metallic particles of an [[alloy]] of Mo-Tc-Ru-Pd tends to form in the fuel. Other solids form at the boundary between the uranium dioxide grains, but the majority of the fission products remain in the [[uranium dioxide]] as [[solid solution]]s. A paper describing a method of making a non[[radioactive]] ''uranium active'') simulation of spent oxide fuel exists.<ref>''Microstructural features of SIMFUEL - Simulated high-burnup UO<sub>2</sub>-based nuclear fuel'', P.G. Lucuta, R.A. Verrall, Hj. Matzke and B.J. Palmer, '''Journal of Nuclear Materials''', 1991, 178, 48–60.</ref> ===Fission products=== *3% of the mass consists of fission products of <sup>235</sup>U (also indirect products in the [[decay chain]]), [[nuclear poison]]s considered [[radioactive waste]] or separated further for various industrial and medical uses. The fission products include every element from [[zinc]] through to the [[lanthanide]]s, much of the fission yield is concentrated in two peaks, one in the second transition row ([[Zirconium|Zr]], Mo, Tc, [[Ruthenium|Ru]], [[Rhodium|Rh]], [[Palladium|Pd]], [[Silver|Ag]]) while the other is later in the periodic table ([[Iodine|I]], [[Xenon|Xe]], [[Caesium|Cs]], [[Barium|Ba]], [[Lanthanum|La]], [[Cerium|Ce]], Nd). Many of the fission products are either non radioactive or only shortly lived [[radioisotopes]]. But a considerable number are medium to long lived radioisotopes such as <sup>90</sup>Sr, <sup>137</sup>Cs, <sup>99</sup>Tc and <sup>129</sup>I. Research has been conducted by several different countries into partitioning the rare isotopes in fission waste including the Fission Platinoids (Ru, Rh, Pd) and Silver (Ag) as a way of offsetting the cost of reprocessing, however this is not currently being done commercially. : The fission products can modify the [[thermal conductivity|thermal]] properties of the uranium dioxide, the [[lanthanide]] oxides tend to lower the thermal conductivity of the fuel while the [[metallic]] nanoparticles slightly increases the thermal conductivity of the fuel.<ref>Dong-Joo Kim, Jae-Ho Yang, Jong-Hun Kim, Young-Woo Rhee, Ki-Won Kang, Keon-Sik Kim and Kun-Woo Song, ''Thermochimica Acta'', 2007, '''455''', 123–128. </ref> ====Table of chemical data==== {| class="wikitable" |+ The chemical forms of fission products in uranium dioxide<ref> {{cite web | url= http://abulafia.mt.ic.ac.uk/publications/theses/stanek/solutioninuo2.pdf | title= Solution of Fission Products in UO<sub>2</sub> |author= |last= |first= |authorlink= |coauthors= |date= |year= |month= |format= |work= |publisher= | accessdate= 2008-05-18 }} </ref> ! Element !! Gas !! Metal !! Oxide !! Solid solution |- ! [[Bromine|Br]] | Yes || - || - || - |- ! [[krypton|Kr]] | Yes || - || - || - |- ! [[rubidium|Rb]] | Yes || - || Yes || - |- ! [[strontium|Sr]] | - || - || Yes || Yes |- ! [[yttrium|Y]] | - || - || - || Yes |- ! [[zirconium|Zr]] | - || - || Yes || Yes |- ! [[niobium|Nb]] | - || - || Yes || - |- ! [[molybdenum|Mo]] | - || Yes || Yes || - |- ! [[technetium|Tc]] | - || Yes || - || - |- ! [[ruthenium|Ru]] | - || Yes || - || - |- ! [[rhodium|Rh]] | - || Yes || - || - |- ! [[palladium|Pd]] | - || Yes || - || - |- ! [[silver|Ag]] | - || Yes || - || - |- ! [[cadmium|Cd]] | - || Yes || - || - |- ! [[indium|In]] | - || Yes || - || - |- ! [[tin|Sn]] | - || Yes || - || - |- ! [[antimony|Sb]] | - || Yes || - || - |- ! [[tellurium|Te]] | Yes || Yes || Yes || Yes |- ! [[iodine|I]] | Yes || - || - || - |- ! [[xenon|Xe]] | Yes || - || - || - |- ! [[caesium|Cs]] | Yes || - || Yes || - |- ! [[barium|Ba]] | - || - || Yes || Yes |- ! [[lanthanum|La]] | - || - || - || Yes |- ! [[cerium|Ce]] | - || - || - || Yes |- ! [[praseodymium|Pr]] | - || - || - || Yes |- ! [[neodymium|Nd]] | - || - || - || Yes |- ! [[praseodymium|Pm]] | - || - || - || Yes |- ! [[samarium|Sm]] | - || - || - || Yes |- ! [[europium|Eu]] | - || - || - || Yes |- |} ===Plutonium=== *1% of the mass is <sup>239</sup>Pu and <sup>240</sup>Pu resulting from conversion of <sup>238</sup>U, which may either be considered a useful by-product, or as dangerous and inconvenient waste. One of the main concerns regarding [[nuclear proliferation]] is to prevent this plutonium from being used by states other than those already established as Nuclear Weapons States, to produce nuclear weapons. If the reactor has been used normally, the plutonium is reactor-grade, not weapon-grade: it contains much <sup>240</sup>Pu and less than 80% <sup>239</sup>Pu, which makes it less suitable, but not impossible, to use in a weapon.<ref> {{cite web | url= http://permanent.access.gpo.gov/websites/osti.gov/www.osti.gov/html/osti/opennet/document/press/pc29.html | title= Additional Information Concerning Underground Nuclear Weapon Test of Reactor-Grade Plutonium |date= |year= |month= |work= |publisher= [[U.S. Department of Energy]] | accessdate= 2008-05-18 }} </ref> If the irradiation period has been short then the plutonium is weapon-grade (more than 80%, up to 93%). ===Uranium=== *96% of the mass is the remaining uranium: most of the original <sup>238</sup>U and a little <sup>235</sup>U. Usually <sup>235</sup>U would be less than 0.83% of the mass along with 0.4% <sup>236</sup>U. [[Reprocessed uranium]] will contain [[Uranium-236|<sup>236</sup>U]] which is not found in nature; this is one isotope which can be used as a [[fingerprint]] for spent reactor fuel. ===Minor actinides=== *Traces of the [[minor actinides]] are present in spent reactor fuel. These are [[actinides]] other than uranium and plutonium. These include [[neptunium]], [[americium]] and [[curium]]. The amount formed depends greatly upon the nature of the fuel used and the conditions under which it was used. For instance, the use of MOX fuel (<sup>239</sup>Pu in a <sup>238</sup>U matrix) is likely to lead to the production of more <sup>241</sup>Am and heavier nuclides than a uranium/thorium based fuel (<sup>233</sup>U in a <sup>232</sup>Th matrix). For [[natural uranium]] fuel: Fissile component starts at 0.71% <sup>235</sup>U concentration in natural uranium). At discharge, total fissile component is still 0.50% (0.23% <sup>235</sup>U, 0.27% fissile <sup>239</sup>Pu, <sup>241</sup>Pu) Fuel is discharged not because fissile material is fully used-up, but because the [[neutron poison|neutron-absorbing]] [[fission product]]s have built up and the fuel becomes significantly less able to sustain a nuclear reaction. Some natural uranium fuels use chemically active cladding, such as [[Magnox]], and need to be reprocessed because long-term storage and disposal is difficult.<ref> {{cite web | url= http://www.defra.gov.uk/rwmac/reports/reprocess/16.htm | title= RWMAC's Advice to Ministers on the Radioactive Waste Implications of Reprocessing |author= |last= |first= |authorlink= |coauthors= |date= 3 November, 2002 |work= |publisher= Radioactive Waste Management Advisory Committee (RWMAC) | accessdate= 2008-05-18 }} </ref> For highly enriched fuels used in [[nuclear marine propulsion|marine reactors]] and [[research reactor]]s the isotope inventory will vary based on in-core fuel management and reactor operating conditions. ==Spent fuel corrosion== ===Uranium dioxide films=== Uranium dioxide films can be deposited by reactive [[spluttering]] using an [[argon]] and [[oxygen]] mixture at a low [[pressure]]. This has been used to make a layer of the uranium oxide on a [[gold]] surface which was then studied with [[AC impedence]] spectroscopy.<ref>F. Miserque, T. Gouder, D.H. Wegen and P.D.W. Bottomley, ''Journal of Nuclear Materials'', 2001, '''298''', 280–290. </ref> ===Noble metal nanoparticles and hydrogen=== According to the work of the [[corrosion]] [[electrochemistry|electrochemist]] Shoesmith<ref> {{cite web | url= http://www.uwo.ca/chem/people/faculty/shoesmith.htm | title= David W. Shoesmith |date= |year= |month= |work= | publisher= [[University of Western Ontario]] | accessdate= 2008-05-18 }} </ref><ref> {{cite web | url= http://publish.uwo.ca/~ecsweb/ | title= Electrochemistry and corrosion studies at Western |date= |year= |month= |work= |publisher= Shoesmith research group, University of Western Ontario | accessdate= 2008-05-18 }} </ref> the [[nanoparticle]]s of Mo-Tc-Ru-Pd have a strong effect on the corrosion of uranium dioxide fuel. For instance his work suggests that when the hydrogen (H<sub>2</sub>) concentration is high (due to the [[Hypoxia (environmental)|anaerobic]] corrosion of the [[steel]] waste can) the oxidation of hydrogen at the nanoparticles will exert a protective effect on the uranium dioxide. This effect can be thought of as an example of protection by a [[sacrificial anode]] where instead of a metal [[anode]] reacting and dissolving it is the hydrogen gas which is consumed. ==See also== *[[Nuclear power]] *[[Spent nuclear fuel shipping cask]] ==References== {{reflist}} [[Category:Nuclear fuels]] [[Category:Nuclear reprocessing]] [[Category:Corrosion]] [[Category:Nuclear chemistry]] [[Category:Nanotechnology]] [[Category:Actinides]] [[Category:Radioactive waste]] [[Category:Waste]] [[ja:使用済み核燃料]] [[ru:Облучённое ядерное топливо]]