Verbrauchter Kernbrennstoff

2006-09-07T18:39:18Z

CSMR: /* Uranium */

'''Used nuclear fuel''' (often called '''spent nuclear fuel''') is [[nuclear fuel]] that has been irradiated in a [[nuclear reactor]] (usually at a [[nuclear power plant]]) to the point that it is no longer useful in sustaining a nuclear reaction. If not [[nuclear reprocessing|reprocessed]] to retrieve the remaining usable [[uranium]] and [[plutonium]], it is a form of [[radioactive waste]].

Used nuclear fuel is currently planned for disposal in deep geological formations, such as [[Yucca Mountain]].

==Nature of used fuel==
===Nanomaterial properties===

Used [[enriched uranium|low enriched uranium]] nuclear fuel is an example of a [[nanomaterial]] which existed before the term [[nano]] became [[fashion]]able, 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 [[cesium]], hence many of these bubbles contain a lot of 137Cs. 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.

:For details of how to make a non[[radioactive]] ''uranium active'') simulation of spent oxide fuel see: ''Microstructural features of SIMFUEL - Simulated high-burnup UO2-based nuclear fuel'', P.G. Lucuta, R.A. Verrall, Hj. Matzke and B.J. Palmer, '''Journal of Nuclear Materials''', 1991, 178, 48-60.

===Fission products===

*3% of the mass consists of fission products of 235U (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]], [[Cesium|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 90Sr, 137Cs, 99Tc and 129I. 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.

====Table of chemical data====

{| border="1"
|+ The chemical forms of fission products in uranium dioxide [http://abulafia.mt.ic.ac.uk/publications/theses/stanek/solutioninuo2.pdf]
! Element !! Gas !! Metal !! Oxide !! Solid solution
|-
! Br
| Yes || - || - || -
|-
! Kr
| Yes || - || - || -
|-
! Rb
| Yes || - || Yes || -
|-
! Sr
| - || - || Yes || Yes
|-
! Y
| - || - || - || Yes
|-
! Zr
| - || - || Yes || Yes
|-
! Nb
| - || - || Yes || -
|-
! Mo
| - || Yes || Yes || -
|-
! Tc
| - || Yes || - || -
|-
! Ru
| - || Yes || - || -
|-
! Rh
| - || Yes || - || -
|-
! Pd
| - || Yes || - || -
|-
! Ag
| - || Yes || - || -
|-
! Cd
| - || Yes || - || -
|-
! In
| - || Yes || - || -
|-
! Sn
| - || Yes || - || -
|-
! Sb
| - || Yes || - || -
|-
! Te
| Yes || Yes || Yes || Yes
|-
! I
| Yes || - || - || -
|-
! Xe
| Yes || - || - || -
|-
! Cs
| Yes || - || Yes || -
|-
! Ba
| - || - || Yes || Yes
|-
! La
| - || - || - || Yes
|-
! Ce
| - || - || - || Yes
|-
! Pr
| - || - || - || Yes
|-
! Nd
| - || - || - || Yes
|-
! Pm
| - || - || - || Yes
|-
! Sm
| - || - || - || Yes
|-
! Eu
| - || - || - || Yes
|-
|}

===Plutonium===

*1% of the mass is 239Pu and 240Pu resulting from conversion of 238U, 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 240Pu and less than 80% 239Pu, which makes it less suitable, but not impossible, to use in a weapon [http://permanent.access.gpo.gov/websites/osti.gov/www.osti.gov/html/osti/opennet/document/press/pc29.html]. 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 238U and a little 235U. Usually 235U would be less than 0.83% of the mass along with 0.4% 236U.

[[Reprocessed uranium]] fuel will contain some 236U which is not found in nature; this is one isotope which can be used as a [[fingerprint]] for used reactor fuel.

===Minor actinides===

*Traces of the [[minor actinides]] are present in used reactor fuel. These are [[actinides]] other than uranium and plutonium. These include [[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 (239Pu in a 238U matrix) is likely to lead to the production of more 241Am than the use of a uranium/thorium based fuel (233U in a 232Th matrix). Also present as a minor actinide is 237Np, this neptunium isotope is fissile but also can be converted into 238Pu by neutron bombardment.

For [[natural uranium]] fuel:
Fissile component starts at 0.71% 235U concentration in natural uranium). At discharge, total fissile component still 0.50% (0.23% 235U, 0.27% fissile 239Pu, 241Pu) Fuel is discharged not because it is fully used-up, but because the neutron-absorbing fission products have built up and the fuel then 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 [http://www.defra.gov.uk/rwmac/reports/reprocess/16.htm].

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 [[preasure]]. This has been used to make a layer of the uranum oxide on a [[gold]] surface which was then studied with [[AC impedance]] spectrscopy.

F. Miserque, T. Gouder, D.H. Wegen and P.D.W. Bottomley, ''Journal of Nuclear Materials'', 2001, '''298''', 280-290.

===Noble metal nanoparticles and [[hydrogen]]===

According to the work of the [[corrosion]] [[electrochemistry|electrochemist]] Shoesmith[http://www.uwo.ca/chem/people/faculty/shoesmith.htm][http://publish.uwo.ca/~ecsweb/] 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 (H2) concentration is high (due to the [[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.

[[Category:Nuclear materials]]
[[Category:Nuclear reprocessing]]
[[Category:Nuclear technology]]
[[Category:Corrosion]]
[[Category:Nuclear chemistry]]
[[Category:Nanoparticles]]
[[Category:Nanomaterials]]
[[Category:Nanotechnology]]
[[Category:Actinides]]
[[Category:Radioactive waste]]
[[Category:Waste types]]

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Verbrauchter Kernbrennstoff