PUREX

PUREX(plutonium uranium reduction extraction) is achemicalmethod used to purify fuel fornuclear reactorsornuclear weapons.^[7]PUREX is thede factostandard aqueousnuclear reprocessingmethod for the recovery ofuraniumandplutoniumfrom usednuclear fuel(spent nuclear fuel,orirradiatednuclear fuel). It is based onliquid–liquid extraction ion-exchange.^[8]

PUREX is applied tospent nuclear fuel,which consists primarily of very highatomic-weight(actinoidor "actinide" )elements(e.g.uranium,plutonium,americium) along with smaller amounts of material composed of lighter atoms, notably thefission productsproduced by reactor operation.

The actinoid elements in this case consist primarily of the unconsumed remains of the original fuel (typicallyU-235,U-238,and/orPu-239).

Chemical process

Structure of uranyl nitrate complex that is extracted in PUREX.^[9]

The fuel is first dissolved innitric acidat a concentration around 7M.Solids are removed by filtration to avoid the formation ofemulsions,referred to asthird phasesin the solvent extraction community.

Theorganic solventconsists of 30%tributyl phosphate(TBP) in ahydrocarbonsuch askerosene.Uranyl(VI)UO²⁺
₂ions are extracted in the organic phase as UO₂(NO₃)₂·2TBP complexes; plutonium is extracted as similarcomplexes.The heavier actinides, primarilyamericiumandcurium,and the fission products remain in the aqueous phase. The nature of uranyl nitrate complexes with trialkyl phosphates has been characterized.^[10]

Plutonium is separated from uranium by treating the TBP-kerosene solution with reducing agents to convert the plutonium to its +3 oxidation state, which will pass into the aqueous phase. Typical reducing agents include N,N-diethyl-hydroxylamine,ferrous sulphamate,andhydrazine.Uranium is then stripped from the kerosene solution by back-extraction into nitric acid at a concentration around 0.2 M.^[11]

PUREX raffinate

The termPUREXraffinatedescribes the mixture of metals innitric acidwhich are left behind when theuraniumandplutoniumhave been removed by the PUREX process from anuclear fueldissolution liquor. This mixture is often known as high levelnuclear waste.

Two PUREX raffinates exist. The most highly activeraffinatefrom the first cycle is the one which is most commonly known as PUREX raffinate. The other is from the medium-active cycle in which the uranium and plutonium are refined by a secondextractionwithtributyl phosphate.

Deep blue is the bulk ions, light blue is thefission products(group I is Rb/Cs) (group II is Sr/Ba) (group III is Y and thelanthanides), orange is thecorrosionproducts (from stainless steel pipework), green are the major actinides, violet are theminor actinidesand magenta is theneutron poison)

Currently PUREX raffinate is stored instainless steeltanks before beingconverted into glass.The first cycle PUREX raffinate is veryradioactive.It has almost all of thefission products,corrosionproducts such asiron/nickel,traces of uranium, plutonium and theminor actinides.

Pollution

The PUREX plant at theHanford Sitewas responsible for producing 'copious volumes of liquid wastes', resulting in the radioactive contamination of groundwater.^[12]

Greenpeacemeasurements inLa HagueandSellafieldindicated that radioactive pollutants are steadily released into the sea, and the air. Therefore, people living near these processing plants are exposed to higher radiation levels than the naturally occurringbackground radiation.According toGreenpeace,this additional radiation is small but not negligible.^[13]

History

The PUREX process was invented byHerbert H. AndersonandLarned B. Aspreyat theMetallurgical Laboratoryat theUniversity of Chicago,as part of theManhattan ProjectunderGlenn T. Seaborg;their patent "Solvent Extraction Process for Plutonium" filed in 1947,^[14]mentionstributyl phosphateas the major reactant which accomplishes the bulk of the chemical extraction.^[15]

List of nuclear reprocessing sites

La Hague site
Mayak
Thermal Oxide Reprocessing PlantandB205atSellafield
Tokai, Ibaraki
West Valley Reprocessing Plant
Savannah River Site
Hanford Site
Idaho Chemical Processing Plant, (nowIdaho National Laboratory)
Radiochemical Engineering Development Center,Oak Ridge National Laboratory

References and notes

^Greenwood, pp. 1255, 1261
^"Reprocessing plants, world-wide".European Nuclear Society.Archived fromthe originalon 22 June 2015.Retrieved29 July2008.
^An Evaluation of the Proliferation Resistant Characteristics of Light Water Reactor Fuel with the Potential for Recycle in the United States
^Is U.S. Reprocessing Worth The Risk?,Steve Fetter and Frank N. von Hippel, Arms Control Today, September 1, 2005.
^L.C. Walters (September 18, 1998)."Thirty years of fuels and materials information from EBR-II".Journal of Nuclear Materials.270(1): 39–48.Bibcode:1999JNuM..270...39W.doi:10.1016/S0022-3115(98)00760-0.
^[1]PUREX and PYRO are not the same, Hannum, Marsh, Stanford.
^Gregory Choppin;Jan-Olov Liljenzin;Jan Rydberg (2002).Radiochemistry and Nuclear Chemistry, Third Edition.p. 610.ISBN 978-0-7506-7463-8.
^Paiva, A. P.; Malik, P. (2004). "Recent advances on the chemistry of solvent extraction applied to the reprocessing of spent nuclear fuels and radioactive wastes".Journal of Radioanalytical and Nuclear Chemistry.261(2): 485–496.doi:10.1023/B:JRNC.0000034890.23325.b5.S2CID 94173845.
^Burns, J. H.; Brown, G. M.; Ryan, R. R. (1985). "Structure of dinitratodioxobis(triisobutyl phosphate)uranium(VI) at 139 K".Acta Crystallographica Section C Crystal Structure Communications.41(10): 1446–1448.Bibcode:1985AcCrC..41.1446B.doi:10.1107/S0108270185008125.
^J.H. Burns (1983). "Solvent-extraction complexes of the uranyl ion. 2. Crystal and molecular structures of catena-bis(.mu.-di-n-butyl phosphato-O,O')dioxouranium(VI) and bis(.mu.-di-n-butyl phosphato-O,O')bis[(nitrato)(tri-n-butylphosphine oxide)dioxouranium(VI)]".Inorganic Chemistry.22(8): 1174–1178.doi:10.1021/ic00150a006.
^Greenwood, Norman N.;Earnshaw, Alan (1997).Chemistry of the Elements(2nd ed.).Butterworth-Heinemann.p. 1261.ISBN 978-0-08-037941-8.
^Gerber, M.S. (February 2001)."History of Hanford Site Defense Production (Brief)"(PDF).Fluor Hanford/US DOE.Retrieved2009-10-01.
^"Greenpeace on La Hague (German version)".Retrieved2016-04-30.
^US patent 2924506,Anderson, Herbert H. and Asprey, Larned B. & Asprey, Larned B., "Solvent extraction process for plutonium", issued 1960-02-09
^P. Gary Eller; Bob Penneman & Bob Ryan (2005)."Pioneer actinide chemist Larned Asprey dies"(PDF).The Actinide Research Quarterly.Los Alamos National Laboratory. pp. 13–17. Archived fromthe original(PDF)on 2014-02-01.

External links

Processing of Used Nuclear Fuel Archived2007-02-04 at theWayback Machine,World Nuclear Association
Reactor-Grade Plutonium and Development of Nuclear Weapons,Analytical Center for Non-proliferation
PUREX Process, European Nuclear Society
Mixed Oxide Fuel (MOX)Archived2013-03-01 at theWayback Machine– World Nuclear Association
Disposal Options for Surplus Weapons-Usable Plutonium– Congressional Research Service Report for Congress
Brief History of Fuel Reprocessing

[1] Greenwood, pp. 1255, 1261

[EuroNuclear-2] "Reprocessing plants, world-wide".European Nuclear Society.Archived fromthe originalon 22 June 2015.Retrieved29 July2008.

[3] An Evaluation of the Proliferation Resistant Characteristics of Light Water Reactor Fuel with the Potential for Recycle in the United States

[4] Is U.S. Reprocessing Worth The Risk?,Steve Fetter and Frank N. von Hippel, Arms Control Today, September 1, 2005.

[5] L.C. Walters (September 18, 1998)."Thirty years of fuels and materials information from EBR-II".Journal of Nuclear Materials.270(1): 39–48.Bibcode:1999JNuM..270...39W.doi:10.1016/S0022-3115(98)00760-0.

[6] [1]PUREX and PYRO are not the same, Hannum, Marsh, Stanford.

[7] Gregory Choppin;Jan-Olov Liljenzin;Jan Rydberg (2002).Radiochemistry and Nuclear Chemistry, Third Edition.p. 610.ISBN 978-0-7506-7463-8.

[8] Paiva, A. P.; Malik, P. (2004). "Recent advances on the chemistry of solvent extraction applied to the reprocessing of spent nuclear fuels and radioactive wastes".Journal of Radioanalytical and Nuclear Chemistry.261(2): 485–496.doi:10.1023/B:JRNC.0000034890.23325.b5.S2CID 94173845.

[9] Burns, J. H.; Brown, G. M.; Ryan, R. R. (1985). "Structure of dinitratodioxobis(triisobutyl phosphate)uranium(VI) at 139 K".Acta Crystallographica Section C Crystal Structure Communications.41(10): 1446–1448.Bibcode:1985AcCrC..41.1446B.doi:10.1107/S0108270185008125.

[10] J.H. Burns (1983). "Solvent-extraction complexes of the uranyl ion. 2. Crystal and molecular structures of catena-bis(.mu.-di-n-butyl phosphato-O,O')dioxouranium(VI) and bis(.mu.-di-n-butyl phosphato-O,O')bis[(nitrato)(tri-n-butylphosphine oxide)dioxouranium(VI)]".Inorganic Chemistry.22(8): 1174–1178.doi:10.1021/ic00150a006.

[11] Greenwood, Norman N.;Earnshaw, Alan (1997).Chemistry of the Elements(2nd ed.).Butterworth-Heinemann.p. 1261.ISBN 978-0-08-037941-8.

[Gerber2001-12] Gerber, M.S. (February 2001)."History of Hanford Site Defense Production (Brief)"(PDF).Fluor Hanford/US DOE.Retrieved2009-10-01.

[13] "Greenpeace on La Hague (German version)".Retrieved2016-04-30.

[14] US patent 2924506,Anderson, Herbert H. and Asprey, Larned B. & Asprey, Larned B., "Solvent extraction process for plutonium", issued 1960-02-09

[15] P. Gary Eller; Bob Penneman & Bob Ryan (2005)."Pioneer actinide chemist Larned Asprey dies"(PDF).The Actinide Research Quarterly.Los Alamos National Laboratory. pp. 13–17. Archived fromthe original(PDF)on 2014-02-01.

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