InvestigationintotheRadiolysisofPUREXSolventSystems

GregoryP.Horne

ClintA.Sharrad andSimonM.Pimblott

ColinR.Gregson,HowardE.Sims,andRobinJ.Taylor.

ThePUREXProcessandRadiation

• ThePUREXsolventsystemisexposedtoamulti‐componentradiationfield;γ‐rays,α‐particles,β‐particles,neutrons,andfissionfragments.

• Nitrousacid(HNO2)isakeydegradationproductasitiscapableofalertingthePUREXsolventsystemsphysicalandchemicalproperties.

• Choppin,G.,Liljenzin,J.,andRydberg,J.,RadiochemistryandNuclearChemistry3rdEdition,ButterworthHeinemann,2002.• Moyer,B,A.,IonExchangeandSolventExtractionaSeriesofAdvancesVolume19,CRCPress,2010.• Schulz,W.W.,andNavratil,J.D.,ScienceandTechnologyofTributyl PhosphateVolume1,CRCPress, 1984.• Schulz,W.W.,andNavratil,J.D.,ScienceandTechnologyofTributyl PhosphateVolume2,CRCPress, 1987.• SchulzW.W.,Burger,L.L.,andNavratil,J.D.,ScienceandTechnologyofTributyl PhosphateVolume3,CRCPress, 1990.

ResearchAims

Provide a fundamental radiolytic foundation for the radiolysis of thePUREX solvent system, with regards to the radiolytic yield of HNO2 as afunction of:

• RadiationQuality– Gammarays– Protonbeams– AlphaparticlesfromPuandAmdecay

• AbsorbedDose– 100Gy to1600Gy

• SolventSystemFormulation

– NaNO3(aq) andHNO3(aq)– NaNO3/HNO3:dodecane– NaNO3/HNO3:30%TBP‐dodecane

RadiationSources60Co– GammaRadiolysis

• Foss Therapy Services Model‐812 Cobalt‐60 Self‐Contained Irradiator Unit,delivering γ‐rays with an average energy of 1.25 MeV.

• Dose rates of ~88 Gy min‐1.

MAGNOXPu– AlphaRadiolysis• LegacyreprocessedPufromMAGNOXreactorfuel.• Mixedisotopics – 238Pu,239Pu,240Pu,241Pu,242Pu,and241Am.• Pu‐HNO3 solutioninitialactivityof~1.2x107 MeVs‐1,whichequatestoadoserateof~33.5Gy day‐1.

ESAAm– AlphaRadiolysis• FreshlyseparatedAmfrom18yroldMAGNOXPu,bytheESAproject.• Isotopicpurityis~100%241Am,chemicalpurityis99.58%.• Am‐HNO3 solution,possessinganinitialactivityof~1.2x107 MeVs‐1,whichequatestoadoserateof~33.5Gy day‐1.

• Shinn,M.B.,Industr.Engng.Chem.Anal.Ed.,1941,13,33‐35.• Kershaw,N.F.,andChamberlin,N.S.,Industr.Engng.Chem.Anal.Ed.,1942,14,312‐313.• Bendschneider,K.,andRobinson,R.J.,TheUniversityofWashingtonOceanographicLaboratoriesTechnicalReportNo.8,1952.

TheShinnMethod

+HNO2

+

γ andα RadiolysisofAeratedHNO3Solutions

HNO3 HNO3

γ α

[HNO2]asaFunctionofDosein0.1MHNO3

IndirectRadiationEffects

NO3¯+eaq¯→→HNO2NO3¯+epre¯→→ HNO2NO3‾+H→→HNO2

DirectRadiationEffects

NO3¯⇝ NO3¯*→NO2¯+O

HNO3⇝HNO3*→HNO2 +O

[HNO2]asaFunctionofDosein0.1MHNO3

SecondaryRadiationInducedProcesses

NO32¯+OH→NO3¯+OH‐

NO2 +OH→HONO2

HNO2 +OH→NO2 +H2O

NO2¯+OH→NO2 +OH‐

HNO2 +H2O2→HOONO+H2O

LinearEnergyTransferEffects

• Spinks,J.W.T.,Woods,R.J.,AnIntroductiontoRadiationChemistry,JohnWiley&Sons,1963.• Savel’ev,Y.I.,Ershova,Z.V.,andVladimirova,M.V.,Sov.Radiochim.,1967,9,225‐230.• Kazanjian,A.R.,Miner,F.J.,Brown,A.K.,Hagan,P.G.,andBerry,J.W.,Trans.FaradaySoc., 1970,66,2192‐2198.

• Radiolytic yields of radicals decrease with increasing LET.

• HNO2 is essentially formed from radical precursors (eaq¯ and H), and thus its

radiolytic yield can be expected to be lower for high LET radiation.

Reference(Source) G(HNO2)

Thiswork(Pu) ≤0.43

Thiswork (Am) 0

Savel’ev etal (Po) 0

[HNO2]asaFunctionofDosein0.1MHNO3

RadiationChemistry

IncreasingLETdecreases

radiolyticyieldofHNO2.

• The Pu oxidation state equilibrium:

K =

= 3.2 in 0.1 M HNO3

• Pu(IV) possesses a disproportionation:

3Pu4+ + 2H2O⇌ 2Pu3+ + PuO22+ + 4H+

• Reactions with H2O2:2Pu4+ + 2H2O2→ 2Pu3+ + 2H2O + O2

2PuO22+ + 2H2O2→ 2PuO2+ + 2H2O + O2

• HNO2 oxidises Pu(III) to Pu(IV):HNO2 +H+ +NO3¯→2NO2 +H2O

2NO2⇌N2O4Pu3+ +N2O4→Pu4+ +NO2¯+NO2

PlutoniumRedoxChemistry

• Wick,O.J.,PlutoniumHandbook‐ AGuidetotheTechnologyVolumes1and2,AmericanNuclearSociety,1980.

• Artyukhin,P.I.,Medvedovskii,andGel’man,A.D.,Russ.J.Inorg.Chem.,1959,4,596.

• Dukes,E.K.,J.Am.Chem.Soc.,1960,82,9‐13.• Koltunov,V.S.,andMarchenko,V.I.,Sov.Radiochem.,1973,15,787.

• Vladimirova,M.V.,J.AlloyComp.,1998,271‐271,723‐727.• Schulz,W.W.,andNavratil,J.D.,ScienceandTechnologyofTributylPhosphateVolume1,CRCPress, 1984.

• SchulzW.W.,Burger,L.L.,andNavratil,J.D.,ScienceandTechnologyofTributyl PhosphateVolume3,CRCPress, 1990.

[HNO2]asaFunctionofDosein0.1MHNO3

RadiationChemistry

IncreasingLETdecreases

radiolyticyieldofHNO2.

RedoxChemistry

Plutoniumoxidationstates

competewithbulk

homogeneousprocessesfor

HNO2 anditsprecursors.

[HNO2]asaFunctionofDosein1MHNO3

[HNO2]asaFunctionofDosein6 MHNO3

DaughterNuclideRecoilEnergy??

• Spinks,J.W.T.,Woods,R.J.,AnIntroductiontoRadiationChemistry,JohnWiley&Sons,1963.• Savel’ev,Y.I.,Ershova,Z.V.,andVladimirova,M.V.,Sov.Radiochim.,1967,9,225‐230.• Kazanjian,A.R.,Miner,F.J.,Brown,A.K.,Hagan,P.G.,andBerry,J.W.,Trans.FaradaySoc., 1970,66,2192‐2198.

• Average recoil energy for Pu and Am Average daughter nuclei is ~89 keV; a

magnitude in considerable excess of that required to break chemical bonds.

• The maximum energy a heavy charge particle may transfer (Qmax) in a single

energy transfer event is described by the following equation:

Qmax =

2 2

Qmax (Energytransfertoorbitale¯)~0.82eV

Qmax (EnergytransfertoHnucleus)~1.49keV

Qmax (EnergytransfertoNnucleus)~18.7keV

Qmax (EnergytransfertoOnucleus)~21.1keV

PreliminaryConclusions

• The radiolytic yield of HNO2 is very much dependent upon radiationquality and the chemical properties of the radionuclides inducingradiolysis.

• Important to understand both the radiation chemistry AND theinherent chemical properties of the radionuclides/elements involved,and the interplay between all of the solvent system components.

• http://periodictable.com/Samples/094.3/s13.JPG

Acknowledgements