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german-eco-tcIST2008

lecture on technetion in radioactive wastes and environmental

Konstantin4
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german-eco-tcIST2008

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  1. IST-2008 , Port-Elizabeth 7-10 Oct. 2008, South Africa recent advances in technetium environmentally focused studies Konstantin E. German

  2. 2008 – The Year of Tc • Plan of presentation • Tc in the environments – sources, history and modern trends. • Tc in acidic and basic HLW. • Different methods of Tc HLW treatment (insoluble residues, liquid wastes discharges, in-tank storage, vitrification, plants decommissioning, transmutation projects ) • Chemical species of Tc in waste and environment • Physico-chemical aspects of Tc (colloids and nanoparticles)

  3. Saying “Tc” here we mean Tc-99g • b-emitter(T½=2*105 y)accumulating with ~6% yield by U, Np or Pu fission = 0.8 – 1 kg/t-U • Tc concentration in reprocessing solutions~ 5-80 mg/L • Oxidation states: 0, +1, + 2, +2.5, +3, +4 , +5, +6, +7 • Insoluble e-phases = Tc metal alloys with Mo, Ru, Pd • Volatile as: • Tc2O7, HTcO4 at T>100oC • TcO2 and Tc-metal(T>350oC+O2); • MTcO4 for M = Na, K, Cs atT>600oC = vitrification? • In WATER : Extremely high migration rate : TcO4-

  4. Technetium in the environment in 1986, NEA_TDB –RARD in 1999 • An exceptional issue of “Technetium in the environment” in 1986 although made of independent parts was a complete presentation of all the pre-Chernobyl ideas and results : “Technetium in the Environment” (Proc. CEC-RPP – SERE CEA Seminar - Cadarache, 1984), Eds.: G. Desmet and C. Myttenaere, Elsevier Publishers, L&N-Y. (1986). • 13 years later an excellent review of NEA-TDB summed up the chemical thermodynamics of Tc : Rard J.A., Rand M.H., Anderegg G., Wanner H., Chemical thermodynamic of technetium. Eds. Sandino Amalia M., Osthols E. NEA (1999) Elsiever Publ. Amsterdam. • Time passed being characterized with the controversy of nuclear industry present and future status, drastic for Tc-99 originating mostly as the uranium fission product. • The definite stop in nuclear development would fix Tc further accumulation but now is clearly not the case and we appreciate the authors were continuing efforts in Tc environmentally focused sciences. • This report is devoted to some principal results of my laboratory with some others mentioned when necessary.

  5. Technogenic sources of Tc to the environments • Tc present on Earth • From U and Th spontaneous fission = 50 kg • From Mo(n,g)Mo99(b)Tc99 reaction s = 50 kg • Accumulation of 99Тс in nuclear industry  2.5 g/d / 100 MWin NPP reactors = 8.5 ton/year Discharge sources of Tc : • Explosions in atmosphere 140 TBq (Tera=1012) = 220kgChernobyl accident = 82 kg • NPP 1МBq /year 1000 МWt (electr.), i.е. : • In2007release from NPP was 400 МBq Тс = 200g • Reprocessing plants 10% of NuFuCy • 1952-1986 : = 2000kg Тс • Enrichment U (oper. with recycl. U):90%  4.1010Bk Тс/y= 4,5 kg-Tc/y • 3-5 time rise in Tc discharges on decommissioning

  6. Dilution in natural waters (only two isotopes b-3H and99Tc) (UK, Russia -historic) Underground injection HLW, MLW (Tomsk, Krasnoyarsk, Dimitrovgrad) Tank farms storage (military wastes, historic wastes) Vitrification of historic wastes, vitrification of raffinates Metal forms New venture forms Separation and storage Separation ant transmutation Different approaches to handling the Tc-radwastes

  7. The 1995-2005 years were Тс marked by severe confrontation of Norwegian “greens” with Sellafield authorities for B205-MAGNOXdischarges into the Irish sea - 180 kg-Тс/year Тс-to-sea standard for Sellafield ( B205 + EARP-B211 + THORP ) • 1995-2000 - 200 ТBq-Тс • 2000-2003 - 90 ТBk-Тс • TPPBr- April 23-24 - 2003 EARP B211 = 10 HLW tanks 1050 cub. m each : 5 tanks for“MAC” 2 tanks– sludge 2 tanks - THORP 1 – empty in 2003

  8. Pollution of the North sea, caused by Sellafield, UK) Тс content In the samples collected in 1999 - 2001 • water = 0.01- 0.07 Bq/L • algae = 510 Bq/kg ( ! ) • lobsters = 33 - 42 Bq/kg ( ! ) (acc. to Bellona, Norvege) Risks of refused distribution of Norvege sea-foods

  9. Tc discharges in 2002-2005 The sum of total-beta activity (excluding tritium) from all nuclear installations has fallen significantly over thepast 15 years. Total emissions are dominated by discharges from the nuclear fuel plant at Springfields andto a lesser extent the reprocessing plant at Sellafield. The two installations together contribute approximately98 % of the overall discharges. The high, but decreasing total-beta discharges from Sellafield are mainlyattributable to the radionuclide Technetium-99. The reduction of Sellafield’s total-beta discharges from 2002to 2005 is a result of the significant reduction in Technetium-99 discharges, due to the vitrification process,since 1994 for oxide fuels and 2003, for magnox fuels. Discharge of Tc-99 to sea (primarily from treatment ofstored Magnox wastes) has been reduced between 1994 and 2005. The total beta discharges from Sellafield(2002: 112 TBq, 2003: 83 TBq, 2004: 73 TBq, 2005: 43 TBq) were previously mainly attributable to theradionuclide Technetium-99 (2002: 85 TBq, 2003: 37 TBq, 2004 14 TBq, 2005: 6,7 TBq ), for whichabatement technology was installed in 2004. The reduction of Sellafield’s total beta discharges in 2005 isdue to the reduction of Technetium-99 (2004 14 TBq, 2005: 6,7 TBq),

  10. Tc releases in Europe Mayak Karachay lake VVER 3*10-2 • For other European facilities the annual Tc release is negligible, no Tc was detected in Baltic sea due to Chernobyl accident (Holm, Aarkrog, 1990-91)

  11. Tc behavior during the underground HLW storage • Pretreatment : рН + complexones + . . . (contradictory demands : criticity risks - migration ) • Injection into the sandy levels – collectors • Migration control • Tc sorption at the minerals and rocks was studied before • Main conclusions • Тс(VII) has high migration mobility • Тс(IV) may form both immobile TcO2 and mobile complexes clay Guerman K.E., Kosareva I.M., Peretroukhin V.F., Savushkina M.K., Egorov N.N., Kudryavtsev E., Revenko Yu.A. ICEM'95. V.1. Cross-cutting Issues and management of high-level waste and spent fuel. (Eds.: S.Slate, Feizollahi, C.Creer), NY, 1995, p. 713 – 722 .

  12. Tc speciation in simulated radioactive wastes conditionned for the underground injections (1980-88, 1994, 2000) • TcO4- - is highly migrative • Radiolyses in presence of organic components lead to the reduction of Тс(VII) to Tc(V, IV, III) • Acetate complexes Тс(V, IV, III) exist but the data are scattered and the structure not systematically studied • Acetate complexes of Тс(III) could co-exist withTc(VII) . EXAFS ROBL_ESRF

  13. Russians experience of Tc separation and conversion (decl. avail. for CEA France 1994-1997) Spitsyn V.I., Kuzina A.F., ProkopchukYu. Z., ChepurkovG.Ya. , German K.E., Oblova A.A.,Kryuchcov S.V. Preparation of technetium metal by thermal decomposition oftetrabutylammoniumpertechnetate in inert gas atmosphere. Report IPCAS, N-P-2907, 1983. Spitsyn V.I., Kuzina A.F., ProkopchukYu.Z., ChepurkovG.Ya., German K.E., Oblova A.A., Kryuchcov S.V., Dzekun E.G., Sokhina L.P. Precipitation technology for technetium separationfrom radioactive wastes. Report Mayak/IPCAS- 1984. Spitsyn V.I., Kuzina A.F., ProkopchukYu.Z., ChepurkovG.Ya., German K.E., Oblova A.A.,Kryuchcov S.V., Tzarenko A.F., Akopov G.A., Krinitsyn A., Kapitonov V.I., GalkinA.,Maksimenko A., Berezuk N., Mezentsev V.I. Technology of technetium recovery from radwastes.ReportMayak /IPCAS/ Khlopin Radievy.Inst.,1985, N P-3171. 32 p. Spitsyn V.I., Kuzina A.F., ProkopchukYu.Z., ChepurkovG.Ya., Guerman K.E., OblovaA.A.,Kryuchcov S.V., Kapitonov V.I., Mezentsev V.I. Improuvment of anion exchange technetiumrecovery from radwastes using TBP as eluent. Report Mayak -IPC AS. 1985, N P-3066 , 82 P. German K.E., Kuzina A.F., Spitsyn V.I. Patent: Method of technetium carbide preparation. USSR. Patent No 1258016, 1986.2

  14. Russian approach to Tc separation in PUREX included (1980-1986): extraction at the first extraction stage, back extraction at the U-Pu separation stage, anion-exchange separation at QuatPhosBase AER, purification at VP-1AP-AER, denitrification with formic acid or H2O-SH, precipitation of KTcO4 or R4NTcO4 and its conversion to metal Tc • Conversion to metal: • Search for the conditions ( Ar-6%H2, gaz product evaquation, • Products - volatile and solid, • Russ. Inorg. Chem-2002 -47-No5 p[(C4H9)4N]OH (aqueouse)[(C4H9)4NOH]p(aqueouse) (8) [(C4H9)4N]+ (aqueouse) + TcO4- (aqueouse)  [(C4H9)4N]TcO4 (solide) (9) [(C4H9)4NOH]p (aqueouse) + TcO4-(aqueouse) [(C4H9)4NOH]p-1TcO4 (aqueouse) + OH- (10) HTcO4 H+ +TcO4- (TcKa) TcKa/( TcKa + [H+]) = [TcO4-] /([TcO4-]+ [HTcO4]) = [TcO4-] /[Tc]tot The TcKa was found equl to 4.02 M which is in very good agreement with [1]] [i] 1 - Ashley K.R., Ball J. R. Solv. Extr. Ion Exchange, 1994, 12(2), p.239-259.

  15. Co-precipitation of Tc(VII) with Bu4NReO4from 100 ml 1.0 M NaOH, [ TcO4-] = 5*10-4 M, [ Bu4N+] = 0.005 - 0.02 M, reagent = 0.1M NH4ReO4 DV= +3%

  16. Eh-pH Pourbaix diagram for Tc • The solubility of Tc(IV) remains independent of pH until around 13.5, when a small increase can be seen which continues to increase linearly with pH. • Modelling suggests that this increase occurs as the species TcO(OH)3− is formed. The formation constant was estimated with data from this study and was found to be logK2=−21.6±0.3. • Authors: Peter Warwick | S. Aldridge | Nick Evans | Sarah Vines - Rad. Acta 2007 TcO(OH)3− E. Breynaert, D. Dom, J. Vancluysen,A. Maes 2007-8 Tc(OH)4(H2O)2 and

  17. Tc oxides & hydroxides Tc2O5- decomposition of Tc2O5*nH2O at 100oC Tc2O5*nH2O – gamma in NaOH + i-BuOH Tc4O5*14H2O hydrolisis of K3Tc2Cl8 Tc4O5 - thermolisis of Tc4O5*14H2O • Mazzi,1974 - Tc2O3 InorganicaChimicaActa, Volume 9, 1974, Pages 263-268 G. A. Mazzocchin, F. Magno, U. Mazzi, R. Portanova Possible fractional reduction of polymers Preparation and Characterization of Phosphine Complexes of Technetium Possessing a Metal-Metal Bond Order of 3.5. F. A. Cotton, S.C. Haefner and A. P. Sattelberger Inorg. Chem. 1996, 35, 1831. Haefner - Sattelberger [Mo3O4(DMF)9]4+

  18. No stable Tc silicates were found before – but now we know about Tc sodalite although losing in structure stability to cancrinite in presence of common nitrate Pertechnetates are volatile at temp.> 600oC Reduced Tc valence forms – Tc(IV) no interaction with silicates Tc(0) no interaction with silicates both volatilize in air at 350 oC Tc separation before HAW vitrification is preferable Tc under HAW vitrification conditions

  19. Methods for Tc separation from alkaline and neutral solutions • Not a problem compared to acidic, quite efficient are several methods used in Russia in 1980-85 - Not easy when Tc species is different from Tc(VII)(Schroeder, 1996 - Hanford: treatment with S2O8 etc. • EXTRACTION Ketones : Aceton, Methyl-ethyl-ketone,) ТPPBr/ТPAsBr/CCl4 Polyglicoles • Chromatography QuatPhosBase(KHL-Rad-Inst) +VP-1АP(IPCERAS) (= RAILEX) for technology HPLC - DIONEX-AS11 (for anallyt separation from MoO4/I/Br/ClO4/TcO4) solidexTPPBr (developed for HLWB205-MAGNOX)

  20. The SRS waste volumes (Table 2.4 of "Integrated Database Report - 1993: S.Spent Fuel and Radioactive Waste Inventories, Projections, and Characteristics,”] Tc-99 quantities (Table 2.11), and Tc-99 concentrations calculated from these data Volume, Tc-99, Ci [Tc-99], [Tc], 106 Kd litersCi/liter g/liter total Liquid 61.4 1.68E+04 2.74E-03 0.162 - Sludge 13.9 1.14E+04 8.20E-03 0.483 3 Salt Cake 53.8 2.78E+03 5.17E-04 0.0305 0.2 Overall waste 129.1 3.098E+04 2.40E-03 0.141 - Question to be answered : Which components absorb Tc with Kd higher than 3 and are resistant to leaching?

  21. 99Tc concentrations found in various tank sludgesat SRS The discovery of relatively high 99Tc concentrations in inorganic mineral sludge heels taken from some tanks at the US-DOE Savannah River Site (SRS) has prompted investigations of Tc uptake from alkaline highly active waste (HAW) by solid adsorbents

  22. Sludgecomponentsascarriersfor Tc(VII) and Tc(IV) TiO2 was also tested

  23. Study of Tc uptake with Aluminosilicates under oxidizing conditions at 70-130oC • Literature data have demonstrated the possibility of ClO4- and MnO4- co-crystallisaton with aluminosilicates : purple Na8[AlSiO4]6(MnO4)2 (Weller,1999 etc.) OUR EXPERIMENTS on TcO4- (reaction: NaAlO2+Na2SiO3+NaOH) • TcO4- is too large and therefore it is excluded from the aluminosilicate structure in both cancrinite and sodalite

  24. [Tc] = 0.2 M in NaNO3 solutions - cancrinite in NaNO3-free solutions - sodalite Although NMR spectrum presented shift typical for coordinated Tc(VII) its concentration is very low Dissolution in NaHF2 and LSC has shown : [Tc] in solid cancrinite was 57 mg/kg ~ 100 times less than in initial solution Tc is excluded from the aluminosilicate structure of cancrinite Case of Aluminosilicates formed in concentrated Tc(VII) solution

  25. Precipitation of cancrinite Leaching conditions: NaOH M Tc yield, % Leaching agent: T, oC Leaching yield , Tc, % 3 hour 1 day 10 days 2.0 18.9 1M NaOH 20 0.8 1 3.7 4.0 32 2M NaOH 20 0.8 1.2 2.0 2.0 25.2 0.1M NaOH + 0.25 M H2O2 60 25 26.9 27 2.0 18.9 0.1M NaOH + 0.5 H2O2 18 4 6.9 7 4.0 32 0.1M NaOH + 0.5 H2O2 18 6.5 6.9 11 Study of Tc uptake with Aluminosilicates (AS)under reducing conditions (0.2M N2H5Cl, 1M NaNO3, T = 800С, t = 3 d) • Under reducing conditions Tc uptake by AS is important • Tc(IV) in AS is resistant to leaching due to occlusion

  26. Tc(VII) was sorbed by TiO2 from neutral solution with Kd = 30 ml/g. However, the Kd at pH=10 was only 3.3 ml/g No affinity to Tc(VII) was noted for TiO2 at pH=12 and higher. Among the minerals tested for Tc(VII) uptake, high-density TiO2 was the most efficient Study of Tc(VII) sorption by crystalline TiO2under oxidizing conditions MST and Silicotitanates not tested yet..?

  27. Study of Tc uptake withNaoxalateunderoxidizing and reducingconditions NaOH + H2C2O4 = Na2C2O4 X-ray diffraction tests : the precipitate is sodium oxalate Na2C2O4 (PDF#20-1149) • Tc(VII) is excluded from the Na oxalate structure under oxidizing conditions (Kd = 1-2) • Under reducing conditions Tc(IV) forms a separate TcO2*1.6H2O phase - no interaction between Tc hydroxide and Na oxalate were detected • Tc precipitate is not resistant to leaching with 0.1 N NaNO2

  28. Reduced Tc : 17-35% of Tc(IV) as TcCl62- is co-precipitated with cryolite N2H5NO3 inhibits co-precipitation Oxidizing conditions: Kd is less 1 Tc(VII) is excluded from cryolite structure Study of Tc uptake withCryolite Na3AlF6underoxidizing and reducingconditions 6F-+NaAlO2+Na2CO3 X-ray diffraction tests : the precipitate is cryolite Na3AlF6

  29. No [NH4F] initial,M [Na2CO3] in final solution, M [N2H5NO3], in final solution, M Tc(IV) uptake, % 1 2 3 4 5 8 9 10 2,0 2.5 3.0 4,0 6,0 2,0 2,0 2,0 0,6 0.6 0,6 0.6 0,6 0,4 0,8 0,6 - - - - - - - 0,1 20 23 26 28 35 25 17 0 Study of Tc(IV) uptake with Cryolite Na3AlF6under reducing conditions • Tc(IV) is added as Na2TcCl6 to (NH4F+NaAlO2) solution • No additional reducing agent in exp. No 1-9 • Leaching test were impossible to quantify relative to real cryolite in tanks as complete peptization occurred.

  30. Study of Tc(IV) uptake with FeOOH under reducing conditions • Reducing agent: 0.02M FeSO4, T = 600С, time = 3 h • Precipitate : FeOOH/Fe2O3 ThoughTc adsorbed better on iron hydroxides from 0.5–2.0 M NaOH than from 3.0-4.0 M NaOH, the precipitates formed at lower NaOH concentration were more easily leached by the NaOHleachant Tc leaching with H2O2 was 20 % and with Na2S2O8 was70-100% in 100 days

  31. Study of Tc(IV) uptake with MnOOH under reducing conditions • Reaction NaOH + Na2MnO4+ N2H5OH= MnOOH X-ray diffraction tests : the freshly precipitated solid was Mn2O3 , the aged precipitate was manganite MnOOH (PDF#18-805) MnOOH precipitation MnOOH leaching to 0.1 NaOH (1,3,4) and Na2S2O8(2) • Manganese(III) oxides were effective Tc carriers and underwent chemical transformations on ageing that increased leaching resistanceto most agents.

  32. Boehmite sorbs perrhenate and pertechnetate By Peng-Chu Zhang*, James L. Krumhansl and Patrick V. Brady Sandia National Laboratories, Albuquerque, USA Radiochim. Acta 88, 3692373 (2000) • Al(OH)3 - Aluminum hydroxide - gibbsite ; • Boehmite [AlO(OH)] -aluminum oxyhydroxide • Al2O3 aluminum oxide - corund Boehmite and Al-oxyhydroxide gels sorb ReO4a non-radioactive analogue of TcO4 from NaNO3 solutions.Sorption appears to be substantially electrostatic (though thereappears to be a specific preference for ReO4 over NO3andis most effective at pH = 8. Measured Kd’s lie between 5 and105 ml g-1, depending on the solid, pH, and ionic strength.ReO4 and TcO4 are both partially removed from high pHHanford-type acid waste simulants upon neutralization and formationof Al-rich sludges. It was proposed that sequestrationof Tc by boehmite limits dissolved Tc levels in the nearand sub-surface environment and for that purpose boehmitemight be relied on as a backfill, or reactive barrier, to limitenvironmental transport of Tc. How Mo-Tc generators could do work being made of Al oxide - oxyhydroxide ???

  33. Tc(VII) + S2- • Induction period of the reaction of pertechnetate with Na2S varies from 4 to 100 minutes dependingontheconcentration of reagents, pH and T • Reaction of pertechnetate with Na2S is completedwithinonetotenhoursdependingontheconcentration of reagents • Reaction isfastifcomparedtoslow Tc2S7(TcS3,33) sedimentation (undermostconditions) duetocolloidformation • David Shuh, Wayne Lukens, Carol Burns, Final report on Project Number: EMSP-73778, 2004 :

  34. Separationof Tc2S7colloidesfrom Na2SsolutionbyMicrofilterfuge (RAININ Instr. Co) with ultrafiltrationmembranes- 30000 NMWL Sedimentation of colloides Tc2S7 • Formationofcolloides Tc2S7 is completedin 50 hoursunder these conditions • [Tc] in the solutionsat times from 50 to 150 hourscorresponds to true solubility of Tc2S7 [Na2S] [Na2S]

  35. The reduction of Tc(VII) to Tc(V,IV,III ) by abiotic and biotic processes • The reduction of Tc(VII) to Tc(IV) by abiotic and biotic processes has recently been the subject of extensive studies because it has a significant effect on the mobility of technetium in waste streams, vadose zones, sediments, and groundwater. These reaction processes are the basis for certain remediationtechnologies such as permeable barriers composed of zero-valent iron particles (i.e., as metallic iron) or sodium-dithionite reduced soils, which are being tested for immobilization of groundwater contaminants.

  36. Transmutation target : Tc/Ru recovery • Tc-Ru acidic and pyrochemicalsolubilization problem N. Schroeder approach : homogeneous transmutation

  37. Microbial reduction of Tc(VII) • Microbial reduction of Tc(VII) has been suggested as a potential mechanism for removing technetium from contaminated groundwaters and waste streams (e.g., Lovley 1993, 1995, Lyalikova,German et all. 1994). • Certain dissimilatory metal reducing bacteria and sulfate reducing bacteria have been determined to be capable of coupling the oxidation of organic carbon or hydrogen to the reduction of Tc(VII) to Tc(IV) • Lyakikova,German,Khizhnyak , Peretrukhin 1994 , 1998, • Gavrilov, German et all. 2007 , • Lloyd and Macaskie 1996; • Lloyd et al. 1997, 1998, 1999, 2000a,b; • Wildung et al. 2000; • Fredrickson et al. 2000).

  38. Reduction of pertechnetate by haloalkaliphilic strains of HalomonasTatiana Khijniak*, Natalia Medvedeva-Lyalikova, Monique SimonoffMicrobiology Ecology – 2003/44 • It was shown by Khizhniak , 2003 that haloalkaliphilic bacteria, isolated from soda-lake environments were capable of reducing Tc(VII)O4− to the Tc(V), Tc(IV) and Tc(III) at pH 10 in carbonate medium, whereas no reduction took place without bacteria or in the presence of dead biomass. • After 34 h of incubation, 55% remained as Tc(VII), 36% was found as Tc(IV) and 8% as Tc(V) and after 2 months 80% of the technetium was reduced. • Technetium had a toxic effect on bacteria. Reduction of TcO4− was drastically decreased at concentration above 1.5 mM. • The microbial reduction has been suggested as a potential mechanism for the removal of Tc from contaminated environments or waste streams. • Thermophilic : fresh water crenarchaeonPyrobaculumislandicum(Kashefi and Lovley 2000) , • Last year we demonstrated that thermophilic representatives of both prokaryotic domains—Bacteria and Archaea, inhabiting marine and freshwater hydrothermal • environments, possess the capacity for Tc reduction

  39. Characterization of technetium(VII) reduction by cellsuspensions of thermophilic bacteria and archaeaN. Chernyh , S. Gavrilov, V. Sorokin & K. German …Appl Microbiol Biotechnol (2007) 76:467–472 Washed cell suspensions of the anaerobic hyperthermophilic archaea Thermococcus pacificus (a) and Thermoproteusuzoniensis (b) (both at 85oC ) and the anaerobic thermophilic gram-positive bacteria Thermoterrabacterium ferrireducens ( c , at 65oC ) and Tepidibacter thalassicus (d, at 50oC ) reduced technetium [99Tc(VII)], supplied as soluble pertechnetate with molecular hydrogen as an electron donor, forming highly insoluble Tc(IV)-containing grayish-black precipitate.

  40. Thank you for your Attention !

  41. Masataka Ogawa (1865 - 1930)

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