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2018-Technetium as a point for Drawbacks in Nuclear Fuel Cycle

Lecture given at 3d European Summer SChool on Modern Energy

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2018-Technetium as a point for Drawbacks in Nuclear Fuel Cycle

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  1. The II Int. school for Advanced treatment of radioactive wastes, IPCE RAS, MOSCOW-2018Some general drawbacks in the treatment of radioactive wastes from spent nuclear fuel reprocessing K.E.German Russian Academy of Sciences A.N. Frumkin Institute of Physical Chemistry and Electrochemistry

  2. The main problems bonded to Tc … And its solutions based on the fundamental studies in IPCE RAS Development of separation technologies Attempts of application (corrosion, metallurgy, catalysts). Tc in Spent NF Discussion: Spent Fuel Storage, Separate long-term storage or Transmutation Improvements of separation technologies (SPIN-program (France), Adv.-ORIENT Cycle (Japan), PO Mayak- IPCRAS- Radium institute Russian program. Scientific International collaboration of IPCE RAS with USA, France Japan and Poland “Renaissance” of Transmutation program Plan of the presentation

  3. Our motivation for exploring Tc chemistry for the Closed Fuel Cycle • Tc-99 is a key dose contributor at HLW repositories if TRU elements are greatly reduced by recycling • long half-life of Tc (t1/2 = 2.14 x 105 years), • high mobility, and solubility under oxidizing conditions • Methods for managing the long-term threat of Tc to the environment • Stable waste form/repository system providing with strict limits for Tc release over a long period of time (~1 million years?). • Transmutation of radioactive Tc to stable Ru im nuclear rectors.

  4. Main problems of Tc • Tc is important item in Nuclear Industry • Tc redistribution in PUREX produces flows with long-lived high radioactive wastes • Tc interferes at U/Pu separation stage in PUREX process • Tc accumulation in High burn-up fuel together with Mo, Ru, Rh • Tc in nuclear waste vitrification: Tc-Mo-Ru metal phases, Tc(VII) volatility "In this article, "tons" refers to metric tons. 1

  5. High level solid Tc/Mo/NM wastes dissolution and vitrification Increasing burn-up in the SNF leads to lower oxidative potential – the metals like Mo, Tc, Ru forming mutual e-phase (white inclusions) that is insoluble in nitric acid – formation of HLSW. In vitrification of HLLW the same metals (Mo, Tc, Ru) are either volatile (oxic conditions) or forming metal e-phase dendrites (reducing conditions) that lead to several furnace problems (Rokkasho-mura vitrification ) Investigation of these phases by means of X-ray, diffraction, NMR, EXAFS and others could help us in handling them

  6. Another precipitating compound at SNF dissolution stage No Technetium Inside but Pu is VERY possible

  7. Experience and practice

  8. Experience and practice

  9. Experience and practice

  10. Some examples of Russian experience in PUREX improvement • The first cycle flowsheet of RT-1 plant is essentially similar to the THORP flowsheet but is distinguished by more reliable joint stripping of Pu, Np, and Tc due to fairly low acidity. • This is attained owing to introduction of a special cycle for separation of Pu and Np using large amounts of Fe(II); • As a result, there are serious problems with evaporation of the raffinate of Pu-Np purification cyces and with localization of Tc in the high-level waste. • [Zilberman, Radiochemistry 2008]

  11. Classical Purex processweak-acid Main problems : increasing burn-up leads to Important interference by Tc at 2 extractor

  12. Strong-acid mode of PUREX PROCESS • MAIN PROBLEM : • Interference by Tc at 2 extractor • Uranium Product is contaminated with Tc

  13. Russian reprocessing plant RT-1 , PUREX part Separation of U from Pu in extraction reprocessing of WWER-440 and BN-600 SNF on the RT-1 facility (PA «Mayak») using the reductive agent U(IV)+hydrazine, and the complexing agent (DTPA)

  14. Russian reprocessing plant (RT-1, PO MAYAK, Ozersk) • Main problem : • DTPA complexes precipitation (Tc/DPu) • Tc presents in all streams

  15. Technetium interfering role in the PUREX Pu/U separation stage Extract U,Pu, Np(Tc(STc1st extcyc =80 -90%)) Reducing agent + complexing agent • Difficulties in stability of U/Pu separation at UK, Russian and French facilities • Catalytic Tc effects in many chem. reactions • Variable Tc redox states • Tc - Waste problems • Tc-DTPA complex precipitation Reductive separation of U, Pu, Np (Tc) Back extract Pu, Np (Tc(IV)) Extract U (Tc(VII)) • Variable red-ox states • Variable species

  16. DTPA – Tc : EXAFS • Radiochemistry, 2011, Vol. 53, No. 2, pp. 178–185.

  17. DTPA – Tc : EXAFS • MODEL STRUCTURES of Tc-DTPA (K.German, A. Melentiev, et all Radiochemistry, 2010-2011) 7

  18. Formation of the 3rd phase is undesireble in PUREX but for complicated compositions sometimes occures - Тс-DTPA • K. German, A. Melentiev, 2012 and 2016

  19. French mode of PUREX Process (UP-3 RP, La Hague)

  20. Лит. данные по реакции Tc с N2H5+ Конечные хим. формы в реакции Тс(VII) c N2H5+согласно разным авторам варьируют от Tc(2+) до Tc(VII)= необходимы структ. и спектроскоп. данные

  21. Chemical species of Tc at the reducing separation U\Pu step

  22. Russian new design for RT-2 (GHK,Krasnoyarsk) Never finished…

  23. Prof. Zilberman and colleagues : SUPERPUREX (KHI, St-Petersburg/Gatchina)

  24. C(Np)=1,6*10-3 моль/л, С(Tc)=1,15*10-3 моль/л, C(HNO3)=1,67 моль/л, C0(N2H5NO3)=0,3 моль/л, t=450C,l=1 см Reducton of Np(V) by hydrazinein presence of Tc(VII) in 1.5 M HNO3 (Tc catalytic effect) Np (V) Tc Np (V)+Tc(VII) Gas evolut. Tc(IV)+Tc(X) Np (V) Np (IV) Np(IV) The end of the process Starting up

  25. Some important features of liquid waste problems and its actual or possible solutions feed reductor D E P U U P (U/Pu) . Pu

  26. Analysis of Tc in PUREX reprocessing (NRC-4)

  27. USA - Advanced Fuel Cycle Initiative • Goals of Advanced Fuel Cycle Initiative (AFCI) separations technology program of GNEP (accord. : • Preclude or significantly delay the need for a second geologic repository in this century • Reduce volume and cost of high-level waste • Separate TRU elements for fissioning in thermal or fast neutron-spectrum reactors • Reduce the proliferation risk of the fuel cycle • Facilitate Generation IV nuclear energy systems • Aqueous-based liquid-liquid extraction technology is baseline process because it is most mature - generic name for process variants: UREX+

  28. UREX+1a Process Outline U, Tc UREX • Chop/dissolve fuel in HNO3; U and Tc separated in UREX step - TBP • in hydrocarbon solvent • Cs/Sr extracted using • calix-crown and crown ether • in FPEX process • Transuranics and lanthanide • fission products extracted in • TRUEX step with CMPO, back- • extracted with DTPA/lactic acid • Transuranics and lanthanide • fission products separated • using TALSPEAK, di-2-ethyl- • hexylphosphoric acid extracts • lanthanides from actinides FPEX Cs, Sr Non-Ln FPs TRUEX Np, Pu, Am, Cm TALSPEAK Lanthanide FPs by G.Jarvinen and K.Czerwinski

  29. USA, Germany Boyd G., Cobble J., Parker G. C. Coleman et all (Oak Ridge, extraction with trilaurylamine) Rapp A.F. Davison S.A, Trop H., Cotton F.A. Schwochau K. Russia, Czechoslovakia V. Spitsyn, A. Kuzina, (extraction with acetone, ion exchange) V. Shvedov, Kotegov, later - G. Akopov, A. Krinitsyn (extraction, ion exchange) L. Zaitseva, V. Volk (crystallization and other) Arapova, Yu. Prokopchuk, G. Chepurkov (extraction, ion exchange) Macasek F., Kadrabova (Slovakia) Elaboration of separation methods and extensive fundamental studies (by 1957 – 1977)

  30. Industrial scale separation of Tc-99g Five main approaches were elaborated, each one has its advantages and disadvantages • Precipitation \ co-precipitation (USA, Russia) • Selective gas adsorption (USA, Kentucky) • Anion exchange (USA, Russia) • Adsorption at carbon (Japan) • Liquid-Liquid Extraction (USA, Russia, France, Japan)

  31. Separation of Tc from HAW of gas-diffusion plant in USA • Separation of Tc as TcF6 was made with MgF2 filters at 125oC in 1960 – 1963 from HAW of gas-diffusion plant in Kentucky, USA (Total = 25 kg Tc) Tomlinson, Judson, Zahn, ICPUAE,1964 • Back side : releases of Tc from decommissioned plant

  32. The reaction of the cascade relevant technetium fluorides with water • “ … A signifcant number of anecdotal reports of "pouring Tc" from cascade instrument lines exist. Observations of a finning, viscous brownish-red material with high beta activity suggests the presence of this acid, or perhaps a mixture of it, in low(er) temperature copper lines. HTcO, has a relatively low vaporpressure (61 torr at 100OC) at temperatures typical to the cascade, 21 and could also easily migrate as a gas phase compound” / D. W. Simmons. An Introduction to Technetium in the Gaseous Diffusion Cascades. Technical report K/TSO–39. Oak Ridge, Tennessee, USA - September 1996 /

  33. Development of ion-exchange technology for Tc separation in IPCE RAS (1971-1976) Prof. A.F. Kuzina (Tc Group leader till 1985 ) presents her Tc samples prepared in the Institute from the concentrate separated from radioactive wastes generated at Krasnoyarsk Reprocessing Plant to Glean SEABORG (1978)

  34. Separation of macro amounts of Tc-99g in USSR • 1 kg of Tc was converted to metal in hot cell of IPCE RAS and distributed among different Russian institutes • In 1971-1976 IPC RAS in collaboration with Krasnoyarsk Mining Enterprise has separated from HAW some kilograms of K99TcO4 • In 1983 -1986 collaboration of PO “Mayak”, IPCE RAS and Radium Institute resulted in elaboration of anion-exchange technology for Tc separation and 40 kg of K99TcO4. This work was awarded with the special Diploma of the Russian authorities • Anna KUZINA and Victor SPITSYN analyzing the sample of Tc metal

  35. Some new Tc(VII) compounds synthesised in IPCE RAS and NLVU for reprocessing of SNF

  36. New compounds (continued) Some other new interesting compounds have been made by K.Czerwinski and co-workers in 2007- 2013

  37. A few examples of new Tc compound structures made in IPCE RAS (K.German, M.Grigoriev, A.Maruk etc.) [Anil-H]TcO4 [GuH]ReO4 [Bu4N]TcO4 [Pr4N]TcO4 [(AnO2)2(MO4)4*3H2O]n , (An = U, Np; M = Tc, Re) [Tc2Ac4](TcO4)2 LiTcO4*3H2O

  38. Pyrochemical reprocessing of BN-1200 SNF (PRORYV project, Russia, 2020) • Tc behavior not well studied • Na2TcCl6 + Li2TcCl6 eutectic • Reducing cond.: e-phases • Oxidizing cond.: TcO3Cl, … • Nuclear Science Pyrochemical Separations Workshop Proceedings - Avignon, France - 14-16 March 2000 Published by : OECD Publishing Version: E-book (PDF Format)

  39. Nuclear Science Pyrochemical Separations Workshop Proceedings - Avignon, France - 14-16 March 2000 Published by : OECD • NaCl + LiCl eutectic • 450-650 oC, … Cl2, … O2 • Na2TcCl6 + Li2TcCl6 • CLUSTER Tc compounds: • Na3Tc2Cl8 ? • M2+xTc6Cl12+y ? Possible Tc species in pyrochemical reprocessing of spent nuclear fuel

  40. 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

  41. 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 was: Which components absorb Tc with Kd higher than 3 but/and are resistant to leaching?

  42. Sludge components as carriers for Tc(VII) and Tc(IV) TiO2 was also tested

  43. Experimental conditions for precipitation and leaching tests: Precipitation tests: • Wastes are alkaline • Tc is redox sensitive • Sharp differences in the redox potential within the tanks are observed, So, both: • oxidizing [Tc(VII)] • and reducing [Tc(IV)] • conditions were tested in 0.1- 5 N NaOH + 0-5 N NaOH. Leaching modes: • Surface leaching. • Complete dissolution. Leaching agents • all precipitates : 0.1N NaOH • aluminosilicates - NaHF2 • Na oxalate - 0.1N NaOH, NaNO2 • FeOOH - 0.1N NaOH, H2O2 • MnOOH - 0.1N NaOH, H2O2 • TiO2 - 0.1- 3N NaOH Methods: Liquid scintillation counting (LSC) of solutions, XRD, NMR, IR

  44. 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 NaOH leachant Tc leaching with H2O2 = 20 % and with Na2S2O8 =70-100%/100 days

  45. Tc & HLW Vitrification • Tc is volatilized at 750 – 850 oC under oxidizing conditions as • MTcO4 (M = Na, Cs)

  46. Transmutation target : Tc/Ru recovery • Tc-Ru acidic and pyrochemicalsolubilization problem

  47. Tc transmutation target The nascent metal can either conglomerate upon further heating to give stable compact metal samples or react with the gaseous decomposition products to produce Tc carbide, which is more stable under given conditions. The first process takes place at a high argon (or argon–6% hydrogen mixture) flow rate and moderate heating rates or when the samples contain 1–5% of occluded water serving to remove the gaseous decomposition products as aerosols. The second process takes place at low Ar flow rates, high heating rates, and in the thermolysis of preliminarily dehydrated samples. The exhaust contains CO2 , H2O, R3N, and some unidentified products; among solid decomposition products, Tc, Tc6C, TcO2, and C are identified. The thermolysis of almost all technetium compounds with tetraalkylammonium cations leads to the formation of technetium metal or Tc6C. Preparation of Technetium Metal for Transmutation into Ruthenium / V.Peretrukhin, S.Rovnyi, V. Ershov, K. German, A. Kozar / Russian Journal of Inorganic Chemistry, Vol. 47, No. 5, 2002, pp. 637–642.

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