Radiochemical analysis of 41 Ca, 90 Sr, 129 I and 36 Cl in waste samples

Transcription

1 Radiochemical analysis of 41 Ca, 90 Sr, 129 I and 36 Cl in waste samples Xiaolin Hou Risø National Laboratory for Sustainable Energy, Technical University of Denmark

2 Main Radionuclides in the nuclear waste and used materials in the view of measurement Gamma radionuclides 60 Co, 133 Ba, 137 Cs, 134 Cs, 106 Ru, 152,154, 155 Eu, 58 Co, 54 Mn, 59 Fe, 110m Ag, 94 Nb. Beta Emitter 3 H, 14 C, 36 Cl, 41 Ca, 55 Fe, 63, 59 Ni, 93 Zr, 93 Mo, 90 Sr, 99 Tc, 129 I. Alpha emitter (transuanics) Pu, 241 Am, 243,244 Cm, 237 Np

3 Waste samples and the relevant critical radionuclides for decommissioning Graphite (reactor) 3 H, 14 C, 55 Fe, 63, 59 Ni, 60 Co, 152 Eu Concrete (normal or heavy) 41 Ca, 60 Co, 55 Fe, 63, 59 Ni, 133 Ba, 152 Eu Steel/stainless steel 55 Fe, 63, 59 Ni, 36 Cl, 93 Zr, 93 Mo, 94 Nb, 60 Co, 152 Eu, transuranics Aluminium 60 Co, 63 Ni, 55 Fe, 36 Cl Lead, 60 Co, 63 Ni, 55 Fe Water 3 H, 14 C, 63 Ni, 99 Tc, 129 I, 90 Sr, 60 Co, 137 Cs, transuranics Ion exchange resin 55 Fe, 63,59 Ni, 14 C, 99 Tc, 36 Cl, 93 Zr, 93 Mo, 94 Nb 90 Sr, 129 I, 137 Cs, 60 Co, 135 Cs, transuranics

4 Nuclide 41 Ca in the concrete Activation products of calcium isotopes Target isotope Aboundance % Reaction Cross section, bar Half life Decay 41 Ca Ca(n, γ) 41 Ca y EC 45 Ca Ca(n, γ) 45 Ca d β- 47 Ca Ca(n, γ) 47 Ca d β, γ 49 Ca Ca(n, γ) 49 Ca min. β, γ 41 Ca (21.03x10 5 y) EC (421.4 kev, 100%) 41 K (stable) Energy of X-rays and Auger electrons : kev Determination: X-ray spectrometry (<0.08%) LSC (10-20%)

5 Sr & Ca: Alkline earth element

6 Determination 41 Ca in concrete Separation fro matrix Decomposition of heavy concrete by alkali fussion Leaching Ca by acids Separation from active metals such as 60 Co, 152 Eu, 55 Fe, 63 Ni, 65 Zn, 54 Mn, 51 Cr,etc. Precipitation with Fe(OH) 3 by hydroxides at ph9 Separation from other alkaline metals, such as 133 Ba, 226 Ra and 90 Sr. BaCrO 4 and SrCrO 4 precipitation BaCl 2 and SrCl 2 precipitation in HCl solution Ca(OH) 2 precipitation in NaOH solution Concrete in the reactor Ordinary concrete Heavy concrete (50-70% BaSO 4 was added)

7 Decomposition of concrete for 41 Ca and other radionuclides For Ordinary concrete, silicates of calcium does not easily be decomposed by acids For heavy concrete, some calcium exists as CaSO 4, which does not dissolved by acid. Alkaline fusion have to be used for the decomposition of concrete for the determination of calcium isotopes. Precipitate, CaCO 3, BaCO 3 Concetre Add Na 2 CO 3 /NaOH, fuse at 700 o C for 2-3 hours Fused sample Dissolve with HCl Solution, CaCl 2 Separation procedure Leaching with water, filter through a filter paper and wash with water Fitrate, Na, K, Mg, Al, SO 4 2- etc.

8 Separation of Ca and Sr from other metals by hydroxides precipitation followed by carbonate precipitation Element /nuclide Recovery, % Element / nuclide Decontamination factor Ca 97.7± Cs (4.5±0.3) Sr 97.9± Co (1.2±0.4) Ba 97.3± Eu (8.5±0.5) Fe (2.5±0.1) Ni (2.5±0.2) 10 5

9 The new method for the separation of Ca from Sr and Ba Separation of Sr from Ca by Ca(OH) 2 precipitation Ca(OH) 2 : insoluble, Ksp = Sr(OH) 2 and Ba(OH) 2 : Soluble in alkine solution Precipitate Ca as Ca(OH) 2 at mol/l NaOH, repeat 3 times, 85% Ca can be recovered, and the decontamination factor for Sr and Ba are higer than 5x10 4

10 Separation of Ca from Sr and Ba by 3 repeated steps of Ca(OH) 2 precipitations at different NaOH concentrations [NaOH] Decontamination factor, 3 precipitations Recovery of Ca, % mol/l Ba Sr 1 prec. 2 prec 3 prec

11 Procedure for simultaneous determination of 41 Ca Residue, Silicate, BaSO 4 Concrete Precipitate, M(OH)x Leaching with HCl + HNO 3 at heating, filter Filtrate, (metals, Ca, Sr, etc) Add Fe carrier, Add NaOH to ph9, centrifuge Supernatant, Ca, Sr, Ba Supernatant, Sr, Ba, Ra Precipitate, Co, Eu, Fe, Add NaOH to 0.5 mol/l, centrifuge Precipitate Ca(OH) 2 Dissolve with HCl, add Fe3+, and NaOH to ph9, centrifuge Supernatant Ca, Sr, Ba Add NaOH to 0.5 M, centrifuge, repeat For 55 Fe and 63 Ni Filtrate, Cs, K Add Na 2 CO 3, centrifuge Precipitate, Ca, Ba, Sr, Ra CO 3 Precipitate 41 Ca Add HCl to dissolve 41 Ca solution Supernatant, Sr, Ba LSC measurement

12 Spectra of 41 Ca in heavy concrete from DR Sample Spectrum Spectrum of 41 Ca in concrete ,000...A6\Q024201N A6\Q044401N A6\Q054501N Sample Spectrum Spectrum of 41 Ca, 55 Fe and 63 Ni in concrete...a2\q020201n A2\Q010101N A2\Q030301N A3\Q010201N A4\Q010201N A4\Q020101N ,000

13 Quench correction for LSC of 41 Ca Counting efficiency, % y = x R 2 = SQP(E)

14 Features of Method for 41 Ca A separation of 41 Ca from concrete is easy to operate Good decontamination from interferring radionuclides (>10 4 ) The chemical yields of the separation procedures for 41 Ca is 80-90%. The detection limits for 41 Ca is Bq. Hou X.L., Radiochim Acta, 2005

15 Core B Core A Sampling of concrete and graphite from danish reactor, DR-2

16 Results of 41 Ca in concrete from Danish reactor, DR-2

17 90 Sr in water, graphite, resin, concrete One of main fission products (Y=5.8%) Beta emitter, measured by GM detector or LSC. It has to be separated from other radionuclides before measurement. For some waste, it may contain 89 Sr (50.5 d), it can be also measured by LSC with 90 Sr.

18 Analytical Procedure for 90 Sr Sample Carbonate precipitate from water Ash and Acid leaching from solid sample Decomposed sample or Coprecipitate Separation of Sr from Ca, Cs, metals and transuranics Separation of Sr from Ra and Ba Measurement of 89 Sr+ 90 Sr Measure 89 Sr by Cherenkov radiation

19 Decomposition of solid sample Graphite, resin Ashing at o C residue Concetre Add Na 2 CO 3 /NaOH, fuse at 700 o C for 2-3 hours Fused sample Leaching with water, filter through a filter paper and wash with water solution Separation procedure Precipitate, SrCO 3, BaCO 3 Fitrate, Na, K, Mg, Al, SO 4 2- etc. Dissolve with HCl Solution, CaCl 2 Separation procedure

20 Method for the Separation of Sr solvent extraction liquid membrane extraction extraction chromatography (Sr-Spec resin ) ion-exchange chromatography strontium rhodizonate precipitation Sr(NO 3 ) 2 precipitation in 70% HNO 3 (can be used for separation of Sr from a large amount of Ca)

21 Solubilities of Ca, Sr,Y Ba and Ra compounds Ca(OH) 2 : insoluble, Ksp = Sr(OH) 2 : Soluble in alkine solution SrCl 2, BaCl 2 and RaCl 2 : soluble in water SrCl 2 : soluble in HCl<9.5 mol/l solution BaCl 2 and RaCl 2 : insoluble in HCl >9 mol/l solution Y 2 (SO 4 ) 3 : soluble in water Sr(Ba, Ra)SO 4 : insoluble in water

22 The new method for the separation of Sr Separation of Sr from Ca: Ca(OH) 2 precipitation Separation of Sr from Ba and Ra Ba(Ra)Cl 2 precipitation in concentrated HCl solution Separation of 90 Y from Sr, Ra and Ba Sr(Ra, Ba)SO 4 precipiatation

23 Sepation of Sr from Ca by Ca(OH) 2 85 Sr added (Bq) Ca added (g) 85 Sr (Bq) Recovery of Sr (%) Precip. Supern. Ca in supernatant (g) Ca decontamination (%) * Concentration of NaOH in the solution: 0.5 mol/l

24 Separation of Sr from Ba by BaCl 2 and BaCrO 4 [HCl], mol/l Tracers added (Bq) 85 Sr 133 Ba Supernat. 133 Ba (Bq) * Precipitate 85 Sr (Bq) * Recovery of Sr, % Deconta m. of Ba, % ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±1.3 BaCrO ± ± ± ±0.4 * Average and standard deviation of two determinations

25 Separation of Y from Ra, Sr, and Ba by sulphate precipitation Tracer Added Supernat. Precipitate Recovery of Y, % Decontam.of Sr, Ba, Ra % Y, mg ± ± Sr, Bq ± ± ± Ba, Bq ± ± ± Ra, Bq ± ± ±1.4

26 Separation procedure of 90 Sr Solution Add 85 Sr, SrCl 2, ph8-10,add (NH 4 ) 2 CO 3, stand overnight Supernatant Precipitate (SrCO 3 ), Ca, Ra, Ba, transit metals, transuanics Add HNO 3 to disolve, Fe 3+, add NaOH to 0.5 mol/l, centrifuge Precipitate (Ca(OH) 2, Fe, transuranics Precipitate (Sr, Ba, Ra)SO 4 Supernatant, Sr Add HNO 3, Y, Sr and Ba, 3 weeks ingrowth of 90 Y, add H 2 SO 4, centrofuge Supernatant, Y-90 Add H 2 C 2 O 4, centrofuge Precipitate, Y 2 (C 2 O 4 ) 3 H 2 O β Meaurement of Y-90, calculation of Sr-90 Chen, Hou, Nielsen, Dahlgaard, Yu, Anal. Chim. Actc, 466 (1): , 2002

27 Sample Spectrum R1\Q050501N R1\Q070701N Sr in sample Fig.1 Beta spectrum of Sr sample separated from DR1 sample Sr in standard , Sample Spectrum Cherenkov counts of Y-90 after 2.8 days of the separation of Y-90...V0\Q051501N V1\Q051501N V1\Q051501N Fig.2 Cherenkov radiation of Sr sample separated from one DR1 sample Cherenkov counts after 7 hour of the separation of Y ,000

28 Combined procedure for simultaneous determination of 41 Ca and 90 Sr Concrete (1) Add Ca, Ba,Sr, 85 Sr, Fe, Co, Eu, leaching with aqua regia, filter Precipitate Ca(OH) 2 Supernatant, Sr, Ba, Ra Residue, (Silicate, BaSO 4 ) Precipitate, M(OH)x ( 60 Co, 152 Eu, 55 Fe, 63 Ni, transuranics, etc.) Discard Supernatant, Cs, K Filtrate, (metals, Ca, Sr, etc) (2) Add NaOH to ph9, centrifuge Supernatant, Ca, Sr, Ba, Cs, K (3) Add Na 2 CO 3, centrifuge Precipitate, (Ca, Ba, Sr, Ra)CO 3 (4) Dissolve with HCl, Add NaOH to 0.5 mol/l, centrifuge Supern. Ca, (5) Dissolve with HCl, add Sr,Ba, Fe, Co, Eu, add NaOH to ph9, centrifuge Precipitate, Co, Eu, Fe, (6) Add NaOH to 0.5 mol/l, centrifuge Precipitate 41 Ca Supern. (7) Dissolve with HCl LSC for 41 Ca measurement ICP-OES for Ca (8) Add Y, keep 3 weeks for ingrowth of 90 Y, add Na 2 SO 4, centrifuge Supernatant, 90 Y (9) Add NH 4 OH, centrifuge Precipitate, Y(OH) 3 (10) Dissolve with HCl, add H 2 C 2 O 4, filter Y 2 (C 2 O 4 ) 3 precipitate LSC or GM counter measurement of 90 Y

29 Analytical Method for 129 I and their detection limits Method Liquid scintillation γ-spectrometry Detection limit (atoms) (1 mbq) ( 0.1 Bq) 129 I (1.57x10 7 y) β-, 196 kev, 100% 129m Xe, 8.88d ICP-MS Radiochemical neutron 10 8 activation analysis Accelerator mass 10 6 spectrometry (AMS) IC, 96.6% γ, 39.6 kev, 3.4% 129 Xe (stable)

30 Separation procedure of iodine in solid samples Solid samples decompose sample by combustion, acid digestion, or alkali fusion solution Extracting with CCl 4, Back-extracting with H 2 SO 3, repeat Iodide separated convert to MgI 2 or AgI Measurement by LSC Iodine Sample RNAA Gamma measurement AMS

31 Separation of 129 I from soild waste by combustion method Flask 1: 3 H, 129 I, 99 Tc Flask 2,3: 14 C, 129 I oxygen Oven-A Oven-B Sample quartz wool with CuO Washing flask Diluted acid (HCl) NaOH solution

32

33 Schematic diagram of acid digestion system of for separation of 36 Cl and 129 I 1-Heating mantle; 2-three-necked flask; 3-sample in acid mixture; 4- bubbling tube; 5-separating funnel for adding acids; 6,7-reflux condenser; 8- receiver; 9-wash bottle containing water; 10, 11-absorption bottles containing 0.4 mol/l NaOH

34 Separation of 129 I from soild waste by Alkali fusion Solid samples (concrete) add NaOH/Na 2 CO 3, iodine carrier, fusion at 600 C for 2 h Fusee cake Leaching with H2O, filter to remove residue (precipitation) Solution with 129 I Convert iodine to iodide, extract with CCl 4, abck extract with NaSO3 Separated Iodine

35 Beta spectrum of 129 I by LSC Sample Spectrum I1\Q010101N I1\Q010101N I β counts in SP11 - background counts in SP ,000

36 Determination of 36 Cl 36 Cl is long-lived radionuclides (3x10 5 yrs) 36 Cl decays mainly by pure beta emission of Emax=708.6 kev. 36 Cl measurement is normally carried out by LSC and AMS

37 Determination of 36 Cl and 129 I in graphite --- Sample decomposition Ashing at 900 C: ---iodine and part of Cl are lost. Decomposition at 900 C with O 2 and trapping iodine in NaOH solution: ---good recovery for iodine, but not good for chlorine Leaching with acid (HNO 3 ) at heating: --- not complete remove iodine and Cl from graphite, and loss of the leached iodine. Digestion with HNO 3 and trapping iodine and chlorine with NaOH: ---- Not complete removal of iodine and chlorine How to Do?

38 Determination of 36 Cl and 129 I in graphite --- Sample decomposition Graphite can be completely dissolved in a mixture of acids: HNO 3 +H 2 SO 4 +HClO 4 The optima ratio of mixture is: H 2 SO 4 :HNO 3 :HClO 4 =15:4.1 A closed dissolution system is used for dissolve graphite in heating, Cl on the condenser tube and trap solution, while iodine mainly in the trap solution.

39 Schematic diagram of dissolution system of graphite for determination of 36 Cl and 129 I 1-Heating mantle; 2-three-necked flask; 3-sample in acid mixture; 4- bubbling tube; 5-separating funnel for adding acids; 6,7-reflux condenser; 8- receiver; 9-wash bottle containing water; 10, 11-absorption bottles containing 0.4 mol/l NaOH

40 Determination of 36 Cl and 129 I in concrete --- Sample decomposition Leaching with acid (HNO 3 ) at heating: --- not complete remove iodine and Cl from graphite, and loss of the leached iodine. Digestion with HNO 3 and trapping iodine and chlorine with NaOH: ---- Not complete removal of iodine and chlorine Alklinal fussion using NaOH and Na 2 CO 3, dissolution of fused cake in water, the supernatant is used for 129 I and 36 Cl: ---- sample is completely decomposed and iodine and Cl are released. Iodine and Cl are not lost in alkaline medium

41 Determination of 36 Cl and 129 I in stainless steel --- Sample decomposition Stainless steel is normally dissolved with HCl or HCl+HNO3: --- could not be used for 36 Cl because of too much Cl in HCl is introduced. Single acid, HNO 3, could not dissolve stainless steel. 10M H 2 SO 4 with H 3 PO 4 is sucessfully used for dissolve stainless steel for 129 I and 36 Cl: ---- sample is completely decomposed and iodine and Cl are released.

42 Separation of Cl from matrices and other radionuclides Specific precipitation of Cl - with Ag + (AgCl) can be used to selectively separation of Cl from matrix and other radionuclides (except iodine and bromine). Iodine ( 129 I) should be first separated from the solution before AgCl precipitation. 129 I can be separated by solvent extraction using CHCl 3 No need to separate Br, since no long-lived radioisotopes of Br in the waste and environmental samples. The separated AgCl can be dissolved in NH 4 OH and mixed with scintillation cocktail for LSC: But less AgCl can be used and high quench effect. How to improve?

43 Separation of Ag + and Cl in anion exchange chromatography Cl-36, Bq or Ag, x100 mg c) d) b) a) Ag + Cl - 100mg Cl, 0.2 M NH4NO3-0.6 M NH4OH eluting 200mg Cl 0.2 M NH4NO3-0.6 M NH4OH eluting 50 mg Cl, 0.1 M NH4NO3-0.6 M NH4OH eluting 100 mg Cl, 0.1 M NH4NO3-0.6 M NH4OH eluting volume, ml

44 Combined Analytical procedure for 36 Cl and 129 I Graphite, steel Add stable Cl and I carriers, dissolve with acids, combine the absorption solutions and dissolved solution Heavy Concrete Add stable Cl and I carriers and NaOH and Na 2 CO 3, fuse at 500 C, leaching with H 2 O, cenrifuge to separate the supernatant Organic phase, Back-extract with NaHSO 3 solution, repeat extraction and back-extraction Aqueous phase, 129 I LSC for 129 I ICP-MS for I Hou et al., Anal. Chem., 2007 Add NaHSO 3, transfer to a separation funnels, add CCl 4, HNO 3, and NaNO 2 to extract, repeat the extraction Washes, Ag + etc. discard Aqueous phase, AG 1 4 column Add Ag +, centrifuge, dissolve AgCl with NH 3, separate solution, add HNO 3 to re-precipite AgCl, redissolve AgCl with NH 3, load to the column Effluent, 36 Cl Wash with NH 3 Eluting with 0.1 M NH 4 NO M NH 4 OH Evaporate, dissolved with H 2 O ICP-MS for Cl LSC for 36 Cl

45 Recovery of Cl and decontamination factors for other elements and radionuclides in the chemical separation procedure Element AgCl precipitation Anion exchange Whole procedure Cl (recovery, %) ±3.2 I ( 125 I) S tritium C (CO 2-3 ) Co ( 60 Co) Eu ( 152 Eu) Cs ( 137 Cs) Ba ( 133 Ba) Sr ( 85 Sr) Ni ( 63 Ni) Fe ( 55 Fe)

46 Performance of the procedure for 36 Cl Recovery of Cl: >70% Decontamination factors for most of radionculides: >10 6 Detection limit using LSC : 14 mbq Decommissioing samples, concrete, graphite, stainless steel, aluminum, lead, have been sucessfully analysed for 36 Cl

47 Distribution of 36 Cl in the concrete core from Danish research reactor DR-2 with comparison to 55 Fe, and 63 Ni Activity concentration, Bq/g 1.0E E E E-02 55Fe 63Ni 36Cl 1.0E Distance to core, cm

48 Concentrations of 36 Cl in samples from the graphite thermal column, aluminum tanks and lead shielding in the concrete core from DR-2 reactor Sample Code 36 Cl, Bq/g mean±sd 63 Ni, Bq/g 36 Cl/ 63 Ni Activity ratio Graphite 5.5 Yi 0.18± Graphite 5.5 Yy 3.58± Graphite 5.5 Ii 22.6± Graphite 5.5 Iy 6.61± Graphite 7.5 Yi 6.37± Graphite 7.5 Yy 5.57± Graphite 7.5 Ii 39.9± Graphite G 3.33± Aluminum B ± Aluminum B ± lead B ±

49 Combined analytical procedure for 36 Cl, 129 I, 41 Ca, 63 Ni and 55 Fe