Development of radiochemical analysis strategies for decommissioning activities. Dr. Daniel Zapata-García Environmental radioactivity laboratory, PTB

Transcription

1 Development of radiochemical analysis strategies for decommissioning activities Dr. Daniel Zapata-García Environmental radioactivity laboratory, PTB

2 OUTLINE 1. INTRODUCTION EMRP Project: MetroDECOM Aim of the work Radiochemistry 2. RADIOCHEMICAL ANALYSES Separation scheme Sample treatment Results 3. SUMMARY AND FUTURE WORK 2 / 19

3 INTRODUCTION Sept Aug WORKPACKAGES WP1: Characterization of materials present on decommissioning sites WP2: Measurement facility for waste segregation WP3: Implementation of free release measurement facility on a decommissioning site WP4: Radioactive waste repositories monitoring WP5: Development of reference materials and standard sources 3 / 19

4 INTRODUCTION Sept Aug WP1: Characterization of materials present on decommissioning sites Improve the characterisation of materials and items at decommissioning sites Mapping inside nuclear facilities Sampling strategies for radiochemical analyses Scale factors Radiochemical analysis procedures Separation of target radionuclides Matrices: steel, concrete, graphite Straightforward: able to be done on site 4 / 19

5 INTRODUCTION Radiochemistry That part of chemistry which deals with radioactive materials. It includes: 1. the production of radionuclides and their compounds by processing irradiated materials or naturally occurring radioactive materials 2. the application of chemical techniques to nuclear studies 3. the application of radioactivity to the investigation of chemical, biochemical or biomedical problems. Radioanalytical chemistry (analytical radiochemistry) The part of analytical chemistry in which the application of radioactivity is an essential step in the analytical procedures. Radiochemical separation Separation by a chemical means of the radioactive isotopes of a specific element from a mixture of radionuclides. Source: International Union of Pure and Applied Chemistry Nomenclature for radioanalytical chemistry (IUPAC Recommendations 1994) 5 / 19

6 INTRODUCTION RADIOCHEMICAL SEPARATIONS Based on the chemical properties of the substances: Reactivity Formation of complexes Precipitation reactions Sr-90 Sr-90 Y-90 + e - + ν Sr-90 In order to measure the amount of Sr-90 Y-90 It is necessary to separate Sr-90 and Y-90 because their β-spectra overlap. 6 / 19

7 Sr (resin) INTRODUCTION RADIOCHEMICAL SEPARATIONS SEPARATION OF Sr-90 AND Y-90 NH 3 HNO 3 media (3 M) Sr and Y in solution 0.05 M HNO 3 HNO 3 media Sr and Y in solution 4,4 (5 )-di-t-butylciclohexano-18-crown-6 Diluent: 1-octanol ph 9 Y(OH) 3 precipitates Sr remains in solution Sr Y 3+ Sr 2+ 7 / 19

8 Sr UTEVA TEVA RADIOCHEMICAL ANALYSES RADIOCHEMICAL SEPARATION SCHEME EXTRACTION CHROMATOGRAPHY PROS Rapid Selective Low volume of residues TANDEM arrangement 3 M HNO M Al(NO 3 ) 3 Pu Electroplating 1 % NH 4 OCl in 2 M HCl α-spectrometry CONS Radionuclides in solution Use of tracers U 0.1 M HCl Sr 0.05 M HNO 3 Electroplating Sr/Y Precipitation α-spectrometry Gas-flow proportional counting γ-spectrometry 8 / 19

9 RADIOCHEMICAL ANALYSES RADIOCHEMICAL SEPARATION SCHEME Tests with aqueous solutions One radionuclide / one cartridge Three radionuclides / three cartridges (TANDEM arrangement) 9 / 19

10 Recovery RADIOCHEMICAL ANALYSES RESULTS 100% 1 radionuclide 3 radionuclides 75% 50% 25% 0% Pu-242 U-232 Sr-85 Pu-242 U-232 Sr-85 Good response in most of the cases for both the single and TANDEM analyses High variability in the TANDEM tests of uranium Tests on the retention of U in TEVA Dialogue with Triskem: UTEVA lot might be too old 10 / 19

11 Sr UTEVA TEVA RADIOCHEMICAL ANALYSES RADIOCHEMICAL SEPARATION SCHEME: REAL SAMPLES Concrete Steel Graphite Pu Electroplating α-spectrometry U Electroplating α-spectrometry Solution Sr Sr/Y Fällung Gas-flow proportional counting γ-spectrometry 11 / 19

12 RADIOCHEMICAL ANALYSES SAMPLE TREATMENT: CONCRETE Concrete: Mixture of oxides Prime K1 (Katanax) Fusion: 0.5 g concrete Pt /Au crucible Li 2 B 4 O 7 /LiBO 2 Wetting agent: LiBr Temperature: 1000 C Time: < 15 min 12 / 19

13 RADIOCHEMICAL ANALYSES SAMPLE TREATMENT: CONCRETE PROBLEM: short after the fusion, silicates start to polymerise in the solution (whether observed or not) and the separation cartridges get blocked during the separation. EXTRA STEPS IN THE SAMPLE TREATMENT Concrete Fusion Li 2 B 4 O 7 /LiBO 2 Polymerisation of silicates with PEG + Filtration Treatment with HNO 3 /HF + evaporate to dryness Ca(PO 4 ) 3 precipitation + filtration Dissolution with HNO 3 + Al(NO 3 ) 3 13 / 19

14 RADIOCHEMICAL ANALYSES SAMPLE TREATMENT: STEEL Steel: alloy of Fe and C & other elements to adjust properties: Cr, Mo, Ni, V Dissolution using acids: 4 g steel Aqua regia (75 % HCl, 25 % HNO 3 ) PROBLEM Main element in solution is Fe 14 / 19

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16 RADIOCHEMICAL ANALYSES SAMPLE TREATMENT: STEEL CO-PRECIPTITATION OF An WITH CaC 2 O 4 Steel sample Dissolution HNO 3 /HCl Co-precipitation with CaC 2 O 4 + Filtration Treatment with HNO 3 /HCl + evaporation to dryness Dissolution with HNO 3 + Al(NO 3 ) 3 16 / 19

17 RADIOCHEMICAL ANALYSES SAMPLE TREATMENT: GRAPHITE Graphite: allotropic form of C; low reactivity Acid digestion in closed vessel microwave system: 0.2 g graphite H 2 SO 4 and HNO 3 Evaporation to dryness Dissolution in HNO 3 + Al(NO 3 ) 3 Very stable and clear solutions 17 / 19

18 Recovery RADIOCHEMICAL ANALYSES SAMPLE TREATMENT + RADIOCHEMICAL SEPARATION SCHEME 100% 75% Graphite (0.2 g) 50% Stahl Steel (4 g) 25% Beton Concrete (0.5 g) 0% Lower yields than with aqueous solutions. Effect of the matrix: Pu-242 U-232 Sr-85 Good recoveries in the case of graphite and concerte. Lower values for steel, with very low recovery for U. 18 / 19

19 RADIOCHEMICAL ANALYSES Straightforward sample treatment procedures for the complete dissolution and removal of specific interferent elements have been developed. Simultaneous radiochemical separation scheme for Pu, U and Sr has been developed and successfully applied to the matrices of interest. Duration Amount of sample Radiochemical separations Pu U Sr Concrete ~ Steel ~ Graphite 19 / 19

20 Physikalisch-Technische Bundesanstalt Braunschweig and Berlin Bundesallee Braunschweig Dr. Daniel Zapata-García Telefon: Stand: 10/16