The Analyst s dilemma Maintaining analytical quality The challenges of decommissioning analysis Phil Warwick GAU-Radioanalytical
The changing analytical landscape Historically, radioanalyticalcharacterisation has been required for... - Radiological protection - Process control - Environmental monitoring - Routine waste sentencing 16/01/2012 2
The changing analytical landscape With decommissioning, the analytical requirements have shifted to focus more on... - Waste exemption - Waste stream fingerprinting - Waste characterisation of unusual matrices - Land remediation 16/01/2012 3
More challenging matrices Diverse matrices with widely varying histories require characterisation. Examples include... - Heterogeneous soft wastes - Construction materials (metals / concretes) - Ion exchange resins / desiccants - Sludges (highly variable composition) - Oils 16/01/2012 4
Changes in analytical requirements Historically, analytical schedules have focussed on activation and fission products which dominate the fingerprint in terms of activity and pose the greatest radiological risk e.g... 60 Co 90 Sr, 137 Cs 239+240 Pu, 241 Am 16/01/2012 5
Changes in analytical requirements However, in decommissioning / waste fingerprinting, a broader range of radionuclides are often required for analysis. Often low activity concentrations of long-lived nuclides need to be measured in the presence of shorter lived nuclides with significantly greater activity concentrations. 41 Ca (1.03 x 10 5 y irradiation of bioshieldconcrete) 79 Se (6 x 10 5 y fission product) 93 Zr (1.5 x 10 6 y fission + activation product) 113m Cd (14 y irradiation of Cdmetal) 151 Sm (90 y fission product) 16/01/2012 6
Factors impacting analytical quality Highly trained & experienced staff Use of validated procedures Robust QA / QC systems Suitably calibrated instrumentation 16/01/2012 7
Key stages in analysis Use of validated procedures Experienced / trained staff Validated procedures Sample collection / storage Homogenisation / sub-sampling Solubilisation / liberation of analyte Separation / purification of analyte Quantification of analyte Knowledge of analyte distribution & association with matrix Knowledge of potential interferences Suitable calibration standards Clear / accurate reporting of data Method validation 16/01/2012 8
Sampling Use of validated procedures 16/01/2012 9
Radionuclide association with matrix Use of validated procedures Speciation of 3 H in reactor bioshieldconcrete 100 1000 3 H recovery (% ) 80 60 40 20 Inner Middle Outer 800 600 400 200 T em p. (ºC ) 0 0 120 240 360 480 600 720 0 120 240 360 480 600 720 0 120 240 360 480 600 720 0 Combustion time (min) Potentially impacts on sampling, storage and analysis procedures 16/01/2012 10
Sample dissolution Use of validated procedures 2500 2000 Aqua regia HF/HClO 4 Aqua regia 1500 Bq/g 1000 500 0 Leach 1 Leach 2 Leach 3 Leach 4 Leaching of 241 Am from debris 16/01/2012 11
Instrument calibration Suitably calibrated instrumentation Traceable standard solutions do not exist for some of the radionuclidesnow being requested. For liquid scintillation analysis, proxy radionuclidesare often used which is not ideal. 16/01/2012 12
Predicted Efficiency (%) Predicted Efficiency (%) 100 90 80 70 60 93 Zr (β - E max 60.6 kev, 1 st forbidden unique) VS 63 Ni (β - E max 65.9 kev, allowed) 50 10 20 30 40 50 60 70 100 90 3 H Efficiency (%) 93 Zr 63 Ni Predicted 93 Zr Efficiency (%) 100 90 80 70 60 50 50 60 70 80 90 100 Predicted 63 Ni Efficiency (%) 79 Se (β - E max 151 kev, 1 st forbidden unique) VS 14 C (β - E max 157 kev, allowed) 80 10 20 30 40 50 60 70 3 H Efficiency (%) 79 Se 14 C Predicted 79 Se Efficiency (%) 100 90 80 80 90 100 Predicted 14 C Efficiency (%) Use of proxy radionuclides for LSC calibration Suitably calibrated instrumentation 151 Sm (β - E max 76.3 kev, allowed) VS 63 Ni (β - E max 65.9 kev, allowed) Predicted Efficiency (%) 90 80 70 60 151 Sm 63 Ni 50 10 20 30 40 50 60 70 3 H Efficiency (%) Predicted 151 Sm Efficiency (%) 90 80 70 60 50 50 60 70 80 90 100 Predicted 63 Ni Efficiency (%) 16/01/2012 13
CN2003 calibration of 41 Ca & 45 Ca Suitably calibrated instrumentation Efficiency (%) Efficiency (%) 40 30 20 10 110 100 41 Ca (EC ) 0 680 700 720 740 760 780 800 820 840 90 80 SQPE 45 Ca (β - E max 257keV, allowed) SQPE Measured Predicted Measured Predicted 70 680 700 720 740 760 780 800 820 840 Bq/g 60 50 LSC 40 AMS Predicted 30 20 10 0 0 20 40 60 80 100 distance (cm) 16/01/2012 14
113m Cd eff % 98.0 97.8 97.6 97.4 97.2 97.0 96.8 96.6 y = 0.0709x 2-0.6274x + 97.353 R 2 = 0.9999 Gamma spec. LSC Sample A 8.7 ± 1.6 12.0 ± 0.8 Sample B 8.6 ± 1.4 11.2 ± 0.8 Suitably calibrated instrumentation 96.4 96.2 96.0 0 1 2 3 4 4M HCl (ml) Gamma emission probabilities (collaboration with PTB) Published 0.023 Revised 0.01839 Gamma spec. LSC Sample A 11 ± 2 12.0 ± 0.8 Sample B 11 ± 2 11.2 ± 0.8 Warwick & Croudace (2009) Radiocarbon, LSC2008, p429-434 Kossertet al (2011) Appl. Radiat. Isot., 69, 500-505 16/01/2012 15
Reference materials Robust QA / QC systems Reference materials are required for method validation and ongoing quality control purposes. Reference standards are required that more closely reflect the matrices and contaminant form encountered in decommissioning samples. Range of matrices Analyte present in form comparable with real samples Range of certified analytes to reflect nuclides encountered Presence of contaminants comparable to those found operationally. 16/01/2012 16
Summary Decommissioning analysis has resulted in new challenges for the radiochemical laboratory. High quality analysis relies on a good understanding of the distribution and association of the analyte with the matrix. Careful consideration must be given to instrument calibration, particularly for less common radionuclides. There is a clear requirement for more representative matrix-matched standards for method validation and quality control. 16/01/2012 17