Maintaining analytical quality The challenges of decommissioning analysis

Transcription

1 The Analyst s dilemma Maintaining analytical quality The challenges of decommissioning analysis Phil Warwick GAU-Radioanalytical

2 The changing analytical landscape Historically, radioanalyticalcharacterisation has been required for... - Radiological protection - Process control - Environmental monitoring - Routine waste sentencing 16/01/2012 2

3 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

4 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

5 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 Co 90 Sr, 137 Cs Pu, 241 Am 16/01/2012 5

6 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

7 Factors impacting analytical quality Highly trained & experienced staff Use of validated procedures Robust QA / QC systems Suitably calibrated instrumentation 16/01/2012 7

8 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

9 Sampling Use of validated procedures 16/01/2012 9

10 Radionuclide association with matrix Use of validated procedures Speciation of 3 H in reactor bioshieldconcrete H recovery (% ) Inner Middle Outer T em p. (ºC ) Combustion time (min) Potentially impacts on sampling, storage and analysis procedures 16/01/

11 Sample dissolution Use of validated procedures Aqua regia HF/HClO 4 Aqua regia 1500 Bq/g Leach 1 Leach 2 Leach 3 Leach 4 Leaching of 241 Am from debris 16/01/

12 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/

13 Predicted Efficiency (%) Predicted Efficiency (%) Zr (β - E max 60.6 kev, 1 st forbidden unique) VS 63 Ni (β - E max 65.9 kev, allowed) H Efficiency (%) 93 Zr 63 Ni Predicted 93 Zr Efficiency (%) Predicted 63 Ni Efficiency (%) 79 Se (β - E max 151 kev, 1 st forbidden unique) VS 14 C (β - E max 157 kev, allowed) H Efficiency (%) 79 Se 14 C Predicted 79 Se Efficiency (%) 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 (%) Sm 63 Ni H Efficiency (%) Predicted 151 Sm Efficiency (%) Predicted 63 Ni Efficiency (%) 16/01/

14 CN2003 calibration of 41 Ca & 45 Ca Suitably calibrated instrumentation Efficiency (%) Efficiency (%) Ca (EC ) SQPE 45 Ca (β - E max 257keV, allowed) SQPE Measured Predicted Measured Predicted Bq/g LSC 40 AMS Predicted distance (cm) 16/01/

15 113m Cd eff % y = x x R 2 = Gamma spec. LSC Sample A 8.7 ± ± 0.8 Sample B 8.6 ± ± 0.8 Suitably calibrated instrumentation M HCl (ml) Gamma emission probabilities (collaboration with PTB) Published Revised Gamma spec. LSC Sample A 11 ± ± 0.8 Sample B 11 ± ± 0.8 Warwick & Croudace (2009) Radiocarbon, LSC2008, p Kossertet al (2011) Appl. Radiat. Isot., 69, /01/

16 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/

17 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/