Addressing Uncertainty in Radiochemistry Measurements M. C. Nichols, CHP RETS-REMP meeting
June, 2009RETS-REMP meeting Guidelines for Using Quality Control and Performance Testing (PT) Data USNRC regulatory guide 4.15 revision 1, performance testing –Specification in for performance testing –Acceptance criteria –Uncertainty estimates from PT data Revision 2, based on MARLAP –Total propagated uncertainty
June, 2009RETS-REMP meeting USNRC Regulatory Guide 4.15, Rev. 1 Performance testing –Measure accuracy (normalized deviation) –Measure precision (normalized range) Basis: “Environmental Radioactivity Laboratory Intercomparison Program”, EPA 600/ , January 1977
June, 2009RETS-REMP meeting Acceptance Criteria Confidence interval estimates Normalized deviation and normalized ranged in the EPA cross check program Ratio and resolution based on US NRC Inspection Procedure-84750
June, 2009RETS-REMP meeting Confidence Limit
June, 2009RETS-REMP meeting EPA Cross Check - Accuracy
June, 2009RETS-REMP meeting EPA Cross Check - Precision
June, 2009RETS-REMP meeting NRC IP Resolution - divide each NRC result by its associated uncertainty Uncertainty defined as the relative uncertainty, 1S, of NRC results calculated from counting statistics Ratio - licensee result / NRC result Criteria - gives a range of acceptable ratios as a function of resolution
June, 2009RETS-REMP meeting Single Laboratory Precision Counting uncertainty Providers specification Use performance testing history Construct an uncertainty budget –May be available for specific procedures (gamma spectroscopy) –Build on existing quality control data
June, 2009RETS-REMP meeting
June, 2009RETS-REMP meeting
June, 2009RETS-REMP meeting Variance - Future Prediction
June, 2009RETS-REMP meeting Sr-90 Concentration (pCi/Liter) Prediction Interval (1S) Coefficient of Variation % % % % % % Prediction Intervals for Sr-90
June, 2009RETS-REMP meeting Suggestions for Performance Testing Data Two components to the evaluation of performance data –Uncertainty of the known value –Uncertainty of the measured value Regression - use replicate measurements for each performance testing round Uncertainties from performance testing results are limited to the range of testing
June, 2009RETS-REMP meeting Uncertainty Budget Define the process including components of the activity estimate Identify uncertainty estimates for each component Use software tools to create uncertainty budgets (e.g. Gumcalc)
Efficiency
June, 2009RETS-REMP meeting Example - Uncertainty for Balance Measurement
June, 2009RETS-REMP meeting
June, 2009RETS-REMP meeting Strontium-89 Uncertainty at 18.5 mg cm -2, Efficiency ± (95% CL).
June, 2009RETS-REMP meeting Summary All performance testing evaluation is based on an estimate of measurement uncertainty Performance testing data will provide an estimate of total measurement uncertainty Measurements outside the range of PT data and new program requirements will require assessment of measurement uncertainty Laboratories currently have sufficient data to construct these estimates
June, 2009RETS-REMP meeting References –Ellison, S.L.R., M. Rosslein, and A. Williams, EURACHEM/CITAC guide CG 4: quantifying uncertainty in analytical measurement, 2nd edition –MARLAP, Multi-agency radiological laboratory analytical protocols manual (final) volume i (epa 402-b a), volume ii (epa 402-b b), volume iii (epa 402-b c)volume ivolume iivolume iii –Mccroan, K. D., Gumcalc v 1.0. Freeware developed for the MARLAP project. –USEPA, Environmental radioactivity laboratory intercomparison program”, EPA 600/ –USNRC, 2007 Quality assurance for radiological monitoring programs (inception through normal operations to license termination) -- effluent streams and the environment, revision 2, ML , July, 2007 ML –USNRC, NRC inspection manual procedure for radioactive waste treatment, effluent, and environmental monitoring