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Presented by Steven Landsman CH2M Hill Plateau Remediation Contract

Use of VSP to Support the Radiological Controls Program for the Hanford Plateau Remediation Contract. Presented by Steven Landsman CH2M Hill Plateau Remediation Contract. Hanford Area is App. 500 Square Miles 2015 Vision shrinks the contaminated footprint to about 25 square miles

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Presented by Steven Landsman CH2M Hill Plateau Remediation Contract

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  1. Use of VSP to Support the Radiological Controls Program for the Hanford Plateau Remediation Contract Presented by Steven Landsman CH2M Hill Plateau Remediation Contract

  2. Hanford Area is App. 500 Square Miles • 2015 Vision shrinks the contaminated footprint to about 25 square miles • Large outdoor areas need to be surveyed after remediation

  3. VSP Use At Hanford • Used primarily to determine radiological posting requirements • Does not clear or release the area • Determines radiological controls needed for worker/public health and safety • Used at 105KW to determine sludge depth/mass in the fuel storage basin

  4. VSP Use at Hanford • Evaluates the radiological contamination status of large outdoor areas • When conditions are unknown • After stabilization or remediation efforts • After a spill or uncontrolled release of contamination • Evaluation of areas once work has been completed

  5. VSP Use at Hanford • Develops survey plans specific to an area • Larger Areas divided into 2000 m2 survey units • Default survey method uses a combination of random and judgmental survey locations • Alternate survey designs can be developed for larger areas • Results of survey evaluated to determine the radiological posting required for the area

  6. VSP Use at Hanford • Default survey plan was developed using Combined Judgmental and Random (CJR) sample design • Specified number (18) of randomly located samples (survey points) are identified to be performed • Predetermined number (10) of judgmental samples (survey points) are specified in the plan • Statistical model based on binary outcomes (contamination detected or not detected)

  7. VSP Use at Hanford • CJR statistical method used to determine number of randomly located survey points • 95% confidence level specified • Null hypothesis is that at least 95% of the survey unit is less than the action threshold for contamination • If proven false, the survey unit fails • Posting is determined by the magnitude of the contamination measurement

  8. VSP Use at Hanford Example of the Use of the Default Survey Plan Process Using Combined Random/Judgmental Survey Locations

  9. Remediated Area near the Plutonium Finishing Plant, including structural foundations after building demolition

  10. VSP Use at Hanford

  11. Random Survey Location Map for Radiological Surveys Based on the Sample Design Criteria. Radiological Control Technicians were required by the survey plan to select at least 10 additionalsurvey locations in each survey unit based on their best judgment of where contamination could be expected to be found.

  12. VSP Use at Hanford Survey Results • No contamination above action levels found at randomly selected locations • Judgmental sampling found one are approximately 400 cm2 in size that had fixed contamination above action levels • After removal of discovered contamination, survey was repeated using different randomly selected locations • Survey Results showed no contamination above action levels • Area downposted (postings removed)

  13. VSP Use at Hanford Example of an Alternative Survey Plan Design for a Survey Unit Larger than 2000 m2

  14. VSP Use at Hanford • WIDS Site 100-K-63 was remediated to CERCLA Remedial Action Work Plan goals • Area originally posted as a Contamination Area • Posting criteria needed to be determined after completion of remediation • Site is approximately 63,000 m2 in size

  15. 100-K-63 WIDS Site After Remediation

  16. VSP Survey Design: Employ Prior Belief to Achieve High Confidence that a High Percentage of the Decision Area (WIDS Site 100-K-63) is Acceptable

  17. VSP Use at Hanford • design accounts for prior belief that the survey unit has been successfully remediated. • belief that the area does not contain concentrations of radionuclides above CERCLA Remedial Action Guidelines (RAGs) allows calculation of the number of randomly located survey points that establish a high confidence that a large fraction of the decision area is acceptable for down-posting--provided that surveys are below action levels (i.e. 20 dpm/100 cm2 alpha direct, 5,000 dpm/100 cm2 beta-gamma direct on the soil). • The VSP sample design selected to be used for the confirmatory closure survey is a special case of the Combined Judgmental and Random (CJR) sampling design • the number of judgmental samples is zero • the ratio of the contribution of the judgmental samples to the random samples is set to one (1) • Under these conditions, the CJR module reduces to the same Bayesian acceptance sampling model employed by Wright (1992), Grieve (1994), and Axelrod (2005), with the exception that the CJR implementation in VSP ensures that the desired 'proportion of the decision area that is acceptable' be large enough to ensure that larger decision areas (or populations) will require more samples than smaller decision areas.

  18. Survey Unit showing survey locations for the 100-K-63 WIDS Site Down-Posting Survey After Remediation. Survey Locations are 1 square meter grids.

  19. VSP Use at Hanford RESULTS • Survey results were all less than action levels • Based on survey results, WIDS Site 100-K-63 was downposted from CA status to no radiological posting required

  20. VSP Use at Hanford Sludge Depth Measurements in the 105KW Basin and Pits

  21. VSP Use at Hanford Sludge accumulation

  22. Accumulation of sludge and debris near Knock-out Pot Processing Equipment

  23. Release of Sludge from a Knock-out Pot during Processing of Fuel Fragments

  24. VSP Use at Hanford • Need to demonstrate that end-point criteria for sludge removal is met • Sample Design to measure sludge depth in the 105KW Basin • Depth measurements used to generate estimates of the volume of sludge remaining in the basin after cleanup • Sample Design will also support dose rate measurements in the Basin

  25. VSP Use at Hanford • Two Separate Sample Designs used to tackle the issue • Construct a confidence interval on the true mean • to determine number of samples needed for non-parametric sample design for each bay • To determine the number of samples in each Pit area assuming parametric distribution • Basin Bays sample design using stratified sampling • Stratified sampling used due to higher accumulations of sludge at floor/wall boundaries, at the base of equipment in the bays than in open areas of the basin

  26. VSP Use at Hanford • Construct a Confidence Interval on the True Mean • Two sided confidence interval selected • Assumed Non-parametric for the basin bays because of the uneven distribution of sludge • Assumed parametric design for the pits because they are relatively undisturbed

  27. VSP Use at Hanford Sampling Design To Construct a Confidence Interval on the True Mean for the Basin Bays

  28. VSP Use at Hanford Sampling Design for the Basin Pits

  29. VSP Use at Hanford Sampling Design for the Basin Bays to Estimate the population mean using Stratified Sampling

  30. Sample Locations for Pit Areas of the 105KW Basin

  31. Example of the Stratified Design for measuring sampling sludge depths in the Basin Bays. Strata 1 is yellow, Strata 2 is salmon color, and Strata 3 is light green. Other area of the bay were excluded from sampling due to the presence of equipment or significant debris piles that would preclude accurate measurements.

  32. VSP Use at Hanford Results Work packages are being prepared to measure sludge depths • sample location information generated by VSP will be incorporated into the packages • Results of the sludge depth measurements will be entered into VSP to validate the statistical assumptions used to generate the sample designs • Dose rates will also be taken at each of the locations • Work is expected to be completed in the first quarter of FY13.

  33. VSP Use at Hanford Summary • VSP is incorporated into the technical basis for determining radiological postings for large outdoor areas • A default survey plan using VSP sample design criteria has been included procedurally in the Radiation Controls program • Other VSP sample designs can be used as needed, based on approval by the Company Technical Authority • VSP is also being used to characterize facilities prior to deactivation or demolition

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