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Title: Soil Segregation technology: reducing uncertainty and increasing efficiency during radiological decommissioning - a case study

The regulatory release of sites and facilities (property) for restricted or unrestricted use has evolved beyond prescribed levels to model-derived dose and risk based limits. Dose models for deriving corresponding soil radionuclide concentration guidelines are necessarily simplified representations of complex processes. It is not practical to obtain data to fully or accurately characterize transport and exposure pathway processes. Similarly, it is not possible to predict future conditions with certainty absent durable land use restrictions. To compensate for the shortage of comprehensive characterization data and site specific inputs to describe the projected 'as-left' contaminated zone, conservative default values are used to derive acceptance criteria. The result is overly conservative criteria. Furthermore, implementation of a remediation plan and subsequent final surveys to show compliance with the conservative criteria often result in excessive remediation due to the large uncertainty. During a recent decommissioning project of a site contaminated with thorium, a unique approach to dose modeling and remedial action design was implemented to effectively manage end-point uncertainty. The approach used a dynamic feedback dose model and soil segregation technology to characterize impacted material with precision and accuracy not possible with static control approaches. Utilizing the remedial action goal 'over excavation' and subsequent auto-segregationmore » of excavated material for refill, the end-state (as-left conditions of the refilled excavation) RESRAD input parameters were re-entered to assess the final dose. The segregation process produced separate below and above criteria material stockpiles whose volumes were optimized for maximum refill and minimum waste. The below criteria material was returned to the excavation without further analysis, while the above criteria material was packaged for offsite disposal. Using the activity concentration data recorded by the segregation system and the as-left configuration of the refilled excavation, the end state model of the site was prepared with substantially reduced uncertainty. The major projected benefits of this approach are reviewed as well as the performance of the segregation system and lessons learned including: 1) Total, first-attempt data discovery brought about by simultaneously conducted characterization and final status surveys, 2) Lowered project costs stemming from efficient analysis and abstraction of impacted material and reduced offsite waste disposal volume, 3) Lowered project costs due to increased remediation/construction efficiency and decreased survey and radio-analytical expenses, and 4) Improving the decommissioning experience with new regulatory guidance. (authors)« less
Authors:
;  [1] ;  [2] ;  [3]
  1. Civil and Environmental Consultants, Inc., Pittsburgh PA (United States)
  2. Shonka Research Associates, Inc., Marietta GA (United States)
  3. ADA Consultants, Baton Rouge LA (United States)
Publication Date:
OSTI Identifier:
21290856
Report Number(s):
INIS-US--09-WM-07266
TRN: US10V0181038267
Resource Type:
Conference
Resource Relation:
Conference: WM'07: 2007 Waste Management Symposium - Global Accomplishments in Environmental and Radioactive Waste Management: Education and Opportunity for the Next Generation of Waste Management Professionals, Tucson, AZ (United States), 25 Feb - 1 Mar 2007; Other Information: Country of input: France; 9 refs
Research Org:
WM Symposia, 1628 E. Southern Avenue, Suite 9 - 332, Tempe, AZ 85282 (United States)
Country of Publication:
United States
Language:
English
Subject:
12 MANAGEMENT OF RADIOACTIVE WASTES, AND NON-RADIOACTIVE WASTES FROM NUCLEAR FACILITIES; DECOMMISSIONING; EFFICIENCY; LAND USE; RADIATION DOSES; RADIOACTIVE WASTE DISPOSAL; RADIOACTIVITY; REMEDIAL ACTION; SEGREGATION; SOILS