Radiological Survey Types in Support of Decommissioning

Professional Training Programs

Introduction

• Lecture overview

– Review the decommissioning survey types

– Describe the MARSSIM radiation survey and site investigation process

– Ultimate objective is to demonstrate compliance with the release criteria

– MARSSIM Chapters 2, 3, and 5

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MARSSIM Overview

• Complex yet integrated investigation process to determine a site’s radiological status and provide necessary data to support license termination.

• MARSSIM decision-making is founded on the seven step data quality objective (DQO) process.

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Release Criteria

• Regulatory agencies establish release criterion (e.g., 25 mrem/y).

• Pathway modeling to convert to measurable concentrations called DCGLs:

– Derived concentration guideline levels

– For both soil concentrations (pCi/g) and surface activity on structures (dpm/100 cm2)

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Decommissioning Project Phases

• Assessment

• Developmental

• Operations

• Closeout

• Scoping/Characterization

• Remediation Plan

• Remedial Actions

• Final status survey/ confirmatory survey

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Radiation Survey and Site Investigation Process

• Historical site assessment (HSA)

• Scoping survey

• Characterization survey

• Remedial actions (RA)/RA support survey

• Final status survey – Classify site areas – Divide into survey units

– Demonstrate compliance with release criteria

• Confirmatory surveys

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Historical Site Assessment

• HSA entails thorough record review and personnel interviews

• Provides initial information of potential contaminants

• Provides initial inputs for classifying site based on contamination potential

• Provides focus for the level of effort for field surveys—areas with greatest contamination potential receive higher intensity surveys, a graded approach

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Historical Site Assessment

Objectives • Identify potential sources of contamination

• Differentiate areas according to contamination potential (impacted or non-impacted)

• Provide input to scoping and characterization survey design

• Provide assessment for potential contaminant migration pathways

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Historical Site Assessment

HSA Information Sources • Licensing documents

• Operational records

• Employee interviews

• Review of similar sites

• Aerial photographs

• Review the following series of aerials. What information can be found?

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Ca. 1958

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Ca. 1990

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Ca. 1958

Ca. 1990

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Historical Site Assessment

• Review radioactive materials licenses

– Radionuclides used and quantities

– Chemical and physical form

– Operations for which materials were used

– Locations where material was used

– Total quantities

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Historical Site Assessment

• Site operational records

– Records on waste disposal practices and material transport routes

– Records of spills or effluent releases

– Site plot plans and aerial photos show facility modifications over time

• Contacts and interviews

– Provides information on undocumented events or clarifications to operations

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Historical Site Assessment

• Evaluation of HSA results

– Determine the current status of the site and provide initial classification

• Decisions following HSA:

– Site is impacted and requires further investigation: scoping, characterization, remediation

– Site is non-impacted—low probability of residual radioactivity, site release possible

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Classification of Areas

• Areas with higher potential for contamination receive higher degree of survey effort

• Impacted

– Class 1

– Class 2

– Class 3

• Non-impacted

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Historical Site Assessment

• Evaluation

– Estimate potential for contamination from:

– Site operations and waste disposal practices

– Major contaminants and relative ratios among multiple contaminants (for DCGLs)

– Contaminants chemical/physical form (for DCGLs)

– Time since operations and material use (allows for decay)

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Historical Site Assessment

• Evaluation

– Site operations influence on contaminant potential

– Sealed sources = low probability, review of leak test records may be all that is needed

– Unsealed sources = different story

» Potential for contaminated process areas, piping, ductwork, transport routes, material storage/disposal areas

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Historical Site Assessment

• Evaluation

– Identify potential contaminated media

– Surface soil

– Subsurface soil

– Building surfaces

– Process equipment

– Support equipment

– Other media as applicable

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Historical Site Assessment Summary

• Site diagram showing classification of impacted areas: Class 1, 2, or 3 (classification may change)

• Serves as basis for scoping survey design

• Anticipate data deficiencies and unknowns, expect to use your professional judgment

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Example Conceptual Site Model

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Scoping Survey Classification

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Scoping Survey

• HSA inputs used to design the scoping surveys

• Site land areas and buildings classified as Class 1, 2, and 3

– Class 1 expected to contain contamination above release guideline, Class 3 lowest potential for contamination

– Scoping used to confirm contamination in Class 1 areas and plan for future characterization

– Expands upon HSA data by collecting judgmental samples in potential areas of concern

– Supports classification of site areas

– Identifies site contaminants and their variability

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Scoping Survey

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Two Outcomes

• Judgmental sampling IDs contamination:

– Provides general idea of contamination extent

– Provides new information and input for planning characterization

• Contamination is not identified:

– If minimum survey coverage during scoping = a Class 3 FSS design – it may be possible to randomly sample and be finished

– Requires sufficient detection capabilities, etc.

Characterization Survey

• Most intensive of the site investigations

• Clearly defines contamination boundaries

• Primary objective is to determine the nature and extent of contamination—builds upon the HSA and scoping survey results

• Other objectives:

– Evaluating remediation alternatives

– Health and safety issues

– Data used to develop site-specific DCGLs

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Characterization Classification

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Characterization Survey

• Builds on knowledge of the site and answers questions resulting from scoping survey surprises (and there can be many of these)

• Should have a very clear picture of the site—information used to develop a concise decontamination scope-of-work and plan

• Data generated are used to feed the planning inputs for the final status survey and may also be used as final status data to support license termination

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Survey Activities

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Characterization Survey

• For many areas, should consider balance between characterization and remediation

• Where no remediation is anticipated, characterization data may be used as final status data—need to plan accordingly

• Characterization survey also provides contaminant standard deviation in survey unit—allows FSS sample size determination

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Characterization Survey

• Following example: GPS/gamma count rate integrated system to capture over 1M data points, team traversed over 500 miles of terrain, all data now available for presentation to regulators, serves as final status data for >99% of the site

• Collected and analyzed over 1,000 direct measurements and 1,200 soil samples, data generated used both as FSS data where no further action required and for planning FSS in areas requiring remediation

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Characterization Results

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Building Characterization Results

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Characterization Results

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Remedial Action Support Survey

• Final status survey planning is statistically based on an estimated contaminant mean concentration and variability

• Remediation changes these values from what was determined during characterization

• Remedial action support surveys ensure adequacy of clean-up, performed in real-time, and provide inputs for the final status survey planning

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Final Status Survey

• Provides THE data submitted to the regulator to support license termination request

• Objective is to demonstrate that residual radioactivity in each survey unit satisfies release criteria

• All radiological parameters must satisfy the DCGLs and conditions

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Final Status Survey

• Two statistical tests are used to plan and evaluate final status survey data

– Wilcoxon Rank Sum (contaminants in background)

– Sign test (contaminants not in background)

• Null hypothesis: Residual radioactivity exceeds the release criteria

• Survey design relies on DQOs to set acceptable decision errors

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Confirmatory Survey

• Performed by regulatory agency or independent third party

• Provides data to substantiate results of FSS

• Confirmatory activities include review of survey procedures and results, and independent field measurements

• Streamlining approach more efficient

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