ML19301A034

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Use of Performance Assessment in Finding Optimal Solutions to Decommissioning and Radioactive Waste Disposal Problems Cynthia Barr, Richard Chang, and Chris Grossman United States Nuclear Regulatory Commission Regulatory Framework of Decomm
ML19301A034
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Issue date: 10/29/2019
From: Cynthia Barr, Richard Chang, Christopher Grossman
Office of Nuclear Material Safety and Safeguards
To:
Barr C
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Download: ML19301A034 (22)
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Use of Performance Assessment in Finding Optimal Solutions to Decommissioning and Radioactive Waste Disposal Problems Cynthia Barr, Richard Chang, and Chris Grossman United States Nuclear Regulatory Commission Regulatory Framework of Decommissioning, Legacy Sites & Wastes Tromsø, Norway October 29-November 1, 2019

Optimization Approaches

  • NRC conducts safety reviews focusing on radiological risks
  • Federal agencies, including NRC, perform environmental reviews to evaluate the environmental impacts of proposed federal actions to inform the decision-making process
  • NRC uses independent modeling and analysis to help perform these reviews, to ask better questions, and to make better decisions 2

Dose Modeling

  • For decommissioning sites, typically dose modeling is used to assess risk and determine clean-up levels 3

Radioactive Waste Disposal For radioactive waste disposal, typically performance assessments are used to assess risk and determine compliance with dose-based criteria 4

Examples

  • Two examples are provided to help illustrate NRC staffs approach to performing complex decommissioning and low-level waste disposal facility reviews 5

First Example

Background

  • The risks of radium were originally unknown
  • After risks were known, sites of historic radium contamination were inconsistently regulated
  • The Energy Policy Act of 2005 amended the Atomic Energy Act giving the NRC the authority to regulate discrete sources of radium
  • NRC issued the Naturally Occurring and Accelerator-Produced Radioactive Material rule in 2007 addressing its new authorities
  • NRC has taken actions to identify and address sites with risk-significant quantities of radium 7

Historic Radium Uses 8

Image source: Buchholtz and Cervera, 2008

Project Objectives NRC contracted with Oak Ridge National Laboratory (ORNL) to conduct research with three general objectives:

1. Identify sites where radium was used/processed
2. Gather available site information (e.g.,

nature and extent of contamination)

3. Develop methodology to prioritize sites based on potential hazard to public 9

Project Objective Results

  • Objective 1: Using historical records, databases, and literature searches, ORNL identified factory locations where radium-226 was used.
  • Objective 2: ORNL reviewed site information and data to determine operational history, remedial activities, current status of structures and radiological/site conditions, access controls, demographics, and past and current government involvement.
  • Objective 3: ORNL established a 4 tier prioritization system.

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Initial Site Visits

- Details conduct of initial site visits

- Procedures for use of radiation survey instruments to easily determine whether immediate controls are necessary

- Immediate controls are necessary if survey readings indicate

  • 0.40 uSv/hr (40 uR/hr) above background (industrial sites)
  • 0.15 uSv/hr (15 uR/hr) above background (residential sites)
  • Note: These values are associated with the public dose limit of 1 mSv/yr (100 mrem/yr) found in 10 CFR 20.1301 11

Dose Assessment

  • Dose Assessment Technical Basis Document

- Screening levels developed using the 0.25 mSv/yr (25 mrem/yr) criterion found in 10 CFR 20.1402

- Scenarios include

  • Industrial building occupancy
  • Residential building occupancy
  • Resident farmer (soils)

- Reduces burden on site owners 12

Dose Assessment (cont)

- DandD screening code used with its default scenarios, pathways, and parameters with

  • Consideration of removable fraction
  • Revised resuspension factor consistent with expected conditions at radium contaminated sites
  • Revised occupancy times and breathing rates for residential (rather than industrial) building occupancy
  • Considers area of contamination (higher screening values for smaller areas)

- Inspectors confirm whether the site is consistent with screening value assumptions

- Site-specific modeling may be necessary

  • To adequately assess risk
  • If screening values are too stringent 13

Site Disposition

  • NRC dispositioned identified sites by confirming that:

- A site did not warrant a visit

- A site warranted a visit, and surveys conducted confirmed the site had one of the following:

  • No radium contamination exceeding NRCs unrestricted use standards
  • Radium contamination exceeding the unrestricted use standards and requires remediation.

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Results

  • All sites identified have been dispositioned
  • 5 sites need to perform cleanup or more characterization

- 2 site cleanups have been completed

- 2 site cleanup plans have been approved

Second Example

  • Western New York Nuclear Service Center or West Valley Demonstration Project 16

Background

  • Site of commercial spent nuclear fuel reprocessing between the years of 1966-1972
  • Shut-down in 1972 because the licensee determined the plant was not economically viable
  • Decontamination and decommissioning of process buildings, treatment ponds, high-level waste tanks, and radioactive waste disposal facilities is ongoing.
  • Soils, groundwater, and surface water/sediments are radiologically contaminated.

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Technical Challenges and Working Groups

  • Erosion--Erosion Working Group (WG)

- Collect calibration data

- Collect data to parameterize the models

- Update erosion modeling

  • Inventory--Exhumation WG

- Decrease uncertainty in inventory estimates

- Evaluate the costs and benefits of full or partial exhumation

  • Engineered barrier performance--

Engineered Barrier WG

- Evaluate in-place closure containment technologies

- Evaluate engineered barrier performance 18

Environmental Review

  • An Environmental Impact Statement (EIS) was prepared to assess the environmental impacts of various alternatives including

- Sitewide removal

- Sitewide close-in-place

- Phased decision-making (preferred alternative)

  • The EIS considers radiological and non-radiological impacts and is used to inform decision-making 19

NRC Independent Modeling

  • To assist with review of the EIS and Decommissioning Plan (DP), NRC staff constructed independent models to identify the most risk-significant sources, and parameters 20 Image Credit: David Esh and Allen Gross

Offsite Radioactivity

  • Detected during aerial surveys
  • On Seneca Nation territory
  • Dose modeling and radiological surveys performed to assess risk
  • NRC staff performed an independent review and analysis
  • NRC concluded offsite radioactivity was low risk
  • Results presented to the Seneca Nation
  • Limited resources better spent on on-site clean-up 21

Conclusions

  • Complex decommissioning and legacy sites are unique and require novel approaches to addressing technical or programmatic challenges
  • Screening analyses can be used to help prioritize clean-up of sites and determine where additional effort is needed
  • Additional data collection and modeling; or remediation can be performed as necessary to meet established criteria
  • Independent analyses are important to better understanding risks, to make more optimal decisions, and ensure limited resources are spent cost-effectively 22
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