ML22308A051
| ML22308A051 | |
| Person / Time | |
|---|---|
| Issue date: | 11/03/2022 |
| From: | Leah Parks Office of Nuclear Material Safety and Safeguards |
| To: | |
| C. Barr, NMSS/DUWP 301-415-4015 | |
| Shared Package | |
| ML22301A159 | List: |
| References | |
| Download: ML22308A051 (15) | |
Text
Exposure Scenarios for Unrestricted Release Decommissioning Sites Leah Parks Risk Analyst DRP Public Workshop November 3, 2022
Overview
- Unrestricted Release Criteria
- Critical Group and Potential Exposure Groups
- Steps in Performing a Dose Assessment
- Exposure Pathways
- Elimination of Pathways
- Consideration of Likelihood
Unrestricted Release Criteria 10 CFR 20.1402 A site will be considered acceptable for unrestricted use if the residual radioactivity that is distinguishable from background radiation results in a TEDE to an average member of the critical group that does not exceed 25 mrem (0.25 mSv) per year, including that from groundwater sources of drinking water, and that the residual radioactivity has been reduced to levels that are as low as reasonably achievable (ALARA).
10 CFR 20.1501 Each licensee shall make or cause to be made, surveys of areas, including the subsurface, that (1) May be necessary for the licensee to comply with the regulations in this part; and (2) Are reasonable under the circumstances to evaluate (i) The magnitude and extent of radiation levels; and (ii) Concentrations or quantities of residual radioactivity; and (iii) The potential radiological hazards of the radiation levels and residual radioactivity detected.
What Is the Critical Group?
Consider Habits (time fraction spent on site)
Actions, (workers vs. resident)
Characteristics (inhalation rate, soil ingestion)
Or individual or relatively homogenous group of individuals expected to receive the highest exposure within the assumptions of the particular scenario (NUREG/CR-5512, Volume 1)
Critical group the group of individuals reasonably expected to receive the greatest exposure to residual radioactivity for any applicable set of circumstances (10 CFR 20.1003)
Who is the Average Member?
- the average member of the critical group is an individual who in turn is assumed to represent the most likely exposure situation based on prudently conservative exposure assumptions and parameter values within the model calculations
- (Draft NUREG-1549)
Performing a Dose Assessment
- Define site conceptual model
- Contamination Source
- Environmental Transport
- Receptor
- Determine appropriate exposure scenarios
- Ensure computer codes and calculations are appropriate for the conceptual model 6
Site Conceptual Model 7
Contamination Source
- Radionuclides
- Media (soil, water, etc.)
- Physical and chemical form
- Area and depth
- Distribution 8
- DCGLs are not appropriate to assess risk for DRPs
- MARSSIM guidance does not apply for DRPs
Exposure Group Examples Office worker Residential farmer Urban construction worker Resident Recreational user Maintenance worker Industrial worker
DRP Potentially Exposed Groups
- Resident
- Recreational User
- Industrial Worker
- Child
DRP Potential Exposure Pathways External
- Standing Nearby
- On Skin
- In Eye Internal
- Ingestion
- Inhalation Cancer risk Threshold effects
Framework for Probability Scenario Type Description Compliance Exposure Scenarios (Results Compared to Dose Standards)
Screening May be applied for most facilities without further analysis Bounding Bounds doses from other scenarios Reasonably Foreseeable Likely within next 100 years Other Exposure Scenarios (Results Used to Inform Decisions)
Less Likely But Plausible Possible but not likely within 100 years Implausible Exposure Scenarios (No Analysis is Required)
Implausible Could not occur
Risk-Informed approach A risk-informed approach focuses on important issues Risk is defined by the risk triplet
- Scenario
- Probability
- Consequence Less likely scenarios are used to inform decisions but not compared to 25 mrem/yr dose standard Risk-insignificant radionuclides and exposure pathways may be removed from detailed analysis
Less Likely But Plausible Low Probability scenarios may fall under LLBP approach Qualitative Likelihood Probability is not multiplied by dose to compare to a limit
Discussion Questions
- Who are the potentially exposed individuals?
- How do you determine the likelihood of interaction with a particle?
- What are the risk significant exposure pathways for DRPs?