ML22308A051

Presentation 3b Parks DRP Exposure Scenarios November 3, 2022 DRP Workshop Presentation

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: ML22308A051 ML22312A365
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 10 CFR 20.1501

• A site will be considered acceptable for

• Each licensee shall make or cause to be unrestricted use if the residual made, surveys of areas, including the radioactivity that is distinguishable from subsurface, that background radiation results in a TEDE to * (1) May be necessary for the licensee to an average member of the critical group comply with the regulations in this part; that does not exceed 25 mrem (0.25 mSv) and per year, including that from groundwater * (2) Are reasonable under the sources of drinking water, and that the circumstances to evaluate residual radioactivity has been reduced to levels that are as low as reasonably - (i) The magnitude and extent of achievable (ALARA). 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?

the group of individuals reasonably expected to receive the greatest exposure to residual radioactivity for any applicable set of circumstances (10 CFR 20.1003)

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

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

• DCGLs are not appropriate to assess risk for DRPs

• MARSSIM guidance does not apply for DRPs 8

Exposure Group Examples

• Office worker

• Residential farmer

• Urban construction worker

• Resident

• Recreational user

• Maintenance worker

• Industrial worker

DRP

• Resident Potentially

• Recreational User Exposed

• Industrial Worker Groups

• 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)

• May be applied for most facilities without further Screening 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

• A risk-informed approach focuses on important issues

• Risk is defined by the risk triplet

- Scenario Risk-Informed - Probability approach - 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?