ML18127A060
| ML18127A060 | |
| Person / Time | |
|---|---|
| Issue date: | 04/11/2018 |
| From: | Amy Snyder NRC/NMSS/DDUWP/MDB |
| To: | |
| AMSnyder NMSS/DUWP/MDB 415.6822 T5D48 | |
| References | |
| Download: ML18127A060 (60) | |
Text
NRC Evaluation of WNYNSC Off-Site Field Sampling and Dose Assessment Report Overview, Data Evaluation Discussion, and and Potential Exposure 1
Overview Amy Snyder, Senior Project Manager Materials Decommissioning Branch Division of Decommissioning, Uranium Recovery, and Waste Management Office of Nuclear Materials Safety and Safeguards Amy.Snyder@NRC.gov 301 415-6822 2
- U.S Nuclear Regulatory Commission (NRC) Roles and Responsibilities at West Valley
- Data Evaluation Discussion
- Potential Dose Assessment Discussion
4
NRC License
- NRC Licensee: New York State Energy Research and Development Authority (NYSERDA)
- 1980 West Valley Demonstration Project Act Cooperative Agreement between NYSERDA and U.S. Department of Energy (DOE)
License Amended NRC roles and responsibilities 5
Atomic Energy Act 6
- Regulatory authority of 10 CFR Part 50 License
- Ensure Public health and safety for licensed facilities/activities
- Inspect licensed facilities/activities
- Terminate license
West Valley Demonstration Project Act 7
NRC responsible for:
Prescribing requirements for decontamination and decommissioning - completed Providing review and consultation to DOE on the project - on going Monitoring the activities under the project for the purpose of assuring health and safety - on going Cooperating Agency on DOE Environmental Impact Statement under the National Environmental Policy Act -
Decommissioning - on going
After West Valley Demonstration Project Act 8
NRC will have regulatory responsibility for:
Authorizing termination of the license, should NYSERDA seek license termination.
License Termination:
10 Part 50 License NYSERDA submits a license amendment application
Decommissioning Plan for NRC approval
Environmental review to determine if an Environmental Impact Statement is needed to support the licensing action
Why Sampling and Analysis?
9
- Aerial Survey data -
a lot of uncertainty
Not used to determine compliance with public health and safety
- In the absence of other data or information that is relevant and less uncertain, the only way to determine what is in areas above background is to sample and analyze (Measure or Account for Radionuclides of Concern)
Independent Assessment 10 Technical Review of NYSERDAs submittal Staff evaluates NYSERDAs submittal against requirements
Applicable guidance documents Sampling and Analysis and Data Assessment Dose Assessment
What needed to be done?
11 NYSERDA to
- Determine what are the Areas of Interest-where to sample
- Determine what is in the Areas of Interest
- Demonstrate by evaluation or measurement that the public dose is less than 25 mrem/y (benchmark)
NRC to evaluate NYSERDAs submittal to confirm that the public dose is less than 25 mrem/y.
Data Evaluation Discussion Gregory Chapman, Health Physicist, CHP Materials Decommissioning Branch Division of Decommissioning, Uranium Recovery, and Waste Management Office of Nuclear Materials Safety and Safeguards Gregory.Chapman@NRC.gov 301 415-8718 12
Purpose of the Off-Site Characterization and Dose Assessment
- Determine whether the aerial survey truly identified areas containing elevated Cs-137 levels and, if so, whether there is a safety concern created by West Valley
- Ground truth measurements
- Are there elevated concentrations of radioactivity?
- Did the materials come from WNYNSC?
- Are there safety concerns?
13
Areas of Consideration - Area 1 14
Areas of Consideration - Area 2 15
Areas of Consideration - Area 3 16
Areas of Consideration - Area 4 17
Areas of Consideration - Area 5 18
Quick Review of Dose Limits/Background
- Occupational Dose Limits
- Worker: 5,000 mrem/y
- Minors: 500 mrem/y
- Embryo/Fetus: 500 mrem/gestation
- Public Dose Limits
- 100 mrem/y during operations
- 2 mrem/h, 50 mrem/y for requiring area restrictions
- Decommissioning Dose Criteria
- Unrestricted Use: 25 mrem/y (all applicable pathways)
- Restricted Use: 25 mrem/y w/restrictions, 100 to 500 mrem/y if restrictions fail.
- Background from natural sources: ~300 mrem/y 19
Survey Activities Performed by NYSERDA Review of Aerial Survey
- Identify areas of greatest Cs-137 contamination Limited scanning of the identified area
- Transects of each area/sub-area/sub-region Radiation measurements
- Exposure rate, gamma detector count response (fluence measurement)
For reference areas and identified areas of concern Sampling
- Establish reference data set (3 different data sets for varying geography)
- Multiple discrete depth intervals (to 1 meter depth BGS)
- Biased sampling based on review of scanning
- Minimum number of samples from randomly selected locations within the identified area + from any identified elevated area
- Analysis primarily by gamma spec with some samples analyzed for isotopics by specific procedures, all samples analyzed for gross alpha/gross beta
- Additional samples taken from special request areas 20
Radionuclides of Interest Nuclide Surface Soil DCGLs (pCi/g)
Am241 29 C14 16 Cm243 35 Cm244 65 Cs137 15 I129 0.33 Np237 0.26 Pu238 40 Pu239 25 Pu240 26 Pu241 1200 Sr90 4.1 Tc99 21 U232 1.5 U233 8.3 U234 8.4 U235 3.5 U238 9.8 21
Cs-137 Facts
- Often proven to be the most important contributor to environmental radiation dose to humans
- Primary Sources in Biosphere (Globally)
- 90% from atmospheric testing of nuclear weapons
- 6% from Chernobyl Accident
- 4% from nuclear fuel reprocessing activities
- Why its important
- General Abundance
- Moderate half-life (30 yr), Decent beta/gamma emissions
- Readily transports through environment and food chains
- In solution, readily assimilates into plants and animals due to chemical characteristics similar to potassium
- Strongly binds, sometimes irreversibly, to clays in soil/sediment
- Has been well studied and modeled
- NCRP Report No. 154, published in 2006 22
Sampling Planned vs Achieved Area Approximate Size of Area (m2)
Planned/Final Planned Sample Locations Actual Sample Locations Planned Samples to be Collected Actual Samples Collected 1.1 NA 1
1 3
4 1.2 NA 1
1 3
3 1.3 NA 1
1 3
5 1.4 NA 1
0 3
0 2.1 42/22 4
4 12 12 2.2 350/194 4
4 12 15 3.1 46,933/25,833 24 24 60 71 3.2 1,028/511 4
4 10 13 4.1 12,913/18,551 24 24 60 71 4.2 9,378/10,073 15 24 38 70 4.3 2,591/25,718 15 24 38 71 4.4 44,329/4,738 24 15 60 45 4.5 550/15,702 4
24 10 60 5.1 1,374/1,324 4
4 10 14 5.2 902/6,604 4
15 10 43 5.3 5,845/573 15 4
38 14 5.4 0/1,791 4
13 5.5 0/312 4
13 5.6 0/888 4
12 23
NRC Staffs High Level Considerations Were the right areas sampled?
Were the data evaluated properly?
Do the conclusions make sense?
24
Elevated Areas Identified from Aerial Survey
- NRC staff used GIS software and data from the aerial survey to independently map elevated areas of Cs-137 detection.
- Not all the same algorithms used by DOE
- Consistent results as in plan/report
- Also verified that samples were obtained within these areas by plotting GPS coordinates of sampling locations (previous area maps are NRC generated)
- Provides reasonable assurance of sampling elevated contaminants in these areas 25
Scanning Survey Review
- Scanning in this instance used solely to try and identify trends/anomalies in the detected radiation fluence across the site
- Would determine biased sampling locations
- Multiple ways to consider the data
- Common is to plot based on color coding to identify anomalies/trends
- Less common is to identify highest measurements (>3 ), plot, and see if clustered/indicate elevated area
- Multiple figures in the report showing each area/sub-area/sub-region
- Some areas not accessible or heavy overgrowth, surveyed using modified methods
- Some obstructions limited scanning
- Only identified a trend in sub-area 3.1 26
27
Reference Data Set Determinations
- 3 different reference data sets
- WNYNSC, Seneca Flood Plain, Seneca Non-Flood Plain
- All sampled for gross alpha/gross beta/Cs-137 + some extended analysis
- None indicated elevated fission product/activation product/or chemically separated Uranium/Thorium/Radium
- Cs-137 (fission product) most likely the result of fallout. Not inconsistent with literature for NY.
28
Exposure Rate Summary Area/Sub-Area Average Gross Bkg Exposure Rate
(µrem/h)
Average Gross Exposure Rate
(µrem/h)
NRC Net Exposure Rate
(µrem/h)
NYSERDA Net Exposure rate
(µrem/h) 1 (includes all sub areas) 3.8 +/- 0.4 5.0 +/- 1.0 1.2 0.7/2.3 2.1 7.8 +/- 1.0 4
3.9 2.2 4.0 +/- 0.8 0.2 0.05 3.1 8.3 +/- 1.7 4.5 3.9 3.2 4.8 +/- 1.3 1
0 4.1 5.2 +/- 0.8 5.9 +/- 0.9 0.7 0.6 4.2 5.2 +/- 1.0 0
0 4.3 5.1 +/- 1.3 0
0 4.4 4.9 +/- 1.0 0
0 4.5 4.9 +/- 1.0 0
0 5.1 6.0 +/- 3.9 6.5 +/- 0.9 0.5 1.8 5.2 4.8 +/- 0.7 0
0.2 5.3 4.8 +/- 0.4 0
0.3 5.4 5.3 +/- 0.8 0
0.6 5.5 5.8 +/- 0.8 0
1.1 5.6 4.8 +/- 0.8 0
0.1 29 NYSERDA estimates a 5.5 urem/h exposure rate equates to ~25 mrem/y
Sampling Summary Net Soil Concentrations (Avg - Avg Bkg)
Top (pCi/g)
Near Top (pCi/g)
Near Bottom (pCi/g)
Bottom (pCi/g)
Area/Sub-Area NRC avg NYSERDA avg NRC avg NYSERDA avg NRC avg NYSERDA avg NRC avg NYSERDA avg 1 alpha
-4.1
-3.4
-4.5
-3.3 0-5cm, 5-15cm beta 1.9 2.5
-5.8
-5.3 Cs-137 1.9 1.8 0.0 0.0 2.1 alpha
-2.5
-1.6
-1.9
-2.4 0-5cm, 5-15cm beta 1.8 1.1 1.8 1.4 Cs-137 0.2 0.2 0.3 0.2 2.2 alpha
-1.8
-2.0
-5.0
-4.0 0.2 1.1 0-5cm, 5-15cm, 15-100cm beta 1.3 0.7
-9.5
-9.4
-2.0
-1.8 Cs-137 1.4 1.4 0.0 0.0
-0.1 0.0 3.1 alpha
-0.7 0.2 1.4 2.3 2.1 2.4
-1.3
-0.7 0-15cm, 15-30cm, 30-60cm, 60-100cm beta
-1.5
-0.6 3.6 3.8
-2.0
-1.1
-5.3
-4.9 Cs-137 0.8 0.8 1.4 1.3 2.2 2.2 0.3 0.1 3.2 alpha
-0.3 0.5
-2.8
-2.4
-7.4
-6.6 0-15cm, 15-30cm, 30-60cm, 60-100cm beta
-4.4
-3.7
-5.8
-4.9
-6.8
-6.1 Cs-137 0.2 0.3 0.1 0.1 0.0 0.0 4.1 alpha 0.7 0.1 1.5 1.1 2.4
-0.1
-1.4
-1.4 0-15cm, 15-30cm, 30-60cm, 60-100cm beta 1.8
-2.0
-0.8
-0.9
-2.8
-3.8 0.5 0.7 Cs-137 0.9 0.7 1.1 0.8 0.5 0.2 0.2 0.1 4.2 alpha 0.7 0.4 1.9 1.8
-2.5
-3.4
-0.4
-1.0 0-15cm, 15-30cm, 30-60cm, 60-100cm beta 2.2 1.5 0.5
-0.9
-4.7
-5.7
-1.5
-1.8 Cs-137 1.2 1.0 2.1 1.5 0.4 0.2 0.1 0.0 4.3 alpha 0.8 0.3
-0.5
-1.0
-3.0
-1.4
-1.1
-2.3 0-15cm, 15-30cm, 30-60cm, 60-100cm beta 1.8 1.0
-2.3
-2.6
-0.6
-7.4
-2.1
-2.7 Cs-137 1.0 0.8 0.9 0.6 0.5 0.1 0.2 0.1 4.4 alpha
-1.1
-1.2 4.0 0.5
-3.6
-3.8
-2.7
-3.5 0-15cm, 15-30cm, 30-60cm, 60-100cm beta
-0.1
-0.8
-3.1
-3.4
-6.1
-7.2
-3.5
-3.7 Cs-137 0.5 0.4 0.8 0.6 0.1 0.1 0.0 0.0 4.5 alpha
-0.5
-0.1 1.5 1.0 2.9 2.0 2.4 2.0 0-15cm, 15-30cm, 30-60cm, 60-100cm beta 1.5 1.1 0.0 0.0
-1.8
-2.4
-1.8
-1.8 Cs-137 0.7 0.6 0.5 0.4 0.1 0.1 0.1 0.0 5.1 alpha
-1.1
-3.5 3.8 0.9 1.6 4.8
-14.9
-14.9 0-15cm, 15-30cm, 30-60cm, 60-100cm beta
-3.7
-3.2
-0.2
-3.5
-5.5
-3.5
-21.2
-21.2 Cs-137 0.2 0.2
-0.1
-0.1 0.1 0.1 0.0 0.0 5.2 alpha
-2.7
-3.7
-0.4
-1.9 1.9
-1.3
-1.0
-2.3 0-15cm, 15-30cm, 30-60cm, 60-100cm beta
-5.1
-5.6
-2.4
-3.6
-5.3
-6.5
-10.5
-11.9 Cs-137 0.3 0.3 0.0 0.0 0.0 0.0 0.0 0.0 5.3 alpha
-3.0
-3.8
-2.2
-2.6
-0.7 2.5
-11.9
-11.9 0-15cm, 15-30cm, 30-60cm, 60-100cm beta 0.2 1.5
-7.7
-8.5
-9.4
-7.4
-18.2
-18.2 Cs-137 0.4 0.5 0.0 0.0 0.0 0.0 0.0
-0.02 5.4 alpha
-1.9
-2.9
-3.2
-3.0
-6.3
-3.1
-8.6
-8.6 0-15cm, 15-30cm, 30-60cm, 60-100cm beta
-3.4
-2.1
-9.7
-10.5
-10.0
-8.0
-20.1
-20.1 Cs-137 0.3 0.3
-0.1
-0.1 0.0 0.0 0.0 0.0 5.5 alpha
-1.8
-2.6
-6.4
-6.3 1.5 4.7
-12.9
-12.9 0-15cm, 15-30cm, 30-60cm, 60-100cm beta
-4.9
-3.5
-11.1
-11.8
-11.1
-9.1
-18.3
-18.3 Cs-137 0.3 0.4
-0.1
-0.1 0.0 0.0 0.0 0.0 5.6 alpha
-5.1
-6.0
-5.2
-5.9 15.0
-17.1
-17.1 0-15cm, 15-30cm, 30-60cm, 60-100cm beta
-1.5
-3.9
-9.1
-9.5 7.1
-23.1
-23.1 Cs-137 0.6 0.5
-0.1 0.0 0.0 0.0 0
30
Comparison of Weighted Average Area/Sub-Area Analyte NRC Weighted Ave (pCi/g)
NYSERDA Weighted Ave (pCi/g) 1 alpha 0
0 beta 0.623 0.007 Cs-137 0.6 1.7 2.1 alpha 0
0 beta 1.9 1.3 Cs-137 0.23 0.19 2.2 alpha 0.20 0
beta 0.07 0
Cs-137 0.07 0.066 3.1 alpha 0.82 1.1 beta 0.53 0.56 Cs-137 1.1 1.0 3.2 alpha 0
0.19 beta 0
0 Cs-137 0.05 0.11 4.1 alpha 1.04 0.170 beta 0.454 0.276 Cs-137 0.512 0.318 4.2 alpha 0.393 0.307 beta 0.405 0.225 Cs-137 0.669 0.447 4.3 alpha 0.113 0.023 beta 0.263 0.154 Cs-137 0.499 0.276 4.4 alpha 0.605 0.069 beta 0
0 Cs-137 0.238 0.192 4.5 alpha 2.045 1.541 beta 0.219 0.167 Cs-137 0.249 0.185 5.1 alpha 1.062 1.578 beta 0
0 Cs-137 0.044 0.06 5.2 alpha 0.566 0
beta 0
0 Cs-137 0.054 0.057 5.3 alpha 0
0.753 beta 0.034 0.222 Cs-137 0.050 0.068 5.4 alpha 0
0 beta 0
0 Cs-137 0.039 0.043 5.5 alpha 0.456 1.413 beta 0
0 Cs-137 0.043 0.052 5.6 alpha 4.506 0
beta 2.138 0
Cs-137 0.088 0.095 31
Primary Reasons for Discrepancies
- NYSERDA used weighted averaging while NRC staff did not
- Weighting based on radiation measurement uncertainties could introduce biases
- Also used propagated uncertainties
- Treatment of outliers
- NYSERDA evaluated and omitted or substituted data if analysis did not collaborate anomalies or if the natural radionuclide concentrations did not match up with the gross analytical values.
- NRC staff conservatively picked from all replicate data and made no omissions or substitutions 32
Home Owner and Reach Data Set Evaluations 33 0
5 10 15 20 25 30 Gross Alpha Supplemental Data Compare (pCi/g) 0 5
10 15 20 25 30 35 40 Gross Beta Supplemental Data Compare (pCi/g)
Home Owner and Reach Data Set Evaluations 34
-0.1 0
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 Cs-137 Supplemental Data Compare (pCi/g)
Conclusions
- NYSERDA - No exceedances of DCGLs in these areas and no significant exposure rates measuredno safety concerns
- NRC - Verified that, on average and with conservative data set, the concentrations are below the applied DCGLs and the measured exposure rates are not significantly elevated.
- Concentrations are so low that one cannot definitively ascertain where material originated although there are limited prospects 35
Dose Assessment Discussion Cynthia Barr, Senior Systems Performance Analyst Performance Assessment Branch Division of Decommissioning, Uranium Recovery, and Waste Management Office of Nuclear Materials Safety and Safeguards Cynthia.Barr@NRC.gov 301-415-4015 36
Dose Assessment Review
- NYSERDA used various methods of estimating potential doses to members of the public for each of the areas under investigation, including the following:
Data Based Assessments 37
- Results from the 2014 Aerial Radiological Survey to estimate external dose
- Tissue equivalent dose rate survey meter data to estimate external dose
- DOEs 2012 Annual Site Environmental Report (ASER) results to calculate fish dose.
Dose Assessment Review (cont)
Modeled Based Assessments
- RESRAD OFFSITEcurrent land use
- RESRAD ONSITEreasonably foreseeable land use (Areas 1 through 3)
- Comparison against WVDP, Phase 1 Decommissioning Plan DCGLs 38
Analysis Approaches There are two different analysis approaches to estimating dose:
- Dose modeling approach
- Derived concentration guideline level (DCGL) approach
- Both entail use of modeling 39
Why is dose modeling needed?
- There is no dose meter available to estimate dose
- At the time of decommissioning
- During the 1,000 year analysis period 40
- The analysis requires the use of mathematical models to estimate dose through various pathways.
Dose Modeling The dose modeling approach uses actual (or estimated) measurements of radioactivity at a site to assess the potential dose to the average member of the critical group. Various pathways of exposure are considered.
41
DCGL approach
- The DCGL approach allows a licensee to calculate, a priori, a concentration limit (DCGL) for each radionuclide based on the dose criteria, and then demonstrate that the residual radionuclide concentrations are below these DCGLs.
- Using this approach, the final status survey results are compared to the DCGLs
- A sum of fractions approach is used 42
RESRAD Family of Codes Developed by Argonne National Laboratory Originally for the U.S. Department of Energy (DOE)
Pathway analysis programs (external, inhalation, and ingestion),
- RESRAD: originally contaminated soil in the natural environment
- RESRAD-BUILD: inside buildings.
- RESRAD-OFFSITE: extends RESRAD to handle offsite locations Widely used by DOE, NRC licensees, and NRC staff.
Underwent external verification.
Probabilistic analysis (NRC-sponsored) 43
Exposure pathways considered in RESRAD 44
What is the standard being used?
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 20.1402 Radiological criteria for unrestricted use 45
What is the definition of 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)
Considers
- Habits (time fraction spent on site)
- Actions (worker or resident)
- Characteristics (e.g., inhalation, and ingestion) 46
Areas Reviewed by NRC
- Source Inventory/Concentrations
- Exposure Scenarios
- Conceptual Models
- Parameter Selection
- Evaluation of Results 47
Current Exposure Scenarios
- Area 1--Resident homemaker
- Area 2--Recreational hiker (with hunting)
- Area 3--Resident farmer
- Areas 4 and 5--Collector and Hunter (Also considered resident farmer in Areas 1 and 2.2) 48
SNI RESRAD OFFSITE Model Domains 49 Sub-Areas 4.1 through 4.5 Sub-Areas 5.1 through 5.6
NYSERDAs Results 50 Method Aerial Bicron OFFSITE ONSITE FISH Method Type External Dose Measurement External Dose Measurement Dose Modeling Dose Modeling Biota Sampling Area 1 0.0 8.0 1.0 1.7
<0.1 Area 2 0.1 0.4 5E-03 0.13
<0.1 Area 3 1.8 3.9 0.8 7.3
<0.1 Area 4 3.7 1.9 (11.9*)
0.57 NA 0.6 Area 5 1.3 4.6 (8.5*)
0.1 NA NA Note: Maximum value listed for any subarea within an area.
- Uses maximum soil sample concentration and assumes receptor spends all of his time (e.g., performs all activities) in that single hot spot location.
Potential Technical Issues
- Weighted averaging approach (i.e., weighted based on uncertainty in measurement and based on thickness of contamination)
- Conceptual model issues in RESRAD OFFSITE
- Some parameter selections 51
Conservatisms
- Assumed gross alpha and gross beta above background were attributable to Pu-239 or Am-241; and Sr-90, respectively
- conservative because these radionuclides deliver relatively high doses for the same concentration compared to other alpha/beta emitters
- The mean gross alpha and gross beta concentrations are not statistically greater than mean background concentrations
- Expanded analyses reveal no detections of Pu-239, Am-241, or Sr-90 and are generally consistent with naturally occurring radionuclides 52
Mitigation of uncertainty
- Multiple methods of analysis by NYSERDA
- Independent calculations by NRC staff to evaluate technical issues
- RESRAD ONSITE analyses
- Conceptual model issues (co-location of sources)
- Evaluation of indistinguishability with background
- Comparison to Screening Values in NUREG-1757, Volume 2 Appendix H 53
Conclusions
- NRC has reasonable assurance that the risk associated with offsite residual radioactivity is low (below the unrestricted use limits in 10 CFR Part 20, Subpart E [20.1402])
- The concentration of the primary radionuclide of concern, Cs-137, is significantly below the screening values.
54
Additional Slides 55
Fission Fission occurs when a neutron interacts with a fissile atom causing the nucleus to split (e.g., U-235)
Each fission results in the production of additional neutrons which can produce more fission events
Fission Products Fission fragments are highly radioactive isotopes Most fission fragments produced in reactor fuel will be contained within the fuel rods (80% of the total energy released from fission is kinetic energy of fragments)
Some fission products decay to other isotopes that are also radioactive (4-5% of the total energy released from fission is heat from fission product decay)
Fission Products
- Radioiodines; e.g., I-131 (Thyroid)
- Noble gases, primarily Kr and Xe, are an external (submersion) hazard to the whole body, skin or lens of eye
Activation Products Co-60: produced by neutron activation of stable Co-59, which corrodes off of valve parts and control rod blades, enters the coolant and becomes radioactive by neutron capture N-16: O-16 absorbs neutron; 7 MeV gamma ray with 7 second half-life Other activation products (Fe-59, Mn-54, and Zn-65, & H-3)