ML22269A335
| ML22269A335 | |
| Person / Time | |
|---|---|
| Issue date: | 09/12/2022 |
| From: | Caponi L, David Esh, Laplante P, Chris Mckenney, Ridge A NRC/NMSS/DDUWP/RTAB |
| To: | |
| Ridge A, 301-415-5673 | |
| References | |
| Download: ML22269A335 (24) | |
Text
Using TableCalculator to Evaluate Parametric and Model Uncertainty in the Development of the NRC LLRW Classification Tables September 12-13, 2022 Low-Level Radioactive Waste Forum Fall 2022 Meeting Christianne Ridge, David Esh, Louis Caponi, Patrick LaPlante*, and Christepher McKenney U.S. Nuclear Regulatory Commission
- Center for Nuclear Waste Regulatory Analyses
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Background===
- NRC developed waste classification limits in the early 1980s by considering the potential dose to an inadvertent intruder in agricultural, construction, and discovery scenarios
-NRC evaluated other scenarios (e.g., accident, groundwater contamination) that did not directly affect the limits
- In 2013, the Commission directed the NRC staff to consider whether to revise the low-level waste classification tables after completing the ongoing revision to 10 CFR Part 61
- TableCalculator replicates the calculations in the original Fortran codes the NRC used to develop the tables and allows sensitivity analyses
- Like the IMPACTS code it is based on, TableCalculator is intended for use in generic regulatory calculations, not site-specific analyses 2
Cap Waste Inhalation of dust Direct radiation from dust cloud Direct radiation from waste volume Deposition of dust Soil to root transfer Plant-to-animal-to-human Plant-to-animal product-to-human 3
Intruder Agriculture Class A: 102 years Class C: 502 years Intruder-Agriculture limiting for most non-TRU nuclides 3
Intruder Construction Cap Waste Inhalation of dust Direct radiation from dust cloud Direct radiation from waste volume Includes modified food pathways to account for non-equilibrium deposition and subsequent root uptake: (i) plant-human; (ii) plant-animal-human; and (iii) plant-animal product-human 4
Class A: 102 years Class B: 102 years short discovery exposure Class C: 502 years Intruder-Construction limiting for most TRU nuclides 4
Purpose
- Why did NRC develop TableCalculator?
-Enhance transparency and knowledge management for the technical bases for the existing limits
-Prepare to respond to stakeholder comments by creating a tool to easily evaluate what-if scenarios
-Evaluate model uncertainty by identifying differences between the original calculations and a more modern probabilistic intrusion analysis 5
- Why am I here today? To discuss processes the NRC staff could use to develop risk insights to evaluate whether to revise the LLW classification table
Original Calculations & Adjustments
- Calculations were based on a critical organ approach (ICRP 2) with the following dose limits:
-5 mSv (500 mrem) to the total body or bone
-15 mSv (1.5 rem) to the liver, kidney, lung, or gastrointestinal tract/lower large intestine
-30 mSv (3 rem) to the thyroid
- NRC then adjusted certain limits based on other factors (e.g.,
assumptions about waste accessibility or dilution) 6
- Nonetheless NRC staff and stakeholders often refer to the limits representing a 5 mSv (500 mrem) total effective dose equivalent (TEDE), although that is an inaccurate simplification
Documentation of LLRW Classification Calculations
- Fortran codes and data files for the original calculations are available in public documents
- Detailed explanations are provided in the Draft EIS and supporting documents
- Scenarios, assumptions, equations, and parameter values underlying the intruder dose calculations and subsequent adjustments are publicly available.
- Some are not trivial to trace 7
Tool Availability 8
Publicly available without fee: https://ramp.nrc-gateway.gov/
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- Request support with website button for installation issues or problems running code
- Contact authors for questions or comments about the calculations or mathematical implementation Christianne.Ridge@nrc.gov David.Esh@nrc.gov
Installation Step 1: Download the GoldSim Player from the GoldSim Technology Group (no cost) https://www.goldsim.com/Web/Customers/Downloads/Player/
Step 2: Download TableCalculator from the NRC RAMP website (no cost membership required): https://ramp.nrc-gateway.gov/
Step 3: Open the TableCalculator file with the GoldSim Player program. To enable reference links in TableCalculator, place technical references from RAMP webpage in the same folder as the TableCalculator file 12
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14 Main Settings
Default inputs yield results used in the 1980s development of the waste classification limits Key Outputs 15
Links provide explanations and references for adjustments made during rulemaking in the 1980s Key Outputs (continued) 16
Pathway results were previously calculated but not output by the code Information about dominant exposure pathways provides insights Additional Outputs 17
Tool offers Behind the Scenes look at the model Visible relationships and in-line documentation 18 Model View
Comparison with a Modern Analysis
- Staff from the Southwest Research Institute, Center for Nuclear Waste Regulatory Analyses (CNWRA) developed a modern probabilistic intruder assessment based on BDOSE
- BDOSE is a Biosphere Dose Model previously developed by CNWRA staff
- BDOSE is implemented in GoldSim, a commercial software package developed by GoldSim Technology Group of Issaquah, WA
- Comparing results from TableCalculator and the modern analysis helps staff understand the impacts of different modeling approaches
- The ability to change input parameters and evaluate intermediate model results provided insights into the reasons underlying the differences between the results of the two approaches 19
Comparison with a Modern Analysis (continued)
- In some cases, large differences between the result of a modern analysis and the original results could be explained by changes to bone dosimetry between ICRP 2 and ICRP 26/30
- Some differences could be explained by differences in the conceptual model for root uptake of radionuclides by plants
- For other radionuclides, the difference was dominated by regulatory adjustments the NRC made to the table values during the 1980s rulemaking process 20
Class C Ni-59
- Adjustments for Class C waste and metal wasteform increased limit by x 100
- Using ICRP-72 DCFs increased the derived concentration
- Revising conceptual model for plant uptake of radionuclides decreased derived concentration
- Significant difference between drilling and excavation scenario (scenario uncertainty larger than parametric uncertainty) 21
Class A Sr-90
- No regulatory adjustments applied
- Using ICRP-72 DCFs increased derived concentration
- Revising conceptual model for plant uptake of radionuclides decreases derived concentration 22
Class A Sr-90 Probabilistic Sensitivity Analysis
- Scatter plots show projected dose at time of intrusion vs.
key parameter values for 750 realizations of modern analysis
- Parameters with the greatest correlation to the projected dose for Class A Sr-90 were
- Non-leafy vegetable transfer factor
- Non-leafy vegetable consumption
- Leafy vegetable consumption 23
Conclusions
- Future NRC review of waste classification tables directed by the Commission will include the staffs technical analyses, programmatic considerations, and stakeholder input
- Sensitivity analyses with the TableCalculator tool help the staff assess the significance of assumptions in the original analysis and will help staff respond to stakeholder comments
- Comparison of deterministic sensitivity analyses results with the results of a modern probabilistic intrusion analysis provides risk insights into key parameters and areas of conceptual model uncertainty
- TableCalculator is publicly available without cost on the Radiation Protection Computer Code Analysis and Maintenance Program website:
- Like the original codes it is based on, TableCalculator is only intended for regulatory, generic calculations, not site-specific analyses 24