ML18107A147
| ML18107A147 | |
| Person / Time | |
|---|---|
| Issue date: | 04/13/2018 |
| From: | Thomas Nicholson NRC/RES/DRA |
| To: | |
| References | |
| Download: ML18107A147 (22) | |
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Environmental Modeling and Monitoring for Risk-Informed Performance-Based Assessments Thomas Nicholson Office of Nuclear Regulatory Research George Alexander and David Esh Office of Nuclear Material Safety and Safeguards ICEMM Annual Public Meeting April 25, 2018 Rockville, Maryland 1
Key Messages
- The fusion of site characterization and monitoring data with modeling is important to the NRC staff.
- Risk insights and performance indicators may be used to implement a risk-informed, performance-based regulatory approach.
- Risk-informed, performance-based regulation allows the NRC to make better decisions, increases efficiency, and decreases regulatory burden.
- Fusion of modeling with characterization and monitoring data allows NRC staff to focus on what matters and why it matters.
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Terminology What does the NRC staff mean when we use the terms Environment and Safety Significant for Environmental Modeling and Monitoring?
Environmental Qualification
- A process for ensuring that equipment will be capable of withstanding the ambient conditions that could exist when the specific function to be performed by the equipment is actually called upon to be performed under accident conditions.
examples: ground- and surface-water flooding, seismic events Safety-Significant
- When used to qualify an object, such as a system, structure, component .., this term identifies that object as having an impact on safety, whether determined through risk analysis or other means, that exceeds a predetermined significance criterion.
examples: ability of ground-water units to attenuate radionuclides; engineered covers; spent fuel pools; subsurface pipes and drains 3
Terminology
- Monitoring and Model Data Fusion is the concept of coupling information sources, as temporal and spatial data, from a wide variety of monitoring programs and their instrumentation, to the model which quantitatively analyses and simulates the system of concern.
- Fusion involves the active processing and synthesizing of various data sources into a unified model database, and where the model informs the monitoring programs as to what, when, where and how the data is to be obtained and translated into modeling assumptions and inputs such as boundary conditions and parameters.
- Performance indicators are quantitative measures of the operation of a system and/or subsystems, both engineered and natural, that shows how it is performing when measured against established thresholds.
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Schematic of a below-ground engineered system designed for normal and abnormal environmental 5
conditions during operations and following closure
Conceptual Site Model Conceptual Site Model (CSM) is an abstract, qualitative representation of the relevant Features, Events and Processes (FEPs) that affect performance at the site.
Objective is to develop, test and build confidence in the CSMs which include the engineered facility, its structures, systems and components including backfill, and the environmental FEPs relevant for both modeling and monitoring strategies and programs.
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Simple illustration of a Conceptual Site Model showing the relationship between the engineered and natural systems. 7
Performance Indicators -
A quantitative measure of the operation of a system and/or subsystems, both engineered and natural, that shows how it is performing when measured against established thresholds.
examples: ground-water recharge; soil moisture content; contaminant attenuation due to hydro-biogeochemical processes Integration of Modeling and Monitoring uses Performance Indicators which are important to both.
examples: ground-water potentiometric levels and gradients; radionuclide concentrations; contaminant fluxes and travel times 8
Performance Indicators (continued)
Identify Performance Performance Indicators Indicators Site Modeling Risk Monitoring Characterization Insights 9
Ground-Water and Contaminant Monitoring Based upon the CSM, a monitoring strategy is developed to both detect and later monitor abnormal releases prior to possible offsite migration 10
Monitoring Data Needs Understanding of the Conceptual Site Model and the desired Performance Indicators help to determine data needs:
What, where, when and how data should be collected for short and long-term performance under both normal and abnormal conditions Processing of monitored data for use in numerical models to establish and verify assumptions and inputs such as boundary conditions and parameter values Testing of Conceptual Site Models and their numerical models to evaluate risk assessment estimates.
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Risk-Significant Scenario Offsite Ground-Water Pumping Wells 12
Risk Methodologies Risk - the combined answer to three questions that consider (1) what can go wrong, (2) how likely it is, and (3) what its consequences might be. These three questions allow the NRC staff to understand likely outcomes, sensitivities, areas of importance, system interactions, and areas of uncertainty, which can be used to identify risk-significant scenarios.
Iterative process for modeling and monitoring assessments using risk methodologies for assessing uncertainties (both aleatory and epistemic) of the normal and abnormal scenarios.
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Monitoring Performance Indicators Direct and indirect monitoring methods (e.g., monitoring wells and geophysical instrumentation) help to quantify performance indicators (e.g., contaminant flux at the boundary)
Analysis of Monitoring Performance Indicators 14
Decision-Making Risk-informed decision-making is an approach to regulatory decision-making, in which insights from probabilistic risk assessment are considered with other engineering and scientific insights.
Decision-making is both Risk-Informed and Performance-Based Monitoring and Model Data Fusion helps to integrate observations and calculations using selected Performance Indicators to build confidence in and reasonable assurance of decision-making 15
Characterization, Modeling, and Monitoring of Short- and Long-term Erosion Adapted from NUREG-2175 16
Monitoring Across Temporal &
Spatial Scales Adapted from SRR-CWDA-2014-00006 and SRNS-TR-2017-00227 17
Development of Confidence in Ground-Water Models Adapted from 2017 Draft DOE Groundwater Compliance Action Plan for the Gunnison, CO, Processing Site 18
Summary
- Understanding of the Conceptual Site Model and the desired Performance Indicators help to determine data needs
- Decision-making is both Risk-Informed and Performance-Based
- Monitoring and model data fusion helps to integrate observations and calculations using selected Performance Indicators to build confidence in and reasonable assurance of decision-making
- Uncertainty coupled to multiple biases leads to a lack of reasonable assurance
- Importance of using multiple independent reviewers to evaluate the integrated monitoring and modeling programs Thank you for your attention 19
Back-up Slides 20
Performance Indicators -
A quantitative measure of the operation of a system and/or subsystems, both engineered and natural, that shows how it is performing when measured against established thresholds.
examples: ground-water recharge; soil moisture content; contaminant attenuation due to hydro-biogeochemical processes Integration of Modeling and Monitoring uses Performance Indicators which are important to both.
examples: ground-water potentiometric levels and gradients; radionuclide concentrations; contaminant fluxes and travel times Site Risk Modeling Monitoring Characterization Insights 21
In Situ Uranium Recovery Process 22