Elizabeth J. Kelly

Separating Variability and Uncertainty in Environmental Risk Assessment—Making Choices

This article reviews some of the current guidance concerning the separation of variability and uncertainty in presenting the results of human health and ecological risk assessments. Such guidance and some of the published examples of its implementation using two-stage Monte Carlo simulation methods have not emphasized the fact that there is considerable judgment involved in determining which input parameters can be modeled as purely variable or purely uncertain, and which require explicit treatment in both dimensions. Failure to discuss these choices leads to confusion and misunderstanding of the proposed methods. We conclude with an example illustrating some of the reasoning and statistical calculations that might be used to inform such choices.

Optimal inspection of a finite population

ABSTRACT This article presents a method for determining an optimal quality control (QC) inspection frequency for a manufacturing process where a specified number of items will be produced and where, if the process goes out of control and generates a defective item, it stays out of control. In addition, there is a QC inspection procedure than can detect a defective item. The frequency of inspection is based on minimizing the total cost. The total cost includes the cost of QC inspections plus the cost of manufacturing defective items. In this application the cost of manufacturing defective items is, after identifying a defective item, the cost of checking previously manufactured items until it is determined when the process went out of control, i.e., until a good item is found.

Selection of 3013 Containers for Field Surveillance

This report revises and combines three earlier reports dealing with the binning, statistical sampling, and sample selection of 3013 containers for field surveillance. It includes changes to the binning specification resulting from completion of the Savannah River Site packaging campaign and new information from the shelf-life program and field surveillance activities. The revised bin assignments result in changes to the random sample specification. These changes are necessary to meet the statistical requirements of the surveillance program. This report will be reviewed regularly and revised as needed. Section 1 of this report summarizes the results of an extensive effort to assign all of the current and projected 3013 containers in the Department of Energy (DOE) inventory to one of three bins (Innocuous, Pressure and Corrosion, or Pressure) based on potential failure mechanisms. Grouping containers into bins provides a framework to make a statistical selection of individual containers from the entire population for destructive and nondestructive field surveillance. The binning process consisted of three main steps. First, the packaged containers were binned using information in the Integrated Surveillance Program database and a decision tree. The second task was to assign those containers that could not be binned using the decision tree to a specific bin using container-by-container engineering review. The final task was to evaluate containers not yet packaged and assign them to bins using process knowledge. The technical basis for the decisions made during the binning process is included in Section 1. A composite decision tree and a summary table show all of the containers projected to be in the DOE inventory at the conclusion of packaging at all sites. Decision trees that provide an overview of the binning process and logic are included for each site. Section 2 of this report describes the approach to the statistical selection of containers for surveillance and consists of a revision of the earlier statistical sampling report. The requirement of 99.9% probability of observing at least one of the worst 5% (99.9/5%) of the containers with a potential for degradation is used to determine the number of containers in the random sample for the Pressure and Corrosion and the Pressure bins. Sampling requirements for the Innocuous bin are not based on the 99.9/5% requirement; rather, they are based on evaluating the assumption of no significant degradation of, or variability between, containers relative to corrosion or pressure generation within the Innocuous bin population as valid. Section 3 of this report focuses on the actual selection of 3013 containers for surveillance. Surveillance containers are identified by the year that the surveillance should be performed. In addition to the randomly selected containers, containers were selected from the entire population, based on engineering judgment for each of these years. The judgmental sampling targets containers with the greatest potential for gas generation and/or corrosion. The factors used for judgmental sample selection are documented in this section. A more detailed discussion of the FY 2005 sample selection process is contained in the previous FY 2005 sample selection report.

Quality quandaries: Statistical detective work to understand the isotopic ratios in Drum 68660 and the radioactive release at WIPP

KEY POINT An incident at the Department of Energys Waste Isolation Pilot Plant (WIPP) in 2014 resulted in the release of radioactive material into the environment. Initially, it was known that at least one drum in WIPP, identified as drum 68660, was involved. However, questions remained. Could the air-monitor isotopic ratios measured in WIPP at the time of the release be explained by materials in drum 68660 or were other drums involved? Could internal conditions in drum 68660 have caused the breach? What were the implications for 68660s sister drum? These questions needed to be answered as quickly as possible. This analysis, which was completed in three weeks, combined combinatorics and uncertainty analysis to provide scientists with the timely evidence they needed to either answer these important questions or to design experiments to answer them.

Selection of 3013 Containers for Field Surveillance. Fiscal Year 2016 Update

This update is the eighth in a series of reports that document the binning and sample selection of 3013 containers for the Field Surveillance program as part of the Integrated Surveillance Program. This report documents changes made to both the container binning assignments and the sample selection approach. Binning changes documented in this update are a result of changes to the prompt gamma calibration curves and the reassignment of a small number of Hanford items from the Pressure bin to the Pressure and Corrosion (P&C) bin. Field Surveillance sample selection changes are primarily a result of focusing future destructive examinations (DEs) on the potential for stress corrosion cracking in higher moisture containers in the P&C bin. The decision to focus the Field Surveillance program on higher moisture items is based on findings from both the Shelf-life testing program and DEs.

Understanding the Rule of 7: Statistical Properties for Various Sample Sizes

ABSTRACT Motivated by an engineers question to understand the “Rule of 7” sample size rule of thumb, this article studies the statistical properties for a sample size of 7 and well as other sample sizes. Properties of ranges, tolerance intervals and confidence intervals, are considered. Sample size recommendations are made.

SAVY-4000 Surveillance and Life Extension Program Fiscal Year 2013 Annual Report

The Packaging Surveillance Program section of the DOE M441.1-1/sup>1, Nuclear Material Packaging Manual (DOE, 2008) requires DOE contractors to “ensure that a surveillance program is established and implemented to ensure the nuclear material storage package continues to meet its design criteria.” In order to ensure continuing safe storage of nuclear material and the maximization of risk reduction, TA-55 has established a Surveillance Program to ensure storage container integrity for operations within its specified design life. The LANL SAVY-4000 Field Surveillance Plan2 defines the near-term field surveillance plan for SAVY-4000 containers as required by the Manual. A long-term surveillance plan will be established based on the results of the first several years of surveillance and the results of the lifetime extension studies as defined in the Accelerated Aging Plan3. This report details progress in positioning the Surveillance Program for successful implementation in FY14 and status of the Design Life Extension Program in terms of its implementation and data collection for FY13.

Selection of 3013 containers for field surveillance: LA-14310, Revision 1

This document is the fifth in a series of reports that document the binning, statistical sampling, and sample selection of 3013 containers for field surveillance. 1,2,3,39 Revisions to binning assignments documented in this report are primarily a result of new prompt gamma data. This report also documents changes to the random sample specification resulting from these binning changes and identifies and provides the rationale for the engineering judgment sample items for Fiscal Year (FY) 2008 and 2009. This revision also updates the changes to the previous surveillance sample resulting from changes to the order that specific containers undergo surveillance. This report will continue to be reviewed regularly and revised as needed to meet the requirements of the surveillance program.

Using ecological site scoping to evaluate contaminant transport pathways

Los Alamos National Laboratory (LANL) has developed an ecological screening evaluation process that emphasizes the development and testing of an ecological exposure and transport pathway site conceptual model. LANL developed this screening approach in partnership with personnel from the State of New Mexico regulatory authority (the New Mexico Environment Department or NMED). A key part of the screening evaluation process is the completion of an innovative ecological scoping checklist. This checklist helps to (1) determine if complete pathways to ecological receptors exist; (2) determine how the impacted media should be aggregated spatially for screening, establishing the functional/operational boundaries of the assessment; and (3) gather information to develop the site conceptual model (SCM). The SCM includes contaminant sources, dominant transport pathways and exposure routes, and potential receptors. The scoping checklist consists of a series of questions and placeholders for field notes, which are intended to guide the risk assessor in developing the SCM, and provide the decision-makers with consistent information on receptors, potential transport pathways and potential exposure pathways. This paper summarizes the LANL/NMED scoping checklist and gives examples of its application at the LANL Environmental Restoration (ER) sites.

General Assessment Endpoints for Ecological Risk Assessment at Los Alamos National Laboratory

A critical component of any ecological risk assessment is the specification of the assessment endpoints. However, selecting assessment endpoints for risk assessment is often a formidable task, particularly for sites with extensive and diverse ecological resources, such as those found at Los Alamos National Laboratory. The General Assessment Endpoint (GAE) process provides a comprehensive, systematic and defensible basis for reaching consensus with regulators and other stakeholders on the assessment endpoints for ecological risk assessments. This paper provides an overview of the GAE process and reports on a pilot project to implement the process for the Pajarito Plateau ecosystem, the ecosystem potentially affected by the Laboratorys legacy hazardous waste.