ML22216A180
| ML22216A180 | |
| Person / Time | |
|---|---|
| Issue date: | 11/30/2022 |
| From: | Carmen Franklin, Grasso J, Levine C NRC/RES/DRA/HFRB |
| To: | |
| Grasso, John 301-415-3502 | |
| Shared Package | |
| ML22216A166 | List: |
| References | |
| RIL 2022-08 | |
| Download: ML22216A180 (59) | |
Text
Human Reliability Analysis of See-and-Flee Actions Using the Integrated Human Event Analysis System for Events and Condition Assessment (IDHEAS-ECA) Method Date Published: November 2022 Prepared by:
C. Franklin J. Grasso C. Levine (Intern student from University of Maryland)
Office of Nuclear Regulatory Research
Disclaimer Legally binding regulatory requirements are stated only in laws, U.S. Nuclear Regulatory Commission (NRC) regulations, licenses, including technical specifications, or orders, not in research information letters (RILs). A RIL is not regulatory guidance, although the NRCs regulatory offices may consider the information in a RIL to determine whether any regulatory actions are warranted.
Abstract This report demonstrates the use of the Integrated Human Events Analysis System for Events and Condition Assessment (IDHEAS-ECA) human reliability analysis method to estimate the reliability of administrative Items Relied on for Safety (IROFS). Specifically, this study estimated the reliability of see-and-flee IROFS in three different scenarios (contexts) to demonstrate the breadth and depth of IDHEAS-ECA in incorporating performance influencing factors effects to estimate the reliability of IROFS. This capability of IDHEAS-ECA is essential for assessing the reliability of IROFS, such as see-and-flee, reliably and with sound technical basis. However, NUEG-1520s guidance on integrated safety analysis does not have this capability. As a result, IDHEAS-ECA can be added to the Office of Nuclear Material Safety and Safeguards (NMSS) tool set to assess administrative IROFS reliability and supplement the guidance in NUREG-1520. This report also demonstrates that IDHEAS-ECA can identify dominant reliability drivers.
The information in this report will be useful for licensees to effectively use limited resources to improve reliability, and for the NRC staff to evaluate the impacts of the reliability.
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Table of Contents List of Figures .............................................................................................................................v List of Tables ............................................................................................................................. vi Acknowledgments ..................................................................................................................... vii 1 IDHEAS-ECA Developmental Background.......................................................................... 1 2 Purposes............................................................................................................................. 2 3 IDHEAS-ECA HRA Process ................................................................................................ 3 3.1 Using IDHEAS-ECA App to Calculate Pc ..................................................................... 4 3.2 Using IDHEAS-ECA App to calculate Pt ....................................................................... 5 4 Scenarios ............................................................................................................................ 6 5 Operating Experience ......................................................................................................... 8 6 Technical Approach ............................................................................................................ 9 6.1 Human Reliability Analysis Qualitative Analysis ........................................................... 9 6.2 Cognitive Failure Modes Analysis ................................................................................ 9 6.3 Timing Analysis ...........................................................................................................10 6.4 Sensitivity Analysis .....................................................................................................12 7 Results for See-and-Flee Analysis .....................................................................................12 7.1 Confined Space Scenario ...........................................................................................12 7.1.1 HEP Calculation ...................................................................................................12 7.1.2 Leading HEP Contributors ...................................................................................17 7.2 Large Space ...............................................................................................................18 7.2.1 HEP Calculation ...................................................................................................18 7.2.2 Leading HEP Contributors ...................................................................................23 7.3 Outdoor Area ..............................................................................................................23 7.3.1 HEP Calculation ...................................................................................................23 7.3.2 Leading HEP Contributors ...................................................................................28 7.4 Sensitivity Analysis .....................................................................................................28 8 Conclusion .........................................................................................................................30 9 References ........................................................................................................................33 Appendix A: Base Human Error Probabilities and Performance-Influencing Factor Weights ... A-1 Appendix B: See-And-Flee Scenarios (Questions from RES and Answers from NMSS) ......... B-1 iv
List of Figures Figure 3-1 HEP quantification structure of an administrative IROFS ......................................... 4 Figure 3-2 Critical task, CFMs, PIF, and PIF Attributes in the IDHEAS-ECA app ...................... 5 Figure 3-3 Calculate Pt using IDHEAS-ECA app. ...................................................................... 6 Figure 6-1 IDHEAS-ECA App Pt interface ................................................................................11 Figure 7-1 Normal distribution of the estimated time-required (curve) and the total time available (60 seconds, shown by the thick line) for Confined Space scenario ...........................16 Figure 7-2 Normal distribution curve of the time-required (curve) along with the time-available (60 seconds, shown by the thick line) for see-and-flee in the Large Space scenario .................22 Figure 7-3 Normal distribution of the estimated time-required (curve) along with total time-available (60 seconds, shown by the thick line) for the see-and-flee in Outdoor Area scenario .27 Figure 7-4 Sensitivity Analysis: Pt vs. Time-Available for the Large Space Scenario ................29 v
List of Tables Table 6.3-1 Example of Time-Required Estimates Chosen for Final Analysis Based on Individual Analyses ...................................................................................................................10 Table 7.1-1 Confined Space CFM Analysis (Pc) ........................................................................13 Table 7.1-2 Confined Space Timing Analysis (Pt).....................................................................15 Table 7.1-3 Overall HEP for see-and-flee in Confined Space Scenario ....................................16 Table 7.1-4 Leading Contributors to Pc Analysis ......................................................................17 Table 7.2-1 Large Space CFM Analysis (Pc) ............................................................................18 Table 7.2-2 Large Space Timing Analysis (Pt) ..........................................................................21 Table 7.2-3 Overall HEP for see-and-flee in Large Space scenario..........................................22 Table 7.2-4 Leading Contributors to Pc Analysis ......................................................................22 Table 7.3-1 Outdoor Area CFM Analysis (Pc) ...........................................................................24 Table 7.3-2 Outdoor Area Timing Analysis (Pt).........................................................................26 Table 7.3-3 Overall HEP for see-and-flee in Outdoor Area Scenario ........................................28 Table 7.3-4 Leading Contributors to Pc Analysis for Outdoor Area ...........................................28 Table 7.4-1 Analysts estimated time-required data for Pt sensitivity analysis ...........................29 Table A-1 Base HEP for Scenario Familiarity ..................................................................... A-1 Table A-2 Base HEP for Information Availability and Reliability .......................................... A-3 Table A-3 Base HEPs for Task Complexity ........................................................................ A-4 Table A-4 PIF Weights for Environmental PIFs .................................................................. A-8 Table A-5 PIF Weights for System and I&C Transparency ................................................. A-9 Table A-6 PIF Weights for Human-System Interface .......................................................... A-9 Table A-7 PIF Weights for Equipment and Tools .............................................................. A-10 Table A-8 PIF Weights for Staffing ................................................................................... A-11 Table A-9 PIF Weights for Procedures, Guidance, and Instructions ................................. A-12 Table A-10 PIF Weights for Training .................................................................................. A-12 Table A-11 PIF Weights for Teamwork and Organizational Factors ................................ A-14 Table A-12 PIF Weights for Work Processes .................................................................. A-15 Table A-13 PIF Weights for Multitasking, Interruption, and Distraction ............................... A-15 Table A-14 PIF Weights for Mental Fatigue and Time Pressure and Stress ....................... A-17 Table A-15 PIF Weights for Physical Demands .................................................................. A-18 vi
Acknowledgments The authors would like to thank the individuals who contributed the technical bases and their insights to this report.
Dr. April Smith, who was a Reliability and Risk Analyst in the Office of Nuclear Material Safety and Safeguards, Division of Fuel Management, provided the see-and-flee scenarios and helped the authors understand and build in analyst assumptions. Dr. Smith was instrumental in coordinating with the Office of Nuclear Regulatory Research (RES) management to facilitate this project.
The authors also appreciate Dr. Y. James Chang, who was a Risk and Reliability Engineer in the Human Factors and Reliability Branch of RES Division of Risk Analysis, advised the authors in using IDHEAS-ECA to perform the analysis. Dr. Chang is a developer of the Integrated Human Event Analysis System for Event and Condition Assessment (IDHEAS-ECA) method and software app.
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1 IDHEAS-ECA Developmental Background The Commission issued Staff Requirements Memorandum (SRM) M061020 directing the Advisory Committee on Reactor Safeguards (ACRS) to work with the [NRC] staff and external stakeholders to evaluate the different Human Reliability models in an effort to propose either a single model for the agency to use or guidance on which model(s) should be used in specific circumstances (Ref. 1). This SRM direction led to the development of the Integrated Human Event Analysis System (IDHEAS) suite of human reliability analysis (HRA) methods, including IDHEAS for event and condition assessment (IDHEAS-ECA). IDHEAS-ECA aims to solve the variability issues that motivated the issuance of SRM-M061020, including analyst-to-analyst variability (different analysts using the same HRA method generates significantly different results) and method-to-method variability (the same analysts using different HRA methods generate significantly different results). In the significance determination process (SDP) of the NRCs reactor oversight program, the differences could result in different regulatory decisions.
The NRC staff began development of the IDHEAS suite methods by performing a large-scale psychological literature review to establish a cognitive basis (NUREG-2114) followed by the development of a generic methodology (IDHEAS-G) for performing HRA (Ref. 2 and 3). The IDHEAS-ECA HRA method (Research Information Letter RIL-2020-02) was developed based on IDHEAS-G to perform HRA for probabilistic risk assessment (PRA) applications, including event and conditional assessment (ECA) in SDP, accident sequence precursor, and baseline PRA (Ref. 4). The staff developed a software app to facilitate the IDHEAS-ECA implementation.
NRR, Region offices, and RES staff applied IDHEAS-ECA in ECA and ASP and concluded significant improvement in reducing analyst-to-analyst variability. The Electric Power Research Institute and US nuclear industry evaluated the IDHEAS-ECA method with positive feedback.
In 2021, ACRS wrote a letter (ML21076A421) which provided recommendations to the Commission addressing SRM-M060120 (Ref. 5). Some of the ACRS recommendations are:
- IDHEAS-G meets the primary intent of the 2006 Commission SRM, as a single HRA model for the agency to use.
- The derived detailed application methods are expected to meet the intent of the Commission direction in the SRM for guidance on which model(s) should be used in specific circumstances.
- IDHEAS-ECA provides a specific derived application. It should be updated periodically to reflect user feedback and to synchronize with model and guidance refinements. Peer review is needed.
The staff conducted a public meeting (ML21096A176) to collect public comments on the IDHEAS suite methods (Ref. 6). The staff has addressed all public comments. The NRC contracted Pacific Northwest National Laboratory to peer review the IDHEAS data basis. The review comments are addressed in periodic IDHEAS updates.
Currently, fuel facilities use the integrated safety analysis (ISA), as described in NUREG-1520, Standard Review Plan for Fuel Cycle Facilities License Applications, to assess the risk of various hazards such as criticality, chemical, fire, and natural phenomena (e.g., floods, high winds, tornadoes, and earthquakes) (Ref. 7). The administrative IROFS in ISA are about the human and organizational actions to prevent initiating events from propagating to exceed the consequence thresholds specified in 10 CFR 70.61. ISA uses the risk-indexing method to 1
assess the reliability of administrative IROFS. The IROFS reliability is represented by the failure probability index number (FPIN). NUREG-1520, Rev.2 provides limited instruction on assessing the administrative IROFS FPIN, including, (1) FPIN is -1 or -2 for an administrative IROFS in response to a rare unplanned demand, and (2) FPIN is -2 or -3 for an enhanced administrative IROFS or an administrative IROFS for routine planned operations. Such instructions aim for quick assessment and tend to be conservative. Situations could arise which need a detailed analysis that ISA does not have instructions for. In such situations, IDHEAS-ECA can be used.
In addition, ISA requires assessing the degree of dependence between IROFS. However, NUREG-1520 provides little instruction in assessing the dependence. IDHEAS-ECAs dependence model can assess the dependence with a sound technical basis.
This report provides a demonstration of using IDHEAS-ECA to assess the reliability of the see-and-flee administrative IROFS. The see-and-flee IROFS occurs when a worker needs to promptly leave the workplace and go to a safe location after seeing or sensing the presence of uncontrolled hazardous material (e.g., Uranium Hexafluoride) in the workplace. Depending on the context of the event requiring see-and-flee action, the probability of a successful see-and-flee could vary significantly. NUREG-1520s instruction is insufficient to assess the see-and-flee reliability in different contexts, and the assessed results may not be conservative. This report demonstrates the use of IDHEAS-ECA to perform detailed analyses to assess the see-and-flee reliability in three different contexts (confined space, large space, and outdoor area). The demonstration shows IDHEAS-ECAs ability to calculate the reliability with consideration of the effects of a wide spectrum of factors which could influence human reliability. As a result, IDHEAS-ECA can support ISA reviewers to perform a detailed analysis or to determine the proper FPIN.
Section 2 provides a concise purpose statement for this report. Section 3 discusses the HRA process of applying IDHEAS-ECA, using the IDHEAS-ECA app.
2 Purposes The two purposes of this report are (1) to make the IDHEAS-ECA method known to NMSS so they can identify the areas of their regulatory responsibilities in which IDHEAS-ECA may be useful, and (2) for NMSS to provide user feedback to improve IDHEAS-ECA for fuel facility applications.
To achieve these purposes, this report estimates the reliability of the see-and-flee IROFS in three different contexts, using IDHEAS-ECA. The exercise demonstrates that IDHEAS-ECA is applicable to assess the administrative IROFS reliability. In addition, the demonstration shows the ease of implementing the IDHEAS-ECA method (using the IDHEAS-ECA app) and the ability to perform detailed analyses to estimate the administrative IROFS reliability in different contexts.
IDHEAS-ECA does not aim to replace the risk-indexing method currently used for ISA, instead it aims to supplement the risk-indexing method when a detailed analysis is needed to assess the administrative IROFS reliability. Section 4 discusses the see-and-flee events and the three different contexts of the event in this study.
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3 IDHEAS-ECA HRA Process IDHEAS-ECA specifies eight steps to perform an HRA that are briefly described below (Ref. 4).
Steps 1 through 8 present an overview of the IDHEAS-ECA process and the flow of information.
(1) Step 1: Analyze the event scenario. Analyzing an event includes developing the scenario narrative and timeline, determining the scenario context, and identifying the human action (administrative IROFS), e.g., see-and-flee, to be modeled. The administrative IROFS may contain several critical tasks, which are the human cognitive and physical activities critical to the success of the administrative IROFS. IDHEAS-ECA calculate the reliability of each critical task to calculate the reliability of the administrative IROFS.
(2) Step 2: Analyze the administrative IROFS. This includes defining the administrative IROFS and identifying the critical tasks. The administrative IROFS definition should discuss its failure impacts on the worker, environment, and public safety as specified in Part 70.61. The critical tasks are used in the latter steps to calculate their reliabilities, which, in turn, are used to calculate the reliability of the administrative IROFS In this report, the reliabilities of critical tasks and of administrative IROFS are represented by human error probabilities (HEPs), which is the failure probability of performing the critical tasks or administrative IROFS.
(3) Step 3: Model the failure of the critical tasks (identified in Step 2). This includes characterizing the critical tasks, identifying cognitive activities required to achieve the critical tasks, and subsequently identifying the cognitive failure modes (CFMs) applicable to the critical tasks. IDHEAS-ECA classifies five CFMs: failure in information detection, failure in understanding the situation, failure in decisionmaking, failure in action execution, and failure in interteam coordination.
(4) Step 4: Assess the performance influencing factors (PIFs) applicable to every CFM. The CFM and PIFs are identified based on the results of scenario analysis (Step 1),
Administrative IROFS definition (step 2), and critical tasks characterization (step 3).
(5) Step 5: Calculate the Pc. Pc is the probability of cognitive error of performing the administrative IROFS. The calculation assumes that there is sufficient time available to complete the IROFS. The failure probability caused by time insufficiency is calculated in Step 6. IDHEAS-ECA use a hierarchical structure that includes the following elements:
critical tasks, CFMs, and PIFs to calculate Pc (see figure 3-1). The Pc of the administrative IROFS is the probabilistic sum of the Pc of the critical tasks. The Pc of a critical tasks is a function of the CFMs, PIFs and PIF Attributes applied to the critical task. Figure 3-2 shows the graphical user interface of IDHEAS-ECA app to identify the applicable CFMs, PIFs, and PIF Attributes applicable to a critical task.
(6) Step 6: Calculate the Pt. Pt is the failure probability of implementing the administrative IROFS simply because the time available to perform the IROFS is insufficient.
Calculating Pt assumes the individual(s) performing the IROFS as trained. IDHEAS-ECA calculates Pt based on two distributions: time-required and time available. Pt is the probability that the time-required exceeds the time-available. IDHEAS-ECA calculates Pt by looking at performing the administrative IROFS as a whole. IDHEAS-ECA does not calculate Pt for each individual critical task.
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(7) Step 7: Calculate the administrative IROFS HEP. The administrative IROFS HEP is the probabilistic sum of and of the administrative IROFS. That is, Administrative IROFS HEP = 1 (1 Pc )(1 Pt ), as shown in figure 3-1. The IDHEAS-ECA software calculates the overall HEP automatically using the results from steps 5 and 6.
(8) Step 8: Analyze uncertainties in the HRA, perform sensitivity and dependency analyses, and document the results.
Figure 3-1 HEP quantification structure of an administrative IROFS 3.1 Using IDHEAS-ECA App to Calculate Pc IDHEAS-ECA models five macrocognitive functions. Failures of these macrocognitive functions correspond to the five CFMs for calculating the HEPs. These five macrocognitive functions are:
- Detection (D) is noticing cues or gathering information in the work environment.
- Understanding (U) is the integration of pieces of information with a persons mental model to make sense of the scenario or situation.
- Decisionmaking (DM) includes selecting strategies, planning, adapting plans, evaluating options, and making judgments on qualitative information or quantitative parameters.
- Action Execution (E) is the implementation of the decision or plan to change the course of the scenarios, typically by changing the status of physical components or systems.
- Interteam Coordination (T) focuses on how various teams interact and collaborate with each other.
The first four macrocognitive functions (D, U, DM, and E) may be performed by an individual or a team, and Interteam Coordination is performed by multiple groups or teams that are not usually trained together. CFMs are failures of the macrocognitive functions.
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IDHEAS-ECA uses PIFs and PIF Attributes to represent the context and calculate the HEP. A PIF attribute is an assessable characteristic of a PIF and describes a way that the PIF challenges the macrocognitive functions and, therefore, increases the likelihood of error in performing the macrocognitive functions. That, in turn, increase the error probabilities of critical tasks and IROFS. The PIF attributes were identified from cognitive and behavioral studies, as well as human error data from various sources.
Appendix A in this report shows the CFMs base HEPs and PIF weights of each PIF attribute.
The base HEPs represent the failure probability of performing the macrocognitive function in an optimal condition (i.e., no negative factors affecting performance) and under a teamwork environment. The values in appendix A represent the percentage change with the effect of the PIF attribute. For example, a PIF weight of 1.1 represents a 10-percent increase in HEP. The bases of the values shown in appendix A are documented in the draft Integrated Human Event Analysis System for Human Reliability Data (IDHEAS-DATA) report (Ref. 8). Below, figure 3-2 shows a screenshot of the IDHEAS-ECA app for selecting PIF attributes.
Figure 3-2 Critical task, CFMs, PIF, and PIF Attributes in the IDHEAS-ECA app 3.2 Using IDHEAS-ECA App to calculate Pt IDHEAS-ECA defines Pt as the probability that personnel could not complete a required human action because of not having sufficient time. The IDHEAS-ECA app provides a graphical user interface (see figure 3-3) for the analysts to specify the uncertainty distributions of the time-required and the time-available to calculate Pt. The IDHEAS-ECA app uses a Monte Carlo sampling technique to take one million data points from each of the two distributions to calculate the Pt. IDHEAS-ECA also provides a constant (fixed) value option (instead of a distribution) for the time-available. If the constant value is selected for the time-available, the Pt is calculated directly by using the time-required distribution and the constant time-available, instead of using Monte Carlo sampling.
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Figure 3-3 Calculate Pt using IDHEAS-ECA app.
4 Scenarios This study evaluates three see-and-flee scenarios, in which the see-and-flee actions take place in either a confined space, large space, or outdoor area of a hypothetical fuel cycle facility. In a release event, workers are expected to recognize (see) the release, leave (flee) the area immediately, and actuate a release alarm. For all three scenarios, this analysis assumes that the worker will see a white cloud within 10 seconds of a UF6 release. The definition of a successful see-and-flee event, is when the worker takes no longer than 1 minute to flee to a safe area, starting from the occurrence of the release event. There are release alarms in various locations around the facility. When actuated, the alarm accesses all announcement systems in the facility and emits a klaxon siren, alternating with a recorded voice that announces a release has occurred and issues evacuation instructions. The following presents the work-spaces for each of the three see-and-flee scenarios (confined space, large space, and outdoor area):
(1) Confined Space: A release of UF6 occurs in a room that is 50 cubic meters (m3) in volume. The worker is 1 meter from the release and 3 meters from the nearest door. To open the door, the worker must press a large, red button that is on a wall 0.5 meters from the door. After the button is pressed, the door takes approximately 2 seconds to open. Outside of the door is a release alarm that the worker can hit. In the event of a loss of offsite power, the area will lose lighting for 3 seconds before emergency lighting is restored.
(2) Large Space: A release of UF6 occurs in a room that is 50,000 m3 in volume. Three workers are 1 meter from the release and 30 meters from the nearest door. To open the door, the worker must slide their badge through a card reader. After the worker slides their badge through the card reader, the door takes approximately 4 seconds to open.
Inside the room, approximately 0.3 meter from the door is a release alarm. In the event of a loss of offsite power, the area will lose lighting for 3 seconds before emergency lighting is restored. For the large area, assume there are two other workers, and they are working within 2 feet from each other.
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(3) Outdoor Area: A release of UF6 occurs from a cylinder in a tank farm. The worker is in the tank yard, 1 meter from the release and 30 meters from the tank farm gate. To open the gate, the worker must pick up and slide a 20-pound, large, metal vertical L-pin through a metal well. The L-pin is 2 meters tall and must be lifted 0.5 meter to clear the metal well. A release alarm is located on the wall of a building 30 meters from the tank farm gate. At night, lights provide adequate visibility under normal and emergency (e.g., loss of offsite power) conditions. Workers are discouraged from working in the tank farm during inclement weather (e.g., fog, rain, snow, etc.). However, depending on business needs, a worker may still choose or be directed to carry out duties in the tank farm.
The following additional factors which may affect the workers performance when implementing see-and-flee actions are listed below:
TRAINING
- The licensee trains workers once every 6 months. The training consists of instructing workers on the following:
- recognizing what a UF6 release might look like
- tripping the nearest release alarm
- knowing which facility components may be involved in a UF6 release
- knowing the nearest exit
- knowing the consequences of not immediately evacuating the area
- knowing to leave the area within 1 minute
- Once every 2 years, the licensee holds a drill that simulates a UF6 release in the main process building.
SEE
- When a UF6 release occurs, hydrogen fluoride is produced. Hydrogen fluoride is irritating at low concentration but is not sensed at high concentration.
- Released UF6 may react with airborne moisture to produce hydrofluoric acid which has a noxious odor and uranyl fluoride which is visible as white airborne particulate matter.
- Workers wear personal protective equipment, which includes safety glasses, coveralls, hard hats, and steel-toed boots.
- Workers may detect a release via sound, smell, skin irritation, hearing an alarm, or seeing fog or perhaps a spray.
- All work areas are well lit.
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FLEE
- A large release may impair a workers ability to see.
- The workspace may present a variety of obstacles. The following obstacles apply for each scenario:
- Confined Space: There are no trip hazards on the floor. The room has a large pipe 1.5 meters above the ground that runs through the middle of the room. At 3 meters from the door, the worker may be behind the pipe.
- Large Space: The room contains a variety of components and equipment, including pipes, valves, conveyor belts, tanks, and computer workstations. There are alleys approximately 1-meter wide between major pieces of equipment and indicators on the wall for the nearest exit. The floor is known to be slippery.
- Outdoor Area: The cylinders in the tank farm are stored in racks that are 1.5 meters tall. There are 1-meter-wide alleys between storage racks.
The ground is asphalt, and small potholes have formed in most walkways.
These potholes are up to 10 centimeters wide.
The analysis incorporated several assumptions made by the analysts in response to the parameters listed above and the information provided by NMSS staff based on their knowledge of see-and-flee response to UF6. Appendix B gives the full list of questions and answers provided by NMSS staff for consideration and clarification for the see-and-flee scenarios. One notable assumption that was relevant in the analysis was that if the activity, which the worker was performing in each scenario before detecting the release of UF6, were left undone, then the facility could potentially be in an unsafe condition.
5 Operating Experience Uranium hexafluoride (UF6) is a colorless gas or a white sand-like solid that emits radioactive particles which can be harmful when inhaled or if they penetrate the skin. UF6 is also a highly corrosive chemical that can burn skin upon contact and irritate the nose, throat, and lungs, causing coughing, wheezing, and shortness of breath if inhaled (Ref. 9). The NRC issued the information notice 2007-22 Recent hydrogen fluoride exposures at fuel cycle facilities (ML071410230) to raise awareness of UF6 hazards in fuel processing facility (Ref. 10).
NUREG-1198, Release of UF6 from a Ruptured Model 48Y Cylinder at Sequoyah Fuels Corporation Facility: Lessons-Learned Report, issued June 1986 (Ref. 11), documented a UF6 release event that occurred on January 4, 1986, which resulted in one death and several injuries. A cylinder grossly overfilled with UF6 ruptured due to hydraulic overpressurization. The rupture occurred because the UF6 changed states from solid to liquid after being heated in a steam chest. The released UF6 reacted with airborne moisture to produce hydrofluoric acid which has a noxious odor and uranyl fluoride which is visible as white airborne particulate matter. The release filtered through the ventilation system, and, within minutes, the entire building became uninhabitable. The lessons-learned report stated that there was a potential 8
delay in identifying a UF6 release. There were no monitors for detecting airborne or waterborne UF6 releases at the facility, even though ionization and conductivity detectors were commercially available. Breathing apparatuses were not readily available for workers leaving the affected areas. In addition, all emergency equipment was lost during this incident.
The International Atomic Energy Agency issued a 1996 report, Significant Incidents in Nuclear Fuel Cycle Facilities (Ref. 12), that addressed other high-level historical trends of release and contamination incidents since the 1950s. In 1970, a French facility accidentally released UF6 when a cylinder valve was broken, causing a leak. Six workers were injured from burns on their hands and feet from the UF6 release that was combined with carbon dioxide. This report also describes two other release events that directly affected workers, but they were not UF6 releases.
6 Technical Approach This study was achieved through collaboration between the staff of the NMSS Division of Fuel Management, who provided three see-and-flee scenarios with specific context, and the staff of the Office of Nuclear Regulatory Researchs (RES) Division of Risk Analysis (DRA), Human Factors and Reliability Branch (HFRB), who applied the IDHEAS-ECA methodology to calculate the HEPs of the see-and-flee IROFS in three different scenarios.
6.1 Human Reliability Analysis Qualitative Analysis IDHEAS-ECA steps 1 to 3 are for HRA qualitative analysis (i.e., systematically collecting and organizing information that affects human performance). The qualitative analysis includes analyzing the event scenario, identifying and defining the administrative IROFS, and identifying and analyzing the critical tasks of the administrative IROFS. To perform the qualitative analysis, the RES staff first analyzed the information provided by Dr. April Smith (NMSS staff) for each scenario (i.e., see-and-flee in Confined Space, Large Space, and Outdoor Area). The scenarios were discussed in depth with Dr. Smith, who also answered the RES staffs questions about the scenarios. The questions and answers help specifying clear assumptions for this analysis.
Appendix B provides the questions and answers.
The see-and-flee IROFS in this study is modeled with a critical task, which contains four CFMs:
detection, understanding, decisionmaking, and action execution. Detection means detecting the abnormality by seeing the cloud of smoke created by UF6 contacting with moisture, and skin irritation. Understanding means correctly interpreting that the abnormal situation requires a prompt evacuation from the workplace. Decisionmaking means deciding to put the work at hand aside and leave the workplace immediately. Action execution means to promptly exit the workplace. The success criterion for the see-and-flee IROFS in this study is for the worker to evacuate the workplace within one minute after the abnormality starts. The workers activities in the three scenarios (confined space, large space, and outdoor area) are identical at high-level, but differences exist in the details (e.g., the evacuation path and distance).
6.2 Cognitive Failure Modes Analysis To calculate the Pc, the analysts used available information to choose the CFMs and PIF attributes applied to the critical task. Every member of the analysis team performed their own separate analysis for each scenario, then met to discuss the justifications for each PIF attribute 9
chosen in their analyses. Based on these discussions, a consensus was reached on what to include in the final analysis for each scenario. The results from the final analysis of each scenario are presented in section 7 of this report.
The critical task of seeing and fleeing has four applicable CFMs:
(1) CFM1: Failure of Detection: The worker fails to detect the signs of the release.
(2) CFM2: Failure of Understanding: Given a successful detection of the sign of a release, the worker fails to assess and understand that the release is toxic and requires an immediate evacuation.
(3) CFM3: Failure of Decisionmaking: The worker fails to make the decision to flee as quickly as possible although he or she detects the signs and correctly assesses the situation. The worker may decide to finish the work at hand before evacuating from the workplace. Wrapping up the task in hand could take longer than the worker expected and resulting in an evacuation delay.
(4) CFM 4: Failure of Action Execution: The worker fails to flee away the site within the time available even though he or she makes the correct decision of fleeing. The worker needs to navigate through the evacuation path and open the door to exit the workplace.
(5) CFM 5: Failure of Interteam Coordination, is not applicable because the critical task is performed individually and does not require team coordination.
6.3 Timing Analysis IDHEAS-ECA uses the time-available and the time-required for a timing analysis. The time-available in this study is set to be one minute, a constant value. That is the workers need to leave the workplace within one minute to succeed the see-and-flee IROFS in all scenarios. The time-required is the actual time that the workers took to leave the workplace. The time-required is treated as a distribution in this study. The time-required distribution represents the uncertainty caused by various factors that affect the workers time to see-and-flee. This study did not collect the time-required data on site. Instead, the authors of this report estimated the lower bound and upper bound values of the time-required for each scenario. The estimates were performed by each author independently, as shown in the example in table 6.3-1.
Table 6.3-1 Example of Time-Required Estimates Chosen for Final Analysis Based on Individual Analyses Shortest time required Longest time required estimate (s) estimate (s)
Teammate 1 12 52 Teammate 2 10 44 Teammate 3 17 31 Value used in analysis 10 52 10
Due to a lack of information about the most appropriate distribution to represent the time-required uncertainty, the authors decided to use normal distribution. For the normal distribution, the mean was calculated based on the average of the minimum lower bound estimate and the maximum upper bound estimate of the three authors. The lower bound and upper bound are interpreted as about the 5th percentile and 95th percentile. There are about four standard deviations between the 5th percentile and 95th percentile (The exact values should be the 4.8th percentile and 95.2th percentile). As a result, the standard deviation is calculated by the maximum upper bound estimate minus the minimum lower bound estimate then divided by 4.
An example of the calculations used for the mean and standard deviation of the normal distribution based on the estimates in table 6.3-1 are shown below:
( + ) (52 + 10)
Mean = 2
= 2
= 31 s Range = Max upper bound estimate - Min lower bound estimate = 52 - 10 = 42 s 42 Standard Deviation Used = = = 10.5 s 4 4 Finally, a constant of 60 seconds was used as the total allowable time (time-available) in each scenario based on the description in section 4. A normal distribution with the specified mean and standard deviation for the time-required and the constant time-available were input into the IDHEAS-ECA app to calculate Pt (see figure 6-1). Alternatively, Equation (3.8) in NUREG-2256 can be used to calculate Pt using these same parameters (i.e., a normal distribution for time-required and a constant value for time-available). The Pt in this case can also be calculated using the following equation in Microsoft Excel:
Pt = 1 - NORM.DIST(time-available, Mean, Standard Deviation, true)
Pt = 1 - NORM.DIST(60, 31, 10.5, true) = 2.87E-3 Figure 6-1 IDHEAS-ECA App Pt interface 11
6.4 Sensitivity Analysis The Pt is a leading contributor to the failure probability of see-and-flee IROFS. Section 7.4 documents a sensitivity analysis on Pt. Two sensitivity analyses were performed. The first sensitivity analysis varies the time-required to assess the effects on Pt while the time-available remains constant (one minute). The time-required variation is based on the estimates of the analysts. The second sensitivity analysis varies the time-available while the time-required distribution remains the same. The details are discussed in Section 7.4.
7 Results for See-and-Flee Analysis This section provides the HRA results for the three scenarios evaluated using the IDHEAS-ECA guidance report (Ref. 4). The HEPs were calculated by using the IDHEAS-ECA app. This section addresses IDHEAS-ECA steps 4 to 8.
7.1 Confined Space Scenario 7.1.1 HEP Calculation Table 7.1-1 defines the HFE and critical task for the Confined Space scenario, then gives every PIF attribute selection for each CFM and the justification for each selection. The table also shows the calculated HEP for each CFM (PCFM) and the total Pc for the entire Confined Space scenario. Note that the table only lists the PIFs that impact task performance (i.e., at least one attribute of the PIF is applicable to the CFM). The table does not list the remaining PIFs because they were assessed as having no impact on the CFMs. All base HEPs and PIF weights can be found in Appendix A of this report.
Table 7.1-2 gives the estimated values for the timing analysis of the Confined Space scenario, including the estimated max upper bound time estimate, minimum lower bound time estimate, the ranges, and mean times (all in seconds) for completing the see-and-flee IROFS. The table also shows the standard deviation of the time-required and total time-available used in the analysis and the calculated Pt for the Confined Space scenario.
Figure 7-1 shows the normal distribution curve for the time required on the same plot as the total available time. To create this curve, the overall mean time and standard deviation of the time required, and total (constant) time available from table 7.1-2 were input into the IDHEAS-ECA app, which calculated the Pt.
Table 7.1-3 shows the total Pc and Pt again, along with the overall HEP calculated for the Confined Space scenario.
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Table 7.1-1 Confined Space CFM Analysis (Pc)
CONFINED SPACE: CFM Analysis (Pc)
HFE: Fail to flee confined space in 1 minute Critical Task: Flee confined space within 1 minute CFM Selection PIF and Attribute Justification HEP (PCFM)
Selection Failure of Scenario The worker is 1.02E-02 Detection Familiarity: SF3: experienced, has Scenario trained adequate training, but on but infrequently has never performed performed actual scenario
- Effect Level at 1*
Work Processes: The worker is working WP2: Lack of or alone ineffective peer checking or supervision (PIF weight factor = 10)
Multitasking, The worker is performing Interruption and a routine task Distraction: MT1:
Distraction by other ongoing activities that demand attention
- Effect Level at 1*
(PIF weight factor
= 1.2)
Failure of Scenario The worker is 1.20E-02 Understanding Familiarity: SF3: experienced, has Scenario trained adequate training, but on but infrequently has never performed performed actual scenario
- Effect Level at 1*
CONFINED SPACE: CFM Analysis (Pc)
HFE: Fail to flee confined space in 1 minute Critical Task: Flee confined space within 1 minute CFM Selection PIF and Attribute Justification HEP (PCFM)
Selection Work Processes: The worker is working WP2: Lack of or alone ineffective peer checking or supervision (PIF weight factor = 1.1)
Multitasking, The worker is performing Interruption and a routine task Distraction: MT1:
Distraction by other ongoing activities that demand attention
- Effect Level at 1*
(PIF weight factor
= 1.1)
Failure of Scenario The worker is 1.78E-01 Decisionmaking Familiarity: SF3: experienced, has Scenario trained adequate training, but on but infrequently has never performed performed actual scenario
- Effect Level at 1*
Task Complexity: If the worker does not C25: Competing or complete their routine conflicting goals task, the facility could be (Base HEP = 0.14) left in an unsafe condition. Worker needs to decide whether to finish the routine task or flee the area.
14
CONFINED SPACE: CFM Analysis (Pc)
HFE: Fail to flee confined space in 1 minute Critical Task: Flee confined space within 1 minute CFM Selection PIF and Attribute Justification HEP (PCFM)
Selection Work Processes: The worker is working WP2: Lack of or alone ineffective peer checking or supervision (PIF weight factor = 1.1)
Mental Fatigue, The worker knows they Stress, and Time need to leave the room Pressure: MF2: within 1 minute Time pressure due according to training to perceived time urgency (PIF weight factor =
1.1)
Failure of Action Mental Fatigue, The worker knows they 3.00E-04 Execution Stress, and Time need to leave the room Pressure: MF2: within 1 minute Time pressure due according to training to perceived time urgency (PIF weight factor = 3)
Total Pc 1.97E-01 Table 7.1-2 Confined Space Timing Analysis (Pt)
CONFINED SPACE: Timing Analysis (Pt)
Macrocognitive Estimated Time Range (s) Mean Time (s)
Function (s)
Detection 1-10 9 5.5 Understanding 0-7 7 3.5 15
CONFINED SPACE: Timing Analysis (Pt)
Macrocognitive Estimated Time Range (s) Mean Time (s)
Function (s)
Decisionmaking 2-15 13 8.5 Action Execution 7-20 13 13.5 Overall 10-52 42 31 Standard deviation used = 10.5 seconds Total time-available = 60 seconds Total Pt = 2.87E-03 Figure 7-1 Normal distribution of the estimated time-required (curve) and the total time available (60 seconds, shown by the thick line) for Confined Space scenario Table 7.1-3 Overall HEP for see-and-flee in Confined Space Scenario CONFINED SPACE: Overall HEP = 1 - (1 - Pc) (1 - Pt)
Total Pc 1.97E-01 16
CONFINED SPACE: Overall HEP = 1 - (1 - Pc) (1 - Pt)
Total Pt 2.87E-03 Overall HEP 1.99E-01 Table 7.1-4 Leading Contributors to Pc Analysis CONFINED SPACE: Leading Pc Contributor Lead Contributor HEP from the Lead Pc without Overall HEP without Contributor Leading Leading Contributor Contributor Decisionmaking: 1.40E-01 3.41E-02 3.69E-02 Task Complexity:
Competing or Conflicting Goals 7.1.2 Leading HEP Contributors In the Confined Space scenario, the leading contributor to the overall HEP value of 1.99E-01 was Failure of Decisionmaking on making the decision to flee from the area. The main driver was the Task Complexity PIF, specifically, the PIF Attribute Competing or conflicting goals, which adds a base HEP of 1.40E-01 to the overall HEP. The HEP of 2.87E-03 from the Pt analysis was not a leading contributor to the overall HEP. As described in section 6, the Pt analysis was based on time estimates for performing each macrocognitive function, and not on real data. Table 7.1-2 shows the estimates used in this analysis. The leading time estimate that influenced Pt was the time required for Action Execution to flee from the area. The Action Execution time estimate considers the size of the room, the large pipe 1.5 meters above the ground that runs through the middle of the room, the worker being 3 meters from the exit door, the worker pressing a button on a wall and is 0.5 meters from the exit door, and the approximately 2 seconds needed to open the door. For Task Complexity, the analysis assumed that the worker was performing some type of routine activity before the release. For all three scenarios, NMSS staff stated that there were some activities, though routine, that if left undone may put the facility into an unsafe condition. However, workers are trained to drop everything they are doing and leave the area immediately. The attribute Competing or conflicting goals under the Task Complexity PIF has a base value of 1.40E-01 (0.14) in IDHEAS-ECA. This translates to 86 percent of workers deciding to flee the confined space once the UF6 release is detected, and 14 percent of workers in this scenario deciding to complete the routine task rather than flee the area immediately. Removing this PIF would reduce the probability of workers staying in the confined space when there is a release.
17
7.2 Large Space 7.2.1 HEP Calculation Table 7.2-1 defines the HFE and critical task for see-and-flee IROFS of the Large Space scenario and gives every PIF Attribute selection for each CFM and the justification for each selection. The table also shows the calculated Pc for each CFM and the total Pc for the entire see-and-flee IROFS. Note that the table only lists the PIFs that impact task performance (i.e., at least one PIF Attribute is applicable to the CFM). The table does not list the remaining PIFs because they were assessed as having no impact on the CFMs.
Table 7.2-2 gives the estimated values for the timing analysis of the Large Space scenario, including the estimated lower bound and upper bound values of the time-required, the range, and mean (all in seconds) for completing the macrocognitive functions and for the overall analysis. The table also shows the standard deviation and total time available used in the analysis, and the calculated Pt for the Large Space scenario.
Figure 7-2 shows the normal distribution curve on the same plot as the total available time. To create this curve, the overall mean time, standard deviation, and total time available from table 7.2-2 were plugged into the IDHEAS-ECA app, which calculated the Pt.
Table 7.2-3 shows the total Pc and Pt again, along with the overall HEP calculated for see-and0flee in the Large Space scenario.
Table 7.2-1 Large Space CFM Analysis (Pc)
LARGE SPACE: CFM Analysis (Pc)
HFE: Fail to flee large space in 1 minute Critical Task: Flee large space within 1 minute CFM Selection PIF and Attribute Justification HEP (PCFM)
Selection Failure of Scenario The worker is 1.20E-03 Detection Familiarity: SF3: experienced, has Scenario trained adequate training, but on but infrequently has never performed performed actual scenario
- Effect Level at 1*
LARGE SPACE: CFM Analysis (Pc)
HFE: Fail to flee large space in 1 minute Critical Task: Flee large space within 1 minute CFM Selection PIF and Attribute Justification HEP (PCFM)
Selection Multitasking, The worker is performing Interruption and a routine task Distraction: MT1:
Distraction by other ongoing activities that demand attention
- Effect Level at 1*
(PIF weight factor = 1.2)
Failure of Scenario The worker is 1.10E-02 Understanding Familiarity: SF3: experienced, has Scenario trained adequate training, but on but infrequently has never performed performed actual scenario
- Effect Level at 1*
Multitasking, The worker is performing Interruption and a routine task Distraction: MT1:
Distraction by other ongoing activities that demand attention
- Effect Level at 1*
(PIF weight factor = 1.1) 19
LARGE SPACE: CFM Analysis (Pc)
HFE: Fail to flee large space in 1 minute Critical Task: Flee large space within 1 minute CFM Selection PIF and Attribute Justification HEP (PCFM)
Selection Failure of Scenario The worker is 1.63E-01 Decisionmaking Familiarity: SF3: experienced, has Scenario trained adequate training, but on but infrequently has never performed performed actual scenario
- Effect Level at 1*
Task Complexity: If the worker does not C25: Competing or complete their routine conflicting goals task, the facility could be (Base HEP = 0.14) left in an unsafe condition. The worker needs to decide whether to finish the task or flee the area.
Mental Fatigue, The worker know they Stress, and Time need to leave the room Pressure: MF2: within 1 minute Time pressure due according to training to perceived time urgency (PIF weight factor =
1.1)
Failure of Action Environmental Floor in Large Space 3.50E-04 Execution Factors: ENV9: scenario is known to be Slippery surface slippery (PIF weight factor
= 1.5) 20
LARGE SPACE: CFM Analysis (Pc)
HFE: Fail to flee large space in 1 minute Critical Task: Flee large space within 1 minute CFM Selection PIF and Attribute Justification HEP (PCFM)
Selection Mental Fatigue, The worker knows they Stress, and Time need to leave the room Pressure: MF2: within 1 minute Time pressure due according to training to perceived time urgency (PIF weight factor = 3)
Total Pc 1.74E-01 Table 7.2-2 Large Space Timing Analysis (Pt)
LARGE SPACE: Timing Analysis (Pt)
Macrocognitive Estimated Time Range (s) Mean Time (s)
Function (s)
Detection 1-10 9 5.5 Understanding 0-7 7 3.5 Decisionmaking 2-15 13 8.5 Action Execution 15-50 35 32.5 Overall 18-82 64 50 Standard Deviation Used = 16 seconds Total time available = 60 seconds Total Pt = 2.66E-01 21
Figure 7-2 Normal distribution curve of the time-required (curve) along with the time-available (60 seconds, shown by the thick line) for see-and-flee in the Large Space scenario Table 7.2-3 Overall HEP for see-and-flee in Large Space scenario LARGE SPACE: Overall HEP 1 - (1 - Pc) (1 - Pt)
Pc 1.74E-01 Pt 2.66E-01 Overall HEP 3.94E-01 Table 7.2-4 Leading Contributors to Pc Analysis LARGE SPACE: Leading Pc Contributor Lead Contributor Contribution Value Pc without Overall HEP without Leading Leading Contributor Contributor Decisionmaking: 1.40E-01 2.34E-02 2.83E-01 Task Complexity:
Competing or Conflicting Goals 22
7.2.2 Leading HEP Contributors The leading contributors to the overall HEP of 3.94E-01 were the Pt, which contributed an HEP of 2.66E-01, and the CFM Failure of Decisionmaking. The main driver to the HEP of the CFM was Task Complexity: Competing or conflicting goals, which added a base HEP of 1.40E-01.
As for the Confined Space scenario, team members used estimates of time available as an independent variable. As described in section 6, the Pt analysis was based on time estimates for completing the see-and-flee, and not on real data. Table 7.2-2 shows the estimates used in this analysis. The leading time estimate for Pt was the time for Action Execution. The Action Execution time estimate considered the size of the room, and that the worker was 1 meter from the release and 30 meters from the nearest door. To open the door, the worker must slide their badge through a card reader and traverse the slippery floor. For Task Complexity, the same assumptions (that the worker was performing routine tasks before the release) were made.
Team members considered this assumption for the Failure of Decisionmaking CFM. The Task Complexity PIF Attribute Competing or conflicting goals contributed a base HEP of 1.40E-01 (0.14). This translates to 86 percent of workers deciding to flee the large area once the UF6 release is detected, and 14 percent of workers in this scenario deciding to complete the routine task rather than flee the area. Removing this PIF would significantly reduce the probability of workers staying in the large area when there is a release.
7.3 Outdoor Area 7.3.1 HEP Calculation Table 7.3-1 defines the HFE and critical task for performing see-and-flee in the Outdoor Area scenario and gives every PIF attribute selection for each CFM and the justification for each selection. The table also shows the calculated HEP (Pc) for each CFM and the total Pc for the see-and-flee. Note that the table only lists the PIFs that impact task performance (i.e., at least one attribute of the PIF is applicable to the CFM). The table does not list the remaining PIFs because they were assessed as having no impact on the CFMs.
Table 7.3-2 gives the estimated values for the timing analysis of the Outdoor Area scenario, including the estimated lower bound and upper bound values of the time-required, the ranges, and the mean (all in seconds) for completing the macrocognitive functions and for the overall see-and-flee. The table also shows the standard deviation and total time-available used in the analysis, and the calculated Pt for the Outdoor Area scenario.
Figure 7-3 shows the normal distribution curve on the same plot as the total available time. To create this curve, the overall mean time, standard deviation, and total time available from table 7.3-2 were plugged into the IDHEAS-ECA app to calculate the Pt.
Table 7.3-3 shows the total Pc and Pt again, along with the overall HEP calculated for the Outdoor Area scenario.
23
Table 7.3-1 Outdoor Area CFM Analysis (Pc)
OUTDOOR AREA: CFM Analysis (Pc)
HFE: Fail to flee outdoor area in 1 minute Critical Task: Flee outdoor area within 1 minute CFM Selection PIF and Attribute Justification HEP (PCFM)
Selection Failure of Scenario The worker is 1.02E-02 Detection Familiarity: SF3: experienced, has Scenario trained adequate training, but on but infrequently has never performed performed actual scenario
- Effect Level at 1*
Work Processes: The worker is working WP2: Lack of or alone ineffective peer checking or supervision (PIF weight factor = 10)
Multitasking, The worker is performing Interruption and a routine task Distraction: MT1:
Distraction by other ongoing activities that demand attention
- Effect Level at 1*
(PIF weight factor = 1.2)
Failure of Scenario The worker is 1.20E-02 Understanding Familiarity: SF3: experienced, has Scenario trained adequate training, but on but infrequently has never performed performed actual scenario
- Effect Level at 1*
OUTDOOR AREA: CFM Analysis (Pc)
HFE: Fail to flee outdoor area in 1 minute Critical Task: Flee outdoor area within 1 minute CFM Selection PIF and Attribute Justification HEP (PCFM)
Selection Work Processes: The worker is working WP2: Lack of or alone ineffective peer checking or supervision (PIF weight factor = 1.1)
Multitasking, The worker is performing Interruption and a routine Distraction: MT1:
Distraction by other ongoing activities that demand attention
- Effect Level at 1*
(PIF weight factor
= 1.1)
Failure of Scenario The worker is 1.78E-01 Decisionmaking Familiarity: SF3: experienced, has Scenario trained adequate training, but on but infrequently has never performed performed actual scenario
- Effect Level at 1*
Task Complexity: If the worker does not C25: Competing or complete their routine conflicting goals task, the facility could be (Base HEP = 0.14) left in an unsafe condition. The worker needs to decide whether to finish the task or flee the area.
25
OUTDOOR AREA: CFM Analysis (Pc)
HFE: Fail to flee outdoor area in 1 minute Critical Task: Flee outdoor area within 1 minute CFM Selection PIF and Attribute Justification HEP (PCFM)
Selection Work Processes: The worker is working WP2: Lack of or alone ineffective peer checking or supervision (PIF weight factor = 1.1)
Mental Fatigue, The worker knows they Stress, and Time need to leave the room Pressure: MF2: within 1 minute Time pressure due according to training to perceived time urgency (PIF weight factor =
1.1)
Failure of Action Mental Fatigue, The worker knows they 3.00E-04 Execution Stress, and Time need to leave the room Pressure: MF2: within 1 minute Time pressure due according to training to perceived time urgency (PIF weight factor = 3)
Total Pc 1.97E-01 Table 7.3-2 Outdoor Area Timing Analysis (Pt)
OUTDOOR AREA: Timing Analysis (Pt)
Macrocognitive Estimated Time Range (s) Mean Time (s)
Function (s)
Detection 1-10 9 5.5 Understanding 0-7 7 3.5 26
OUTDOOR AREA: Timing Analysis (Pt)
Macrocognitive Estimated Time Range (s) Mean Time (s)
Function (s)
Decisionmaking 2-15 13 8.5 Action Execution 17-60 43 33.5 Overall 20-92 72 56 Standard Deviation Used = 18 seconds Total time available = 60 seconds Total Pt = 4.12E-01 Figure 7-3 Normal distribution of the estimated time-required (curve) along with total time-available (60 seconds, shown by the thick line) for the see-and-flee in Outdoor Area scenario 27
Table 7.3-3 Overall HEP for see-and-flee in Outdoor Area Scenario OUTDOOR AREA: Overall HEP 1 - (1 - Pc) (1 - Pt)
Total Pc 1.97E-01 Total Pt 4.12E-01 Overall HEP 5.28E-01 Table 7.3-4 Leading Contributors to Pc Analysis for Outdoor Area OUTDOOR AREA: Leading Pc Contributors Lead Contributors Contribution Value Pc without Overall HEP without Leading Leading Contributor Contributor Decisionmaking: 1.40E-01 3.41E-02 4.32E-01 Task Complexity:
Competing or Conflicting Goals 7.3.2 Leading HEP Contributors The leading contributors to the overall HEP of 5.28E-01 were the Pt, which contributed an HEP of 4.12E-01, and the Task Complexity: Competing or conflicting goals PIF attribute for the Failure of Decisionmaking CFM, which added a base HEP of 1.40E-01.
As described in the Confined Space and Large Area scenarios, the Pt analysis was based on the times estimated by the analysts instead of real data. Table 7.3-2 gives the estimates used in this analysis. The leading time estimate for Pt would be the time required for Action Execution.
The Action Execution time estimate considered the size of the tank yard that the worker would have to travel to successfully exit and the worker having to pick up and slide a 20-pound, large, metal vertical L-pin through a metal well.
For Task Complexity, the analysis assumed that the worker was performing a routine task when the release happened. This assumption is represented by the CFM Failure of Decisionmaking, Task Complexity PIF Attribute Competing or conflicting goals. The PIF Attribute contributed a base HEP of 1.40E-01. Removing the attribute of Competing or conflicting goals from the Decisionmaking CFM would reduce the overall HEP to 4.32E-01 from 5.28E-01.
7.4 Sensitivity Analysis A sensitivity analysis shows how changing a variable would affect the results of interest. The first sensitivity analysis was on Pt. Sections 7.1-7.3 show the time-required estimates of the three authors. Each author estimated the boundaries of the time-required in all three scenarios 28
and calculated the Pt. Table 7.4-1 shows the Pt each user calculated for each scenario before combining their estimates for the final analysis.
The second sensitivity analysis varied the time-available to show the impacts on Pt. This analysis used the estimated normal distribution curve from the Large Space scenario. In this analysis, the time-required distribution remains the same, while the time-available was changed in increments of 10 seconds from 30 seconds to 120 seconds. Figure 7-4 shows the plot of the Pt vs. available time. The results shows that Pt is very sensitive to time-available. With a change of 60 seconds in time-available, Pt would change about an order of magnitude.
Each sensitivity analysis is discussed further in the following section.
Table 7.4-1 Analysts estimated time-required data for Pt sensitivity analysis Sensitivity Analysis: Pt Scenario User 1 User 2 User 3 Confined Space (Pt) 1.13E-03 2.21E-04 1.31E-04 Large Space (Pt) 2.28E-02 1.03E-02 5.00E-01 Outdoor Area (Pt) 1.29E-01 3.55E-02 8.41E-01 Figure 7-4 Sensitivity Analysis: Pt vs. Time-Available for the Large Space Scenario 29
8 Conclusion The following PIF attributes were included in each of the three scenarios in the Pc analysis:
Scenario Familiarity: Scenarios trained on but infrequently performed, Multitasking, Interruption, and Distraction: Distraction by other ongoing activities that demand attention (Weak), Task Complexity: Competing or conflicting goals, and Mental Fatigue, Stress, and Time Pressure: Time pressure due to perceived time urgency.
Scenario Familiarity: Scenarios trained on but infrequently performed was chosen in each scenario for Detection, Understanding, and Decisionmaking, but not for Action Execution. From effect level 1 to 10 (with 1 having the smallest impact on HEP and 10 having the largest), effect level 1 was chosen because the worker in these scenarios has had training and has done drills on see-and-flee events but has never needed to perform the actual scenario. This PIF attribute was not selected for Action Execution because the execution of leaving the room/area in these scenarios is a relatively simple task, which the worker has assumedly done many times. This PIF attribute highlights the importance of having adequate training and drills. Without properly scheduled training and drills, the effect level of this PIF attribute could have been higher, which would increase the Pc.
Multitasking, Interruption, and Distraction: Distraction by other ongoing activities that demand attention was chosen in each scenario for Detecting and Understanding, but not for Decisionmaking and Action Execution. Since the worker is assumed to be performing a routine activity, this may distract them from detecting the white cloud that results from a release of UF6.
If they do detect the white cloud, their focus on the routine task may still inhibit them from understanding the significance of the white cloud. Once the workers understand that the white cloud is a possible UF6 release, they will no longer be distracted by the ongoing activity; therefore, this PIF attribute will no longer apply to Decisionmaking or Action. The lowest effect level (i.e., weak) was chosen for this PIF attribute because the task was described as routine.
Again, regularly scheduled training is recommended for workers to easily detect a release and understand what to do immediately.
Task Complexity: Competing or conflicting goals was chosen in each scenario for Decisionmaking and no other CFM. This PIF attribute alone made Decisionmaking the biggest CFM contributing to the Pc. In each scenario, the worker was assumed to be performing a routine activity. Dr. Smith noted that, if the activity were left undone, the facility could potentially be in an unsafe condition (refer to appendix B). However, workers are trained to drop everything they are doing and leave the area immediately. The IDHEAS cognitive model considers this a competing goal with the potential of the worker deciding to drop everything and leave as trained or deciding to complete the routine activity to keep the facility in a safe condition. This PIF attribute caused the Pc to be on the order of 10-1 instead of 10-2 in all scenarios. This PIF attribute is highly situational, and its influence depends on what kind of activity is being performed by the worker who witnesses the release. If abandoning the activity at hand would have adverse consequences, the worker would be more reluctant to flee immediately than if they were expecting little consequence. For further credible review, reviewing the training procedures and interviewing the workers would provide insight for assessing the reliability of see-and-flee. Again, regular training is recommended so workers understand the dangers of a UF6 release and the importance of leaving the workplace immediately.
Mental Fatigue, Stress, and Time Pressure: Time pressure due to perceived time urgency was chosen in each scenario for Decisionmaking and Action Execution, and not for Detection 30
and Understanding. Once the worker understands that the cloud of smoke detected could mean a UF6 release, they know from their training that they have one minute to flee the area. This causes a sense of urgency due to time pressure for the Decisionmaking and Action Execution portion of the critical task. It is important for workers to leave the scene as soon as they can.
However, the one-minute requirement could cause time pressure. This PIF Attribute highlights the importance of performing regular drills, so workers are more familiar with performing these tasks under time pressure.
The Pc analyses of the Confined Space and Outdoor Area scenarios were identical. The Large Space analysis and the other scenarios differed in only two ways: (1) Work Practices: Lack of or ineffective peer checking or supervision was not chosen as a PIF attribute for Detection, Understanding, and Decisionmaking in the Large Space scenario, and (2) Environmental Factors: Slippery surface was chosen as a PIF attribute for Action because it was mentioned that the floor has been known to be slippery in the Large Space scenario description.
In the Confined Space and Outdoor Area analyses, the workers were assumed to be alone; therefore, they had no peers or supervisors to help them with the Detection, Understanding, and Decisionmaking process. In the Large Space scenario, the worker was assumed to be with two other workers. Having peers present does not affect Action Execution because leaving the area is a simple, solitary task. These two differences caused the Pc of the Large Space scenario to be about 2 percent lower than the other scenarios. Obviously, having slippery floors in a facility could be hazardous, especially in scenarios where the worker needs to flee the scene quickly.
However, and perhaps more importantly, this highlights the effectiveness of peer checking.
Simply having other workers present in these scenarios lowers the Pc.
The Pt was largest in the Outdoor Area scenario and smallest in the Confined Space scenario in the final analysis (tables 7.1-2, 7.2-2, and 7.3-2) and in all three individual analyses (table 7.4-1). Estimated times for Detection, Understanding, and Decisionmaking were the same in all three scenarios, meaning only the estimated Action Execution time was different in each scenario. The estimated times for Action Execution in these scenarios were based on (1) the distance of the worker to the exit at the time of the UF6 release and (2) the complexity of opening the exit door. Shortening the workers distance to the exit or making the exit door easier to open should reduce the Pt in these scenarios by reducing the time it takes to accomplish the critical task.
The Pt was greater than the Pc in both the Large Space and Outdoor Area scenarios, which suggests that a worker in these scenarios is more likely to fail the critical task due to time constraints rather than due to a PIF. One way to lower the Pt would be to increase the time available for the worker to complete see-and-flee. The sensitivity analysis summarized in figure 7-4 shows how increasing the time available lowers the Pt. However, the analysis uses time estimates instead of actual data to calculate Pt. Table 7.4-1 shows that the user could have had a large influence on the resulting Pt. A more accurate analysis could be done if field data were collected on the time it takes to complete the human action in the critical task in each scenario and analyzed using the IDHEAS-ECA method aided by the IDHEAS-ECA app.
This report uses see-and-flee IROFS as an example to demonstrate the use of IDHEAS-ECA to assess the reliability of performing see-and-flee in confined space, large space, and outdoor area. The analysis demonstrates that IDHEAS-ECA can assess the reliability with explicit consideration of effects of a wide range of performance influencing factors. The analysis also demonstrated IDHEAS-ECAs ability to identify the dominant drivers of the reliability of see-and-31
flee IROFS. This information is invaluable for licensees to decide cost-effective actions to improve reliability and for NRC reviewers to assess impacts on safety. NUREG-1520s ISA guidance does not provide the breadth and depth to assess the reliability of see-and-flee IROFS. IDHEAS-ECA provides NMSS the capability to assess the reliability of IROFS similar to the see-and-flee example with sound technical basis.
32
9 References
- 1. U.S. Nuclear Regulatory Commission, Staff RequirementsMeeting with Advisory Committee on Reactor Safeguards, 2:30 p.m., Friday, October 20, 2006, Commissioners Conference Room, One White Flint North, Rockville, Maryland (Open to Public Attendance), SRM M061020, November 8, 2006. Agencywide Documents Access and Management System (ADAMS) Accession No. ML063120582
- 2. Whaley, A. M., J. Xing, R. L. Boring, S. M. L. Hendrickson, J. C. Joe, K. L. Le Blanc, S. L.
Morrow, Cognitive Basis for Human Reliability Analysis, NUREG-2114, U.S. Nuclear Regulatory Commission, January 2016. ML16014A045
- 3. Xing, J., Y. J. Chang, and J. DeJesus Segarra, The General Methodology of an Integrated Human Event Analysis System (IDHEAS-G), NUREG-2198, U.S. Nuclear Regulatory Commission, May 2021. ML21127A272
- 4. Xing, J., Y. J. Chang, and J. DeJesus, Integrated Human Event Analysis System for Event and Condition Assessment (IDHEAS-ECA), RIL 2020-02, U.S. Nuclear Regulatory Commission, 2020. ML20016A481
- 5. Sunseri, M. W., NRC Human Reliability Methods, ACRS Letter to U.S. Nuclear Regulatory Commission Chairman C. T. Hanson, March 30, 2021. ML21076A421
- 6. Peters, S., J. Xing, Y. J. Chang, Presentations for 04-08-2021 public meeting Integrated Human Event Analysis System (IDHEAS) Public Feedback Session, U.S. Nuclear Regulatory Commission, April 2021. ML21096A176
- 7. U.S. Nuclear Regulatory Commission, Standard Review Plan for Fuel Cycle Facilities License Applications," NUREG-1520, Rev. 2, U.S. Nuclear Regulatory Commission, June 2015. ML15176A258
- 8. Xing, J., Y. J. Chang, and J. DeJesus, DraftIntegrated Human Event Analysis System for Human Reliability Data (IDHEAS-DATA), RIL-2021-XX, U.S. Nuclear Regulatory Commission, 2020. ML20238B982
- 9. New Jersey Department of Health and Senior Services, Hazardous Substance Fact Sheet:
Uraium Hexafluoride, December 2001.
http://www.nj.gov/health/eoh/rtkweb/documents/fs/1970.pdf
- 10. U.S. Nuclear Regulatory Commission, Recent Hydrogen Fluoride Exposures At Fuel Cycle Facilities, Information Notice 2007-22, U.S. Nuclear Regulatory Commission, June 2007. ML071410230
- 11. U.S. Nuclear Regulatory Commission, Release of UF6 from a Ruptured Model 48Y Cylinder at Sequoyah Fuels Corporation Facility: Lessons-Learned Report, NUREG-1198, U.S. Nuclear Regulatory Commission, June 1986. ML070080302
- 12. International Atomic Energy Agency, Significant Incidents in Nuclear Fuel Cycle Facilities, IAEA-TECDOC-867, Vienna, Austria, 1996.
https://inis.iaea.org/collection/NCLCollectionStore/_Public/27/060/27060437.pdf 33
- 13. Xing, J., Y. J. Chang, and J. DeJesus Segarra, Integrated Human Event Analysis System for Event and Condition Assessment (IDHEAS-ECA), NUREG-2256, U.S. Nuclear Regulatory Commission, October 2022. ML22300A117.
34
Appendix A: Base Human Error Probabilities and Performance-Influencing Factor Weights This appendix was taken from Appendix B of NUREG-2256 (Ref. 13). This appendix presents the base human error probabilities (HEPs) of the three base performance-influencing factors (PIFs) in tables A-1 through A-3. It presents the PIF weights for the rest of the PIFs in tables A-5 through A-15. Each table is for one PIF, with the following exceptions: Table A-4 gives PIF weights for several PIFs in the environmental PIF category, and table A-14 gives PIF weights for two PIFs: (1) Mental Fatigue and (2) Time Pressure and Stress.
Each row in these tables is for one attribute, with the first row for the No impact state of a PIF.
The first column in a table is an identifier assigned for a PIF attribute. For example, the attributes for PIF Scenario Familiarity have the identifiers SF1, SF2, and SF3, while SF0 is the identifier for No impact, the base state of the PIF. The second column is the description of every PIF attribute. The remaining five columns show the base HEP of a cognitive failure mode (CFM) or the PIF weight on the CFM imposed by the PIF attribute of the row. These five columns are for Failure of Detection (D), Understanding (U), Decisionmaking (DM), Action Execution (E), and Interteam Coordination (T). One exception is Table A-3, in which the base HEPs are separately presented for each CFM.
The base HEPs for the No impact states of the base PIFs in tables A-1, A-2, and A-3 (i.e., SF0, Inf0, C0, C10, C20, C30, and C40) are shown as zero. However, in the case that the three base PIFs are in their No impact state, is not zero and should be assigned a value of the lowest HEP of a CFM, which is 1x10-4 for failure of Detection or Action Execution, and 1x10-3 for failure of Understanding, Decisionmaking, or Interteam Coordination.
Table A-1 Base HEP for Scenario Familiarity PIF Attribute D U DM E T SF0 No impact 0 0 0 0 0
- Frequently performed tasks in well-trained scenarios
- Routine tasks SF1 Unpredictable dynamics in 6.6E-4 6.6E-3 6.6E-3 6.6E-4 NA known scenarios
- Shifting task objectives
- Dynamic decisionmaking is required A-1
PIF Attribute D U DM E T SF2 Unfamiliar elements in the 5E-3 5E-2 5E-2 5E-3 NA scenario
- Nonroutine, infrequently performed tasks
- Unlearn a technique and apply one that requires the application of an opposing philosophy SF3 Scenarios trained on but E-3 E-2 E-2 E-3 NA infrequently performed Scenario is unfamiliar, rarely 1.2E-2 E-1 E-1 3.3E-2 NA performed
- Notice adverse indicators that are not part of the task at hand
- Notice incorrect status that is not a part of the routine tasks Extremely rarely performed 3.3E-2 3E-1 3E-1 3.5E-1 NA
- Lack of plans, policies, and procedures to address the situation
- No existing mental model for the situation
- Rare events such as the Fukushima accident SF4 Bias or preference for wrong NA 2.6E-2 2.6E-2 NA NA strategies exists, mismatched mental models NA = not applicable.
A-2
Table A-2 Base HEP for Information Availability and Reliability PIF Attribute D U DM E T Inf0 No impact: Key information 0 0 0 0 0 is reliable and complete Inf1 Information is temporarily NA 5E-3 5E-3 NA NA incomplete or not readily available Inadequate updates of information
- Feedback information is not available in time to correct a wrong decision or adjust the strategy implementation
- Different sources of information are not well organized; thus, personnel cannot readily access all the information needed
- Primary source of information is not available, and secondary source of the information is in lower resolution Information is moderately NA 5E-2 5E-2 NA NA incomplete
- Key information is masked
- Key indication is missing A-3
PIF Attribute D U DM E T Inf2 Low unreliable or uncertain NA E-2 E-2 NA NA
- Personnel is aware that source of information could be temporally unreliable
- Pieces of Information change over time; thus, they become uncertain by the time personnel use them Moderately unreliable or NA 5E-2 5E-2 NA NA uncertain
- Source of information could be unreliable, and personnel likely recognize this
- Conflicts in key information Highly unreliable NA E-1 E-1 NA NA
- Key information is misleading
- Key information is inaccurate NA = not applicable.
Table A-3 Base HEPs for Task Complexity PIF Attribute Detection C0 No impact on HEP 0 C1 Detection overload with multiple competing signals Few (<7): 3E-3
- Track the states of multiple systems Multiple (7-11):
- Monitor many parameters 1E-2
- Memorize many pieces of information detected Many (11-20):
- Many types or categories of information to be detected 1E-1 Excessive amount
(>20): 3E-1 A-4
PIF Attribute Detection C2 Detection is moderately complex E-3
- Criteria are not straightforward
- Information of interest involves complicated mental computation
- Comparing for abnormality C3 Detection demands for high attention E-3
- Need split attention
- Need sustained attention over a period of time
- Need intermittent attention C4 Detection criteria are highly complex E-2
- Multiple criteria to be met in complex logic
- Information of interest must be determined based on other pieces of information
- Detection criteria are ambiguous and need subjective judgment C5 Cues for detection are not obvious 5E-2
- Detection is not directly cued by alarms or instructions
- Personnel need to actively search for the information C6 No cue or mental model for detection E-1
- No rules, procedures, or alarms to cue the detection
- Detection of the critical information is entirely based on personnels experience and knowledge Table A-3 Base HEPs for Task Complexity (continued)
PIF Attribute Understanding C10 No impact: straightforward diagnosis with clear 0 procedures or rules C11 Working memory overload E-2 for
<11 messages
- Need to decipher many messages (indications, alarms, spoken messages) 5E-2 for 11-15
- Multiple causes for situation assessment: Multiple E-1 for 15-20 independent influences affect the system, and 3E-1 for >20 system behavior cannot be explained by a single influence alone A-5
PIF Attribute Understanding C12 Relational complexity (number of unchunkable topics or 2E-2 for 2 relations relations in one understanding task) 4.5E-2 for 3
- Relations involved in a human action are very relations complicated for understanding E-1 for 4 relations
- Need to integrate (use together) multiple relations 3E-1 for more than 4 relations C13 Understanding complexity: requiring high level of E-2 comprehension C14 Potential outcome of situation assessment consists of E-2 multiple states and contexts (not a simple yes or no)
C15 Ambiguity associated with assessing the situation E-1
- Key information for understanding is cognitively masked
- Pieces of key information are intermingled or coupled C16 Conflicting information, cues, or symptoms E-1 Table A-3 Base HEPs for Task Complexity (continued)
PIF Attributes Decisionmaking C20 No impact: simple, straightforward choice 0 C21 Transfer step in procedure: integrating a few cues 4.5E-3 C22 Transfer procedure (multiple alternative strategies to 1.2E-2 choose): integrating multiple cues C23 Decision criteria are intermingled, ambiguous, or difficult to 1E-2 assess C24 Multiple goals difficult to prioritize (e.g., advantage for 3.3E-2 incorrect strategies)
C25 Competing or conflicting goals (e.g., choosing one goal will 1.4E-1 block achieving another goal, low preference for correct strategy, reluctance and viable alternative)
C26 Decisionmaking involves developing strategies or action 5E-2 plans C27 Decisionmaking requires diverse expertise distributed 1E-1 among multiple individuals or parties who may not share the same information or have the same understanding of the situation A-6
PIF Attributes Decisionmaking C28 integrating a large variety of types of cues with complex 1.7E-1 logic Table A-3 Base HEPs for Task Complexity (continued)
Action PIF Attributes Execution C30 No impact: simple execution with a few steps 0 C31 Straightforward procedure execution with many steps E-3 C32 Non-straightforward procedure execution 5E-3
- Very long procedures, voluminous documents with checkoff provision
- Multiple procedures needed C33 Simple, continuous control that requires monitoring parameters 3.4E-4 C34 Continuous control that requires manipulating dynamically 2.6E-3 C35 Long-lasting action, repeated discontinuous manual control (need 2E-2 to monitor parameters from time to time)
C36 No immediacy to initiate execution: time span between 5E-3 annunciation (decision for execution made) and operation C37 Complicated or ambiguous execution criteria E-2
- Multiple, coupled criteria
- Restrictive, irreversible order of multiple steps
- Open to misinterpretation C38 Action execution requires close coordination of multiple personnel 5E-2 at different locations (e.g., transport fuel assemblies with fuel machines)
C39 Unlearn or break away from automaticity of trained action scripts 1E-1 A-7
Table A-3 Base HEPs for Task Complexity (continued)
Interteam PIF Attributes Coordination C40 No impact: clear, streamlined, crew-like communication and 0 coordination C41 Complexity of information communicated 1.5E-3
- Simple: 1.5E-3 E-2
- Moderate: E-2
- Extremely high: E-1 E-1 C42 Complex or ambiguous command and control E-2 C43 Complex or ambiguous authorization chain E-2 C44 Coordinate activities of multiple diverse teams or E-2 organizations Table A-4 PIF Weights for Environmental PIFs PIF Attribute D U DM E T ENV0 No impact: nominal weather and 1 1 1 1 1 environmental factors ENV1 Coldness on action execution NA NA NA 1.5 NA
- Moderate cold (<5°C): 1.5 2
- Extreme coldness on manipulating 5 instrumentation: 2 20
- Extreme coldness on physically demanding execution: 5
- Extreme coldness on high-precision manipulations (e.g., connecting lines to pump, remove air from lines and pumps): 20 ENV2 Moderate coldness (<5°C) for 1.1 1.1 1.1 NA 1.1 nonexecution ENV2 Extreme coldness for nonexecution 2 2 1.1 NA 2 ENV3 Heat (>33°C) or high humidity 1.1 1.1 1.1 1.5 1.1 ENV4 Poor lighting, low luminance (L = 0.15, 2 NA NA 2 NA compared to no impact L = 1.5) for reading information or execution ENV5 Strong ambient light, glare, reflection 2 NA NA 1.5 NA A-8
PIF Attribute D U DM E T ENV6 Very low visibility (e.g., heavy smoke or 5 NA NA 5 NA fog) for detecting targets or execution ENV7 Loud or burst noise 1.7 1.1 1.1 1.1 1.1 ENV8 Wearing heavy protective clothes and/or NA NA NA 1.5 NA gloves ENV9 Slippery surface (e.g., icing) NA NA NA 1.5 NA ENV10 Strong winds, rain, or objects close to NA NA NA 1.5 NA road on physically demanding tasks ENV11 Strong winds, rain, or objects close to NA NA NA 2 NA road impeding vehicle movement ENV12 High or chaotic traffic impeding vehicle NA NA NA 1.5 NA movement ENV13 Unstable or vibrating surface or work site NA NA NA 2 NA NA = not applicable; °C = degrees Celsius.
Table A-5 PIF Weights for System and I&C Transparency PIF Attribute D U DM E T SIC0 No impact 1 1 1 1 NA SIC1 System or I&C does not behave as intended 1.1 1.1 1.1 1.1 NA under special conditions SIC2 System or I&C does not reset as intended 1.1 1.1 1.1 10 NA SIC3 System or I&C is complex or nontransparent NA 2 NA NA NA for personnel to predict its behavior SIC4 System or I&C failure modes are not NA 2 NA NA NA transparent to personnel NA = not applicable; I&C = instrumentation and control Table A-6 PIF Weights for Human-System Interface PIF Attribute D U DM E T HSI0 No impact: well-designed HSI supporting the 1 1 1 1 1 task HSI1 Indicator is similar to other sources of 1.5 NA NA NA NA information nearby HSI2 No sign or indication of technical difference from 3 NA NA NA NA adjacent sources (meters, indicators)
HSI3 Related information for a task is spatially 1.5 2 NA NA NA distributed, not organized, or cannot be accessed at the same time HSI4 Unintuitive or unconventional indications 2 NA NA NA NA A-9
PIF Attribute D U DM E T HSI5 Poor salience of the target (indicators, alarms, 3 NA NA NA NA alerts) out of the crowded background HSI6 Inconsistent formats, units, symbols, or tables 5 NA NA NA NA HSI7 Inconsistent interpretation of displays NA 5.7 NA NA NA HSI8 Similarity in elements: wrong element selected NA NA NA 1.2 NA in operating a control element on a panel within reach and similar in design in control room HSI9 Poor functional localization: 2-5 displays or NA NA NA 2 NA panels needed to execute a task HSI10 Ergonomic deficits NA NA NA 3.38 NA
- Controls are difficult to maneuver
- Labeling and signs of controls are not salient among crowd
- Inadequate indications of states of controls:
small unclear labels, difficult reading scales
- Maneuvers of controls are unintuitive or unconventional HSI11 Labels of the controls do not agree with NA NA NA 5 NA document nomenclature, confusing labels HSI12 Controls do not have labels or indications NA NA NA 10 NA HSI13 Controls provide inadequate or ambiguous NA NA NA 4.5 NA feedback, i.e., lack of or inadequate confirmation of the action executed (incorrect, no information provided, measurement inaccuracies, delays)
HSI14 Confusion in action maneuver states NA NA NA 10 NA (e.g., automatic resetting without clear indication)
HSI15 Unclear functional allocation (between human NA NA NA 9 NA and automation)
HIS = human-system interface: NA = not applicable.
Table A-7 PIF Weights for Equipment and Tools PIF Attribute D U DM E T TP0 No impact: Tools and parts are well 1 1 1 1 1 maintained under proper administrative control TP1 Tools/parts are complex or difficult to 1.1 NA NA 1.1 NA use A-10
PIF Attribute D U DM E T TP2 Failure modes or operational 1.1 NA NA 1.1 NA conditions of the tools are not clearly presented (e.g., ranges, limitations, requirements)
TP3 Tool does not work properly due to 1.1 NA NA 1.1 NA aging, lack of power, incompatibility, improper calibration, etc.
TP4 Document nomenclature does not 2 NA NA 2 NA agree with equipment labels TP5 Personnel are unfamiliar with or rarely 2 NA NA 2 NA use the tool/parts TP6 Tools or parts lack proper 2 NA NA 2 NA administrative control (so could be missing or temporally not available)
NA = not applicable.
Table A-8 PIF Weights for Staffing PIF Attribute D U DM E T STA0 No impact: adequate staffing 1 1 1 1 1 STA1 Shortage of staffing (e.g., key 1.1 1.1 1.1 1.1 1.1 personnel are missing, unavailable or delayed in arrival, staff pulled away to perform other duties)
STA2 Lack of backup/lack of peer check or 1.1 1.1 1.1 1.1 1.1 cross-checking (e.g., an overseer or independent reviewer is not available)
STA3 Ambiguous or incorrect specification 1.1 1.1 1.1 1.1 1.1 of staff roles and responsibilities STA4 Inappropriate staff assignment 1.1 1.1 1.1 1.1 1.1 (e.g., lack of skills)
STA5 Key decision-makers knowledge and 1.1 1.1 1.1 1.1 1.1 ability are inadequate to make the decision (e.g., lack of required qualifications or experience)
STA6 Lack of administrative control on 1.1 1.1 1.1 1.1 1.1 fitness for duty A-11
Table A-9 PIF Weights for Procedures, Guidance, and Instructions PIF Attribute D U DM E T PG0 No impact: well-validated procedures 1 1 1 1 1 like most EOPs PG1 Procedure design is less than 1.2 1.1 1.1 1.2 1.1 adequate (difficult to use)
- Requires calculation (e.g., unit conversion)
- No placeholders
- Graphics or symbols not intuitive
- Inconsistency between procedure and displays PG2 Procedure requires judgment 1.6 1.6 1.6 3 1.1 PG3 Procedure lacks details 2.2 2.2 2.2 2.2 1.1 PG4 Procedure is ambiguous, confusing 1.5 5 5 3 5 PG5 Mismatch: Procedure is available but 1.1 17 17 1.1 10 does not match the situation (e.g., needs deviation or adaptation)
PG6 No verification in procedure for 20 NA NA 20 10 verifying key parameters for detection or execution PG7 No guidance to seek confirmatory NA 30 30 NA 10 data when data may mislead for diagnosis or decisionmaking EOP = emergency operating procedure; NA = not applicable.
Table A-10 PIF Weights for Training PIF Attribute D U DM E T TE0 No impact: Professional 1 1 1 1 1 staff have adequate training required TE1 Inadequate training Frequent Frequent Frequent Frequent Frequent frequency/refreshment (<6 (<6 (<6 (<6 (<6 months): 1 months): 1 months): 1 months): 1 months): 1 Infrequent Infrequent Infrequent Infrequent Infrequent (6-12 (6-12 (6-12 (6-12 (6-12 months): months): months): months): months):
1.2 1.2 1.2 1.2 1.2 Highly Highly Highly Highly Highly infrequent infrequent infrequent infrequent infrequent
(>4 years): (>4 years): (>4 years): (>4 years): (>4 years):
5 10 10 10 5 A-12
PIF Attribute D U DM E T TE2 Inadequate training 1.5 1.5 1.5 1.5 1.5 practicality: no hands-on training
- Not drilled together
- Training on parts, not whole scenario together TE3 Inadequate training on 1.1 2 2 2 NA procedure adaptation:
Training focuses on procedure following without adequately training personnel to seek alternative interpretations, evaluate the pros and cons of alternatives, and adapt the procedure for the situation TE4 Inadequate amount of 1.8 3 3 6.1 NA training: no qualification exam
- Less than adequate training specification or requirement TE5 Operator inexperienced 3 3 3 3 NA (e.g., a newly qualified tradesman, but not an expert)
TE6 Poor administrative control 2 2 10 10 NA on training (e.g., not included in the Systematic Approach to Training Program)
TE7 Inadequate training or 14 NA NA NA NA experience with sources of information (such as applicability and limitations of data or the failure modes of the information sources)
TE8 Inadequate specificity on 20 NA NA NA NA urgency and the criticality of key information, such as key alarms TE9 Not trained to seek NA 10 10 NA NA confirmatory information when dismissing critical data A-13
PIF Attribute D U DM E T TE10 Premature termination of NA 15 NA NA NA critical data collection in diagnosis due to inadequate training on system failure modes TE11 Poor training on assessing NA NA 5 NA NA action margin in deciding implementation delay TE12 Poor training on interpreting NA NA 11 NA NA procedure in the context of the scenario for decisionmaking TE13 Poor training on the NA NA NA 10 NA importance of data in frequently checking data for execution NA = not applicable.
Table A-11 PIF Weights for Teamwork and Organizational Factors PIF Attribute D U DM E T TF0 No impact: adequate, crew-like teams 1 1 1 1 1 TF1 Inadequate team 2 2 2 2 2
- Inadequate teamwork resources (short of personnel, knowledge gaps)
- Distributed or dynamic teams
- Poor team cohesion (e.g., newly formed teams, lack of drills, experience together)
TF2 Poor command and control 1.5 1.5 1.5 1.5 1.5
- Unclear allocation of functions and responsibilities
- Inadequate coordination between site personnel and decision-makers (e.g., adapt or modify planned actions based on site situation)
- Inadequately verify the plan with decision-makers
- Inadequate supervision in overseeing action execution and questioning current mission A-14
PIF Attribute D U DM E T TF3 Poor information management in NA NA NA NA 2 multiple-team tasks TF4 Poor communication capabilities NA NA NA NA 2 between teams TF5 Competing resources available for NA NA NA NA 1.5 multiple teams NA = not applicable.
Table A-12 PIF Weights for Work Processes PIF Attribute D U DM E T No impact: licensed personnel with 1 1 1 1 1 WP0 good work practices Lack of practice of self- or 10 1.1 1.1 10 1.1 WP1 cross-verification (e.g., 3-way communication)
Lack of or ineffective peer-checking, 10 1.1 1.1 10 1.1 WP2 supervision WP3 Poor work prioritization, scheduling 1.1 1.1 1.1 1.1 1.1 WP4 Lack of or ineffective instrumentation 1.1 1.1 1.1 1.1 1.1 (e.g., pre-job briefing) for personnel to be aware of potential pitfalls in performing the tasks WP5 Lack of or ineffective instrumentation 1.1 1.1 1.1 1.1 1.1 (e.g., supervision) for safety issue monitoring and identification WP6 Lack of or ineffective instrumentation 1.1 1.1 1.1 1.1 1.1 for safety reporting WP7 Hostile work environment 1.1 1.1 1.1 1.1 1.1 Table A-13 PIF Weights for Multitasking, Interruption, and Distraction PIF Attribute D U DM E T MT0 No impact 1 1 1 1 1 MT1 Distraction by other Weak: 1.2 1.1 1.1 Weak: 1.2 Weak: 1.2 ongoing activities that Moderate: 2 Moderate: Moderate:
demand attention 2 2 High: 2.8 High: 2.8 High: 2.8 A-15
PIF Attribute D U DM E T MT2 Interruption taking away Weak: 1.1 Weak: 1.1 Weak: 1.1 Weak: 1.1 Weak: 1.1 from the main task Moderate: Moderate: Moderate: Moderate: Moderate:
2.8 1.5 1.5 2.8 2.8 Frequent or Frequent or Frequent Frequent Frequent long: 4 long: 1.7 or long: or long: 4 or long: 4 1.7 MT3 Concurrent visual Low NA NA NA NA detection and other demanding:
tasks 2 Moderate demanding:
5 High demanding:
10 MT4 Concurrent auditory Auditory/ NA NA NA NA detection and other visual: 10 tasks Auditory/
auditory:
20 MT5 Concurrent diagnosis NA Low NA NA NA and other tasks demanding:
3 High demanding:
30 MT6 Concurrent go/no-go NA NA 2 NA NA decisionmaking MT7 Concurrently making NA NA 5 NA NA intermingled complex decisions/plans MT8 Concurrently executing NA NA NA 2.3 NA action sequence and performing another attention/working memory task MT9 Concurrently executing NA NA NA 5 NA intermingled or interdependent action plans A-16
PIF Attribute D U DM E T MT10 Concurrently NA NA NA NA 5 communicating or coordinating multiple distributed individuals or teams NA = not applicable.
Table A-14 PIF Weights for Mental Fatigue and Time Pressure and Stress PIF Attribute D U DM E T FS0 No impact 1 1 1 1 1 FS1 Sustained (>30 minutes) 2.5 1.1 1.1 2.5 1.1 high-demanding cognitive activities requiring continuous attention (e.g., procedure-situation mismatches demand constant problem-solving and decisionmaking, information changes over time and requires sustained attention to monitor or frequent checking)
FS2 Time pressure due to perceived time 2 2 1.1 3 1.1 urgency Lack of self-verification due to needs to 10 2 2 10 2 FS3 rush the task completion (speed-accuracy trade-off)
FS4 Reluctance to execute an action plan NA NA NA 2 NA due to potential negative impacts (e.g., adverse economic impact, or personal injury)
FS5 Long working hours (greater than 1.5 1.5 1.1 1.5 1.1 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br />) with high cognitively demanding tasks Sudden increase in workload from a 1.2 1.2 NA 1.2 1.2 FS6 long period of low to high FS7 Sudden decrease in workload from high 1.8 1.1 NA 1.8 1.2 to normal FS8 Emotional stress (e.g., anxiety, 1.2 1.2 1.2 1.2 1.2 frustration)
Physical stress or fatigue (e.g., long 1.1 1.1 1.1 1.1 1.1 hours1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> of exposure to ambient noise, FS9 disturbed dark and light rhythms, air pollution, disruption of normal work-sleep cycles, ill health)
FS10 Sleep deprivation 2 1.2 1.1 2 1.2 NA = not applicable.
A-17
Table A-15 PIF Weights for Physical Demands PIF Attribute D U DM E T PD0 No impact 1 PD1 Physically strenuous: possibly exceeding physical limits NA NA NA 1.5 NA (e.g., lifting heavy objects, moving heavy things, opening/closing rusted or stuck valves)
PD2 High spatial or temporal precision NA NA NA 2 NA PD3 Precise motor coordination of multiple persons NA NA NA 2 NA PD4 Unusual, unevenly balanced loads (e.g., reaching high NA NA NA 5 NA parts)
PD5 Loading or unloading objects using crane/hoist NA NA NA 10 NA NA = not applicable.
A-18
Appendix B: See-And-Flee Scenarios (Questions from RES and Answers from NMSS)
Overall (Priority) Questions:
- 1. Question: What are the hazardous properties of hydrogen fluoride (i.e., Highly toxic when inhaled, highly toxic by ingestion, corrosive)?
Answer: HF is highly toxic via multiple pathways. Inhalation, ingestion and dermal contact are primary pathways. It takes very little to cause long term damage and not much more to cause death. https://www.epa.gov/aegl/hydrogen-fluoride-results-aegl-program
- 2. Question: Would UF6 cause worker to choke, cough, etc. once in contact?
Answer: Yes.
- 3. Question: What task/s is the worker performing prior to release? Can we assume he/she would be performing some type of routine activity? (potential multi-tasking, interruptions, distractions, or decision-making points)? Are there any tasks being done that need to be completed prior to exiting?
Answer: Assume that the worker is performing some type of routine activity. As we discussed, there are some activities, though routine, that if left undone, may put the facility into an unsafe condition. However, workers are trained to drop everything they are doing and leave the area immediately. There may be one worker that is required to activate an alarm before leaving the area.
- 4. Question: How long has the worker been on the clock? Prior shifts? Over 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br />?
Complex tasks?
Answer: Assume that the worker is halfway through a 10-hour shift and, as stated in Q3, is performing a routine task.
- 5. Question: Large or small release? Release rate?
Answer: Please assume two release rates of UF6: 150 g/min and 300 g/min. These rates are comparable to average release rates from real releases. UF6 reacts with water in the air to produce uranyl fluoride and hydrogen fluoride, both of which are toxic. However, HF is the limiting toxic agent.
B-1
- 6. Question: Is 1 minute a reasonable amount of time to successfully flee based on leak rate and room and tank size?
Answer: One minute is a standard time that licensees cite. Operating experience suggests that the actual time can be more or less. A result from this project may be that the probability of successfully leaving the area in one minute is relatively low. Assume two tank sizes, 200 lbs. and 2000 lbs.
- 7. Question: How long does the worker have to exit the room before becoming too hazardous? What are the success criteria vs. training expectation of exiting in time (Time Available)?
Answer: Workers are trained to leave the area immediately. How long the worker has will depend on the release rate and room volume.
- 8. Question: What is the probability that the worker will properly assess the white cloud based on their training?
Answer: Workers are trained to assume any white cloud is dangerous and to leave the room immediately. Licensees assume the probability is 1; however, operating experience says less than 1, but there is not much more detail than that.
- 9. Question: Can we get a copy of the training material (procedure/guidance)?
Answer: This scenario is a compilation of multiple events at several facilities.
- 10. Question: Are there any sensors that can detect a release before the worker?
Answer: No.
- 11. Question: Any other workers or teamwork involved?
Answer:
- a. Assume for the confined area that there are no other workers in the area.
- b. For the large area, assume there are two other workers, and they are working within two (2) feet of one another. However, for a recent event, in a large area, there were three workers in the area.
B-2
- 12. Question: Can you explain, HF is irritating at low concentration but not sensed at high concentration?
Answer: At low concentration, the mucus membranes, respiratory tract, and skin will exhibit signs of exposure, e.g., sneezing, coughing and contact dermatitis. However, at higher concentrations, the skin may not show signs of damage for up to several hours after exposure. Because it can penetrate the skin and continue to cause internal damage, this potential lack of detection makes it particularly dangerous.
Questions for Large Area Scenario:
- 1. Question: Are there any equipment, pipes, valves, belts, or tanks low hanging or low to the ground causing worker to potentially need to step over, duck or trip if attempting to exit in a timely fashion?
Answer: Assume there are no equipment, pipes, valves, etc. near the ground. However, assume there are valves, pipes, equipment, etc. at waist level and higher that the worker can run into. Also, assume the large area is configured with equipment, pipes, etc. such that there are a few main alleys from which many smaller corridors emanate.
- 2. Question: Would there be any noise in the room i.e. loud machines running?
Answer: Yes, and the worker is wearing hearing protection.
Questions for Confined Space Scenario:
- 1. Question: What is the diameter, length, and direction of the large pipe that runs through the middle of the room?
Answer: Assume the pipe diameter is 24 cm, length 5 m and direction is perpendicular to the wall with the alarm button.
Questions for Outdoors Scenario:
- 1. Question: Can we assume worker has the fitness to perform the action (opening gate)?
Answer: Yes.
- 2. Question: Night or day?
Answer: Results for both would be great.
B-3
- 3. Question: Should we account for inclement weather?
Answer: Assume no inclement weather.
Additional Questions:
- 1. Question: Is the facility operating in normal mode?
Answer: Yes.
- 2. Question: Could the release cause the worker/s to become distorted in any way based on size, thickness of cloud and hazardous properties?
Answer: Yes.
- 3. Question: What are the boundary conditions, which describes the expected systems, site, and personnel status immediately after the initiating event? What are the assumptions prior to the rupture/release?
Answer: Assume that immediately after the initiating event, personnel have entered emergency operations. Prior to the rupture/release personnel are performing their routine, day-to-day operations, and the facility is in normal mode.
- 4. Question: Workers may detect a release via sound, smell, skin irritation, hearing an alarm, or seeing fog or perhaps a spray. Which condition/s should we consider for this example?
Answer: Assume that workers see the fog.
- 5. Question: How long has the worker been working at the facility (years, months)?
Answer: Assume years.
- 6. Question: Do all staff at facility have the same training?
Answer: All staff have the same training for immediately leaving the area upon seeing a white cloud.
B-4
- 7. Question: Are workers up to date on training?
Answer: Yes.
- 8. Question: Source of UF6 release for each scenario?
Answer: For all scenarios, assume the release if from a ruptured valve stem on a tank.
- 9. Question: Does this type of event occur frequently? Has worker been in this situation before?
Answer: Assume similar scenarios have occurred 2 times in the last five years. Assume, however, that the workers have not been in this situation before.
- 10. Question: Do you have any blueprints to help visualize the scenarios?
Answer: Unfortunately, no. The scenario is based on a fictitious facility.
B-5