ML19212A722
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| Issue date: | 07/31/2019 |
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Introduction to Human Reliability Analysis (HRA)
NRC-RES Fire PRA Workshop Module IV August 5 - 9, 2019 Rockville, MD
Objectives Introduce Human Reliability Analysis (HRA), in the context of PRA for nuclear power plants before discussing HRA in the context of Fire PRA.
Provide students with a basic understanding of HRA:
- What is HRA?
- Where does HRA fit into PRA?
- What does HRA model?
- What are the keys to performing HRA?
- How can we understand human error?
- What guidance is there for performing HRA?
- What are the HRA concerns or issues for fire PRA?
- Is there a standard for performing HRA?
Introduction to HRA Slide 2 Fire PRA Workshop 2019, Rockville, MD
Introduction to HRA Outline What is HRA?
What does HRA model?
What are the keys to performing HRA?
How can we understand human error?
What guidance is there for performing HRA?
What are the HRA concerns or issues for fire PRA?
Is there a standard for performing HRA?
Any final questions?
Introduction to HRA Slide 3 Fire PRA Workshop 2019, Rockville, MD
Human Reliability Analysis (HRA) .
Is generally defined as:
- A structured approach used to identify potential human failure events (HFEs) and to systematically estimate the probability of those errors using data, models, or expert judgment Is developed because:
- PRA reflects the as-built, as-operated plant
- HRA is needed to model the as-operated portion (and cross-cuts many PRA tasks and products)
Produces:
- Identified and defined human failure events (HFEs)
- Qualitative evaluation of factors influencing human errors and successes
- Human error probabilities (HEPs) for each HFE Introduction to HRA Slide 4 Fire PRA Workshop 2019, Rockville, MD
HRA . (continued)
Requires inputs from many sources and technical disciplines, including:
- Plant information:
Design information such as post-initiating event behavior Engineering (e.g., thermal hydraulics and room heat-up calculations)
Plant operations (procedures and how they are used)
Plant hardware (ergonomics of monitoring and control interfaces, both inside and outside of the main control room)
- PRA model information:
Accident progression following an initiating event Systems and operator actions modeled in response
- HRA discipline - cognitive and behavioral science
- Etc., etc., etc.
Is performed by a multi-disciplinary team Introduction to HRA Slide 5 Fire PRA Workshop 2019, Rockville, MD
Introduction to HRA Outline What is HRA?
What does HRA model?
What are the keys to performing HRA?
How can we understand human error?
What guidance is there for performing HRA?
What are the HRA concerns or issues for fire PRA?
Is there a standard for performing HRA?
Any final questions?
Introduction to HRA Slide 6 Fire PRA Workshop 2019, Rockville, MD
Overview of PRA Process PRAs are performed to find severe accident weaknesses and provide quantitative results to support decision-making.
Three levels of PRA have evolved:
Level An Assessment of: Result 1 Plant accident initiators and Core damage frequency systems/operators response and contributors 2 Reactor core melt, and Categorization and frequency and modes of frequencies of containment containment failure releases 3 Public health consequences Estimation of public and economic risks Introduction to HRA Slide 7 Fire PRA Workshop 2019, Rockville, MD
PRA Classification Internal Hazards - risk from accidents initiated internal to the plant
- Includes internal events, internal flooding and internal fire events External Hazards - risk from external events
- Includes seismic, external flooding, high winds and tornadoes, airplane crashes, lightning, hurricanes, etc.
At-Power - accidents initiated while plant is critical and producing power (operating at >X%* power)
Low Power and Shutdown (LP/SD) - accidents initiated while plant is <X%* power or shutdown
- Shutdown includes hot and cold shutdown, mid-loop operations, refueling
- X is usually plant-specific. The separation between full and low power is determined by evolutions during increases and decreases in power.
Introduction to HRA Slide 8 Fire PRA Workshop 2019, Rockville, MD
Principal Steps in PRA LEVEL LEVEL LEVEL 1 2 3 Initiating Accident Accident RCS / Source Release Offsite Health &
Event Sequence Sequence Containment Term Category Conseqs Economic Analysis Analysis Quantif. Response Analysis Character. Analysis Risk Analysis and Analysis Quantif.
Meteorology Success Systems Uncertainty Phenomena Uncertainty Uncertainty
& & Model &
Criteria Analysis* Analysis Sensitivity Sensitivity Sensitivity Analysis Analysis Analysis Population Distribution Emergency Data Response Analysis* Human Reliability Analysis* Pathways Model LERF Assessment Health Effects Economic Effects
Principal Steps in PRA (continued)
First, well look at how HRA fits into Event Tree (ETs) models.
Introduction to HRA Slide 10 Fire PRA Workshop 2019, Rockville, MD
Human Events in Event Trees Nature of event trees (and where HRA fits in):
Typically used to model the response to an initiating event Features:
- Generally, a unique system-level event tree is developed for each initiating event group
- Identifies systems/functions required for mitigation
- Identifies operator actions required for mitigation
- Identifies event sequence progression
- End-to-end traceability of accident sequences leading to bad outcome Primary use
- Identification of accident sequences which result in some outcome of interest (usually core damage and/or containment failure)
- Basis for accident sequence quantification Introduction to HRA Slide 11 Fire PRA Workshop 2019, Rockville, MD
Simple Event Tree Post-Reactor Emergency Emergency Accident Initiating Protection Coolant Coolant Heat Event System Pump A Pump B Removal Sequence - End State/Plant Damage State A B C D E
- 1. A
- 2. AE - plant damage
- 3. AC Success
- 4. ACE - plant damage
- 5. ACD - plant damage Failure
System-Level Event Tree Development A system-level event tree consists of an initiating event (one per tree), followed by a number of headings (top events), and sequences of events defined by success or failure of the top events Top events represent the systems, components, and/or human actions required to mitigate the initiating event To the extent possible, top events are ordered in the time-related sequence in which they would occur
- Selection of top events and ordering reflect emergency procedures Each node (or branch point) below a top event represents the success or failure of the respective top event
- Logic is typically binary Downward branch - failure of top event Upward branch - success of top event
- Logic can have more than two branches, with each branch representing a specific status of the top event Introduction to HRA Slide 13 Fire PRA Workshop 2019, Rockville, MD
System-Level Event Tree Development (continued)
Dependencies among systems (to prevent core damage) are identified
- Support systems can be included as top events to account for significant dependencies (e.g., diesel generator failure in station blackout event tree)
Timing of important events (e.g., physical conditions leading to system failure) determined from thermal-hydraulic (T-H) calculations Branches can be pruned logically to remove unnecessary combinations of system successes and failures
- This minimizes the total number of sequences that will be generated and eliminates illogical sequences Branches can transfer to other event trees for development Each path of an event tree represents a potential scenario Each potential scenario results in either prevention of core damage or onset of core damage (or a particular end state of interest)
Introduction to HRA Slide 14 Fire PRA Workshop 2019, Rockville, MD
Functional Event Tree Initiating Reactor Short term Long term Event Trip core cooling core cooling SEQ # STATE IE RX-TR ST-CC LT-CC 1 OK 2 LATE-CD 3 EARLY-CD 4 ATWS Introduction to HRA Slide 15 Fire PRA Workshop 2019, Rockville, MD
Critical Safety Functions Example safety functions for core and containment
- Reactor subcriticality
- Reactor coolant system overpressure protection
- Early core heat removal
- Late core heat removal
- Containment pressure suppression
- Containment heat removal
- Containment integrity Introduction to HRA Slide 16 Fire PRA Workshop 2019, Rockville, MD
Example BWR Mitigating Systems Function Systems Reactivity Reactor Protection System, Standby Liquid Control, Control Alternate Rod Insertion RCS Safety/Relief Valves Overpressure Protection Coolant Injection High Pressure Coolant Injection, High Pressure Core Spray, Reactor Core Isolation Cooling, Low Pressure Core Spray, Low Pressure Coolant Injection (RHR)
Alternate Systems- Control Rod Drive Hydraulic System, Condensate, Service Water, Firewater Decay Heat Power Conversion System, Residual Heat Removal (RHR)
Removal modes (Shutdown Cooling, Containment Spray, Suppression Pool Cooling)
Introduction to HRA Slide 17 Fire PRA Workshop 2019, Rockville, MD
Example PWR Mitigating Systems Function Systems Reactivity Control Reactor Protection System (RPS)
RCS Overpressure Safety valves, pressurizer Power-Operated Relief Valves Protection (PORVs)
Coolant Injection Accumulators, High Pressure Safety Injection (HPSI),
Chemical Volume and Control System (CVCS), Low Pressure Safety Injection (LPSI), High Pressure Recirculation (may require LPSI)
Decay Heat Power Conversion System, Auxiliary Feedwater (AFW),
Removal Residual Heat Removal (RHR), Feed and Bleed (PORV +
HPSI)
Introduction to HRA Slide 18 Fire PRA Workshop 2019, Rockville, MD
System Success Criteria Identify systems which can perform each function Often include if the system is automatically or manually actuated.
Identify minimum complement of equipment necessary to perform function (often based on thermal/hydraulic calculations, source of uncertainty)
- Calculations often realistic, rather than conservative May credit non-safety-related equipment where feasible Introduction to HRA Slide 19 Fire PRA Workshop 2019, Rockville, MD
Example Success Criteria Short Term Long Term Reactor IE Core Core Trip Cooling Cooling Power Conversion Power Conversion System System Auto Rx Trip or or Transient or 1 of 3 AFW 1 of 3 AFW or or Manual Rx Trip 1 of 2 PORVs 1 of 2 PORVs and 1 of 2 ECI and 1 of 2 ECR Auto Rx Trip Medium or or 1 of 2 ECI 1 of 2 ECR Large LOCA Manual Rx Trip Introduction to HRA Slide 20 Fire PRA Workshop 2019, Rockville, MD
What does HRA do with ET information?
For example, the HRA analyst:
From initiating event and subsequent top events on ET:
- Identifies the procedures and procedure path that lead to successful mitigation of the initiating event From success criteria:
- Determines what defines an operator failure (e.g., fewer pumps started than needed, actions performed too late in time)
From plant behavior timing provided by T-H calculations:
- Determines what plant parameters, alarms, and other indications are available to help operators:
understand the plant state (initially and as the accident progresses) use procedures appropriately to respond to specific accident sequence Any plant function-related human failure events (HFEs) can be defined.
Introduction to HRA Slide 21 Fire PRA Workshop 2019, Rockville, MD
What does HRA do with ET information?
(continued)
From the various branches on the event tree (combined with success criteria and timing information):
- Identifies (or confirms) what operator actions, if failed, could result in down branches and certain plant damage states (alone or in combination with system failures) (i.e., define an HFE)
- Identifies what specific operator actions (e.g., fails to start HPI Train A pump, turns off Safety Injection) would result in a down branch (i.e., define an HFE)
- Identifies what procedure paths might be plausibly taken that would result in operator failures
- Identifies what plant information (or missing information) might cause operators to take inappropriate procedure paths These inputs also can be as factors influencing the selection of screening values for human failure events.
Introduction to HRA Slide 22 Fire PRA Workshop 2019, Rockville, MD
Principal Steps in PRA (continued)
Next, well see how HRA is included in Fault Tree (FT) models.
Introduction to HRA Slide 23 Fire PRA Workshop 2019, Rockville, MD
Human Events in Fault Trees Characteristics of fault trees (and where HRA fits in):
Deductive analysis (event trees are inductive)
Start with undesired event definition Used to estimate system failure probability Explicitly model multiple failures Identify ways by which a system can fail Models can be used to find:
- System weaknesses
- System failure probability
- Interrelationships between fault events Introduction to HRA Slide 24 Fire PRA Workshop 2019, Rockville, MD
Human Events in Fault Trees (continued)
Fault trees are graphic models depicting the various paths of combinations of faults that will result in the occurrence of the undesired top event.
Fault tree development moves from the top event to the basic event (or faults) which can cause it.
Fault tree consists of gates to develop the fault logic in the tree.
Different types of gates are used to show the relationship of the input events to the higher output event.
Fault tree analysis requires thorough knowledge of how the system operates and is maintained.
Introduction to HRA Slide 25 Fire PRA Workshop 2019, Rockville, MD
Specific Failure Modes Modeled for Each Component Each component associated with a specific set of failure modes/mechanisms determined by:
- Type of component (e.g., motor-driven pump, air-operated valve)
- Normal/Standby state Normally not running (standby), normally open
- Failed/Safe state Failed if not running, or success requires valve to stay open Introduction to HRA Slide 26 Fire PRA Workshop 2019, Rockville, MD
Typical Component Failure Modes Active Components
- Fail to Start*
- Fail to Run*
- Fail to Open/Close/Operate*
Additional failure mode is component is unavailable because it is out for test or maintenance
- In addition to hardware failures that have these failure modes, an operator error of commission (that suppresses actuation or operation, or turns off equipment) also can cause these failure modes.
Introduction to HRA Slide 27 Fire PRA Workshop 2019, Rockville, MD
Active Components Require Support Signal needed to actuate component
- Safety Injection Signal starts pump or opens valve If system is a standby system, operator action may be needed to actuate (and failure to actuate is modeled as an HFE)
Support systems might be required for component to function
- Service water or component water cooling
- Room cooling Introduction to HRA Slide 28 Fire PRA Workshop 2019, Rockville, MD
Simplified Fault Tree for Failure of Emergency Coolant Injection (ECI)
ECI fails to deliver
> 1 pump flow Injection lines fail Pump segments fail Suction lines fail MV1 fails closed MV2 fails closed PS-B fails PS-A fails V1 fails closed MV3 fails closed T1 fails Introduction to HRA Slide 29 Fire PRA Workshop 2019, Rockville, MD
Fault Tree Symbols Symbol Description Logic gate providing a representation OR Gate of the Boolean union of input events.
The output will occur if at least one of the inputs occur.
Logic gate providing a representation of the Boolean intersection of input AND Gate events. The output will occur if all of the inputs occur.
A basic component fault which Basic Event requires no further development.
Consistent with level of resolution in databases of component faults.
Introduction to HRA Slide 30 Fire PRA Workshop 2019, Rockville, MD
What does HRA do with FT information?
From the top events and types of equipment modeled in the fault tree:
- Identify and define any human failure events (HFEs) that could result in system, train, or component failures (e.g., starting, actuating, opening/closing)
From review of procedures and other documents related to testing and maintenance:
- Identify and define operator failures to restore systems, trains, or components following testing or maintenance
- Determine the frequency of testing and preventive maintenance
- Determine what post-testing and post-maintenance checks are performed These inputs also can be used in selecting appropriate screening values for HFEs.
Introduction to HRA Slide 31 Fire PRA Workshop 2019, Rockville, MD
Introduction to HRA Outline What is HRA?
What does HRA model?
What are the keys to performing HRA?
How can we understand human error?
What guidance is there for performing HRA?
What are the HRA concerns or issues for fire PRA?
Is there a standard for performing HRA?
Any final questions?
Introduction to HRA Slide 32 Fire PRA Workshop 2019, Rockville, MD
Human Reliability Analysis Starts with the basic premise that the humans can be represented as either:
- A component of a system, or
- A failure mode of a system or component.
Identifies and quantifies the ways in which human actions initiate, propagate, or terminate accident sequences.
Human actions with both positive and negative impacts are considered in striving for realism.
A difficult task in a PRA since the HRA analyst needs to understand the plant hardware response, the operator response, the accident progression modeled in the PRA.
Not everything the operator does is modeled in the PRA!
Introduction to HRA Slide 33 Fire PRA Workshop 2019, Rockville, MD
Human Reliability Analysis Objectives Ensure that the impacts of plant personnel actions are reflected in the assessment of risk in such a way that:
a) both pre-initiating event and post-initiating event activities, including those modeled in support system initiating event fault trees, are addressed.
b) logic model elements are defined to represent the effect of such personnel actions on system availability/unavailability and on accident sequence development.
c) plant-specific and scenario-specific factors are accounted for, including those factors that influence either what activities are of interest or human performance.
d) human performance issues are addressed in an integral way so that issues of dependency are captured.
Ref. ASME RA-Sa-2009 Introduction to HRA Slide 34 Fire PRA Workshop 2019, Rockville, MD
Categories of Human Failure Events in PRA Operator actions can occur throughout the accident sequence:
- Before the initiating event (i.e., pre-initiator)
- As a cause of the initiating event
- After the initiating event (i.e., post-initiator)
Introduction to HRA Slide 35 Fire PRA Workshop 2019, Rockville, MD
Categories of Human Failure Events:
Pre-Initiator HFEs Sometimes called latent errors because they are not revealed until there is a demand for the affected system (after the initiating event).
Examples:
- Failure to restore valve lineup following routine system testing
- Failure to rack-in pump breaker in following preventive maintenance
- Mis-calibration of instruments Most frequently relevant outside main control room Some of these failures are captured in equipment failure data.
For HRA, the focus is on equipment being left misaligned, unavailable, or not working exactly right (accounting for post-test/post-maintenance verification).
Introduction to HRA Slide 36 Fire PRA Workshop 2019, Rockville, MD
Categories of Human Failure Events:
Initiating-Event Related Operator actions can contribute to the occurrence of or cause initiating events (i.e., human-induced initiators)
In PRAs, such events are most often
- Included implicitly in the data used to quantify initiating event frequencies, and
- Therefore not modeled explicitly in the PRA Operator actions can be particularly relevant for operating conditions other than power operation
- Human-caused initiating events can have unique effects (e.g.,
causing drain-down of reactor or RCS during shutdown)
- Actions that cause initiating events may also have implications for subsequent human response (i.e., dependence can be important)
Introduction to HRA Slide 37 Fire PRA Workshop 2019, Rockville, MD
Categories Of Human Failure Events:
Post-Initiator HFEs Post-initiator HFEs account for failures associated with response to an initiating event Typically reflect failure to take necessary action (in main control room or locally)
- Failure to initiate function of manually-actuated system
- Failure to back up an automatic action
- Failure to recover from other system failures Reconfigure system to overcome failures (e.g., align electrical bus to alternative feed)
Make use of an alternative system (e.g., align fire water to provide pump cooling)
Most often reflect failure to take actions called for by procedures Introduction to HRA Slide 38 Fire PRA Workshop 2019, Rockville, MD
Other Classifications of Human Failure Events Another way to classify human failure events (HFEs) from the perspective of the PRA is:
- Error of omission (EOO)
- Error of commission (EOC)
Errors of omission (EOOs):
- A human failure event resulting from a failure to take a required action, leading to an unchanged or inappropriately changed and degraded plant state.
- Examples:
Failure to start auxiliary feedwater system Failure to block automatic depressurization system signals Introduction to HRA Slide 39 Fire PRA Workshop 2019, Rockville, MD
Other Classifications of HFEs (continued)
Errors of commission (EOCs):
- A human failure event resulting from a well-intended but inappropriate, overt action that, when taken, leads to a change in the plant and results in a degraded plant state.
- Often, these events represent good operating practice, but applied to the wrong situation (especially, when understanding the situation is difficult).
- Examples:
Prematurely terminating safety injection (because operators think SI is not needed; but for the specific situation, SI is needed).
Introduction to HRA Slide 40 Fire PRA Workshop 2019, Rockville, MD
Other Classifications of HFEs (continued)
Pre-initiator HFEs can be either EOOs or EOCs:
- These HFEs usually represent failures in execution (i.e.,
failures to accomplish the critical steps; these steps are typically already decided so no decision-making is required).
- Execution failures are often caused by inattention (or over-attention) failures
- Examples:
Inattention: Skipped steps (especially, following interruptions or other distractions)
Over-attention: Repeated or reversed steps Introduction to HRA Slide 41 Fire PRA Workshop 2019, Rockville, MD
Other Classifications of HFEs (continued)
Most post-initiator HFEs that are modeled are EOOs:
- These HFEs can represent either failures in execution or cognitive failures (such as failures in diagnosis of the plant condition or decision-making regarding procedure use for a particular situation).
- Most PRAs only include EOOs; however, EOCs have been involved in many significant accidents, both in nuclear power industry and others.
- Later, well see that the fire PRA methodology for NFPA-805 requires that certain EOCs be addressed.
Introduction to HRA Slide 42 Fire PRA Workshop 2019, Rockville, MD
Introduction to HRA Outline What is HRA?
What does HRA model?
What are the keys to performing HRA?
How can we understand human error?
What guidance is there for performing HRA?
What are the HRA concerns or issues for fire PRA?
Is there a standard for performing HRA?
Any final questions?
Introduction to HRA Slide 43 Fire PRA Workshop 2019, Rockville, MD
What are the keys to performing HRA?
The key is to.
Introduction to HRA Slide 44 Fire PRA Workshop 2019, Rockville, MD
What are the keys to performing HRA?
understand the problem.
Introduction to HRA Slide 45 Fire PRA Workshop 2019, Rockville, MD
What are the keys to performing HRA?
Why do you need to understand the problem?
- 1. To be able to identify, define, and model (i.e., place appropriately in the plant logic model) HFEs such that they are consistent with, for example:
the specific accident sequence associated plant procedures and operations expected plant behavior and indications engineering calculations that support the requirements for successful accident mitigation consequences that are risk-significant Introduction to HRA Slide 46 Fire PRA Workshop 2019, Rockville, MD
What are the keys ? (continued)
Why do you need to understand the problem? (continued) 2.To appropriately select an HRA quantification method to (usually) indirectly represent how operators are expected to behave, based on, for example:
their procedures and training plant-specific (and maybe even crew-specific) styles for responding to accidents plant-specific operating experience general understanding of human error, behavior and cognitive science, human factors and ergonomics knowledge of HRA methods and their underlying bases
- 3. To support and justify the HFEs and their quantification Introduction to HRA Slide 47 Fire PRA Workshop 2019, Rockville, MD
What are the keys ? (continued)
How do you develop this understanding?
- Perform an appropriately thorough qualitative analysis, performed iteratively and repeatedly throughout the entire HRA process until the final HRA quantification is done.
How do you know when are you done?
- Usually, one or more of the following has occurred:
The accident sequence analyst tells you that you should move on to a new problem/HFE (that is more risk-significant).
Your deadline has arrived.
Your money is spent.
Introduction to HRA Slide 48 Fire PRA Workshop 2019, Rockville, MD
What are the keys ? (continued)
Increasingly, the HRA/PRA recognizes the importance of HRA qualitative analysis.
More focus on qualitative analysis is appearing in recent or upcoming HRA/PRA guidance, e.g.,
- Joint EPRI/NRC-RES Fire HRA guidance (NUREG-1921/EPRI 1023001, July 2012)
- ATHEANA (NUREG-1624, Rev. 1)
- EPRIs HRA Calculator This emphasis is supported or based on recent studies such as:
- International HRA Empirical Study - Phase 1 Report (NUREG/IA-0216, Volume 1, 2009)
Introduction to HRA Slide 49 Fire PRA Workshop 2019, Rockville, MD
What are the keys to performing HRA?
An important key to building an understanding of the problem is Introduction to HRA Slide 50 Fire PRA Workshop 2019, Rockville, MD
What are the keys to performing HRA?
context.
Introduction to HRA Slide 51 Fire PRA Workshop 2019, Rockville, MD
What are the keys to performing HRA?
Context has long been recognized as important, e.g.,
- SHARP1 (1992) discusses the importance of addressing human interactions for plant-specific and accident sequence-specific scenarios.
However, a commonly held belief, still evident in popular accounts of incidents and reflected in how some people regard what new technologies ought to accomplish, is:
- If we could just eliminate the human, wed never have any problems.
This corresponds with the so-called blame culture or human-as-a-hazard view Introduction to HRA Slide 52 Fire PRA Workshop 2019, Rockville, MD
What are the keys ? (continued)
Of course, the human here is the one on the sharp end, i.e., the last one to touch any equipment or try to respond to an accident.
But, humans also are involved in design, planning, inspection, testing, manufacturing, software development, etc., etc., etc.
Lets look at some everyday examples of what humans on the sharp end have to contend with as a way of understanding the impact of context and how we may be set up for failure.
Introduction to HRA Slide 53 Fire PRA Workshop 2019, Rockville, MD
What are the keys to performing HRA?
Introduction to HRA Slide 54 Fire PRA Workshop 2019, Rockville, MD
What are the keys to performing HRA?
Introduction to HRA Slide 55 Fire PRA Workshop 2019, Rockville, MD
What are the keys to performing HRA?
Introduction to HRA Slide 56 Fire PRA Workshop 2019, Rockville, MD
What are the keys HRA? (continued)
Recent research on human error and human actions involved in serious accidents has contributed to building a new perspective on the role of humans in technology and the role of context.
Examples of research/researchers include:
- James Reason, Human Error, 1990, Managing the Risks of Organizational Accidents, 1997, The Human Contribution: Unsafe Acts, Accidents and Heroic Recoveries, 2008, Organizational Accidents Revisited, 2015.
- Donald R. Norman, The Design of Everyday Things, 1988.
- E. M. Roth and R.J. Mumaw, An Empirical Investigation of Operator Performance in Cognitively Demanding Simulated Emergencies, NUREG/CR-6208, 1994.
- Steven Casey, Set Phasers on Stun: And Other True Tales of Design, Technology, and Human Error, 1998.
- Others, such as: Eric Hollnagel, David Woods, Micah Endsley Introduction to HRA Slide 57 Fire PRA Workshop 2019, Rockville, MD
What are the keys ? (continued)
Some of the key messages from this body of research are:
- The operator is often set-up for failure by prior events, pre-existing conditions, failed or misleading information, unusual and unfamiliar plant conditions and configurations, procedures that dont match the situation, and so on.
- But, he doesnt always fail
[E]ven the best [trouble-shooters] have bad days. It is my impression that the very best trouble-shooters get it right about half the time. The rest of us do much worse. (Reason, The Human Contribution, page 66)
- So, hes the last line of defense after all other previous designs and plans have failed.
Introduction to HRA Slide 58 Fire PRA Workshop 2019, Rockville, MD
What are the keys ? (continued)
Suggestions for some practical exercises on context 1.You want a book off the shelf in your living room. You even go to the living room to get the book. However, after you return to your home office, you discover that you never got the book.
2.You have a doctors appointment. Despite reminding yourself of the location for the doctors office while you drive away from home, you end up at your childrens school instead.
3.You drive yourself to work every day on the same route, you have a good driving record, and you drive defensively. Somehow, you end up in a collision with another vehicle.
All unlikely, right? Now, think about how the context might cause you to make one of these mistakes.
Introduction to HRA Slide 59 Fire PRA Workshop 2019, Rockville, MD
What are the keys ? (continued)
Suggestions for some practical exercises on context
- 1. In Reasons Human Error, the context was an interruption, namely knocking a bunch of books off the shelf. After picking up all the books, you forget why you were there in the first place.
- 2. Ive done this. I got distracted by thinking about a work problem and/or was focused on the radio music. My automatic pilot kicked in and, instead of stopping at the doctors office (~1 mile before the turnoff to the school), I did what I usually do 2x per day - drove to the school.
- 3. This one is easy (i.e., lot of options for added context).
- Potential distractions, e.g.: Call coming in on the cell phone, passengers in car (Bring Your Child to Work Day?), etc.
- Added challenges, e.g.: Rain/ice/snow, fogged or iced up windows, road construction.
- Unexpected equipment problems, e.g.: Fuel low light comes on, run out of windshield washer fluid.
Introduction to HRA Slide 60 Fire PRA Workshop 2019, Rockville, MD
Introduction to HRA Outline What is HRA?
What does HRA model?
What are the keys to performing HRA?
How can we understand human error?
What guidance is there for performing HRA?
What are the HRA concerns or issues for fire PRA?
Is there a standard for performing HRA?
Any final questions?
Introduction to HRA Slide 61 Fire PRA Workshop 2019, Rockville, MD
How can we understand human error?
Lesson 1:
Introduction to HRA Slide 62 Fire PRA Workshop 2019, Rockville, MD
How can we understand human error?
Human error is not random.
Introduction to HRA Slide 63 Fire PRA Workshop 2019, Rockville, MD
How can we understand human error?
But, why does human error seem random?
Remember our exercise about context?
- How many different possible contexts would you estimate can influence your everyday life?
- For the actions typically addressed by HRA, the range of contexts has been constrained to:
- Existing, licensed and operating nuclear power plants (NPPs)
- NPP accidents represented in Level 1, at-power, internal events PRA
- Actions taken by licensed operators
- Operator actions taken (mostly) in the control room (that has been extensively designed and redesigned, reviewed and re-reviewed)
- Operator actions that are addressed by Emergency Operating Procedures (EOPs) (that have been validated and demonstrated with decades of experience)
- Operator actions that are adequately trained
- Etc., etc., etc.
Introduction to HRA Slide 64 Fire PRA Workshop 2019, Rockville, MD
How can we understand human error?
Lesson 2:
Introduction to HRA Slide 65 Fire PRA Workshop 2019, Rockville, MD
How can we understand human error?
Human error is not the cause of a mishap.
Introduction to HRA Slide 66 Fire PRA Workshop 2019, Rockville, MD
How can we understand human error?
Remember.
-The operator is often set-up for failure
-And, the operator is on the sharp-end (i.e., simply the last one to touch the problem).
To illustrate this concept, here is Reasons Swiss Cheese model of event causation (1990 and 1997)
Introduction to HRA Slide 67 Fire PRA Workshop 2019, Rockville, MD
The Swiss Cheese Model of Event Causation Some holes due Hazards to active failures Other holes due to Harm latent conditions Successive layers of defenses, barriers, & safeguards Introduction to HRA Slide 68 Fire PRA Workshop 2019, Rockville, MD
How can we understand human error?
Lesson 3:
Introduction to HRA Slide 69 Fire PRA Workshop 2019, Rockville, MD
How can we understand human error?
Human error can be predicted.
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Human error can be predicted because Peoples behavior is almost always rational
- adaptive - i.e., goals are achieved
- satisficing - i.e., best under the circumstances Peoples actions will tend to be
- practical people do what works
- economical people act so as to conserve resources And, in the case of NPPs, we have lots of rules and regulations to follow that are taken seriously; this further constrains likely behaviors and influences that HRA must model.
Introduction to HRA Slide 71 Fire PRA Workshop 2019, Rockville, MD
Human error can be predicted because People follow familiar paths Maximize use of habits (good and bad)
Minimize cognitive strain People use rapid pattern-matching to detect and interpret faults and errors Very effective at detecting most problems, but Not very effective at detecting our own errors People also use
- shortcuts, heuristics, and expectation-driven actions.
- efficiency-thoroughness trade-offs Introduction to HRA Slide 72 Fire PRA Workshop 2019, Rockville, MD
Practiced actions become automatic Human error is not the cause of a mishap.
whether we want them to or not.
Introduction to HRA Slide 73 Fire PRA Workshop 2019, Rockville, MD
How can we understand human error?
Lesson 4:
Introduction to HRA Slide 74 Fire PRA Workshop 2019, Rockville, MD
How can we understand human error?
By combining Lessons #1 through #3 Introduction to HRA Slide 75 Fire PRA Workshop 2019, Rockville, MD
How can we understand human error?
Human errors are not isolated breakdowns, but rather are the result of the same processes that allow a systems normal functioning.
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How can we understand human error for HRA/PRA?
First, previous PRA studies serves as guides for what types of operator actions are important to include in PRA models, what factors are the most important influences on operator performance, and so on.
Second, HRA methods are developed principally for operators in NPPs; consequently, some basic understanding and expectations of NPP operator behavior, control room design, procedure use, operator training and education, etc. has been built-in the methods.
Introduction to HRA Slide 77 Fire PRA Workshop 2019, Rockville, MD
How can we understand human error for HRA/PRA?
(continued)
Third, HRA methods attempt to bridge the gap between the real operational experience in NPPs and psychology by:
- filtering out behaviors, performance influences, and other factors that are not typically important for operator response to accident scenarios modeled in PRAs
- Providing the HRA analyst with a focused set of issues to address in NPP HRA/PRA Fourth, the HRA analyst should perform qualitative HRA tasks (i.e., make plant-specific assessments and observations of operator performance in order to identify which factors or issues are important for the specific plant and study).
Introduction to HRA Slide 78 Fire PRA Workshop 2019, Rockville, MD
How can we understand human error for HRA/PRA?
(continued)
- As part of qualitative analysis, the HRA analyst further develops an understanding and ability to predict operator actions by addressing The context for the operator action
- The context includes both:
- 1. Plant/facility conditions, configuration, and behavior, and
- 2. Operator behavior influencing factors (sometimes called performance shaping factors (PSFs), performance influencing factors (PIFs), or driving factors)
Introduction to HRA Slide 79 Fire PRA Workshop 2019, Rockville, MD
How can we understand human error for HRA/PRA?
(continued)
- Performance shaping factors usually capture important behavior-influencing aspects of, for example:
- Time available (often not defined as a PSF, but a very important factor)
- Procedures
- Operator training
- Human-machine interfaces
- Action cues and other indications
- Crew staffing and organization
- Crew communication The important aspects of these factors can change with the plant/facility, NPP operation, operator action and location, etc.
Introduction to HRA Slide 80 Fire PRA Workshop 2019, Rockville, MD
How can we understand human error for HRA/PRA?
(continued)
Then, the HRA analyst can match up the results of qualitative HRA with aspects of HRA quantification methods to predict why such potential operator failures might occur, e.g.,
- Classifications, categories, or types of operator failures:
Errors of omission and commission (dependent on the PRA model for definition)
Slips/lapses, mistakes, and circumventions Skill-, rule-, and knowledge-based errors
- Explanations of operator failures using information processing models, e.g.,
Failures in detection, situation assessment, response planning, and/or response execution
- Explanations of operator failures using a filtered set of causes (i.e., cause-based models)
- Explanation of operator failures using performance shaping factors Introduction to HRA Slide 81 Fire PRA Workshop 2019, Rockville, MD
How can we understand human error for HRA/PRA?
(continued)
Which approach for explaining operator failure do you use?
- Depends on a variety of factors but, especially, the type of operation or action being modeled.
- Often helpful to use more than one way of classifying operator failure because different HRA quantification methods Use different classification and categorization schemes Emphasize different PSFs, driving factors, or other elements of context Represent different types of operator actions, behavior models, and so forth
- Which approach helps to best explain why the HRA analyst thinks the operator might fail?
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How can we understand human error?
- So, its important for an HRA analyst to do his best to
- Understand the problem by understanding the context, operator actions and potential failures or errors, etc. (i.e., perform some HRA qualitative analysis)
- Match the problem to the HRA method that best represents the critical aspects of the problem
- In other words, HRA method selection is important and should be done after you have some understanding of the problem, including the likely operator actions and potential operator failures (errors).
- In the next presentation topic, well provide resources for guidance on performing HRA, including the most common HRA processes and methods.
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Introduction to HRA Outline What is HRA?
What does HRA model?
What are the keys to performing HRA?
How can we understand human error?
What guidance is there for performing HRA?
What are the HRA concerns or issues for fire PRA?
Is there a standard for performing HRA?
Any final questions?
Introduction to HRA Slide 84 Fire PRA Workshop 2019, Rockville, MD
HRA Guidance - How To.
From our last presentation:
- Human error literature describes human behavior.
- Guidance, on the other hand, is a description of how-to do something..
In this presentation, we will discuss guidance for performing HRA associated with:
1.HRA processes 2.HRA quantification methods Introduction to HRA Slide 85 Fire PRA Workshop 2019, Rockville, MD
HRA Process An HRA process is a prescribed set of steps for how to perform an HRA that also identifies products of HRA, i.e.,
- 1. Identification and definition of human failure events (HFEs),
- 2. Qualitative analysis that supports #1 and #2, and
- 4. Documentation of all of the above.
Two examples of published stand-alone HRA processes:
- EPRIs SHARP1 - A Revised Systematic Human Action Reliability Procedure, EPRI TR-101711, December 1992
- NRCs Good Practices for Implementing Human Reliability analysis (HRA), NUREG-1792, April 2005
- Stand-alone means that they are not connected with a specific HRA quantification method.
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SHARP1 Developed in 1980s as a frameworkfor incorporating human interactions into PRA with emphasis on the iterative nature of the process.
- Structured in stages for systematically integrating HRA into the overall plant logic model of the PRA.
- Describes and compares selected HRA methods for quantification.
SHARP1 uses three broad categories of human interactions:
- Type A: Pre-initiating event interactions
- Type B: Initiating event interactions
- Type C: Post-initiating event interactions CP: Actions dictated by operating procedures and modeled as essential parts of the plant logic model CR: Recovery actions Emphasizes the importance of dependencies between human interactions (especially with respect to premature screening of important interactions) and defines four classes of dependencies.
Introduction to HRA Slide 87 Fire PRA Workshop 2019, Rockville, MD
NRCs Good Practices for HRA Written to establish good practices for performing HRA and to assess the quality of HRA, when it is reviewed.
Are generic in nature; not tied to any specific methods or tools.
Written to support implementation of RG 1.200 for Level 1 and limited Level 2 internal event, at-power PRAs (using direct links between elements of good practices and RG 1.200).
Developed using the experience of NRC staff and its contractors, including lessons learned from developing HRA methods, performing HRAs, and reviewing HRAs.
Introduction to HRA Slide 88 Fire PRA Workshop 2019, Rockville, MD
HRA Processes vs. Methods Neither SHARP1 nor NRCs Good Practices specify or dictate which HRA method should be used to perform HRA quantification Some resources provide both processes and methods:
- THERP (NUREG/CR-1278)
- ATHEANA (NUREG-1624, Rev. 1)
- Fire HRA Guidelines (NUREG-1921/EPRI TR 1023001)
ATHEANA and the Fire HRA Guidelines provide:
- Approaches for identifying HFEs (e.g., EOCs)
- Techniques for doing certain aspects of qualitative HRA (e.g.,
determining if an operator action is feasible and, therefore, suitable to be included in PRA)
Introduction to HRA Slide 89 Fire PRA Workshop 2019, Rockville, MD
What are some common HRA methods?
Technique for Human Error Rate Prediction (THERP)
Accident Sequence Evaluation Program (ASEP) HRA Procedure
- Simplification from THERP Cause-Based Decision Tree Method (CBDTM)
Human Cognitive Reliability (HCR)/Operator Reliability Experiments (ORE) Method Standardized Plant Analysis Risk HRA (SPAR-H) Method A Technique for Human Event Analysis (ATHEANA)
Introduction to HRA Slide 90 Fire PRA Workshop 2019, Rockville, MD
Characteristics Addressed by HRA Methods Plant behavior and conditions Timing of events and the time available for human action Locations of the human actions Equipment available for use by the operators based on the sequence Indications and cues used by the operators and changes in parameters as scenario proceeds Environmental conditions Relevant training and experience Applicability and usefulness of procedural or other guidance Introduction to HRA Slide 91 Fire PRA Workshop 2019, Rockville, MD
Fire HRA Guidelines (NUREG-1921/EPRI 1023001)
First report addressing fire-related HRA that goes beyond the screening level presented in NUREG/CR-6850 Provides a systematic process to identify and define fire HFEs, address fire-specific PSFs, and assess HEPs Started with existing Level 1 PRA/HRA practices, but evolved over time as fire HRA practitioners identified key differences in fire HRA and recommended strategies for addressing fire-specific concerns Contains 3 quantification methods developed for fire HRA, including a new Scoping approach Provides guidance for detailed fire HRA using specific methods Forms the basis for this training course Introduction to HRA Slide 92 Fire PRA Workshop 2019, Rockville, MD
Introduction to HRA Outline What is HRA?
What does HRA model?
What are the keys to performing HRA?
How can we understand human error?
What guidance is there for performing HRA?
What are the HRA concerns or issues for fire PRA?
Is there a standard for performing HRA?
Any final questions?
Introduction to HRA Slide 93 Fire PRA Workshop 2019, Rockville, MD
What are the HRA concerns or issues for fire PRA?
Introduction to HRA Slide 94 Fire PRA Workshop 2019, Rockville, MD
What are the HRA concerns or issues for fire PRA?
New operator actions to identify and model
- Fire response operator actions in fire procedures
- Strategy for the use in response to Fires Errors of Commission (EOCs) to identify, screen and define
- Per the Standard, the possibility that operators respond to spurious indications as if they are real must be considered.
- Screening provides a way to limit the number of EOCs modeled in the fire PRA New environmental hazards to model as Performance Shaping Factors (PSFs)
- Fire effects of smoke, heat, and toxic gases on operators, including transit paths
- Impact of breathing apparatus and protective gear on operator performance, including communications Introduction to HRA Slide 95 Fire PRA Workshop 2019, Rockville, MD
What are the HRA concerns or issues for fire PRA?
(continued)
More challenging contexts
- Potentially wide variations in size, location, and duration of fires and their effects on plant systems and functions Different types of operator actions
- More local actions
- Multiple tasks such as pulling fuses and then operate valve locally Other PSFs or influencing factors
- Design of ex-control room equipment control locations and alternate shutdown panels But, this, and more, will be addressed starting tomorrow.
Introduction to HRA Slide 96 Fire PRA Workshop 2019, Rockville, MD
Introduction to HRA Outline What is HRA?
What does HRA model?
What are the keys to performing HRA?
How can we understand human error?
What guidance is there for performing HRA?
What are the HRA concerns or issues for fire PRA?
Is there a standard for performing HRA?
Any final questions?
Introduction to HRA Slide 97 Fire PRA Workshop 2019, Rockville, MD
Endorsement and Guidance for PRA In 1995, the U.S. Nuclear Regulatory Commission (NRC) issued a Policy Statement on the use of probabilistic risk analysis (PRA), encouraging its use in all regulatory matters.
Regulatory Guide 1.200 issued in March 2009 is intended to be consistent with the NRCs PRA Policy Statement.
It is also intended to reflect and endorse guidance provided by standards-setting and nuclear industry organizations, such as the ASME/ANS PRA Standard (2009).
Introduction to HRA Slide 98 Fire PRA Workshop 2019, Rockville, MD
NRC Regulatory Guide 1.200 Title is An Approach for Determining the Technical Adequacy Of Probabilistic Risk Assessment Results for Risk-informed Activities Provides NRC staff position for one approach to determining technical adequacy of a PRA to support a risk-informed activity For each technical element (e.g., HRA)
- Defines the necessary attributes and characteristics of a technically acceptable HRA
- Allows use of a standard in conjunction with a peer review to demonstrate conformance with staff position
- Endorses ASME/ANS standard and NEI peer review guidance (with some exceptions)
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RG 1.200 Tech Attributes and Characteristics for Level I HRA Introduction to HRA Slide 100 Fire PRA Workshop 2019, Rockville, MD
RG 1.200 Tech Attributes and Characteristics for Fire HRA Introduction to HRA Slide 101 Fire PRA Workshop 2019, Rockville, MD
Reg Guide vs. Standard RG 1.200 scopes out what is needed in a technically acceptable PRA/HRA, and in some cases amplifies the PRA Standard requirements ASME/ANS PRA Standard defines requirements* for a quality PRA
- Specifies what you need to do.
- Requirements have been established to ensure PRA quality commensurate with the type of PRA application and/or regulatory decision
- The use of the word Requirements is Standard language and is not meant to imply any regulatory requirement Introduction to HRA Slide 102 Fire PRA Workshop 2019, Rockville, MD
ASME/ANS RA-Sa-2009 Standard for Level 1/Large Early Release Frequency Probabilistic Risk Assessment for Nuclear Power Plant Applications Part 2 identifies Requirements for Internal Events At-power PRA Part 4 identifies Requirements for Fires At-power PRA Many of the technical requirements in Part 2 are fundamental requirements for performing a PRA for any hazard group Fire PRA portion adds to and draws from Internal Events section, so have to satisfy elements from both Introduction to HRA Slide 103 Fire PRA Workshop 2019, Rockville, MD
Objective (Paraphrased) from HRA Technical Element of ASME/ANS PRA Standard The objective of the human reliability element of the PRA is to ensure that the impacts of plant personnel actions are reflected in the assessment of risk in such a way that:
- Both pre-initiating event and post-initiating event activities addressed
- Logic model elements are defined to represent the effect of such personnel actions
- Plant-specific and scenario-specific factors are accounted for
- Human performance issues are addressed in an integral way so that issues of dependency are captured Introduction to HRA Slide 104 Fire PRA Workshop 2019, Rockville, MD
ASME/ANS PRA Standard Provides two levels of technical requirements:
- High level requirements (HLRs)
- Supporting requirements (SRs)
HLRs
- provide minimum requirements for a technically acceptable baseline PRA.
- defined in general terms and reflect the diversity of approaches and accommodate future technological innovations.
SRs define the requirements needed to accomplish each HLR Introduction to HRA Slide 105 Fire PRA Workshop 2019, Rockville, MD
ASME/ANS PRA Standard (continued)
SR definitions acknowledge that, depending on the application, the level of detail, the level of plant specificity and the level of realism can vary Three capability categories are defined, and the degree to which each is met increases from Category I to Category III Each SR is defined to a different Capability Category Within a PRA, even the HRA element can be a mixture of capability categories.
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Capability Category Definitions Capability Category I:
- Scope and level of detail are sufficient to identify relative importance of contributors down to system or train level.
- Generic data and models are sufficient except when unique design or operational features need to be addressed.
- Departures from realism* have moderate impact on results.
Capability Category II:
- Scope and level of detail are sufficient to identify relative importance of significant contributors down to component level, including human actions.
- Plant-specific data and models are used for significant contributors.
- Departures from realism have small impact on results.
- the degree to which the expected response of the plant is addressed Introduction to HRA Slide 107 Fire PRA Workshop 2019, Rockville, MD
Capability Category Definitions (continued)
Capability Category III:
- Scope and level of detail are sufficient to identify relative importance of contributors down to component level, including human actions.
- Plant-specific data and models are used for all contributors.
- Departures from realism have negligible impact on results.
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SRs May Differ Across Capability Categories Introduction to HRA Slide 109 Fire PRA Workshop 2019, Rockville, MD
PRA Standard HLRs for Internal Events HRA (Part 2 Requirements)
Pre-Initiator Post Initiator HR-A Identify HFEs HR-E Identify HFEs HR-B Screen HFEs HR-C Define HFEs HR-F Define HFEs HR-D Assess HEPs HR-G Assess HEPs HR-H Recovery HFEs HR-I Document HFEs/HEPs Introduction to HRA Slide 110 Fire PRA Workshop 2019, Rockville, MD
PRA Standard HLRs for Fire HRA (Part 4 Requirements)
Post Initiator Refers to Part 2 HRA-A Identify HFEs HR-E HRA-B Define HFEs HR-F (incorporate in PRA model)
HRA-C Assess HEPs HR-G HRA-D Recovery HFEs HR-H HRA-E Document HFEs/HEPs HR-I Introduction to HRA Slide 111 Fire PRA Workshop 2019, Rockville, MD
Examples of ASME/ANS Standard Post-Initiator HRA High Level Requirements (HLRs)
HLR-HR-G The assessment of the probabilities of the post-initiator HFEs shall be performed using a well defined and self-consistent process that addresses the plant-specific and scenario-specific influences on human performance, and addresses potential dependencies between human failure events in the same accident sequence.
HLR-HR-H Recovery actions (at the cutset or scenario level) shall be modeled only if it has been demonstrated that the action is plausible and feasible for those scenarios to which they are applied. Estimates of probabilities of failure shall address dependency on prior human failures in the scenario.
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Example of ASME/ANS Standard Post-Initiator HRA Supporting Requirement (SR)
HR-G1
- Capability Category I: Use conservative estimates (e.g.,
screening values) for the HEPs of the HFEs in accident sequences that survive initial quantification.
- Capability Category II: Perform detailed analyses for the estimation of HEPs for risk-significant HFEs. Use screening values for HEPs for non-risk-significant human failure basic events.
- Capability Category III: Perform detailed analyses for the estimation of all human failure basic events.
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Meeting RG and Standard Requirements Peer Reviews are conducted to evaluate the degree to which a PRA has met the RG and Standard requirements Findings and Observations (F&Os) are written where deficiencies are found
- It is expected that these F&Os be addressed before a Licensee Amendment Request (LAR) is submitted for NFPA 805 transition Fire PRA/Fire HRA task interfaces are important to address for technical adequacy and standard compliance
- One could apply a different HRA method, for example, a screening HEP during the quantification of a detailed Fire PRA scenario.
- In this case, the overall quantification may be acceptable (e.g., PRA Standard Capability Category I), or it may lead to further refinement if best-estimate results (e.g., PRA Standard Capability Category II) are needed.
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Guidance from NUREG-1921 and this Course NUREG-1921 Fire HRA Guidelines provides assistance (but no guarantee) in meeting the PRA Standard, with emphasis on Capability Category II Table 2-1 identifies Fire PRA/Fire HRA task interfaces by PRA Standard element such as accident sequence analysis
[AS] or quantification [QU]
Appendix D correlates PRA Standard sections to Guidelines sections and provides a roadmap for users to perform an assessment of their own fire HRA against the PRA Standard requirements The Fire HRA Track presented this week will identify key HLRs and SRs in performing fire HRA/PRA.
Introduction to HRA Slide 115 Fire PRA Workshop 2019, Rockville, MD
Introduction to HRA Outline What is HRA?
What does HRA model?
What are the keys to performing HRA?
How can we understand human error?
What guidance is there for performing HRA?
What are the HRA concerns or issues for fire PRA?
Is there a standard for performing HRA?
Any final questions?
Introduction to HRA Slide 116 Fire PRA Workshop 2019, Rockville, MD