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Human Performance in Reactor Safety. George E. Apostolakis Massachusetts Institute of Technology Presented at the Quality Colloquium, Harvard University August 21, 2007. Error Categorization. Pre- and Post-Initiating Event Errors of Omission and Commission

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human performance in reactor safety
Human Performance in Reactor Safety

George E. Apostolakis

Massachusetts Institute of Technology

Presented at the

Quality Colloquium, Harvard University

August 21, 2007

error categorization
Error Categorization
  • Pre- and Post-Initiating Event
  • Errors of Omission and Commission
  • Slips and Mistakes
latent conditions
Latent Conditions
  • Weaknesses that exist within a system that create contexts for human error beyond the scope of individual psychology.
    • Examples: poor procedures, inadequate training, bad management policies, poor organizational learning
  • They have been found to be significant contributors to incidents.
  • Incidents are usually a combination of hardware failures and human errors (latent and active).
post ie errors
Post-IE errors
  • Models still being developed.
  • Typically, they include detailed task analyses, identification of performance shaping factors (PSFs), and the subjective assessment of probabilities.
  • PSFs: System design, facility culture, organizational factors, stress level, others.

The ATHEANA Framework





Human Error



Plant Design,





Human Failure















NUREG/CR-6350, May 1996.


Public Health and Safety as a Result of Civilian Nuclear Reactor Operation

NRC’s Overall Safety Mission

Reactor Safety

Radiation Safety


Initiating Events

Mitigating Systems

Barrier Integrity

Emergency Preparedness

Occupational Radiation Safety

Public Radiation Safety

Physical Protection


Safety Conscious Work Environment

Problem Identification and Resolution

Performance Indicators, NRC Inspections,

Other Information Sources

Data Sources

Reactor Oversight Process

Strategic Performance Areas


Cross-cutting Issues

safety culture
Safety Culture

“Safety culture is that assembly of characteristics and attitudes in organizations and individuals which establishes that, as an overriding priority, nuclear plant safety issues receive the attention warranted by their significance.”

International Nuclear Safety Advisory Group, Safety Culture, Safety Series No. 75-INSAG-4, International Atomic Energy Agency, Vienna, 1991.

performance based evaluation of safety culture
Performance-Based Evaluation of Safety Culture
  • NRC Objectives:
    • Include only information that is within NRC’s regulatory jurisdiction
    • Eliminate information that could only be obtained through surveys
    • Include only information that is indicative of safety culture
  • “Components” of Safety Culture
    • Decision making
    • Work control
    • Work practices
    • Resources
decision making
Decision Making

Decisions demonstrate that nuclear safety is an overriding priority. The authority for decisions affecting nuclear safety are formally defined, communicated to applicable personnel, and implemented as designed. Decisions are made using a systematic process, especially when faced with uncertain or unexpected plant conditions, to ensure safety is maintained. Conservative decision-making is demonstrated through using conservative assumptions and options being rejected based upon a requirement to demonstrate that the action is safe rather than a requirement to prove it is unsafe. Decisions consider risk insights and potential consequences and contingencies and maintain design margins and long-term equipment reliability. Interdisciplinary input and reviews are obtained on safety-significant or risk-significant decisions, and the results of decisions are communicated to personnel who have a need to know the information in order to perform work safely, in a timely manner. Effectiveness reviews of safety-significant decisions are conducted to verify the validity of the underlying assumptions, identify possible unintended consequences, and determine how to improve future decisions.

work control
Work Control

Planning and coordinating work activities ensure nuclear safety. When planning work activities, personnel maintain awareness of the potential risks of work activities and recognize the possibility of mistakes and worst-case scenarios. When planning and coordinating work activities appropriately incorporate:

  • risk insights,
  • job site conditions which may impact human performance, equipment, and personnel nuclear safety
  • task sequencing to optimize safety system availability,
  • the impact of changes on the plant and human performance,
  • the impact of the work on different job activities, and
  • the need for planned contingencies, compensatory actions, and abort criteria.
work practices
Work Practices

Human error prevention techniques are communicated, understood, and used commensurate with the risk of the assigned task, such that work activities are performed safely. Error-free human performance is supported by pre- and post-evolution briefings, as appropriate, correct labeling of components, and communications on the status of activities, including any changes. Procedural compliance is defined, communicated, understood and procedures are followed by personnel. There is supervisory and management oversight of work activities such that nuclear safety is supported and human performance, including fitness for duty, is monitored and opportunities for improvement are addressed. Work groups maintain interfaces with offsite organizations, and communicate, coordinate, and cooperate with each other during activities in which interdepartmental coordination is necessary to assure plant and human performance. Personnel do not proceed in the face of uncertainty or unexpected circumstances.


Personnel, equipment, programs, procedures, and other resources are available and adequate to assure nuclear safety, including those necessary for:

  • physical improvements,
  • minimization of long-standing equipment issues,
  • work packages
  • sufficient qualified personnel to maintain work hours within working hours guidelines,
  • training of personnel,
  • optimization of maintenance and engineering backlogs,
  • complete, accurate and up-to-date design documentation,
  • simulator fidelity and availability, and
  • emergency facilities and equipment