A Study on Human Factors in Maintenance of a Nuclear Power Plant Park Young Ho Dept. of Nuclear & Quantum Engineering Korea Advanced Institute of Science and Technology September

Table of Contents 1. Introduction 1) Background 2) Objective and Scope of the Thesis 2. Characteristics of Maintenance in a NPP 3. Human Factors in Maintenance of a NPP 4. Summary and Further Study 5. References

Introduction 1. Background  In human factors research, more attention has been devoted to the operation of a nuclear power plant (NPP) than to their maintenance. However, more NPP incidents are caused by inadequate maintenance rather than by faulty operation. Also there are few researches of human factors in maintenance of NPP.  There is a trend in NPP toward introducing digital technology into safety and non-safety system. Various information about plant condition can be used by digitalization.  Support systems for maintenance will be developed based on an information- oriented NPP.  In the context, it is necessary to study on cognitive task of personnel involved in maintenance and interaction between they and support system.

Introduction  Cause of incidents in Korean NPP,1990~2005, Data source :NSIC

Introduction 2. Objective and Scope of the Thesis  Objective  Ultimate purpose of the thesis is to study on distribution cognitive task of personnel involved in maintenance, using Rasmussen’s decision making model.  Scope  Describe characteristics of maintenance that are policy, strategy and programs  Classify personnel who are operator, inspector, engineer and maintainer involved in maintenance  Propose model of cognitive task distribution of personnel  Consider change of cognitive task distribution when including support system.  Verify task distribution of personnel involved in maintenance

Characteristics of Maintenance 1. Maintenance Policy  Maintenance is an important part of physical asset management in NPP or is the process used to preserve functional capabilities of physical assets at specified levels. Physical assets are the systems, structures, and components (SSCs).  Senior maintenance management establishes maintenance policy to support the overall plant, personnel safety, and financial performance goals.  SSC Availability Objectives  Personnel Safety Objectives  Economic Objectives 2. Maintenance Strategy  The policy objectives stated above are achieved by adopting a maintenance strategy founded on the following two maxims:  For mission-critical items, perform preventive maintenance  For items with considerable economic impact, preventive maintenance should be considered  For others, fix after failure, that is, depend only on corrective maintenance

Characteristics of Maintenance 3. Maintenance Program  Corrective maintenance  Reactive approach.  Restoring a failed product or system to an operational state  Preventive maintenance  Periodic maintenance (Time Based) Consisting of servicing, parts replacement, surveillance or testing at predetermined intervals.  Predictive maintenance (Condition Based) Performed continuously or at intervals and governed by observed condition to monitor, diagnose or trend system condition indicators.  Reliability-Centered Maintenance (RCM)  A process that is used to determine the maintenance requirements of any physical asset in its operating context.  Focus Effect of failure in the mission. Reducing the probability of occurrence of the failure modes  RCM ⇒ Periodic maintenance ↓, Predictive maintenance ↑

Characteristics of Maintenance Maintenance Policy Maintenance Strategy Maintenance Program Preventive Corrective Periodic Predictive Scheduled Emergency Planning Operation Condition Assessment Condition Monitoring 4. Relation of Maintenance Policy, Strategy, and Program SSC Availability Objectives Personnel Safety Objectives Economic Objectives How to distribute maintenance program

Human Factors in Maintenance of NPP 1. A Framework For Cognitive Task analysis  This framework (model) enables the description of decision task in terms of the necessary information processes and represent operators’ performance in various situations and at different levels of training.  It then also can be used to characterize information processing by computers. Important data for directing subsequent activities Possible consequence according to goal or policy Correction procedure Detection Observation Identification Evaluation Target State Select Target Procedure Execution Need for intervention Present state of affairs Based on evaluation Define task Execute

Human Factors in Maintenance of NPP  Decision ladder (Rasmussen)  Schematic map of the sequence of information processes involved in a control decision.  Rational, causal reasoning connects the “states of knowledge” in the basic sequence.  Stereotyped processes can by-pass intermediate stages.

Human Factors in Maintenance of NPP 2. Cognitive task distribution in maintenance  General maintenance procedure of NPP  Operator reports a component failure event  Engineer examines field, manual, operation condition to get some information about failure  Engineer makes a work plan  Operator permits a work  Maintainer takes the diagnostic tests, using the measurement instrument  Engineer examines diagnostic test results  The failure component is diagnosed and maintained  All maintenance activities are documented as part of general knowledge to update the equipment design, operation, and maintenance.

Human Factors in Maintenance of NPP  Categorization of maintenance information  Equipment specification information Manufacturer specification and installation  Equipment maintenance information Measurement data in various tests ( e.g., performance or diagnostic tests) Records of failure analysis and maintenance  Documentation information Some general knowledge and standards associated with equipment measurement, diagnosis, and maintenance.  Expertise information The contact information and skill of maintenance experts and researchers

Human Factors in Maintenance of NPP  Classification of personnel involved in maintenance CorrectivePredictivePeriodic OperatorFailure Detection-- Inspector-Failure Detection- EngineerAnalysis, Plan MaintainerImplementation  Interaction among the personnel

Human Factors in Maintenance of NPP  Cognitive task distribution

Human Factors in Maintenance of NPP  Corrective maintenance

Human Factors in Maintenance of NPP  Predictive Maintenance

Human Factors in Maintenance of NPP  Decision ladder of corrective and preventive maintenance

Conclusion  Tasks tend to concentrate on engineer  Operator : Detection, Observation  Engineer : Identification, Evaluation, Target state, Select Target, Procedure  Maintainer : Execution  A particularly dangerous situation occurs when less than perfectly informative information is passed from observer to observer. The lack of perfect reliability or diagnostic may become lost as the information is transmitted. (Wickens- Chapter8 Decision making)  Need of Support System for maintenance  In order to reduce task of engineer  It is necessary to communicate ideas and information clearly

Conclusion  Summary  Describe relation of maintenance policy, strategy and program  Propose task distribution of personnel involved in maintenance, using Rasmussen’s Decision making model.  First, personnel are divided into three parts that are operator (inspector), engineer, maintainer  Second, tasks related to maintenance are distributed on the basis of them  Maintenance need support system, in order to reduce task of engineer and communicate ideas and information clearly  Further Study  Verify task distribution of personnel involved in maintenance Experiment, using diagnostic strategy in maintenance Cause classification of incident reports in Korean NPP (15 or 20 years)

Summary and Further Study 1. J. Rasmussen, “Strategies for State Identification and Diagnosis in Supervisory Control Tasks, and Design of Computer- Based Support Systems”, Advances in Man-Machine Systems Research, Vol 1, P , Katsuji Isobe, Shinya Shibuay, Nobuyuki Tabata. ”Human Factors in nuclear power plant maintenance an empirical study.” Human Factors Department, Tokyo Electric Power, Maintainability of Digital Systems: Technical Basis and Human Factors Review Guidance, NRC, NUREG/CR Improving Maintenance Effectiveness Guidelines, EPRI, TR , March Guidelines for the Conduct of Maintenance at Nuclear Power Stations, INPO, INPO , June Wickens & Hollands, “Engineering Psychology and Human Performance”, Third Edition, Chapter 8, p Hyung Muck Kang, Kyung Soo Park, “A Study on the development a Qualitative Human Error Analysis in a Nuclear Power Plant”, KAIST, Dce Xuzhu Dong, Steven D. Sheetz “Information Model for Power Equipment Diagnosis and Maintenance”, Virginia Tech., IEEE, 2002,