Review on Reliability Centered Maintenance for NPPs September 27 th, 2010 Nuclear I&C and Information Engineering LabKAIST Bo Gyung Kim - Failure Modes and Effects Analysis(FMEA)

KAIST Nuclear I&C and Information Engineering Lab Contents References Introduction ◦ Background Reliability Centered Maintenance(RCM) ◦ Signification & Principles Failure Modes and Effects Analysis(FMEA) ◦ Definition ◦ Purpose & Limitations ◦ Fuzzy Logic System with FMEA Summary & Conclusion Further Work

KAIST Nuclear I&C and Information Engineering Lab References MOUBRAY, J., “RCM – Reliability-centered Maintenance”, Second Edition, Industrial Press Inc. (1997). IAEA-TECDOC-1590, Application of Reliability Centred Maintenance to Optimize Operation and Maintenance in Nuclear Power Plants, IAEA. Miha Mraz, Failure Mode and Effects(and Criticality) Analysis Fault Tree Analysis, University of Ljubljana Faculty of Computer and Information Science, 2009/2010. Antonio Cesar Ferreira Guimares and Celso Marcelo Franklin Lapa, Fuzzy FMEA applied to PWR Chemical and Volume Control System, Progress in Nuclear Energy, Vol. 44, No. 3, pp , Antonio C.F. Guimaraes, Celso Marcelo Franklin Lapa, Effects Analysis Fuzzy Inference System in Nuclear Problems Using Approximate Reasoning, Annals of Nuclear Energy 31 (2004) 107–115. P. A. A. GARCIA, R. SCHIRRU and P. F. FRUTUOSO E MELO, A Fuzzy Data Envelopment Analysis approach for FMEA, Progress in Nuclear Energy, Vol. 46, No. 3-4, pp , 2005.

KAIST Nuclear I&C and Information Engineering Lab Background ◦ The power industry worldwide has been the subject of major reviews and reforms in recent years, which have resulted in changing demands in respect of enhanced safety, reliability, environmental safeguards and commercial competition. ◦ Reliability Centered Maintenance is a maintenance Optimization tool which has a role in providing an effective response to such demands on the industry, by enhancing the effectiveness of operations and maintenance programs. ◦ Classical RCM focuses on the functional failures of systems and components. A systematic process is employed to determine the functions of physical assets, failure modes, consequences of failure, and their significance. In its most comprehensive form this process is described as a failure modes and effects analysis (FMEA). Introduction

KAIST Nuclear I&C and Information Engineering Lab Reliability Centered Maintenance Signification of Reliability centered maintenance ◦ Reliability centered maintenance (RCM) is a technique initially developed by the airline industry that focuses on preventing failures whose consequences are most likely to be serious.  In 1984 the Electric Power Research Institute (EPRI) introduced RCM to the nuclear power industry. Part of the motivation was that the preventive maintenance programs at many nuclear power plants were based on vendors' overly conservative recommendations, without sufficient consideration of actual duty cycles or overall system functions. ◦ The utilities which comprise the EPRI RCM Users Group have accepted the following definition for their use:  Reliability centered maintenance (RCM) analysis is a systematic evaluation approach for developing or optimizing a maintenance program.  RCM utilizes a decision logic tree to identify the maintenance requirements of equipment according to the safety and operational consequences of each failure and the degradation mechanism responsible for the failures.

KAIST Nuclear I&C and Information Engineering Lab Reliability Centered Maintenance The Principles of RCM ◦ The RCM analysis process centers on the functions of plant and equipment, the consequences of failure and measures to prevent or cope with functional failure. ◦ The process must establish answers to the following questions and an effective response to them.  What are the functions and performance standards of the plant?  In what ways does it fail to fulfill its functions?  What causes each functional failure?  What happens when each failure occurs?  In what way does each failure matter?  What can be done to predict or prevent each failure?  What should be done if a suitable proactive task cannot be found?

KAIST Nuclear I&C and Information Engineering Lab Reliability Centered Maintenance 1 Functions and Performance Standards - Define the required functions and performance standards of the asset in its operating context 2 Functional Failures - Define the functional failure(e.g. No capability. Degrees of reduced capability) 7 Default Actions - Assess default action required if no appropriate proactive task exists (i.e. run-to- failure, failure finding or redesigned) 3 Failure Mode - Define failure modes causing these functional failures 5 Failure Consequences - Define consequences of each failure mode (hidden, safety- environmental, operational, non- operational consequences 4 Failure effects - Define effects of each failure modes(i.e. what happens when failure mode occurs) 6 Proactive Tasks - Assess whether any proactive task should be done and the task interval

KAIST Nuclear I&C and Information Engineering Lab Failure Modes and Effects Analysis Definition of FMEA ◦ The failure modes and effects analysis (FMEA) is a procedure in product development and operations management for analysis of potential failure modes within a system for classification by the severity and likelihood of the failures.  A successful FMEA activity helps a team to identify potential failure modes based on past experience with similar products or processes, enabling the team to design those failures out of the system with the minimum of effort and resource expenditure, thereby reducing development time and costs. Ranking and scale ◦ One of these scales rates all the characteristics to numbers between 1 and 10 in the following way:  Severity: 1 – no effect or danger; 10 – very severe or catastrophic effects.  Occurrence: 1 – not likely to occur, 10 – almost inevitable.  Detection: 1 – almost certain to detect, 10 – almost impossible to detect the failure.

KAIST Nuclear I&C and Information Engineering Lab Failure Modes and Effects Analysis Define requirements and expected outcomes Identify failure modes What are the potential effects of failure mode? How could we detect the cause of failure? Identify potential causes How serious are those effects? Control Plan Detection Severity Occurrence Risk Priority Number(RPN) X X

KAIST Nuclear I&C and Information Engineering Lab Failure Modes and Effects Analysis A Example of FMEA Table

KAIST Nuclear I&C and Information Engineering Lab Failure Modes and Effects Analysis Failure Mode and Effect Analysis(FMEA) of CVCS Traditional FMEA scales for RPN

KAIST Nuclear I&C and Information Engineering Lab Failure Modes and Effects Analysis Purpose of FMEA ◦ Development of system requirements that minimize the likelihood of failures ◦ Development of methods to design and test systems to ensure that the failures have been eliminated ◦ Evaluation of the requirements of the customer to ensure that those do not give rise to potential failures ◦ Identification of certain design characteristics that contribute to failures, and minimize or eliminate those effects ◦ Tracking and managing potential risks in the design. This helps avoid the same failures in future projects ◦ Ensuring that any failure that could occur will not injure the customer or seriously impact a system

KAIST Nuclear I&C and Information Engineering Lab Failure Modes and Effects Analysis Limitations ◦ If used as a top-down tool, FMEA may only identify major failure modes in a system. Fault tree analysis (FTA) is better suited for "top- down" analysis.  When used as a "bottom-up" tool FMEA can augment or complement FTA and identify many more causes and failure modes resulting in top- level symptoms.  It is not able to discover complex failure modes involving multiple failures within a subsystem, or to report expected failure intervals of particular failure modes up to the upper level subsystem or system. ◦ Additionally, the multiplication of the severity, occurrence and detection rankings may result in rank reversals, where a less serious failure mode receives a higher RPN than a more serious failure mode.  The reason for this is that the rankings are ordinal scale numbers, and multiplication is not defined for ordinal numbers. The ordinal rankings only say that one ranking is better or worse than another, but not by how much.

KAIST Nuclear I&C and Information Engineering Lab Failure Modes and Effects Analysis Fuzzy Logic System with FMEA ◦ The fuzzy logic system is a name for the systems which have relationship with fuzzy concepts (like fuzzy sets, linguistic variables, and so on) and fuzzy logic.  The most popular fuzzy logic systems in the literature may be classified into three types: pure fuzzy logic systems, Takagi and Sugeno’s fuzzy system, and fuzzy logic systems with fuzzifier and defuzzifier. ◦ The knowledge-based fuzzy systems allow for descriptive or qualitative representation of expressions such as ‘‘remote’’ or ‘‘high’’, incorporate symbolic statements that are more natural and intuitive than mathematical equation.  Direct methods with multiple experts were used to aggregate opinions of individual experts.  One of the most common methods is based on a probabilistic interpretation of membership functions.

KAIST Nuclear I&C and Information Engineering Lab Failure Modes and Effects Analysis ◦ Fuzzy membership function  Making use of the toolbox simulator of Matlab, each experts was invited to define each membership function and the values in the universe of discourse using the interpretations of the linguistic terms described in Table. Interpretations of the linguistic terms for developing the fuzzy rule system

KAIST Nuclear I&C and Information Engineering Lab Failure Modes and Effects Analysis Example of FMEA and Fuzzy Ranking (AFWS)

KAIST Nuclear I&C and Information Engineering Lab Summary / Conclusion Plant and equipment are installed and employed to do what the users want them to do. Maintenance is undertaken in a variety of forms, to ensure that the plant and equipment continues to do what the users want it to do. Reliability Centered Maintenance determines what maintenance needs to be performed and what testing and inspection needs to be performed to support the maintenance strategy. Failure mode and effects analysis (FMEA) is one of RCM’s practical applications and is an important technique that is used to identify and eliminate known or potential failures to enhance reliability and safety of complex systems and is intended to provide information for making risk management decisions. In the case of extensive FMEA, a more number of rules in the knowledge base will be necessary to mapping all analysis situations. So, fuzzy approach combines with the expert knowledge and experience can be used in FMEA problems safety data are unavailable or unreliable.

KAIST Nuclear I&C and Information Engineering Lab Further Work Research on fuzzy Logic System Study about other applicable analyses methods to increase reliability for the next seminar

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