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Aging assessment of PWR (Pressurized Water Reactor) Auxiliary Feedwater Systems

Description: In support of the Nuclear Regulatory Commission's Nuclear Plant Aging Research (NPAR) Program, Oak Ridge National Laboratory is conducting a review of Pressurized Water Reactor Auxiliary Feedwater Systems. Two of the objectives of the NPAR Program are to identify failure modes and causes and identify methods to detect and track degradation. In Phase I of the Auxiliary Feedwater System study, a detailed review of system design and operating and surveillance practices at a reference plant is being conducted to determine failure modes and to provide an indication of the ability of current monitoring methods to detect system degradation. The extent to which current practices are contributing to aging and service wear related degradation is also being assessed. This paper provides a description of the study approach, examples of results, and some interim observations and conclusions. 1 fig., 1 tab.
Date: January 1, 1988
Creator: Casada, D.A.
Partner: UNT Libraries Government Documents Department

Optimizing the efficiency and reliability of fluid system operations: An ongoing process

Description: At most industrial facilities, motor loads associated with pumps and fans are the dominant electric energy users. As plant loads and consequent system functions change, the optimal operating conditions for these components change. In response, modifications to system operations are often made with only one consideration in mind - keeping the system on line. At the Y-12 plant in Oak Ridge, a fluid system energy efficiency improvement methodology is being developed to facilitate the systematic review and modification of system design and operations to increase operational efficiency. Since the bulk of the changes are associated with reducing the numbers and/or loads of motor-driven pumps or fans, there are direct benefits in reduced electrical generation and consequent waste heat production and air emissions. This paper will discuss the types of inefficiencies that tend to evolve as system functional requirements change and equipment ages, describe some of the fundamental parameters that are useful in identifying these inefficiencies, provide examples of design and operating changes being made, and detail the resultant savings in energy.
Date: May 1, 1996
Creator: Casada, D.A.
Partner: UNT Libraries Government Documents Department

The use of the motor as a transducer to monitor pump conditions

Description: Motor current and power analysis methods have been developed to assist in the condition monitoring of a variety of motor-driven devices. The successful implementation of motor current signature analysis (MCSA) as a diagnostic for valves led to its application to other devices and to refinements in the methodologies used. A variety of pump applications, ranging from 5 to over 1200 horsepower have been analyzed, including low and high specific speed and suction specific speed pumps. For some of the pumps, the full range of flow conditions from shutoff to runout has been studied. Motor current and power analysis have been found to provide information that is complementary to that available from conventional diagnostics, such as vibration and pressure pulsation analysis. Inherent signal filtering associated with rotor to stator magnetic field coupling does limit the high frequency response capability of the motor as a transducer; as a result certain phenomena, such as vane pass energy, is not readily apparent in the motor electrical signals. On the other hand, the motor-monitored parameters have often been found to be much more sensitive than vibration transducers in detecting the effects of unsteady flow conditions resulting from both system and pump specific sources such as suction cavitation. By combining motor equivalent circuit models with pump performance characteristics, shaft power and torque fluctuation estimates have been assessed. The usefulness of motor data in assessing some common sources of pump problems, such as mechanical and hydraulic imbalance, misalignment, and unstable flow conditions is shown. The results of testing several motor-driven pumps, including comparisons with vibration and pressure pulsation analysis are discussed. The development of a single figure of merit for pump load stability (as a function of pump flow rate and type) is presented.
Date: December 31, 1995
Creator: Casada, D.A. & Bunch, S.L.
Partner: UNT Libraries Government Documents Department

The use of the motor as a transducer to monitor system conditions

Description: Motor current and power analysis methods have been developed to assist in the condition monitoring of a variety of motor-driven devices. The early work in this area was conducted at Oak Ridge National Laboratory (ORNL) on motor-operated valves in the mid-to-late 1980`s in support of the US Nuclear Regulatory Commission`s Nuclear Plant Aging Research Program. The successful implementation of motor current signature analysis (MCSA) as a diagnostic for valves led to its application to other devices and to refinements in the methodologies used. Motor current and power analysis have been found to provide information that is complementary to that available from conventional diagnostics, such as vibration and pressure pulsation analysis. Inherent signal filtering associated with rotor to stator magnetic field coupling does limit the high frequency response capability of the motor as a transducer; as a result, certain phenomena, such as pump or fan vane pass energy, is not readily apparent in the motor electrical signals. On the other hand, the motor-monitored parameters have often been found to be much more sensitive than vibration transducers in detecting the effects of unsteady process conditions resulting from both system and process specific sources.
Date: January 26, 1996
Creator: Casada, D.A. & Bunch, S.L.
Partner: UNT Libraries Government Documents Department

Detection of pump degradation

Description: This Phase II Nuclear Plant Aging Research study examines the methods of detecting pump degradation that are currently employed in domestic and overseas nuclear facilities. This report evaluates the criteria mandated by required pump testing at U.S. nuclear power plants and compares them to those features characteristic of state-of-the-art diagnostic programs and practices currently implemented by other major industries. Since the working condition of the pump driver is crucial to pump operability, a brief review of new applications of motor diagnostics is provided that highlights recent developments in this technology. The routine collection and analysis of spectral data is superior to all other technologies in its ability to accurately detect numerous types and causes of pump degradation. Existing ASME Code testing criteria do not require the evaluation of pump vibration spectra but instead overall vibration amplitude. The mechanical information discernible from vibration amplitude analysis is limited, and several cases of pump failure were not detected in their early stages by vibration monitoring. Since spectral analysis can provide a wealth of pertinent information concerning the mechanical condition of rotating machinery, its incorporation into ASME testing criteria could merit a relaxation in the monthly-to-quarterly testing schedules that seek to verify and assure pump operability. Pump drivers are not included in the current battery of testing. Operational problems thought to be caused by pump degradation were found to be the result of motor degradation. Recent advances in nonintrusive monitoring techniques have made motor diagnostics a viable technology for assessing motor operability. Motor current/power analysis can detect rotor bar degradation and ascertain ranges of hydraulically unstable operation for a particular pump and motor set. The concept of using motor current or power fluctuations as an indicator of pump hydraulic load stability is presented.
Date: August 1, 1995
Creator: Greene, R. H.; Casada, D. A. & Ayers, C. W.
Partner: UNT Libraries Government Documents Department

Efforts by the nuclear industry to evaluate check valve failures

Description: Recent studies identified approximately 4000 check valve failures that occurred from 1984-1991. Of these, approximately 1600 were determined to be significant enough to require further analysis. This is to be compared with the existing check valve population of nearly 21,000 valves. The strategy proposed in this paper is to establish a refined, centralized check valve failure/reliability database based in part on existing Institute of Nuclear Power Operations (INPO) Nuclear Plant Reliability Data System (NPRDS) data. Ideally the database would be maintained in a central location, augmented with specific component information, overall reliability information, and updated at least biannually. The data would be available to sort and search as desired. The conceptual plan is provided and possible uses of the database are given.
Date: December 31, 1994
Creator: Hart, K.; McElhaney, K.L. & Casada, D.A.
Partner: UNT Libraries Government Documents Department

Condition monitoring and testing for operability of check valves and pumps

Description: A detailed analysis of historical failure data available through the Institute of Nuclear Power Operations` Nuclear Plant Reliability Data System (NPRDS) has been conducted for both check valves and pumps. This analysis, which originated as a part of the Nuclear Regulatory Commission`s (NRC) effort to evaluate the effects of age and wear on nuclear systems components, involved the manual review and characterization of several thousand component failure records according to parameters inherent in the NPRDS database and supplemented by those defined by the analyst for each component type. For example, failure information relative to component size, age, system of service, and NSSS vendor was readily available from the NPRDS database and could be compared relatively easily. Determination of parameters such as extent of degradation, affected area, and detection method, however, had to be determined based on manual review and characterization of individual failure narratives. This paper discusses some of the results of the analyses of historical check valve failure data from 1984 through 1992 and pump failure data from 1990 through 1993. A comparison of the findings of the analyses is made, and emphasis is placed on evaluation of the effectiveness of certain failure detection methods for each component type. Generally speaking, while it was observed that check valve degradation or failure was likely to be detected by code or regulatory required testing, it was discovered that pump degradation or failure was most likely to be discovered by voluntarily implemented plant programs. Failure rates were found to be strongly influenced by the valve or pump application. The type of plant (BWR or PWR) was the overall failure rate and the method of failure detection.
Date: December 31, 1995
Creator: Casada, D.A. & McElhaney, K.L.
Partner: UNT Libraries Government Documents Department

A characterization of check valve degradation and failure experience in the nuclear power industry: 1984-1990. Volume 1

Description: Check valve operating problems in recent years have resulted in significant operating transients, increased cost and decreased system availability. As a result, additional attention has beau given to check valves by utilities (resulting in the formation of the Nuclear Industry Check Valve Group), as well as the US Nuclear Regulatory Commission and the American Society of Mechanical Engineers Operation and Maintenance Committee. All these organizations have the fundamental goal of ensuring reliable operation of check valves. A key ingredient to an engineering-oriented reliability improvement effort is a thorough understanding of relevant historical experience. A detailed review of historical failure data, available through the Institute of Nuclear Power Operation`s Nuclear Plant Reliability Data System, has been conducted. The focus of the review is on check valve failures that have involved significant degradation of the valve internal parts. A variety of parameters are considered, including size, age, system of service, method of failure discovery, the affected valve parts, attributed causes, and corrective actions.
Date: September 1, 1993
Creator: Casada, D.A. & Todd, M.D.
Partner: UNT Libraries Government Documents Department

Identifying Energy Savings Opportunities in Industrial Pumping Systems

Description: In most industrial settings, energy consumed by pumping systems is responsible for a major part of the overall electricity bill. In some cases, the energy is used quite efficiently; in others, it is not. Facility operators may be very familiar with pumping system equipment controllability, reliability, and availability, but only marginally aware of system efficiency. There are some good reasons to increase that awareness: As budgets shrink and the intensity of both domestic and international competition increases, the pressure to find additional methods to reduce operating costs will grow. The reliability of pumps correlates with their efficiency; that is, pumps operated near their design, or best efficiency point, will tend to perform more reliably and with greater availability. More frugal and efficient use of the earth's limited natural resources is essential. The cost of energy consumed by pumps usually dominates the pump life cycle cost. Many end users, already strained to support day-to-day facility operations, lack the time and resources to perform a methodical engineering study of the many pumps within their facilities to understand their associated energy costs and the potential opportunities for energy savings. Under the auspices of the United States Department of Energy's (USDOE) Motor Challenge Program, screening guidance documents and computer software have been developed to help end users, consultants, and equipment distributors recognize, both qualitatively and quantitatively, pumping system efficiency improvement opportunities. A key element in the Motor Challenge optimization strategy is to encourage a systems approach to how motors, drives, and motor-driven equipment are engineered, specified, operated, and maintained by industry. Because pumps have been identified as the single largest end use application, accounting for 25% of motor systems energy use in all manufacturing industries in the United States, they are a natural target in any effort to improve motor-driven systems' energy consumption. The ...
Date: August 23, 1999
Creator: Casada, D.A. & McElhaney, K.L.
Partner: UNT Libraries Government Documents Department

Aging assessment of auxiliary feedwater systems

Description: A study of Pressurized Water Reactor Auxiliary Feedwater (AFW) Systems has been conducted by Oak Ridge National Laboratory (ORNL) under the auspices of the Nuclear Regulatory Commission's Nuclear Plant Aging Research Program. The study has reviewed historical failure experience and current monitoring practices for the AFW System. This paper provides an overview of the study approach and results. 7 figs.
Date: January 1, 1989
Creator: Casada, D.A. (Oak Ridge National Lab., TN (USA))
Partner: UNT Libraries Government Documents Department

Detection and effects of pump low-flow operation

Description: Operating experience and previous studies have shown that a significant cause of pump problems and failures can result from low- flow operation. Operation at low-flow rates can create unstable flows within the pump impeller and casing. This condition can result in an increased radial and axial thrust on the rotor, which in turn causes higher shaft stresses, increased shaft deflection, and potential bearing and mechanical seal problems. Two of the more serious results of low-flow pump operation are cavitation and recirculation. Cavitation is the formation and subsequent collapse of vapor bubbles in any flow that is at an ambient pressure less than the vapor pressure of the liquid medium. It is the collapse of these vapor bubbles against the metal surfaces of the impeller or casing that causes surface pitting, erosion, and deterioration. Pump recirculation more damaging than cavitation. If located at the impeller eye, recirculation damages the inlet areas of the casing. At the impeller tips, recirculation alters the outside diameter of the impeller. If recirculation occurs around impeller shrouds, it damages thrust bearings. Recirculation also erodes impellers, diffusers, and volutes and causes failure of mechanical seals and bearings. This paper reports on a utility pump failure caused by low-flow induced phenomena. ORNL is investigating the results of low-flow pump operations by evaluating the types of measurements and diagnostic techniques that are currently used by licensees to detect pump degradation. A new, enhanced application of motor current and power data analysis has been developed that uses a signal comparison methodology to produce an instability ratio indicative of normal or unstable flow conditions. Examples of this type of low-flow detection technique are presented in this paper along with a brief discussion of the various types of technologies currently being used by licensees to evaluate pump operation and determine possible degradation.
Date: December 1, 1993
Creator: Casada, D. A. & Greene, R. H.
Partner: UNT Libraries Government Documents Department

Comparison of induction motor field efficiency evaluation methods

Description: Unlike testing motor efficiency in a laboratory, certain methods given in the IEEE-Std 112 cannot be used for motor efficiency in the field. For example, it is difficult to load a motor in the field with a dynamometer when the motor is already coupled to driven equipment. The motor efficiency field evaluation faces a different environment from that for which the IEEE-Std 112 is chiefly written. A field evaluation method consists of one or several basic methods according to their physical natures. Their intrusivenesses and accuracies are also discussed. This study is useful for field engineers to select or to establish a proper efficiency evaluation method by understanding the theories and error sources of the methods.
Date: October 1, 1996
Creator: Hsu, J.S.; Kueck, J.D.; Olszewski, M.; Casada, D.A.; Otaduy, P.J. & Tolbert, L.M.
Partner: UNT Libraries Government Documents Department

Insights gained from aging research

Description: The US NRC Office of Nuclear Regulatory Research has implemented hardware-oriented engineering research programs to identify and resolve technical issues related to the aging of systems, structures, and components (SSCs) in operating nuclear power plants. This report provides a summary of those research results which have been compiled and published in NUREGS and related technical reports. The systems, components and structures that have been studied are organized by alphabetical order. The research results summary on the SSCs is followed by an assessment guide to emphasize inspection techniques which may be useful for detecting aging degradation in nuclear power plants. This report will be updated periodically to reflect new research results on these or other SSCs.
Date: March 1, 1992
Creator: Blahnik, D.E.; Casada, D.A.; Edson, J.L.; Fineman, D.L.; Gunther, W.E.; Haynes, H.D. et al.
Partner: UNT Libraries Government Documents Department