Maintenance Outages Research Articles

Airborne arsenic and urinary excretion of arsenic metabolites during boiler cleaning operations in a Slovak coal-fired power plant.

Little information is available on the relationship between occupational exposure to inorganic arsenic in coal fly ash and urinary excretion of arsenic metabolites. This study ws undertaken in a coal-fired power plant in Slovakia during a routine maintenance outage. Arsenic was measured in the breathing zone of workers during 5 consecutive workdays, and urine samples were obtained for analysis of arsenic metabolites--inorganic arsenic (Asi), monomethylarsonic acid (MMA), and dimethylarsinic acid (DMA)--prior to the start of each shift. Results from a small number of cascade impactor air samples indicated that approximately 90% of total particle mass and arsenic was present in particle size fractions >/= 3.5 micron. The 8-hr time-weighted average (TWA) mean arsenic air concentration was 48.3 microg/m3 (range 0.17-375.2) and the mean sum of urinary arsenic (SigmaAs) metabolites was 16.9 microg As/g creatinine (range 2.6-50.8). For an 8-hr TWA of 10 microg/m3 arsenic from coal fly ash, the predicted mean concentration of the SigmaAs urinary metabolites was 13.2 microg As/G creatinine [95% confidence interval (CI), 10.1-16.3). Comparisons with previously published studies of exposure to arsenic trioxide vapors and dusts in copper smelters suggest that bioavailability of arsenic from airborne coal fly ash (as indicated by urinary excretion) is about one-third that seen in smelters and similar settings. Arsenic compound characteristics, matrix composition, and particle size distribution probably play major roles in determining actual uptake of airborne arsenic.

Airborne Arsenic and Urinary Excretion of Arsenic Metabolites during Boiler Cleaning Operations in a Slovak Coal-Fired Power Plant

Little information is available on the relationship between occupational exposure to inorganic arsenic in coal fly ash and urinary excretion of arsenic metabolites. This study ws undertaken in a coal-fired power plant in Slovakia during a routine maintenance outage. Arsenic was measured in the breathing zone of workers during 5 consecutive workdays, and urine samples were obtained for analysis of arsenic metabolites--inorganic arsenic (Asi), monomethylarsonic acid (MMA), and dimethylarsinic acid (DMA)--prior to the start of each shift. Results from a small number of cascade impactor air samples indicated that approximately 90% of total particle mass and arsenic was present in particle size fractions >/= 3.5 micron. The 8-hr time-weighted average (TWA) mean arsenic air concentration was 48.3 microg/m3 (range 0.17-375.2) and the mean sum of urinary arsenic (SigmaAs) metabolites was 16.9 microg As/g creatinine (range 2.6-50.8). For an 8-hr TWA of 10 microg/m3 arsenic from coal fly ash, the predicted mean concentration of the SigmaAs urinary metabolites was 13.2 microg As/G creatinine [95% confidence interval (CI), 10.1-16.3). Comparisons with previously published studies of exposure to arsenic trioxide vapors and dusts in copper smelters suggest that bioavailability of arsenic from airborne coal fly ash (as indicated by urinary excretion) is about one-third that seen in smelters and similar settings. Arsenic compound characteristics, matrix composition, and particle size distribution probably play major roles in determining actual uptake of airborne arsenic.

Investigation of System Responses of the Maanshan Nuclear Power Plant to the Loss of Residual Heat Removal During Midloop Operation Using a RELAP5/MOD3 Simulation

Because several abnormal incidents involving the loss of the residual heat removal (RHR) system during refueling and maintenance outages have occurred in pressurized water reactors, the importance of investigating the physical phenomena with respect to these events has been recognized. RHR cooling is a major means to remove core decay heat after a reactor power plant shutdown. If the RHR system is lost and an alternate means for heat removal cannot be established in time, the core will boil off, and the primary system will be pressurized, which potentially results in uncovering of the fuel rods and failure of the temporary boundaries. The objective of this paper is to simulate the Maanshan nuclear power plant (MNPP) responses to the loss of the RHR system during midloop operation under variable outage conditions. Without gravity feed, the current investigation concentrates on the effects of different liquid levels, the existence of vents, and the number of active steam generators. Based on the simulated results, the total heat removal capability of one active steam generator and the pressurizer venting process is sufficient to remove core decay heat of 11.1 MW, which corresponds to the power level 3 days after plant shutdown, in the event that RHR cooling fails during midloop operation. The primary system will be stabilized, and the pressure throughout the transient will not exceed the design pressure of the nozzle dams or the temporary seals. The heat removal capability of the pressurizer vent plays a crucial role in system pressurization during loss of RHR and in the severity of this event, as shown by the calculated results of the open and closed MNPP, respectively. If only one or two active steam generators serve as an alternate cooling means, the increased pressure will exceed the design criteria of the temporary low-pressure boundaries. Then, for the closed conditions of MNPP, the loss-of-RHR event during midloop operation has the potential to induce another loss-of-coolant accident and to cause more serious consequences.

Black-start and restoration of a part of the Italian HV network: modelling and simulation of a field test

ENEL (Italian Electricity Board) planned a set of operator guidelines for the restoration of parts of their national grid starting from selected hydroelectric power plants and progressively reaching thermal power generating units. In order to improve hydrothermal power system restoration reliability, ENEL periodically executes field tests taking advantage of the maintenance outages of the thermal groups. The paper concerns the modelling and simulation of an experimental test performed on the Italian W network near the French border. The study makes use of a stability code provided with user defined model facilities, enabling an accurate description of loads and regulation equipment during the restoration process.

Application of partial discharge testing to motor and generator stator winding maintenance

Deterioration of stator winding insulation continues to be one of the predominant causes of large motor and generator failures. Over the past several years, practical methods have been developed for measuring the partial discharge activity in the high voltage insulation of stator windings, since partial discharges are a symptom of most of the insulation failure mechanisms in motors and generators rated 4 kV or more. The turbine generator analyzer (TGA) test has now been specifically developed to enable industrial plant staff to reliably perform a partial discharge test on operating motors and turbine generators. This paper presents several case studies of the use of these new partial discharge test technologies on rotating machines. Test results show that machines with deteriorated windings have a partial discharge activity at least 30 times higher than good windings. The availability of these test methods enables plant staff to economically and reliably plan stator winding maintenance, avoid unexpected failures and often extend the time between major maintenance outages.

Economic Performance of the SCE Stirling Dish

In 1982 McDonnell Douglas Aerospace (MDA) and United Stirling AB (USAB) of Sweden formed a joint venture to develop and market a solar Stirling dish system. Eight modules were built and extensively tested from 1984 to 1988. Power production and daily energy-conversion efficiency as determined by field testing were characterized and modeled into a computer program. Included in this simulation are models of mirror soiling rate, wind spillage loss, mirror washing, and other maintenance outage time, operation and maintenance (O&M) costs, and equipment purchase cost. An economic model of a hybrid (combustion) receiver has been included in the simulation for illustrating the value of using solar energy when available and other fuels such as methane, natural gas, hydrogen, etc. when solar energy is not available or adequate. This paper describes the simulation and presents comparisons of the simulation to test data. The simulation also estimates both the O&M expenses and levelized energy costs for different production volumes.

Considerations in the control of PWR-type multimodular reactor plants

Issues in the control of PWR-type multimodular reactor plants are discussed with emphasis on the need for operation under conditions of unbalanced loads, operating strategies for both single- and multireactor systems, and the coordinated adjustment of power and temperature. One defining characteristic of a multimodular plant is that each unit will probably be loaded differently so as to compensate for the effects of varying maintenance outages and, if desired, to stagger refuelings. A second characteristic is interdependency in that, with several reactors connected to a common turbine, a change in any one unit will propagate to the others. The combination of these two factors makes operation of a multimodular plant differ from that of existing single-reactor ones. For example, conventional sliding-T/sub ave/ load maps cannot be applied directly to a multimodular system because, with the exception of the highest-powered unit, each reactor's temperature will be a function of not only its power level but also that of the most heavily loaded one. Similarly, withdrawal of the control rods in a fully loaded PWR will, in the presence of a large negative temperature coefficient, cause hot and cold leg temperatures to rise but leave power and core /spl Delta/T unchanged. In a multimodular system, there will be a shift in power to the affected reactor. These and other differences in the behavior of multimodular and single-reactor systems are delineated. The paper concludes with some practical suggestions on the operation of PWR-type multimodular plants. >

On-line artificial intelligence diagnostics for utility generating stations

The system architecture and functional operation are described in a centralized state-of-the-art artificial intelligence (AI) expert system for utility application. Experience gained has proven to be invaluable in refining the expert system knowledge bases and has led to other developments which have expanded the coverage of the system. The increased ability of on-line customers to implement predictive maintenance planning has proven to be a cost-saving tool for scheduled maintenance outages. In addition, this paper addresses the elements involved in the installation and operation of the generator AI diagnostic (GenAID) system from the customer's vantage point, such as its economic justification, required system installation activities, and training and operating procedure changes needed to integrate the GenAID system into the existing plant operations.

ITER layout: Alternatives for improved maintenance

International Thermonuclear Experimental Reactor maintenance mission objectives and their effect on systems layout are reviewed through the example of the torus vacuum pumping systems. Applying maintenance requirements to this system has resulted in significant improvements in component accessibility. Further changes currently under review could result in a reduction in vacuum duct length, the addition of duct shielding to reduce neutron activation, a pump and valve assembly which can be serviced from the floor rather than solely from a crane, and provision for transport cacks to enter the pump room through an equipment airlock, large enough to permit the entry of robotic devices as well as construction equipment. This rearrangement could offers savings in overall height of the pump and valve assembly. An innovation in valve configuration will allow for on-line removal of the large vacuum valve seal discs without loss of vacuum. This has potential for reduced maintenance outage time and operating cost.

Different approaches to reliability as applied to the generation — transmission system and its components

The generation-transmission system may be regarded as a hierarchical organization in which the various interconnected components form more or less complex subsystems (nuclear, thermal and hydro units, substations, transmission lines, etc). Each component has a share in the reliability of the electric power system. How should their reliability and that of the system be studied? The objective of the paper is to describe the current state of the art for the methods and models used at Electricité de France. The main stress is on probabilistic studies of, in particular nuclear unit maintenance and repair operation outages, 400 kV network planning, substation reliability and nuclear power plant safety. Future work will be based on a synergy of the methods used in these various areas.

Transportation problem as a model for optimal schedule of maintenance outages in power systems

The possibility is examined of adopting the binary generalized transportation problem for scheduling optimization of unit outages for maintenance. Two models for the s scheduling, based on the transportation problem and taking into consideration various constraints, are developed. A practical application of one of the mathematical programming models is given.

Nuclear Component Wear Measurements

Cobalt-60 has been identified as the principal isotope responsible for the buildup of radiation in light water reactors. The 60Co is produced from stable cobalt being released to the coolant and becoming activated to 60Co during residence in the core. The release occurs because of the corrosion and wear of cobalt-containing alloys exposed to the coolant. This study was directed toward measuring the cobalt released by wear of cobalt-based alloys. Plastic replicas were made of worn components during maintenance outages. Subsequent profilometer measurements were made on the replicas using nearby unworn areas as reference surfaces to enable a calculation of the cobalt released by wear. The calculated release rates on a variety of seven components were estimated from 0.04 g/yr for a main coolant pump on a pressurized water reactor to 30 g/yr for a feedwater regulator valve on a boiling water reactor.

Space and Schedule Considerations for Backfitting SO2 Removal Systems

A representative sample power plant is utilized to illustrate and discuss methods used to meet the unique space and schedule requirements which face the engineer in backfitting flue gas desulfurization (FGD) systems. The entire feasibility of installing a FGD system may depend on the capability of obtaining enough space in the immediate area of the chimney for scrubbers and in other areas for thickeners, reactant material systems, and sludge processing and disposal systems. Suggestions are given for relocating and combining equipment and pipe racks for space conservation. Layout and placement of the needed systems with respect to distance from the plant is explained and charted. The schedule considerations which will minimize plant outages during construction are explained. Special concern is given to scheduling tie‐in work during regular maintenance outages. The space and schedule restraints, construction schedules, and specification considerations are directed toward enabling one to backfit an economical and efficient FGD system.

A Computationally Efficient Optimal Maintenance Scheduling Method

This paper addresses the optimal preventive maintenance scheduling problem (OMSP). The importance of OMSP is due to the fact that system reliability and operating cost of an electric utility are affected by the maintenance outage of generating facilities.

A Computationally Efficient Optimal Maintenance Scheduling Method

This paper addresses the optimal preventive maintenance scheduling problem (OMSP). The importance of OMSP is due to the fact that system reliability and operating cost of an electric utility are affected by the maintenance outage of generating facilities.

Electrical system design for future AGR power stations

The necessity to cool a reactor safely after it is tripped has always made the heaviest safety demands on the electrical system, independent of reactor type. In earlier gas-cooled reactor stations sufficient essential plant was provided to cope with the maximum breach which could credibly occur in the reactor pressure circuit, with a spare plant allowance to cover maintenance and fault outage assuming loss of grid at this time. Now, cooling plant is designed to meet reliability criteria. To make sure it does this, its performance is examined systematically, over the range of possible faults, and its failure modes analysed. These modes include random and common-mode component failure, in combination with hazards such as high winds, earthquakes, fires or turbine disintegration. To safeguard the cooling function in such circumstances it has been necessary to subdivide the essential electrical plant and its associated mechanical drives into functionally independent subsystems, called trains. Because the changed safety requirements have involved more plant, more widely separated, they have increased costs. Such cost increases have been minimised by balancing the risks over the systems, integrating electrical and mechanical plant layout in the reactor buildings, and reducing the size of the essential prime movers. This size reduction has been made possible by interposing frequency converters between them and the largest (gas circulator) drives. Expensive site fitting is reduced and the possibility of fouls, or failures to segregate is avoided by means of a comprehensive (1:20) scale model

島根原子力発電所の運転実績

Shimane Nuclear Power Plant was built in the period between February, 1970 and March 29, 1974 on which this went into commercial operation.The plant has been maintained smooth operation and has entered the third annual maintenance outage. Maximum exposure of the fuel bundle has reached about 16, 000 MWD/T. From the fuel bundle inspection and the operating data such as reactor water and off-gas activities, it has been shown that the fuel has been operated soundly.Here are the summary of the plant facility and the operating experience.

Portland General Electric Company Report on the Operating and Startup Experience with Control and Instrumentation and Electrical Systems at the Trojan Nuclear Plant

The Trojan Nuclear Plant is an 1178 MWe nuclear plant located on the Columbia River 40 miles northwest of Portland, Oregon. The Nuclear Stream Supply System vendor is Westinghouse with a General Electric turbine generator. The reactor is rated and licensed for 3423 MWt (1178 MWe) and the turbine generator is designed for 3570 MWt(1219 MWe). The startup phase testing of Trojan commenced on November 21, 1975, upon receipt of our NRC Operating License. The startup testing program was completed on May 22, 1976, following 100 hours of full-power operation, at which time a scheduled summer maintenance outage began. Some of the highlights and milestones of the startup testing program are described.

The potential for application of energy storage capacity on electric utility systems in the United States-part I

This paper briefly describes the results of the first phase of the systems analysis part of a research project to assess energy storage systems suitable for use by electric utilities. U.S. electric utility systems load and generation data that were collected and analyzed in order to select a number of systems most representative of the electric utility industry are described. The representative systems in turn are used to determine the potential total amount and distribution of off-peak energy available on individual systems on an annual, seasonal, weekly and daily basis. The amount of off-peak energy is described as functions of annual hourly load shape, capacity level assumed available for producting off-peak energy, generator performance characteristics (forced and maintenance outages), and energy storage device round trip efficiency.

Practical methods in the computation of LOLP variances and confidence limits

An earlier paper described a method for recognizing the uncertainty in loss-of-load probability (LOLP) as computed for a single-area system due to uncertainty in generator forced outage rates. This was done by treating generator forced outage rates as random variables with known means and variances and computing, exactly, the resulting mean and variance of LOLP. The mean and variance of LOLP were then used to compute, approximately, the limits between which LOLP can be expected to vary with specified probability. The present paper presents approximate methods for computing the variances and covariances of generating capacity outage state probabilities and of LOLP variance in systems with or without maintenance outages. These approximate methods offer significant savings in computer time and storage as compared to exact methods while maintaining excellent accuracy.