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On-Line Maintenance Huffman, Ken . Nuclear Plant Journal ; Glen Ellyn  Vol. 28, Iss. 2,  (Mar/Apr 2010): 20,22-23.

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ABSTRACT  

On-line maintenance and risk-informed initiatives in general, have played a large part in the confidence that

underpins the "nuclear renaissance" in the United States. As of March 2010, U.S. utilities and other developers had

submitted applications for 28 new nuclear units to the Nuclear Regulatory Commission. The plant designs these

applications are based on, informed by U.S. operating experience, are expected to benefit from risk-informed

applications such as online maintenance. FULL TEXT  

Introduction

On-line maintenance refers to maintenance performed while the main electric generator is connected to the grid.

Nuclear power plants can realize many benefits from performing maintenance activities during power operation.

The U.S. Nuclear Regulatory Commission (NRC), for example, attributes the following benefits to on-line

maintenance in Regulatory Guide 1.182:

* Increased system and plant reliability

* Reduction of plant equipment and system material condition deficiencies that could adversely impact plant

operations

* Reduction of work scope during plant refueling outages.

Nuclear plants are also able to achieve longer fuel cycles and shorter refueling outages through on-line

maintenance. In the United States in the 1980s and early 1990s, most nuclear power plants operated with a

refueling cycle of 12 months and an average refueling duration of three months. Today, U.S. nuclear units operate

on an 18- or 24-month refueling cycle, with average outages of just over one month. The relationship between on-

line maintenance and outage length reduction, operating interval extension and plant economics is well reported in

the literature.

On-line maintenance can also contribute to improved plant safety. By conducting maintenance on-line, plants can

resolve equipment and system issues before they can adversely impact operations. Operational and reliability

improvements have resulted in a factor of three reductions in forced outages and a factor of five reductions in the

automatic SCRAM (trip) rate at U.S. nuclear power plants. Both measures are indicative of improved plant safety.

Figure 1 provides a timeline of key events led by the NRC, the Electric Power Research Institute (EPRl), and the

Nuclear Energy Institute (NEI) in the evolution of on-line maintenance in the U.S. nuclear power industry. Other

industry organizations - the Institute of Nuclear Power Operations, the reactor owners groups, and individual

companies and plants - also contributed to this evolution. Recognition of all such activities, however, is beyond the

scope of this article. The graphic also illustrates the integration of regulations, technical tools, and utility actions

that drove implementation.

Enlarge this image.

Application

Not all maintenance tasks can be performed on-line. Plants often employ maintenance task screening methods to

assess which tasks are most suitable for on-line maintenance. Such screening considerations, described in several

references, provide specific practical and regulation-based criteria for determining what situations are most

suitable for online maintenance.

General scenarios in which on-line maintenance is likely to be used include:

* Systems and components that do not have safety functions and are not essential to power generation

* For example, non-power-block work on buildings or structures (offices, storage structures) that support station

staff, and the heating, ventilating and air conditioning (HVAC) and support systems for those structures

* Systems and components required to maintain shutdown safety margins

* For example, work on systems and components that are utilized during refueling outages for functions such as

decay heat removal, inventory control, reactivity control and containment closure

* Systems and components that may be called upon to provide a safety function or generation function where the

risk associated with unavailability for maintenance is low

* For example, work on systems and components with redundant backups, such as feedwater, instrument air, and

control room ventilation.

About one-half of the equipment in nuclear power plants in the United States is maintained through preventive

maintenance programs. This equipment is contained in categories designated as "critical" or "important," as shown

in Figure 2. Although these categories are subject to individual plant interpretation and some level of periodic

industry redefinition, they represent the most likely candidates for on-line maintenance.

Enlarge this image.

Although this paper was developed based on U.S. experience, on-line maintenance in nuclear power plants has

been successfully applied elsewhere, including France, Spain, Switzerland, and Canada. Nuclear plants in a number

of other countries, as well as other sectors of the power industry, have expressed interest in online maintenance as

well.

To assess the degree to which online maintenance is applied in the nuclear power industry, EPRI surveyed its

Nuclear Maintenance Applications Center (NMAC) participants in 2008. The survey data primarily reflects U.S.

plant experience. International respondents indicated that they apply on-line maintenance to the extent allowed by

their regulations, including safety significant systems and components.

All survey respondents indicated that they apply on-line maintenance, and more than 80% reported that they apply

it to safety significant systems and components. Overall, the survey showed that more than 70% of maintenance is

performed on-line. It also showed that online maintenance of non-safety significant equipment is more common

than on-line maintenance of safety significant equipment. These results are consistent with industry screening

criteria for selecting on-line maintenance activities.

Implementation

Effective implementation of on-line maintenance depends on coordinated efforts between configuration risk

management, work management, and maintenance (see Figure 3).

Configuration risk management - A plant's configuration risk management process is used to assess the risk

impact of equipment out-of-service and to maintain plant risk at desired levels. Specific to on-line maintenance,

configuration risk management can help in determining:

* Whether the unavailability of a system or component is more significant during on-line or shutdown conditions

* Whether a sy stem or component has a safety or essential generation function in specific plant configurations

* The increased risk associated with the unavailability of a system or component that may serve a safety or

essential generation function.

When performing on-line maintenance on safety or generation risk significant equipment, utilities must carefully

control the plant configuration and which systems and functions are available. Such control is provided through

close coordination of configuration risk management and work management.

Enlarge this image.

Work management process - The work management process, and the work planning activity in particular, ensures

that resources to support on-line tasks are properly scheduled to maximize effectiveness. The work management

process also helps ensure that unintended plant configurations do not occur that could change the risk

significance of equipment that is unavailable.

Maintenance process - Familiarity with the technical basis for equipment maintenance tasks and the time intervals

between repetitive tasks (task intervals) is critical. This technical basis determines the amount of maintenance

work necessary to ensure adequate equipment performance and whether the maintenance task intervals are

appropriate. Also, timely and successful completion of maintenance tasks becomes more important when these

tasks are performed while the plant is on-line because of the potential impact of delays in maintenance completion

on plant operations. Nuclear power plants must have high confidence that task work scope can be completed

within allocated time windows. Plants typically take extra measures to ensure success: additional advanced

planning and work area walkdowns, pre-task briefings, contingency parts procurement, staff selection, technical

support resources, management staff attention, etc.

These maintenance practices often carry over to other maintenance activities and allocation of maintenance staff

resources. For example, U.S. nuclear plants often create and equip "Fix it Now" teams with the necessary

resources and expertise to address emergent issues that could arise and interfere with on-line activities.

Performance and Safety Benefits

Some have questioned whether the industry's efforts to improve plant performance have compromised plant

safety. The concern is that actions to shorten refueling outages and extend fuel cycles could reduce safety. U.S.

industry data prove otherwise, demonstrating that performance and safety are not mutually exclusive objectives.

Through actions including on-line maintenance, the average capacity factor at U.S. nuclear power plants increased

from roughly 70% to about 90% between 1 992 and 2002. It has remained at this level ever since. Over a similar

time period, from 1992 to 2005, studies using the U.S. Nuclear Regulatory Commission's PRA models from NUREG-

1 150 show that calculated core damage frequencies have been reduced by a factor of four.

EPRl reviewed the observed rate of significant safety events over the same time period to validate the calculated

core damage frequency results. The analysis found the relative rate of significant safety events and the relative

calculated core damage frequencies to be consistent.

The improvement can be attributed to several factors associated with risk analysis:

* Improved understanding of the relative significance of various plant events based upon risk analysis

* Identification of plant-specific sources of risk and identification of relatively inexpensive changes to reduce risk

* Improved understanding of what safety equipment is truly important in event prevention or mitigation

* Reduction of failure rates for key equipment identified as risksignificant through PRA studies.

Several less-technical elements also support these improvements. These include regulatory understanding and

support, cross-utility sharing of information and benchmarking, application of performance measures to gauge

progress, and corrective action programs to drive improvement.

Looking Forward

On-line maintenance and risk-informed initiatives in general, have played a large part in the confidence that

underpins the "nuclear renaissance" in the United States. As of March 2010, U.S. utilities and other developers had

submitted applications for 28 new nuclear units to the Nuclear Regulatory Commission. The plant designs these

applications are based on, informed by U.S. operating experience, are expected to benefit from risk-informed

applications such as online maintenance.

Despite the heightened level of current interest in the nuclear renaissance, many believe that the renaissance

actually began several years ago, when operating plants began demonstrating sustained excellence. The U.S.

nuclear industry has significantly improved safety and performance over the past few decades, due in large part to

individual plant accomplishments, industry-led initiatives, and changes in regulatory requirements and processes,

included in these improvements are on-line maintenance and other risk-informed and performance-based

techniques. Together, these improvements have enabled the nuclear power industry to increase plant reliability

and capture efficiency gains, substantially increasing electricity generation output without adding new capacity.

Performance improvements over the past 20 years at operating U.S. plants have provided the equivalent electrical

production of 27 new 1000 MWe plants.

This performance has significantly increased the value of operating plants and led to about 90% of these plants

electing to pursue renewal of their initial 40-year operating licenses. The remaining plants are expected to follow

and plants are now beginning to discuss research in support of longer-term operation.

AuthorAffiliation

By Ken Huffman, Electric Power Research Institute.

AuthorAffiliation

For a copy of the complete version of the white paper excerpted in this article, please contact Ken Huffman. The

white paper also includes a complete set of references.

Contact: Ken Huffman, Electric Power Research Institute, telephone: (704) 595-2555, email: khuffinan@epri. com. DETAILS

Subject: Maintenance management; Nuclear power plants; Advantages; Efficiency; Risk

management

Location: United States--US

Classification: 9190: United States; 5130: Maintenance management; 8340: Electric, water &gas

utilities

Publication title: Nuclear Plant Journal; Glen Ellyn

Volume: 28

Issue: 2

Pages: 20,22-23

Number of pages: 3

Publication year: 2010

Publication date: Mar/Apr 2010

Publisher: EQES, Inc.

Place of publication: Glen Ellyn

Country of publication: United States, Glen Ellyn

Publication subject: Public Health And Safety, Energy

ISSN: 08922055

Source type: Trade Journals

Language of publication: English

Document type: Feature

Document feature: Diagrams Charts Tables

ProQuest document ID: 235849120

Document URL: https://search.proquest.com/docview/235849120?accountid=134966

Copyright: Copyright EQES, Inc. Mar/Apr 2010

Last updated: 2015-05-16

Database: ProQuest Central

Bibliography Citation style: APA 6th - American Psychological Association, 6th Edition

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