NUREG/CR-5057

PNL-6397

I~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Aging Mitigation and

Improved Programs for

Nuclear Service

Diesel Generators

Prepared by K. R. Hoopingarner, F. R. Zaloudek

Pacific Northwest Laboratory

Operated by

Battelle Memorial Institute

Prepared for

U.S. Nuclear Regulatory Commission
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NUREG/CR-5057

PNL-6397

RG, RM, R1, R2

Aging Mitigation and

Improved Programs for

Nuclear Service

Diesel Generators

Manuscript Completed: October 1989

Date Published: December 1989

Prepared by

K. R. Hoopingarner, F. R. Zaloudek

Pacific Northwest Laboratory

Richland, WA 99352

Prepared for

Division of Engineering

Office of Nuclear Regulatory Research

U.S. Nuclear Regulatory Commission

Washington, DC 20555

NRC FIN B2911
ABSTRACT

Recent NRC sponsored aging research work on nuclear service diesel generators has resulted in a recommendation that an improved engine management

program should be adopted for aging mitigation and reliability improvement.

The center of attention should be to ensure diesel-generator operational

readiness. This report emphasizes a "healthy engine concept" and recommends

parameters to be monitored to determine engine condition. The proposed program and approach recommended in this report represent balanced management

where diesel generator testing, inspections, monitoring, trending, training,

and maintenance all have appropriate importance.

Fast-starting and fast-loading tests of nuclear service diesels causes

very rapid wear of certain engine components. This report documents this

aging and wear mechanism and recommends ways to largely eliminate this unique

aging stressor. Current periodic intrusive maintenance and engine overhaul

practices have been found to be less favorable for safety assurance than

engine overhauls based on monitoring and trending results or on a need to

correct specific engine defects. This report recommends that the periodic

overhaul requirements be re-evaluated.

Diesel generator research on aging and wear is sponsored by the U.S.

Nuclear Regulatory Commission (NRC), Office of Nuclear Regulatory Research.

The research reported in this report was conducted by Pacific Northwest

Laboratory (PNL), which is operated for the Department of Energy by Battelle

Memorial Institute.

iii
SUMMARY

NRC PROGRAM IDENTIFICATION

The Nuclear Plant Aging Research (NPAR) Program was established by the

NRC's:Office of Nuclear Regulatory Research, Division of Engineering, Electrical and Mechanical Engineering Branch, to evaluate the effects of aging on

selected safety-related components, systems and support systems. It is

addressing how the aging process may change current safety margins of key

components in safety-related systems and how aging degradation can initiate

failure.

The NPAR study of diesel generator aging was performed in two phases.

In Phase I, plant operating experience and data were used to produce a new

data base related to aging, reliability, and operational readiness of nuclear

service diesel generators. Phase II is chiefly concerned with aging mitigation measures.

PNL DIESEL GENERATOR MANAGEMENT PROGRAM

This-report proposes a management, testing, and maintenance program for

emergency diesel generators that was developed as a product of Phase II of

this effort. The proposed program would lead to three expected results:

1) the reduction of several of the stressors identified in Phase I that have

been shown to accelerate aging of diesel generators, 2) an improved state of

reliability and operational readiness, and 3) improved confidence in the

future availability and reliability of the diesel-generator.

The proposed new program would integrate testing, inspection, monitoring, trending, maintenance, and other elements for a better diesel generator

aging mitigation approach. The new recommended program is further described

in Section 5.0. The more important elements of the new proposed program are

summarized in the following paragraphs.

An improved diesel-generator testing program including slow starting and

loading would induce little aging effects in the emergency diesel-generator.

By contrast, the current fast starting and loading testing requirements can

produce substantial harm and significant aging effects through the production

of large mechanical and thermal stresses, inadequate lubrication during ini-'

tial acceleration, high rotating and sliding pressures, overspeeding, etc.

During the monthly testing program, adequate data should be collected for

abqut 30 engine operating parameters that Could indicate degrading performance or an impending component failure. These parameters of interest are

detailed in' Appendix A of this report. For many important components such a

program could then detect approaching performance failure and'allow orderly

repair. Monitoring and trending will not be able to detect all degraded

v
performance, of course, but the deterioration that will be detected is significant for aging and reliability concerns. These recommended tests are

presented and further discussed in Section 5.2.

Condition monitoring and trending is an important development to show

the possible presence of long-term component or system degradation. This

activity should detect many potential component/system failures before the

system actually fails. Cost and safety benefits would accrue from the avoidance of both equipment damage and unscheduled downtime by anticipating these

failures and providing timely repair/maintenance. The monthly test program

should ensure that the operating parameters listed in Appendix A are within

their maximum and minimum limits as applicable. However, it is not necessary

to trend every parameter for effective results. Deviations from normal

engine conditions towards either maximum or minimum allowed limits need not

be trended until perhaps fifty percent of the allowed range of values is

exceeded. Obviously, the chief safety concern is to operate the diesel

generator within the manufacturer's recommended values. When a limiting

value is being approached the utilities should trend the approach to avoid

failures and schedule repair before limits are exceeded.

Several recommendations were developed regarding maintenance procedures

and training. One important recommendation is that teardown of the diesel

engines solely for the purpose of inspection should be avoided unless there

is a definite indication that its operation is degraded or there is an

impending component failure based on performance data trends. Analyses of

failure data have also been performed by the U.S. Navy and the airline

industry which show a definite average, short-term adverse effect of such

teardowns on the engine reliability.

Understanding of the governor, as well as the engine/generator, must be

developed by providing the maintenance staff with adequate training and

motivation. The staff associated with each plant should be given training

equivalent to that offered by the specific engine and governor manufacturer

that supplied the engines for that plant.

Finally, it was recommended that engine inspections and preventive

maintenance be increased to mitigate the aging and wear results of the

vibration stressor. This maintenance should focus on the engine or instrumentation mounted on the engine or the engine skid. Normal engine vibrations

have a known and severe influence on control system instruments and their

calibration. Vibration cannot be eliminated, but its effects can be mitigated by keeping fasteners/fittings tight and by frequently recalibrating

instrumentation subject to this vibration.

EDG MISSION ANALYSIS AND RECOMMENDATIONS

The role of the diesel generator safety mission related to the aging

study is reviewed in this report in Section 3. To respond to a large-break

LOCA event with a corresponding loss of all offsite power, a diesel generator

vi
needs to start promptly and deliver its full emergency loads until the emergency is over. This mission profile is the basis and focus of current regulatory requirements'and testing.: With over 100O.reactor years of operation'

in U.S. regulatory history without a large-break LOCA event for primary"'water

containment and with the recent Criterion 4 (leak-before-break) rulemaking,

it may be concluded that the true mission'envelope for the diesel-generator

may be redefined with consequential benefits..

For a loss of offsite power, with or without'a small-break LOCA event,

the related needs for emergency electrical power and-the diesel' mission

profile are much less stringent. In.this case, the need for power'is

extended to about'5 minutes or so and the emergency power level needs.are

reduced, but the time duration for emergency power may remain for several

days. Thus, in summary it appears that the prevention of station blackout is

the most realistic mission envelope.

,The most probable risk-responsive requirements for the diesel-generator

missionhare very high reliability with the durability to produce power over 3

to 4 days until the emergency passes and the reactor cooling requirements

rapidly drop off. This is essentially the 'station blackout" issue. But,

accepting this mission envelope for the diesel-generator system also results

in the reduction in aging degradation'of many important engine components

through l1ess harmful test requirements. A more practical mission envelope

for the diesel generator system appears to be:

a total duration - 2 to 3 days

* diesel start and load time - within 5 minutes

! power level - less than calculated full load (core and containment

sprays not needed). Also, by usual design practice,,less than the

engine'nameplate rating'by a conservative margin. .~~~~~~~~~ .,g .

In consideration of the mission analysis it appears that safety concerns are

better served by testing the engines for reliability rather than maximum

starting accelerations and very rapid loading which it seems is not needed.

REGULATORY IMPLEMENTATION

The NPAR aging.study'was originally intended to develop research for NRC

consideration related to potential safety'problems caused by the aging .. process.- General applications of the study results were expected to be used

for 1) diesel reliability improvement,' 2) plant technical specification

modification, 3) improvement of resource applications by the NRC and the

utilities, and 4) development of specific research information needed to

change some regulatory requirements. All of these end uses of the research'

have been accomplished or are under active consideration. Collectively, the

safety implications of these changes and research recommendations are

important..

vii
Current regulatory requirements for fast-start testing, fast engine

loading, and overload testing are being reconsidered by the NRC. In association with certain nuclear plant technical specifications, these current

requirements may lead to greater future safety problems and unreliability.

Regulatory guide requirements for routine testing have been proposed to

include slow-start testing, slower engine loading, and diesel overload

testing objectives that can be supported by the study results.

NRC Regulatory Accomplishments

In response to various industry proposals, research information, and NRC

staff initiatives much has been accomplished in the area of diesel-generator

aging and reliability. The current status includes much activity and the NRC

staff accomplishments reported in this summary may soon be out-of-date.

Based on various historical conditions the NRC staff has issued Regulatory Guide 1.155, "Station Blackout" in August, 1988 which identifies a need

for a reliability program. This reliability program for emergency diesel

generators is intended to maintain and monitor reliability levels selected

for compliance with the Station Blackout Rule 10 CFR 50.63 (6/68).

Regulatory Guide 1.9,- Revision 3, "Section, Design, Qualification,

Testing, and Reliability of Diesel GEnerator Units Used as Onsite Electric

Power Systems at Nuclear Power Plants" is in the final NRC approval process

and is expected to be issued in 1989. It integrates into a single guide

material previously addressed in Regulatory Guides 1.108, 1.9 Revision 2 and

Generic Letter 84-15. Regulatory Guide 1.108 will be withdrawn after the

issue of Regulatory 1.9, Revision 3.

A Research Information Letter was issued by the NRC during 1989 which

recommends a balanced program of testing, inspection, monitoring, trending,

and maintenance for aging mitigation and for assuring diesel generator

operational readiness. The recommended guidelines for this reliability

program follow the results and recommendations included in this report. The

NRC in November 1988 issued a report to the NRC staff proposing changes to

the standard technical specifications including many examples obtained from

the NPAR diesel generator task.

Proposed NRC Actions

Regulatory Guide 1.137, Fuel-Oil Systems for Standby Diesel Generators,

has not been revised since October 1979. Aging considerations for the system

and the fuel oil contents needs to be addressed. The scope of the changes

recommended are outlined in Section 7.1 and include reducing the needed fuel

oil storage to a 3 to 4 day supply, defining tank lining materials, addressing independence and redundancy guidelines, and reconsideration of the

specifications for stored fuel to include usual and expected aging changes.

The standard technical specifications including diesel generator specific issues needs to be addressed. The research information gathered in the

NPAR Diesel program suggests that current technical specifications are not

viii
always conservative nor effective. In particular, those related to fast

engine starting and loading, frequent sensor calibration, engine startup

during abnormal plant conditions, frequent starts and special test requirements need to be carefully evaluated.

ix
CONTENTS

ABSTRACT . . . . . . . . . . . . . . . . . . . . . . . . . .

SUMMARY . . . . . . . . . . . . . . . . . . . . . . . . . .

1.0 INTRODUCTION . . . ... . ......... .

1.1 BACKGROUND . . . . . . . . .. . .. .

2.0 SUMMARY OF THE NPAR DIESEL GENERATOR AGING STUDY . . .

2.1 SCOPE AND METHODOLOGY . . . . . . . . . . .. . .

2.2 TECHNICAL SAFETY ISSUES AND RESEARCH RESULTS . . .

2.2.1 Aging Related Failures and Their Causes..

2.2.2 Aging Trends . . . .. . . . .

2.2.3 Correction of Aging-Induced Failures . . .

2.3 STRESSORS . . . . . . . . . . . . . . . . . . . .

. 0 . . .

0 . 6 . .

. . 6 . .

0 # 0 . *

. 0 . . .

. 0 . . .

iii

v

1.1

1.2

2.1

2.1

2.2

2.2

2.5

2.7

n * 2.9

2.4 SUMMARY OF NPAR STUDY CONCLUSIONS AND RECOMMENDATIONS

2.4.1 Improved Diesel Generator Testing . . . . . . . . . .

2.4.2 Condition Monitoring and Trending . . . . . . . . . .

2.4.3 Maintenance Training, and Inspection . . . . . . . .

3.0 THE EMERGENCY DIESEL GENERATOR MISSION AND DESIGN FEATURES .

3.1 MISSION ANALYSIS . . . . . . . . . . . . . . . . . . . . . .

3.1.2 Related Mission Studies ...............

3.2 RECOMMENDED EMERGENCY POWER MISSION PROFILE . . . . . ... .

3.3 RECENT RELATED NRC REGULATORY ACTIONS . . . . . . . . . . .

4.0 MAINTENANCE ISSUES . . . . . . . . . . . . . . . . . . . . . . .

4.1 MAINTENANCE/RELIABILITY STUDIES . . . . . . . . . . . . . .

4.2 IMPLICATIONS FOR NUCLEAR SERVICE EMERGENCY DIESEL

GENERATORS . . . . . . . . . . . . . . . . . . . . . . . . .

2.10

2.11

2.11

2.12

3.1

3.1

3.4

3.4

3.6

4.1

4.1

4.4

* xi
4.3 MAINTENANCE/REGULATORY ISSUES . . . . . . . . . . .

5.0 RECOMMENDED DIESEL GENERATOR PROGRAM . . . . . . . . . .

5.1 TESTING, MONITORING AND TRENDING . . . . . . . . . .

5.1.1 Recommended Periodic Testing and Monitoring

4.4

5.1

5.2

Procedure . . . . . . . . . . . . . . . . . .

5.1.2 Other Periodic Monitoring . . . . . . . . . .

5.1.3 Testing After Specific Faults and Maintenance

5.1.4 Trending of Performance Parameters . . . . .

5.2 INSPECTION . . . . . . . . . . . . . . . . . . . .

5.2.1 Weekly Inspections . . . . . . . . . . . . .

5.2.2 Monthly and Quarterly Inspections . . . . . .

5.3 MAINTENANCE . . . . . . . . . . . . . . . . . . . .

5.4 TRAINING . . . . . . . . . . . . . . ... . . . . . .

5.5 MODIFICATIONS . . . . . . . . . . . . . . . . . . .

6.0 PROGRAM DEVELOPMENT RECOMMENDATIONS . . . . . . . . . . .

6.1 OTHER DEVELOPMENTAL ACTIVITIES . . . . . . . . . . .

7.0 RECOMMENDED REGULATORY IMPLEMENTATION . . . . . . . . . .

7.1 REGULATORY GUIDES .................

7.2 TECHNICAL SPECIFICATIONS . . . . . . . . . . . . . .

8.0 REFERENCES . . . . . . . . . . . . . . . . . . . . . . .

. . . . 5.3

. . . . 5.5

! . ... 5.5

. . . . 5.6

. . . . 5.6

. . . . 5.7

. . . . 5.8

. . . . 5.9

. . . . 5.10

. . . . 5.10

. . . . 6.1

. . . . 6.2

. . . . 7.1

. . . . 7.1

. . . . 7.2

. . . . 8.1

APPENDIX A - RECOMMENDED DIESEL GENERATOR MONTHLY TEST PARAMETERS . A.1

xii
FIGURES

2.1 Percent of Failures Due to Aging . . . . .. . . . . . . . 2.6-

2.2 Change in Failure Rate Over Time . . . . . . . . . . . . . 2.8

4.1 Types of Failure Behavior Observed in Age-Reliability

Studies . . . .. . . . . . . . . . . . . . . . ........ . 4.2

TABLES

2.1 System and Components Contributing Most to Diesel Generator

Failures . . . . . . . . . . . . . . . . . . . . . 2.3

2.2 Overall Causes of Diesel Generator Failure . . . . . . . . . . . 2.3

2.3 Systems and Components Subject to Aging-Induced Failures

Resulting in Loss of Function of Unit . . . . . . . . . . . . . . 2.4

2.4 Causes of Aging-Related Failures that Result in Loss of

Function or Reliability . . . . . . . . . . . . . . . . . . . . . 2.4

2.5 Summary of Most Frequent Corrective Actions for Aging

Failures . . . . . . . . . . . . ... . . . . . . . . . . . . . . 2.8

2.6 Corrective Actions for Components Most Susceptible to Aging . . . 2.9

2.7 Workshop Participant's View of Major Aging Stressors . . . . . . 2.10

4.1 Results of Equipment Age-Reliability Analyses . . . . . . . . . . 4.3

xiii
1.0 INTRODUCTION

Commercial nuclear power stations use large diesel generators to supply

Class lE emergency standby power to support the operation of emergency safety

and plant protection system loads. During a loss of power to the emergency

plant buses, the diesel generators must provide backup power to operate critical reactor safety equipment. Generally, each nuclear unit is provided with

two diesel generators, each rated at 3,000 to 10,000 horsepower.

The potential serious consequences of the failure of these diesel generators to produce power following a loss of off-site power have caused considerable regulatory attention to be directed at their reliability. Since

aging of the diesel generators and their associated systems could contribute

to their failure (Davis et al. 1985), the U.S. Nuclear Regulatory Commission

(NRC) has included the consideration of diesel generators in the Nuclear

Plant Aging Research (NPAR) Program.

The NPAR program was established by the NRC's Office of Nuclear Regulatory Research, Division of Engineering, Electrical and Mechanical Engineering

Branch, to evaluate the effects of aging on selected safety-related components, systems and support systems. It is addressing how the aging process

may change current safety margins of key components in safety-related systems

and how aging degradation can initiate failure. The goals of the NPAR program are to:

* identify and characterize aging and service wear effects which, if

unchecked, could cause degradation of systems, components, and

civil structures and thereby impair plant safety

* identify methods for inspection, surveillance, monitoring, and

evaluation of the residual life of structures, systems, and components and civil structures that will assure a timely detection of

significant aging effects before a loss of safety function develops

* evaluate the effectiveness of operations, maintenance, repair, and

replacement practices in mitigating the rate and extent of degradation caused by aging.

The NPAR study of diesel generator aging was performed in two phases.

In Phase 1, plant operating experience, data, expert opinion and statistical

methods were used to produce a new data base related to aging, reliability,

and operational readiness of nuclear service diesel generators. Phase II is

chiefly concerned with aging mitigation measures. Phase I of this program

has been completed and the results of assessments of wear and aging experience have been published (Hoopingarner et al. 1987, Vol. I and 2). Methods

for testing and aging mitigation (Hoopingarner et al. 1988) have been published as part of the Phase II work.

The purpose of this report is to describe a proposed management, testing

and maintenance program for emergency diesel generators that was developed as

a product of Phase II of this effort. The proposed program would lead to

1.1
three expected results: 1) reduce stressors identified in Phase I that lead

to accelerated aging of nuclear service diesel generators, 2) provide an

enhanced state of reliability and operational readiness, and 3) provide

improved confidence in future diesel-generator availability.

The research reported in this document was conducted by the Pacific

Northwest Laboratory (PNL), which is operated for the Department of Energy by

the Battelle Memorial Institute.

1.1 BACKGROUND

The aging of a nuclear service emergency diesel generator may be envisioned as the cumulative deterioration of components and supporting systems.

This aging can lead to a loss of reliability to start, assume the defined

emergency loads, and once started to continue to run for the duration of the

emergency or, in case of routine operational verification testing, the

duration of the test. This deterioration may be the result of wear, metal

fatigue, oxidation, bacterial action, vibration, accumulation of deposits,

maladjustment, etc., and it may occur gradually over months and years, or

relatively rapidly over a shorter period.

The necessity of achieving and maintaining a high level of diesel generator reliability has long been recognized as an essential element of nuclear

plant safety and has received considerable regulatory attention. During the

period from 1959 to 1973, diesel generator availability was assured by testing conducted on a monthly basis and during refueling. In 1975, a report by

the U.S. Atomic Energy Commission (AEC) evaluated diesel generator failures

being experienced during this period and concluded that one specific problem

was dominant and identified it as the starting of the engine (AEC 1975).

This experience led to the general perception that if a diesel generator

could start, it would likely continue to accept load and continue to operate

reliably.

In 1977, Regulatory Guide 1.108 (Rev. 1) was issued and it defined a

routine testing schedule that related the testing frequency to the number of

failures being experienced. This guide requires that the diesel generators

be "fast, cold" started at intervals of at least 31 days. If two failures

are experienced in the last 100 valid tests, then the maximum test interval

is decreased to 14 days. If three failures are experienced in the last

100 valid starts, the maximum test interval is further decreased to 7 days.

Finally, if four or more failures are experienced in the last 100 valid

tests, starting tests must be performed at least every three days. The

requisites for a valid test are delineated in the guide. The thrust of this

requirement was to encourage utilities with diesel generators with high failure rates to make major improvements to avoid the high costs of frequent

starting tests.

"Fast, cold" starting refers to plant technical specification requirements that the engine be started within 10 to 12 seconds from ambient conditions and fully loaded within 30 to 45 seconds. In general, if a licensee

uses a keep-warm system for either the jacket cooling system or the oil

1. 2
system or both, the thermal condition provided by these systems becomes a

part of.the ",ambi.ent condition." The 10 to 12 second start time and 30 to 45

second full-load time was. not specified in Regulatory Guide 1.108 'but was

determined from fuel cladding temperature calculations defined in 10 CFJ 50',

Appendix K. These requirements were'then made a part of each plant's technical specifications..,

'With Regulatory Guide 1.108 requirements in place and with some industry

changes in practice, starting failures were no longer dominant, and failures

such as fatigue and wear of engine components from fast start testing were

observed. In 1982, a summary of diesel generator performance presented to

the Advisory Committee for Reactor Safeguards (ACRS) recommended that

1).routine test starts-on a,3-day.frequency should be eliminated, 2) testing

shouldbe focussed on unreliable diesel generators and major repair action

should be pursued, rather than Just more testing, and 3) when a failure has

occurred,. an initial test of redundant units.should be conducted with a

followup test about every 3 days to provide increased' assurance that a new

failure'has not occurred (Beard.1982).

NUREG/CR-2989 reported ani'nvestigation of diesel generator reliability

based on data from the 1976 to 1980 period and concluded that their average

reliability was 0.975. Human errors and hardware'related common mode failures were observed to be 0.2%. No one type of equipment failure was dominant. The most frequently observed failures were control and logic problems

(14.7'%) followed by governor failure '(12.3 %). Several'actionswere recommended to'improve diesel generator reliabil'ity including 1) periodic governor

maintenance, 2) performance of root cause. analyses,,3) adding corrosion

inhibitors to jacket cooling water, 4)-upgrading operati'ng/maintenance

procedures, and 5) installing an additional diesel generator unit.'

The NRC'recognized the possibility-of detrimental effects-of the very

testing that was.originally.meant.to.assure the diesel generators'. reliabil.-

ity. In December of 1983', Generic'Lette'r 83-41 was'issued which requested

licensees to provide information related to potential detrimental effects of

'fast, cold" starts. This letter was followed by Generic Letter 84-15 in

July 1984.which described changes, in requirements to improve'diesel generator

reliability. This action requested that the licensees take action to reduce

"fast, cold",-starting'tests and e'ncouraged them to propose technical specification changes. The.generic letter also described'a goal-oriented reliability'programdeveloped by the staff and invited licensee comments;on this

program.

Recently, a major change has been-made to 10'CFR 60, General Design"Criteri~on 4,,which, accepts leak-before-break analysis and detection for large

bore primary system piping-.This change could.jresult in a relaxation of

emergency diesel generator start.time, .but new criteria have not yet been

promulgated. Studies by the Electric'Power Research Institute (Muralidharan

1986 and Schwartz 1988) and others have indicated that the emergency power

requirements are on the order ofA to 2 minutes for a loss-of-coolant.

accident (LOCA)'with a simultaneous loss of off-site power and on the order

of 5 minutes or more for a loss of off-site power withou't a LOCA.

1.3
Although NRC is moving away from frequent fast-starting requirements and

allowing some "slow-start" testing, the technical specifications for the

majority of U.S. nuclear power stations still call for fast, cold starting,

exclusively, for monthly tests of diesel generators. In addition, at the

present time, most stations have not installed the necessary hardware

modifications to permit both slow-start testing and fast-start response of

the diesel-generator system.

The historical approach taken by NRC for assuring diesel generator

reliability had the objectives of developing statistical data on the past

reliability of the tested units and providing incentives to licensees to

perform major mechanical improvements to reduce the expense of performing

frequent testing. However, it provides no information on the long-term

degradation of the performance of components and related systems which could

lead to future failures and which could be corrected before an actual failure

occurs or before a unit's reliability is compromised. The detection time to

statistically determine unacceptable performance deterioration is considered

to be excessive.

In response to these historical conditions, the NRC staff has acted by

the issue of Regulatory Guide 1.155, "Station Blackout" in August, 1988 which

identifies a need for a reliability program. This reliability program for

emergency diesel generators is designed to maintain and monitor reliability

levels selected for compliance with the Station Blackout Rule 10 CFR 50.63

(6/68).

Regulatory Guide 1.9, Revision 3, "Section, Design, Qualification,

Testing, and Reliability of Diesel Generator Units Used as Onsite Electric

Power Systems at Nuclear Power Plants" is in the final NRC approval process

and is expected to be issued in 1989. It integrates into a single guide

pertinent guidance previously addressed in Regulatory Guides 1.108, 1.9

Revision 2 and Generic Letter 84-15. Regulatory Guide 1.108 will be withdrawn after the issue of Regulatory Guide 1.9, Revision 3 is consistent with

industry guidance contained in NUMARC-8700, Appendix D and with the recommendations contained in this report.

Many prior operational and testing practices deleterious to engine

reliability and life, such as cold fast starts, have been deleted. The

development of Regulatory Guide 1.9, Revision 3 has utilized information

obtained through the NPAR Program, Diesel Generator Task.

1.4
2.0 SUMMARY OF THE NPAR DIESEL GENERATOR AGING STUDY

Emergency diesel generators were included in the NPAR program because of

1) the safely -implications of the failure of the diesel generators-during an

emergency situation (Davis et al..1985), 2) the correlation of risk and aging

trends (Davis et al. 1985), and joint recommendations.of several NRC offices

including Nuclear Reactor Regulation (NRR), Nuclear Regulatory Research

(RES), Inspection and Enforcement (IE), and Analysis and Evaluation of

Operational Data (AEOD).

For the purpose of this study, subsystems supporting the emergency diesel generators were included along with-the diesel generators themselves,

because together they form a complex.overall system which will fail to perform its safety function if any component functions less than adequately.

Specific components and subsystems considered as part of the diesel generator

system include the 1) diesel engine, 2) governor, 3) starting system, 4) turbocharger and intake combustion air system, 5) cooling system, 6) fuel oil

storage and delivery system, 7) lubricating oil system, 8) exhaust system,

9) generator, 10) exciter and voltage regulator system, and 11) instrument

and control system. Not included in this study were the 1) remote control

and surveillance system, 2) external electrical. power supply system supplying

ac and dc power to various systems, prewarming system and the pre-lube system, and,3) Class IE electrical distribution system.

2.1 SCOPE AND METHODOLOGY

In the NPAR Program emergency diesel generator study, diesel generator

systems as defined in Section 2.0 were evaluated tot1) determine which components .and subsystems were subject to aging, how they failed, and with what

frequency, 2) determined the adequacy of surveillance, inspection, and trending methods, and 3),-assessed.the role of maintenance and other industrial.

practices in resolving aging' effects.. The overall objective of this study

was to provide information to assist the regulatory organizations.and plant

operators to understand the role of aging in emergency diesel generators.

The study to date was performed in two phases. Phase I, which was completed and provided general background material forthis, report, was concerned'with defining which diesel generator system components fail and the

principal causes of the observed failures. This work was based on failure

information on components within the defined system boundary obtained from

the Nuclear Plant Reliability Data System (compiled by the Institute for

Nuclear Power Operations), Licensee Event Reports, Nuclear Power Experience

(Stoller 1982) and Emergency Diesel Generator Component Tracking System

(compiled by TDI Owners Group). These data were analyzed statistically and

reviewed subjectively by a panel of diesel experts to determine which components were most susceptible to aging, the principal causes of these failures,

and the maintenance procedures that either contributed to failures or prevented them. The panel of diesel experts was made up of recognized industrial experts in diesel engine design, application, installation, operation

2.1
and maintenance. Current inspection, surveillance, and maintenance practices

were reviewed to determine any relationships between these practices and the

type and number of failures being encountered.

Phase II of this study is underway and is the basis for this report.

The principal objective of Phase II is to develop information and recommendations to assist regulatory organizations and plant operators to assure

maximum diesel generator reliability. This activity will be performed with

interaction with the NRC Staff, industry, and code and standards committees.

2.2 TECHNICAL SAFETY ISSUES AND RESEARCH RESULTS

This report is based on the results of the Phase I activity of the

Diesel Generator Aging Research Program which is reported in detail in

(Hoopingarner, et al 1987). The principal issues addressed in Phase I

included the following:

* failures which occur most often in emergency diesel generator

systems

* subsystems and components involved in these failures

* fraction of the failures due to aging

* observable aging trends

* important aging stressors

• potential corrective actions and mitigating measures.

About 500 reported diesel generator failure incidents occurring from 1965 to

1984 were randomly selected from each of the 4 data sources listed in Section 1.1 to form a representative data base which resulted in 1,984 cases of

diesel generator system failure. Diesel engines tabulated in this representative data base included those manufactured by ALCO, Allis Chalmers, Caterpillar, Cooper Bessemer, Fairbanks Morse, Electromotive Division of General

Motors, Nordberg, Transamerica Delaval, and Worthington.

2.2.1 Aging Related Failures and Their Causes

Systems and components that contributed most to all diesel generator

failures are summarized in Table 2.1. The most significant causes of failure

are summarized in Table 2.2. Of the 1,984 incidents of diesel generator

failure in the representative data base, 1,064 were judged to be related to

some form of aging. Of these 1,064 aging failures, 629 resulted in the loss

of function of the diesel generator system or impaired its reliability.

Systems and components identified as being major contributors to this group

are shown in Table 2.3. The principal causes of failures that resulted in

loss of function or impairment of reliability are summarized in Table 2.4.

2.2
TABLE 2.1. System and Components Contributing Most to Diesel.,

Generator Failures

Percent of

Systems and Components All Failures

Instrument and Control Systems 25

Governor 10

Sensors 3

Relays 2

Startup Components 2

Fuel System 11

Piping on Engine 3

Injector Pumps 2

Starting System 10

Controls 3

Starting Air Valve 2

Starting Motors 2

Air Compressor 1

Switchgear System 10

Breakers 3

Relays 2

Instrument and Controls I

Cooling System 9

Pumps 2

Heat Exchangers 2

Piping 2

Lubricating System 7

Heat Exchangers 2

Pumps 2

Lube Oil 1

Other Systems 28

TABLE 2.2. Overall Causes of Diesel Generator Failures

Percent of

Failure Cause All Failures

Poor manufacture or construction quality control 22

Adverse conditions - vibration, shock 17

Human error - maintenance 13

Adverse environment - dust, humidity, chemicals, etc. 13

Unknown 11

Maladjustment/misalignment 8.

Other 16

2.3

-
TABLE 2.3. Systems and Components Subject to Aging-Induced Failures

Resulting In Loss of Function of Unit

Percentage of

Systems and Components Aging-Related Failures

Instruments and Control Systems 26

Governor 12

Control Air System 3

Wiring and Terminations 2

Sensors 2

Fuel System 15

Engine Piping 7

Injector Pumps 5

Injectors and Nozzles 2

Starting System 10

Starting Air Valve 5

Controls 2

Starting Motor 2

Cooling System 10

Piping 3

Pumps 2

Heat Exchangers 2

Engine Structure 9

Crankcase 3

Cylinder Liners 2

Main Bearings 2

Other Systems 30

TABLE 2.4. Causes of Aging-Related Failures that Result in Loss of

Function or Reliability

Percentage of

Failure Cause Aging-Related Failures

Adverse conditions - vibration, shock 32

Poor manufacture or construction quality control 23

Adverse environment - dust, humidity, etc 15

Human error - maintenance, operation 9

Poor design - wrong application or component 7

Other 15

The instruments and control system appeared to be the most vulnerable

to failure in all categories. Within both this specific system and for all

systems considered, the governor was the single component most subject to

failure from all causes. The control air system, wiring, terminations, and

sensors appeared to exhibit a significantly high failure rate, but considerably below that of the governor.

2.4
The analysis indicated that, for all systems and components, the primary

causes of failure could be grouped into vibration, thermal'and physical

shock, and other adverse conditions. In this group, vibration loosening was

the primary mechanism of degradation. Vibration and vibration loosening were

also major matters of concern for the instrument and control system.

The fuel system was found to be second in aging-related degradation.

Engine piping, injector pumps, and injectors experienced the most failures.

The most prevalent degradation mechanism was vibration loosening. For the

injector pumps, failure mechanisms were distributed'between poor manufacture/

construction, vibration, and environmental influences.

The third system most afflicted by aging degradation was the starting

system with the air admittance valves, controls, and starting motors being

the most troublesome components. Adverse environmental conditions were

identified as the principal cause. Poor system'des'ign also appeared to be a

major contributor to failure. These findings indicated that, in general,

these systems may be designed without sufficient consideration for potential

degradation due to moisture intrusion with subsequent corrosion, fouling, and

other damage.

In the study, cooling systems were found to experience aging degradation

of piping, pumps, and heat exchangers. While pump and pump failures were

caused principally by vibration loosening of fasteners, the causes of heat

exchanger failure were distributed between vibration, environmental factors,

and manufacturing/construction quality. Vibration damage to heat exchangers

was generally caused by loose internal components.

The fifth most cited system in the aging study was the engine structure.

Components found prone to aging failures included the crankcase, cylinder

liners, and main bearings. Crankcase. failures were due to vibration and

improper operation. Cylinder liner failures were associated with poor manufacturing/construction, thermal stresses, and design problems, while the main

bearing failures were caused by oil contamination, poor maintenance, and

design.' These failures tended to occur early in the service life and

declined to less importance after five years of operation.--

2.2.2 Aging Trends

An analysis of the data base to determine trends in aging related failures as plants become older is summarized in Figure 2.1. This figure shows

the not unexpected fact that as plants'grow older, the percentage'of failures

from aging increases. The percentage of aging failures appears to increase

from about 45% the first year of plant commercial operation, at which time

the diesel generators might have had several years of testing and operation,

to about 65% in the 15th year. This, does not imply that the numbers of

failure's are inc'reasing,-only that the 'aging related fraction is larger.

To put Figure 2.1 in the proper perspective, it should be noted that the

numbersiof failures decline continuously with increasing plant age. This is

due to two factors, less failures per plant and fewer plants in each

increasing age group. Another point to be made is the effect of better
I nn

I Good Data I Limited Data

0

0 so X VX~~~~~~~~~~~~~~~~~

C

60 O 4

040

00

0 2 4 6 8 10 12 14

Age of Plant at Time of Failure (yr)

FIGURE 2.1. Percent of Failures Due to Aging

operational and maintenance performance in reducing diesel generator failures. If plants could somehow reduce all failures due to human errors,

faulty new components, and similar causes then the only expected failure

causes remaining would be time-dependent degradation and wearout failures.

In this case, the aging trend would go to 100%. This operational and

maintenance improvement appears to be happening in the plants, thus, the

increase in the percentage of failures due to aging.

The analysis of the data indicates that the percentage of aging failures

due to vibration, adverse environment, and overstressing from unanticipated

conditions stays relatively constant. Some components exhibit an early

"burn-in" period during which they exhibit an increased aging failure rate,

while others experience an increased aging failure rate as they become

older. For example, the following components seems to exhibit a decrease in

aging failures after 5 years of operation:

* instrument and control system relays

* fuel system piping on engine

* starting air valve

* lubricating system heat exchangers

* lubricating oil

* crankcase

2 .6
* pistons

* breakers.

The aging failure percentage rate of the following components increases

slightly or remains constant after 5 years of operation:

* governor

* injector pumps

* coolant pumps

* cooling system piping

* starting system controls

* starting motors

* lube oil pumps

* turbochargers.

* electric generator

* switchgear relays.

A general review of the aging failure data indicates that manufacturing,

construction, and poor design problems tend to be reconciled early. Time

independent-causes of aging failure tend to be maintenance, operation, and

maladjustment/misalignment induced degradation. Time-dependent causes ofaging failure tend to be adverse operating conditions (e.g., vibration and

shock) and adverse environmental conditions (e.g., dust, chemical exposure,

etc.). It may be assumed that the change of the overall failure rate appears

as shown in Figure 2.2. Here the total failure rate exhibits an early

"burn-in" period where the early problems from design, manufacturing and

construction are discovered and resolved, thereby increasing the system's

reliability. After these problems are resolved, the time dependent failure

rate stays relatively constant over a relatively long period. Finally, as

exposure to adverse operating and environmental conditions increases, the

time-dependent failure rate should increase. Evidence of general wearout has

not been detected.

2.2.3 Correction of Aging-Induced Failures

Actions employed to correct the aging-related failures reported in the

data base are summarized in Table 2.5. -This table shows that 78% of the

aging failures were corrected by replacement of the aged part or by some form

of maintenance such as realignment or readjustment. The types of corrective

actions performed on the components most susceptible to aging are summarized

in Table 2.6.

2.7
t

A (T)

T -*

I1- Burn-In 1I - Maturity & I * Wearout -

FIGURE 2.2. Change in Failure Rate Over Time

M.

TABLE 2.5. Summary of Most Frequent Corrective Actions for Aging Failures

Action

Code

Percent of AgingCorrective Action Related Failures

Replacement - same type of component

Maintenance - realignment or adjustment

Replacement - new or upgraded component

Repair - welding or replacement

Enhanced preventive maintenance

rs

m

rn

52

26

13

5

2

1

r

PM

Redesign d

Only cylinder liners, pistons, starting air valves and cooling system

heat exchangers were identified as needing replacement by new or upgraded

parts when an aging failure was encountered. The remaining systems and components were repaired by replacement with a similar part, adjustment, or

repair of the failed part. Secondary corrective actions included improved

maintenance training, preventive maintenance, and improved management procedures. These secondary corrective actions appeared to enhance the primary

2.8
TABLE 2.6. Corrective'Actions for Components Most Susceptible to Aging

System Component Action Code

Instrumentation and Controls Governor rs,m

Fuel System Injector Pumps m,rs,pm

Piping on Engine m,rs

Starting System Controls m,rn,pm

Starting Air Valve m,rn,pm

Starting Motors rs,pm

Cooling System Pumps rs

Piping rs

Heat Exchangers rs,mr

Lubricating System Pumps rs

Heat Exchangers rs

Intake and Exhaust Turbocharger rs,pm

Engine Structure Crankcase rs

Cylinder Liners m,rn

action. For example, the secondary corrective action for vibration loosening

was, generally, enhanced preventive maintenance, which, of course, would tend

to prevent the recurrence of the original failure.

2.3 STRESSORS

The statistical analysis of the failure data base resulted in the identification and ranking of the stressors identified in Table 2.4 that can lead

to the failure'of diesel-generator components. Another valuable ranking of

these stressors and their relative importance was obtained from an industrywide workshop on diesel generator aging held under the auspices of the NPAR

Program (Hoopingarner 1987, Vol. 2). Attending were representatives of U.S.

utilities, vendors, contractors, consultants, and the national laboratories..

One of the principal objectives of this workshop was to obtain the industry's

perception of issues and problems regarding nuclear service diesel generators

and to identify potential solutions.

The workshop attendees identified essentially the same aging stressors

as found in' the statistical analysis of the data base and summarized in

Table 2.4. However, they ranked them in a somewhat different order of importance as shown in Table 2.7. This table suggests that the principal stressors leading to the aging of diesel generator components are environmentally

related. The second, third and fourth most important stressors were, in

order; maintenance practices, testing practices, and operating practices.

Additional important stressors were identified which included vibration,

fuel/lubricant degradation, and gasket/seal degradation. It was apparent

from the expressed concern about aging'degradation factors such as vibration,

fuel/lubricant degradation, gasket degradation, and environmental'stressors

such as dust, water, and heat, the workshop participants perceived that

deterioration of diesel generator systems to be relatively influenced by

their normal operating environment.

2.9
TABLE 2.7. Workshop Participant's View of Major Aging Stressors

Rank Major Stressors

1.

2.

3.

4.

5.

6.

7.

8.

9.

10.

11.

12.

13.

14.

Environmentally induced - dust, water, heat, oil, chemical, etc.

Maintenance errors - inadequate training, etc.

Fast starts and other regulatory induced factors

Design inadequacy - wrong application, or poor component

Operation induced - inadequate training and skills

Vibration induced

Fuel or lubricant degeneration

Gasket, seal, or organic material degeneration

Inadequate spares - quality, storage, ordering problems, data and

specifications

Corrosion

Thermal stress

Manufacturing or quality problems

Fatigue not related to vibration

Others

The workshop participants identified several additional aging stressors

not identified or adequately emphasized earlier in the statistical analyses.

These included 1) periodic testing procedures that overstressed engine components and related systems by imposing frequent cold, fast starts to verify

operational readiness, 2) operational and maintenance inattention caused by

the infrequent operation of the units and the highly formalized maintenance

procedures for safety-related nuclear plant components, and 3) the absence of

any plant or industry-wide trending/failure analysis practices to identify

failing components before they actually fail. Fully 60% of the workshop participants identified trending/failure analysis as the recommended method to

ameliorate aging failures in emergency diesel generators.

2.4 SUMMARY OF NPAR STUDY CONCLUSIONS AND RECOMMENDATIONS

The NPAR Diesel Generator Phase I Study identified the system components

most susceptible to aging failure, and these components are summarized in

Table 2.3. It also identified the stressors listed in Tables 2.4 and 2.7 as

those most important in causing these failures. Based on Phase I results,

other input provided by the industry, and new Phase II research, it was concluded that a significant reduction of aging effects can be achieved and a

long-term improvement of diesel-generator system reliability can be obtained.

The key to this reduction of aging effects and reliability improvement is

1) the reduction in the fast-start stressor imposed by current regulations,

2) the implementation of new recommended testing and trending procedures and

3) improved maintenance practices. To provide this key, a new program is

recommended that would integrate testing, inspection, monitoring, trending,

modification, personnel training and maintenance. The new recommended program is further described in Section 5.0. The more important elements of

the new proposed program are discussed in the following paragraphs.

2.10
2.4.1 Improved Diesel Generator Testing

To eliminate the fast-start testing stressor that was perceived by the.

industry representatives as one of the major causes of diesel-generator aging

failures, it was recommended that the presently required fast-start, statistically-based testing methodology be replaced with an alternate testing procedure requiring slower starting and loading procedures used commonly in

non-emergency power applications.

Diesel experts consulted during the NPAR Phase II research provided

recommendations regarding improved testing procedures to obtain data on about

30 operating variables that would provide the necessary information to

establish engine/generator conditions (Hoopingarner et al. 1988). They also

evaluated slow-start, slow-load testing in comparison to current fast-start

and load procedures and concluded that the slower starts would adequately

test all important system components. One possible exception is the load

sequencing relays which, alternatively, could be electrically and electronically tested using commonly available plant testing equipment to ensure

proper operation.

A correctly managed monthly testing program involving slow starting and

loading would induce little aging effects in the emergency diesel-generator.

By contrast, the current fast starting and loading testing requirements can

produce substantial harm and significant aging effects through the production

of large mechanical and thermal stresses, inadequate lubrication during

initial acceleration, high rotating and sliding pressures, overspeeding, etc.

During this monthly slow starting and loading testing program, adequate data

should be collected for key engine operating parameters that could indicate

degrading performance or an impending component failure. For many important

components such a program could then detect approaching performance failure

and allow orderly repair long before the current testing procedure could

induce the actual failure. Monitoring and trending will not be able to

detect all degraded performance, of course, but the deterioration that will

be detected is significant. These recommended tests will be presented and

discussed in Section 5.2.

2.4.2 Condition Monitorina and Trending

The diesel experts further recommended that some of the more important

data developed in the operational surveillance testing described in Section

2.4.1 be monitored and trends established to show the possible presence of

long-term component or system degradation. This should detect many potential

component/system failures before the system actually fails. By anticipating

these failures and providing timely repair/maintenance, cost and safety benefits would accrue from the avoidance of both equipment damage and unscheduled

downtime. From the monetary standpoint alone, the payback period from such a

monitoring and trending program could be less than a year, based on nonnuclear service experience.

In contrast, the present testing program performed according to Regulatory Guide 1.108 is a reactive process; it provides chiefly statistical

information on the ability of the unit to start and assume the prescribed

2.11
load. However, it provides no assurance regarding future engine operability.

The engine status as indicated by this approach can be shown to lag true

engine condition by a year or more. Preliminary analysis by Monte Carlo

methods shows that statistically one could expect to detect a 6% step change

with only a 60% probability in a 50 test series.

2.4.3 Maintenance Training, and Inspection

Several recommendations were developed regarding maintenance procedures

and training. One important recommendation is that teardown of the diesel

engines solely for the purpose of inspection be avoided unless there is a

definite indication that its operation is degraded or there is an impending

component failure based on performance data trends. Analyses of failure data

have also been performed by the U.S. Navy and the airline industry which show

a definite average, short-term, adverse effect of such teardowns on the

engine reliability.

It was also recommended that licensee maintenance organizations should

not treat engine governors as "black boxes" which are often left alone until

a failure occurs. These governors were shown to be a major cause of engine

failure and must have regular and careful inspection, adjustment, and preventive maintenance based on a firm understanding of its mechanism and

service needs.

This understanding of the governor, as well as the engine/generator,

must be developed by providing the maintenance staff with adequate training

and motivation. The staff associated with each plant should be given

training equivalent to that offered by the specific engine and governor

manufacturer that supplied the engines for that plant. Further, the personnel should be provided with failure fault diagrams with defined corrective

actions for both maintenance and operation of the units. These troubleshooting aids should list information on the most common causes of failure to

start and run along with a sequence of corrective actions. The availability

of such information in a real plant emergency speeds up the process ofrestarting the engines, when the failed component and problems are relatively

minor in nature.

Finally, it was recommended that engine inspections and preventive

maintenance be increased to mitigate the aging and wear results of the

vibration stressor. This maintenance should focus on the engine or instrumentation mounted on the engine or the engine skid. Normal engine vibrations

have a known and severe influence on control system instruments and their

calibration. Vibration cannot be eliminated, but its effects can be ameliorated by keeping fasteners/fittings tight and by frequently recalibrating

instrumentation subject to this vibration.

2.12
3.0 THE EMERGENCY DIESEL GENERATOR MISSION AND DESIGN FEATURES

U.S. nuclear power plants are-required to have both onsite and offsite.

sources of emergency electrical power to assure that the plant can be shutdown without endangering public health and safety. In almost all plants, the

onsite source of emergency power is provided by redundant diesel generators

which are called upon to supply power upon loss of the off-site sources. The

capacity and capability of either the onsite or offsite sources is required

to be sufficient to assure that 1) the nuclear fuel design limits and design

conditions of the reactor coolant pressure boundary are not exceeded as a

result of anticipated operational occurrences and 2) the core is cooled and

containment integrity and other vital functions are maintained in the event

of postulated accidents.

The design of the onsite emergency power system is governed by Regulatory Guide 1.9 which references the requirements of The Institute of Electrical and Electronics Engineers, Inc. (IEEE) Standard 387-1977.

3.1 MISSION ANALYSIS

The redundant diesel generators supplying emergency power are connected

to one of two or more redundant Class IE electrical power distribution systems supplying equipment capable of placing the plant in a safe shutdown

condition following an accident accompanied by a loss of off-site power.

Each emergency generator is capable of automatically starting and accelerating to rated speed, and subsequent loading of all engineered safety

features and essential shutdown loads, in the required sequence, within the

minimum time intervals established by the plant's safety analysis. They are

designed to be capable of continuous operation at rated load, voltage, and

frequency until manually stopped or automatically tripped. Generally, the

diesel generators are started up if any engineered safety system is triggered

regardless of the availability of offsite emergency power. If the power from

the offsite emergency buses is interrupted or degraded, the equipment loads

associated with each Class IE distribution system are sequentially-connected

such that the voltage will not fall to less than 75% of rated voltage and

frequency will not be less than 95% of rated frequency. Generally, the diesel generators are started and accelerated to full speed in approximately

10 seconds and fully loaded within 1 minute if a loss of offsite power accompanies the triggering of safety systems. If there is no loss of off-site

power, the emergency diesel generators are operated continuously to maintain

readiness. Under this condition, other auxiliary equipment may be connected

manually through administrative procedures to the emergency buses up to the

capacity of the emergency generators. This loading is especially important

with port-scavenged two-cycle diesel engines which cannot be run unloaded for

long periods of time without the buildup of combustion product deposits which

can threaten their continued availability.

The diesel engines used for nuclear service emergency power are very

large and are the type commonly used in ship propulsion and stationary power

applications. For these uses the engines are started and partially loaded

3.1
and then thoroughly warmed up before the application of full load, and operated continuously for extended periods. With this type of service, they

have proved to be very long lived and dependable. In nuclear emergency power

application, the conditions of service differ appreciably, and the stressots

developed by this service can lead to accelerated aging. The more important

stressors include the following:

1. The engine is required to accelerate rapidly, producing maximum

piston ring-cylinder wall forces and bearing forces at a time when

normal lubricant films have not been completely formed. The

resulting metal-to-metal contact can result in cylinder wall and

cam surface scuffing and accelerated main bearing and connecting

rod bearing wear.

2. The rapid acceleration can produce amplified crankshaft torsional

vibration as the crankshaft rapidly encounters successive harmonics

of its natural frequency without opportunity for damping from normal mechanisms. This amplification was thought to cause the

observed crankshaft cracking in some Enterprise engines which were

not equipped with torsional vibration dampers. Amplified torsional

vibration may also occur in other components such as the enginedriven water pumps and the camshaft and gears.

3. The rapid acceleration and loading of the engines without allowing

for thermal equilibration can lead to high mechanical and thermal

stresses in the cylinder block and crankcase that can cause distortions of the engine structures. These distortions can, in turn,

lead to metal-to-metal contact (scuffing) and accelerated wear of

components. Such scuffing may also be a source of very high temperature and subsequent crankcase explosions.

4. Following the rapid acceleration to speed, an overspeed condition

occurs as the governor acts to gain control of the engine rpm.

This overspeed condition can result in increased stresses in engine

and generator components that can accelerate mechanical wear and

loosen generator wiring.

5. The turbocharger overspeeds immediately after rapid engine acceleration which could enhance wear, especially since the turbocharger

bearing lubrication is not completely established at this time.

6. The brief periods of operation between long standby periods provide

opportunity for bacterial growth and degeneration of the fuel and

lubricants. Water from condensation or small leaks may also contaminate the lube-oil system. Condensation can contaminate the

fuel oil, which typically stays in the tanks for years because of

low use factors. Longer periods of operation help both of these

problems.

Stressors associated with fast-starting and loading in response to

accident signals are certainly important. However, because of their frequency, the most important stressors are those associated with the periodic

3.2
fast-start-testing mandated by regulations that simulate the starting and

loading sequence.that would be encountered.during an emergency. Real.emer-,

gency.(unplanned) fast starts.amount to only.2% oft.all starts, and .the rest

are tests (EPRI 1987). Of the unplanned starts,'only about one-half was

followed by loading. On the average, there are oinly 5 incidents involving,

loss-of-offsite-power in the U.S. per year '(EPRI.1987).

Testing programs and other guidelines for the diesel -generators are

currently defined by Regulatory'Guides 1.9, 1.108 and.1.137 and include:

* capability.qualification tests'

* start and load acceptance qualification test's

* margin tests

* preoperational tests

* availability and proper functior, tests .(performed to verify that

safety-related loads do not exceed the emergency generator rating

and that each unit is suitable for starting, accepting and supplying the required loads)

* monthly.availability tests performed while the reactor is in operation' (fast starting with.assumption'of load up to the nameplate

rating). If failures'are'.'experienced, test frequency requirements

,could be dramatically accelerated as described in Section 1.1.

The role of the diesel generator safety mission related to the.aging

study has been'reviewed with the following'results., To respond to a largebreak LOCA event with a corresponding loss'of all' offsite power, a diesel

generator needs to start promptly.and deliver its full emergency loads until

the emergency is-over. 'This mission profile is the basis and focus of current regulatory requirements and testing. For small-break LOCA events with a

loss of offsite power, the'related need's for emergency electrical power and

the diesel mission profile are much less stringent.. Inthis case, the need

for power is extended to about 5 minutes or so and the emergency power level

needs are reduced, but the time duration for emergency power may remain for

several days. ..

With over 1000 reactor years of operation in U.S. regulatory history

without a large-break LOCA event-for.primary water containment and with the

recent criterion 4 (leak-before-break) rulemaking,.it may be.concluded that

the true mission envelope for the diesel-generator.may be redefined with

consequential benefits.' The most.realistic mission envelope appears to be:

* total duration" - 2'to '3days,,'

* diesel start and load time - within 5 minutes

3.3
* power level - less than calculated full load (core and containment

sprays not needed). Also, by usual design practice, less than the

engine nameplate rating by a conservative margin.

3.1.2 Related Mission Studies

The 10- to 12-second starting time imposed by the typical plant Technical Specification is the result of 10 CFR 50, Appendix A, requirements

which mandate a conservative approach to mitigating a large-break loss ofcoolant accident (LOCA) with a coincident loss-of-offsite-power. Recentl'y,

the NRC outlined a new, more realistic, approach for performing LOCA analyses. Under sponsorship of the Nuclear Safety Analysis Center (NSAC),

studies were performed by General Electric (Muralidharan 1986) and Westinghouse (Schwarz 1988) to investigate the implications of this more realistic

analysis and calculation method for the emergency diesel generator starting

time.

Both studies revealed that considerable relaxation of the approximately

10-second starting time requirements may be possible. The results of the.

General Electric study indicated that the start time could be increased to'

118 seconds in a typical BWR/6 without the peak fuel temperatures exceeding

the 22000F limit imposed by 10 CFR 50, Appendix K, for a combined LOCA and

loss-of-offsite-power. In the Westinghouse study, it was shown that the

start time could be increased to 53 seconds in a typical Westinghouse fourloop plant without exceeding this 22006F peak cladding temperature limit.

However, for starting times greater than about 45 seconds, containment

temperatures may exceed limits for in-containment safety equipment making

this the effective emergency diesel generator starting time limitation for

Westinghouse plants.

The effect of extended emergency diesel generator start time on certain

non-LOCA accident scenarios was also investigated by Westinghouse. These

non-LOCA accidents include 1) steam system piping failure, 2) feedwater system piping failure, and 3) loss of power to station auxiliaries. In these

accident scenarios, the emergency diesel generators must provide power to the

safety injection pumps and/or to the auxiliary feedwater pumps. It was concluded that the delay of power to the safety injection pumps accompanying a

45-second emergency diesel generator start time was acceptable. However, it

was also concluded that a similar delay of power to the auxiliary feedwater

pumps would cause auxiliary feedwater to be delivered later than assumed in

currently accepted licensing calculations and, therefore, may cause a reduction of existing margins. The amount of margin reduction was not quantified

in the Westinghouse report.

A similar investigation of the effect of non-LOCA accidents was not

included in the General Electric study.

3.2 RECOMMENDED EMERGENCY POWER MISSION PROFILE

The operating envelope of conditions for diesel-generators should

address testing conditions, non-LOCA emergency power conditions, and LOCA

3.4
centered conditions. The testing profile and conditions are discussed in

paragraph 5.1 and will not be addressed here. The recommended emergency

power mission then may-be reduced to a design envelope of conditions and a

more realistic envelope of the most probable requirements for emergency

power.

At this time, LOCA-related rulemaking has not reduced requirements for

emergency power, equipment qualification, and some other issues that appear

to be closely related to the LOCA design requirements. Therefore, it is

recommended that present design requirements and large-break LOCA operating

conditions be retained for qualification purposes. But, as discussed in the

mission analysis and for aging concerns, there is little justification to

continue with the routine testing of this equipment for fast-starting and

rapid-loading capabilities associated with the large-break LOCA conditions

and requirements.

The most probable risk-responsive requirements for the diesel-generator

mission are very high reliability with the durability to produce power over 3

to 4 days until the emergency passes and the reactor cooling requirements

rapidly drop off. This is essentially the 'station blackout" issue. But,

accepting this mission envelope for the diesel-generator system also results

in the reduction in aging degradation of many important engine components

through less harmful test requirements.- Several diesel experts have been

consulted for assurance that a gradual engine start and load sequence does,

indeed, test adequately for the mission requirements. A properly structured

test program will test reliability and durability much more appropriately

than current requirements outlined in Regulatory Guide 1.108. Aging issues

and concerns are also addressed in an appropriately structured test program,

and the envelope of design and operational requirements may also be checked

with reduced aging and wear effects.

The conservative diesel-generator mission profile, which should be the

basis for-testing and for setting certain engine control components, is

recommended to be established as follows:

* Reliability

- very high, greater than 0.95 for each engine

* Duration

- three to four days appears adequate

Start Time

- design and qualification, 45 seconds maximum

- routine testing for reliability verification, within 1 minute

should be acceptable, but 30 seconds .is an acceptable

compromise with conservative margins

- other testing--no requirements

3.5
* Start and Load Time

- for design and qualification, 105 seconds maximum (BWRs)

- for design and qualification, 45 seconds maximum (PWRs)

- for routine testing, rapid loading should be avoided.

(recommended gradual loading over a minimum time of

5 minutes)

- for six months or outage testing, same as design and qualification time [if General Design Criterion No. 4 (leak-beforebreak) is further relaxed to include emergency power faststarts may be eliminated].

3.3 RECENT RELATED NRC REGULATORY ACTIONS

Unresolved Safety Issue, USI A-44, "Station Blackout," has been resolved

by the issuance of the Station Blackout Rule (10 CFR 50.63) and Regulatory

Guide 1.155, "Station Blackout," released in August 1988. Section 1.2 of RG

1.155 establishes the need for a reliability program. This is directly

related to, and supported by, the findings of the aging research for a need

for an improved aging mitigation program. Aging mitigation actions improve

reliability and thus, in reality, the two programs have common needs and

corrective actions.

Generic Issue B-56, "Diesel Reliability" is currently in an advanced

stage of the resolution process. Again, the reliability focus will result in

resolution features and recommendations similar to the findings of the aging

mitigation research. Release of proposed Regulatory Guide 1.9, Revision 3 is

expected to resolve this issue.

3.6
4.0 MAINTENANCE ISSUES

Emergency diesel generators in nuclear service already exhibit excellent

reliability. In a recent suivey of U.S. of the reliability of diesel generator in U.S. nuclear plants, it was reported that the failure rate was only

1.4% for both testing and planned demands, and 2.2% for unplanned demands

between 1983 and 1985 (Wyckoff 1986 and Nuclear Engineering International

1987). During these years, there were 0.075 losses of diesel generator power

per site-year of all durations and only 0.023 losses per site-year that were

longer than 30 minutes. On the basis of these data, It was concluded by EPRI

and the Nuclear Safety Analysis Center (NSAC) that there is little opportunity for improvement. However, the consequences of a total loss of emergency

diesel generator power, during certain reactor design events, is so unacceptable from the standpoint of public health and safety, that available and

reasonable methods to further improve reliability cannot be ignored.

In addition to the reduction of aging stressors as discussed in Section 3.0, another avenue available to enhance emergency diesel generator

reliability and to mitigate aging is to employ a more focused maintenance

program. Cost-effective maintenance attention on the EDG units before failures occur will improve their availability. In addressing maintenance

issues, it is useful to first examine maintenance/reliability programs in

other applications.

4.1 MAINTENANCE/RELIABILITY STUDIES

Studies of maintenance/reliability practices used in airline and military systems were examined to determine the essential features of each.

Specific studies examined were performed by United Airlines (Noland 1978) on

aircraft power plants and the Department of Defense (Prichard 1984) on military shipboard systems. The concern in both of these studies was the development of an age-reliability analysis methodology and data that would support

decisions on whether to overhaul machinery or equipment at predetermined

intervals.

On the basis of large amounts of data on the failure rates of many complex systems and components, it was possible In both studies to categorize

aging, expressed as the variation of the probability of failure with time,

into seven different types illustrated in Figure 4.1.

The Type IV failure probability behavior suggests that the failure rate

may remain constant indefinitely and that overhaul of the equipment will do

nothing to improve the failure rate. In this case, it would, of course, be

inappropriate to overhaul the equipment at any time unless it suffers damage

or its performance deteriorates. The Type VI behavior indicates early

"wear-in" or "infant mortality" followed by a stable failure rate. Infant

mortality is the price often paid for overhauling equipment, and, in such

cases, there is little or no reliability benefit obtained from an overhaul.

In reality, the type VI failure rate curve is closely related to the type I

failure rate curve and perhaps represents the first part of the type I

4.1
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FIGURE 4.1. Types of Failure Behavior Observed in Age-Reliability Studies

diagram. Type II, Type III, and Type VII behavior are the "classical" wearout patterns showing definite increases of the failure probability especially

when the equipment exceeds a certain age. This equipment will benefit from

an overhaul without the penalty of infant mortality. However, the total

fraction of equipment involved in these failure types ranges from 7 to 18% in

the two studies. Thus, the "classical" equipment percentage is much less

4.2
than anticipated by most knowledgeable people.- Type V behavior shows a pronounced'increase in failure rate followed by a steady failure rate. Overhaul

of this equipment would be beneficial, but it is problematical if the

improved failure behavior is worth the cost. The other failure.behaviors

shown in Figure 4.1 are combinations of the above''basic behavior patterns.

For these cases, some benefit in failure rate can be obtained, but it will

require careful timing to assure that the overhaul is to be cost effective.

With Type I behavior, timing is especially important because benefits from

avoiding "wear-out" behavior is counteracted by the "infant-mortality"

behavior.

The results of the Department of Defense and United Airlines studies

have established the percentage.of systems, subsystems and equipment items

exhibiting these seven types of failure behavior for a large data base of

shipboard and aircraft propulsion failures. These results are summarized in

Table 4.1.

The results shown in Table 4.1 show the important fact that, in .73% of

the equipment surveyed in the Navy study and 82% of the equipment considered

in the United Airlines study, Type IV and VI behavior was observed and routine overhauls would not be beneficial over the time period studied.. For an

additional 9% of the equipment in the Navy study, and 7% in the. United Airline study, overhaul was found to be of only transitory'benefit:(Type V) and

of questionable value. Clearly, for only 18% of the equipment in the Navy

study, overhauls were necessary to maintain a reasonably low failure' rate

(Types II and III). For about 30%, it could actually be harmful. Only 11%

or less of the equipment in the United Airlines studies could benefit from

routine overhaul.

The.basic conclusion of both studies was that a purely time-based maintenance, at fixed overhaul periods, is ineffective in improving reliability

of equipment and can actually cause more trouble than it cures. In fact,

Prichard (1984) concluded that, without any available'performance data for a

specific piece of equipment, an equipment manager would be more often right

than wrong in deciding not to overhaul it. Noland (1979) argued that systematic diagnostic monitoring of equipment performance would.provide more

information of developing deterioration 'and would enable the application of

timely maintenance and overhaul such that overall reliability could be

TABLE 4.1. Results of Equipment Age-Reliability Analyses

Failure Navy United

' Type Study Airlines

I 0% 4%

II 14% ':2%

III . 4% 0%

IV 41% 14%

V 9% 7%

VI 32% 68%

VII 0% 5%

4.3
enhanced. He also argued for a closer liaison between maintenance and design

engineers in the identification of persistent deterioration problems so that

the design engineers can more effectively engage in product improvement.

4.2 IMPLICATIONS FOR NUCLEAR SERVICE EMERGENCY DIESEL GENERATORSNuclear service emergency diesel generator systems consist of thousands

of components. The percentages of components having the types of failure

patterns identified in the Navy and United Airlines studies have not been

determined, but should not differ substantially from the experience of the

referenced research. If the results of these studies are extrapolated to

nuclear service diesel generators, it can be concluded that through timebased maintenance there is less than a 20% chance of improving the overall

failure rate, even for a short time. This conclusion is further supported by

the results of the Navy study on shipboard emergency diesels. Although these

units are generally smaller than nuclear plant diesel generators, the components and subsystems are similar, and they can be expected to behave similarly. The Navy study indicated that these emergency diesels, on an overall

basis, exhibited a Type IV failure pattern indicating that little improvement

in the failure rate could be expected from a time-based maintenance program

alone. The study indicated, however, that with Type IV behavior, improvements may be obtainable through long-term monitoring and trending. Therefore, a similar reliability benefit should occur for nuclear plant emergency

diesel generators through a well planned and executed trending and reliability program.

This conclusion was arrived at independently by PNL's diesel generator

experts who also recommended a program of diagnostic monitoring and trending

to ensure diesel generator reliability. The details of their recommended

program will be described and discussed in Section 6.

4.3 MAINTENANCE/REGULATORY ISSUES

Monthly testing for statistical information performed according to

Regulatory Guide 1.108 with failure reporting is a reactive process with no

assurance of future operability. A good overall program of testing, monitoring and trending, on the other hand, is an active process that can detect

many incipient failures before a component or system actually fails. Therefore, it provides a method by which emergency diesel generator reliability

and availability can be effectively increased.

To take advantage of the potential benefits of an improved testing, monitoring, and trending program on diesel generator reliability, it is recommended that regulatory attention on the overview requirements should be

reviewed. Each utility should outline their overall emergency diesel generator operation, test and maintenance program and especially their revised

inspection, monitoring, and trending activities. This regulatory attention

should include methods proposed by the licensee to establish normal,

degraded, and unsatisfactory performance for the EDG system.

4.4
- 1 5.0 RECOMMENDED DIESEL GENERATOR PROGRAM

This section presents a recommended diesel generator management program

that integrates testing, inspection, monitoring, trending'and maintenance

activities. It was developed for the purpose of enhancing the reliability of

nuclear service diesel generators by a group of diesel engine experts working

with PNL's NPAR staff in a'workshop reported by Hoopingarner et al'.: (1988).

The recommended program is similar to programs already successfully used

by many small.utilities that depend on diesel generators as a source of baseload or peaking power. It was developed with the intent of 1) reducing the

aging stressors associatecdwith present regulatory test requirements while

providing enhanced confidence in the diesel generator's capability to respond

to accident situations, 2) providing information to-identify potentially

failing systems and components to allow their timely replacement/repair

before a failure actually occurs, and 3) enhancing the utilities' response to

potential or actual failures of dieskb1 generator components or subsystems.

The key elements of the recommended plan are as follows:

* Testing Monitoring and Trending - The approach of monthly testing

should be changed from the current regulatory approach requiring

fast starting and loading-to a new approach that would allow slower

starting and would enable the acquisition of surveillance information. This new approach would eliminate the fast-start aging

stressor identified in Section 3.0 and would result in obtaining

operating data on key engine performance parameters as recommended

by studies described in Section 4.0. These parameters could'be

monitored and trended to either 1) ensure normal performance or

2) reveal future engine problems. The recommended program of

testing, monitoring, and trending is described in detail in

Section 5.1.

* Inspection Proaram - If not already performed by a licensee, a'

program of weekly, monthly, quarterly, and annual inspections - should be undertaken to assure that the effects of operating and

environmental stressors are detected and repairs effected before

they have time to cause a more serious condition or failure. The -principal focus of these inspections should be on systems and

components identified in the Diesel Generator Aging Research program (Hoopingarner, et al. 1987). This inspection program is - described in Section 5.2.''

* Maintenance Program - Amaintenance program responsive to the test-. 7

ing,-monitoring, and-trending program should be undertaken. Tear--

downs of a satisfactorily'perfotming engine simply for the purpose

of 'inspection should be avoided unless the monitoring and trending

program indicates unacceptable degradation of a system or component

performance.- Spare qualified parts and components should be on - hand to facilitate frequent or impending repairs predicted by the

'5.1
trending activities. The maintenance program should include frequent calibration and servicing of instrumentation mounted on the

engine skid. The recommended maintenance program is described in

Section 5.3.

* Personnel Training - Training programs should reenforce the onsite

maintenance capability for systems and components identified as the

most susceptible to aging degradation with particular emphasis on

1) the engine governor and the instrument and control system.

Plant personnel should be trained in the use of monitoring and

trending in the identification of required maintenance. Maintenance supervisory staff should be provided with failure fault

diagrams with defined corrective actions to enhance maintenance

response speed to malfunctions, especially if they should occur

during a real plant emergency. This training program is described

in Section 5.4.

* System Modifications - The implementation of the above features may

require the installation and calibration of some sensors. These

will vary from engine-to-engine depending on the manufacturer and

details of the installation. These gages and sensors do not need

to be safety-grade equipment and need to be only local read-out

types, such as dial-type pressure gages. The failure of these

gages will not typically lead to engine failure, especially with

the usual presence of plant operators. Modifications are further

described in Section 5.5.

5.1 TESTING, MONITORING AND TRENDING

Section 1 of this report discussed the basis for the diesel generator

testing requirements of Regulatory Guide 1.108. The requirements had the

original purpose of assuring diesel generator availability by routine testing

under accident conditions accompanied by a loss of offsite power as determined by very conservative criteria defined in 10 CFR 50, Appendix K. The

starting and loading times required varied from plant-to-plant, but typically

were 10 to 12 seconds starting time and 30 to 45 seconds to full load.

Recent operating experience and research results discussed in Section 2

have suggested that fast starting and loading during this testing has a deleterious effect on engine reliability and can actually result in some engine

component failures. Furthermore, studies performed by EPRI and others discussed in Section 3 have indicated that the fast starting and loading

requirement mandated by 10 CFR 50, Appendix K is overly conservative.

Instead, these studies indicate that the emergency power requirement is of

the order of 1 to 2 minutes for a loss of coolant accident accompanied by a

loss-of-offsite-power and 5 minutes, or more, for a loss-of-offsite-power

occurring alone.

5.2
5.1.1 Recommended Periodic Testing and Monitoring Procedure

It is recommended that thq-primary purpose of monthly testing"should be

changed to a new approach ofsurveillance testing. The purpose of the

monthly surveillance testing should be to obtain data on key engine performance parameters that indicate-the trends in component and subsystem condition. These performance parameters will provide both short-term and longterm trended information on degraded performance which can be a precursor for

component or.subsystem failure. For each engine manufacturer and Installation, the licensee should be required to establish an overall testing'and

monitoring system that identifies these key paramenters and indicators. A

suggested list of parameters of interest for this purpose is presented in

Appendix A.

The monthly.engine testing should follow the guidelines listed below:

1. The engine should be slow started following the manufacturer's

recommended procedures and loaded to'avoid the fast-start stressor.

Good practice is to prelube the-engine, open-the indicator cocksand roll the engine with the fuel rack in-the off position'and look

for signs of water which would.indicate coolant leakage into a

cylinder. If no leakage is indicated, the' indicator cocks may be

closed and the engine may be started 'normally. Following starting,

it should be allowed to idle for about 5 minutes at either alowRPM, which is not close to any crankshaft critical speed, or at

synchronous speed. During this time, key engine parameters 'should

be recorded and the engine checked for unusual noises or noise

levels. The idle time for two cycle, port scavenged, engines

should be limited to 10 minutes to avoid the possibility of exhaust

manifold fires. The engine should then be brought up to speed and

fully loaded over a period of 10 minutes or more to allow the

pistons and liners to-expand at the same rate'and','thereby,: reduce:

wear on these components.' During acceleration through the'engine's'-

critical speeds, acceleration should be swift, but not at maximum

acceleration, i.e., -at less than full -fuel', rack setting. For -' regulatory purposes,- full engine test load should be defined-as

the plant deisign emergency load which-is,'generally, 70%''to 90% of

the engine nameplate rating.

2. It is recommended that the test run time should be'between 12 and - -14 hours and spread over three working shifts to:provide'the opportunity for plant personnel-to gain familiarity'with the-sounds of a

properly operating engine and operating procedures. Three sets 'of

.data should-be collected at 1-hour intervals, -or-more, during the'

run.period. Due to fuel oil-:torage requirements and other plant-: " specific conditions, the recommended run time may not be entirely

practical at all plants. For these situations, the run time should

be until temperature stability occurs, about one hour, and the ' operational data (Appendix A parameters) should be obtained in two

periods at least one-half hour apart.

5.3
3. The diesel generators should be started approximately 2 hours

before the end of a work shift. After the full engine test load is

achieved and the engine temperatures stabilize, the first set of

performance data should be collected by the shift personnel starting the engine. Another set of data should be collected at 1 to

4 hour intervals; at least one set should be obtained by each

shift.

4. A detailed, written, test procedure and data sheets should be used.

The data sheets should indicate maximum and minimum allowable values for each significant performance parameter recorded. Data from

previous tests should be readily available for comparison purposes.

If any parameters fall outside of the acceptable range, the cause

should be determined by engineering/maintenance staff and the test

discontinued, if the conditions threatens the integrity of the

engine.

5. The test program should be scheduled so that within a few months

each shift has the opportunity to start and load the engine. This

will provide an opportunity for all assigned staff to start the

engine or to observe a start. Alternatively, the engine could be

unloaded, shutdown and restarted each shift during the test to

provide this opportunity. These extra starts will not add to aging

concerns when properly performed on a prelubed and thermally stable

engine.

6. Routine monitoring and trending of the diesel engine base vibrations and diesel start time may be performed. However, it is

important to understand that normal variations in these parameters

are extremely large and can be misleading. Other operational

parameters are more indicative of engine conditions and should be

relied upon instead. These comments do not apply to generator

vibration which should be measured and monitored.

7. Data collection, recording, and instrument calibration processes

and procedures should follow the plant's quality assurance requirements for surveillance of similar safety equipment.

The slow-starting procedure recommended above is typical of the way that

large diesel engines are started by small utilities that use diesels for

base-load or peaking-power applications. In these applications, it is not

unusual to achieve over 100,000 hours of operation in the 35 to 50 year lifetime of an engine even with daily or more frequent starting and stopping. It

is not unexpected to achieve 20,000 hours or more between major overhauls.

Therefore, the starting procedure recommended for these surveillance tests

will not introduce any unusual aging stressors. However, if an engine has

not been fast-started by a reactor emergency response signal in a 6-month

period, it should be fast-start tested in similar fashion as currently

performed to check that the control circuits operate within acceptable

limits.

5.4
An alternate method of fast-starting and loading the engine whicheliminates some of the fast-start stressors is as follows:

* Emergency start the engine to determine if it starts in the

prescribed time (10 to 12 seconds) without load..

* Allow engine to idle for 5 minutes.

* Shut down the engine, then immediately restart it, using the fast- ,

start system. Note: the engine start time and then the time to

full load to determine if the engine reached full load within the

required time period after starting.

This alternate fast-starting procedure will allow oil films and proper

lubrication to be established before load is applied and, therefore, reduce

wear. It should also verify the engine's ability to start and take load

within the prescribed times.

5.1.2 Other Periodic Monitoring

It is recommended that certain aging-related parameters and data should

be collected on a quarterly basis and during plant outages. Fuel oil, lubricating oil, and cooling water analysis should be done quarterly and the

results monitored and trended so that aging mitigation measures and action

can be undertaken. Crankshaft deflection tests should be performed during

the refueling outage and the 110% load test performed. During this overload

test, all data listed in Appendix A should be recorded, but the principal

data of interest are cooling and lubrication system performance parameters,

turbocharger temperatures, and cylinder temperatures.

5.1.3 Testing After Specific Faults and Maintenance

The present general practice is to fast start an engine after a malfunction and/or any significant maintenance to ensure engine operability.

Because of aging concerns, this practice is not recommended. Other tests or

requalification measures may be superior to this practice. For-example,

malfunctions attributable to human error or a clearly defined fault should

require the specific correction for the error or fault and an appropriate

component test at most. Maintenance on a specific engine system or-component

should require a subsystem or component test to ensure operability., In both

examples, the engine should not be started or tested because engine operability is adequately ensured by the less severe test procedure.

In cases of major engine rebuilding where highly stressed moving components are replaced (e.g., crankshaft, connected rods and other components

where metal fatigue is a conc ern or has previously incurred) the engine

should be operated for 3 x 10° stress cycles at design loads before the

engine is returned to full operational status. This number of stress cycles

is generally accepted as sufficient to demonstrate high cycle fatigue -

resistance in ferritic steels (PNL 1985). A load cycle is assumed to be one

revolution for a 2-cycle engine and two revolutions for a 4-cycle engine.

5.5
Engine cylinder liners, gear trains, bearings and, generally, pistons should

not be considered to be highly stressed and should not be subjected to such

stress cycle testing.

5.1.4 Trending of Performance Parameters

Without parameter trending, data monitoring would have little predictive

value to the licensees and the NRC. The practice of trending involves the

plotting of the data obtained for selected performance parameters obtained

during the testing and monitoring activity versus total engine operating

hours. (Note that trending involves only the variable engine parameters

listed in Appendix A. Load and governor settings, for example, are not

parameters that need to be trended, but they need to be held uniform from

test-to-test and carefully recorded for each test.) Data plots should be

retained over the lifetime of the diesel generator unit. To predict failure,

or the time at which performance of the engine, component or subsystem

reaches unacceptable limits, it is necessary to only consult these plots and

observe the rate at which the curves through the data points approach limiting values for each parameter. For some parameters, as discussed earlier,

data taken from test-to-test will continuously trend to these limiting

values, and, for others, the data values will remain constant over a long

period of time, only to degrade rapidly at the end of life. An example of

the latter is the lifetime performance of a bearing. For this case, bearing

temperature and oil pressure will remain virtually constant over long

periods; however, near the end of life, bearing temperature will rise rapidly

and oil pressure will drop. Unfortunately, the temperature rise may be very

quick and progress from about normal to abnormal and failure may occur in a

matter of hours. Fortunately filter deposits in the lube-oil system, oil

analysis and other techniques are available to more directly detect bearing

wear.

A key element of effectively using performance data trends to predict

equipment failure is the prior establishment of limiting values for each

parameter, It is recommended that these values be established for each

diesel generator unit by the licensee using information from the engine and

generator manufacturer. Fortunately, experience with diesel engines applications and electrical generation equipment spans many decades, and acceptable

and unacceptable operation is well understood and recognized. Therefore, the

process of establishing limits on operating parameters should be quite

straightforward. Another point is not all parameters need to be trended nor

do they need to be trended over the entire range of values. For example, an

oil pressure may start out at a value and would be expected to eventually

drop to some minimum acceptable value. Trending may be deferred until the

oil pressure drops to less than 50% of the acceptable operating range.

5.2 INSPECTION

It is conventional practice that diesel engines used for marine and nonnuclear stationary power applications receive weekly, monthly and outage

inspections, each with different goals. When these engines were adapted for

5.6
nuclear plant emergency power application, fewer inspections were assumed to

be required. It was perceived that this service required fewer operating

hours and was less rigorous than conventional engine service. However, it

has been found in the aging research program that nuclear emergency power

service is, in reality, severe service, and a more complete inspection program could be extremely effective in mitigating aging problems and enhancing

start and run reliability. Therefore, a comprehensive inspection program

involving weekly, monthly, quarterly, and annual inspection is recommended.-

This inspection program is described in the following sections.

These inspections should be performed by the same personnel who have

preventative maintenance responsibility for the diesel generators. The

yearly outage inspection team should include a manufacturer's representative

or a diesel consultant in addition to plant personnel. All inspections

should follow a prepared checklist and should be performed according to the

plant's quality assurance program.

5.2.1 Weekly Inspections

In general, weekly inspections include day and shift inspections and

should follow the good practice standards for conventional diesel generator

systems and the manufacturers recommendations. The inspecting personnel - should check for oil and water leaks, signs of vibration-induced loosening of

fasteners, and environmental stressor conditions identified in the aging'

research (Hoopingarner et al. 1987). Such stressors collectively account for

over 40% of diesel generator failures observed. -In addition, the engine

governor and associated linkage should be lubricated and checked for free

operation. Other items to be included in weekly inspection program are as

follows:

* The engine oil/water keep-warm system should be checked for correct

operation and temperature settings.

* Lubricating oil levels should be checked in the engine, governor,

turbocharger and outboard bearing, as applicable. Also check for

water in the oil.

* The engine prelube system should be checked for correct oil level

and pressure, as applicable.

* Engine cooling water inventory and cooling system valve settings,

should be checked.

* The air start system should be checked for air pressure, presence

of moisture downstream of the dryers, and valve settings.

* Breaker and relay status should be checked, especially following

maintenance periods.

5.7
5.2.2 Monthly and Ouarterly Inspections

The monthly and quarterly inspections should concentrate on systems,

subsystems and components identified in the diesel generator aging research

program as being particularly susceptible to aging such as the governor and

the instrument and control system. The power train and generator units need

less attention since they are much less susceptible to aging-related failures

than other engine components.

Monthly inspections should include, but not be limited to, the following

items:

* Check filters and louvers in the combustion air and diesel room

cooling air systems.

* Check the position of the fuel oil duplex filter manual valve to

assure that the fuel is being directed through one filter with the

other held in reserve.

* Check for vibration loosening of fasteners or vibration induced

damage. Should be done while the engine is operating for best

results.

* When a lubricating oil filter is changed, sample the surface and

cut open the filter and visually examine it for unusual contamination or wear particles.

* With the engine running, check the engine and associated subsystems

for oil or water leaks, and check for exhaust leaks.

* With engine running under load, check diesel exhaust smoke color or

take smoke meter reading.

The monthly inspection should also include the weekly inspection items and

can replace one weekly inspection.

Quarterly inspections should include the following items:

• Clean and inspect the strainers and filters in the starting air

system.

* Sample the fuel oil in the storage and day tanks for 1) gum or

jelly formation and 2) bacterial growth at any water condensate

fuel oil interfaces.

* Sample the lubricating oil and analyze for wear particles, water

contamination, and oxidation.

* Inspect the fuel oil filters and replace at the recommended

frequency or as shown by station procedures.

5.8
* Inspect the combustion air and exhaust manifolds, especially in'

two-cycle engines, for oil and-carbon deposits that could

constitute a fire hazard.,

* Inspect relay enclosures and control cabinets for dust and dirt and

clear where necessary.

* With the engine operating, visually check all skid-mounted equipment for vibration loosening and damage, especially valve operators, instruments', equipment mounts, and tubeland pipe fittings. -

* Check instrument and control settings and perform tests of any

components in this system that have been prone to failure or

deterioration, as shown by plant records.

* Check governor oil level, overspeed governor setting and governor

performance in controlling speed and frequency.

These monthly and quarterly inspections probably have the most value if

scheduled to follow closely the monthly start-run test. Signs of vibration-'

induced loosening and problems associated with the environmental stressors

may be detected before they have time to progress to a more serious condition

or to failure.

5.3 MAINTENANCE

A preventative maintenance program should be coupled with the inspection

program recommended in Section 5.2 to discover and correct problems before

they threaten the reliability of the diesel generator. Program attention

should be principally directed at the important identified aging stressors

and equipment particularly susceptible to these stressors. -For example,

vibration was the stressor identified to cause the highest percentage failure

in diesel generator aging studies (Hoopingarner et al. 1987). Preventative

maintenance should focus on aging and wear effects of this stressor and ' emphasize calibration, repair, and replacement of skid-mounted instrumentation, because of its potential sensitivity to this vibration.

One piece of equipment that should be given particular attention in the

preventative maintenance program is the governor, because its failure is a

major cause of engine unavailability. Governors must have regular and careful maintenance, adjustment, and preventative maintenance based on a firm.

understanding of the governor and'its service needs.,

It is recommended that the spare parts inventory for each installation

be given careful consideration to assure that adequate spare parts are on

hand to allow rapid repair/replacement of those parts that the trending pro-.

gram identifies as requiring frequent attention. With an ample parts inventory on hand, failures or approaching failure can be dealt with

expeditiously.

5.9
Finally, it is strongly recommended that an engine not be torn down

solely for the purpose of inspection, unless the monitoring and trending program provides evidence of an internal malfunction or impending malfunction.

It was indicated earlier that such disassembly could actually detract from

engine reliability. This should not be interpreted to imply that engine

components or subsystems with a known qualified lifetime should be operated

beyond this lifetime, simply because monitoring and trending shows no difficulties. However, such positive monitoring and trending results should be

considered by the regulatory staff to, perhaps, justify a longer qualified

lifetime for the component or subsystem.

5.4 TRAINING

It is recommended that a minimum of two persons for each nuclear unit be

given maintenance training equivalent to that offered by diesel engine and

governor manufacturers for their customers. Such persons should be at the

appropriate working level; these persons should be used to train other

personnel.

Additional training should be given all maintenance personnel on those

components and systems most susceptible to aging failure and on the effects

of the identified stressors for aging. The governor and instrumentation and

control system should be given particular attention in the training program.

The development and use of failure/fault diagrams by licensees is also

recommended. These diagrams are trouble-shooting aids which list the most

common causes of each specific malfunction, such as failure to start, and a

recommended sequence of inspections and corrective actions to correct the

malfunction. The availability of such information could conceivably permit

the recovery and starting a malfunctioning engine in a real plant emergency

within several minutes. Training would be required to implement this

recommendation.

5.5 MODIFICATIONS

Many diesel generators in nuclear plants have already been equipped with

pre-lube and keep-warm systems to mitigate the wear and aging effects of

fast-start testing. It is recommended that any engines which have not been

so equipped should be provided with these systems. In addition, a method of

using the auxiliary pump or other equipment should be developed to assist

the lubrication of the upper crankshaft assembly of opposed piston engines

before planned or test starts. Such a system would reduce wear and aging of

this assembly. Other engine types would also benefit from this practice for

valve deck lubrication and various other components such as the turbocharger

that are not presently receiving adequate lubrication during the fast

starting and loading time period.

To avoid aging influence of vibration on the skid mounted instrumentation and controls, it is recommended that they be moved to another location

5. 10
not subject to vibration where this is practical. This will avoid one of the

most important stressors to the instrument and control system and could

result in a substantial increase in the overall reliability of the diesel

generator.

5.11
6.0 NPAR PROGRAM DEVELOPMENT RECOMMENDATIONS

The integrated program of testing, monitoring, trending, inspection and

training described in this report is complex and would benefit from a pilot

development program Implemented with the cooperation of industry at one or

more nuclear power units. The objectives of this program are: 1) to create

a program that will serve as a guide to all utilities in the development of

their own effective and regulation-compliant program, 2) provide NRC with

the background information on the implementation and control of such a program, 3) develop data on the benefits of this program on diesel generator

reliability, and 4) provide preliminary cost-benefit'data for industry motivation. It is recommended that this work involve an independent organization

which can provide required technical supervision, evaluation of the results,

statistical analyses, cost/benefit studies, and comparisons with the reliability of similar diesel generators in other plants not fully compliant with

the provisions of this program.

The work may be performed in 5 tasks as follows:

Task 1--Program Implementation - This task should provide the

groundwork for the implementation of the testing, surveillance, and

trending activities. It will include the development of

- testing procedures

- lists of specific monitoring data to be acquired

- definition of acceptable ranges of monitored data

- data sheets and recording procedures

- trending procedures.

. Task'2--Equipment Modifications - Review the installation of any

instrumentation needed for the implementation of the monitoring

program developed in Task 1 on the diesel generator to be studied.

Implement other equipment modifications recommended in this report

as necessary. Such equipment modifications are anticipated to be

minimal. Present diesel-generator installations have most of the

necessary instrumentation already in place.

Task 3--Training of Personnel - In this task, plant personnel

should be trained in the performance of the testing, monitoring,

and trending program developed in Task 1. Maintenance personnel

should be given other maintenance training as recommended in this

document.

6.1
* Task 4--Monitoring and Trending - The program developed in Task 1

should be performed over a period of less than 1 year. Modifications to procedures, data acquisition methods, and items will be

made as the need is identified to streamline the program and to

achieve maximum benefits.

* Task 5--Data Analysis and Reportinc - Maintenance activities and

failure rates experienced during the period of study should be

analyzed to determine reliability improvements and projected cost

savings of this program. These results will be reported to the NRC

and industry by means of periodic technical reports, topical

reports, and journal articles.

It is anticipated that the above program could be completed within one year

to obtain valid results, after cooperation agreements and other preliminary

actions are completed. If results are desired on a faster schedule, accelerated testing could be accomplished by a more frequent engine start-run and

monitoring schedule during the implementation period only.

6.1 OTHER DEVELOPMENTAL ACTIVITIES

It is recommended that a program be undertaken to develop the necessary

hardware and software to analyze the status of the diesel generator control

system and to report its status to operating personnel. These systems

should, continuously or on demand, 1) determine the status of the engine

emergency start circuits, unloaders, sequencers, relays, contacts, and all

wiring and 2) provide a warning signal to test/operations personnel in case

of a possible malfunction or fault. The development of such a system is not

necessary for the implementation of the recommended testing, monitoring and

trending program; however, its availability will provide an enhanced state of

diesel generator reliability, since it will enable plant staff to determine

the state of availability of this system without subjecting the diesel generator to the aging stressors associated with fast start and run tests now

performed to provide this information. Along with this development, regulatory requirements must be reevaluated and revised to take advantage of this benefit.

6.2
7.0 RECOMMENDED REGULATORY IMPLEMENTATION

The NPAR aging study was originally intended to develop data and recommendations for NRC consideration related to potential safety problems caused

by the aging process. The general application of this study was extended in

Phase II to use the diesel research information for 1) diesel reliability

improvement, 2) plant technical specification modification, 3) improvement of

resource application by the NRC and the utilities, and 4) development of

specific recommendations to change some regulatory requirements.- All of

these end uses of the research have been accomplished or are under active

consideration. Collectively, the safety implications of these changes and - recommendations are important.

7.1 REGULATORY GUIDES

Current regulatory guides and requirements for fast-start testing, fast

engine loading, and overload testing are being reconsidered by the NRC. In

association with certain nuclear plant technical specifications, these current guides and requirements may lead to greater future safety problems and

unreliability. Regulatory guide requirements for routine testing have been

redefined to include slow-start testing, slower engine loading, and diesel

overload testing objectives that can be supported by the study results.

Nuclear Regulatory Guide 1.108 addressing diesel-generator testing requirements will be withdrawn and combined into a new single Regulatory Guide 1.9,

"Selection, Design, Qualification, Testing, and Reliability of Diesel Generator Units Used As Onsite Electric Power Systems at Nuclear Power Plants."

Diesel Statistical probabilities, especially statistics based on 100 valid

start'and run tests, are very difficult to defend on a technical basis due to

the very long time period needed to collect the data (maybe 5 years). A

better regulatory approach is a monthly operational readiness test ("health

checkup") of the diesel generator system. This concept has been included in

the 1989 draft of Regulatory Guide 1.9. This draft is supported by the

research results.

Regulatory Guide 1.137, Fuel-Oil Systems For Standby Diesel Generators,

has not been revised since October 1979. Aging considerations for the system

and the fuel oil contents needs to be addressed. The scope of the changes

should include the following important aging related considerations:

* The licensees should be encouraged to operate the engines and thus

use and replace oil. Reasonable regulatory guidelines to match

Regulatory Guide 1.9 recommendations need to be developed to meet

this objective. For older plants especially, this could include

the relaxation of oil-on-hand guidelines to 3 to 4 days minimum.

With modern transport possibilities, especially heavy-lift

helicopters, this is reasonable.

• The recommended tank lining materials need to be defined better.

7.1
* For common cause failure considerations, tank and equipment

redundancy needs to be addressed.

* A few other details need to be addressed to conform to revised

Regulatory Guide 1.9 and proposed technical specification

guidelines.

7.2 TECHNICAL SPECIFICATIONS

The plant standard technical specifications related to the dieselgenerator system should be modified to add to safety assurance. The research

information gathered in the NPAR Diesel program confirms opinions developed

by industry and regulatory personnel over many years of experience that current technical specifications are not always conservative nor effective. In

particular, those related to fast engine starting and loading, frequent sensor calibration, engine startup during abnormal plant conditions, frequent

starts and special test requirements need to be carefully evaluated. This

process has been started by the NRC staff.

7.2
8.0 REFERENCES

Hoopingarner, K.R ., J. W. Vause, D. A. Dingee, J. F. Nesbitt. 1987. Aging

of Nuclear Station Diesel Generators: Evaluation of Operating Experience.

NUREG/CR-4590, PNL-5832, Vol.-1, prepared by Pacific Northwest Laboratory for

the U.S. Nuclear Regulatory Commission, Washington, D.C.

Hoopingarner, K. R. and J. W. Vause. 1987. Aging of Nuclear Station Diesel

Generators': Evaluation of Operating Experience. Workshop. Volume Il '.

NUREG/CR-4590, PNL-5832, Vol. 2, prepared by Pacific Northwest Laboratory for

the U.S. Nuclear Regulatory Commission, Washington, D.C.

AEC Technical Report. June 1975. Diesel Generator Operating Experlence at.

Nuclear Power Plants. OOE-ES-002. '

NRC Regulatory Guide 1.108 Revision 1. 1977. Periodic Testing of Diesel

Generator Units Used-as Onsite Electric Power Systems at Nuclear Power

Plants.

10 CFR 50, Appendix K. Code of Federal Regulations, Chapter 10, Part 50

Appendix K.

Beard, J. T. September 1982. Recent Operatina Experience with Emeraencv

Diesel Generators. Presentation to the NRC/ACRS Subcommittee on AC/DC Power

Systems.

NRC Technical Report, NUREG/CR-2989. 1983. Reliability of Emeraency Onsite

AC Power'Systems.

NRC Generic Letter, 83-41. December 1983. Fast Cold Starts of Diesel

Generators.

NRC Generic Letter, 84-15. July 1984. Proposed Staff Actions to Imorove and

Maintain Diesel Generator Reliability.

Davis, T., A. Shafaghi, R. Kurth, and F. Leverenz. 1985. Importance Ranking

Based on.AAina Considerations of Components Included in Probabilistic Risk

Assessments. NUREG/CR-4144, PNL-5389, Pacific Northwest Laboratory,

Richland, Washington.

Stoller, S. M. 1982. Nuclear Power Experience. S. M. Stoller Corporation,

Boulder, Colorado.

TDI Owners Group (TDI OG). 1985. TDI Diesel Generator. Desian Review and

Ouality Revalidation Report. Revision 1. Prepared by TDI Owners Group.

Hoopingarner, K. R., B. J. Kirkwood, P. J. Louzecky. 1988. Study Group

Review of Nuclear Service Diesel Generator Testing and Aging Mitiaation.

PNL-6287, Pacific Northwest Laboratory, Richland, Washington.

8.1
U.S. NRC. 1979. Regulatory Guide 1.9: Selection. Design. and Qualification

of Diesel-Generator Units Used as Standby (Onsite) Electric Power Systems at

Nuclear Power Plants. Revision 2. U.S. Nuclear Regulatory Commission,

Washington, D.C.

U.S. NRC. 1979. Regulatory Guide 1.137: Fuel-Oil Systems for Standby

Diesel Generators. Revision 1. U.S. Nuclear Regulatory Commission,

Washington, D.C.

Muralidharan, R. 1986. Effect of Diesel Start Time on BWR/6 Peak Cladding

TemDerature-Licensing Basis Sensitivity Calculations. EPRI-NSAC-96, Electric

Power Research Institute, Palo Alto, California.

Schwarz, W. R. 1988. The Effect of Diesel Start Time Delay on Westinghouse

PWRs. EPRI-NSAC-130, Electric Power Research Institute, Palo Alto,

California.

U.S. NRC. 1988. Regulatory Guide 1.155: Station Blackout. U.S. Nuclear

Regulatory Commission, Washington, D.C.

Nowlan, F. S. 1978. Reliability-Centered Maintenance. AD-A066-579,

prepared by United Airlines for Office of Assistant Secretary of Defense,

Washington, D.C., December 1978.

Prichard, J.W. 1984. "Equipment Age-Reliability Analysis." Naval Engineers

Journal, September 1984.

PNL. 1985. Review of Resolution of Known Problems in Engine Components for

Transamerica Delaval Inc. Emergency Diesel Generators, PNL-5600, Pacific

Northwest Laboratory, Richland, Washington.

Nuclear Engineering International. 1987. EPRI Finds the Reliability of U.S.

Diesel Generators is Excellent. May 1987, pp. 54-55.

Wyckoff, H. L. 1986. The Reliability of Emergency Diesel Generators at U.S.

Nuclear Power Plants, EPRI-NSAC-108, ELectric Power Research Institute,

Palo Alto, California.

8.2
:

APPENDIX A

RECOMMENDED DIESEL GENERATOR MONTHLY TEST PARAMETERS

..
APPENDIX A

RECOMMENDED DIESEL GENERATOR MONTHLY TEST PARAMETERS

General Data

Date of test

Time of test

Ambient air temperature

Barometric pressure

Relative humidity (if convenient)

Total hours on engine (hour meter)

Governor setting (manual or automatic)

kW/load

Volts

Kilovars

A. 1
Parameter

General Data Required Primary Use of Data

Generator Data (Alternator)-

Alternator winding temperature(s) 1.

2.

Evaluate condition of windings

Detect loss of cooling capacity

Alternator bearing temperature (One or two

bearings) (Oil temperature)

1. Detect bearing problems

Engine Cooling Water

Water pressure to engine 1 .

2.

3.

Or

Water temperature to and from engine

(water pressure at these same points also

checks these conditions)

1.

2.

3.

Ensure engine operability (mission safety)

Detect plugged jacket water system

Check pump condition

Monitor control val-ve operation

Monitor heat exchanger performance

Higher engine load will increase temperature

difference

Monitor heat exchanger fouling

Detect incorrect control valve operation

Or

Water temperature to and from

cooler (could be radiator)

engine water 2.

2 .

Water temperature to and from raw water cooler 1.

2 . Monitor fouling

Water pump operation

Fouling and water flow of turbocharger

Monitor turbocharger loading

Water temperature to and from turbocharger

(where water cooled). Exhaust gas AP and

AT may also be used.

Water temperature to and from turbocharger

after cooler

Water pressure and temperature to and from

L.O. cooler

1.

2 .

1. Monitor cooler fouling

1. Monitor cooler fouling
we

Parameter

General Data Required.

Lubricating Oil

'Oil pressure to engine

,Oil temperature to and from enginer(oil sump

temperature)

oil pressure to and from L.O. filter

0il,temperature to and from L.O.. cooler

Oil pressure to turbocharger

Oil0temperatureto -,and from turbocharger

Air to Enqlne . - ,

Ambient air temperature, barometric pressure

and relative humidity (Note: These are on

pave A.1.also.,)

Air pressure and temperature to turbocharger

Air pressure to-and from after cooler

1.

2.

3.

4.

1 .

2.

3.

1.

2.

2.

2.

1 .

2-.

1.

' I- lr. '11,, 5*

Ensure engine operability

Detect filter plugging

Troubleshooting'.for regulating valve, engine

,wear -

Detect incorrect oil, viscosity too low or high

Detect fouling'of heat exchanger

Monitor control valve operation

Detect low oil flow..

Detect filter element plugging

Detect-damaged elements (low delta p)

Detect fouling.

Monitor control valve operation

Detect incorrect pressure regulating valve

setting - Ensure 'engine operability

Monitor turbocharger bearings

, It.. 1., PrimarvUse of Data

1. Needed for monitoring "standard air conditions"

for,-efficiency calculations or trouble-shooting

1. Turbocharger efficiency calculations

1.- Turbocharger efficiency calculations ' 2. Air-side cooler fouling detection
Parameter

General Data Reouired Primary Use of Data

Exhaust

Exhaust temperature out of each cylinder

Cylinder No. 1

Cylinder No. 2

Etc.

Exhaust temperature to turbocharger turbine

(preturbine temperature), more than one

thermocouple may be required

Exhaust temperature from turbine

1. Monitor fuel injector performance

2. Detect broken rockerarms, worn rings or valve

problems

3. Acceptable balance between cylinders

1.

2.

Turbocharger efficiency

Safety to ensure temperature limit to turbocharger is not exceeded

1. Monitor turbocharger performance and condition

Fuel Oil

Fuel oil pressure to and from engine filter 1. Detect filter plugging or damage

Fuel oil pressure to and from fuel oil pump 1.

2.

Monitor regulating valve adjustment

Monitor pump wear

Fuel Pump Rack Setting

All cylinders 1. Compare to cylinder exhaust temperatures for

performance (both should be reasonably even)

2. Monitor cam timing

Miscellaneous Data

Turbocharger R.P.M. 1. Monitor turbine efficiency

2. Detect fouling of compressor discharge, turbine

conditions, or blade fouling

3. Detect poor engine combustion

Crankcase vacuum or pressure 1.

2.

Monitor excessive ring blow-by

Detect faulty ejector/blower
Parameter

General Data Reauired Primary Use of Data

Misce, la eo Dt . (cntnud

Miscellaneous Data (continued)

Amount of oil added

Lubricating oil analysis (quarterly

recommended)

Engine cooling water analysis (quarterly

recommended)

1. Monitor engine operation, ring wear and valve

guide wear - . ''I 

1.

2.

1 .

2.

Detect wear particles

Monitor fuel oil dilution

Detect corrosion products

Ensure correct water chemistry

More optional quarterly monitoring could

;Include: - I I

en

Firing pressures for each cylinder

Fuel oil metering/heat rate

1. Information on ring, valve, and combustion

conditions when compared to rack position and

exhaust temperature.

1. 10% degradation in fuel consumption rate is

indicative of problems developing such as

injector fouling.
NUREG/CR-5057

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NRC FORM 336 UiSl NUCLEAR UILAtTORYCOSUISON 1. REPORTtNUMBER(A8S9edhPP: g-OPSaddV.Aio.. fWI

320s.327 BIBUOGRAPHIC DATA SHEET NUREG/CR-5057

SEE INSTRUCTIONS ON THE REVERSE PNL-6397

2. TITLE ANO SUBTITLE S. LEAVE BLANK

Aging Mitigation and Improved Programs for

Nuclear Service Diesel Generators 4. DATE REPORT COMPLETED

MONT" | VYEAR

S, AUTHOR(SI October 1989

K.R. Hoopingarner S. DATE REPORT ISSUED

F.R. Zaloudek MONTH YEAR

December 1989 7. PERFORMING ORGANIZATION NAME AND MAILING ADDRESS fIaCh# *S Co*J 8 PROJECTfTASIWUORK UNIT NUMBER

Pacific Northwest Laboratory ,IN OR GRANT "USTER

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10. SPONSORING ORGANIZATION NAME AND MAILING ADDRESS fies*1 Ze Cee lie, TVPE OF REPORT

Division of Engineering

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U.S. Nuclear Regulatory Commission bPERIOD COVERED ilusiw 41b.i

Washington, DC 20555

12 SUPPLEMENTARY NOTES

13. ABSTRACT ovo e r)

Recent NRC sponsored aging research work on nuclear service diesel generators has

resulted in a recommendation that an improved engine management program should be adopted

for aging mitigation and reliability improvement. The center of attention should be to

ensure diesel-generator operational readiness. This report emphasizes a "healthy engine

:oncept" and recommends parameters to be monitored to determine engine condition. The

)roposed program and approach recommended in this report represent balanced management

iherediesel generator testing, inspections, monitoring, trending, training, and maintenance all have appropriate importance.

Fast-starting and fast-loading tests of nuclear service diesels causes very rapid

wear of certain engine components. This report documents this aging stressor. Current

periodic intrusive maintenance and engine overhaul practices have been found to be less

favorable for safety assurance than engine overhauls based on monitoring and trending

results or on a need to correct specific engine defects. This report recommends that

the periodic overhaul requirements be re-evaluated.

Diesel generator research on aging and wear is sponsored by the U.S. Nuclear

Regulatory Commission (NRC), Office of Nuclear Regulatory Research. The research reported

in this report was conducted by Pacific Northwest Laboratory (PNL), which is operated

for the Department of Energy by Battelle Memorial Institute. 14 DOCUMENT ANALYSIS-. KEYWORCDSESCRIPTORS - - -

Nuclear plant-aging research, emergency diesel generator, EDG, aging

stressor, aging degradation, EDG management, emergency power,

recommended regulatory implementation

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