Information Notice 1998-41, Spurious Shutdown of Emergency Diesel Generators from Design Oversight
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D.C. 20555-0001
November20, 1998
NRC INFORMATION NOTICE 98-41: SPURIOUS SHUTDOWN OF EMERGENCY DIESEL
GENERATORS FROM DESIGN OVERSIGHT
Addressees
All holders of operating licenses for nuclear power reactors, except for those who have ceased
operations and have certified that fuel has been permanently removed from the reactor vessel.
Purpose
The U.S. Nuclear Regulatory Commission (NRC) Is issuing this information notice to alert
addressees to recent inspection findings related to a design deficiency that leads to an
automatic shutdown of the emergency diesel generator (EDG) when the starting air supply
pressure depletes. It is expected that recipients will review the Information for applicability to
their facilities and consider actions, as appropriate, to avoid similar problems. However, suggestions contained In this information notice are not NRC requirements; therefore, no
specific action or written response Is required.
Background
The Riverbend Nuclear station has three emergency diesel generators. Two of these EDGs are
built by Tansamerica Delaval, and are individually supported by non-safety related air
compressors, powered by non-classl E power supply, that maintain sufficient Inventory of high
pressure starting air in the safety related accumulators. This air provides the motive force for
the engine starting system and also supplies a pneumatic control logic system that trips the
EDG when certain non-emergency engine parameters are sensed to exceed its set limits. The
air accumulators are maintained at 235-250 psig, and control air pressure for the logic system is
maintained by a regulator at approximately 60 psig. The control air maintains a static air
pressure on engine sensors during engine operation. Air pressure loss, following an engine
start, may be due to system leakage or through a tripped engine protection sensor that reached
an unacceptable level. When the EDG Is operating In the emergency mode, the declining
control air pressure first unbypasses the protective trips that were bypassed for the emergency
mode, and further decrease In pressure results in an engine trip. The starting air system Is
equipped with a pressure switch that actuates an alarm In the main control room If the air
accumulator pressure drops below 210 psig. The alarm response procedure requires that an
operator Investigate the problem at the engine control panel. The operating procedure requires
a supplemental air source If EDG operation is required for more than 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> while the offsIte
power Is unavailable to power the associated air compressor.
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IN 9841 November 20, 1998
Description of Circumstances
On November 14, 1989, at River Bend Nuclear Station, the Division I EDG tripped within one
minute after starting, as a result of a failed temperature sensor for the No. 7 main bearing. As
designed, the sensor bled control air pressure down from 60 psig to 10 psig, and the diesel
control logic card, sensing the low pressure, tripped the EDG. During a telephone conversation
with the NRC on January 3, 1990, the NRC staff questioned long-term operability of the
emergency diesels, since sufficient leakage from the control air system, with the compressors
unavailable (in the absence of non-1 E power), would eventually cause the non-emergency
diesel trips to become unbypassed and could trip the EDG. The NRC staff questioned the
availability of a long term supply of control air. In response, the licensee reviewed procedures
and made changes to ensure availability of a long-term air supply.
On June 24, 1998, as a result of questions from NRC inspectors, the licensee discovered that
they had failed to complete necessary measures to ensure a long-term air supply for EDG
control air. Although operations had written procedures for Installing a backup air supply, plant
staff had neither assembled and staged the materials nor demonstrated the ability to supply
control air within 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> as stated in the procedure. On June 25, 1998, the licensee completed
staging the materials, Including charged air bottles, and demonstrated the ability to connect the
backup air supplies within approximately 30 minutes. The licensee is evaluating the appropriate
permanent resolution to ensure a long-term supply of control air.
Discussion
The problems described emphasize the need for licensees to ensure reliability of systems that
perform critical support functions for safety-related systems. Licensees are responsible for
ensuring the capability of safety related systems to perform their functions during design
events. In some EDG designs, the starting air system also performs a critical control function
that may necessitate ensuring availability of the starting air system throughout the duration of
certain analyzed events, such as station blackout. The same problem existed at Comanche
Peak Nuclear station and it was resolved by Improving the design with safety grade power
supply and air compressor for continued supply of air when the EDG is operating. Other
support systems may exist that perform critical support functions for long-term reliability of
safety related systems. In addition, relying on operator action as a corrective measure for an
inadequate design Is inappropriate without training the personnel Involved In procedures that
implement the compensatory measures.
This Information notice requires no specific action or written response. However, recipients are
reminded that they are required to consider Industry-wide operating experience (including NRC
information notices) where practical, when setting goals and performing periodic evaluations
IN 98-41 November 20, 1998 under Section 10 CFR 50.65, "Requirement for Monitoring the Effectiveness of Maintenance at
Nuclear Power Plants." If you have any questions about the Information in this notice, please
contact one of the technical contacts listed below or the appropriate Office of Nuclear Reactor
Regulation (NRR) project manager.
Roe, Acting Director
sion of Reactor Program Management
Office of Nuclear Reactor Regulation
Technical contacts:
Charles Marschall, RIV
301-415-1176
817-860-8185 E-mail: txk@nrc.gov
E-mail: csm~nrc.gov
Attachment: List of Recently Issued NRC Information Notices
hi
>Attachment
November 20, 1998
Page 1 of I
LIST OF RECENTLY ISSUED
NRC INFORMATION NOTICES
Information
Date of
Notice No.
Subject
Issuance
Issued to
98-40
98-39
Design Deficiencies Can Lead
Reduced ECCS Pump Net Positive
Suction Head During Design-Basis
Accidents
10/26/98
98-38
98-37 Summary of Fitness-for-Duty
Program Performance Reports for
Calendar Years 1996 and 1997 Metal-Clad Circuit Breaker
Maintenance Issued Identified
By NRC Inspections
Eligibility of Operator License
Applicants
Inadequate or Poorly Controlled
Non-Safety-Related Maintenance
Activities Unnecessarily Challenged
Safety Systems
Threat Assessments and
Consideration of Heightened
Physical Protection Measures
10/24/98
10/15/98
10/01/98
9/18/98
9/4/98
All holders of operating licenses
for nuclear power reactors, except
those licensees who have
permanently ceased operations
and have certified that fuel has
bee permanently removed from
the vessel
All holders of operating licenses
for nuclear power reactors
All holders of operating licenses
for nuclear power reactors.
All holders of operating licenses
for nuclear power reactors, except those who have
permanently ceased operations
and have certified that fuel has
been permanently removed from
the reactor vessel.
All holders of operating licenses
for nuclear power reactors
All U.S. NRC fuel cycle facilities
power and non-power reactor
licensees (Safeguard Issues, not
for public disclosure.)
98-36
98-35 OL = Operating License
CP = Construction Permit
IN t41 November 20, 1998 under Section 10 CFR 50.65, "Requirement for Monitoring the Effectiveness of Maintenance at
Nuclear Power Plants." If you have any questions about the information in this notice, please
contact one of the technical contacts listed below or the appropriate Office of Nuclear Reactor
Regulation (NRR) project manager.
Orig /s/'d by
Jack W. Roe, Acting Director
Division of Reactor Program Management
Office of Nuclear Reactor Regulation
Technical contacts:
Charles Marschall, RIV
301-415-1176
817-860-8185 E-mail: txk@nrc.gov
E-mail: csm@nrc.gov
Attachment: List of Recently Issued NRC Information Notices
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Tech Editor concurred on 10/8/98 DOCUMENT NAME: S:\\DRPMSECY\\98-41.IN *SEE PREVIOUS CONCURRENCE
To receive a copV of this document, indicate in the box C=Copy w/o attachmentenclosure E=Copy with attachment/enclosure N = No copy
OFFICE
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DATE
11/14/98
11/15/98
111/16/98_
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OFFICIAL RECORD COPY
IN 98-xx
November xx, 1998 under Section 10 CFR 50.65, "Requirement for Monitoring the Effectiveness of Maintenance at
Nuclear Power Plants." If you have any questions about the information in this notice, please
contact one of the technical contacts listed below or the appropriate Office of Nuclear Reactor
Regulation (NRR) project manager.
Jack W. Roe, Acting Director
Division of Reactor Program M agement
Office of Nuclear Reactor R ulation
Technical contacts:
Charles MarscI, RIV
301-415-1176
817-860-81 E-mail: txk@nrc.gov
E-mail: cs @nrc.gov
Attachment: List of Recently Issued NRC Information No ces
DOCUMENT NAME: G:kTXKAEDGIN1 To receive a copy of this document, indicate in the box C=Copy w/o attachmen nclosure E=Copy with attachment/enclosure N = No copy
OFFICE
PECB:DRPM
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NAME
TKoshy
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DATE
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1I5/98 T./98 OFF
IAL RECORD COPY
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- -oIN 98-xx
November xx, 1998 staff had not assembled and staged the materials and demonstrated the ability to supply control
air within 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br />, as called for in the procedures. The licensee initiated a condition report to
pressure decreased. In addition, the licensee discovered that the loss of control air pressure
would cause the diesels to trip, perhaps in as little as fourteen hours. Early on June 25, plant
staff completed staging the materials, including charged air bottles, and demonstrated the
ability to connect the backup air supplies within approximately 30 minutes. The licensee is
evaluating the appropriate permanent resolution to ensure a long-term supply of control air.
Discussion
The problems described emphasize the need for licensees to ensure reliability of systems that
perform critical support functions for safety-related systems. Licensees are responsible for
verifying the adequacy of the design of safety-related systems through performance of design
reviews, use of alternate or simplified calculational methods, or by performance of a suitable
testing program. In some EDG designs, the starting air system also performs a critical control
function that may necessitate ensuring availability of the starting air system throughout the
duration of certain analyzed events, such as station blackout. Other support systems may exist
that perform critical support functions for long-term reliability of safety related systems. In
addition, relying on operator action as a long-term corrective measure foran inadequate design
is inappropriate without training the personnel Involved in procedures that implement the
compensatory measures.
This information notice requires no specific action or written response. However, recipients are
reminded that they are required to consider industry-wide operating experience (including NRC
information notices) where practical, when setting goals and performing periodic evaluations
under Section 10 CFR 50.65, "Requirement for Monitoring the Effectiveness of Maintenance at
Nuclear Power Plants." If you have any questions about the information in this notice, please
contact one of the technical contacts listed below or the appropriate Office of Nuclear Reactor
Regulation (NRR) project manager.
Jack W. Roe, Acting Director
Division of Reactor Program Management
Office of Nuclear Reactor Regulation
Technical contacts:
Charles Marschall, RIV
301-415-1176
817-860-8185 E-mail: txk@nrc.gov
E-mail: csm@nrc.gov
Attachment: List of Recently Issued NRC Information Notices
DOCUMENT NAME: G:\\TXK\\EDGIN1 To receive a copy of this document, Indicate In the box C=Copy wlo attachmentlencosure E=Copy with attachment/enclosure N = No copy
OFFICE
PECB:DRPM
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CPEill: (A)D:DRPMil
NAME
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DATEOI/98 I/98 AL/98 R
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/C/98 OFFICIAL RECORD COPY