Information Notice 1991-13, Inadequate Testing of Emergency Diesel Generators (Edgs)
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D.C. 20555
March 4, 1991 NRC INFORMATION NOTICE NO. 91-13:
INADEQUATE TESTING OF EMERGENCY
DIESEL GENERATORS (EDGs)
Addressees
All holders of operating licenses or construction permits for nuclear power
reactors.
Purpose
This information notice is intended to alert addressees to inadequacies in the
testingof emergency diesel generators at'nuclear power plants. Specifically, some EDG testing has not adequately verified the capability of the-EDG to carry
its maximum expected loads and other tests have failed to properly verify the
operation of the load shedding logic for the EDG. These testing deficiencies
indicate that other licensees may have similar deficiencies that have not yet
been detected. 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-do-not constitute NRC requirements; therefore no specific action or
written response is required.
Description of Circumstances
Yankee Atomic Electric Company, the licensee'for the Yankee Nuclear Power
Station (Yankee Rowe), recently identified that the EDGs at the Yankee'Rowe
plant were undersized for their maximum accident electrical load demand. The
EDGs failed to reach their technical specification (TS) required loading of
400 kilowatts (kW) while connected in parallel to the electrical grid.' The
licensee then retested the EDGs using a resistor bank in place of the grid.
Using this test configuration, Yankee Atomic determined that the frequency of
the generator dropped to 58 hertz with a maximum electrical output of 385 kW.
The licensee attributed the reduction in power output, in part, to high ambient
air temperatures that reduced engine power and cooling. The licensee had not
considered the effect of ambient air temperature during previous testing.
The
existing air temperature was within design basis limits. Although high
ambient air temperature was the immediate cause of the failure to attain
400 kW, the root cause was the fact that the engines were undersized. The
manufacturer's rating of 400 kW also failed to consider the effects of ambient
air temperature. The licensee calculated that the dependable capacity of these
EDGs was between 359 kW and 399kW. Yankee Atomic eventually replaced all
3 EDGs with models capable of producing 600 kW (450 kW continuous) because the
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March 4, 1991 estimated electrical load on the EDGs is very close to 400 kW and modifications
to the original EDGs failed to raise their output capabilities. The Omaha
Public Power District, the licensee for Fort Calhoun Station, Unit 1, reported
a similar problem with their EDGs.
At Fort Calhoun, the EDGs could temporarily
achieve their design rating at high ambient temperatures, but they could not
maintain this power level for an extended period of time.
At the Vermont Yankee Generating Station, during a safety system functional
inspection, the U.S. Nuclear Regulatory Commission (NRC) staff determined that
the surveillance testing of the station EDGs was inadequate.
The staff found
that there was insufficient electrical loading during testing as well as
insufficient compensation for the expected electrical power factor (pf).
Specifically, the plant surveillance test for the EDGs required that the EDGs
maintain a load of 2500 to 2750 kW, which is equivalent to 2500 to 2750
kilovolt-amperes (kMA) at pf-1.0.
The licensee considered this limit suffi- cient to meet the maximum load of 2471 kW specified in the final safety analy- sis report (FSAR).
However, during subsequent analysis-, the licensee
determined that the worst-case EDG loading could actually reach 2751 kW.
In
addition, the EDG would realistically experience an electrical power factor of
0.85 lagging, causing the actual generator output current to be significantly
higher (i.e., assuming generator output voltage is maintained roughly constant, generator output current and kYA at pf=0.85 are approximately 1.18 times the
generator output current and kVA at pf- 1.0.) Therefore, the existing surveil- lance did not adequately demonstrate the capability of the EDG to carry its
accident-kW-and-current loading-.-- As a-result-,-the -licensee-is-modffying -tts--
EDG testing requirements to ensure that both the engine and the generator will
be appropriately tested to demonstrate their capability to produce the accident
electrical load.
At Millstone Nuclear Power Station, Unit 3, the Northeast Nuclear Energy
Company (the licensee) determined that its testing of the EDG load shedding
circuitry was inadequate. In particular, the surveillance tests did not verify
the load shedding of five nonsafety-related loads and two safety-related loads.
This condition was a violation of TS requirements and had existed from initial
plant operation in April 1986 until January 1990.
Subsequent testing verified
that the load shedding circuits operated properly.
Discussion:
The events at Yankee Rowe, Fort Calhoun, and Vermont Yankee illustrate the
failure of EDG testing to demonstrate properly the capability of the EDGs to
assume the design-basis electrical loading during an accident. The intent of
the required surveillance testing is to assure that the EDG can dependably
carry its accident loads. It is important that the worst-case conditions
(frequency, voltage, electrical power factor, and environment) be considered
when the EDG is tested.
In particular, the effects of the electrical power
factor and the environment may have been overlooked. It is important that
procedures give personnel performing the test sufficient information to allow
them to load the EDG to simulate worst-case conditions. Since the simulation
of environmental conditions is generally impractical, it may be necessary to
use analysis to correct for environmental conditions or to show that the effect
IN 91-13 March 4, 1991 of such conditions Is negligible for the EDG. Information from the vendor may
help in determining what changes, if any, may be necessary. It is also
important for procedures to give adequate guidance to ensure that the EDG is
not inadvertently overloaded during the 'test.
The last event illustrates the failure of EDG testing to verify adequately the
proper operation of all of the logic necessary to support the EDG in an acci- dent.' Millstone Unit 3 was given as an example, but other similar cases have
been reported.
Generic Letter 88-15, OElectric Power Systems -
Inadequate Control Over Design
Processes,' discussed problems similar to those in this information notice.
This information notice requires no specific-action or written response. If
you have any questions about the information in this notice, please contact one
of the technical contacts listed below or the appropriate NRR project manager.
es
iDirector
Division of Operational Events Assessment
Office of Nuclear Reactor Regulation
Technical Contacts: C. H. Woodard, Region I
(215) 337-5261
A. J. Kugler, NRR
(301) 492-0834 Attachment:
List of Recently Issued NRC Information Notices
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March 4, 1991
Page 1 of I
LIST OF RECENTLY ISSUED
KRC INFORMATION NOTICES
Information
Notice No.
91-12
91-11 Date of
86-99, Supp. 1
89-32, Sapp. 1
91-10
91-09
91-08
90-77, S"u.
1
91-07 Subject
Potential Loss of Net Positive
Suctio
Head (MPSH)
of Standby
Liquid Control System Pumps
Inadequate Physical Separation
ad Electrical Isolation of
Non-safety-related Circuits
from Reactor Protection System
Circuits
Deyradation of Steel Con- t.7_m
ts
Surveillance Testing of Low- Temperature Overpressure-
Protection Systemw
Sumary of Semlaniwal Program
Performance Reports on Fitness- for-Duty (FFD) In the Nuclear
Industry
Counterfeiting of Crane Valves
Medical Examinations for
Licensed Operators
Inadvertent Reaoval of Fuel
Ass clies from the Reactor Core
Maintenance Deficiency Assoc- iated with General Electric
Horizontal Custom 8000
Induction Motors
Issuance
Issued to
02/15/91
All holders of OLs
or CPs for boiling
water reactors (BWRs).
02/20/91
All holders of OLs
or CPs for W-designed
nuclear power reactors.
02/14/91
All holders of OLs or
CPs for nuclear power
reactors.
02/12/91
All holders of OLs or
CPs for nuclear power
reactors.
02/12/91
All holders of OLs or
Cps for nuclear power
reactors.
02/05/91
All holders of OLs or 4
Cps for nuclear power
reactors.
02/05/91
All holders of OLs or
CPs for nuclear power, test and research
reactors.
02/04/91
All holders of OLs or
CPs for pressurized- water reactors (PiRs).
02/04/91
All holders of OLs or
Cps for nuclear power
reactors.
K
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OL : Operating License
CU Connstruction Permit
IN 91-13 March 4, 1991 of such conditions is negligible for the EDG.
Information from the vendor may
help in determining what changes, if any, may be necessary.
It is also
important for procedures to give adequate guidance to ensure that the EDG is
not inadvertently overloaded during the test.
The last event illustrates the failure of EVG testing to verify adequately the
proper operation of all of the logic necessary to support the EDG in an acci- dent. Millstone Unit 3 was given as an example, but other similar cases have
been reported.
Generic Letter 88-15, OElectric Power Systems -
Inadequate Control Over Design
Processes," discussed problems similar to those in this information notice.
This Information notice requires no specific action or written response. If
you have any questions about the information in this notice, please contact one
of the technical contacts listed below or the appropriate NRR project manager.
Original Signed by
Charles E Rossi
Charles E. Rossi, Director
Division of Operational Events Assessment
Office of Nuclear Reactor Regulation
Technical Contacts:
C. H. Woodard, Region I
(215) 337-5261 A. J.
(301)
Kugler, NRR
492-0834 Attachment:
List of Recently Issued NRC Information Notices
- SEE PREVIOUS CONCURRENCES
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01/31/91 DOCUMENT NAME: IN 91-13
IN 91-XX
February xx, 1991 what changes, if any, may be necessary. Procedures should also give adequate
guidance to ensure that the EDG is not inadvertently overloaded during the
test.
The last event illustrates the failure of EDG testing to verify adequately the
proper operation of all of the logic necessary to support the EDG in an acci- dent. Millstone Unit 3, was given as an example, but other similar cases have
been reported. The TS surveillance tests should verify that logic, such as the
load shedding logic, which supports the accident response of the EDGs, will
perform its intended function.
This information notice requires no specific action or written response. If
you have any questions about the information in this notice, please contact one
of the technical contacts listed below or the appropriate NRR project manager.
Charles E. Rossi, Director
Division of Operational Events Assessment
Office of Nuclear Reactor Regulation
Technical Contacts:
C. H. Woodard, Region I
(215) 337-5261 A. J.
(301)
Kugler, NRR
492-0834 Attachment:
List of Recently Issued NRC Information Notices
Document Name: EDGIN
- SEE PREVIOUS CONCURREIqQO
D/DOEA:NRR
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- NRR*RPB:ADM
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01/14/91
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- C/SPLB:DST:NRR*C/SELB:DST:NRR
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01/31/91
IN 91-XX
January xx, 1991 The last event illustrates the failure of EDG testing to verify adequately the
proper operation of all of the logic necessary to support the EDG in an acci- dent. Millstone Unit 3, was given as an example, but other similar cases have
been reported. The TS surveillance tests must verify that the logic associated
with the various sequences (loss of offsite power, loss of coolant accident, load shedding and sequencing, etc.) will perform its intended function.
This information notice requires no specific action or written response. If
you have any questions about the Information in this notice, please contact one
of the technical contacts listed below or the appropriate NRR project manager.
Charles E. Rossi, Director
Division of Operational Events Assessment
Office of Nuclear Reactor Regulation
Technical Contacts:
C. H. Woodard, Region I
(215) 337-5261 A. J.
(301)
Kugler, NRR
492-0834 Attachment:
List of Recently Issued NRC Information Notices
Document Name:
EDGIN
- SEE PREVIOUS
D/DOEA:NRR
CERossi
01/
/91
- OGCB:DOEA:NRf
.AJKugler
12/20/90
CONCURRENCES
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IN 90-XX
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~Page 4 of
third event illustrates the failure of EDG testing to)
erify th proper operation of edtof the logic necessary to support
At
the ES[)
in an accident.
Millstone, Uhit 3, was given as an example, but other similar cases have been reported.
The TS surveillance tests
must verify that the logic associated with the various sequences (loss
of offsite power, loss-of-coolant accident, load shedding and
sequencing, etc.) will perform its
intended function.
This information notice requires no specific action or written
response.
If you have any questions about this matter, please contact
one of the technical contacts listed below or the appropriate NRR
project manager.
Charles E. Rossi, Director
Division of Operational Events Assessment
Office of Nuclear Reactor Regulation
Technical Contacts: C. H. Wbodard, Region I
(215) =7-5261
T. Koshy, Senior Resident Inspector, Yankee Rowe
(413) 424-5242 Attachment:
1. List of Recently Issued NRC Information Nbtices
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The thir event illustrates~ the failure of EDG tes-ting to adequatzlY
verily the- proper oporsatior of all of the logic rowt*sHryY to wUoort, thp ED( in an accident.
Milletcrot Wkit 3, was qivenl as an Qxamplpe, but other similar easm have, bmen reported.
Thm TS Eurei~lfleci
tests
rImit veri+/-fy that the logic asswiated with the various coqueasC9(loss
of of fritc
pavpr-, 105; of coolant accident, loaid shedding and
fWqLanrirx;, ec~t.) will por-forml its intended funiction.a
'This~ informatkio rotice requidres no specific action or wr-itten
rep-n
If yct have any queirtion about this niattar, please contact
one of the technicial centacto listed below or the appropriata NR
project m".ager.
Charles E. Rossi, Director
Divisicn' of Operatimal E>.nts Assesirent
Off ice of Uclak)Nr IL-=tor Regulation
Technical Cnter-teg C. H. tWkiodard, Regian!I
(215) qq7u-MU'
T. mfsthy, Sonior Resident. Inspectors YVnkm, Rc~
(413) 424-5242 I.. List of Rec-ently Issued NC Iinformationi W~tices
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ty the prowr operatib of &11 of tho logic nrlpsoty to uPport
the EX In an Oident. fistC2W Uit Zs was given as an example, but other
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The TS irul 11
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with the variculs Wu3!n
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of aftsite por, loss zT cmlnt accidonts load shucddinM and
aaquenwti
atc.) will Farform its Intanded fLrlctiu.
This information notice requires no speci'C action or written
respcn3e.
If yu have any qu-st3uns atcut this matter, pleas cotat
ane of tte tectnAcal cantacts lsted tolow or the appropriate Wf(
projet m&oer.
Charles E. *
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DtiSion
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Operationl Evwte Areswrmnt
Office of tL=lear Reetoir ftgulation
Tchnilcal Cmt.eti Co He 1nerds flgiIn I
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1. List of FRecntly IEszud NKC Informaticn Nbticez
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