ML20058Q010
| ML20058Q010 | |
| Person / Time | |
|---|---|
| Site: | Beaver Valley |
| Issue date: | 12/21/1993 |
| From: | Chris Miller NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I) |
| To: | Sieber J DUQUESNE LIGHT CO. |
| Shared Package | |
| ML20058Q014 | List: |
| References | |
| NUDOCS 9312280035 | |
| Download: ML20058Q010 (4) | |
See also: IR 05000412/1993081
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UNITED STATES
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NUCLEAR REGULATORY COMMISSION
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DEC 21 1993
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Docket No. 50-412
Mr. J. D. Sieber
Senior Vice President
Nuclear Power Division
Duquesne Light Company
Post Office Box 4
Shippingport, Pennsylvania 15077
,
Dear Mr. Sieber:
,
SUBJECT:
NRC AUGMENTED INSPECTION TEAM (AIT) REGARDING THE
FAILURE OF THE EMERGENCY DIESEL GENERATOR LOAD
SEQUENCERS NRC INSPECTION REPORT 50-412/93-81
The enclosed report refers to the NRC Augmented Inspection Team (AIT), led by
Mr. James Trapp of this office, on November 9-19,1993, at the Unit 2, Beaver Valley
Power Station in Shippingport, Pennsylvania. The purpose of this inspection was to review
the circumstances regarding the failure of both trains of the emergency diesel generator load
sequencers. At the conclusion of the inspection, ' ie team findings were discussed with you
and members of your staff at an exit meeting th'.t was open for public observation on
December 2,1993.
The scope of the inspection included dev5 ping a detailed event description, evaluating the
root causes for the events, assessing the efectiveness of corrective actions, and evaluating
the safety significance of the event. The 11 pection consisted of selective examination of
procedures and representative records, observations of testing and inspections, and interviews
with personnel.
The failure of both emergency diesel generator load sequencers would prevent automatic
initiation of the emergency core cooling systems in the event of an accident with a loss of
offsite power. The failure of both load sequencers was a significant event because a common
cause resulted in the failure of multiple trains of a system designed to mitigate the
consequences of an accident. Based on the safety significance of this event, the NRC
dispatched an AIT.
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9312280035 931221
ADOCK 05000412
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DEC 21 1993
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Duquesne Light Company
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The cause for the failure of the load sequencers was determined to be a malfunction of
digital miemprocessor based timer / relays. The malfunction in the timer / relays was caused
by voltage spikes induced when auxiliary relays in the load sequencer circuits were
deenergized. Several diodes were installed across relay coils in the load sequencer circuits to
reduce the magnitude of the voltage spikes. The AIT reviewed your corrective actions and
concluded that the installation of the diodes was an acceptable response to this failure.
The team concluded that the root cause of the failures was inadequate design control. The
modification process that installed the microprocessor based timer / relays in 1990 did not
place adequate control on the selection and review for suitability of the new timer / relays.
The susceptibility of microprocessor based equipment to voltage disturbances and
electromagnetic interference was well known at the time of this design change. It does not
appear that adequate detail was provided in the design specification generated for the
timer / relays or in the commercial grade qualification testing for these components. Weak
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design control was also cited as the cause for the failure of six load sequencer timer / relays
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during the previous failure of the load sequencers in 1992. We are also concerned thai
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during the installation of the diodes, a malfunction was identified during post modification
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testing with the starting sequence step of the auxiliary feedwater pump. This malfunction
required additional design changes to the sequencer and pump starting logic.
Based on the potential of recurring design control issues and the significance of this event,
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we are planning to schedule an enforcement conference to discuss the circumstances
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surrounding this issue. The details and schedule for the enforcement conference will be
provided in a separate correspondence.
In accordance with 10 CFR 2.790 of the Commission's regulations, a copy of this letter and
the enclosed inspection report will be placed in the NRC Public Document Room.
We will gladly discuss any questions you have concerning this inspection.
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Sincerely,
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Charles L. Miller, Acting Deputy Director
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Division of Reactor Safety
Enclosure: NRC Region I Inspection Report No. 50-412/93-81
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DEC 2 l 1993
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Duquesne Light Company
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cc w/ encl:
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G. S. Thomas, Vice President, Nuclear Senices
D. E. Spoerry, Vice President, Nuclear Operations
L. R. Freeland, General Manager, Nuclear Operations Unit
K. D. Grada, Manager, Quality Services Unit
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N. R. Tonet, Manager, Nuclear Safety Department
H. R. Caldwell, General Superintendent, Nuclear Operations
K. Abraham, PAO (2)
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Public Document Room (PDR)
Local Public Doewnent Room (LPDR)
Nuclear Safety Information Center (NSIC)
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NRC Resident Inspector
Commonwealth of Pennsylvania
State of Ohio
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DEC 21 1933
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Duquesne Light Company
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bec w/ encl:
Region I Docket Room (with concurrences)
W.127arus, DRP
D. Lew, DRP
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bec w/ encl (VIA E-MAIL):
W. Butler, NRR
G. Edison, NRR
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W. Dean, OEDO
bec w/enci (AIT REPORTS ONLY):
The Chairman
Commissioner Rogers
Commissioner Remick
Commissioner de Planque
J. Taylor, EDO
T. Murley, NRR
DCD (OWFN Pl-37) (Dist. Code #IE10)
A. Chaffee, NRR/ DORS /EAB
E. Jordan, AEOD
P. Boehnert, Chairman, ACRS (AIT Reports Only)
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K. Raglin, AEOD (AIT Reports Only)
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