Category:NRC Information Notice[Table view]The following query condition could not be considered due to this wiki's restrictions on query size or depth: <code> [[:Beaver Valley]] OR [[:Millstone]] OR [[:Hatch]] OR [[:Monticello]] OR [[:Calvert Cliffs]] OR [[:Dresden]] OR [[:Davis Besse]] OR [[:Peach Bottom]] OR [[:Browns Ferry]] OR [[:Salem]] OR [[:Oconee]] OR [[:Mcguire]] OR [[:Nine Mile Point]] OR [[:Palisades]] OR [[:Palo Verde]] OR [[:Perry]] OR [[:Indian Point]] OR [[:Fermi]] OR [[:Kewaunee]] OR [[:Catawba]] OR [[:Harris]] OR [[:Wolf Creek]] OR [[:Saint Lucie]] OR [[:Point Beach]] OR [[:Oyster Creek]] OR [[:Watts Bar]] OR [[:Hope Creek]] OR [[:Grand Gulf]] OR [[:Cooper]] OR [[:Sequoyah]] OR [[:Byron]] OR [[:Pilgrim]] OR [[:Arkansas Nuclear]] OR [[:Braidwood]] OR [[:Susquehanna]] OR [[:Summer]] OR [[:Prairie Island]] OR [[:Columbia]] OR [[:Seabrook]] OR [[:Brunswick]] OR [[:Surry]] OR [[:Limerick]] OR [[:North Anna]] OR [[:Turkey Point]] OR [[:River Bend]] OR [[:Vermont Yankee]] OR [[:Crystal River]] OR [[:Haddam Neck]] OR [[:Ginna]] OR [[:Diablo Canyon]] OR [[:Callaway]] OR [[:Vogtle]] OR [[:Waterford]] OR [[:Duane Arnold]] OR [[:Farley]] OR [[:Robinson]] OR [[:Clinton]] OR [[:South Texas]] OR [[:San Onofre]] OR [[:Cook]] OR [[:Comanche Peak]] OR [[:Yankee Rowe]] OR [[:Maine Yankee]] OR [[:Quad Cities]] OR [[:Humboldt Bay]] OR [[:La Crosse]] OR [[:Big Rock Point]] OR [[:Rancho Seco]] OR [[:Zion]] OR [[:Midland]] OR [[:Bellefonte]] OR [[:Fort Calhoun]] OR [[:FitzPatrick]] OR [[:McGuire]] OR [[:LaSalle]] OR [[:05000000]] OR [[:Zimmer]] OR [[:Fort Saint Vrain]] OR [[:Shoreham]] OR [[:Satsop]] OR [[:Trojan]] OR [[:Atlantic Nuclear Power Plant]] OR [[:Crane]] </code>.
All holders of operating licenses or construction permits for nuclear power
reactors.
Purpose
This information notice is being provided to alert addressees to potential
problems caused by plants operating with ground(s) in the vital direct
current (dc) distribution systems (which are normally ungrounded systems).
It is expected that recipients will review the information for applicabi- lity 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
During recent NRC maintenance inspections at Quad Cities (50-254/88011 and
50-265/88012), Oconee (50-269/88-17, 50-270/88-17, and 50-287/88-17), and
D. C. Cook (50-315/88016 and 50-316/88018) power reactor facilities, it was
found that' plants had been operating with multiple grounds in the dc distri- bution systems fur extended periods.
Specific examples are as follows:
(1) Quad Cities Unit 2 operated for a significant period of time with known
grounds on the negative side of the 125-Vdc system. During this period, when-a momentary ground occurred on the positive side of the circuit a
fuse in the auto-start circuitry of a diesel generator blew, disabling
the auto-start function of the diesel generator for approximately 6 months. This condition was not properly recognized or evaluated by
the licensee; it was identified during an 18-month surveillance test.
(2) Oconee Nuclear Station operated for approximately 4 months with the
125-Vdc system ground alarm activated.
However, during this period
no station procedure or shift surveillance requirements existed to
verify the operability of the ground detection system. As a result
of the maintenance inspections, this ground detection alarm system
was found to be inoperable; it had not been calibrated since 1976.
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IN 88-86 October 21, 1988 (3) D. C. Cook Unit 1 had a negative dc system ground for approximately
7 months before it was cleared. A safety evaluation for continued
operation with the ground or other grounds that might be masked had
never been performed until requested by the NRC.
The licensees of Quad Cities and D. C. Cook were issued notices of violation.
Safety evaluations were performed to support continued operation while the
grounds existed.
A review of selected licensee event reports of dc system grounds (see Attach- ment 1) indicates that plant equipment is frequently rendered inoperable or
is started unexpectedly because of grounds.
Discussion:
The dc power system provides control and power to safety-related valves, instrumentation, emergency diesel generators, and many other components
and systems during all phases of plant operation, including abnormal
shutdowns and accident situations.
Because of its importance to plant
safety, the dc system requires a high degree of reliability and avail- ability.
Most nuclear power plant dc systems are two-wire ungrounded, combination
battery/charger systems equipped with ground detection.
Typical ground
detection system features include a remote annunciator and a local indicator
and/or recorder. Ground detectors are incorporated in the dc system so that
if a single ground point does occur, immediate steps can be taken to clear
the ground fault from the system.
Failure to respond to a single ground will mask subsequent grounds.
Multiple
grounds can cause the indiscriminate operation of equipment, which may have
safety consequences.
Grounds can cause control circuit fuses to fail and
can render important safety equipment inoperable as previously described.
Furthermore, batteries have a designed capacity to supply power during a
station blackout condition, and this capacity can be affected by the presence
of unanalyzed loads in the form of multiple grounds.
It is recognized that troubleshooting and finding grounds on a-dc system are
difficult tasks that may affect plant operation.
The licensees previously
mentioned have reviewed their designs and conditions for potential impact
on safety system operability and have taken corrective actions to minimize
the effect of grounds.
0
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IN 88-86 October 21, 1988 No specific action or written response is required by this information notice.
If you have any questions about this matter, please contact one of the technical
contacts listed below or the Regional Administrator of the appropriate regional
office.
ha
E Rossi, Director
Division of Operational Events Assessment
Office of Nuclear Reactor Regulation
Technical Contacts: Z. Falevits, Region III
(312) 790-5772
S. N. Saba, NRR
(301) 492-1052 Attachments:
1. Selected Licensee Event Reports
2. List of Recently Issued NRC Information Notices