Protecting People and the EnvironmentUNITED STATES NUCLEAR REGULATORY COMMISSION
INS No. 6835
IN 84-38
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF INSPECTION AND ENFORCEMENT
WASHINGTON, DC 20555
May 17, 1984
Information Notice No. 84-38: PROBLEMS WITH DESIGN, MAINTENANCE, AND
OPERATION OF OFFSITE POWER SYSTEMS
Addressees:
All power reactor facilities holding an operating license (OL) or
construction permit (CP).
Purpose:
This information notice is provided as a notification of potentially
significant problems pertaining to the design, maintenance, and operation of
offsite power systems. It is expected that recipients will review their
facilities and consider actions, if appropriate, to preclude similar
problems occurring at their facilities. However, suggestions contained in
this information notice do not constitute NRC requirements and, therefore,
no specific action or written response is required.
Description of Circumstances:
Turkey Point Nuclear Units 3 and 4 recently experienced a series of events
that included reactor trips, unscheduled shutdowns, and loss of offsite
power to Unit 3. These events occurred as a direct result of problems with
the design, maintenance, and operation of the offsite power systems.
The first event occurred on February 12, 1984, when an improperly calibrated
relay for the startup transformer of oil fired Units 1 and 2 sensed a
current differential and isolated the portion of the switchyard bus feeding
the single Unit 3 startup transformer and a new 3C auxiliary transformer for
that unit. The Unit 3 reactor tripped on loss of an electrically driven main
feedwater pump powered from the 3C auxiliary transformer and bus. With the
start-up transformer also lost, emergency diesel generators were required to
provide power to the vital buses and the unit was stabilized on natural
circulation. Later that day, while attempting to restore offsite power to
Unit 3 from the Unit 4 new 4C auxiliary transformer, a switching error
resulted in reactor trip of Unit 4. There were no written procedures for
realignment of offsite power systems following the loss of offsite power to
one of the units (Unit 3 in this case).
Another event occurred on February 16, 1984, when the Unit 4 reactor tripped
and Unit 3 experienced loss of offsite power. This event was initiated by a
relay in the recently installed offsite power cross-tie feeder switchgear
that included buses 3C and 4C. This relay was mounted on a metal-clad
switch-gear door that was improperly installed, which caused it to bind. The
vibrations
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IN 84-38
May 17, 1984
Page 2 of 2
from forcing the door open or closed actuated the relay. This resulted in a
Unit 4 trip from loss of power to the 4C bus which supplied one electrically
driven main feedwater pump. Seconds later, jarring of a similarly mounted
relay caused isolation of the switchyard quadrant feeding Unit 3 and result-
ant loss of power to the 3C bus, loss of one electrically driven main feed-
water pump, reactor trip, and loss of power to the Unit 3 startup transform-
er.
Following these events, the licensee informed the NRC that the new 3C and 4C
auxiliary transformers and associated equipment were added with the
objective of enhancing the availability of offsite power,systems. The design
changes for these additions were classified as non-safety-related but were
covered in the quality assurance program. However, they were not reviewed
with respect to the requirements of 10 CFR 50.59 by the plant nuclear safety
committee.
As a followup to these events, the licensee instituted short- and long-term
corrective action programs to review the overall design of offsite power
systems and to strengthen the procedures and administrative controls. As a
part of the short-term program, functional testing of 4-kV breakers for non-
safety-related buses was performed; this test revealed loose bolts,
misaligned and dirty contacts, worn parts, and the mechanical failure of one
breaker to trip. The short-term corrective actions program was completed
before unit startup.
A partial listing of other similar loss-of-offsite-power events is provided
in Attachment 1 to this notice.
The general concern is that design, maintenance, and operational problems in
electrical equipment considered to be non-safety related can greatly degrade
access to offsite power sources. This is not consistent with the General De-
sign Criteria objectives. The concern is particularly valid where station
service loads are arranged, as at Turkey Point Units 3 and 4, such that a
single electrical fault can cause a transient resulting in a plant trip and
also defeat immediate access to offsite power sources. The concern is also
particularly valid for facilities with multiunit plants or a common switch-
yard for nuclear and non-nuclear units.
If you have any questions regarding this matter, please contact the Regional
Administrator of the appropriate NRC regional office or this office.
Edward L. Jordan, Director
Division of Emergency Preparedness
and Engineering Response
Office of Inspection and Enforcement
Attachments:
1. Partial List of Recent Loss of Offsite Power Events
2. List of Recently Issued IE Information Notices
Technical Contact: R. Singh, IE
(301) 492-8068
.
Attachment 1
IN 84-38
May 17, 1984
PARTIAL LIST OF RECENT LOSS-OF-OFFSITE-POWER EVENTS
Plant/Date Event Summary
1. LaSalle 1, Partial loss of offsite power caused by a
10/26/83 procedural error and personnel oversight when
securing a Unit 2 transformer.
2. Summer 1, Internal fault at Parr Steam Plant (a
9/11/83 non-nuclear unit) caused loss of offsite
power.
3. Brunswick 1, Personnel error caused loss of offsite power
4/26/83 when a 230 kV bus was inadvertently tripped.
4. Quad Cities 2, Preferred power was being taken out of service
6/22/82 for maintenance, and a personnel error caused
a reactor trip resulting in complete loss of
offsite power. Twenty-two minutes into the
event, one of the emergency diesel generators
tripped as a result of underexcitation.
5. Prairie Island 1, During an attempted start of a cooling tower
7/8/81 pump, an improperly set undervoltage
protection relay caused a partial loss of
offsite power.
6. Salem 1 and 2, Partial loss of offsite power to both units
5/21/81 resulting from a design deficiency in the, gas
turbine Unit 3.
7. Monticello, A bus fault was caused by operator error. A
4/27/81 design error caused the undervoltage relays to
trip all offsite power sources instead of
isolating only the faulted bus.
8. LaCrosse, Loss of offsite power caused by an operator
2/1/81 opening a wrong breaker.
9. Beaver Valley 1, Loss of 138 kV bus resulted in partial loss of
2/1/81 offsite power. During the event, the auto load
sequencer of one of the emergency diesel
generators failed as a result of improper
wiring (design error) and a disconnected
timer relay.
