Information Notice No. 79-29, Loss of Nonsafety-Related Reactor Coolant System Instrumentation During Operation
November 16, 1979
MEMORANDUM FOR: B. H. Grier, Director, Region I
J. P. O'Reilly, Director, Region II
J. G. Keppler, Director, Region III
K. V. Seyfrit, Director, Region IV
R. H. Engelken, Director, Region V
FROM: Norman C. Moseley, Director, Division of Reactor
Operations Inspection, IE
SUBJECT: Information Notice No. 79-29, LOSS OF
NONSAFETY-RELATED REACTOR COOLANT SYSTEM INSTRUMENTATION
The subject document is transmitted for issuance on November 16, 1979. The
Information Notice should be issued to all power reactor facilities holding
operating licenses and construction permits.
Also enclosed is a draft copy of the transmittal letter.
Norman C. Moseley, Director
Division of Reactor Operations
Office of Inspection and Enforcement
1. Draft Transmittal Letter
2. Information Notice No.
CONTACT: H. W. Woods, IE
(Transmittal letter for Information Notice No. 79-29 to each holder of an
NRC Operating License and Construction Permit.)
Information Notice No. 79-29
This Information Notice is provided as an early notification of a possibly
significant matter. It is expected that recipients will distribute this
Notice to their operating personnel and will review the information for
possible applicability to their facilities. No specific action or response
is requested at this time. However, we anticipate that further NRC
evaluations will result in issuance of an IE Circular, Bulletin, or NRR
Generic Letter in the near future which will recommend or request specific
applicant or licensee actions. If you have questions regarding the matter,
please contact the Director of the appropriate NRC Regional Office.
1. Information Notice No.
2. List of IE Information
Notices Recently Issued
SSINS No.: 6300
NUCLEAR REGULATORY COMMISSION
OFFICE OF INSPECTION AND ENFORCEMENT
WASHINGTON, D.C. 20555
November 16, 1979
Information Notice No. 79-29
LOSS OF NONSAFETY-RELATED REACTOR COOLANT SYSTEM INSTRUMENTATION DURING
This notice contains information regarding a loss of reactor coolant system
instrumentation as a consequence of a failure of a static transfer switch to
transfer to an alternate supply.
At 3:15 p.m. on November 10 with Unit 3 of the Oconee Station at 100 percent
power, the main condensate pumps tripped, apparently as a result of a
technician performing maintenance on the hotwell level control system. This
led to reduced feedwater flow to the steam generators, which resulted in a
high reactor coolant system (RCS) pressure reactor trip and simultaneous
turbine trip at 3:16:57 p.m. At 3:17:15 p.m., the inverter power supply,
nonsafety-related, feeding all power to the integrated control system (ICS)
tripped and failed to automatically transfer its loads from the DC power
source to the regulated AC power source. The inverter had tripped due to
blown fuses, resulting in loss of RCS indicators and recorders in the
control room, except one wide range RCS pressure recorder.
This condition existed for approximately three minutes, until an operator
could reach the equipment room and switch the inverter manually to the
regulated AC source. As a result of the power failure to the ICS, all valves
controlled by the system assumed their respective fail positions. This
resulted in a cool down of the RCS to 1635 psi and 530 degrees F. The
operator, expecting this condition, started all makeup pumps and opened the
associated high pressure injection valves to the RCS which limited the rate
of RCS pressure reduction and associated reduction in pressurizer level. At
3:20:42 p.m., power was restored to the ICS and RCS conditions were
Although RCS cooldown limits were exceeded, the pressurizer and steam
generators did not go dry, and at least 79 degrees F subcooling was
maintained during this event. No engineered safety features actuation
setpoints were reached, and, except for the components discussed above, no
component malfunctions occurred.
The licensee has installed a redundant electromechanical transfer switch
between the loads and the regulated supply. This switch will actuate and
power the loads from the regulated supply should the original static switch
fail to transfer.
Longer term resolution of the need or desirability to separate these
instruments onto diverse electrical supplies or to provide redundant
instrumentation display channels for operator use from essential power
supplies are also under
Information Notice No. 79-29 November 16, 1979
Page 2 of 2
consideration. It is anticipated that further NRC evaluations will result in
issuance of an IE Circular, Bulletin, or NRR Generic letter in the near
future which will recommend or request specific applicant or licensee
This Information Notice is provided to inform licensees of a possibly
significant matter. It is expected that recipients will disseminate the
information to all operational personnel working at their licensed
facilities. If you have questions regarding this matter, please contact the
Director of the appropriate NRC Regional Office.
No written response to this Information Notice is required.
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