Protecting People and the EnvironmentUNITED STATES NUCLEAR REGULATORY COMMISSION
SSINS No.:
IN 84-69, Supplement 1
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF INSPECTION AND ENFORCEMENT
WASHINGTON, DC 20555
February 24, 1986
Information Notice No. 84-69, SUPPLEMENT 1: OPERATION OF EMERGENCY
DIESEL GENERATORS
Addresses:
All nuclear power reactor facilities holding an operating license (OL) or a
construction permit (CP).
Purpose:
Information Notice 84-69, issued on August 29, 1984, was provided to alert
recipients of potentially significant safety problems that can arise when
one or more emergency diesel generators (EDGs) are operated in modes other
than the prescribed standby service mode, such as loaded on non-emergency
buses parallel with offsite power sources. The purpose of this supplement is
to reemphasize the need for licensees to review the information provided in
IN 84-69, in addition to the information contained herein, for applicability
to their facilities and consider actions, if appropriate, to preclude
similar problems at their facilities. However, suggestions contained in this
supplement do not constitute NRC requirements; therefore, no specific action
or written response is required.
Description of Circumstances:
Following a 10 CFR 50.72 report made to the NRC Headquarters Operations
Center on August 12, 1985, it was discovered that Crystal River Unit 3 was
continuously running the one operable EDG loaded in parallel with the grid
while the other EDG was declared inoperable. Crystal River Technical
Specifications require fast starting of the operable EDG (i.e., verifying
that the diesel starts from ambient conditions and accelerates to the
required speed within a required period of time) within 1 hour after the
declaration of an inoperable EDG and every 8 hours thereafter. Because of a
concern about increased EDG wear and reduced overall EDG reliability, the
licensee chose to keep the EDG running loaded parallel to the offsite grid
rather than fast starting the EDG every 8 hours.
The licensee believed that continuous running was an acceptable alternative
to the test starts required by the Technical Specifications and that the EDG
was operable per Technical Specifications while running in parallel with the
offsite power system. The licensee indicated also that it was aware of IN
84-69 and had implemented procedures that prohibited operating the EDG
parallel to the grid during inclement weather (e.g. , lightning, heavy
winds).
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IN 84-69, Supplement 1
February 24, 1986
Page 2 of 3
Discussion:
When an EDG is operated connected to offsite or nonvital loads, the
emergency power system is not independent of disturbances on the nonvital
and offsite power systems that can adversely affect emergency power
availability. The situation is of particular concern when the onsite
emergency power system is already in a degraded condition due to an EDG
being inoperable and the operable EDG is loaded on non-emergency loads. In
this condition, a disturbance in the non-emergency power system could result
in both a loss of offsite power and a disabling of the remaining emergency
power source. Although the events described in IN 84-69 occurred due to
weather conditions, the concerns of the IN apply to parallel operation of
EDGs with non-emergency loads at all times.
If a fault develops while the EDG is connected to non-emergency buses, EDG
availability for subsequent emergency demands may be affected. In some
design configurations, the EDG would trip as a result of overcurrent or
reverse power, actuate a lockout device, and require local operator action
to reset the lockout. In such cases, the EDG is recoverable, but the
timeliness of its availability is not comparable to that of having the EDG
in its normal standby service.
In other design configurations the EDG may not trip, but the operation of
the load sequencer may be adversely affected. The load sequencer timers are
often linked with the closing of the EDG output breaker or with detection of
loss of voltage on the bus. If the EDG does not trip, conditions are not
proper for the designed operation of the load sequencers. Consequently, the
EDG cannot perform automatically in a manner comparable to that of having
the EDG in its normal standby mode.
Another potential concern deals with the vulnerability of the EDG to trip
signals which are bypassed for emergency demands but are operable for manual
starts and during running for test purposes. The EDG would be more
vulnerable to such trips.
The licensee's concern regarding excessive test starts is valid. In this
particular case, the licensee was encouraged to address that concern more
directly by submitting changes to the plant Technical Specifications. Such
changes were approved for North Anna Unit 2 on April 25, 1985.
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IN 84-69, Supplement 1
February 24, 1986
Page 3 of 3
No specific action or written response is required by this information
notice. If you have any questions about this matter, please contact the
Regional Administrator of the appropriate regional office or this office.
Edward L. Jordan, Director
Division of Emergency Preparedness
and Engineering Response
Office of Inspection and Enforcement
Technical Contacts: Joseph G. Giitter, IE
(301) 492-9001
J. T. Beard, NRR
(301) 492-7465
Attachment: List of Recently Issued Information Notices
