Information Notice No.80-03 - Main Turbine Electrohydraulic Control System
SSINS No.: 6870
Accession No.:
7912190666
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF INSPECTION AND ENFORCEMENT
WASHINGTON, D.C. 20555
January 31, 1980
Information Notice No. 80-03
MAIN TURBINE ELECTROHYDRAULIC CONTROL SYSTEM
Description of Circumstances:
On September 6, 1979, while performing a routine startup of the Trojan
Nuclear Plant, a speed control problem was encountered during warmup of the
General Electric turbine and increase of turbine speed to normal operating
speed (1800 RPM). Technicians were notified and trouble shooting in
accordance with the technical manual* was commenced to resolve the apparent
oscillation between the primary and backup speed control circuits which was
hindering normal turbine startup operations. The technical manual indicates
that it is permissible to remove either the primary or backup low value gate
circuits which contain speed and acceleration error amplifiers. Upon removal
of the primary low value gate circuits which contain speed and acceleration
error amplifiers. Upon removal of the primary low value gate circuit card,
the backup card amplifiers, coming from a saturated condition, became the
controlling circuit. During the shift in control circuits (primary to
backup), the speed/acceleration error signal went to maximum which resulted
in a full open signal to the turbine control valves. Under existing plant
conditions this appeared to the safety injection system as a major steam
break downstream of the main steam isolation valves which resulted in a
safety injection system actuation and reactor trip.
The Electrohydraulic Control System (EHC) technical manual indicated that
slight load changes are likely when a low value gate card is removed. The
effect on an unloaded turbine appears to be much more significant and tests
conducted by
*GEK Instruction Book 11381-D, "Speed Control Unit", Maintenance Section,
Page 4.
.
Information Notice No. 80-03 January 31, 1980
Page 2 of 2
Trojan personnel indicate that the transient is initiated whether the
turbine is at a set speed or in an acceleration mode to a set speed.
Discussions with General Electric personnel by the licensee have been
initiated in an attempt to verify the phenomenon observed and, if
applicable, alert other facilities which operate a turbine with a MK 1 EHC
System regarding the potential operation of the control valves when trouble
shooting the speed control unit in accordance with existing instructions.
This information is provided as an early notification of a possible
significant matter. It is expected that recipients will review the
information for possible applicability to their facilities. No specific
action or response is requested to at this time. If further NRC evaluations
so indicate, an IE Circular or Bulletin will be issued to recommend or
request specific licensee actions. If you have questions regarding this
matter, please contact the. Director of the appropriate NRC Regional Office.
Enclosure:
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