United States Nuclear Regulatory Commission - Protecting People and the Environment

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.

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