Protecting People and the EnvironmentUNITED STATES NUCLEAR REGULATORY COMMISSION
SSINS No: 6835
IN 86-07
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF INSPECTION AND ENFORCEMENT
WASHINGTON, DC 20555
February 3, 1986
Information Notice No. NO 86-07: LACK OF DETAILED INSTRUCTION AND
INADEQUATE OBSERVANCE OF PRECAUTIONS
DURING MAINTENANCE AND TESTING OF DIESEL
GENERATOR WOODWARD GOVERNORS
Addressees:
All nuclear power reactor facilities holding an operating license (OL) or a
construction permit (CP)
Purpose:
This notice is provided to alert recipients of a potentially significant
problem with the maintenance of Woodward Governors used on standby diesel
generators Loss of engine speed control has resulted from inadequate oil
inventory following maintenance on the governor This notice is also
provided to make recipients aware of the importance of starting the engines
in a highly controlled manner, especially following maintenance activities,
to preclude excessive engine speed while confirming proper operation
It is expected that recipients will review this information for
applicability to their facilities and consider actions, if appropriate, to
preclude a similar problem from occurring However, suggestions contained in
this information notice do not constitute NRC requirements; therefore, no
specific action or written response is required
Description of Circumstances:
During startup of a standby diesel generator at Grand Gulf Unit 1, the
diesel engine oversped for about 15 seconds This startup was the first
following preventive maintenance on the governor The overspeed damaged
numerous engine components, including connecting rods, rod bearings, main
bearings, link pin bushings, wrist pin bushings, and the engine base It is
not known whether the manual trip, the overspeed trip, or excessive
vibration terminated the overspeed
Because the governor was suspected as the cause of the overspeed, it was
removed without modification and returned to the manufacturer, Woodward
Governor, for testing Those tests demonstrated that the governor was
ineffective in controlling speed because of an inadequate inventory of oil
It is postulated that inadequate filling and venting by licensee personnel
following the maintenance work resulted in the low oil level
8601290059
IN 86-07
February 3, 1986
Page 2 of 3
Based on Information available; the inadequate venting after refilling with
oil has been attributed to use of an outdated technical manual, oil capacity
figures for the governor and associated components not being available, no
detailed procedure for filling and venting, and inexperienced or
insufficiently trained personnel
During normal operation, the governor is actuated by an electrical signal
from the generator and a mechanical signal from the engine However, both
signals depend on the same hydraulic actuator and a common oil supply to
control engine speed In this case, the electrical signal was deactivated
because the generator field had no excitation, as was required by the
licensee's procedure Because the remaining mechanical governor is
relatively slow-acting (in comparison to the electric governor), a reduction
in the governor control setting is usually made during initial startup after
maintenance to limit engine speed overshoot At Grand Gulf the governor
control reduction had been omitted from the procedure With the governor oil
level low, the licensee concluded that a lower governor control setting
would not have prevented the overspeed
In addition to the above, the engine has an overspeed trip device that uses
engine lube oil as its actuating fluid, thus making it independent of the
hydraulic governor This trip was ineffective in preventing engine overspeed
because it was found by the licensee to be relatively slow acting in
relation to the engine acceleration experienced during the overspeed A
design change to reduce the overspeed trip response time is being considered
by Transamerica Delaval
Discussion:
The corrective action taken at Grand Gulf in response to the overspeed event
included development of: (1) detailed procedures for venting trapped air
from hydraulic governors and associated components during oil refilling
operations and (2) detailed procedures that establish highly controlled
conditions for initial startup following such maintenance activities Highly
controlled conditions included "air rolling" the engine, exercising direct
manual control of the engine, reducing the governor control and overspeed
trip settings, and limiting fuel rack travel
Licensees are reminded that every reasonable effort, as detailed in Generic
Letter 83-28, "Required Actions Based on Generic Implications of Salem ATWS
Events," dated July 8, 1983, should be made to ensure the most recent
technical information is available at plant sites for proper guidance of all
equipment maintenance and testing activities Utilities that use Woodward
Governors on their diesel engines are encouraged to contact Woodward
Governor to ensure they have the latest technical information applicable to
their equipment
IN 86-07
February 3, 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 Contact: W P Haass, IE
(301) 492-9041
Attachment: List of Recently Issued IE Information Notices
[an error occurred while processing this directive]
[an error occurred while processing this directive]
