Failures of Small-Diameter Tubing in Control Air, Fuel Oil, and Lube Oil Systems which Render Emergency Diesel Generators Inoperable
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D.C. 20555
January 25, 1989
Information Notice No. 89-07: FAILURES OF SMALL-DIAMETER TUBING IN
CONTROL AIR, FUEL OIL, AND LUBE OIL
SYSTEMS WHICH RENDER EMERGENCY DIESEL
GENERATORS INOPERABLE
Addressees:
All holders of operating licenses or construction permits for nuclear power
reactors.
Purpose:
This information notice is being provided to alert addressees to events in-
volving breaks or cracking of small-diameter tubing which can render emergency
diesel generators (EDGs) inoperable. Failures apparently caused by vibration
have occurred in the tubing of the instrumentation and control air system as
well as in the fuel oil and lube oil systems of EDGs. These events have sig-
nificant safety implications because of the loss of, or the potential loss of,
ability of safety-related equipment to perform its intended safety function.
It is expected that recipients will review the information for applicability
to their facilities and consider actions, as appropriate, to avoid similar
problems. However, suggestions contained in this information notice do not
constitute NRC requirements; therefore, no specific action or written response
is required.
Description of Circumstances:
Cooper Nuclear Station
During an operability surveillance test of an emergency diesel generator on
October 21, 1988, at Cooper Station (Nebraska Public Power District), a loss
of control air pressure occurred and the "Turbo Bearing Wear" annunciator
alarmed. The control air system is a subsystem of the starting air system.
The starting air goes through two pressure-reducing valves, set at 80 psi and
30 psi, respectively, to supply 30 psi control air. The control air subsystem
maintains the engine at a set speed regardless of engine load and protects the
engine from abnormal conditions through protective trip functions. During
engine operation the control air supplies 80 psi air to hold the fuel racks in
position. If control air is shut off or if any of the diesel generator trips
occur, the 80 psi air flow to the fuel shutoff cylinder is stopped, dumping
the fuel racks and tripping the EDG.
8901180357
. IN 89-07
January 25, 1989
Page 2 of 3
After the overspeed shutdown relay and the valve associated with maintaining
a constant air pressure for the various EDG protective trip mechanisms were
rebuilt, the control air pressure still could not be sustained. Subsequently,
the licensee identified a circumferential crack in a 1/4-inch stainless steel
instrument line during a walkdown inspection of the control air system. The
cracked line allowed the 30 psi control air to bleed off, reducing pressure on
the safety trip valve solenoid which shut down the EDG. Approximately 1 inch
of the line was removed and replaced with a compression fitting. The EDG was
restarted, and the test was successfully completed.
Nebraska Public Power District forwarded the cracked piece of stainless steel
tubing to a testing laboratory for analysis to determine the cause of the
failure. At this time, engine vibration is assumed to be the cause of the
failure. The licensee has introduced design changes to relocate all engine-
mounted instruments subject to high vibration from the engine onto instrument
racks. The modifications are scheduled for the next refueling outage.
Similar events in the instrumentation and control air system previously oc-
curred at Cooper Station in both 1975 and 1981. These problems were thought
to have been resolved by replacement of the original copper tubing with stain-
less steel tubing. The EDGs at Cooper Station were manufactured by Cooper
Energy Systems of Cooper Industries (so-called Cooper-Bessemer EDGs).
Wolf Creek Generating Station
A break in the fuel oil line of an EDG at Wolf Creek Generating Station
resulted in a fire on November 27, 1988. A fuel oil leak emanated from
a compression fitting on a 1/4-inch surge tank line. The leak quickly in-
creased from a drip to a spray over approximately 45 minutes. Since the leak
appeared to be between the nut and the ferrule and was believed to be
correctable with the unit in service, and because the EDG was undergoing a
24-hour endurance test, operations personnel did not shut down the EDG.
When the attending personnel discovered that the leak had increased signifi-
cantly, they notified the shift supervisor, and, consequently, the EDG was
secured by a control room operator. As the load was reduced, the attending
personnel noted flames, reported the fire to control room and security person-
nel, and actuated the fire alarm. Within about 3 minutes from the time the
attending personnel first noticed the fire, the fire was out.
Severe fretting on a horizontal section of the damaged 1/4-inch fuel line was
observed when the section was removed for repair. The fretting apparently was
caused by vibration-induced rubbing against the larger line to which the fuel
line was attached. The broken line also appeared to have been previously
broken and repaired in the same place. At that time, the fuel line had been
shortened, which could have introduced additional stresses at the location of
the new break. A post-event walkdown inspection of the EDG revealed further
evidence of inadequate support and fretting of other small fluid lines.
Previously, on December 4, 1986, a similar event occurred at Wolf Creek that
involved the same fuel line on one of the other EDGs, also during a 24-hour
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January 25, 1989
Page 3 of 3
endurance test. In this instance, the leak through the wall of the 1/4-inch
fuel line was caused by fretting similar to that observed on the fuel line
that failed in the event previously described. In addition, a number of other
problems have occurred involving small-diameter fluid lines on the EDGs as a
result of vibration. In January 1985, two fuel oil leaks resulted from holes
rubbed in a section of 1/2-inch steel tubing. In February 1985, sections of
both the control air system and the fuel oil lines failed to meet minimum wall
thick-ness requirements because of wear from vibration. In December 1987, a
cracked lube oil line fitting caused the EDG to shut down after 10 hours of a
24-hour endurance test. The Wolf Creek EDGs were manufactured by
Colt-Pielstick/Colt Industries.
Discussion:
These events indicate that small-diameter tubing installed on EDGs is suscepti-
ble to vibration-induced failures which could render the EDGs inoperable. The
vibration-induced failures may appear as cracking or breaks as well as holes
and wall thinning caused by rubbing of components that contact. These
failures are not limited just to specific manufacturers, systems, or
materials. The common underlying cause of the failures is the inadequate
design or installa-tion of the supports for the small-diameter tubing in a
vibration environment.
As the potential unavailability of an EDG has such a significant impact on
reactor safety, addressees may wish to review the small-diameter tubing of
the instrumentation and control air system as well as the tubing of the fuel
oil and lube oil systems of their EDGs. It is important to determine whether
vibration can introduce cracks or breaks and whether these failures could lead
to inoperability of the EDGs.
No specific action or written response is required by this information notice.
If you have any questions about this matter, please contact one of the techni-
cal contacts listed below or the Regional Administrator of the appropriate
regional office.
Charles E. Rossi, Director
Division of Operational Events Assessment
Office of Nuclear Reactor Regulation
Technical Contacts: G. L. Constable, RIV
(817) 860-8151
J. P. Jankovich, NRR
(301) 492-1167
W. C. Seidle, RIV
(817) 860-8148
Attachment: List of Recently Issued NRC Information Notices
. Attachment
IN 89-07
January 25, 1989
Page 1 of 1
LIST OF RECENTLY ISSUED
NRC INFORMATION NOTICES
_____________________________________________________________________________
Information Date of
Notice No._____Subject_______________________Issuance_______Issued to________
89-06 Bent Anchor Bolts in 1/24/89 All holders of OLs
Boiling Water Reactor or CPs for BWRs
Torus Supports with Mark I steel
torus shells.
89-05 Use of Deadly Force by 1/19/89 All holders of OLs
Guards Protecting Nuclear for nuclear power
Power Reactors Against reactors.
Radiological Sabotage
89-04 Potential Problems from 1/17/89 All holders of OLs
the Use of Space Heaters or CPs for nuclear
power reactors and
test and research
reactors.
89-03 Potential Electrical 1/11/89 All fuel cycle and
Equipment Problems major nuclear
materials
licensees.
89-02 Criminal Prosecution of 1/9/89 All holders of a
Licensee's Former President U.S. NRC specific
for Intentional Safety license.
Violations
88-23, Potential for Gas Binding 1/5/89 All holders of OLs
Supp. 1 of High-Pressure Safety or CPs for PWRs.
Injection Pumps During a
Loss-of-Coolant Accident
89-01 Valve Body Erosion 1/4/89 All holders of OLs
or CPs for nuclear
power reactors.
88-46, Licensee Report of Defective 12/30/88 All holders of OLs
Supp. 2 Refurbished Circuit Breakers or CPs for nuclear
power reactors.
88-101 Shipment of Contaminated 12/28/88 All holders of OLs
Equipment between Nuclear or CPs for nuclear
Power Stations power reactors.
_____________________________________________________________________________
OL = Operating License
CP = Construction Permit
..
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