United States Nuclear Regulatory Commission - Protecting People and the Environment

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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                                                            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 
..
Page Last Reviewed/Updated Tuesday, November 12, 2013