Information Notice No. 89-53: Rupture of Extraction Steam Line on High Pressure Turbine
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D.C. 20555
June 13, 1989
Information Notice No. 89-53: RUPTURE OF EXTRACTION STEAM LINE ON HIGH
All holders of operating licenses or construction permits for nuclear power
This information notice is being provided to alert addressees to a potential
generic problem involving erosion in carbon steel piping in secondary plant
systems. 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:
On April 18, 1989, a reactor trip from 100 percent power on high pressurizer
pressure occurred at Arkansas Nuclear One, Unit 2 (ANO-2) as a result of a
main turbine trip. The turbine tripped when steam escaping from a ruptured
high pressure steam extraction line caused a spurious actuation of the
electrical hydraulic control system's solenoid operated trip valve. The pipe
rupture occurred about 3 inches below the weld which joins a 12-foot section
of straight 14-inch diameter pipe to a second-stage extraction nozzle on the
high pressure turbine. The pipe wall at the rupture was worn to a thickness
of about 1/32-inch (nominal wall thickness is about 3/8 inches). The 180
degree "fishmouth" rupture was about 3 inches wide. This straight run of
14-inch diameter pipe terminates at an elbow. This elbow was replaced during
the last outage because of erosion induced wall thinning. The elbow
degradation was discovered as a result of the licensee's secondary system
surveillance program for wall thinning. However, the recently failed pipe and
those of similar geometries were not included in the surveillance samples. In
addition, the degraded condition of the pipe was not detected during
replacement of the elbow.
. IN 89-53
June 13, 1989
Page 2 of 2
The high pressure turbine at ANO-2 has two 14-inch second-stage extraction
steam lines. Ultrasonic testing of the second 14-inch second-stage extraction
steam line identified similar wall thinning conditions. The piping for both
extraction steam lines has been replaced.
The root cause assessment of this erosion phenomenon has not been finalized.
The licensee currently believes that the flow turbulence necessary to induce
erosion was likely set up by the geometry of the nozzle-to-pipe connection.
The outside diameters of the nozzle and pipe were essentially equal; however,
the thickness of the nozzle wall was greater than the thickness of the pipe
wall. This resulted in a mismatch between the inside diameter of the nozzle
and the inside diameter of the pipe. The expansion of the steam as it exited
the nozzle is postulated to have caused the accelerated erosion of the pipe.
NRC Information Notice 89-01 "Valve Body Erosion," dated January 4, 1989, and
NRC Information Notice 88-17, "Summary of Responses to NRC Bulletin 87-01,
'Thinning of Pipe Walls in Nuclear Power Plants'," dated April 22, 1988,
provide additional discussion on erosion of piping systems.
No specific action or written response is required by this information notice.
If you have any questions about this matter, please contact the technical
contact listed below or the Regional Administrator of the appropriate regional
Charles E. Rossi, Director
Division of Operational Events Assessment
Office of Nuclear Reactor Regulation
Technical Contact: L. Gilbert, Region IV
Attachment: List of Recently Issued NRC Information Notices
. Attachment 1
June 13, 1989
Page 1 of 1
LIST OF RECENTLY ISSUED
NRC INFORMATION NOTICES
Information Date of
Notice No._____Subject_______________________Issuance_______Issued to________
88-46, Licensee Report of 6/8/89 All holders of OLs
Supp. 3 Defective Refurbished or CPs for nuclear
Circuit Breakers power reactors.
89-52 Potential Fire Damper 6/8/89 All holders of OLs
Operational Problems or CPs for nuclear
89-51 Potential Loss of Required 5/31/89 All holders of OLs
Shutdown Margin During or CPs for nuclear
Refueling Operations power reactors.
88-88, Degradation of Westinghouse 5/31/89 All holders of OLs
Supp. 1 ARD Relays or CPs for nuclear
89-50 Inadequate Emergency 5/30/89 All holders of OLs
Diesel Generator Fuel or CPs for nuclear
Supply power reactors.
89-49 Failure to Close Service 5/22/89 All holders of OLs
Water Cross-Connect or CPs for nuclear
Isolation Valves power reactors.
89-48 Design Deficiency in the 5/22/89 All holders of OLs
Turbine-Driven Auxiliary or CPs for nuclear
Feedwater Pump Cooling power reactors.
89-47 Potential Problems With 5/18/89 All holders of OLs
Worn or Distorted Hose or CPs for nuclear
Clamps on Self-Contained power reactors and
Breathing Apparatus fuel facilities.
89-46 Confidentiality of 5/11/89 All holders of
Exercise Scenarios licenses for fuel
having an approved
OL = Operating License
CP = Construction Permit
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