Information Notice No. 82-22: Failures in Turbine Exhaust Lines
SSINS No.: 6835
NUCLEAR REGULATORY COMMISSION
OFFICE OF INSPECTION AND ENFORCEMENT
WASHINGTON, D. C. 20555
July 9, 1982
Information Notice No. 82-22: FAILURES IN TURBINE EXHAUST LINES
All nuclear power reactor facilities holding an operating license or
This information notice is provided as an early notification of events that
may have safety significance. It is expected that recipients will review the
information for applicability to their facilities. No specific action or
response is required at this time.
Description of Circumstances:
On June 28, 1982, Duke Power Company's Oconee Unit 2, while operating at 95%
power, experienced a 4-ft2 rupture of a 24-in.-diameter, long-radius elbow
in the feedwater heat extraction line which is supplied steam from the
high-pressure turbine exhaust. The rupture has been attributed to piping
degradation that results from steam erosion. The operator, upon hearing
steam noise and observing the absence of main steam (turbine header) line
pressure, believed a streamline break had occurred and manually tripped the
reactor. The main turbine automatically tripped as a result of the reactor
trip. Systems and related parameters responded as expected following the
reactor trip and subsequent recovery.
The steam jet destroyed a non-safety-related electrical load center in the
lower elevation of the turbine building and certain non-safety-related
instrumentation in the vicinity, but did not render any essential equipment
inoperable. Two persons suffered steam burns, serious enough to be
Initial indication of extraction streamline degradation at the Oconee
facility was discovered in 1976 when a pinhole leak occurred on a similar
line in Unit 3. Subsequent to this discovery, a maintenance surveillance
program utilizing ultrasonic examination of extraction steam lines was
begun. In 1980, two elbows on Unit 3 identical to the failed elbow on Unit 2
were replaced because, of steam erosion.
In March 1982, prior to the failure, ultrasonic inspection revealed
substantial erosion of the Unit 2 elbow in the extraction, line; however,
the erosion was less than the licensee's criterion for rejection. The
licensee theorizes that
July 9, 1982
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sustained reduced power operation and resultant lower quality steam
contributed to accelerated erosion and failure of the elbow. Additionally,
the previous inspection program may not have identified the section where
the line was thinnest.
The failed elbow and the identical elbow on the other "C" feedwater heater
supply line have been replaced.
The two corresponding 24-in. elbows on Oconee Unit 1 were ultrasonically
inspected on July 1, 1982. The inspection revealed that a 4-in.2 area in one
of the elbows had been reduced in thickness from 0.375 in. to 0.100 in.
Power operation was subsequently adjusted to 80% and the "C" feedwater
heaters isolated so that the affected steam line was maintained at 125 psig
with no steam flow.
The factor of safety based on material yield at the above pressure is
slightly greater than two. Elbow replacement will be performed on Unit 1
after returning Unit 2 to power.
In addition, the Institute of Nuclear Power Operations (INPO) has identified
four other similar failures of steamlines also apparently resulting from
steam erosion. These failures resulted in plant shutdown. They are Vermont
Yankee on 1/27/82; Trojan 1 on 1/9/82; Zion 1 on 2/12/82; and Browns Ferry 1
on 6/24/82. For example, in Vermont Yankee, a leak occurred in the
12-in.-diameter drain line between the "C" moisture separator and the heater
drain tank, blowing steam into the heater bay area. On Zion 1 a steam leak
occurred in the 150 psig high-pressure exhaust steam line from the' Unit 1
turbine. The leak originated from an 8-in, crack on a weld joining
24-in.-diameter piping with the 37.5-in.-diameter high pressure steam
exhaust pipe leading to the moisture separator reheater. INPO will issue a
Significant Event Report on Nuclear Notepad shortly and is preparing a
Significant Operating Experience Report which is expected to contain
recommendations on this subject.
If you have any questions regarding this matter please contact the Regional
Administrator of the appropriate NRC, Regional Office, or this office.
Edward L. Jordan, Director
Division of Engineering and
Office of Inspection and Enforcement
Technical Contact: O. Merrill
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