Information Notice No. 82-22: Failures in Turbine Exhaust Lines

                                                            SSINS No.: 6835 
                                                            IN 82-22  

                               UNITED STATES 
                          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 
construction permit. 


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 
hospitalized overnight. 

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 


                                                           IN 82-24  
                                                           July 9, 1982  
                                                           Page 2 of 2 

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   
                                     Quality Assurance 
                                   Office of Inspection and Enforcement 

Technical Contact:  O. Merrill 

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