IE Circular 77-08, Failure of Feedwater Sample Probe


                              April 13, 1977 

J. P. O'Reilly, Director, Region I 
N. C. Moseley, Director, Region II 
J. G. Keppler, Director, Region III
E. M. Howard, Director, Region IV 
R. H. Engelken, Director, Region V 


The subject document is transmitted for issuance by close of business within
three days after date of this letter. The Circular should be issued to all 
holders of Reactor Operating Licenses. Also enclosed is a draft copy of the 
transmittal letter. 

                                   Dudley Thompson, Acting Director 
                                   Division of Field Operations 
                                   Office of Inspection and Enforcement 

1. Circular 77-08 
2. Draft transmittal letter

Transmittal letter for Circular 77-08 to each holder of an NRC Operating 


The enclosed Circular 77-08 is forwarded to you for information. If there 
are any questions related to your understanding of the actions required, 
please contact this office. 

                                        (Regional Director) 

IE Circular 77-08  

Circular 77-08                                             Date: 
Page 1 of 2 



Recent events involving failure of sample probes are of concern to the NRC. 

During surveillance testing at the Cooper Nuclear Station on January 21, 
1977, a High Pressure Coolant Injection (HPCI) system check valve was found 
to be non-functional. Inspection of the valve revealed a length of feedwater
sample probe lodged in the valve. The piece of sample probe prevented the 
check valve from fully closing which allowed feedwater to flow backward into
the HPCI system injection line, however, the blocked check valve would not 
have prevented the HPCI system from supplying coolant to the feedwater 
system in the event it was required at the time. 

A similar probe failure occurred at the Brunswick facility on February 17, 
1976. This piece of feedwater sample probe was found lodged in the feedwater
check valve located just outboard of the primary containment. 

These feedwater sample probes are schedule 120 stainless steel, 1-inch OD, 
about 14-inches in length with 3 holes spaced to serve as the sample entry 
ports. The sample probes are inserted and welded to the feedwater lines at 
multiple locations. The Cooper sample probe was located directly opposite 
and above the "T" connection with the HPCI discharge line. 

Due to the non-functioning HPCI check valve at Cooper, the feedwater system 
pressurized the HPCI system suction piping when HPCI surveillance test was 
attempted. This pressurization caused the flange gasket to be blown out of 
the check valve located in the HPCI suction piping from the torus. This 
would not have prevented the HPCI from supplying emergency cooling water in 
the event it had been required. 

Circular 77-08                                                  Date: 
Page 2 of 2 

Both the Cooper and Brunswick failed sample probes were examined by 
metallographic analysis. NRC was orally informed that the probable failure 
mechanism was intergranular stress corrosion cracking which was probably 
induced by chlorides. There was no evidence of fatigue failure. 

Because there are a number of such sample probes used in light water nuclear
power reactors, these failures indicate a need for licensees to verify the 
integrity of similar components in their facilities. In addition, licensees 
should review the potential for such failures at their facilities and should
assess the potential consequences should such a failure occur. Particular 
attention should be given to those installations where a failure and 
subsequent blockage could lead to overpressurization of components of lower 
system design pressure. Operators should be made aware of these failures and
indications of such failures to enable them to respond properly should such 
an event occur. 

No written response to this Circular is required. If you need additional 
information regarding this matter, contact the Director of the cognizant NRC
Regional Office. 


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