United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 91-87: Hydrogen Embrittlement of Raychem Cryofit Couplings

                                UNITED STATES
                        NUCLEAR REGULATORY COMMISSION
                    OFFICE OF NUCLEAR REACTOR REGULATION
                          WASHINGTON, D.C.  20555 

                              December 27, 1991


NRC INFORMATION NOTICE  91-87:  HYDROGEN EMBRITTLEMENT OF RAYCHEM CRYOFIT 
                                COUPLINGS


Addressees 

All holders of operating licenses or construction permits for nuclear power 
reactors. 

Purpose 

The U.S. Nuclear Regulatory Commission (NRC) is issuing this information 
notice to alert addressees regarding the possible hydrogen embrittlement of 
Raychem Cryofit couplings that could result in failure.  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 are not NRC requirements; 
therefore, no specific action or written response is required. 

Description of Circumstances 

In July 1991 at the Seabrook Station, the licensee measured an unidentified 
leakage rate exceeding the 1.0 gpm technical specification limit from the 
Reactor Coolant System while the plant was operating in Mode 1 at 100 
percent power.  The source of the leak was determined to be in the vicinity 
of the pressurizer and, following plant shutdown, was located specifically 
in the gas space sampling line coming from the pressurizer.  The leak was 
caused by a 360-degree circumferential fracture at the midpoint of a Raychem 
Cryofit coupling.  During subsequent line inspection, a second Cryofit 
coupling located in the same line fractured in a similar manner after an 
accidental physical impact.  Both couplings are located downstream of the 
root isolation valve.

Discussion 

Raychem Cryofit couplings are hollow cylindrical devices made of a special 
alloy (50 percent titanium and 50 percent nickel) called Tinel that expands 
as temperature is decreased and contracts as temperature increases (because 
of a phase change).  When the coupling is properly installed, a rapid 
joining of two pipe ends can effectively be performed.  The licensee 
performed a metallurgical examination of the failed couplings and of other 
couplings in the Seabrook Station, correlated the metallurgical findings 
with the various exposure environments, and determined that the cause of the 
coupling failure was hydrogen embrittlement of the Tinel.  The licensee also 
determined that the combination of high hydrogen content in the exposure 
medium and high temperature was the critical determining factor.  No other 
combination of 

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                                                       December 27, 1991
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exposure environments resulted in degradation of the Tinel.  The vendor had 
been unaware of this application limitation for the Cryofit coupling since 
testing in these environments had not been performed.

To address the above findings, the licensee removed and replaced 
approximately 400 of the 3000 or more Cryofit couplings in the Seabrook 
Station with socket-welded joints or compression fittings.  Many of the 
replacements were conservatively selected because of the safety implications 
if they should fail (closely connected to the Reactor Coolant System or 
located on containment penetrations). 

This information notice requires no specific action or written response.  If 
you have any questions about the information in this notice, please contact 
the technical contact listed below or the appropriate Office of Nuclear 
Reactor Regulation (NRR) project manager. 




                                   Charles E. Rossi, Director Division of 
                                   Operational Events Assessment Office of 
                                   Nuclear Reactor Regulation

Technical contact:  Walter P. Haass, NRR 
                    (301) 504-3219

Attachment:  List of Recently Issued NRC Information Notices

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