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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 9112200262 . IN 91-87 December 27, 1991 Page 2 of 2 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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