United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No.80-16 – Shaft Seal Packing Causes Binding in Main Steam Swing Disc Check And Isolation Valves

                                                          SSINS No.: 6870  
                                                          Accession No.:   
                                                          8002280667       

                                UNITED STATES
                        NUCLEAR REGULATORY COMMISSION
                    OFFICE OF INSPECTION AND ENFORCEMENT
                            WASHINGTON, DC 20555 
                                     
                              April 29, 1980  

                                           Information Notice No. 80-16 

SHAFT SEAL PACKING CAUSES BINDING IN MAIN STEAM SWING DISC CHECK AND 
ISOLATION VALVES 

Description of Circumstances: 

Recently two instances of binding of swing check valves have occurred. 
During disassembly of the main steam isolation valves at Indian Point 2, it 
was observed that all four reverse flow check valves were stuck at or near 
fully open. These 28" valves are manufactured by Atwood & Morrill Co. 

Investigation revealed that this condition was apparently caused by 
excessively tight shaft packing which did not allow free movement of the 
valve disc. 

This condition was reported on January 31, 1980. An evaluation determined 
that with the existence of the reported condition in event of a main steam 
line break upstream of a main steam isolation valve together with coincident
single failure of a main steam isolation valve to close in another loop, the
potential existed for blowdown of the contents of two steam generators. 

Main steam line break analyses applicable to Indian Point 2 have been 
performed assuming blowdown of the contents of one steam generator and have 
not considered multiple steam generator blowdown. Therefore, it is possible 
that the reported condition could have contributed to the exceeding of a 
safety limit as defined in the Unit 2 Technical Specifications if a main 
steam line break had occurred. 

The reported condition was corrected by adjusting the packing of these 
valves in all four loops and verifying that valve disc movement is not 
restricted. 

During testing in the hot standby mode at the Trojan Nuclear Plant on April 
15, 1980, three of the four main steam line isolation valves failed to close
when manually actuated. The cause of the occurrence was binding in the shaft
packing. The valve is air opened and is closed by gravity, steam flow and a 
small spring force; the valves were manufactured by Atwood & Morrill Co. The
licensee believes that the valves would have closed during actual operations
with steam flow in the line. The valves were repaired and tested 
satisfactorily. Modifications to the valves to install air operators to help 
close the valves are being investigated by the licensee. 

This Information Notice is provided as notification of a possible 
significant matter. It is expected that the recipients will review the 
information for possible applicability to their facilities and appropriate 
corrective action taken. 

No written response to this Information Notice No. is required. 

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