Protecting People and the EnvironmentUNITED STATES NUCLEAR REGULATORY COMMISSION
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.
