Information Notice No. 82-20: Check Valve Problems

                                                            SSINS No. 6835 
                                                            IN 82-20 

                               UNITED STATES 
                          WASHINGTON, D.C. 20555  

                               June 28, 1982 

Information Notice No. 82-20:   CHECK VALVE PROBLEMS 


All nuclear power reactor facilities holding an operating license (OL) or 
construction permit (CP). 


This information notice is provided as a notification of potentially 
significant problems pertaining to check valves. It is expected that 
recipients will review the information for applicability to their 
facilities. No specific action or response is required at this time. 

Description of Circumstances: 

A number of problems were recently reported involving swing check valves 
supplied by two manufacturers. Palisades Nuclear Plant, which is an 
operating plant, reported severe damage to the internals of 6-inch Alloy 
Steel Products Company (ALOYCO) swing check valves used in the low-pressure 
safety injection system (LPSI). 

Susquehanna Steam Electric Station, which is under construction, reported 
three separate problems with Pacific Company swing check valves that range 
in size from 6 inches to 20 inches installed in the residual heat removal 
(RHR), reactor core isolation cooling (RCIC), and core spray systems. 

The valves are similar in design and service to numerous other swing check 
valves, manufactured by other companies, that have had similar problems in 
the past. (Ref. LER 50-298/77-18, 50-255/81-37; A0 50-331/75-23; IE 
Information Notices 80-41, 81-30 and 81-35) 

Internal Damage to ALOYCO Valves: 

During required modifications of the LPSI system at the Palisades Nuclear 
Plant, Consumers Power Co. of Michigan reported that two of the four LPSI 
swing check valves were found to have internal damage. In both valves the 
disc nut washer and the disc nut pin were missing and the valve body, 
clapper arm, disc clapper arm shaft, and clapper arm support were severely 
worn. The discs were still attached to their clapper arms; however, valve 
seat and disc sealing surfaces were damaged and leaks from the valves could 
have been excessive. 


                                                           IN 82-20 
                                                           June 28, 1982  
                                                           Page 2 of 3 

It was subsequently discovered that the remaining two LPSI check valves had 
similar internal damage. The four LPSI check valves at Palisades were 
manufactured by ALOYCO about 1968. They are 6-inch swing-type check valves 
with weld ends for attachment to Schedule 120 piping. All four valves were 
mounted vertically with the flow direction upward. 

The swing check valves have an inline configuration with a ballooned or 
expanding area in the valve body for movement of the flapper-type disc. The 
disc is substantially larger than the nominal inside diameter of the pipe or
valve. If the disc should become separated from the clapper arm, it would be
trapped within the expanded portion of the valve body. This could lead to 
reduced LPSI flow or (with some small probability) the complete blockage of 
the line. 

Operation of the swing check valve in the direction of flow (normal 
operation) causes the threaded shaft on the back of the valve disc to strike
the valve body as it opens to the full-flow position. (The valve body is the
ultimate limiter of disc opening. During full-flow operation, there 
apparently is sufficient turbulence to cause the disc to chatter against the
valve body. The valves at Palisades, which are used for extended periods 
during shutdown cooling, exhibited about 112 inch of wear of the threaded 
portion of the disc shaft (greater than the height of the disc nut). 
Although the disc nuts had been worn away, none of the discs had separated 
from its clapper arm because of the peening of the shafts to a larger 

The ALOYCO check valves form the boundary between the LPSI and high-pressure
safety injection (HPSI) systems at Palisades. The abnormal wear of the 
check, valves was discovered during modifications of the LPSI piping to add 
leak-testing capability as required by NRC order, dated April 20, 1981, for 
Event V valve configurations. This order required the licensee to perform 
periodic leak-testing of check valves that form the interface between a 
high-pressure system connected to the reactor coolant system (RCS) and a low 
pressure system whose piping leads outside containment. Event V is defined 
as the failure of two in-series check valves to function as a pressure 
isolation barrier between a high-pressure system connected to the RCS and a 
lower pressure system extending beyond containment. This failure could cause 
an overpressurization and . rupture of the low-pressure system, which would 
result in a LOCA that bypasses containment and simultaneously render 
inoperable some of the equipment needed to mitigate a LOCA. 

Problems With Pacific Valves: 

During start-up testing at the Susquehanna Steam Electric Station Unit 1, 
Pennsylvania Power and Light reported three problems with Pacific check 
valves: (1) disc assembly to body interference and excessive packing 
friction, (2) excessive wear at hinge arm/disc stud interface, and (3) disc 
stud breakage. The Pacific check valves are used in many non-safety systems 
as well as the residual heat removal, reactor core isolation cooling, and 
core spray systems.  

                                                           IN 82-20  
                                                           June 28, 1981  
                                                           Page 3 of 3 

1.   Disc Assembly to Body Interference and Excessive Packing Friction 

     The interference problem was attributed to tolerance buildup by the 
     valve manufacturer. Undetected, a deficiency of this type could render 
     the valve unable to perform its safety function. The valves were 
     subsequently reworked at Susquehanna. The packing friction problem was 
     solved by changing packing type. 

2.   Excessive Wear at Hinge Arm/Disc Stud Interface 

     The excessive wear at the hinge arm/disc stud interface was identified 
     on non-safety related valves. The hinges and discs involved in the 
     excessive wear problem have been replaced in the safety related valves.
     The licensee will re-inspect the safety related valves to confirm that 
     the modifications have been effective in reducing wear. These 
     inspections will be performed after the valves have operated for a 
     sufficient time period that wear might be expected. 

3.   Disc Stud Breakage 

     The problem with the fractured stud, which is an integral part of the 
     disc/stud casting, appears to be similar to a earlier failure of an 
     Anchor/Darling valve (50-298/77-18). Although these failures were 
     similar, the cause of the Susquehanna failures appears to be a 
     metallurgical problem that is limited to the Pacific valves in this 
     case. In the safety related valves, the licensee is replacing the CA15 
     discs with discs manufactured from A516 Grade 70 plate with a stud 
     fabricated from the same material threaded and welded to the disc. In 
     the RCIC and HPCI exhaust systems, the swing check valve is being 
     replaced by a lift check valve. The inherent damping action of this 
     type valve is believed by the licensee to make it more able to 
     withstand the erratic steam flow conditions. 

If you have any questions regarding this matter, please contact the Regional
Administrator of the appropriate NRC Regional Office, or this office. 

                                   E. L. Jordan, Director 
                                   Division of Engineering  
                                     and Quality Assurance 

Technical Contact:  M. S. Wegner 

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