United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 86-09: Failure of Check and Stop Check Valves Subjected to Low Flow Conditions

                                                            SSINS No: 6835 
                                                            IN 86-09       

                                UNITED STATES
                           WASHINGTON, DC 20555

                              February 3, 1986

Information Notice No. NO 86-09:   FAILURE OF CHECK AND Stop CHECK VALVES 
                                   SUBJECTED TO LOW FLOW CONDITIONS 


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


This notice is provided to alert recipients of a potentially significant 
safety problem pertaining to check and stop check valves failing under low 
flow conditions It is expected that recipients will review the information 
for applicability to their facilities and consider actions, if appropriate, 
to preclude a similar problem occurring at their facilities However, 
suggestions contained in this notice do not constitute NRC requirements; 
therefore, no specific action or written response is required 

Description of Circumstances: 

Between late November 1985 and early January 1986, Florida Power and Light's
Turkey Point facility experienced numerous failures of the 12 stop check 
valves in the steam supply system to the auxiliary feedwater pumps The stop
check valves are located upstream and downstream of a motor-operated valve 
(MOV) that opens when required to initiate auxiliary feedwater flow The 
stop check valves are normally open and thus allow steam flow to the pumps 
while at the same time preventing backflow through the steam line in the 
event of a steam line break 

The mode of failure of the valve was degradation of the disc and disc nut, 
assembly (see attached sketch) due to low steam flow conditions caused by 
slight leakage past the normally closed MOV The low steam flow rate, was 
hot sufficient to keep the disc open and the disc assembly then vibrated and
chattered causing excessive wear and damage to the valve internals, in 
particular, the disc assembly In many cases (three in November and four in 
January), the disc guide stud had broken off from the disc This allowed the
disc to become cocked in the valve and prevented full closure (thus 
defeating both the check and stop features of the valve) and full opening 
(thus restricting steam flow) In addition, the broken disc guide stud was 
free to travel downstream with steam flow and could have caused damage to 
equipment and components in the flow path 


                                                           IN 86-09        
                                                           February 3, 1986 
                                                           Page 2 of 2     

The licensee performed a failure analysis of the disc assembly to verify the
acceptability of a higher strength material being used in a redesigned disc 
guide In addition, the licensee committed to a program of regular 
radiographic examination of the valves on Unit 3 for the remainder of the 
refueling cycle However, the licensee considers this to be an interim 
repair pending the completion of the study underway by its AFW Enhancement 
Task Force 

A related series of events was discussed in Information Notice No. 82-26, 
"RCIC and HPCI Turbine Exhaust Check Valve Failures" In this case the low 
steam flow rates were the result of testing the RCIC and HPCI turbines at 
less than rated load The corrective actions consisted of changes to test 
procedures, changes to the exhaust system design, and changing to a 
different check valve style 

The information herein is being provided as an early notification of a 
possibly significant matter that is still under review by the NRC staff 
Recipients should review the information for possible applicability to their
facilities If NRC evaluation so indicates, further licensee actions may be 

No specific action or written response is required by this information 
notice If you have any questions about this matter, please contact the 
Regional Administrator of the appropriate regional office or this office 

                                   Edward L Jordan Director 
                                   Division of Emergency Preparedness 
                                     and Engineering Response 
                                   Office of Inspection and Enforcement 

Technical Contact:  George A Schnebli, RII
                    (404) 331-4875

                    Richard J Kiessel, IE
                    (301) 492-8119

1   Sketch of Stop Check Globe Valve
2   List of Recently Issued IE Information Notices

Page Last Reviewed/Updated Friday, May 22, 2015