United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 89-62: Malfunction of Borg-Warner Pressure Seal Bonnet Check Valves Caused by Vertical Misalignment of Disk

                                  UNITED STATES
                          NUCLEAR REGULATORY COMMISSION
                      OFFICE OF NUCLEAR REACTOR REGULATION
                             WASHINGTON, D.C.  20555

                                 August 31, 1989


Information Notice No. 89-62:  MALFUNCTION OF BORG-WARNER PRESSURE SEAL 
                                   BONNET CHECK VALVES CAUSED BY VERTICAL
                                   MISALIGNMENT OF DISK


Addressees:

All holders of operating licenses or construction permits for nuclear power 
reactors. 

Purpose:

This information notice is intended to alert addressees of the potential mal-
functioning of Borg-Warner pressure seal bonnet check valves caused by the 
misalignment of the valve disk.  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 do not constitute NRC requirements; therefore, no 
specific action or written response is required.

Description of Circumstances:

On April 23 and May 5, 1989, during hot functional testing at Comanche Peak 
Unit 1, a combination of procedural errors and malfunctioning check valves 
resulted in the backflow of high temperature water from the steam generators 
through the auxiliary feedwater system to the condensate storage tank.  This 
flow caused abnormally high temperatures, thermal stresses in excess of the 
code allowable stresses, and damage to piping supports.

The procedural errors that occurred during testing on both dates involved 
simultaneously opening both an auxiliary feedwater pump discharge valve 
connecting the pump to the steam generators and an isolation valve in a test 
line leading back to the condensate storage tank.  During the time period 
covering both dates, each of the eight 4-inch Borg-Warner check valves in the 
auxiliary feedwater supply lines leading to the steam generators was jammed 
partially open as a result of improper assembly.  This combination of 
circumstances allowed water from the steam generators to flow back through the 
check valves, a pump discharge valve, and a test line isolation valve to the 
condensate storage tank.

In a separate incident on April 19, 1989, a 3-inch Borg-Warner check valve 
located in the motor-driven auxiliary feedwater pump miniflow recirculation 
line was found to be inoperable.  On examination, the two remaining 3-inch 
miniflow recirculation valves in the auxiliary feedwater system also were 
found to be inoperable.  


8908240375
.                                                            IN 89-62
                                                            August 31, 1989
                                                            Page 2 of 3


Investigation revealed that the valve disks of these three 3-inch valves, as 
well as the eight inoperable 4-inch valves, were all positioned too low in the
valve body relative to the valve seats.  As a result, when the valve disk 
moved toward the seat, the outside upper edge of the disk was caught under the 
inside upper edge of the seat causing the disk to be jammed open with the 
plane of the disk at a large angle relative to the plane of the seat (Figure 
1).  All eleven of the inoperable valves were of the 900 psi pressure seal 
bonnet type.

Discussion:

During the two steam generator water backflow events, the operators made 
almost identical errors, although two different sets of valves were involved.  
On April 23 an auxiliary operator intended to realign valves associated with 
the turbine-driven auxiliary feedwater pump to permit recirculation flow to 
the condensate storage tank.  The procedure required closing the normally open 
turbine pump discharge valve (1AF-041) before opening the turbine pump 
recirculation test line isolation valve (1AF-042).  However, the valves were 
operated simultaneously and the recirculation valve which could be opened 
rapidly, was fully open while the discharge valve which took a half hour to 
close, was still open.  In about 10 minutes the levels in steam generators 1, 
2, and 4 were noticed to be decreasing rapidly.  At about 20 minutes into the 
event, paint on the pipes in the turbine pump room was reported to be 
"bubbling and peeling" and the recirculation valve was closed, terminating the 
backflow.  

On May 5 the operators were conducting an auxiliary feedwater system operabil-
ity test.  The motor-driven auxiliary feedwater pump recirculation test line 
isolation valve (1FA-055) was opened while the motor-driven pump discharge 
valve (1FA-054) was still open.  Again, this was contrary to the procedure in 
use, which required closing the discharge valve prior to opening the test line 
isolation valve.  During this event, only water from steam generator 1 is 
believed to have reached the auxiliary feedwater piping.  The backflow was 
initially stopped when the discharge valve (-054) was fully closed.  However, 
when the operators attempted to restore the valves to the original position to 
resume pumping to the steam generators, the test line isolation valve (-055) 
was inadvertently left partially open, reestablishing the backflow to the con-
densate storage tank.  This backflow persisted for the next hour and a half, 
being interrupted intermittently by the operation of the two auxiliary feed-
water motor-driven pumps.  The operators observing inconsistencies in the flow 
to the steam generators finally realized that the test line isolation valve 
was open and closed it, terminating the backflow.

The reason that the disk assemblies of the malfunctioning check valves were 
positioned too low in the valve bodies was that an essential step was missing 
from the vendor's reassembly procedure.  The disk assembly, as well as the 
valve bonnet and seal, is suspended from and positioned vertically by a 
threaded ring that is screwed into the top of the valve neck, called the 
retainer ring (Figure 1).  The prescribed assembly procedure for the 3- and 
4-inch valves (Borg-Warner Operation and Maintenance Manual, OMM 1003) was to 
install and bottom out the retainer ring.  This had the effect of locating the 
disk assembly too low in the valve.  The original factory assembly process 
included the backing 
.                                                            IN 89-62
                                                            August 31, 1989
                                                            Page 3 of 3


out of the retainer ring while observing the disk through the valve ports 
until the disk had been raised to the correct height.  However, the necessary 
step of backing out the retainer ring to its original factory assembly height 
was not included in the reassembly procedure provided with the 3- and 4-inch 
valves.  All of the auxiliary feedwater check valves had been disassembled and 
inspected in 1983 because of a concern about the adequacy of the disk stud 
fillet welds.  During the following reassembly using the incorrect procedure, 
all of the 3- and 4-inch valve disks were positioned lower than the original 
factory adjusted position.  Larger Borg-Warner check valves (6, 8 and 10-inch) 
could also be affected by this error.  

The April 23 backflow of high temperature water caused a significant amount of 
blistering and flaking of the paint on the auxiliary feedwater supply lines as 
well as some unusual stressing of the auxiliary feedwater piping.  However, 
the May 5 backflow is believed to have caused the most damage.  Several areas 
in the piping are known to have experienced thermal stresses that exceeded the 
code allowable stresses.  In addition, one of the piping supports failed and 
had to be replaced.  As a result, an extensive analysis of the piping, the 
piping supports, and the penetrations had to be made to ensure the continued 
reliability of the auxiliary feedwater system.  

This information notice requires no specific action or written response.  If 
you have any questions about the information in this notice, please contact 
one of the technical contacts listed below or the appropriate NRR project 
manager. 




                              Charles E. Rossi, Director
                              Division of Operational Events Assessment
                              Office of Nuclear Reactor Regulation

Technical Contacts:  H. H. Livermore, NRR
                     (817) 897-1500

                     M. F. Runyan, NRR
                     (817) 897-1500 

Attachments:
1.   Figure 1, Check Valve Shown with
       Disk Jammed in Open Position
2.   List of Recently Issued NRC Information Notices

.                                                            Attachment 2 
                                                            IN 89-62 
                                                            August 31, 1989 
                                                            Page 1 of 1

                             LIST OF RECENTLY ISSUED
                             NRC INFORMATION NOTICES
______________________________________________________________________________
Information                                  Date of 
Notice No._____Subject_______________________Issuance_________Issued to_______

89-61          Failure of Borg-Warner Gate   8/30/89        All holders of OLs
               Valves to Close Against                      or CPs for nuclear
               Differential Pressure                        power reactors. 

88-48,         Licensee Report of Defective  8/22/89        All holders of OLs
Supp. 2        Refurbished Valves                           or CPs for nuclear
                                                            power reactors. 

89-60          Maintenance of Teletherapy    8/18/89        All NRC Medical 
               Units                                        Teletherapy 
                                                            Licensees. 

89-59          Suppliers of Potentially      8/16/89        All holders of OLs
               Misrepresented Fasteners                     or CPs for nuclear
                                                            power reactors. 

89-58          Disablement of Turbine-Driven 8/3/89         All holders of OLs
               Auxiliary Feedwater Pump Due                 or CPs for PWRs. 
               to Closure of One of the 
               Parallel Steam Supply Valves 

89-57          Unqualified Electrical        7/26/89        All holders of OLs
               Splices in Vendor-Supplied                   or CPs for nuclear
               Environmentally Qualified                    power reactors. 
               Equipment 

89-56          Questionable Certification    7/20/89        All holders of OLs
               of Material Supplied to the                  or CPs for nuclear
               Defense Department by Nuclear                power reactors. 
               Suppliers 

89-45,         Metalclad, Low-Voltage        7/6/89         All holders of OLs
Supp. 1        Power Circuit Breakers                       or CPs for nuclear 
               Refurbished With Substandard                 power reactors. 
               Parts 

89-55          Degradation of Containment    6/30/89        All holders of OLs
               Isolation Capability by a                    or CPs for nuclear
               High-Energy Line Break                       power reactors. 

89-54          Potential Overpressurization  6/23/89        All holders of OLs
               of the Component Cooling                     or CPs for nuclear
               Water System                                 power reactors. 
______________________________________________________________________________
OL = Operating License
CP = Construction Permit 
..
Page Last Reviewed/Updated Tuesday, November 12, 2013