Protecting People and the EnvironmentUNITED STATES NUCLEAR REGULATORY COMMISSION
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.
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. IN 89-62
August 31, 1989
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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
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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
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