Protecting People and the EnvironmentUNITED STATES NUCLEAR REGULATORY COMMISSION
SSINS No.: 6835
IN 82-26
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF INSPECTION AND ENFORCEMENT
WASHINGTON, D.C. 20555
July 22, 1982
Information Notice No. 82-26: RCIC AND HPCI TURBINE EXHAUST CHECK VALVE
FAILURES
Addressees:
All boiling water nuclear power reactor facilities holding an operating
license or construction permit.
Purpose:
This information notice is provided as an early notification of a
potentially significant problem pertaining to reactor core isolation cooing
(RCIC) and high pressure coolant injection (HPCI) turbine exhaust check
valve failures. 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 RCIC turbine exhaust check valve failures that have occurred
during the past 20 months are outlined below.
1. On December 10, 1980, Carolina Power and Light Company reported (LER
80-101/03L) a RCIC system turbine trip at Brunswick Steam Electric
Plant, Unit 2, while conducting a RCIC system test. The turbine tripped
on high turbine exhaust pressure due to the turbine exhaust swing check
valve failing in the closed position. Inspection revealed the check
valve disc stem had broken off where it connects to the valve hinge
assembly. This allowed the disc to fall into the discharge part of the
valve and isolate flow. An examination of the check valve disc and
hinge assembly indicated the disc had been rotating inside of the hinge
bore area and caused excessive wear of both components. In addition,
indications that the valve disc had been striking the upper part of the
valve body while in the open position were noted. To return the check
valve to normal operability, the valve seat was lapped, the valve disc
replaced, and the valve was tested satisfactorily.
This LER also referred to a similar failure (LER 79-074/03L) at
Brunswick Steam Electric Plant, Unit 1. This time, disassembly of the
RCIC steam exhaust check valve showed that the stud and nut on the back
of the disc had broken and the disc had separated from the hinge and
had lodged in the valve inlet. A new valve was ordered and installed
upon arrival. The valve failure prevented the RCIC turbine, which had
been used intermittently throughout the day for vessel level control,
from starting following a reactor scram.
8204210398
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July 22, 1982
Page 2 of 4
2. On May 29, 1981, Pennsylvania Power and Light Company reported (ERs
100450/100508) the failure of the RCIC turbine exhaust swing check
valve at Susquehanna Steam Electric Station, Unit 1, while conducting a
RCIC system test. The stud (integrally cast with the disc) which
attached the disc, to the valve hinge broke off. In a subsequent report
on February 5, 1982, they indicated that turbine exhaust steam flow
conditions experienced during testing caused the valve disc to cycle
violently open and close. Since the check valve was sized for full
flow, operational testing of the system at low flow caused the disc
function to be erratic. As a result, the end of the disc stud gradually
wore a hole in the valve bonnet (cover) which served as the stop. This
additional travel allowed the disc edge to impact against the valve
body due to a lack of clearance. The loads and stresses experienced by
the disc resulted in a disc stud fracture. The failure was a brittle
fracture. A second disc, taken from Unit 2, was put in service to
replace the fractured disc. This disc also failed at approximately the
same section as the first. Therefore, they concluded that with both the
valve and system as presently designed, a swing check valve disc will
fail for this service application. This was further evidenced by three
more replacement discs that eventually broke in a similar fashion in
spite of the provision of a specially designed "anvil" nut to replace
the original nut. They are planning on either replacing the existing
valve with a lift type check valve design having an inherent damping
action in the opening position or modifying the existing valve and/or
piping system so that the valve will function properly under both, low
and high flow conditions. (See Information Notice No. 82-20.)
3. On December 10, 1981, Georgia Power Company reported (LER 81-112/03L),a
RCIC isolation at Edwin I. Hatch Nuclear Plant, Unit 2, while
conducting a RCIC rated flow test. An investigation revealed that the
turbine exhaust check valve had internal damage creating a block in the
line causing the rupture diaphragm to fail. The valve was repaired and
the diaphragm replaced. A design change has been approved to replace
the check valve with a better design. The new valve has been ordered
and will be installed as soon as possible.
A generic review, by the licensee, revealed that the HPCI system has
the same valve type in a similiar configuration and that a design
change has been approved to replace the valve.
4. On March 9, 1982, Long Island Lighting Company reported a deficiency
concerning two check valves located in the RCIC turbine exhaust line at
Shoreham Nuclear Power Station. The deficiency was identified while t
testing the turbine and pump using auxiliary steam at low flow
conditions. Examination of the valves disclosed that the slamming and
cyclic action of the valve resulted in wear to the swing check
bushings, the anti-rotation pins, and the swing checks. The valve
bodies showed rubbing marks from the interaction with the swing check.
A systems review of the valve failures, by the licensee, indicated that
damage to these components could have an
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IN 82-26
July 22, 1982
Page 3 of 4
impact on the turbine exhaust back pressure thereby causing the turbine
to trip. All damaged components of the RCIC exhaust check valves will
be replaced and the valves will be rebuilt to assure properly
conditioned and working valves are installed.
Discussion:
All of the above failures deal only with the RCIC turbine exhaust check
valve. However, as noted by Georgia Power Company, the HPCI exhaust system
has the same type valve in a similiar system configuration. Thus it is
reasonable to expect similiar problems with the HPCI turbine exhaust check
valve also. In fact, both services have been identified in the generic
correspondence by General Electric pertaining to this topic.
The first of the generic correspondence is Services Information Letter (SIL)
No. 30, "HPCI/RCIC Turbine Exhaust Line Vacuum Breakers," dated October 31,
1973. In this SIL, General Electric identified the problem of possible
damage to the exhaust line check valve and recommended the installation of
vacuum breakers based on tests conducted at Browns Ferry and Peach Bottom.
The second of the generic correspondence is Application Information Document
(AID) No. 56, "High Pressure Core Injection and Reactor Core Isolation
Cooling Turbine Exhaust Check Valve Cycling," dated December 18, 1981. In
this AID, General Electric identified the possible causes of failure as
improper system operation, improper check valve sizing, inadequate check
valve design, or inadequate exhaust line design. To minimize the possibility
of future problems, they recommend that:
1. Manual starts and monthly system surveillance testing should be
performed in accordance with the Operating and Maintenance Instructions
(specifically, gradually increasing the turbine speed until the rated
pump discharge flow is achieved is not recommended).
2. The exhaust check valve, the exhaust line vacuum breaker, and the
exhaust line sparger should be designed in accordance with the
requirements/ recommendations given in the GE system design
specification.
3. System operation below the recommended turbine rated speed should be
minimized.
4. The exhaust check valve should be located as close as possible to the
containment.
5. The turbine exhaust check valve internals should be visually inspected
on a routine schedule such as at every refueling outage.
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IN 82-26
July 22, 1982
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If you have any questions regarding this matter, please contact the Regional
Administrator of the appropriate NRC Regional Office, or this office.
Edward L. Jordan, Director
Division of Engineering and
Quality Assurance
Office of Inspection and Enforcement
Technical Contact: Richard J. Kiessel
301-492-8119
Attachment:
List of Recently Issued IE Information Notices
