Information Notice No. 83-54: Common Mode Failure of Main Steam Isolation Nonreturn Check Valves
SSINS No.: 6835
NUCLEAR REGULATORY COMMISSION
OFFICE OF INSPECTION AND ENFORCEMENT
WASHINGTON, D.C. 20555
August 11, 1983
Information Notice No. 83-54: COMMON MODE FAILURE OF MAIN STEAM
ISOLATION NONRETURN CHECK VALVES
All nuclear power reactor facilities holding an operation license (OL) or
construction permit (CP).
This information notice is provided as a notification of a potentially
significant problem pertaining to common mode failure of main steam
isolation nonreturn check valves at a nuclear power facility. The apparent
cause of the failure was increased friction due to over tightening of the
packing gland to preclude steam leakage. The increased friction was
sufficient to prevent valve closing under no flow conditions and the
licensee was unable to conclude that the valves would have operated as
designed in the event of a steam line break with reverse flow. No specific
action is required in response to this information notice, but it is
expected that recipients will review the information for applicability to
Description of Circumstances:
On June 8, 1983, Portland General Electric Company reported (LER 83-06)
finding all four main steam nonreturn check valves stuck open after the
Trojan Nuclear Plant had shut down and steam flow had been stopped.
Each of the four main steam lines is equipped with a main steam isolation
valve and a main steam isolation nonreturn check valve. One of the plant's
design-basis accidents is the instantaneous rupture of the main steam line
in any location and the failure of one of the main steam isolation valves to
close. For this postulated event, no more than one steam generator will blow
down if the nonreturn check valves operate properly. Thus, this failure of
the four nonreturn check valves caused a reduction in the defense-in-depth
of protection which could have led to a blowdown of more than one steam
generator if a break were to occur upstream of the main steam isolation
nonreturn check valve in one loop and the main steam isolation valve failed
in another loop. All main steam isolation valves were operable during the
period in question as shown by the periodic operating test records.
The apparent cause of the failure was packing-induced friction which
occurred when the packing gland was tightened to preclude steam leakage past
the packing and valve stem. The packing was tightened following the last
refueling outage and subsequent startup in July 1982. The valves were
previously repacked in the Spring of 1981. The two-year interval between
repacking (Spring of 1981
August 11, 1983
Page 2 of 2
to June 1983) seems to be too long as the packing removed from the valves
was dried and brittle. This condition contributed to the frictional forces
that prevented the valves from closing.
As part of their evaluation of the event, the utility performed an analysis
to determine if the main steam nonreturn check valves would shut during a
design basis event. Based on this analysis, the utility was unable to
conclude that the reverse steam flow would provide sufficient torque to
close the valves.
A contributing factor to the valve failure was the fact that the check
valves had been inadvertently omitted from the Inservice Testing program and
hence, were not routinely tested for operability.
To preclude reoccurrence, the utility is planning on performing the
following corrective actions prior to reaching full power following the 1983
1. The check valve packing will be replaced each refueling outage.
2. Possible gland follower binding will be eliminated by increasing the
inside diameter of the gland follower to allow easier movement along
3. A testing program will be provided to adjust packing before and after
heatup to ensure free movement of the disk while minimizing steam
leakage through the packing.
4. An engineering evaluation will be performed to determine alternative ,
corrective action should this condition persist, including reevaluation
of valve operation with reverse steam flow.
Additionally, the main steam isolation check valves have been added to the
Inservice Testing program.
No written response to this notice is required. If you have any questions
regarding this matter, please contact the appropriate NRC Regional Office,
or this office.
Edward L. Jordan Director
Division of Emergency Preparedness
and Engineering Response
Office of Inspection and Enforcement
Technical Contact: R. J. Kiessel, IE
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