IE Circular No. 80-04, Securing of Threaded Locking Devices on Safety-Related Equipment
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF INSPECTION AND ENFORCEMENT
WASHINGTON, D.C. 20555
IE Circular No. 80-04
Date: March 14, 1980
Page 1 of 3
SECURING OF THREADED LOCKING DEVICES ON SAFETY-RELATED EQUIPMENT
Description of Circumstances:
In recent months, several licensee event reports have been submitted that
address the inoperability of safety-related equipment caused by loosened
threaded locking devices. Some of the events are listed below:
I. MAIN STEAM CHECK VALVE HEX NUT LOCKING DEVICES, TURKEY POINT NO. 3
REPORTABLE OCCURRENCE 250-79-31 (Oct. 22, 1979)
During a planned outage of Turkey Point Unit No. 3 on October 7, 1979,
a two-inch internal diameter hex nut was discovered in the internals
of a steam supply valve for a moisture separator-reheater.
Investigation revealed that the nut was missing from the disc stud of
the 3A main steam check valve. The disc and disc stud were in the
proper position and the valve was fully operable. The 3B and 3C main
steam check valves were inspected and the disc stud, nut and locking
washer were in place although some distress was noted on the 3C locking
washer in that the tack welds on the locking pin had separated.
The licensee installed an improved locking device on the disc stud on
each of the three main steam check valves. The locking device consists
of a tab washer that is prevented from rotating by a pin and by fingers
that extended on either side of the valve arm; the tabs are bent up
against two faces of the hex nut. The main steam isolation valves
(MSIV) have the same type of hex nut locking device. The valves are
Schutte and Koerting SK Type 828.
II. SLIPPAGE AND MISALIGNMENT OF VALVE LINKAGES, DAVIS-BESSE LICENSEE EVENT
REPORT NOS. 78-101 (Nov. 1, 1978), 78-126 (Jan. 26, 1979), 79-068 (July
19, 1979), and 79-098 (Oct. 30, 1979)
These reports involve the inoperability of two service water system
valves and one component cooling water system valve. The valves were
declared inoperable because the nut on the actuator linkage was either
missing or had loosened to the point where there was slippage and
misalignment of the valve linkage. These valves were provided by
Hammel-Dahl. The supplier has provided the licensee with an addendum
to the instruction manual that defines the torque requirements for the
cap screw that is used to retain the actuator link arm to the valve
disc arm.
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IE Circular No. 80-04
Date: March 14, 1980
Page 2 of 3
III. ECCS SUBSYSTEM INOPERABLE - NO. 12 SAFETY INJECTION PUMP IMPELLER
LOCKNUTS LOOSE, SALEM NO. 1, LICENSEE EVENT REPORT NO. 79-68 (Dec. 20,
1979).
The AC supply breaker tripped when No. 12 Safety Injection (SI) pump
was started, to fill the accumulators on October 18, 1979. When the
rotor could not be turned by hand, the upper casing was removed for an
inspection of the pump internals. The radial and thrust locknuts were
found loosened to the extent that they could be removed by hand. The
impeller spacer sleeves were worn and the impeller shaft was slightly
bent. The pump was reworked, tested and returned to service on
November 2, 1979.
The locknuts on the three other Unit 1 and Unit 2 Safety Injection (SI)
Pumps were inspected and two pump impeller locknuts were found loose,
and one pump impeller locknut was found secured with setscrews that had
been installed by mistake at the manufacturing facility and the
impeller was sent back to the manufacturer for rework. The locknuts
on all of the SI pumps were secured using Locktite compound per Public
Service Engineering Department recommendation and the pump
manufacturer's concurrence. The pumps are horizontal, centrifugal, ten
stage units manufactured by Pacific Pumps, Inc.
IV. TARGET ROCK MOTOR OPERATED GLOBE VALVES - BUSHING NOT STAKED, ANO NO.
2 LICENSEE EVENT REPORT 79-93 (Feb. 14, 1980)
While investigating the failure of a High Pressure Safety Injection
(HPSI) header shut-off valve at Arkansas Nuclear One, Unit 2, (ANO-2)
the threaded bushing was found loose. The bushing was not staked or
otherwise secured to prevent movement. This bushing is part of the
mechanism which converts the valve stem rotation to linear travel of
the disk. The full open limit switch is gear driven by the valve
operator and movement of the bushing can alter the relationship between
stem rotation and linear travel such that valve travel in the open
direction may be terminated prematurely by the limit switch. The HPSI
header shut-off valves at ANO-2 are Target Rock, 2-inch, 1500#, ANSI
Motor Operated Globe Valves. Arkansas Power & Light found that a
similar problem exists with the Low Pressure Safety Injection (LPSI)
header shut-off valves which are Target Rock, 6-inch, 1500#, ANSI Motor
Operated Globe Valves. Target Rock has provided Arkansas Power & Light
Company with a procedure for staking the bushing nuts.
V. OTHER EVENTS
Loose locking devices were also identified in one of the IE Bulletins
and two of the IE Circulars issued in 1979: IE Circular 79-04 Loose
Locking Nut on Limitorque Valve Operators, IE Circular 79-19 Loose
Locking Devices on Ingersoll-Rand Pumps, IE Bulletin 79-15 Deep Draft
Pumps.
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IE Circular No. 80-04
Date: March 14, 1980
Page 3 of 3
Recommended Action for Licensee Consideration:
It is recommended that licensees of operating power reactors and holders of
construction permits review the specific items presented in the "Description
of Circumstances" for applicability at their facilities and review their
installation and maintenance procedures to determine whether securing of
locking devices has been addressed in these procedures. It is further
recommended that installation and maintenance procedures for all safety-
related components be reviewed to be sure the securing of locking devices is
adequately covered.
No written response to this Circular is required. If you require additional
information regarding these matters, contact the Director of the appropriate
NRC Regional Office.
Page Last Reviewed/Updated Tuesday, March 09, 2021
Page Last Reviewed/Updated Tuesday, March 09, 2021