Protecting People and the EnvironmentUNITED STATES NUCLEAR REGULATORY COMMISSION
ACCESSION #: 9611140064
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PACIFIC
SCIENTIFIC
HTL/KIN-TECH DIVISION
November 5, 1996 22715 Savi Ranch Parkway,
P.O. Box 87019
Yorba Linda, CA 92686-8719
(714) 283-0283
Attn: Document Control Desk Fax (714) 283-0819
U. S. Nuclear Regulatory Commission
Washington, DC 20555
Reference: Event # 31089 10/3/96
In accordance with 10CFR 21 - Reporting of Defects and Noncompliance the
following report is submitted by:
Pacific Scientific
HTL / Kin-Tech Division
22715 Savi Ranch Parkway
Yorba Linda, CA 92887-4609
Steve Kahm
Director of Quality Control
The defective part is an Inner Thrust Bearing 1801461-01 used in a
PSA 35 Mechanical Shock Arrestor 1801112-** manufactured by Pacific
Scientific. The Mechanical Shock Arrestor ( snubber ) is used as a
restraint on piping systems for a Nuclear Generating Plant.
The defective Inner Thrust Bearing was supplied by:
Markall
3207 W. Pendleton Ave
Santa Ana, CA 92704
PSA 35, Cracked Inner Thrust Bearings - P/N 1801461-01
Cracks were found in a PSA 35 Snubber Inner Thrust Bearings -
1801461-01. This indicated a breakdown in the NDT check in
manufacturing this part.
Page 1 of 3
A snubber acts like a rigid strut when activated and limits the
piping movement to +/- .060 inches between 3 to 33Hz at full
rated load. The worst case failure mode is for the cracked
Inner Thrust Bearing to disintegrate or distort under load
during a sesmic event and cause the snubber to become a rigid
strut. The failed snubber would protect the piping system.
But the piping system would be under stress when the plant
returned to a shut down condition. The snubber would not be
able to telescope and allow the pipe to return to the cold set
position but remain in the hot set position.
The following are the dates for this event:
10/1/96 Trouble and Failure Report (TFR) was written up on the
defective 1801 461-01 Thrust Bearing.
10/3/96 Called NRC OPERATION CENTER 301 816-5100
Mr. Doug Weaver assigned an Event # 31089.
The defective Inner Thrust bearings has been isolated to three
nuclear plants. Attached is a location of the plants to which PSA
35 snubbers were supplied with potential defective thrust bearings.
The USA plants are returning their snubbers for inspection, thrust
bearing replacement and test. We are still working out the return
of the snubbers shipped to Wolsong 3 in Korea.
The NDT acceptance after heat treat should have rejected the cracked
parts. This necessitated a review of the approved vendors NDT
procedures and personnel. On 10/8/96 Pacific Scientific surveyed
the NDT vendor and reviewed their NDT program and tested their
present NDT personnel and found their program acceptable. The
individual who accepted the bad lot of parts had been fired before
our visit.
Internal Purchasing and Assembly Outline Procedures will be changed
to requiring an additional in-house NDT for parts in question. In
addition an assembly visual check of the thrust bearings inspection
point for the PSA 35 and PSA 100 mechanical shock arrestor
assemblies will be added. Expect this procedural changes to be
completed 11/14/96.
Page 2 of 3
Assembled a PSA 35 with a defective thrust bearing and was
successfully tested at different frequencies for a total of 5000
full rated load life cycle. Under these extreme conditions the test
unit demonstrated that the snubber still met Design Specification
requirements even with a defective thrust bearing. Most snubbers
when removed during an outage should normally not see at most 5-10
full rated load cycles. A PSA 35 snubber with a defective thrust
bearing is considered operable for a single outage. Recommend that
units with a potential defective thrust bearing be returned for
examination. But if the unit was installed we recommend that it be
removed at the next outage and sent back to the factory for
examination.
The lot of defective parts have been located and isolated to only
three customers. The two USA plants snubbers were not installed and
the units are being returned to Pacific Scientific. For the Korean
Wolsong 3 plant we are still working out a replacement schedule.
A final report will be completed by November 30, 1996 for submittal.
Regards,
Steve Kahm
Quality Assurance Director
HTL / Kin-Tech Division
Page 3 of 3
Table "LISTING OF UTILITIES WHO HAVE BEEN SHIPPED UNITS WITH SUSPECT
1801461-01 THRUST BEARINGS" omitted.
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