United States Nuclear Regulatory Commission - Protecting People and the Environment

ACCESSION #:  9611140064

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                                              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:


          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


     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.


Steve Kahm

Quality Assurance Director

HTL / Kin-Tech Division

                                                              Page 3 of 3


1801461-01 THRUST BEARINGS" omitted.


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