Headquarters Daily Report
OCTOBER 10, 2000
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REPORT NEGATIVE NO INPUT
ATTACHED INPUT RECEIVED RECEIVED
HEADQUARTERS X X
REGION I X
REGION II X
REGION III X X
REGION IV X
PRIORITY ATTENTION REQUIRED MORNING REPORT - REGION IV OCTOBER 10, 2000
Licensee/Facility: Notification:
Nebraska Public Power District MR Number: 4-00-0017
Cooper 1 Date: 10/10/00
Brownville,Nebraska RESIDENT INSPECTORS
Dockets: 50-298
BWR/GE-4
Subject: FAILURE OF MAGNA-BLAST BREAKER FOLLOWING MODIFICATION
Discussion:
On October 3, 2000, the Service Water Pump D breaker failed to close
during a Technical Specification surveillance. Operators removed the
General Electric Type AMH circuit breaker from service and declared the
pump to be inoperable. Cooper Nuclear Station personnel noted that the
prop spring bracket, part of the trip-free mechanism, had shifted
position causing the breaker to trip free following closure. The breaker
was replaced with a spare, and the failed braker was sent, accompanied by
licensee engineers, to a General Electric facility in Atlanta, Georgia
for evaluation.
Since 1997, Cooper has modified the trip-free mechanicsm of 13
safety-related Magna-Blast breakers, including the subject breaker, in
accordance with General Electric specifications. Subsequent to the
modification, General Electric proliferated a revised (increased) torque
specification for the prop spring bracket bolts. On October 6, General
Electric personnel determined that the failure of the breaker was
directly attributable to the lower torque values used during
modification. The lower torques permitted rotation of the prop spring
bracket, affecting the breaker's capability to reliably close and latch
upon demand. General Electric stated in a letter to the licensee that
this was the first failure ever reported caused by the rotation of the
prop spring bracket. Licensee personnel have stated that General
Electric considers this to be a potential Part 21 issue. An estimated
200-250 breakers nationwide were modified using the lower torque
specification.
General Electric recommended checks and adjustments for each of the
remaining breakers. Over the holiday weekend, plant maintenance
technicians inspected 2 of the remaining 12 breakers. Neither prop
spring bracket was found to have shifted. Additionally, only one bolt
was found to be under the new torque specification, and technicians
stated that the bolt was tight, as found. As a result of these findings,
licensee management decided that the remaining breakers could be
inspected and retorqued via routine planned maintenance practices.
Regional Action:
The Cooper resident inspectors will follow licensee actions to ensure
that the corrective measures are appropriate, timely and comprehensive.
Contact: David Loveless (817)860-8161
Wayne Sifre (817)860-8193
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