Bulletin 76-01: BWR Isolation Condenser Tube Failure
NUCLEAR REGULATORY COMMISSION
OFFICE OF INSPECTION AND ENFORCEMENT
WASHINGTON, D. C. 20555
Inspection and Enforcement Bulletin (IEB)
Number 76-01, March 9, 1976
BWR ISOLATION CONDENSER TUBE FAILURE
DESCRIPTION OF CIRCUMSTANCES:
On February 12, 1976; an electrical fault in the main transformer at the
Millstone Unit 1 facility caused an automatic shutdown of the reactor plant
from full power. Shortly after the shutdown, a small amount of radioactive
steam and water was discharged from the isolation condenser vent as a result
of tube failure in the isolation condenser. This discharge of radioactive
water and steam caused low levels of contamination on the ground immediately
outside of the reactor building. This contamination was removed and no
resulting contamination was found outside the plant area.
Subsequent visual inspection of the isolation condenser tube revealed that
one tube had a one inch hole in the tube wall at the "U" bend.
Metallographic examination showed cracking of the tube in both the bend and
in the straight section adjacent to the bend. Eddy current testing of the
remaining tubes indicated that approximately 30 percent of the tubes have
extensive cracking to a depth greater than that allowed for minimum wall
thickness. In addition, other indications of possible tube defects have been
found in the region of the tube sheet. These possible tube defects are
currently under evaluation.
ACTIONS REQUIRED BY LICENSEES:
All licensees of BWR power reactor facilities with isolation condensers or
an equivalent installation are to take the following actions:
ACTIONS REQUIRED BY LICENSEES:
1. Provide a description of the steps taken or planned to:
a. Assure that the integrity of the isolation condenser tubes is
being maintained during operations. This assurance may be obtained
by the implementation of tube leak detection procedures such as
procedural controls for the temperature, volume and isotopic
content of the shell side water.
b. Assure that the margin of isolation condenser tube integrity is
maintained. This assurance may be obtained by periodic
nondestructive examinations of the tubes. In the event
nondestructive examinations of the tubes cannot be performed,
hydrostatic testing, in accordance with the 1974 ASME Section XI
requirements, is an acceptable alternate. The next nondestructive
or hydrostatic testing should be performed at the first
practicable opportunity, but no later than the next refueling
c. Assure prompt detection and operator response to an isolation
condenser tube break.
2. A report of the above descriptions and plans should be submitted within
20 days after receipt of this bulletin.
3. A report of the performance, the results, and the evaluation of the
next nondestructive examination of the tubes should be submitted within
30 days following completion of the examination.
Reports should be submitted to the Director of the NRC Regional Office, and
a copy should be forwarded to the NRC Office of Inspection and Enforcement,
Division of Reactor Inspection Programs, Washington, D. C. 20555.
Approval of NRC requirements for reports concerning possible generic
problems has been obtained under 44 U.S.C. 3512 from the U. S. General
(GOA Approval B-180255(R0072), expires 7/31/77.)
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