United States Nuclear Regulatory Commission - Protecting People and the Environment

Bulletin 76-01: BWR Isolation Condenser Tube Failure

                       NUCLEAR REGULATORY COMMISSION 
                   OFFICE OF  INSPECTION AND ENFORCEMENT 
                           WASHINGTON, D. C. 20555

                                                            IEB 76-01 
                                                            3/9/76 
                                                            2 pages 

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: 
.

                                                            IEB 76-01 
                                                            3/9/76  
                                                            Page 2 

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 
          outage. 

     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 
Accounting Office.
(GOA Approval B-180255(R0072), expires 7/31/77.) 
Page Last Reviewed/Updated Tuesday, July 23, 2013