United States Nuclear Regulatory Commission - Protecting People and the Environment

Bulletin 74-010: Failures in 4-Inch Bypass Piping at Dresden-2



BL74010 

RO Bulletin No. 74-10                                       Date: 9/18/74 

FAILURES IN 4-INCH BYPASS PIPING AT DRESDEN-2 

The Commonwealth Edison Company notified the Region III Office of the 
Directorate of Regulatory Operations by telephone on September 13-15, 1974 
of the finding of through-wall cracks in each of two 4-inch diameter bypass 
loops around the discharge valves of the recirculation pumps at the Dresden 
2 facility. Early warning of reactor coolant leakage was provided by the 
plant's drywell sump collection system. 

In each instance the cracks were in the heat affected zone of stainless 
steels welds joining the 4-inch piping to weld-o-lets on the 28 inch 
diameter main coolant recirculation piping. The cracks were circumferential, 
from 3/4-inch to 3-inches in length on the OD and extending to substantially
greater lengths on the ID of the pipes. 

In one instance (the "B" loop bypass line), the area containing the crack(s)
can be isolated for repair utilizing valves presently installed. In the 
other instance (the "A" loop bypass line), the area containing the crack(s) 
cannot be isolated from the reactor pressure vessel with existing  valves in 
the piping system. Procedures for the repair of this portion of the piping 
system are presently being considered by the licensee. 

Metallurgical examinations are being conducted by the licensee's consultants
to aid in determining the cause and mechanism of failure. Several days may 
be required or such determination. 

Inspections conducted by the Commonwealth Edison Company at their Quad 
Cities Unit 2 on September 15, 1974 have revealed a crack in similar piping 
at that facility.   

Action Requested of Licensees   

1.   For those boiling water (BWR) facilities presently shutdown, examine 
     (by ultrasonic or other suitable volumetric nondestructive examination 
     technique) all accessible welds in the bypass piping lines around the 
     recirculation valves for evidence of crack indications similar to those
     discussed above. Your written reply to this Bulletin should discuss 
     those welds determined to inaccessible for examination. 
.

RO Bulletin No. 74-10        - 2 -                         Date: 9/18/74 

2.   For those BWR facilities presently operating, conduct the examina- 
     tions discussed in 1. above at the earliest of the following 
     conditions:   

     a.   Next scheduled shutdown.   

     b.   Such time that (within the sensitivity specified in paragraph C.5.
          of Regulatory Guide 1.45) any reactor coolant leakage detection 
          system indicates, within a period of four hours or less, either an
          increase in unidentified leakage to twice the determined normal 
          rate of unidentified leakage by two (2) gpm or more. (In no case, 
          however, shall the rate of leakage exceed that specified by the 
          technical specifications without those actions required of the 
          technical specifications being taken.) 

     c.   Sixty (60) days from the date of this Bulletin.  

3.   Notify this office by telephone within 48 hours and in writing within 
     10 days of the measures you have implemented, or plan to implement, 
     with regard to those actions requested in 1. and/or 2., above.  

4.   Notify this office by telephone within 24 hours (with written 
     confirmation within 10 days) of the results of examinations conducted 
     in response to this Bulletin. A copy of the written notification of 
     examination results (including all attachments) should be sent to the 
     Assistant Director for Construction and Operations, Directorate of 
     Regulatory Operations, AEC Headquarters in Washington, D. C. 

Actions Requested of Licensees May be Modified    

The actions requested of licensees, above, may be modified by this office as
meaningful results are available from the metallurgical, examinations and 
failure analyses presently in progress. 
Page Last Reviewed/Updated Tuesday, July 23, 2013