Bulletin 88-08: Supplement 1, Thermal Stresses in Piping Connected to Reactor Coolant Systems

                                                     OMB No.: 3150-0011
                                                     NRCB 88-08, Supplement 1

                                UNITED STATES
                          WASHINGTON, D. C.  20555

                                June 24, 1988

                                       TO REACTOR COOLANT SYSTEMS


All holders of operating licenses or construction permits for 
light-water-cooled nuclear power reactors.


The purpose of this supplement is to 1) provide preliminary information to 
addressees about an event at Tihange 1 that appears to be similar to the 
Farley 2 event and 2) emphasize the need for sufficient examinations of 
unisolable piping connected to the reactor coolant system (RCS) to assure 
that there are no rejectable crack or flaw indications.  No new requirements 
are included in this supplement.

Description of Circumstances:

Tihange 1 is an 870 MWe, Westinghouse-type, 3-loop, pressurized-water reactor
located at Tihange, Belgium.  On June 18, 1988, while the reactor was 
operating, a sudden leak occurred in a short, unisolable section of emergency 
core cooling system (ECCS) piping that is connected to the hot leg of loop 1 
of the RCS.  The operator noted increases in radioactivity and moisture 
within containment and a decrease of water level in the volume control tank.  
The leak rate was 6 gpm, and the source of leakage was a crack extending 
through the wall of the piping.  The location of the crack and its 
orientation are shown in Figure 1.

The crack, which is in the base metal of the elbow wall and not in the weld 
or heat-affected zone, is 3.5 inches long on the inside surface of the elbow 
and 1.6 inches long on the outside surface.  A crack indication also exists 
in the spool connecting the elbow to the nozzle in the RCS hot leg.  That 
indication is in the heat-affected zone at the weld connecting the spool to 
the elbow.  The indication is circumferential, extends 3.9 inches on the 
inner surface of the spool, and is 100 mils deep.  Two smaller indications 
exist in the vicinity of the weld connecting the elbow to the check valve.

Farley 2 experienced one crack in a short, unisolable section of ECCS piping 
connected to an RCS cold leg as described in Information Notice 88-01, 
"Safety Injection Pipe Failure," and Bulletin 88-08.  That crack, which 
leaked at 0.7 gpm or less, was in the heat-affected zone of the upstream 
elbow weld.  The crack developed slowly rather than suddenly as at Tihange 1.

.                                                     NRCB 88-08, Supplement 1
                                                     June 24, 1988 
                                                     Page 2 of 2 

Actions Requested:

Although the actions requested in NRC Bulletin 88-08 are unchanged, it should
be noted that examinations of high stress locations would include the base 
metal, as appropriate. 

Reporting Requirements:

The reporting requirements set forth in NRC Bulletin 88-08 remain unchanged.

If you have any questions regarding this matter, please contact one of the 
technical contacts listed below or the Regional Administrator of the 
appropriate NRC regional office.

                             Charles E. Rossi, Director
                             Division of Operational Events Assessment
                             Office of Nuclear Reactor Regulation

Technical Contacts:  Roger W. Woodruff, NRR
                     (301) 492-1180

                     Pao Kuo, NRR
                     (301) 492-0907

1.  Figure 1 - Tihange 1 Piping
2.  List of Recently Issued NRC Bulletins


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