Bulletin 88-08: Supplement 1, Thermal Stresses in Piping Connected to Reactor Coolant Systems
OMB No.: 3150-0011
NRCB 88-08, Supplement 1
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D. C. 20555
June 24, 1988
NRC BULLETIN NO. 88-08, SUPPLEMENT 1: THERMAL STRESSES IN PIPING CONNECTED
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
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.
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
Pao Kuo, NRR
1. Figure 1 - Tihange 1 Piping
2. List of Recently Issued NRC Bulletins
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