United States Nuclear Regulatory Commission - Protecting People and the Environment

Bulletin 72-01: Niagra Mohawk Power Corporation



                                                             IEB 72-01

                                 UNITED STATES
                           ATOMIC ENERGY COMMISSION
                            DIVISION OF COMPLIANCE
                                   REGION I
                               970 BROAD STREET
                           NEWARK, NEW JERSEY 07102

                                      June 21, 1972


Niagra Mohawk Power Corporation                           Docket No. 50-220
Attention:  Mr. F. J. Schneider
            Vice President - Operations
300 Erie Boulevard West
Syracuse, New York 13202

Gentlemen:

The attached Directorate of Regulatory OperationsBulletin No. 72-1, "Failed
Hangers for Emergency Core Cooling System Suction Header," is sent to you to
provide you with information we recently received from the Commonwealth Edison
Company concerning the Quad Cities Unit 2 boiling water reactor.  This
information may relate to the design, fabrication and operating experience of
certain components at your facility.

                                       Very truly yours,


                                       James P. O'Reilly
                                       Director

Attachment:
Directorate of Regulatory Operations Bulletin 72-1
"Failed Hangers for Emergency Core Cooling System Suction Header"

cc:  Mr. P. A. Burt, Station Superintendent
.

                                            Date:  June 21, 1972
                                            Directorate of Regulatory
                                            Operations Bulletin 72-1

 
                                  ATTACHMENT

FAILED HANGERS FOR EMERGENCY CORE COOLING SYSTEM SUCTION HEADER

We recently received information from the Commonwealth Edison Company
concerning a problem found during startup testing of the Quad Cities 2 boiling
water reactor which may relate to the design and long term performance
capability of the torus and the emergency core cooling suction header at your
facility.  The information is as follows:

a.  Description of Circumstances

During startup testing the licensee found that four of the pipe hangers which
support the 24-inch diameter torus suction header had failed.  The 24-inch
suction header services as the primary source of water for the emergency core
cooling systems.  Water is supplied to the header from the torus through four
20-inch diameter pipes spaced 90 degrees apart.  The header is supported
between these 20-inch diameter pipes by three equally spaced sets of vertical
and horizontal hangers which are attached to support plates welded to the
torus.  A total of 12 hangers support the 24-inch suction header.  The reactor
was promptly shut down for investigation and repair following the discovery of
the failed hangers.

Three of the four failed hangers were located within a 90 degree section of
the header and resulted in a maximum sag in the header pipe of approximately
six inches within that section.  Four 3/4 inch diameter bolts (threaded their
entire length), which secured pairs of shackles to the support plates welded
to the torus and to the 24-inch diameter pipe, were found to have failed in
double shear.  The cause of the bolt failures has not as yet been determined;
however, it is known that the suction header experienced vibration as a result
of operational testing of the emergency core cooling system.  In addition, the
bolt holes, which were formed by flame cutting and punching, were found to be
irregularly shaped and poorly aligned.

Chicago Bridge and Iron Company, the contractor for the torus and suction
header design and installation, has provided a revised design requiring use of
1-inch diameter high strength bolts with smooth unthreaded bearing surface,
and has increased the size of the shackles.  The change is being implemented
for all the hangers.
.

-                                      2 -

Commonwealth Edison Company and General Electric Company plan to conduct
additional investigation to determine the effect on the suction header and
torus of routine plant operations and testing of the emergency core cooling
systems.

We have also been informed that the Northern States Power Company's Monticello
reactor found one bent suction header hanger bolt and is also currently
replacing the hanger bolts with 1-inch diameter bolts.

b.  Action Requested of the Licensee

It is requested that you conduct the following inspections for each of your
facilities and provide this office with the results of your inspection.

1.  An inspection of the hangers, shackles and support plates for the torus
suction header to assure that all components are in accordance with design,
are in proper position, and do not indicate damage.

2.  Inspect each bolt used to attach the shackle and support plat of each
hanger (a) for deformation, (b) to establish that bolts are of the specified
design, (c) to establish that specified locking devices are installed and (d)
that the bolt shank supporting the header weight from the support and shackle
is not threaded in the bearing area.

If the results of your inspection indicate the existence of conditions similar
to those described above, or if any problems have previously been experienced
with failed hangers or bent hanger bolts at your facility, please include in
your response a description of the problem and the corrective action taken or
planned, if any, and the date of scheduled completion of any planned
corrective action.  This information should be provided to this office, in
writing, within ten days of your receipt of this letter.

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