IE Circular No. 78-14, HPCI Turbine Reversing Chamber Hold down Bolting

                                 UNITED STATES
                         NUCLEAR REGULATORY COMMISSION
                            WASHINGTON, D.C. 20555

IE Circular No. 78-14
Date: July 17, 1978
Page 1 of 2


Recent inspections by the Philadelphia Electric Company of HPCI turbines
at  Peach Bottom 2/3 facilities disclosed broken cap screws and missing
clamping  plates which secure the turbine reversing chambers. The cap
screws are used to  fasten clamping plates and reversing chamber rails to
the support ring.  Additional detailed information is available in Section
6 of the HPCI Terry  Turbine instruction manual. Missing parts were
recovered from components in  the turbine steam exhaust piping and
unrecovered parts are believed to be in  the torus. Subsequent examination
of the cap screws indicated the failures  resulted from fatigue.

The design of the cap screws includes a 1/4 inch deep concentric
counterbore  from the threaded end. Failures generally occurred at the
base of the  counterbore with a few failures occurring at the base of the
screw head. The  screw length of 1-1/4 inches allows about 5/16 inches of
thread engagement in  the support ring.

After review, the vendor (Terry Steam Turbine Company) recommended 
modification of the bolting design to prevent recurrence. An interim
solution  was to replace the 3/8-16 X 1-1/4" long ASTM A574 socket head
cap screws with  similar 1-1/2" long cap screws. This required deeper
drilled and tapped holes  in the support ring to prevent the longer screws
from bottoming. Later, the  General Electric Company advised of a further
modification from Terry Turbine  consisting of bolting the reversing
chamber directly to the support ring,  lockwiring the cap screws and
eliminating the clamping plate. In addition, the  replacement cap screws
were changed to 3/8-16 X l" long ASTM A193 Gr. B6 with  a Rockwell
Hardness of Rc28 or less.

Information supplied by the Terry Steam Turbine Company indicates that
similar  turbines were supplied for HPCI systems at the following
facilities: Browns Ferry Unit Nos. 1, 2, and 3; Brunswick Unit Nos. 1,
and 2; Cooper; Vermont Yankee; Fermi Unit No. 2; J. A. FitzPatrick; Hatch
Unit Nos. 1 and 2; Hope Creek Unit Nos. 1 and 2; Limerick Unit Nos. 1 and
2; Pilgrim Unit No. 1; Shoreham; Susquehanna Unit Nos. 1 and 2. In
addition, HPCI Terry Turbines were  also supplied for Monticello and Duane


IE Circular No. 78-14
Date: July 17, 1978
Page 2 of 2

however, these applications involved smaller machines which incorporated
a  single turbine wheel and reversing chambers which are supported with
out  clamping plates, and therefore are not subject to similar failure of
cap  screws.

All holders of BWR operating licenses or construction permits for
facilities  with a similar HPCI Terry Turbine should be aware of the
potential for failure  of the turbine reversing chamber hold down bolting.
It is recommended that  inspection of the clamping plate cap screws be
included in the next inspection  of these turbines. If the present bolting
design is inadequate, it is further  recommended that the nuclear steam
supplier and vendor be contacted for  assistance in determining the
appropriate modification.  

No written response to this Circular is required. If additional
information is  needed regarding this matter, contact the Director of the
appropriate NRC  Regional Office.


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