IE Circular 77-12, Dropped Fuel Assemblies at BWR Facilities
CR77012
MEMORANDUM FOR: B. H. Grier, Director, Region I
J. P. O'Reilly, Director, Region II
J. G. Keppler, Director, Region III
E. M. Howard, Director, Region IV
R. H. Engelken, Director, Region V
FROM: Harold D. Thornburg, Director
Division of Reactor Operations
Inspection
Office of Inspection and Enforcement
SUBJECT: IE CIRCULAR 77-12, DROPPED FUEL ASSEMBLIES AT BWR
FACILITIES
The subject document is transmitted for issuance by close of business within
three days after date of this letter. The Circular should be issued to only
holders of BWR Operating Licenses. Also enclosed is a draft copy of the
transmittal letter.
Harold D. Thornburg, Director
Division of Reactor Operations
Inspection
Office of Inspection and Enforcement
Enclosures:
1.IE Circular 77-12
2. Draft Transmittal
Letter
CONTACT: C. J. DeBevec
X 28180
.
Transmittal letter for Circular 77-12 to each holder of a BWR Operating
License
ADDRESSEE:
The enclosed Circular 77-12 is forwarded to you for information. No written
response is required. Should you have any questions related to your
understanding of this matter, please contact this office.
Signature
(Regional Director)
Enclosure:
IE Circular 77-12
.
IE Circular 77-12
Date: 9/15/77
Page 1 of 4
DROPPED FUEL ASSEMBLIES AT BWR FACILITIES
Description of Circumstances:
There have been several reported events involving dropped fuel assemblies at
operating boiling water reactor (BWR) facilities. These events are
summarized below.
1. Pilgrim - January 1974 (AO-50-293/74-3). An irradiated fuel assembly
became detached from the grapple and fell in the spent fuel pool. The
fuel assembly had not been completely latched in the grapple.
2. Millstone Unit No. 1 - September 1974 (AO-50-245/74-5). A fuel assembly
was inadvertently released from the grapple and fell in the spent fuel
pool due to the grapple J-hook not being properly engaged.
3. Humboldt Bay - June 1975 (50-133, Report dated 6-11-75). A fuel
assembly was inadvertently released from the grapple and fell in the
spent fuel pool due to the grapple J-hook not being properly engaged.
4. Duane Arnold - June 1975 (AO-50-331/75-31A). A fuel assembly was
inadvertently released from the grapple and impacted on another fuel
assembly in the core due to the grapple not being properly engaged.
5. Brunswick Unit No. 2 - March 1976 (50-324/76-11). A fuel assembly fell
out of the fuel prep machine to a horizontal position across the top of
the spent fuel pool storage racks. A few days prior to this event a
fuel assembly was released from a grapple before being fully inserted
in a spent fuel rack. The assembly tilted but did not fall out of the
rack. Although there was no apparent failure of the cladding, the
assembly was judged not to be re-useable.
6. Peach Bottom Unit No. 3 - January 1977 (50-278177-5). A fuel assembly
was inadvertently released from the grapple and fell across the core.
The assembly drop was attributed to inadvertent
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IE Circular 77-12
Date: 9/15/77
Page 2 of 4
Description of Circumstances (continued)
operation of the grapple open switch (during a period when the
refueling mast controls had to be rotated away from the operator)
followed by a slack cable signal when the fuel assembly nose cone
contacted the core as it was being lowered, thereby satisfying all the
interlocks for the grapple to open.
7. Oyster Creek - May 1977 (50-219, Report dated 5-28-77). A fuel assembly
and mast were inadvertently dropped while lowering the assembly into
the spent fuel racks. The fuel and mast movement were arrested by the
cable drum brake, without further damage, when the operator released
the grapple lower lever. The drop resulted from the shearing of six
bolts coupling the refueling mast speed reducer to the cable drum.
Examination of the failed bolts indicated that all but two had failed
at some earlier time.
The potential problem areas associated with the use of the refueling
equipment at BWR facilities that have been identified as contributing to
these events are summarized below.
1. If the operator does not insure that the fuel grapple hook has properly
grasped the fuel element bail, the fuel element could slip out at any
time.
2. If the fuel grapple open/close switch is moved to the open position
while the hoist is loaded, the interlock will not allow the grapple to
open. However, since the switch is a two position switch, as soon as
the hoist cable is unloaded, even by inadvertent fuel assembly hangup,
the grapple will open.
3. In order to rotate a fuel assembly after it is hoisted up, the entire
fuel hoist (including the control console) must be rotated. This can
result in the control console being rotated 135 degrees from the
operator, thereby contributing to the potential for operator control
manipulation errors.
4. The speed reducer to cable drum coupling bolts (on those refueling
platforms utilizing a bolted connection) are susceptible to failure,
possibly resulting from impact loading due to the oversized coupling
bolt holes.
.
IE Circular 77-12
Date: 9/15/77
Page 3 of 4
All holders of BWR Operating licenses or construction permits should be
aware of the potential faults and malfunctions which could contribute to the
dropping of a fuel assembly at their facility. Certain steps and measures
can be taken to minimize the possibility of a fuel assembly dropping
incident. These include steps to assure that the grapple will properly grasp
the fuel assembly, measures to prevent inadvertent grapple opening, steps to
reduce operator control manipulation errors, and measures to identify
deterioration of or faulty components.
These steps and measures should be implemented by consideration of the
following:
1. Installation of the General Electric Fuel grapple modification for
positive indication of fuel assembly engagement (SIL No. 109, dated
October 31, 1974). This modification provides the operator with a
light, indicating that the fuel assembly bail is properly engaged in
the grapple and that the grapple hook is fully closed.
2. A modification of the two position grapple open/closed switch and/or
circuitry to decrease the potential for accidental opening.
3. The use of a warning light for assurance of the fuel grapple and
assembly engagement could be supplemented (or replaced) with an
interlock which would prevent grapple motion unless positive locking
occurs. In this regard, future operating experience with the warning
light installed should be evaluated to determine need for further
design changes.
4. Refueling plans that minimize manipulations over the core with the
console more than 45 degrees away from the platform.
5. A design review of the speed reducer to cable drum coupling bolts
(where applicable) to assure adequacy and a periodic
visual/nondestructive examination of the subject bolts.
6. Procedures to ensure that the refueling platform and its related
equipment are thoroughly inspected prior to use (i.e. initial fuel
handling and periodic refueling outages). These procedures should
include but not necessarily be limited to checks for the following:
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IE Circular 77-12
Date: 9/15/77
Page 4 of 4
a. Cables not worn or frayed:
b. Bolts, nuts and fasteners tight and secure;
c. All components properly lubricated;
e. Gears, shafts, bearings, etc. not loose or worn
f. Structural members and welds not deformed or cracked; and
b. Technical Specification required interlocks checked.
7. Procedures to conduct shift-wise and daily inspections of selected
refueling equipment critical components such as cables, fasteners,
hoists, and brakes when equipment is in use.
No written response to this Circular is required. If you require additional
information regarding this matter, contact the Director of the appropriate
NRC Regional Office.
Enclosure:
List of IE Circulars
issued in 1977
Page Last Reviewed/Updated Tuesday, March 09, 2021