Information Notice No. 86-58: Dropped Fuel Assembly
SSINS No.: 6835
NUCLEAR REGULATORY COMMISSION
OFFICE OF INSPECTION AND ENFORCEMENT
WASHINGTON, D.C. 20555
July 11, 1986
Information Notice No. 86-58: DROPPED FUEL ASSEMBLY
All nuclear power reactor facilities holding an operating license or a
This information notice is to alert recipients to a potentially significant
problem pertaining to removal of nuclear fuel from the reactor core. The NRC
expects that recipients will review this notice for applicability to their
facilities and consider actions, if appropriate, to preclude a similar
problem occurring at their facilities. However, suggestions contained in
this notice do not constitute NRC requirements; therefore, no specific
action or written response is required.
Past Related Correspondence:
Information Notice No. 80-01, "Fuel Handling Events," January 4, 1980.
Information Notice No. 81-23, "Fuel Assembly Damaged Due to Improper
Positioning of Handling Equipment," August 4, 1981.
Information Notice No. 85-12, "Recent Fuel Handling Events," February 11,
Information Notice No. 86-06, "Failure of Lifting Rig Attachment While
Lifting the Upper Guide Structure at St. Lucie Unit 1," February 3, 1986.
Description of Circumstances:
On February 26, 1986, at Haddam Neck, a spent fuel assembly was
inadvertently lifted from the core when the upper core support structure was
removed from the reactor vessel in preparation for refueling. The assembly
stuck to the structure because of a bent fuel assembly locating pin. These
locating pins protrude at the bottom of the upper core support structure and
insert into the fuel assembly upper nozzle alignment holes when the support
structure is properly in place. One pin was bent toward the center of its
fuel assembly, thus holding the assembly by pinching against the inner side
of the alignment hole. With the support structure lifted above the reactor
vessel, the bottom of the attached assembly did not clear the top of the
vessel. As the structure
July 11, 1986
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was moved laterally, the assembly impacted the core barrel and was knocked
off. The assembly dropped 2-4 feet onto the core. The dropped assembly and
the two assemblies it impacted were damaged; however, no radiological
release occurred during this event. All 3 assemblies and a
symmetrically-burned assembly have been withdrawn from use in the reactor.
The core barrel was superficially scratched and a core baffle former plate
was partially torn. The licensee determined that these latter items do not
prevent continued use of these structural components.
The licensee inspected fuel assemblies that occupied the same core position
as the dropped assembly in previous cycles. The chamfer of the guide pin
alignment holes of these assemblies was also deformed in the location of the
bent pin. No such deformation was identified in other fuel assemblies. This
indicated that the bent pin was the cause of the event and that the
condition may have existed since 1981, but previously did not result in
enough interference to lift the fuel assembly when the upper core support
structure was removed. The bent pin was repaired.
A 240,000-lb capacity crane was used to lift the upper core support
structure weighing 57,000 lb. The stuck fuel assembly weighed only 1200 lb,
so the procedural limit for the lift of 59,000 lb did not ensure that no
fuel assembly was attached to the structure. Load cells of appropriate range
and calibration along with sufficiently restrictive limits may be helpful to
ensure that loads to be lifted are not encumbered. However in this
application, the weight of the fuel assembly is such a small fraction of the
total load, that a load cell may not be a reliable method of detecting an
attached fuel assembly. This event illustrates the need during lifting for
rigorous visual inspection as well as sensitivity to instruments to ensure
unencumbered lifts of heavy loads from the reactor core.
Similar problems have been noted before. As discussed in Information Notice
86-06, a stripped thread on a bolt attaching the lifting rig to the upper
guide structure at St. Lucie 1 may have caused an imperceptible tilt that
later was magnified to the observed tilt of the whole upper guide structure.
This bolt was below the structure where the thread problem could not be
readily observed. As discussed in Information Notice 85-12, fuel assembly
alignment pins did not function properly in an event at Turkey Point 4. In
that case, slight lateral motion of the fuel handling bridge contributed to
the misalignment. Inadequate control of the vertical position of the load
was also highlighted in Information Notice 81-23.
July 11, 1986
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No specific action or written response is required by this information
notice. If you have any questions about this matter, please contact the
Regional Administrator of the appropriate regional office or this office.
Edward L. Jordan Director
Division of Emergency Preparedness
and Engineering Response
Office of Inspection and Enforcement
Technical Contact: Vern Hodge, IE
Attachment: List of Recently Issued IE Information Notices
Page Last Reviewed/Updated Friday, May 22, 2015