United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 86-58: Dropped Fuel Assembly

                                                            SSINS No.: 6835 
                                                            IN 86-58       

                                UNITED STATES
                        NUCLEAR REGULATORY COMMISSION
                    OFFICE OF INSPECTION AND ENFORCEMENT
                           WASHINGTON, D.C. 20555

                                July 11, 1986

Information Notice No. 86-58:   DROPPED FUEL ASSEMBLY 

Addressees: 

All nuclear power reactor facilities holding an operating license or a 
construction permit. 

Purpose: 

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,  
1985. 

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 


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                                                            IN 86-58 
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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. 

Discussion: 

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. 
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                                                            IN 86-58     
                                                            July 11, 1986 
                                                            Page 3 of 3  

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
                    (301) 492-7275

Attachment: List of Recently Issued IE Information Notices 
Page Last Reviewed/Updated Tuesday, November 12, 2013