IE Circular 77-12, Dropped Fuel Assemblies at BWR Facilities


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 
                    Office of Inspection and Enforcement 


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 
                                   Office of Inspection and Enforcement 
1.IE Circular 77-12 
2. Draft Transmittal 

CONTACT:  C. J. DeBevec 
          X  28180 

Transmittal letter for Circular 77-12 to each holder of a BWR Operating 


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. 

                                        (Regional Director) 

IE Circular 77-12 

                                                         IE Circular 77-12 
                                                         Date: 9/15/77  
                                                         Page 1 of 4 


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  

                                                      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 

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 

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: 

                                                      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. 

List of IE Circulars 
     issued in 1977 


Page Last Reviewed/Updated Tuesday, September 01, 2015