United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 83-29: Fuel Binding Caused by Fuel Rack Deformation

                                                            SSINS NO:  6835 
                                                            IN 83-29       

                               UNITED STATES 
                          WASHINGTON, D. C. 20555 
                                May 6, 1983 



All nuclear power reactor facilities holding an operating license (OL) or a 
construction permit (CP) and spent fuel storage facilities. 


This information notice is provided as a notification of a potentially 
significant problem pertaining to spent fuel storage racks. It is expected 
that recipients will review the information for applicability to their 
facilities. No specific action or response is required at this time. 

Description of Circumstance: 

In October of 1982, Maine Yankee Atomic Power Company reported indications 
that the spent fuel racks at Maine Yankee were bulging (LER 50-309/82-033). 
The plant had shut down for refueling and was unloading the reactor core in 
preparation for the ten year in-service inspections. The aluminum-clad boral
(boron-aluminum) plates which form two of the four sides of each fuel cell 
had bulged inward. The deformation was so severe that it caused the fuel 
assembly to bind upon being inserted into the cell. A total of twenty-one 
cells appeared to have deformed, all of which were "Phase I design," 
fabricated before 1975. 

The problem was detected when the licensee attempted to load a fuel assembly
into a cell and the weight indication on the load cell dropped by about 100 
pounds, indicating the fuel assembly was binding in the cell. The inserting 
operation was halted according to procedures and all other unoccupied "Phase
I" cells were tested by inserting a dummy fuel bundle into each cell. 
Occupied cells were tested by attempting to lift the fuel bundle from the 
cell, stopping when the load cell indicated a weight of 100 pounds in excess
of nominal. Fifteen empty cells were identified as having indications of 
deformation, and in six of the occupied cells, the deformation was so severe
that it caused the stored fuel to bind in the cell. 

A deformed empty cell was removed from the rack and visually inspected. 
Bulging was seen in the lower two feet of the cell. A 1/16-inch hole was 
drilled into the top of the plate and into the face of the bulge, venting 
hydrogen. The probable source of the hydrogen was water contamination of the
boral matrix and water-to-aluminum reaction. Venting the gas caused a 
reduction of the deformation. 


                                                              IN 83-29     
                                                              May 6, 1983  
                                                              Page 2 of 2  

A section of the bulged face showed clad separation from the boral matrix 
but no indications of cracking or flaking of the boral. 

The licensee's analysis showed K-eff for the spent fuel in the pool remained
less than 0.95 assuming 0 ppm soluble boron in the water, 3.3% enriched 
fuel, and 68F pool water temperature. Bulging in the boral plates 
changes K-eff since it displaces water and is equivalent to changing the 
physical separation between cells. The analysis treated this parametrically 
over the range of a reduction in equivalent cell separation of 50-92.5%. 
Assuming the normal 1720 ppm boron concentration in the spent fuel pool 
water, an additional reduction of 30% in K-eff was obtained. The licensee 
plans to drill and vent all affected cells as an interim fix. The licensee 
plans to replace the "Phase I design" spent fuel racks. 

Similar problems involving cell bulging or gas liberation have occurred in 
the past. Yankee-Rowe identified gas bubbles in the spent fuel pool in 1963,
indicative of a similar problem. Haddam Neck reported bulging of their racks
from a gas buildup in 1978 and Kewaunee reported a similar situation in 
1980. (LERs 50-213/78-004; 50-305/80-039). 

If you have any questions regarding this matter, please contact the Regional
Administrator of the appropriate NRC Regional Office or this office. 

                              Edward L. Jordan, Director 
                              Division of Emergency Preparedness 
                                and Engineering Response 
                              Office of Inspection and Enforcement 

Technical Contact:  Mary S. Wegner, IE 
                    (301) 492-4511 

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