IE Circular No. 80-17, Fuel Pin Damage Due to Water Jet from Baffle Plate Corner

                                                            SSINS #6830 
                                                            Accession No.: 
                                                            8005050065 

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

                                July 23, 1980

                                                     IE Circular No. 80-17 

FUEL PIN DAMAGE DUE TO WATER JET FROM BAFFLE PLATE CORNER 

Description of Circumstances: 

On May 8, 1989, Portland General Electric submitted a Licensee Event Report 
No. 344/80-06, concerning the April, 1980 discovery of failure of a fuel pin
in each of two assemblies during the past operating cycle.  The LER stated 
that each of the fuel pins was located adjacent to a joint in the core 
baffle, and that the failures had resulted from tube vibration resulting 
from water jet impingement on the fuel pin. 

This general type of damage has been experienced previously.  Three damaged 
fuel pins were found in 1971-72 at a non-domestic power plant.  
Subsequently, one failed pin was found in 1973 and again in 1975 at 
non-domestic plants.  In 1975, one fuel pin failed at Point Beach.  These 
six fuel pin failures involved bypass flow through gaps in the inside corner 
of the baffle (the fuel "sees" a 90 angle, i.e., the edge of a box as seen 
from inside the box).  The baffle joints in these plants had not been peened 
prior to initial core loading.  Joints were peened following discovery of 
the failures, and no subsequent damaged has been observed near the joints 
where the above failures were discovered. 

More recently, in July 1979 fuel pin damage was detected in ten fuel 
assemblies at the Swedish Plant, Ringhals Unit 2.  In November, 1979 fuel 
pin damage was reported at the KO-RI Unit 1 in Korea on two fuel assemblies.  
Most recently in April, 1980 fuel pin failures were discovered in two 
assemblies at the end of Cycle 2 in Trojan.  In all three of the above 
recent instances, the failures were encountered in assemblies which had been 
associated with center injection points (the fuel "sees" a 270 angle, i.e., 
the edge of a box as seen from outside the box).   In addition in all three, 
the core support structures utilized a baffle plate design with a reduced 
number of edge to edge bolts on adjoining baffles. 

An ultimate fix of the baffle joint problem is to peen the entire joint with 
a "flat land" peen technique to reduce the gap between baffle segments.  
Because of scheduling concerns, this was not accomplished at Trojan during 
the recent outage.  Instead, PGE decided to install stainless steel pins 
adjacent to the two baffle joints of concern, and delay further peening 
efforts until the next refueling outage. 

.

                                                  IE Circular No. 80-17
                                                  July 23, 1980 
                                                  Page 2 of 2 

High velocity coolant cross flow ("jetting") through the gaps of the core 
baffle joints can result in damage to only a very limited number (usually 1 
or 2) fuel pins, and only a certain discrete elevations on those pins.  
Since there is no mechanism for propagation of the failures to adjacent 
pins, these failures are not viewed as a significant safety concern.  
However, in order to keep fuel failures and resulting primary coolant 
activity levels as low as possible, we recommend the following actions. 

Recommended Actions for PWR Construction Permit Holders and PWR Licensees: 

1.   Determine core locations that might be subject to water jet impingement
     upon fuel pins that could potentially be damaged by fretting. 

2.   (Licensees only).  Examine fuel pins that were discharged from those 
     locations, or are now at those locations (during the next refueling 
     outage). 

3.   Take appropriate actions of correct/prevent occurrence of this problem.

Although this problem has appeared only in certain Westinghouse PWRs, this 
Circular is being distributed to all PWRs since there may be other designs 
where the "as installed" core baffle may have plant specific features which 
could contribute to similar failures. 

No written response to this Circular is required.  If you desire additional 
information regarding this matter, contact the Director of the appropriate 
NRC Regional Office.