IE Circular No. 80-17, Fuel Pin Damage Due to Water Jet from Baffle Plate Corner
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
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.
Page Last Reviewed/Updated Thursday, March 25, 2021