ML19263E019
| ML19263E019 | |
| Person / Time | |
|---|---|
| Site: | Yankee Rowe |
| Issue date: | 11/30/1978 |
| From: | YANKEE ATOMIC ELECTRIC CO. |
| To: | |
| Shared Package | |
| ML19263E016 | List: |
| References | |
| NUDOCS 7904240347 | |
| Download: ML19263E019 (5) | |
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FIrlAL REPORT OF THE EXX0ll flUCLEAR FUEL EXAMlliATIO 1 AT YAllKEE R0WE - i10VEMBER 1978 4
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e By i
i F. P. Wahlquist ABSTRACT This report summarizes the flovember 1978 examination of Exxon
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iluclear fuel assemblies at the Yankee Rowe reactor.
Television
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examination of six (6) irradiated assemblies showed each assembly to be in excellent physical condition.
Diameter measurements on the i
peripheral fuel rods of three irradiated assemblies yielded an average cladding creepdown of 0.001 to 0.002 inches, which it within design expectations.
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7904240 34[{
's 1.0 If(T R_0 DUCT ION The primary purpose of the 1978 Yanken Powe fuel examination was to repeat the scope of the 1977 fuel examination program on the same five assemblies.
In addition to examining these five discharged assemblies, the 1978 program was expanded to examine an assembly irradiated for one cycle and an unirradiated assembly.
p The examinations consisted of a visual examination of all four v.
sides of the six irradiated assemblies and the diameter measurements of peripheral fuel rods in three irradiated assemblies and the one unir-radiated assembly.
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During this November 1978 Yankee Rowe outage, the utility staff conducted a sipping program on all discharged Exxon Nuclear Co. (EftC)
~h fuel assemblies (burnup s 30,000 tL'D/l1TV).
Based on the measured sipping results, ENC visually examined several of these fuel assemblies.
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Fretting wear on peripheral fuel rods was detected in only two of these discharged assemblies near the top spacer grid.
In one specific fuel rod, the length of rod above the top spacer was physically missing.
The above-background Iodine-131 activity in the primary coolant s
during the previous operating cycle (Cycle 13) is attributed to the f
4 observed fretting wear on these discharged assemblies.
Additional examination of the fuel currently under irradiation is planned for the i
next scheduled outage.
I The following report is confined to the observations and measurements l
performed on the six irradiated and one fresh assembly that were part of t
the pre-planned surveillance program at Yankee Rowe.
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2.0 EXAMIrlATION ACTIVITIES AND TECliNIQUES The Yankee Rowe fuel examination occurred between November 6 -14, l
I 1978.
The fuel assemblies examined, the examinations performed on each I
assembly, and the calculated assembly exposures are listed in the i
following table:
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Calculated Exposure MWD /MTU Cycle 13 Visual Fuel Rod Start End f
Assembly Examination, Diameter Cycle Cycle Increment A561E X
A527E X
X 0
15,286 15,286 I
A487E X
17,315 31,196 13,811 B512E X
X 18,062 32,003 13,941 L:
m B478E X
18,095 31,966 13,871 A511E X
18,471 32,098 13,627 A509E X
X 18,528 32,197 13,669 I
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2.1 VISUAL EXAMIf:ATION TECHNIQUE The visual examination was conducted with an underwater television camera with video tape recording capability.
Video tapes of the examination are available for copying.
Typically, one side of each face of the fuel assembly was scanned in the vertical direction.
For more detailed examination, the TV camera could be noved to within several inches of the peripheral fuel rods.
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N 2.2 ROD DI AMETER MEASU,REME!!T TECHfHQUE The fuel rod diameter neasurgments made during the 1977 refueling outage indicated a greater than anticipated amount of clad l
creep (approximately 0.0045 inches).
One of the objectives of the 1978 l
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program was to determine if the indicated cladding creepdown was accurate or if there had been an error or bias in the 1977 measurements.
b Two modifications were implemented in the 1978 diameter i
measurement technique to improve the quality of the measurements.
The
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first modification was to hang the diameter gauge from the upper tie plate so the operator would not have to support the gauge while positioning it over the fuel rod.
Previously, the gauge was held by the operator
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and moved back and forth while taking data.
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The second change was to use underwater diameter standards arranged in a fixture similar to fuel rods in the assembly rather than having to remove the gauge from the pool for calibration checks.
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fixture with three diameter standard rods was placed in the fuel pool
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t adjacent to the assembly being measured.
The diameter difference 5
between each of the diameter standards was approximately 0.002 inches.
The gauge was calibrated on the fixture before measuring groups of fuel I
rods in an assembly and rechecked following the measurements.
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i P,oth the gauge position modification and the underwater calibration standards improved the quality of the diameter data. Hanging the gauge from the upper tie plate was not completely successful, since changing the support fixture fron one hole in the upper tie plate to an adjacent hole introduced some error.
Repeat mea..rements were made on f
a number of fuel rods to obtain information on the repeatability of a given measurement.
The standard deviation of these was approxinately 0.8 mils.
3.0 EXA!11tlATIOil RESULTS I
3.1 VISUAL OBSERVATIO:lS_
All the assemblies examined appeared to be in excellent condition.
There was no evidence of physical damage to any of the fuel rods.
The crud coating on the fuel rods was somewhat heavier than observed in 1977.
The spacers were still relatively clean and reflected light similarly to that observed during the 1977 inspection.
Small but insignificant dents were observed on a few of the spacer side plates.
Some differential fuel rod growth was noted when scanning across the top of tiie assemblies.
3.2 FUEL R0D DIAMETER MEASUREMEf[TS The average of the diameters in the one-cycle assembly (A527) was 0.3631 inches, which is 1.9 mils less than the ncminal design diameter.
The average diameters measured for the two discharged assemblies (A509 and B512) was 0.3634 inches and 0.3643 inches, respectively.
This 0.8-1.6 mil creepdown is significantly less than indicated by the 1977 l
measurements and verifies that the 1977 measurements were in error.
Cased on these measurements, creepdown appears to have stabilized after the first irradiation cycle.
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