ML20076F231

Shoulder Gap Insp Plans for End of Cycle 3 Refueling Outage

ML20076F231
Person / Time
Site:	Arkansas Nuclear
Issue date:	08/17/1983
From:	ARKANSAS POWER & LIGHT CO.
To:
Shared Package
ML20076F230	List: 2CAN088308, Forwards ANO-2 Shoulder Gap Insp Plans for End of Cycle 3 Refueling Outage, Per 830726 Commitment ML20076F231
References
PROC-830817, NUDOCS 8308250340
Download: ML20076F231 (10)

Text

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c ATTACHMENT 1 ANO-2 SHOULDER GAP INSPECTION PLANS FOR THE END OF CYCLE 3 REFUELING OUTAGE AUGUST 17, 1983 8308250340 830819 PDR ADOCK 05000368 G PDR

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1 ATTACHMENT 1 ANO-2 SHOULDER GAP INSPECTION PLANS FOR THE END OF CYCLE 3 REFUELING OUTAGE

1. Introduction The distance from the top of a fuel rod to the bottom of the upper flow plate is known as shoulder gap. Measurements of this gap at the end of Cycle 1 were somewhat less than expected and the inspection program for the Cycle 2 refueling outage was accordingly expanded. When the outage occurred in late August 1982, it was discovered that a possibility existed that fuel pin to flow plate contact could occur in Batch C fuel during Cycle 3 unless action was taken. The NRC was notified and the t

situation, including fuel modification plans and gap acceptance criteria, was presented to the NRC staff in October 1982. The slides used in the presentation were later forwarded to the NRC under separate

cover (Reference 1). The measurements and fuel assembly modifications proceeded until all 56 Batch C assemblies had been measured and 30 of these had been modified by shimming. Further details of the procedure and a list of the 30 shimmed Batch C assemblies were forwarded to the NRC in the Cycle 2 Fuel Examination Report (Reference 2).

J Although the Batch C assemblies, with one possible exception, are due to be discharged at the end of Cycle 3, the Batch D assemblies are scheduled to receive their third exposure in Cycle 4. While the j Batch D assemblies were constructed so that their initial shoulder gaps

were 0.3 inch larger than the Batch C's, it will still be necessary to verify that the remaining gaps are adequate to avoid closure during Cycle 4.

In the following sections cf this report, the core changes for Cycle 4, a shoulder gap inspection plan, and an analysis approach to determine if the remaining gaps are acceptable will be described. In the event it may become necessary to shim some Batch D assemblies, the modification procedure is discussed.

2. Core Modifications for Cycle 4 A fuel assembly map of the Cycle 3 core is presented in Figure 1. The present plans are to completely off-load the Cycle 3 core to the spent fuel pool so that maintenance can be performed on the service water systems. During refueling, 56 fresh Batch F assemblies will be loaded together with 52 Batch E assemblies, 60 Batch D assemblies, and 8 Batch A assemblies discharged from Cycle 1. The center assembly selection has not been finalized, but will be a Batch C or a Batch A

! assembly. Further details on the assemblies involved are presented in Table I.

The Cycle 3 termination burnup is anticipated to be about 9,750 MWD /MTU. Cycle 4 is expected to achieve a burnup of about 12,500

MWD /MTU. A Cycle 4 core map by assembly serial number is not yet

available. Hcwever, a tentative quarter core map by assembly fuel batch is presented in Figure 2. It has been estimated that the Batch C i

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peak rod fluence received by the end of Cycle 3 will be within 15 percent of the Batch D peak rod fluence projected for the end of Cycle 4.

3. Shoulder Gap Inspection Plan The following differences exist in the situation during the coming outage from that in the Cycle 2 outage.

a. A full evaluation of the end of Cycle 2 data has shown that a well-behaved bounding function exists for Batch C peripheral gap change as a function of fluence through two cycles. An indication of the shape exhibited by this bounding function is shcwn in Reference 1, page 7. Furthermore, an analysis of data from interior and peripheral rods indicates that the bounding function based on peripheral rods applies to all Batch C rods.

b. Evaluation of one cycle Batch D data indicates that Batch D falls under the same bounding function, with the possible exception of the behavior of one rod.

c. It will be possible to obtain third cycle shoulder gap change data from measurements on the Batch C assemblies.

The initial plan, then, will be to measure Batch C gap changes. The majority of assemblies selected will be chosen because each had several shoulder gaps that changed at nearly the bounding rate through their two prior cycles. In addition, to cover the possibility that there is a reversal of previous trends, other Batch C assemblies will be selected that exhibited more modest gap change rates through their first two cycles. These measurements will be used to verify that lower change rates early in life are not a forerunner of limiting change i rates later in life. Due to the flux gradients in each assembly and the inherent scatter in gap change data, the initial group of Batch C assemblies selected for inspection is expected to cover the full range of third cycle behavior.

In addition to the Batch C measurements, a sufficient number of Batch D assemblies will be chosen to provide assurance that the bounding function created from three cycles of Batch C data is also applicable to the Batch D fuel.

Based on the preceding considerations, at least eight Batch C assemblies and nine Batch D assemblies will be selected for shoulder gap measurements on at least two opposing faces. As in the Cycle 2 outage, the data will be taken using a periscope optical measuring device.

4. Analysis Procedure The initial analysis approach will be to use the Batch C data to refine and extend the bounding function. Assuming the Batch D data shows that the bounding function applies, then the Batch D assemblies with their i 2 i

I projected Cycle 4 fluences will be tested for acceptability under the following criterion:

At a 95% probability, the worst rod in the assembly will not have gap closure at the end of cycle.

The initial analysis approach, however, represents a better than 95%

prcbability situation since the bounding function may represent more rapid gap change rates than those that may exist within individual assemblies. Accordingly, if the bounding function approach produces negative results, it may be desirable to pursue a more assembly specific evaluation of the data, possibly with additional measurements as further support. This more detailed evaluation would employ statistical modeling similar to that used in the Cycle 2 outage evaluation of Batch C assemblies.

5. Modification Procedure If Batch D assembly modifications to increase the shoulder gap are needed, they will be performed in essentially the same way the Batch C assemblies were modified. The upper end fitting is removed, four shims installed, and the bundle reassembled with new, modified guide posts.

Additional details of the process were presented in References 1 and 2.

Since the previous outage, some refinements have been added. The shim will be for a 0.4 inch gap increase instead of 0.5, and the replacement guide posts will be for the new shim height. In addition, all of the modified corner posts and the center post will be at the same height.

Under the old procedure used on the Batch C's, a different center post height resulted. The 0.4 inch value was selected after consideration of the dimensional requirements imposed by the core alignment plate.

The decrease in the working spring length will be the gap change, 0.4 inches.

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REFERENCES

1. John R. Marshall to Robert A. Clark, Docket No. 50-368, Letter No. 2CAN128207, dated December 10, 1982.

2. John R. Marshall to Robert A. Clark, Docket No. 50-368, Letter No. 2CAN038307, dated March 30, 1983.

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TABLE I FUEL ASSEMBLY DATA FOR CYCLE 4 REFUELING

a. Cycle 3 Number of Batch and Number pins / Previous Assemblies Sub-batch Wt% U-235/ Shims Cycle Exposures 1 A 236/1.93/0 1, 2 (Center) 8 A 236/1.93/0 1 8 C1 224/2.94/12 1, 2 16 C2 224/2.94/12 1, 2 12 C3 234/2.94/2 1, 2 16 C4 233/2.94/3 1, 2 4 C5 224/2.94/12 1, 2 40 D0 184/3.48/0 2 52/3.03/0

. 20 01 184/3.03/0 2 52/2.73/0 40 E0 184/3.48/0 None 52/2.78/0 12 El 224/2.78/0 None 12/2.28/0 l

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o TABLE I (Continued)

b. Cycle 4 Number of Batch and Number pins / Previous Assemblies Sub-batch Wt% U-235/ Shims Cycle Exposures 8 A 236/1.93/0 1 40 00 184/3.48/0 2, 3 52/3.03/0 20 D1 184/3.48/0 2, 3 52/3.03/0 40 E0 184/3.48/0 3 52/2.78/0 12 El 224/2.78/0 3 12/2.28/0 40 F0 184/4.05/0 None 52/3.30/0 16 F1 224/3.30/0 None 12/2.78/0 1 C or A -- --

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TABLE I (Continued)

c. Principal Batch Differences 4

Change in Shoulder Gap From l' Reference Batch (Inches) Guide Tubes Grids A (Initial Core) Reference Annealed 1 (RXA) Standard l B (Initial Core) Reference Annealed (RXA) Standard i

C (Initial Core) Reference Annealed (RXA) Standard 0 +0.300 Annealed (RXA) Standard

.E +0.150 Cold Worked (SRA) HID-12 3  ;

! F +0.8504 Cold Worked (SRA) HID-1 i

I iTen Batch A assemblies had cold-worked stress relief annealed (SRA) guide tubes instead of the standard recrystallization annealed (RXA) guide tubes.

2HID-1 zircaloy grids have a 2-mil thicker and inch wider perimeter strip.

aEight Batch E bundles each have three anti-bow demonstration grids.

4 Guide tubes are 0.7-inch longer than Batch E; but, with upper end fitting and post adjustments, the assembly length and holdd.own force are unchanged from Batch E.

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• AKC201,-AKC107, or AKA040 Under Consideration

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