ML20149J994
| ML20149J994 | |
| Person / Time | |
|---|---|
| Site: | Crane  |
| Issue date: | 07/22/1997 |
| From: | Langenbach J GENERAL PUBLIC UTILITIES CORP. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| 6710-97-2303, NUDOCS 9707290190 | |
| Download: ML20149J994 (3) | |
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GPU Nuclear, Inc.
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Route 441 South NUCLEAR 6710-97-2303 Post Othee Box 480 Middletown, PA 17057-0480 July 22,1997 Tei 717-944 7s21 U.S Nuclear Regulatory Commission Attention: Document Control Desk Washington, DC 20555 i
Gentlemen:
Subject.
Three Mile Island Nuclear Station Unit I (TMI-1)
Operating License No. DPR-50
-l Docket No. 50-289 i
TMI-l Fuel Assembly Holddown Spring Surveillance Program References-1.
GPUN (Hukill) to USNRC (Novak), TLL-447, "TMI-1 Fuel Assembly Holddown Springs,"
dated September 10,1980.
- 2. USNRC (Stolz) to GPU Nuclear (Hukill),81-098(DGM), "TMI-I Fuel Assembly Holddown Springs," dated April 20,1981.
j This letter is to inform you that, based on fuel vendor recommendations, TMI intends to discontinue the fuel assembly holddown spring surveillance program as established in References 1 and 2.
In 1980 it was determined that small numbers of B&W (now Framatome Cogema Fuels (FCF)) Mark B 15 x 15 fuel assembly helical holddown springs were vulnerable to random failure caused by fatigue-induced stress corrosion cracking (SCC). Justifications provided in Reference I demonstrated that such spring failure is not a safety concern for TMI regarding loss of holddown force, loose parts or interference with normal control rod assembly movement.
In Reference 1, GPU Nuclear (GPUN) committed to corrective actions to reduce the likelihood of spring failures at TMI. These were:
1.
Assurance that future reload fuel assemblies contain holddown springs fabricated according to B&W's revised specification which calls for improved material and process controls. This material will be more resistant to fatigue and stress corrosion crscking.
2.
Establishment of a fuel surveillance program to inspect assemblies during each outage for indications of spring failure or damage to other assembly components.
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In the longer term, and if available, require the use of the B&W improved end fitting on all B&W reload assemblies. The design of this improved end fitting was scheduled to be completed in early 1982.
These actions were determined to be satisfactory by the USNRC in Reference 2.
Subsequent to these commitments all new TM1 reload fuel assemblies ordered from B&W contained holddown springs fabricated according to revised specifications with improved material and process controls. Also, all new fuel has incorporated improved holddown spring and upper end fitting designs. The improved designs for recent fuel batches include the fatigue-resistant shot-peened helical coil spring used in the Cycle 9 and Cycle 10 reloads. An advanced cruciform leaf-spring was introduced in the Cycle 11 reload (currently operating) and is planned for continued use in reload designs for Cycle 12 and beyond.
i Consistent with the corrective action commitments, TMl also established a fuel surveillance program to inspect assemblies for indications of spring failures or damage to other assembly components. As described in Reference 1, in 1980 TMI visually-inspected the holddown springs in all fuel assemblies then in the spent fuel pool. Since then, similar inspections were done on all discharge and reinsenion fuel assemblies during the outage at the end of each cycle. A total of 1270 inspections were done. For Cycles 5 through 10 a total of 10 older design (pre-shot-peened) helical springs were found to be failed, all during Cycle 8 operation.
No failures were found in the shot-peened helical springs at TMI in a total of 192 inspections after Cycles 9 and 10 with exposures in the range of 639 to 1300 Effective Full Power Days (EFPD). Further, spring inspections in all B&W plants, including TMI, found no shot-peeaed spring failures in a total of 962 inspections in assemblies with exposures ranging from 380 to 1400 EFPD. The shot-peened fix, therefore, is considered to have eliminated the fatigue-induced SCC failure phenomenon. The excellent performance of the shot-peened springs is the basis of the vendor recommendation that the surveillance program for helical springs be discontinued.
The advanced cruciform leaf-spring design was introduced to preclude the specific mode of failure of the helical springs and is not pan of the smveillance program. Lead test assembly inspections of the cniciform springs at the B&W Oconee-1 plant have found that the sprmgs performed satisfactorily through three cycles of operation (1400 EFPD). Full batch inspections of 60 cruciform spring assemblies through two cycles (-920 EFPD) at the Oconee-2 plant have confirmed the good performance.
TMI projected cycle designs will use a very limited number of the older pre-shot-peened spring fuel assemblies. For example, Cycle 12, the next operating cycle, will contain 5 older assemblies, Cycle 13 is expected to use only 1. All other helical spring assemblies will contain the shot-peened springs. Therefore, based on the performance of the shotpeened spring design and the vendor recommendation, GPU Nuclear Inc., intends to discontinue the holddown spring surveillance program. However, to insure proper fuel performance in future cycles, every older non-shot-peened spring fuel assembly inserted in the core will be verified
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as having an intact spring based on a visual inspection done after its previous cycle of operation.
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GPU Nuclear, Inc. believes that the commitments of Reference I have been fulfilled and that the objective of the spnng surveillance program to ensure adequate reliability of the Mark-B l
fuel assembly holddown spring has been achieved. If you or your staff have any comments regarding this issue please inform Yosh Nagai of our staff at 973-316-7974 by
- August 15,1997 in order to avoid any potential affect on TMI 12R refueling outage planning.
Sincerely, W
6ucf James W. Lan n ach i
l-Vice President and Director, TMI I
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Administrator, Region I l
TMI NRC Project Manager i
TMI NRC Resident Inspector l
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