ML19320C035
| ML19320C035 | |
| Person / Time | |
|---|---|
| Site: | Davis Besse  |
| Issue date: | 07/10/1980 |
| From: | Crouse R TOLEDO EDISON CO. |
| To: | Reid R Office of Nuclear Reactor Regulation |
| References | |
| 627, TAC-48044, NUDOCS 8007150670 | |
| Download: ML19320C035 (4) | |
Text
{{#Wiki_filter:- e. Docket No. 50-346 TOLEDO License No. NPF-3 g-{3gcg[)pj Serial No. 627 ResucRcncse July 10, 1980 a, awa-t 4#Y M191259-5221 Director of Nuclear Reactor Regulation Attention: Mr. Robert W. Reid, Chief Operating Reactors Branch No. 4 Division of Licensing United States Nuclear Regulatory Commission Washington, D. C. 20555
Dear Mr. Reid:
On May 13, 1980 a failed holddown spring was discovered at tha Davis-Besse Nuclear Power Station, Unit 1, (DB-1) in the upper end fitting of a fuel assembly by remote video inspection. An inspection followed that ultimately identified a total of 19 failed springs in the cycle 1 fuel assemblies. Metallurgical investigation revealed material used in the manufacture of these springs for DB-1 exhibited heightened susceptibility to fatigue and stress corrosion cracking. On June 10, 1980 Toledo Edison and Babcock and Wilcox met .iith your staff in Bethesda, Maryland to discuss the findings of cur reviews and the procedure to be utilized for spring replacement. Spring replacement has been completed on all cycle 1 fuel assemblias r2 turning to the core. The Davis-Besse Nuclear Power Station, Unit 1, Cycle 2 - Reicad Report was submitted February 11, 1980 and later revised on May 21, 1980 (Serial Nos. 590 and 618). Due to the repair made to the affected assemblies, a supplement to our cycle 2 reload report is attached. This describes the information that supports this repair under 10CFR50.59. None of the information in the supplement modifics the reports previously submitted. The hciddown springs in all cycle 2 fuel assemblies will be video inspected at the second refueling outage. Very truly yours, L1~ RPC:TJM: cts Attachment f00I h lll THE TCLECO EDISCN COMPANY EDISCN PLAZA 200 MACISCN AVENUE TCLEDO. CHiO 43652 8007150hfk2
w Dock t No. 50-346 Supplement to Dv'is nesse License No. NPF-3 Nuclear Power Station. Unit 1 Serial No. 627 Cycle 2 - Reload Rcyort July 10, 1980 Attachment REVIEW OF REPAIRED FL"2L ASSEBL'3LY The discovery of a small number of broken holddown springs has resulted in the development of a procedure for the replacement of holddown springs in irradiated fuel assemblies. This procedures does not impose any additional restrictions on the operation of the assemblies. The procedure consists of the removal and subsequent replacement of the upper end fitting plugs and holddown st rings. The fuel assembly upper end fitting (UEF) contains a holddown upr!.ng captured by a holddown spider and UEF plugs. The repaired eno fattine has similar comnonents, but a new holddown spring and UEF plugs are installed. To allow remote underwater repair, replacement plugs are held in place with a shoulder on one end and with flaring at the other end, instead of with welds. See Figure 1 for the new plug configuration. The tools and procedures developed for the repair operation have been performance tested. The repair operation for the irradiated fuel assemblies remaining in cycle 2 had the following steps: 1. Compress the holddown spring. 2. Break welds on UEF plugs and remove plugs. 3. Release holddown spring. 4. Remove holddown spring and spider. 5. Install new holddown spring and the same spider. 6. Compress the holdfawn spring. 7. Install and flare the new UEF plugs. 8. Inspect for satisfactory repair. The plug remover tool has been shown to produce clea'n breaks of the plug welds. The replacement plug provides holddown spider retention in the same manner as the welded plug did. The plug material utilized is compatible with that of the UEF. Several features insure positive retention of the plug in the upper end fitting. The close tolerance slip fit between the plug and the UEF minimizes any offset and prevents any cocking problem during insertion. A shoulder prevents the plug from working-itself to the inside of the UEF and the flare keeps the plug from backing out of the UEF. Further assurance of the plug retention is the spring force exerted on the plug by the spider arms while the plenum is removed and the presence of the grid pads immediately beyond the plug at all times while the plenum is installed. Vibrational levels are extremely. low and there are'no static forces acting parallel to the plug
.s. Docket No.'50-346 License No. NPF-3 Serial No. 627 July'10, 1980 Attachment axis at any ' time. The flare on the interior serves to preclude any protrusion of the plug beyond the OD of the UEF. A video inspection was done for each plug to determine that the plug was inserted properly and that the flaring of the plug was done in an acceptable manner. Each fuel assembly is checked with an envelope gauge to insure that a proper fit up of the upper end fitting and the vessel upper. internals is main-tained. The springs being inserted in this operation have met all load and dimensional requirements. Samples of spring material have been checked 3rd fe'md te 5n"e grain size small enough to enhance the fatigue resist-ance and grain boundaries more resistant to corrosion than the failed material. As a result, the new springs are expected to have improved resistance to. fatigue cracking and stress corrosion cracking relative to the original springs. The replacement springs have equal to or greater holddown capability as compared to the original springs. The holddown' spiders are not replaced, but are reused in this procedure. Any r :idual stress. created in the upper end fitting ears due to the interterence of the plug shoulder with the hole are sufficiently small so as to be negligible. The replacement operation has been qualified to yield a fuel assembly that is functionally identical to the original configuration while providing no material compatability differences. Operating margins are unaffected by the replacement operation. bj a/3-4 i l
r. Docket No. 50-346 l . Lica:13a No. NPF-3 Scrial No. 627 July 10, 1980 Attachment e END FITTING EARS FLARED RIVET r t M xj h SHOLLDER 11 .y K' i -FIGURE 1 REPLACEMENT PLUG FEATURES'
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