ENS 42372
ENS Event | |
|---|---|
23:50 Feb 23, 2006 | |
| Title | Degraded Condition of Shroud Tie Rods |
| Event Description | While performing Unit One [In-Vessel Visual Inspection] IVVI examination of the four Shroud Tie Rods (Upper Support Horizontal Support Surface) the following results were reported:
Tie Rod at 135 degree location: Crack-like indications beginning at the inner corner on both sides of the left support and extend to two thirds of the way to the outer corner with full penetration. Tie Rod at 225 degree location: Crack-like indication beginning at the inner corner on one side of the left support and extending a small portion of the way toward the outer corner. The indication is similar to that described for the shroud tie rod in the 135 degree location except that it is much less pronounced and is only on one side. Tie Rod at 45 degree location: No apparent indications present. Tie Rod at 315 degree location: No apparent indications present. One of the design criteria of the Shroud Tie Rods is to maintain zero separation between the shroud horizontal welds at 100% uprated power, assuming all of the horizontal welds (H1 thru H8) are fully cracked. The Shroud Tie Rods are also designed to maintain structural integrity of the shroud during all design basis accidents and transients. These findings bring into question the ability of these shroud tie rods to have performed their design function with the reactor in operation. This condition constitutes a serious degradation of a principal safety barrier had the unit been operating. The reactor is presently shutdown and the condition discovered does not represent an immediate safety concern for Unit 1. The extent of this condition is believed to be limited to Unit 1, since Unit 2 core shroud tie rods are made of different materials and installed in a different configuration. The licensee notified the NRC Resident Inspector.
Retraction of NRC Event # 42372: After further review and evaluation it has been determined that the eight hour call made February 23, 2006 per the guidance of 50.72(b)(3)(ii)(A) should be retracted. On 02/23/2006 at approximately 2135 EST, Unit 1 was in the refuel mode. During that time routine inspection of the Reactor Vessel Shroud Restraint Tie Rod Assemblies was in progress. The inspections revealed two cracks on the 135 degree assembly and one crack on the 225 degree assembly. In addition the mechanical preload on the 315 degree assembly was found to be below the design value. These assemblies were originally installed as a mechanical replacement of the horizontal shroud welds. An evaluation was performed of the as-found condition that considered the effects of the cracks on the upper supports and the reduced mechanical preload on the 315 degree assembly. The results of the analysis showed that sufficient compression existed for the tie rod assemblies to be considered operable in the as found condition. Inspection and evaluation of the horizontal shroud welds (original plant design) further determined that sufficient intact weld ligament existed to ensure the shroud design function was maintained without relying on the tie rod assemblies. Therefore, the structural integrity of the shroud was and is maintained for normal operation as well as all design basis accidents and transients. The licensee notified the NRC Resident Inspector. Notified R2 DO (M. Lesser) |
| Where | |
|---|---|
Hatch  Georgia (NRC Region 2) | |
| Reporting | |
| 10 CFR 50.72(b)(3)(ii)(A), Seriously Degraded | |
| Time - Person (Reporting Time:+-0.22 h-0.00917 days <br />-0.00131 weeks <br />-3.01356e-4 months <br />) | |
| Opened: | Frank Gorley 23:37 Feb 23, 2006 |
| NRC Officer: | Joe O'Hara |
| Last Updated: | Apr 21, 2006 |
| 42372 - NRC Website
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WEEKMONTHYEARENS 569592024-02-11T15:11:00011 February 2024 15:11:00
[Table view]10 CFR 50.72(b)(3)(ii)(A), Seriously Degraded Primary Containment Degraded ENS 563422023-02-07T22:38:0007 February 2023 22:38:00 10 CFR 50.72(b)(3)(ii)(A), Seriously Degraded Primary Containment Degraded ENS 544632020-01-04T16:09:0004 January 2020 16:09:00 10 CFR 50.72(b)(3)(ii)(A), Seriously Degraded Primary Containment Degraded ENS 525672017-02-20T04:23:00020 February 2017 04:23:00 10 CFR 50.72(b)(3)(ii)(A), Seriously Degraded Containment Penetration Exceeded Allowable Leakage ENS 517422016-02-16T11:31:00016 February 2016 11:31:00 10 CFR 50.72(b)(3)(ii)(A), Seriously Degraded Weld Overlay Flaw Did Not Meet Acceptance Criteria ENS 487952013-02-28T16:55:00028 February 2013 16:55:00 10 CFR 50.72(b)(3)(ii)(A), Seriously Degraded Closed Cooling Water Isolation Valve Fails Local Leak Rate Test ENS 487722013-02-20T10:28:00020 February 2013 10:28:00 10 CFR 50.72(b)(3)(ii)(A), Seriously Degraded Degraded Condition - Containment Penetration Fails Local Leak-Rate Testing ENS 440382008-03-06T09:00:0006 March 2008 09:00:00 10 CFR 50.72(b)(3)(ii)(A), Seriously Degraded Pin Hole Leak Discovered in 1 Inch Instrument Line During Rpv Pressure Test ENS 440052008-02-23T21:00:00023 February 2008 21:00:00 10 CFR 50.72(b)(3)(ii)(A), Seriously Degraded Unacceptable Flaw in Rpv Cap-To-Pipe Weld ENS 432242007-03-09T05:30:0009 March 2007 05:30:00 10 CFR 50.72(b)(3)(ii)(A), Seriously Degraded Main Steam Line Flow Instrument Line Pressure Boundary Leakage ENS 423722006-02-23T23:50:00023 February 2006 23:50:00 10 CFR 50.72(b)(3)(ii)(A), Seriously Degraded Degraded Condition of Shroud Tie Rods 2024-02-11T15:11:00 | |