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| {{#Wiki_filter:WBN 2 Mid-Cycle SG Outage Strategy Jeremy Mayo, Steam Generator Program Manager August 19, 2021 | | {{#Wiki_filter:}} |
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| Agenda Introduction Overall Contingency Strategy Questions 2
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| Introduction
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| * The WBN Unit 2 cycle 3 refueling outage (U2R3) was the third inservice inspection (ISI) for the Unit 2 Model D3 SGs (Alloy 600MA).
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| * This was the first outage to implement Generic Letter (GL) 95-05 voltage based repair criteria (ARC).
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| * Significant in-service inspection scope was performed.
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| * Condition monitoring requirements met for all degradation mechanisms except for GL 95-05 conditional burst probability in SG3 [WBN, Unit 2 Technical Specification (TS) 5.9.9 Item 5]
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| * License Amendment Requests (LARs) submitted and approved since U2R3 Alternate Probability of Detection (ML21027A167)
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| POD of 0.6 for less than 3.2 volts POD of 0.9 for greater than or equal to 3.2 volts and less than 6.0 volts POD of 0.95 for indications greater than or equal to 6.0 volts Temperature Adjustment to Voltage Growth Rate for GL95-05 ARC (ML21161A239)
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| * During the mid-cycle inspection scheduled for September 11, 2021, WBN 2 will be implementing a similar scope of eddy current inspection that was implemented during the U2R3 outage.
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| 3
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| Overall Contingency Strategy
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| * If results are as expected for Condition Monitoring, and Operational Assessment (OA) supports remaining months to SG replacement, no additional contingencies will be needed.
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| SG replacement is scheduled for March 2022 (U2R4 refueling outage).
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| * TVA is developing WBN 2 mid-cycle contingency plans for each activity or condition that is considered high risk.
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| Risk=(Probability x Consequence)
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| * OA for the mid-cycle outage will apply the alternate POD values and temperature adjustment of crack growth rate based on the previous LARs.
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| 4
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| Overall Contingency Strategy (cont.)
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| * TVA is working with Westinghouse on a tube support plate (TSP) locking/displacement contingency if the OA does not support the approximate six months of operation from the mid-cycle outage to the SG replacement outage (U2R4).
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| Locking of a TSP would limit the displacement of that TSP during a main steam line break, thereby minimizing contribution to probability of burst.
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| Modification of TSPs to limit support displacement would be accomplished using sleeves to create bulges on the top and bottom of the support.
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| This modification will be implemented under the 50.59 process.
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| The analysis based on displacement is an exception to GL 95-05 and requires a LAR.
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| Some supports may not need TSP locking to limit displacement.
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| * The implementation of TSP locking and the corresponding revised method for calculating SG tube burst probability proposed for application at Watts Bar Unit 2 has been licensed previously at South Texas Unit 2 (March 8, 2001).
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| Amendment No. 114 approved the application of a 3.0 volt repair criteria for SG tubes experiencing OD SCC at hot leg intersections at TSP elevations with locked tubes that would experience limited displacement during a postulated SLB for one cycle of operation.
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| 5}}
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