05000361/FIN-2012007-09
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Finding | |
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Title | Evaluation of the Effects of Divider Plate Weld Repairs in Unit 3 Replacement Steam Generators |
Description | The team identified an Unresolved Item associated with the adequacy of evaluation and controls for the divider plate weld repairs. The cracking of the divider plate weld in both Unit 3 replacement steam generators required extensive repairs affecting the channel head, divider plate, and tube-sheet. Based on interviews with licensee personnel and the review of documentation for the repairs, the team determined that Mitsubishi did not perform a comprehensive evaluation to assess the impact of the divider plate repairs on the integrity of the tube bundle. The team determined that the areas listed below were not considered or evaluated in sufficient depth to identify the potential adverse effects of the planned weld repairs. Additional Rotations The repair activities for the Unit 3 steam generators required additional rotations of the steam generator assembly while these were oriented in the horizontal position. The repairs resulted in approximately 300 additional rotations in each steam generator, which could have affected the configuration of the tube bundle in terms of anti-vibration bar gaps or distortion. The team identified that Mitsubishi did not fully evaluate the impact of additional rotations on the configuration of the steam generators since rotation was considered a normal evolution in the fabrication process. Heat Input The repair process included extensive heat-adding activities such as grinding, flame cutting, and post-weld heat treatment. While these activities were performed in accordance with the construction code of record and an approved repair plan, they could have resulted in thermal expansion and unintended distortion of steam generator components. For example, the channel heads were removed using flame cutting and Mitsubishis evaluation for the impact of this activity was limited to the base material area in the vicinity of the cut, i.e. the heat affected zone. Mitsubishi did not fully assess the impact this activity could have on the overall configuration of the steam generator in terms of thermal expansion of the tubesheet or distortion. Dimensional Checks after Repair The team identified that Mitsubishi did not perform dimensional verifications (e.g. clearances) of the tube bundle or other secondary side dimensions after the repairs of the Unit 3 steam generators to confirm that critical dimensions were not affected by the repairs. Additional review by the NRC is required following completion of the licensees cause evaluation to fully assess how the repair activities affected the Unit 3 replacement steam generators and then determine whether this issue represents a performance deficiency or constitutes a violation of NRC requirements. |
Site: | San Onofre |
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Report | IR 05000361/2012007 Section 4OA5 |
Date counted | Jun 30, 2012 (2012Q2) |
Type: | URI: |
cornerstone | Mitigating Systems |
Identified by: | NRC identified |
Inspection Procedure: | IP 93800 |
Inspectors (proximate) | C Thurston E Collins E Murphy J Ortega Luciano J Reynoso J Rivera Ortiz A Johnsonb Hagarg Werner J Reynoso J Rivera-Ortiz |
INPO aspect | |
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Finding - San Onofre - IR 05000361/2012007 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Finding List (San Onofre) @ 2012Q2
Self-Identified List (San Onofre)
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