05000389/FIN-2014005-02
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Finding | |
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| Title | Design Basis Review for Unit 2 Steam Generator Tube-to-Tubesheet Joint |
| Description | The inspectors identified an unresolved item (URI) associated with the design of the tube-to-tubesheet joint for the Unit 2 replacement SGs. In April 2014, the channel head of Unit 2 SG-2B experienced impingement damage in the hot leg side, due to a foreign object in the reactor coolant system. The extent of the damage included impingement marks on the tube-to-tubesheet welds. The licensee entered the issue in the CAP as AR 01955927. The inspectors reviewed the licensees one-cycle operability evaluation for this condition (Areva Report 51-9222481- 000) to verify that the licensee provided adequate technical justification demonstrating that the SG would be capable of performing its design function, particularly to maintain tube integrity, during the current cycle. The inspectors did not identify an issue of concern with the licensees operability conclusions, but issued a URI to determine if the foreign material intrusion issue constituted a performance deficiency and/or a violation of NRC requirements. In October 2014, the NRC closed the URI with a non-cited violation for the failure to follow the requirements in reactor vessel maintenance procedures. The inspectors review and disposition of this issue was documented in NRC Inspection Report 05000389/2014004 (ADAMS Accession Number ML14293A668). From October to December 2014, the inspectors had further discussions with the licensee, and reviewed the planned corrective actions to address Unit 2 SG-2B operability for future plant operating cycles. In their review, the inspectors identified an issue of concern related to the design approach for the tube-to-tubesheet welds in the Unit 2 replacement SGs. Specifically, the licensees operability evaluation addressing the impingement damage for the current cycle described the weld at the end of each tube as a seal weld, without further discussion about the structural function of the weld. The inspectors determined that it was necessary to confirm whether the Unit 2 SG tube end welds were credited in the structural analysis of the tube-to-tubesheet joint under design basis loads. The inspectors determined that additional information from the SG vendor was needed to understand the design approach and qualification for the tube-totubesheet joint, including the welds. This issue of concern with the tube-to-tubesheet welds did not adversely affect the licensees operability conclusions for the current cycle. The operability evaluation for SG-2B contained technical data from the vendor to demonstrate that the tube structural integrity and primary-to-secondary leakage criteria would not be challenged due to the performance of the mechanically expanded portion of the tube inside the tubesheet. The licensee provided sufficient information about the tube-to-tubesheet joint design to provide reasonable assurance that the joint, considering the impingement damage to the tube end welds, would meet the performance criteria for SG tube integrity required in the plants Technical Specifications. |
| Site: | Saint Lucie  |
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| Report | IR 05000389/2014005 Section 4OA2 |
| Date counted | Dec 31, 2014 (2014Q4) |
| Type: | URI: |
| cornerstone | Mitigating Systems |
| Identified by: | NRC identified |
| Inspection Procedure: | IP 71152 |
| Inspectors (proximate) | A Goldau A Sengupta B Collins D Bacon J Reyes J Rivera-Ortiz L Suggs P Capehart T Morrisseyj Reyesj Rivera-Ortiz M Riches P Capehart S Sandal T Morrisseyc Fontanae Stamm J Reyes J Rivera-Ortiz S Sanchez T Morrissey B Cecere |
| INPO aspect | |
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Finding - Saint Lucie - IR 05000389/2014005 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Finding List (Saint Lucie) @ 2014Q4
Self-Identified List (Saint Lucie)
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