05000456/FIN-2011012-01
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Finding | |
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| Title | Design of Auxiliary Feedwater System Included Voids in Safety-Related Alternate Suction Flowpaths |
| Description | A URI was identified by the inspectors during the review of voided sections of AF alternate suction piping affecting all AF trains at Braidwood and Byron. Specifically, the inspectors questioned the acceptability of the voids and the potential impact on the AF systems, and an adequate technical justification from the licensee was not readily available. The AF system provides decay heat removal by cooling the steam generators following a reactor shutdown. The normal supply of water to the AF system is from the nonsafetyrelated condensate storage tank (CST), which contains chemically treated water. In the event the CST becomes empty or damaged, the alternate water source is the safetyrelated SX system, which provides lake water at Braidwood and river water at Byron. The design of the AF systems at Braidwood and Byron included a section of SX supply to AF piping that was maintained voided between two valves with a partially open drain. The purpose of this configuration was to prevent SX water intrusion into the steam generators through valve leak-by, which would have an adverse chemical effect since SX water is not chemically treated to the same standards as CST water. Based on the questions raised by NRC inspectors at Byron, similar questions were asked by NRC inspectors at Braidwood on February 4, 2011. At Braidwood, the NRC questions were entered into the CAP as IR 1173517. In response to the questions identified in the subject IR, the Braidwood licensee also concluded that the AF system was operable with the voids present based on the 1993 Byron Engineering letter addressed to the Braidwood and Byron Station Managers. The inspectors at Braidwood also questioned whether this conclusion was valid since no formal documentation supporting the conclusion was included with the 1993 Byron Engineering letter to the Braidwood Station Manager. Despite an exhaustive effort at Braidwood, neither a record of the telephone conversation with the pump vendor or a copy of the Duke Engineering Services letter that provided the basis for the conclusion in the Byron Engineering letter could be found. However, Braidwood was unable to fill the voided piping sections because the sections of piping containing the voids did not have vent valves installed as was the case at Byron. Instead, Braidwood generated Operability Evaluation 11-003, dated February 15, which concluded the AF system was operable with the voids present. This conclusion was based largely upon the 1993 Byron Engineering letter to the Braidwood Station Manager. In the absence of vendor documentation, Braidwood formally requested a more detailed analysis of the acceptability of the voided sections of piping from a vendor on March 23. In the absence of installed vent valves in the voided piping sections, Braidwood attempted to vacuum fill the piping sections for all four AF trains to remove the voids. This was completed on February 26, but was only successful for the 1A AF train due to excessive leakage past the isolation valves used to establish the void. However, the 1A AF piping was not ultrasonically tested to verify that it was water solid. Braidwood subsequently developed engineering change packages for all four AF trains to add vent valves to facilitate filling the voided piping sections. The 2B AF train vent valve installation was completed and the piping filled, vented, and verified water solid on March 25. A similar vent valve installation, followed by a fill, vent, and water solid verification, was accomplished for the 1B AF train on March 26. Preliminary information was received from the vendor for the 2B AF train at Braidwood on March 29 and for both Braidwood Unit 2 AF trains on April 5, which concluded that the void fraction at the 2A and 2B AF pump suction did not meet industry acceptance criteria. As a result, Braidwood declared the 1A and 2A AF trains inoperable since the 1A AF train had not been verified water solid and the vent valve modification to the 2A AF train had not been completed and the piping had not been filled. Vent valves were subsequently installed on the 2A and 1A AF trains at Braidwood, and both trains were filled, vented, verified water solid, and declared operable on March 30, and March 31, respectively. Event Notification 46707 for Braidwood was submitted to the NRC on March 30, 2011, in accordance with 10 CFR 50.72(b)(3)(ii)(B). Vendor analyses for the remaining 1A and 1B Braidwood AF trains and all four Byron AF trains were provided on April 15. The analyses concluded that the void fraction at the pump suction for the 1A AF trains at Braidwood and Byron was within industry acceptance criteria limits. The void fraction at the pump suction for the 1B, 2A, and 2B AF trains at Braidwood and Byron did not meet acceptance criteria limits. After the vendor analyses were received, Braidwood and Byron elected to contract a second vendor to perform full-scale testing of the impact of the AF void configurations at a testing facility. The inspectors reviewed the vendor analyses and discussed a number of questions and concerns with licensee personnel. A large number of simplifying assumptions were used in the vendor analyses, and there were limitations in the accuracy of computer modeling of multi-phase flow and voiding. As a result, the inspectors concluded that useful information could be gained from the full-scale testing planned by Braidwood and Byron. At the conclusion of the inspection, NRC inspectors were following development of the full-scale testing plan. This issue is an Unresolved Item pending NRC review of the fullscale testing and results. |
| Site: | Braidwood  |
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| Report | IR 05000456/2011012 Section 4OA5 |
| Date counted | Jun 30, 2011 (2011Q2) |
| Type: | URI: |
| cornerstone | Mitigating Systems |
| Identified by: | NRC identified |
| Inspection Procedure: | IP 93812 |
| Inspectors (proximate) | C Zoia S Sheldon A Garmoe S Westa Garmoeb Palagi D Reeser E Duncan G O'Dwyer J Benjamin M Perry R Ng |
| INPO aspect | |
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Finding - Braidwood - IR 05000456/2011012 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Finding List (Braidwood) @ 2011Q2
Self-Identified List (Braidwood)
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