05000348/FIN-2011010-04
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Finding | |
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| Description | The team identified an unresolved item (URI) regarding the licensees evaluation of the minimum required submergence for the AFW pumps given the potential for vortex formation in the CST. The CST is a safety related, seismic category I tank that holds up to 500,000 gallons of water and is required by the TS 3.7.6 limiting condition for operation to be maintained at a minimum of 150,000 gallons for use by the AFW system under normal operation and in response to accident conditions. In order to ensure this requirement, the lower 13 3-1/8 of the 46 inside diameter (ID) tank is designed to withstand the effects of tornado missiles. The CST has two 8 AFW suction pipes one for the TDAFW pump and one for both MDAFW pumps. Both suction pipes open at 4 from the tanks bottom facing down. The suction piping centers are approximately 1 3 apart. The CST has an internal bladder that prevents introduction of air under normal operating conditions. The team reviewed calculations BM-95-0961-001, Verification of CST Sizing Basis, Rev. 4, and CBI-72-4859, Condensate Storage Tank, Rev. 0 and made the following observations regarding the design basis of the CST: The CST tornado missile-protected height of 13 3-1/8 is based on the elevation of the 24 condenser hotwell make-up line. The hotwell make-up line is not designed to withstand a design basis seismic event or damage from tornado missiles. The team computed the maximum protected volume (including the unusable lower 4 of the tank) to be approximately 164,841 gallons. The team noted that this volume did not take into account any CST fabrication tolerances. Calculation BM-95-0961-001 established that there was a margin of 4,300 gallons with respect to the TS 3.7.6 requirements for the CST. Although this calculation addressed the losses of CST inventory due to the line break, it did not analyze that this line break would create an air introduction path under the CST bladder, allowing a vortex to form, and adversely affect the usable volume of water in the CST. Additionally, the team noted that calculation BM-95-0961-001 did not evaluate the effects of tornado missile damage to the un-protected portion of the CST. Tornado missile damage to the tank could also create an air introduction path under the CST bladder which would allow a vortex to form. Based on the teams observations, the licensee entered the issue into the CAP as CRs 351170, 353599 and 355457 and performed a prompt determination of operability (PDO) 0-11-06, Prompt Determination of Operability, Rev. 2 which concluded that vortex formation could lead to an additional loss of required CST level of 5.8 or 6,021 gallons. Although the additional water required to account for CST vortexing exceeded the TS minimum required value, the licensee concluded that sufficient water remained available below the condenser hotwell make-up elevation for the CST to be able to perform its safety function. Additionally, the licensee implemented administrative measures to ensure that CST level was maintained above the level determined to be required by the licensees evaluation. The PDO conclusions are supported, in part, by calculation SMSNC335993- 001, CST AFW Pump Suction Submergence Analysis, Ver. 1.0. This calculation utilizes a methodology based on Akalank K. Jain, Air Entrainment in Radial Flow towards Intakes, ASCE Journal of Hydraulic Division, September 1978, to determine the minimum submergence water level in the tank to prevent vortexing. |
| Site: | Farley  |
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| Report | IR 05000348/2011010 Section 1R21 |
| Date counted | Dec 31, 2011 (2011Q4) |
| Type: | URI: |
| cornerstone | Mitigating Systems |
| Identified by: | NRC identified |
| Inspection Procedure: | IP 71111.21 |
| Inspectors (proximate) | E Crowe A Nielsen F Ehrhardt G Kuzo S Sandal B Collins J Sowa C Dykesd Jones M Shlyamberg S Sandal R Nease J Eargle P Wagne |
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Finding - Farley - IR 05000348/2011010 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Finding List (Farley) @ 2011Q4
Self-Identified List (Farley)
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