05000289/FIN-2011005-03
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Finding | |
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| Title | Adequacy of Seismic Gap Flood Seal |
| Description | UFSAR Section 2.6.5, Design of Hydraulic Facilities, stated that a system of dikes protected the site against inundation and wave action for the site design flood of 1 ,100,000 cfs. lt further stated that the licensee committed to provide component protection to the degree which would assure a safe and orderly shutdown for the level of flooding postulated by a PMF of 1,625,000 cfs. As a result of that commitment, several modifications were performed to provide component protection, including a modification to make portions of the seismic gap watertight because those portions of the gap would be directly exposed to standing water during a PMF event. The seismic gap was a three inch nominal gap that separated the reactor building from other adjacent buildings and structures (e.9., fuel handling building, turbine building, etc.). As a result of the TMI external flood re-analysis, Exelon modified the TMI flood barrier system to accommodate the higher maximum flood height. Modification ECR TM 11-00426, Raise Level of External Flood Protection, also re-evaluated the adequacy of the seismic gap flood seal capability. ECR Attachment-17, Reactor Building Elev. 305 ft. Seismic Gap Flood Seal Evaluation, described the seismic gap as filled with Dow Corning 3-6548 silicone RTV foam (i.e., a medium density fire resistant penetration seal) to a nominal depth of two feet, but conservatively assumed a gap depth of 9 inches for the watertight assessment. In order to evaluate the capability of the existing seal to withstand a higher water pressure, Exelon used a friction coefficient derived from test results for a similar material. NPB-92, BISCO Seal Test Equivalency for Use in Conduit Sealing, Rev. 1, documented the test results for BISCO SF-20 foam (i.e., a low density fire resistant penetration seal), which had been performed to determine seal blowout resistance, not to verify or test the seal hydrostatic properties. The inspectors identified that the NPB-92 test results also documented seal water leakage, but the leakage rates were not quantified or evaluated. In addition, drawing E-107-012 provided the seismic gap installation configuration details. The inspectors identified that the drawing details differed from the assumptions in ECR TM 1\\\'1 -00426, such that the inspectors could not independently determine the depth of the foam seal or the specific material in the gap based their review of design and installation records. Therefore, the inspectors were not able to independently verify that the seismic gap was of sufficient depth or proper material to ensure an adequate watertight seal, not only at the revised flood level, but at any flood level that challenges the seal. During this inspection period, Exelon was not able to provide sufficient additional engineering or installation documentation to demonstrate the adequacy of the seismic gap to function as a hydrostatic flood seal. Therefore, the inspectors concluded that the adequacy of the seismic gap to provide the required flood protection was an issue requiring further NRC review to determine if TMI was in compliance with their licensing bases for flood protection. Exelon entered this issue into their corrective action program as lR 1 276881 |
| Site: | Three Mile Island  |
|---|---|
| Report | IR 05000289/2011005 Section 4OA2 |
| Date counted | Dec 31, 2011 (2011Q4) |
| Type: | URI: |
| cornerstone | Mitigating Systems |
| Identified by: | NRC identified |
| Inspection Procedure: | IP 71152 |
| Inspectors (proximate) | C Cahill D Kem D Werkheiser G Hunegs J Heinly J Laughlin J Richmond S Galbreath T Moslakc Cahilld Kern D Werkheiser G Hunegs J Heinly J Richmond K Cronk R Nimitz S Barr T O'Hara |
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Finding - Three Mile Island - IR 05000289/2011005 | |||||||||||||||||||||||||||||||||||||||||||||||
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Finding List (Three Mile Island) @ 2011Q4
Self-Identified List (Three Mile Island)
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