05000387/FIN-2012007-01
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Finding | |
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| Title | Adequacy of Secondary Containment and Standby Gas Treatment System Testing |
| Description | An unresolved item (URI) was identified because additional NRC review and evaluation is needed to determine whether the technical specifications (TS) and associated bases documents were adequate to provide reasonable assurance of operability of the secondary containment boundary and the standby gas treatment system (SGTS). During a review of a modification to the secondary containment boundary, the team identified a potential deficiency related to the adequacy of testing performed to comply with TS surveillance requirements (SR) 3.6.4.1.4 and 3.6.4.1.5, which were associated with verifying secondary containment and SGTS operability. The team questioned whether the allowed configuration for secondary containment during testing could mask potential leakage between the secondary containment zones (through a common boundary) and could potentially make secondary containment inoperable. At Susquehanna, the secondary containments are divided into three zones. Zone 1 is associated with Unit 1, Zone 2 is associated with Unit 2, and Zone 3 encompasses the spent fuel area. These zones are normally maintained at > 0.25 water vacuum via the normal non-safety related ventilation lineup, and the ventilation flow is discharged to the atmosphere via an unfiltered but monitored release path. During a postulated design basis accident, the secondary containment ventilation system is designed to isolate the affected units zone (either Zone 1 or Zone 2) and the spent fuel pool zone (Zone 3). These two zones are automatically placed on recirculation and are discharged through the SGTS via common ventilation ductwork. The unaffected units zone does not isolate and remains on the normal ventilation lineup. During a postulated design basis accident combined with a loss-of-offsite power, all three zones would automatically isolate and be placed on recirculation with discharge via the SGTS. The team reviewed the TS SRs used to verify the operability of secondary containment boundary and the SGTS, as well as the surveillance procedure used to meet TS SRs 3.6.4.1.4 and 3.6.4.1.5. The team found that any of three ventilation line-ups were allowed in the procedure. The acceptable configurations were; 1. All three zones on recirculation connected to the SGTS. 2. Zone 1 (2) and Zone 3 on the recirculation system connected to the SGTS with Zone 2 (1) operable (> 0.25 water column vacuum) and on normal ventilation. 3. Zone 1 (2) and Zone 3 on the recirculation system connected to the SGTS with Zone 2 (1) inoperable (atmospheric pressure). The TS SR acceptance criteria specified that if the SGTS can maintain the tested zone at a vacuum > 0.25 of water in the required time (3.6.4.1.4) and the flow rate through the SGTS is less than the established limit (3.6.4.1.5), then the SRs are considered met. The team found that, as a matter of routine, PPL tested the SGTS as per Items 1 and 2 above to provide reasonable assurance of operability of secondary containment and the SGTS system, and that the test results met the TS surveillance acceptance criteria. The team determined that when the all three zones configuration is used (Item 1 above), the boundaries between zones are not subject to any testing (i.e., the SGTS maintains all three zones at about the same pressure). This configuration does, however, test the secondary containment exterior boundaries and the SGTS for a design basis event with a loss-of-offsite power. Similar to the Item 1 configuration, for either of the two zone configurations (i.e., with the unaffected units non-safety related system in operation, Item 2 above), the common boundary between the zones is not tested. Specifically, the teams review of the test results for this two zone configuration identified that the unaffected units vacuum was better than the units vacuum that was being established by the SGTS. As a result, if there was an opening between the zones (at the common boundary), the normal ventilation lineup would be assisting the SGTS, thus invalidating the test. The team determined that the configuration with one zone inoperable (Item 3 above) represented a valid surveillance test in that it would ensure that potential leakage between the zones would be small enough such that the SGTS could maintain sufficient secondary containment vacuum. However, because this is not the normal configuration, the potential for leakage at the common boundary between the affected and nonaffected zones could exist since normal ventilation creates a better vacuum on the nonaffected unit. This potential leakage would be discharged without filtration to the environment via the normal ventilation system, and manual operator action would be necessary to stop this discharge. In response to the teams concerns, PPL conducted field walkdowns to visually confirm the absence of openings at the internal boundaries. In addition, PPL reviewed the results of recently completed surveillance test data, which indicated the normal ventilation system that was in-service on the zone that was not being tested, was not significantly more negative than the zone tested by the SGTS. In addition, PPL confirmed that operators would receive a control room alarm in the event that the normal ventilation system experiences a high radiation condition in its effluent discharge path, and that the operators would respond and manually place the SGTS in service on that unit. The team determined that the results of PPLs review demonstrated reasonable assurance that the SGTS was capable of performing its intended function. The team will coordinate with the NRCs Office of Nuclear Reactor Regulation to review the adequacy of PPLs SGTS testing methodology to ensure secondary containment boundary integrity. Pending resolution of this issue and determination of any potential enforcement actions, this item is an Unresolved Item. |
| Site: | Susquehanna  |
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| Report | IR 05000387/2012007 Section 1R17 |
| Date counted | Dec 31, 2012 (2012Q4) |
| Type: | URI: |
| cornerstone | Mitigating Systems |
| Identified by: | NRC identified |
| Inspection Procedure: | IP 71111.17 |
| Inspectors (proximate) | C Graves E Burket F Bower J Cherubini J Greives T Daunj Richmondk Mangan P Krohn S Pindale |
| INPO aspect | |
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Finding - Susquehanna - IR 05000387/2012007 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Finding List (Susquehanna) @ 2012Q4
Self-Identified List (Susquehanna)
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