ENS 48525

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v t e ENS Event
11:45 Nov 20, 2012
Title	Condition That Could Have Prevented Automatic Isolation of Reactor Water Cleanup System
Event Description	Susquehanna Unit 2 discovered a condition that could have prevented the primary containment isolation valves for the reactor water cleanup (RWCU) system from automatically isolating on a high differential flow instrumentation signal. The RWCU system high differential flow signal was found to be indicating downscale due to an instrument failure. Both divisions of the RWCU high differential flow isolation logic utilize the same differential flow instrument loop. Thus, this single instrument failure would have prevented automatic isolation of the RWCU inboard and outboard primary containment isolation valves on a high differential flow signal. The other RWCU primary containment isolation instrumentation functions remained operable and the associated RWCU system primary containment isolation valves were capable of being remotely closed by the control room operators. At the time of discovery, Unit 2 was in Mode 2 due to an unplanned shutdown and all control rods had already been fully inserted as part of a soft shutdown sequence. The licensee has notified the NRC Resident Inspector. * * RETRACTION FROM DUTTRY TO KLCO ON 1/11/13 AT 2155 EST * * * Following the ENS report (EN 48525), Susquehanna determined that although the RWCU high differential flow isolation instrumentation would have prevented automatic isolation of the RWCU inboard and outboard primary containment isolation valves on a high differential flow signal, the RWCU high flow isolation instrumentation would detect a high flow condition and generate an isolation signal that would close the isolation valves. The RWCU high differential flow instrumentation is downstream of the RWCU pumps and it calculates the difference (delta) in flow between the inlet and the outlet of the RWCU heat exchangers. The SSES [Susquehanna Steam Electric Station] Technical Specification (TS) Bases Section 3.3.6.1 states that the RWCU Differential Flow signal is to detect a break in the RWCU system (pipe severance and separation). Engineering analysis determined that the RWCU pumps would run-out if a break occurs downstream of the pumps and the RWCU system flow rate would be approximately 1000 gpm, with one RWCU pump in operation. The flow rate would be higher for two RWCU pumps in operation. Therefore, RWCU isolation would occur from the RWCU Flow - High isolation signal due to a flow rate that is greater than 472 gpm (TS Table 3.3.6.1-1). This high flow isolation does not rely on the RWCU high differential flow instrumentation. The above analysis is consistent with the FSAR discussion in section 7.3.1.1a.2.4.1.9.3. Based on the above, Susquehanna has determined that the RWCU isolation function would still be completed if a pipe break occurred downstream of the RWCU heat exchangers and the RWCU high differential flow instrumentation is inoperable. Since there was no loss of safety function of structures or systems that are needed to control the release of radioactive material, this ENS report is retracted. The licensee will notify the NRC Resident Inspector.

ENS 48525 +/- *RETRACTED*
Where
Susquehanna Pennsylvania (NRC Region 1)
Reporting

10 CFR 50.72(b)(3)(v)(C), Loss of Safety Function - Release of Radioactive Material
Time - Person (Reporting Time:+0.75 h0.0313 days <br />0.00446 weeks <br />0.00103 months <br />)
Opened:	Todd Creasy 12:30 Nov 20, 2012
NRC Officer:	Bill Huffman
Last Updated:	Jan 11, 2013
48525 - NRC Website
v • d • e

v t e Emergency Notification System
Susquehanna with 10 CFR 50.72(b)(3)(v)(C), Loss of Safety Function - Release of Radioactive Material
WEEKMONTHYEAR2103-11-21T03:40:00 [Table view]
[ENS list for Susquehanna]

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