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| Entered date | Event description | |
|---|---|---|
| ENS 42571 | 12 May 2006 05:11:00 | While lowering turbine load to 45% for planned maintenance to replace an RCS Loop flow transmitter, Callaway Plant experienced high vibration on two main turbine bearings. The main turbine was manually tripped at 0047 in accordance with off-normal procedures. At 0052, received a Steam Generator High-High Level (P-14) on the "A" S/G resulting in a Feed Water Isolation Signal (FWIS) and Auxiliary Feed Water Actuation (AFAS). The reactor was manually tripped at 0053. Emergency Operating Procedures were completed and exited at 0115. After receiving the main turbine high vibration alarm, the plant reduced power to below the reactor trip/turbine trip setpoint and manually tripped the main turbine. Steam generator level rose to the P-14 feedwater isolation setpoint at which time, the reactor was manually tripped. All rods fully inserted on the trip. Decay heat is being removed by condenser steam dumps. Steam generator level is being maintained with the startup feed pump. The electrical grid is stable. No relief valves or safety valves lifted. The cause of the high vibration is being investigated. The licensee notified the NRC Resident Inspector. |
| ENS 42454 | 30 March 2006 21:40:00 | At 1650 on March 30, 2006, a concern was identified where the operators in the training simulator could not complete realignment of the component cooling water (CCW) flow to the residual heat removal (RHR) heat exchanger in a timely manner under certain accident scenarios. This could result in exceeding the maximum design temperature of the CCW system. In addition, assumptions made in the containment pressure and temperature analysis following a large break loss of coolant accident (LOCA) are non-conservative with respect to when CCW flow to the RHR heat exchangers is manually established in accordance with emergency operating procedures. Callaway plant FSAR indicates CCW system flow is manually aligned to the RHR heat exchangers prior to the recirculation phase of emergency core cooling system (ECCS). If the automatic transfer of the RHR pumps to cold leg recirculation, which happens at the Lo-Lo-1 level of the refueling water storage tank (RWST), occurs before CCW flow has been manually aligned to the RHR heat exchanger, containment sump water at temperatures up to 270F can be circulated through the RHR heat exchanger without CCW flow on the other side of the heat exchanger. The CCW side of the heat exchanger would contain stagnant water. This water can heat up quickly with no established flow and exceed the design rated temperature of the system. Recent simulator scenarios of large break LOCAs have shown that the CCW alignment is not reached before the Lo-Lo-1 RWST alarm level is reached. The CCW alignment is completed as part of procedure ES-1.3, Transfer to Cold Leg Recirculation. A review of two large break LOCA scenarios completed on 3-20-06 show that it takes between 1:00 and 1:30 minutes to initiate the step to align CCW to the RHR heat exchangers and takes between 3:00 and 4:30 minutes to complete the alignment. In addition to CCW system temperature concerns, an assumption that CCW flow is established to the RHR heat exchanger prior to reaching the Lo-Lo-1 level in the RWST is made in the containment temperature and pressure response analyses. As a result, a failure to establish CCW flow to the RHR switchover would result in an adverse impact on the inputs used in the Licensing Bases Containment Analysis. However, preliminary sensitivity runs using containment analyses codes indicate that post-peak temperature and pressure are not significantly affected by this issue. Actions taken: 1650 Declared both trains of CCW inoperable. Declared both trains of ECCS inoperable and entered Technical Specification 3.0.3 1710 Both trains of CCW aligned with flow through the RHR heat exchangers 1711 Exited Technical Specification 3.0.3 The licensee notified the NRC Resident Inspector.
The purpose of this notification is to retract a previous notification made on 3/30/06 (EN# 42454). That report was made per 50.72(b)(3)(v)(D) - Accident Mitigation. An engineering evaluation has determined the RHR and CCW systems would have fulfilled their safety functions had they been necessary to respond to an event. Since the safety functions would have been performed there are no applicable reporting criteria under 50.72 or 50.73 and Event Notification 42454 is retracted. The NRC Resident Inspector will be notified. Notified R4DO (Shaffer). |