05000341/LER-2015-003
| Fermi 2 | |
| Event date: | 03-19-2015 |
|---|---|
| Report date: | 05-05-2015 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| 3412015003R00 - NRC Website | |
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Initial Plant Conditions:
Mode 1 Reactor Power 74 percent
Description of the Event:
On March 19, 2015, at 0647 hours0.00749 days <br />0.18 hours <br />0.00107 weeks <br />2.461835e-4 months <br />, the Fermi 2 annunciators indicated a cooling water leak in the drywell. The Reactor Building Closed Cooling Water (RBCCW) system CC was isolated and both divisions of the Emergency Equipment Cooling Water (EECW) system were started. Approximately four minutes later signs of Division 1 EECW pump cavitation were observed indicating that the leak affected the north (A) reactor recirculation pump AD cooling. The north (A) reactor recirculation pump was tripped at 0652 to prevent motor damage from loss of cooling and the reactor transitioned to single loop operation.
Due to the reduction in reactor AC power from 100 percent to approximately 61 percent following the reactor recirculation pump trip, the heater drains system SJ stopped pumping forward. The loss of forward pumping heater drains led to a power increase to approximately 74 percent due to reduced feedwater temperature. At 0652 hours0.00755 days <br />0.181 hours <br />0.00108 weeks <br />2.48086e-4 months <br /> the reactor entered the Exit region of the power to flow map where core instability is possible.
While initiating actions to insert control rods AC to reduce reactor power in accordance with Abnormal Operating Procedures (AOP), Oscillation Power Range Monitor (OPRM) IG channels 2 and 3 detected power oscillations and initiated an automatic reactor protection system JC scram at 0702 hours0.00813 days <br />0.195 hours <br />0.00116 weeks <br />2.67111e-4 months <br />. At the time of the scram, reactor power was approximately 74 percent and core flow was approximately 45 percent. The OPRM system performed as designed by providing an OPRM Upscale trip based on the Period Based Detection Algorithm when the oscillation magnitudes exceeded the OPRM amplitude and confirmation count setpoint.
In response to the scram signal, all control rods fully inserted. Reactor water level reached a low of approximately 126 inches above top of active fuel and was restored and maintained in the normal operating band by the feedwater and control rod drive systems. Plant procedures were appropriately utilized to complete scram recovery actions. No Safety Relief Valves (SRV) or other safety systems actuated and reactor pressure was maintained by the main turbine bypass valves. Plant systems responded to the scram as designed.
All reactor parameters were maintained within design limits following the scram.
The automatic OPRM upscale scram event is reportable under 10 CFR 50.73(a)(2)(iv)(A) as an event or condition that resulted in the automatic actuation of the reactor protection system and a reactor scram. A four hour non-emergency notification (Event Number 50903) was made to the NRC Operations Center at 1051 on March 19, 2015 in accordance with 10 CFR 50.72(b)(2)(iv)(B) for an actuation of the reactor protection system.
Significant Safety Consequences and Implications:
from exceeding the fuel Safety Limit Minimum Critical Power Ratio (SLMCPR) due to anticipated thermal-hydraulic neutron flux oscillations.
A. General Electric (GE Hitachi Nuclear Energy) evaluation of the event confirmed that the SLMCPR was protected throughout the event by the OPRM reactor trip.
This event posed no significant safety implications because the reactor protection and safety related systems functioned as designed following the automatic reactor trip. All reactor parameters were maintained within design limits following the scram.
Therefore, this event did not pose an actual threat to the health and safety of the public.
Cause of the Event:
The cause of the automatic reactor protection system scram on OPRM Upscale was the neutron flux oscillations following the large core flow reduction and lowering feedwater temperature after the trip of a reactor recirculation pump.
Corrective Actions:
Immediate corrective actions have been taken including a revised Abnormal Operating Procedure (AOP) for reactor recirculation pump trip to reprioritize steps to insert control rods, a revised Reactivity Management Shift Reactivity Briefing Checklist to identify events that have a high probability for flux instability and Just in Time Training (VITT) for all operating crews on the OPRM scram lessons learned.
This event was documented and evaluated in the Fermi 2 Corrective Action Program. The associated root cause evaluation is still in progress and may identify additional corrective actions. These actions will be tracked and implemented by the corrective action program.
Additional Information:
A. Failed Component:
None B. Previous Licensee Event Reports (LERs) on Similar Problems:
There are no similar previous events within the past five years.