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| Entered date | Event description | |
|---|---|---|
| ENS 46297 | 30 September 2010 21:39:00 | USAR Section 2.7.1.2, River Stage and Flow, states flooding protection against the 1,014 foot flood in the auxiliary building is provided by removable flood barriers and sandbagging. When required, these flood barriers are installed in openings leading to safety related equipment on the 1,007 foot and 1,011 foot floor elevations. It has been identified that the condensation drains from the switchgear room's air handling units VA-87 and VA-88 (located in the auxiliary building), and the upper electrical penetration room's air handling units VA-85 and VA-86 (located in the auxiliary building), have no isolation valves or check valves to prevent backflow from the drain line's discharge in the turbine building basement. This means that flooding of the turbine building above approximately the 1011 foot elevation (floor level of the switchgear rooms) would result in water back-flowing via the drain lines into the switchgear rooms. River level is currently at the 999' 6" elevation and stable. Procedure changes are currently being developed to block the affected drain lines. River level has never reached the 1011 foot elevation at the facility. The licensee has notified the NRC Resident Inspector.
A further evaluation of the reported flooding issue determined that the flow into the switchgear rooms would be insufficient to affect the operability of safety related equipment in the auxiliary building; therefore, the incident could not have prevented fulfillment of a safety function nor could it have caused the inoperability of independent trains of safety related equipment. The situation does not constitute an unanalyzed condition. Therefore, this event is being retracted. The NRC Resident Inspector has been notified. Notified R4DO (Powers). |
| ENS 45251 | 9 August 2009 06:25:00 | (The licensee) notified the Nebraska Department of Environmental Quality that a site sewage lift station had overflowed due to blown fuses and released an estimated 20 gallons of raw sewage the Missouri River. The licensee informed the NRC Resident Inspector. |
| ENS 44228 | 21 May 2008 02:29:00 | At 1956, during reactor core reload with a full refueling cavity, power was lost to the #2 non-vital instrument bus. This power loss resulted in closure of the shutdown cooling temperature control valve, HCV-341. The closure of HCV-341 interrupted the cooling capability of the in service shutdown cooling loop. While cycling a condenser motor operated valve a 480 volt ground occurred which resulted in tripping the feeder breaker to motor control center MCC-4B2. MCC-4B2 was supplying power to Instrument Bus 2 via the Inverter 2 test transformer. The test transformer was powering Instrument Bus 2 due to Inverter 2 replacement per plant modification. The loss of the #2 Instrument Bus resulted in HCV-341, the shutdown cooling heat exchangers temperature control valve, failing closed. HCV-341 was manually opened to restore cooling at 2019. At 2049 power was restored to Instrument Bus 2 and the shutdown cooling system was returned to automatic operation. Flow through the core was maintained throughout the event, as the shutdown cooling heat exchanger bypass valve responded by opening to maintain flow. At the time shutdown cooling was lost, 44 of 133 assemblies had been loaded into the vessel and shutdown cooling temperature was approximately 88 degrees F. Time to boil was conservatively calculated to be 22.5 hours per plant procedures which assume decay heat from all 133 assemblies. Shutdown cooling temperature rose approximately one degree during this event. Technical Specification 2.8.1(3)(1) was entered due to no Shutdown Cooling loop in Operation. No reactor coolant boron reductions were in progress. Irradiated fuel assembly loading into the reactor core was secured and actions to restore a Shutdown Cooling loop were being initiated. (Ft. Calhoun) entered) a 4 hour LCO to close all containment penetrations providing direct access from the containment to the outside atmosphere. The licensee notified the NRC Resident Inspector.
Following a detailed review of the event of May 20, 2008, Fort Calhoun station determined that the safety function of removing residual heat from the reactor coolant system was available throughout the entire event. The system is largely manual and the manual functions were not affected by the event. At the time of the loss of power the core was being reloaded. The heat load was very small and the temperature control valve (HCV-341) was closed to allow the system to increase in temperature. When control power to HCV-341 was lost the valve did not change position. Since the ability of the shutdown cooling system to remove residual heat was not impacted by the loss of power and plant procedures have provisions to control the system locally, the safety function of removing decay heat was not lost. Therefore this notification is being retracted. The licensee notified the NRC Resident Inspector. Notified R4DO (William Jones) |
| ENS 43886 | 8 January 2008 20:33:00 | At 11:42 CST, a condition report was initiated that questioned the specified flow path for simultaneous hot and cold leg injection following a large break loss of coolant accident (LOCA). When an unisolated LOCA event exists, simultaneous hot leg and cold leg injection should be implemented if the plant cannot be placed on shutdown cooling within six hours of the LOCA initiation and RCS pressure is less than 120 psia. The procedure is implemented at five and one-half hours to provide adequate time to align simultaneous hot/cold leg injection before the six hour time limit. Injecting to each side of the reactor vessel at an injection rate greater than 165 gpm, ensures that fluid from the reactor vessel (where the boric acid is being concentrated) flows out of the break regardless of the break location and is replenished with a dilute solution of borated water from the other side of the reactor vessel. The action is taken between 5.5 and 6 hours after the LOCA in order to ensure that the buildup of boric acid is terminated well before the potential for boric acid precipitation occurs which could restrict coolant flow through the core. Once the RCS is refilled, the boric acid is dispersed throughout the RCS via natural circulation. If entry into shutdown cooling system operation is anticipated before the 5.5 hour limit, then the realignment to hot/cold leg injection is unnecessary. The potential concern is associated with a charging line thermal relief valve CH-202 bypassing flow from hot leg injection and preventing the required flow rate needed to prevent boron precipitation from occurring. A minimum injection rate of 147 gpm to the cold legs and 159 gpm to the hot legs is required to prevent boric acid precipitation. Total hot leg injection flow is measured at FIA-236. Cold leg injection flow is the total of the four HPSI flow instruments, FI-313, FI-316, FI-319, and FI-322 with 50 gpm the minimum flow indication. A total cold leg injection flow of at least 200 gpm ensures at least 150 pm flow into the core, assuming 25% spillage out the break. This meets the required minimum of 147 gpm. It could not be determined through a review of the design basis documents and associated calculations what, if any, bypass flow is assumed through CH-202. Current procedural guidance in the emergency operating procedures is to align a high pressure safety injection pump to the charging header and provide hot leg injection from auxiliary pressurizer spray valves attached to the charging headers through the pressurizer and into the hot leg. The current procedural guidance does not isolate CH-202 and due to the location of flow instrument FIA-236, it cannot be guaranteed that all the flow through the charging system is being injected into the hot leg or being diverted through the normal charging line. As a result the potential existed which could have prevented the fulfillment of the safety function of a system needed to remove residual heat. Therefore this report is being made in reference to 10 CFR 50.72 (b) (3) (v) (B). Efforts are continuing to review design basis documents and calculations to determine if bypass flow was assumed past CH-202 when determining the minimum hot leg injection rate. As a compensatory measure, Operations management has restricted the use of hot and cold leg injection via the charging header until the design basis review confirms the adequacy of the current procedural guidance or the procedural guidance is revised. Pre-approved alternative methods will be utilized via the emergency operating procedures to perform simultaneous hot and cold leg injection if required. No LCO condition exists. The licensee notified the NRC Resident Inspector.
On January 8, 2008, (Event Number 43886) Fort Calhoun Station reported that there could be a potential reduction of injection flow to the hot leg during Long Term Core Cooling (LTCC) simultaneous hot and cold leg injection. The charging line thermal relief valve/check valve CH-202 could potentially divert flow from hot leg injection and reduce hot leg flow below the required flow rate needed to prevent boron precipitation from occurring. On January 8, 2008 it could not be determined through a review of design basis documents and associated calculations if bypass flow has been assumed through CH-202. Divergence of flow through CH-202 would result if a valve failure occurred. Assuming flow is diverted through CH-202, the operators would not realize that flow was going through the wrong flow path (cold leg) as their flow indication (FE-326) is located upstream of where the flow path to the hot leg and cold legs branch off. Therefore, there was nothing to alert the operator to isolate CH-202 or go to alternate hot leg injection. Previous procedural guidance was not adequate to address this condition. Current procedural guidance is adequate to address this condition as the procedures now require isolating CH-202 for LTCC. A reanalysis was performed to evaluate the required flow rate needed to prevent boron precipitation and ensure adequate LTCC. Calculations performed assumed full flow (failure) through CH-202. Under postulated design scenarios it was determined that adequate flow would have been provided to the hot legs during simultaneous hot and cold leg injection during LTCC. The calculations determined that under the evaluated scenarios, divergence of flow through CH-202 was acceptable, and that the requirements to maintain adequate flow to the core for LTCC decay heat removal and boron flushing would have been met. As a result of the analysis that were performed, it has been determined that the system was capable of performing its design function even under bypass flow conditions through CH-202. Therefore, this event is NOT reportable under 10 CFR 50.72( b) (3) (v) (B) as previously reported. The licensee notified the NRC Resident Inspector. Notified R4 DO (Miller) |
| ENS 43347 | 5 May 2007 15:00:00 | Nebraska Department of Environmental Quality notified of an oil spill while backwashing a screen in the intake structure. Approximately 2 gallons of oil was spilled . Most of the oil spill was contained and was wiped up using oil drip pads. There is no evidence that oil was released to the Missouri River. The NRC Resident Inspector was notified of this offsite notification by the licensee. |
| ENS 42805 | 26 August 2006 13:38:00 | Offsite Notifications have been made to Blair Rescue Squad due to an OPPD electrician suffering second and third degree burns to arms, face and torso while working on switchgear. The employee has been transported via life flight helicopter to Creighton University Hospital. The flash actuated the Switchgear Room Halon system. Operations verified that there was no fire in the Switchgear Rooms. Recovery efforts are under way. A media release is expected." A continuous fire watch has been established in the Switchgear Room as a compensatory measure. The licensee notified the NRC Resident Inspector. |