|Entered date||Site||Region||Scram||Reactor type||Event description|
|ENS 42983||10 November 2006 17:33:00||Kewaunee||NRC Region 3||Automatic Scram||Westinghouse PWR 2-Loop||On 11/10/2006 with a shutdown in progress to repair a degraded bearing on the turbine generator, an automatic reactor trip occurred due to a power range nuclear instrumentation (NI) low range - high flux trip. Reactor power had just been lowered to below 10% power (P-10) where the power range (NI) low range trips become active. The bistable for power range NI N-42 had been tripped due to an unrelated failure on 11/09/2006. When P-10 automatically unblocked, a power range NI low range high flux reactor trip was generated. At the time of the trip, reactor power was well below the trip setpoint of 24.5% power. Following the trip, Main Feedwater Regulating Valve, FW-7A, did not automatically close as required on the reactor trip coincident with Low Tave (554F). The Reactor Operator reported FW-7A was mid-position and attempted to manually close FW-7A. It did not respond. As a result, levels in steam generator A rose to greater than 67%, which initiated feedwater isolation. The feedwater isolation signal tripped the running feedwater pump. With no feedwater pumps running, both Auxiliary Feedwater Pump A and Auxiliary Feedwater Pump B automatically started as required. The High-High steam generator level also resulted in a second reactor trip initiation signal. The Reactor Operator manually controlled Auxiliary Feedwater flow to steam generator A to restore normal level. Following the feedwater isolation, FW-7A fully closed. Following the trip, MS-201B1, the steam supply to main steam reheater B1 was locally isolated to limit the RCS cool down. This was a previously discussed contingency action. Main steam isolation valves remained open and normal condenser heat sink remained available. Further investigation as to the cause of the trip is in progress. Recovery actions per normal operating procedures are in progress. The plant was being shut down at a rate of a half percent power per minute at the time of the trip. All control rods fully inserted on the reactor trip and no safety or relief valves lifted. The plant was aligned for the normal shutdown electrical lineup prior to the trip. The temperature on the generator bearing reached a maximum of 190F with trip guidance set at 225F. The licensee notified the NRC Resident Inspector.|
|ENS 42947||30 October 2006 11:56:00||Kewaunee||NRC Region 3||Automatic Scram||Westinghouse PWR 2-Loop|
During power operation, at 92% rated power, an automatic reactor trip occurred. The reactor protection signal that caused the reactor trip was steam generator 'B' steam flow greater than feedwater flow coincident with low water level on steam generator 'B.' The cause of the plant transient that led to the reactor trip was a loss of Instrument Bus 1 (Red Channel). Instrument Bus 1 unexpectedly deenergized during the performance of maintenance on the inverter (BRA-111) that feeds Instrument Bus 1. Following the reactor trip, the auxiliary feedwater pumps automatically started, as designed, due to a low level in the steam generators. After the trip, non-safety related 4160 Volt AC Bus 4 de-energized and secondary plant feedwater heater 15B relief valve lifted. The cause of the loss of Bus 4 and 158 feedwater heater relief lifting Is under Investigation. The plant is currently stable and in the hot shutdown (HSD) mode. Power was restored to Instrument Bus 1 at 1018. This event is reportable under 10 CFR 50.72(b)(2)(iv)(B) as any event or condition that results in actuation of the Reactor Protection System (RPS) when the reactor is critical because of the automatic reactor trip and under 10 CFR 50.72(b)(3)(iv)(A), any event or condition that results in valid actuation of any of the systems listed below because of the actions of the RPS and the automatic start of the AFW pumps. All control rods fully inserted. Decay heat is being removed by feeding the steam generators with AFW and steaming to the Condenser Dump. The licensee notified the NRC Resident Inspector.
Due to the loss of Bus 4, the running Circulating Water Pump was lost resulting in a loss of normal heat sink to the condenser. The standby Circulating Water Pump was started at 1002 CST and the condenser heat sink was restored. Until the condenser steam dump was restored, the plant was steaming through the steam generator PORVs (atmospheric steam dumps). There is no steam generator tube leakage. The licensee notified the NRC Resident Inspector. Notified R3DO (M. Phillips)
|ENS 42530||26 April 2006 22:39:00||Kewaunee||NRC Region 3||Manual Scram||Westinghouse PWR 2-Loop|
At 2043 (CDT) on 4-26-06, during a plant shutdown with the reactor at approximately 35% power, the operating crew manually initiated a reactor trip. The operating crew had just stopped one of the two condensate pumps and then the remaining feedwater pump tripped unexpectedly. The operating crew recognized the turbine did not trip, as it is expected to automatically trip when no feedwater pumps are running. The automatic turbine trip would have automatically tripped the reactor. Therefore, the operating crew manually initiated a reactor trip. Because the reactor did not automatically trip (i.e., failure of RPS to initiate and complete a reactor trip), the Shift Manager declared an Alert, at 2049, based on Chart F of Table 2-1 EPIP-AD-02. Therefore, this is a one-hour notification in accordance with 10CFR50.72(a)(1)(i) 'The declaration of any of the emergency classes specified in the licensee's approved Emergency Plan.' The manual reactor trip is reportable (4-hour) in accordance with 10CFR50.72(b)(2)(iv)(B) 'Any event or condition that results in an actuation of the Reactor Protection System (RPS) when the reactor is critical except when the actuation results from and is part of a pre-planned sequence during testing or reactor operation.' All systems functioned as expected following the manual reactor trip. Service Water Train B is inoperable because of a one-gallon per minute leak. All rods inserted fully. Decay heat is being removed with the steam dump and secondary PORVs. The condenser is losing vacuum due to the turbine trip. Auxiliary Feedwater Pumps started as required. The licensee notified the NRC Resident Inspector.
At 2049 on April 26, 2006, Kewaunee Power Station staff declared an Alert emergency classification (reference EN# 42530). The Kewaunee Power Station staff has assessed this event. There was no affect on the health and safety of the general public and no release of radiation. No plant personnel were injured and the only plant equipment problem was with the failure of a trip of both feedwater pumps to cause the main turbine to trip. The Kewaunee Power Plant staff has conducted a preliminary investigation of the control room indications and sequential events recorder, which indicates that before the manual reactor trip there was no automatic reactor trip signal present and a failure of the reactor trip breakers did not occur. The Alert was terminated at 0024 CDT (on 04/27/06). The unit is currently in the Hot Shutdown Mode with plans to cool the plant to less than 350 degrees Fahrenheit. The licensee notified the NRC Resident Inspector and will be notifying State and local government and issuing a press release. Notified NRR EO (MJ Ross-Lee), IRD Mgr (P. Wilson), R3DO (H. Peterson), DHS (Holz ), FEMA (Steindurf), NRC/EPA (Crews), DOE (Wyatt), USDA (Timmons), HHS (Peagler).
When performing a review of the event reported on April 26, 2006 (EN# 42530), the Kewaunee Power Station staff determined another reporting criterion was met. An eight-hour report is required to be made per 10 CFR 50.72(b)(3)(iv)(A), 'Any event or condition that results in valid actuation of any of the systems listed in paragraph (b)(3)(iv)(B) of 10 CFR 50.72 except when the actuation results from and is apart of a pre-planned sequence during testing or reactor operation.' 10 CFR 50.72(b)(3)(iv)(B)(6) is PWR auxiliary or emergency feedwater system. As described in EN# 42530, a manual reactor trip of the Kewaunee Power Station was initiated at 2043 on April 26, 2006. The manual reactor trip was initiated when the plant experienced a loss of both feedwater pumps. With a loss of both feedwater pumps and a manual reactor trip, the narrow range water level in both steam generators decreased to the actuation setpoint value for starting the Auxiliary Feedwater Pumps, causing all three Auxiliary Feedwater Pumps to start as designed. Because the steam generator water level was below the actuation setpoint, this was a valid actuation of the auxiliary feedwater system. As a valid actuation of the auxiliary feedwater system, this condition is reportable under 10 CFR 50.72(b)(3)(iv). The untimeliness of the report has been entered into the Kewaunee Power Station's corrective action program. The licensee notified the NRC Resident Inspector. Notified R3DO (H. Peterson).
|ENS 42173||29 November 2005 01:24:00||Kewaunee||NRC Region 3||Automatic Scram||Westinghouse PWR 2-Loop||At 22:19 CST, Main Feedwater Pump B tripped on over current. A secondary plant runback from 100% power was automatically initiated. During the secondary plant runback, the reactor automatically tripped on Steam Generator B low-low level at 22:20 CST. All three Auxiliary Feedwater pumps automatically started due to low-low Steam Generator level. The plant has been stabilized at Hot Shutdown (RCS temperature approximately 547 degrees F, RCS pressure approximately 2235 psig). Investigation into the cause of the trip is on-going. This event is being reported under 10CFR50.72(b)(2)(iv)(B) for actuation of the reactor protection system (RPS) when the reactor is critical and 10CFR50.72(b)(3)(iv)(A) for valid actuation of the Auxiliary Feedwater System. All control rods fully inserted on the automatic trip. Steam generator water levels have recovered to indicate in the narrow range. The current decay heat removal path is auxiliary feedwater to the steam generators steaming through the power operated relief valves. There are no known primary to secondary leaks. All safety related buses are powered from offsite power. Emergency diesel generators are available and in standby. The licensee notified the NRC Resident Inspector.|