Semantic search
| Entered date | Event description | |
|---|---|---|
| ENS 53090 | 25 November 2017 06:02:00 | At 0238 (CST) a manual reactor scram was inserted by placing the Reactor Mode Switch in Shutdown. At 0149 (CST), with reactor power just above the point of adding heat, IRM (Intermediate Range Monitor) channels A, C, and D received a spurious upscale trip signal which immediately cleared. Upon investigation, operability of RPS (Reactor Protection System) scram function for Intermediate Range Detectors was placed in question. This event is being reported 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. The licensee notified the NRC Resident Inspector.
At 0238 (CST) a manual reactor scram was inserted by placing the Reactor Mode Switch in Shutdown. At 0149 (CST), with reactor power just above the point of adding heat, Intermediate Range Monitor neutron flux detector (IRM) channels A, C, and D received a spurious Upscale Trip signal which immediately cleared. Upon investigation, IRM channels A, C, and D were declared Inoperable. IRM G was already Inoperable for another reason. RPS scram function from IRM channels B, E, F, and H was always Operable and available. That event is being reported under 10CFR 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. This Revised Statement to Event Notification # 53090 is being made to make it clear that only four IRM channels (A, C, D, G) were Inoperable and that the IRM RPS SCRAM function was still available from the four remaining Operable IRM channels (B, E, F, and H). The licensee notified the NRC Resident Inspector. Notified R4DO (O'Keefe)
On 11/25/17, at 0149 (CST), with reactor power just above the point of adding heat, Intermediate Range Monitor neutron flux detector (IRM) channels A, C, and D received a spurious Upscale Trip signal which immediately cleared. Upon investigation, IRM channels A, C, and D were declared Inoperable. IRM G was already Inoperable for another reason. At 0238 (CST) a manual reactor scram was inserted by placing the Reactor Mode Switch in Shutdown. RPS scram function from IRM channels B, E, F, and H was always Operable and available. That event was initially being reported 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. After the trip alarms were received, the Operators spent approximately twenty minutes investigating possible causes and implications, and consulted with Reactor Engineering and the Shift Technical Advisor. The investigation showed that the plant was stable and the upscale IRM alarms were spurious. A review of plant technical specifications by the operators determined that a plant shutdown was not required. After further discussions, Operations concluded that a shutdown to allow further investigation of the issue was the prudent course of action. Prior to shutting down, Operations spent approximately twenty minutes reviewing procedures, notifying personnel to exit containment, and conducting a brief. The shutdown was then conducted by inserting a manual reactor scram by placing the reactor mode switch in SHUTDOWN. This was initially reported under 10 CFR 50.72(b)(2)(iv)(B) as an actuation of the RPS. Based on the sequence of events, and Operator actions in conducting the shutdown, the event is considered 'part of a pre-planned sequence during testing or reactor operation' as specified in 10 CFR 50.72(b)(2)(iv)(B) and 10 CFR 50.73(a)(2)(iv)(A). In accordance with NUREG-1022, Section 3.2.6, the event is not reportable as an actuation of RPS. The licensee notified the NRC Resident Inspector. Notified R4DO (Taylor). |
| ENS 52843 | 10 July 2017 05:42:00 | At 2158 (CDT) a door to the Control Room Envelope was left unsecure. GGNS (Grand Gulf Nuclear Station) identified that a loss of Safety Function occurred due to a breach in the Control Room Envelope resulting in inoperability of both divisions of Standby Fresh Air and therefore could have prevented fulfillment of its safety function. The Control Room Envelope was inoperable for one minute. This event is being reported under 10CFR 50.72(b)(3)(v)(D), as any event or condition that, at the time of discovery, could have prevented the fulfillment of the safety function of structures or systems that are needed to mitigate the consequences of an accident. The licensee notified the NRC Resident Inspector. |
| ENS 52663 | 4 April 2017 06:57:00 | At 0010 (CDT), 04/04/2017, the reactor was manually scrammed from approximately 75 (percent) core thermal power due Condensate Storage tank level lowering to 24 feet. All control rods fully inserted and all systems actuated and operated as designed. No safety relief valves actuated. Reactor level and pressure are currently being controlled within normal bands. RCIC (reactor core isolation cooling) was manually initiated for level control. This event is reportable under 10CFR50.72(b)(2)(iv)(B) for the reactor trip and 50.72(b)(3)(iv)(A) for the manual start of the reactor core isolation cooling system. The cause of lowering level was a condensate pipe leak. Decay heat is being removed via steam dumps to the condenser. The electrical grid is stable and supplying plant loads. The licensee has notified the NRC Resident Inspector. |
| ENS 51459 | 7 October 2015 22:47:00 | At 1930 (CDT) on 10-7-2015, GGNS (Grand Gulf Nuclear Station) identified that on October 1, 2015, Secondary Containment was inoperable between 0324 and 0440 and therefore could have prevented fulfillment of its safety function. That event is being reported under 10 CFR 50.72(b)(3)(v)(c), as any event or condition that, at the time of discovery, could have prevented the fulfillment of the safety function of structures or systems that are needed to control the release of radioactive material. During the Standby Gas Treatment drawdown surveillance performed October 1, 2015, Secondary Containment failed technical specification required average enclosure building pressure of less than or equal to -0.311 water gauge at 0324 (CDT) (LCO-1-TS-15-0360 entered). Secondary Containment has two boundaries that can be separately credited for meeting the Tech Spec requirements of TS 3.6.4.1. Two inner doors are required to be open during the surveillance in order to test the outer door. While open, those inner doors were attended by Security personnel provided with communications capability. Following completion of the surveillance, Secondary Containment was returned to operable status at 0440 on 10/1/15 by closing the inner doors and maintaining them closed. A subsequent Standby Gas Treatment drawdown surveillance test on October 6, 2015, was performed satisfactorily. The NRC Resident Inspector was notified. |
| ENS 50795 | 7 February 2015 21:47:00 | A reactor SCRAM occurred at 1856 CST on 2/7/15 from 100 percent core thermal power. The cause of the SCRAM appears to be a Generator/Turbine trip, but it is still under investigation. Appropriate off-normal event procedures were entered to mitigate the transient with all systems responding as designed. No loss of offsite or ESF power occurred. No ECCS initiation signals were reached, and no ECCS or Emergency Diesel Generator initiations occurred. Main Steam Isolation Valves remained open and Safety Relief Valves lifted and reseated as designed. Currently, reactor water level is being maintained by the Condensate and Feedwater system in normal band, and reactor pressure is being controlled via turbine bypass valves to the main condenser. Following the reactor SCRAM, all rods fully inserted and all systems functioned as expected. The plant is in a normal electrical lineup. The licensee has notified the NRC Resident Inspector. |