05000416/LER-2016-005
| 08-22-2016 | On June 25, 2016, at 1407 Central Daylight Time, Grand Gulf Nuclear Station was operating in Mode 1 at approximately 98.75 percent rated thermal power, performing final power ascension to 100% power with Reactor Recirculation Flow Control Valves, when an unplanned automatic reactor SCRAM occurred. All safety systems responded per design. Two Safety Relief Valves opened at the onset of the event to control reactor pressure and reseated properly. All control rods inserted when the signals generated by the Reactor Protection System were received. There were no Emergency Core Cooling System actuations. The shift immediately entered the appropriate Off Normal Event Procedures. The plant was stabilized with pressure control on the main turbine bypass valves and level control on the start-up level control valve. The cause of the event is under investigation by a root cause evaluation team and will be provided in a supplemental report. There were no actual nuclear safety consequences or radiological consequences during the event.
APPROVED BY OMB: NO. 3150-0104 EXPIRES: 10/31/2018 Reported lessons learned are incorporated into the licensing process and fed back to industry. Send comments regarding burden estimate to the FOIA, Privacy and Information Collections Branch (T-5 F53), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by internet e-mail to Infocollects.Resource@nrc.gov, and to the Desk Officer, Office of Information and Regulatory Affairs, NEOB-10202, (3150-0104), Office of Management and Budget, Washington, DC 20503. If a means used to impose an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection. 366A U.S. NUCLEAR REGULATORY COMMISSION ContentsCONTINUATION SHEET2. DOCKET 3. LER NUMBER 05000 416 A. PLANT OPERATING CONDITIONS BEFORE THE EVENTAt the time of the event, Grand Gulf Nuclear Station (GGNS) Unit 1 was in Mode 1 and ascending in power at approximately 99 percent (%) rated thermal power (RTP). All systems, structures and components (SSCs) that were necessary to mitigate, reduce the consequences of, or limit the safety implications of the event were available. No inoperable SSCs at the start of the event contributed to the event. B. DESCRIPTION OF OCCURRENCEOn June 25, 2016, at 14:07 hours, during power ascension while at approximately 99% RTP, Turbine Control Valve (TCV) 'B' initiated a Fast Closure followed by TCV 'D' Fast Closure followed by TCV 'C' Fast Closure resulting in actuation of Reactor Protection System (RPS) Divisions 'A' and 'B' causing an automatic full SCRAM signal. All Control Rods fully inserted as required. Reactor power lowered resulting in Generator Power Differential causing a Main Generator Trip. Reactor Pressure High signal was received and actuated Safety Relief Valves (SRVs) 1621F051D and 1B21F051B. Both SRVs opened once and re-closed approximately 27 seconds later. No other SRVs actuated and Low-Low Set functioned properly. Control room personnel entered the appropriate Off Normal Event and Emergency Procedures. The Feedwater Level Control System responded as designed. Reactor level initially lowered below the Level 3 scram setpoint as a result of void collapse and then rapidly rose as feedwater injected. Level stabilized without reaching the Level 8 feedwater trip setpoint. Reactor water level was transferred to startup level control mode. RPS was reset with reactor water level stable on Startup Level Control and reactor pressure stable on Pressure Reference. No Emergency Core Cooling System (ECCS) initiations and no unexpected group isolations occurred as a result of the transient. C. REPORTABLE OCCURRENCEThis Licensee Event Report (LER) is being submitted pursuant to Title 10 Code of Federal Regulations (10 CFR) 50.73(a)(2)(iv)(A) for an automatic actuation of the reactor protection system (RPS). Telephonic notification was made to the U.S. Nuclear Regulatory Commission (NRC) Emergency Notification System on June 25, 2016, within 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> of the event pursuant to 10 CFR 50.72(b)(2)(iv)(B) and 10 CFR 50.72 (b)(3)(iv)(A) for a valid RPS actuation while the reactor was critical. APPROVED BY OMB: NO. 3150-0104 EXPIRES: 10/31/2018 Reported lessons learned are incorporated into the licensing process and fed back to industry. Send comments regarding burden estimate to the FOIA, Privacy and Information Collections Branch (T-5 F53), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by Internet e-mail to Infocollects.Resource©nrc.gov, and to the Desk Officer, Office of Information and Regulatory Affairs, NEOB-10202, (3150-0104), Office of Management and Budget, Washington, DC 20503. If a means used to impose an information collection does not display a currently valid OMB control number, the NRC may collection. NRC FORM366A U.S. NUCLEAR REGULATORY COMMISSION CONTINUATION SHEET2. DOCKET 3. LER NUMBER 05000 416 D. CAUSEInvestigation of the root cause is ongoing. A supplemental report to this LER will be provided upon completion of the root cause investigation. E. CORRECTIVE ACTIONSImmediate: Tested and replaced the two suspect Main Turbine Control Valve circuit cards Pending Action: An RCE team is currently working to identify additional corrective actions. This LER will be supplemented when the corrective action(s) to preclude recurrence is/are determined. F. SAFETY ASSESSMENTThere were no actual nuclear safety consequences or radiological consequences during the event as all systems operated as designed and there was no release of radioactivity. G. PREVIOUS SIMILAR EVENTSPrevious events or conditions that involved the same underlying concern or reason as this event (i.e. same root cause, failure, or sequence of events) will be documented in the supplemental report when the RCE is finalized. |
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| Grand Gulf Nuclear Station, Unit 1 | |
| Event date: | 06-25-2016 |
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| Report date: | 08-22-2016 |
| 4162016005R00 - NRC Website | |
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