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| Start date | Reporting criterion | Title | Event description | System | LER | |
|---|---|---|---|---|---|---|
| ENS 54147 | 9 May 2019 17:05:00 | 10 CFR 50.73(a)(1), Submit an LER | 60-Day Telephonic Notification of Invalid Engineered Safety Feature Actuation Signal | This 60-day telephone notification is being made in accordance with 10 CFR 50.73(a)(1) and 10 CFR 50.73(a)(2)(iv)(A) to provide information pertaining to an invalid Engineered Safety Feature actuation signal. On May 9, 2019, at Arkansas Nuclear One (ANO) Unit 1, while performing an Emergency Feedwater Initiation and Control (EFIC) Channel B monthly test, a test pushbutton was mispositioned, resulting in an inadvertent initiation of the Emergency Feedwater (EFW) System. In accordance with the Engineered Safeguards Actuation System (ESAS) Trip Test portion of the surveillance, the first technician placed EFIC Train B in the tripped condition. The second technician then went to the front of the control room to verify Remote Switch Matrix (RSM) indications. The first technician recalls thinking he was given the order to reset Train B EFW Bus 1 Trip. Therefore, the first technician performed the step using three-part communication, but there is uncertainty about what was said. Due to the amount of time the second technician spent in front of the control room, the first technician assumed Operations reset the RSM to complete the Train B reset. The second technician returned to the ESAS cabinet and directed the first technician to perform the reset of Train B EFW Bus 1 Trip. The first technician, expecting his next action to be the trip of Train B EFW Bus 2, placed Bus 2 in the tripped condition. This put both buses of Train B EFW in trip and caused the actuation of P-7A EFW Pump. This inadvertent actuation was caused by human error and was not a valid signal resulting from parameter inputs. The 1992 Statements of Consideration define an invalid signal to include human error. Therefore, this actuation is considered invalid. This event was entered into ANO's corrective action program for resolution. This event did not result in any adverse impact to the health and safety of the public. The plant responded as expected. In accordance with 10 CFR 50.73(a)(i) a telephone notification is being made in lieu of submitting a written Licensee Event Report. The licensee has notified the NRC Resident Inspector. | Feedwater Emergency Feedwater Initiation and Control | |
| ENS 53777 | 9 October 2018 05:00:00 | 10 CFR 50.73(a)(1), Submit an LER | 60-Day Optional Telephonic Notification of Invalid Specified System Actuation | This 60-day telephone notification is being made in accordance with 10 CFR 50.73(a)(1) and 10 CFR 50.73(a)(2)(iv)(A) to provide information pertaining to an invalid Engineered Safety Feature actuation signal. On October 9, 2018, Arkansas Nuclear One, Unit 2 was in refueling Mode 6, when a vital inverter failed while aligned from its alternate power source causing a loss of one of four vital instrument buses. The loss of the instrument bus resulted in one of the four engineered safety feature protection channels to enter a tripped state. Because one of the other four channels was already in a tripped state in support of a channel power supply replacement activity, two out of four protection channels were now in the tripped state resulting in a Safety Injection Actuation Signal, Containment Spray Actuation Signal, Containment Cooling Actuation Signal, Recirculation Actuation Signal, Emergency Feed Actuation Signal, and Containment Isolation Actuation Signal. In general, only one train of equipment is protected and assumed to be available during Mode 6 operations. Due to the defense-in-depth plant configuration in Mode 6, which is intended to avoid inadvertent start of emergency systems, the resulting actuations caused no adverse impact to Shutdown Cooling or Spent Fuel Pool cooling operations. At least one train of the following systems was aligned for automatic actuation: Service Water Emergency Diesel Generator Containment Penetration Room Exhaust Fan Other non-essential components which are shed or realigned upon safeguards actuation The few systems and components that were aligned for automatic operation responded as designed, including containment isolation valves and valves associated with the above systems (if aligned for automatic operation). The Service Water system was already in operation and, therefore, no Service Water pumps actuated. All systems and components which were capable of automatic operation performed as designed. The Emergency Diesel Generator started but did not synchronize to the bus. No safety injection occurred to the core. This actuation was caused by equipment failure and was not an actual signal resulting from parameter inputs. The affected actuation signals do not perform a safety function in Mode 6 and are not required to be available or operable. Therefore, this actuation is considered invalid. This event was entered into ANO's corrective action program for resolution. This event did not result in any adverse impact to the health and safety of the public. In accordance with 10 CFR 50.73(a)(i) a telephone notification is being made in lieu of submitting a written Licensee Event Report. The licensee has notified the NRC Resident Inspector. | Service water Emergency Diesel Generator Shutdown Cooling Containment Spray | |
| ENS 42237 | 31 December 2005 20:12:00 | 10 CFR 50.73(a)(1), Submit an LER | Automatic Actuation of the Emergency Feedwater (Efw) Due to a Transient on the "B" Main Feedwater (Mfw) Pump | The EFW actuation occurred when the 'B' MFW pump RPM rose then dropped to ~4000 rpm. The MFW pump then recovered immediately. This transient caused EFIC (Emergency Feedwater Initiation Control) to actuate and both EFW pumps received start signals on invalid low SG level from the EFIC low range level instruments. These instruments measure level based upon a dp (differential pressure) across an orifice and are not considered reliable at 95% power and full MFW flow. All other SG level instruments indicate SG level was above EFIC setpoint during the MFW pump transient. This can be concluded by reviewing the OTSG (Once Through Steam Generator) level prior to and during the transient. Prior to the transient the EFIC low range level instruments indicated a level of ~24 inches. During the transient the EFIC low range level instruments indicated as low as 4 inches. However, the Startup Range level only lowered from ~122 inches prior to the transient to ~120 inches. Both EFW pumps were immediately overridden and stopped once it was verified this was not an actual under feed condition to the OTSGs. No EFW injection into the OTSGs occurred due to the EFW actuation. There was no ongoing maintenance at the time which would have explained the "B" MFW pump transient. The licensee informed the NRC Resident Inspector.
On 12/31/05, an 8-hour notification (EN# 42237) was made by Arkansas Nuclear One reporting an automatic actuation of Emergency Feedwater (EFW). The report was submitted pursuant to the requirements of 10 CFR 50.72 (b)(3)(iv)(A) Valid System Actuation. The actuation of EFW occurred as a result of a "B" Main Feedwater (MFW) pump transient which caused an invalid low Steam Generator (SG) level signal from the Emergency Feedwater Initiation and Control (EFIC) instrumentation. As discussed in the original event report, the low SG level EFIC instruments do not provide valid indication at 95% power and full MFW flow. As a result of the elevated flow rate during this perturbation, an invalid indication below the low SG level setpoint was produced resulting in the system actuation. All other SG level instrumentation indicated that actual SG levels remained within the normal operating band, confirming that no low level condition existed and that this event represented an invalid actuation. Accordingly, this update revises Event Notification 42237 to be submitted pursuant to 10 CFR 50.73 (a)(2)(iv)(A) and the 60-day Optional 10 CFR 50.73 (a)(1) requirement - Invalid Actuation of EFW. EFID and EFW systems functioned as designed in response to the invalid low SG level signal. The original event report stated that there was no EFW injection into the steam generators as a result of the actuation; however, subsequent reviews of historical Safety Parameter Display System (SPDS) data indicated that the electric EFW pump (P-7B) fed the steam generators for approximately 5 seconds during the event. The licensee notified the NRC Resident Inspector. R4DO (Shannon) notified. | Steam Generator Feedwater Safety Parameter Display System Emergency Feedwater Initiation and Control |