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| Start date | Reporting criterion | Title | Event description | System | LER | |
|---|---|---|---|---|---|---|
| ENS 48030 | 23 April 2012 00:58:00 | 10 CFR 50.73(a)(1), Submit an LER | Keowee Hydro Power Station Automatically Started Based on an Invalid Signal | At 1958 (EDT) on 4/22/2012, Oconee emergency power (Keowee Hydro Station Units 1 and 2) automatically started based upon an invalid signal. In progress at the time was the Unit 3 Keowee Emergency Start Channel B Isolations section of the Unit 3 Engineered Safety Features Actuation System Replacement Modification procedure. A step in this procedure provided direction for a jumper to be connected between links B-13 and B-14. However, this jumper was placed between links A-13 and A-14, which caused the start of the Keowee units. During the period the jumpers were inadvertently installed, the Keowee units remained operable and available to supply emergency power to Units 1, 2, and/or 3. Both Keowee units were shutdown from the inadvertent emergency start actuation and the emergency start signal was reset per procedure at 0156 (EDT) hours on 4/23/2012. The cause for the misplaced jumper was determined to be a human performance error by the technicians. As required per NUREG 1022, Rev.2 the following information is provided: (a) The specific train(s) and system(s) that were actuated: In this event, both Keowee Hydro Units 1 and 2 actuated because of the emergency start signal being generated by Channel A. (b) Whether each train actuation was complete or partial: The automatic actuation of the Keowee units was completed. (c) Whether or not the system started and functioned successfully: No problems or issues were identified with the performance of the Keowee Hydro Units in response to the emergency start. Therefore this condition is being reported for Oconee 1, 2, and 3 as an invalid actuation under 10 CFR 50.73 (a)(2)(iv)(A), which allows NRC notification via telephone per 10 CFR 50.73(a)(1). Corrective Actions: - Work was stopped on the Unit 3 Engineered Safety Features Actuation System Replacement Modification procedure; - Immediate investigation was conducted to determine the impact of the jumper activity as well as development of a recovery plan; and - The jumper was removed from links A-13 and A-14 and the Keowee units were shutdown. The NRC Resident Inspector was informed. | ||
| ENS 46544 | 18 November 2010 07:45:00 | 10 CFR 50.73(a)(1), Submit an LER | Invalid Actuation of Motor Driven Emergency Feedwater System | This report is being made per paragraphs 50.73(a)(1) and 50.73(a)(2)(iv)(A) to address an actuation of the Emergency Feedwater (EFW) System on Oconee Unit 3 on 11/18/10 while moving the 3A Motor Driven EFW Pump (MD EFWP) control switch from position 'Auto 1' to 'Auto 2.' EFW is a system named in 50.73(a)(2)(iv)(B). The 3A MD EFWP was inadvertently started during operation of the control switch in the Oconee Unit 3 Control Room. The start signal was a manual start when the operator moved the control switch beyond the intended position. The functioning/behavior of the MD EFWP control switch and human error are being investigated in the site corrective action program. This is considered an INVALID signal with respect to 50.73(a)(2)(iv)(A). The manual start only affected the 3A MD EFWP. On 11/18/10, a Unit 3 startup from a refueling outage was in progress. Unit 3 was in Mode 3. While performing a step in OP/3/A/1102/001 (Controlling Procedure for Unit Startup), the Operator inadvertently started 3A MD EFWP when positioning 3A MD EFWP control switch from position 'Auto 1' to 'Auto 2.' Specific Information Required per NUREG 1022: (a) The specific train(s) and system(s) that were actuated: The specific train(s) and system(s) that were actuated was the 3A MD EFWP and the A train of EFW. The 3B MD EFWP and the Turbine Driven EFW Pump were not affected by this event. (b) Whether each train actuation was complete or partial: The manual actuation was considered complete (i.e. all necessary components responded to the start signal to provide EFW to the Steam Generator (SG). The A train control valve (3FDW-315) was open, as expected for the evolutions in progress. This allowed EFW to reach the SG. C) Whether or not the system started and functioned successfully: The 3A MD EFWP and train started and operated successfully until secured by Operations personnel. Initial Safety Significance: None, there was no significant transient. Corrective Action(s): EFDW was secured within approximately one minute by placing 3A MD EFWP control switch in the Auto 2 position. This event has been entered into the site corrective action program for resolution. The licensee notified the NRC Resident Inspector. | Steam Generator Feedwater Emergency Feedwater System | |
| ENS 45180 | 19 May 2009 20:09:00 | 10 CFR 50.73(a)(1), Submit an LER | Invalid Feedwater System Actuation While Shutdown | On 5-19-09 ONS (Oconee Nuclear Station) Unit 3 was in Mode 3 during startup from a refueling outage. At 1609 EDT the 3A Motor Driven Emergency Feedwater Pump (MDEFWP) unexpectedly started when the control switch was placed in the AUTO2 position as part of system alignment prior to unit startup. Investigation found that the impulse line for the hydraulic oil pressure switch on the operating 3A Main Feedwater Pump was clogged, causing sensed pressure to read below setpoint. Repositioning the control switch enabled the 3A MDEFWP auto start circuitry, which immediately actuated due to the pre-existing false low pressure indication. Several other redundant indications validated that the pressure signal to the pressure switch was false and that actual hydraulic oil pressure remained above the pressure switch setpoint. Although the pressure switch did see low pressure in the impulse line, the actuation is considered invalid since the signal was based on a false reading that did not represent actual plant conditions. Therefore this report is being made under 10 CFR 50.73(a)(1) and 50.73 (a)(2)(iv)(A). Per NUREG-1022, Rev. 2 the following information is requested: A) The specific train(s) and system(s) that were actuated. 3A Motor Driven Emergency Feedwater Pump (MDEFWP) which feeds the 3A Steam Generator (SG). B) Whether each train actuation was complete or partial. The train actuation was considered complete. The pump started per the signal and operated as required/expected in response to the signal. This pump is the only component in the train which receives a specific signal as part of the actuation circuitry. C) Whether or not the system started and functioned successfully. The 3A MDEFWP started and the system functioned successfully. The EFW control valve (3FDW-315) is set to control at 30 inches (SG startup level) versus 25 inches for Main Feedwater control. Therefore the SG level increased and the train then controlled at approximately 30 inches while an investigation determined the reason for the actuation (as explained above). The 3A MDEFWP was stopped at 2050 EDT and returned to normal status. Initial Safety Significance: Due to low feedwater demand at the time, there was little impact on the unit. Since the SG level was maintained above the normal control system setpoint, Main Feedwater flow was automatically reduced to compensate for the EFW flow. The 3A MDEFWP and associated pressure switch/actuation circuit were declared inoperable during pump shutdown and restoration to normal. Corrective Action(s): After troubleshooting identified the clogged impulse line, it was isolated and cleared. The 3A MD EFWP and the associated pressure instruments were returned to service. The licensee notified the NRC Resident Inspector. | Steam Generator Feedwater | |
| ENS 43146 | 9 December 2006 02:43:00 | 10 CFR 50.73(a)(1), Submit an LER | Invalid Efw Actuations Due to an Issue in Sg Dryout Protection Circuit | This report is being made per paragraphs 50.73(a)(1) and 50.73(a)(2)(iv)(A) to address two actuations of the Emergency Feedwater (EFW) System on Oconee Unit 1 on 12/8/06 by the Steam Generator (SG) Dry-out Protection Circuit. EFW is a system named in 50.72(b)(3)(iv)(B). By design, the SG Dry-out Protection Circuit actuates whenever two Extended Start-up level indications (two of two actuation logic) in either SG are lower than the setpoint (i.e. below 21 inches) for more than 30 seconds. This start circuit is not credited in Oconee safety analyses as performing a required safety function, therefore this signal is considered an INVALID signal with respect to 50.73 (a)(2)(iv)(A). Upon actuation, the circuit starts both Motor Driven Emergency Feedwater Pumps (MD EFWPs) on the affected unit. It does not send a start signal to the Turbine Driven Emergency Feedwater Pump. Per the startup procedure, Condensate Booster Pumps (CBP) feed the SGs until a main Feedwater pump (FDWP) is placed in service. Operators begin startup of a FDWP when the Reactor Coolant System (RCS) temperature is between ~395 degrees to 475 degrees. The Unit is then maintained at ~ 475 degrees RCS temperature and 500 - 550 psig SG pressure until a FDWP is in service. On 12/8/06, a Unit 1 startup from a refueling outage was in progress. RCS temperature was approximately 475 deg. (Mode 3) when the RCS heat-up was suspended due to issues with the 1A FDWP Turbine which delayed placing it in service. Steam pressure was being maintained approximately 530 psig (in the procedural band of 500-550 psig) per the unit startup procedure. In addition, a 'SG Hot Soak' was in progress. For this evolution, SG level was raised to 75% (Operating Range) then Operators took manual control to individually blow down 1A and the 1B SGs to low levels (25 inches) while attempting to maintain level above 21 inches. During this evolution, 1B SG levels decreased below minimum level. Operators initiated actions to recover level but at 2143 the 1A and the 1B MD EFW Pumps auto-started on dry-out protection. From their observation of the level displays, the Operators thought that the actuation logic had not been met (i.e. level had not been less that 21 inches for 30 seconds). Therefore they considered the actuation to be spurious. Based on this understanding and concerns about possible overfeeding and RCS overcooling (due to the relatively low decay heat load starting up from a refueling outage), EFW was secured and reset at 2144. SG Blowdown activities continued per procedure. At 2207, in response to lowering 1A SG levels, the dry-out protection feature again initiated an auto start of the 1 A and 1 B MD EFW Pumps. Based on his review of SG levels, the CR SRO believed that the second EFW actuation was invalid and directed that EFW be secured. EFW was secured and reset at 2208. At 2241 hrs SG outlet pressure was lowered and maintained within a band of 490-520 psig. Subsequent review of computer data indicated that a dry-out condition (i.e. less than 21 inches SG level for 30 seconds) did exist for both actuations. Therefore both actuations were valid in that actual plant conditions satisfied the initiation criteria, but, as stated above, the SG Dry-out Protection signal is considered an INVALID signal with respect to 50.73 (a)(2)(iv)(A). Additional review by Mechanical-Civil Engineering personnel determined that the Unit 1 CBPs operate at approximately 15 psig lower discharge pressure than the Unit 2 and 3 CBPs, apparently due to lower discharge pressures on the Unit 1 Hotwell pumps. That being the case, the Unit 2 and 3 CBPs, apparently due to lower discharge pressures on the Unit 1 Hotwell pumps. That being the case, the Unit 1 CBPs in service could not develop sufficient head pressure to maintain adequate flow to the SGs over the full operating operating band of 500 - 550 psig allowed by current operating procedure guidance. As steam pressures approached or exceeded 535 psig, the ability to feed the SGs using the CBPs was reduced, ultimately leading to the dry-out condition. The issue of these pump discharge pressures being slightly lower than expected had not been recognized previous to this event. The event investigation noted that during past startups, a main FDWP was normally placed into service promptly, which may have avoided using the CBPs to feed the SG above 535 psig. In this case, alignment of a main FDWP was delayed, which led to the event. Specific Information Required per NUREG 1022: (a) The specific train(s) and system(s) that were actuated. The specific train(s) and system(s) that were actuated were the 1 A and 1 B Motor Driven (MD) Emergency Feedwater (EFW) Pumps and the associated A and B trains of EFW. The Turbine Driven EFW pump does not receive this signal and was not challenged by the event. (b) Whether each train actuation was complete or partial. Both actuations were considered complete (i.e. all necessary components responded to the start signal and associated control signals to provide EFW to the SG(s)). (c) Whether or not the system started and functioned successfully. In both cases, the system started and operated successfully until secured by Operations personnel. Initial Safety Significance: None, there was no significant transient. Corrective Action(s): As stated above, EFDW was secured and reset at 2208. At 2241 hrs SG outlet pressure was lowered and maintained within a band of 490-520 psig. Unit 1 continued startup and subsequently reached Mode 1. This event has been entered into the site corrective action program for resolution. The licensee notified the NRC Resident Inspector. | Steam Generator Reactor Coolant System Feedwater | |
| ENS 41649 | 29 April 2005 05:05:00 | 10 CFR 50.73(a)(1), Submit an LER | Emergency Hydro Generators Auto Start - Unknown Cause | |||
| ENS 40686 | 20 March 2004 19:59:00 | 10 CFR 50.73(a)(1), Submit an LER | Invalid Actuation of the Motor Driven Emergency Feedwater Pumps | By design, the Steam Generator (SG) Dry-out Protection Circuit actuates whenever two level indications (two of two actuation logic) in either SG are lower than the setpoint for more than 30 seconds. This start circuit is not credited in any ONS safety analysis, therefore this signal is considered an INVALID signal with respect to 50.73 (a)(2)(iv)(A). Upon actuation, the circuit starts both Motor Driven Emergency Feedwater Pumps (MDEFWPs) on the affected unit. It does not send a start signal to the Turbine Driven Emergency Feedwater Pump. Shortly after entering Mode 4, a control operator stopped one of two operating Reactor Coolant Pumps per the Unit shutdown procedure. A second control operator was manually controlling Feedwater and reduced flow to control the system cooldown rate, without recognizing that the 2B SG had reached the low level setpoint for SG Dry-out Protection Circuit actuation. In this event, the 2B SG level trains A and B indicated lower than the setpoint value (-21 inches) for more than 30 seconds, so the SG Dry-out Protection Circuit started the 2A and 2B MDEFWPs. The actuation was considered complete and the system started and functioned successfully. Both MDEFWPs started. The 2B SG control valve, 2FDW-316, opened and fed the 2B SG from the 2B MDEFWP for approximately one minute until the SG level reached the EFDW control setpoint (30 inches). The 2A pump did not feed the 2A SG because 2A SG level remained well above the EFDW control setpoint so there was no demand for the 2A SG control valve, 2FDW-315, to open. The licensee notified the NRC Resident Inspector.
This update is to clarify a typographic misspelling on the first sentence of the last paragraph of this event notification which should read (~(approximately) 21 inches) instead of (-21 inches). Notified R2DO(Julian). | Steam Generator Feedwater |