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10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation +, 10 CFR 50.72(b)(3)(iv)(A), System Actuation +, 10 CFR 50.72(b)(3)(xiii), Loss of Emergency Preparedness +, 10 CFR 50.72(b)(2)(iv)(A), System Actuation - ECCS Discharge +, 10 CFR 50.72#b2ivB +, 10 CFR 50.72#b3ivA +, 10 CFR 50.72#b3xiii + and 10 CFR 50.72#b2ivA +
At 0948 hours (EDT) on 6/8/10, a Unit 1 vi … At 0948 hours (EDT) on 6/8/10, a Unit 1 vital AC bus was lost when the uninterruptible power supply inverter failed while the alternate AC source was out of service for scheduled maintenance. The loss of the vital bus inverter caused a loss of 120 VAC vital bus 1-III. The loss of this vital bus caused the 'A' main feed pump recirculation valve to fail open and also caused 2 of the 3 main feedwater regulating valves to fail to automatic-hold mode of operation. This combination of as designed failures resulted in a reduction in main feedwater flow and resulted in an automatic reactor trip due to a feed flow steam flow mismatch in conjunction with low steam generator level.</br>The loss of vital bus 1-III also resulted in initiation of safety injection due to loss of vital bus 1-III instrumentation in conjunction with the expected momentary RCS cooldown below 543 DEG-F. The safety injection resulted from the high steam flow in conjunction with low RCS T-ave actuation signal. The safety injection actuation also resulted in automatic start of the #1 Emergency Diesel and the #3 Emergency Diesel Generators. Neither EDG was required to load since off-site power remained operable.</br>The loss of vital bus 1-III also resulted in loss of numerous field inputs to the Plant Computer System (PCS) and resulted in non-functionality of the SPDS (Safety Parameter Display System). The PCS itself remains functional along with MCR (Main Control Room) annunciators and sufficient MCR instrumentation to monitor critical safety functions. All three auxiliary feedwater pumps automatically initiated as designed on low-low steam generator level following the trip. Currently, RCS temperature is being maintained stable at 547 degrees. All systems functioned as required following the reactor trip. During the post-trip transient, pressurizer PORV (Power Operated Relief Valve), PCV-1455C, cycled as required to maintain RCS pressure due to the safety injection and the loss of normal letdown.</br>There were no radiation releases due to this event, nor were there any personnel injuries or contamination events. This event is being reported in accordance with 10CFR50.72(b)(2)(iv)(B), 10CFR50.72(b)(2)(iv)(A), 10CFR50.72(b)(3)(iv)(A), and 10CFR50.72(b)(3)(xiii).</br>The NRC Resident Inspector was notified of this event.</br>During the trip, all rods inserted into the core. In addition to the pressurizer PORV lifting, a secondary main steam relief valve lifted. All relief valves properly reseated and there is no known primary to secondary leakage. The plant is in its normal shutdown electrical lineup. Main steam trip valves were isolated during the transient. Decay heat is being removed via main steam bypasses to the condenser and steam generator power operated relief valves.am generator power operated relief valves.
13:48:00, 8 June 2010 +
45,986 +
12:00:00, 8 June 2010 +
13:48:00, 8 June 2010 +
At 0948 hours (EDT) on 6/8/10, a Unit 1 vi … At 0948 hours (EDT) on 6/8/10, a Unit 1 vital AC bus was lost when the uninterruptible power supply inverter failed while the alternate AC source was out of service for scheduled maintenance. The loss of the vital bus inverter caused a loss of 120 VAC vital bus 1-III. The loss of this vital bus caused the 'A' main feed pump recirculation valve to fail open and also caused 2 of the 3 main feedwater regulating valves to fail to automatic-hold mode of operation. This combination of as designed failures resulted in a reduction in main feedwater flow and resulted in an automatic reactor trip due to a feed flow steam flow mismatch in conjunction with low steam generator level.</br>The loss of vital bus 1-III also resulted in initiation of safety injection due to loss of vital bus 1-III instrumentation in conjunction with the expected momentary RCS cooldown below 543 DEG-F. The safety injection resulted from the high steam flow in conjunction with low RCS T-ave actuation signal. The safety injection actuation also resulted in automatic start of the #1 Emergency Diesel and the #3 Emergency Diesel Generators. Neither EDG was required to load since off-site power remained operable.</br>The loss of vital bus 1-III also resulted in loss of numerous field inputs to the Plant Computer System (PCS) and resulted in non-functionality of the SPDS (Safety Parameter Display System). The PCS itself remains functional along with MCR (Main Control Room) annunciators and sufficient MCR instrumentation to monitor critical safety functions. All three auxiliary feedwater pumps automatically initiated as designed on low-low steam generator level following the trip. Currently, RCS temperature is being maintained stable at 547 degrees. All systems functioned as required following the reactor trip. During the post-trip transient, pressurizer PORV (Power Operated Relief Valve), PCV-1455C, cycled as required to maintain RCS pressure due to the safety injection and the loss of normal letdown.</br>There were no radiation releases due to this event, nor were there any personnel injuries or contamination events. This event is being reported in accordance with 10CFR50.72(b)(2)(iv)(B), 10CFR50.72(b)(2)(iv)(A), 10CFR50.72(b)(3)(iv)(A), and 10CFR50.72(b)(3)(xiii).</br>The NRC Resident Inspector was notified of this event.</br>During the trip, all rods inserted into the core. In addition to the pressurizer PORV lifting, a secondary main steam relief valve lifted. All relief valves properly reseated and there is no known primary to secondary leakage. The plant is in its normal shutdown electrical lineup. Main steam trip valves were isolated during the transient. Decay heat is being removed via main steam bypasses to the condenser and steam generator power operated relief valves.am generator power operated relief valves.
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