05000454/FIN-2016001-01
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Finding | |
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| Title | Failure to Enter Technical Specification Limiting Condition for Operation Action Requirement with Auxiliary Feedwater Flow Control Valves Failed Open |
| Description | The inspectors identified an Unresolved Item (URI) associated with the concern that the licensee failed to enter a TS LCO action requirement when all air was isolated to the actuators to the auxiliary feedwater flow control valves, failing them open and unable to be throttled or closed from the control room. Description: On January 3, 2016, the licensee generated Issue Report (IR) 2607148 which requested clarifying guidance from engineering for assessing operability of the 1/2AF005AH auxiliary feedwater flow control valves to the steam generators, when air is isolated from the valve actuators. The IR stated that when procedure BISR 3.4.2200, Surveillance Calibration of Aux Feedwater to Steam Generators A, B, C and D Flow Control Loops, was performed, all air was isolated from the auxiliary feedwater flow control valves to fail them open during the calibration. This was intended to maintain operability of the auxiliary feedwater system during the calibration. At each Byron unit, each of the two auxiliary feedwater pumps had a separate flow path to each of the steam generators, and each flow path had an air-operated flow control valve, a motor-operated containment isolation valve, and a check valve in the flow path. The flow control valves used instrument air as the motive force to throttle and close the valves. Upon a loss of air to the actuator, the flow control valves were designed to fully open via spring pressure, allowing auxiliary feedwater flow to the steam generators. In 2012, the licensee installed safety-related accumulators on each auxiliary feedwater train to supply air to the auxiliary feedwater flow control valve actuators upon a loss of instrument air. This air supply was designed so that if one of the steam generators experienced a steam generator tube rupture and the containment isolation valve in the flow path to that steam generator failed to close, the control room operators could close the flow control valve to limit or isolate auxiliary feedwater flow to the failed steam generator until an equipment operator could locally secure the flow control valve in its closed position. This modification was performed to support the licensees license amendment request for a measurement uncertainty recapture uprate so that operator actions could be credited to prevent the steam generator with a ruptured tube from overfilling and challenging the containment function. Upon completion of the modifications, the licensee updated Table 15.07, Plant Systems and Equipment Credited for Transients and Accident Conditions, in the Accident Analysis section of the licensees UFSAR to include the AF Accumulator Tanks as engineered safeguard feature (ESF) equipment credited for steam generator tube rupture incidents. The safety evaluation in Chapter 10 of the UFSAR was also updated for the Auxiliary Feedwater System to state that in the event of a steam generator tube rupture, operator action was required to isolate auxiliary feedwater flow to the ruptured steam generator within certain time requirements, and that in the event that the containment isolation valve failed to close, the flow path could still be isolated by closing the AF005 valves, with air accumulators sized to ensure sufficient time for local operator action to secure the AF005 valves in the closed position. In response to IR 2607148, the licensees regulatory assurance department documented that the safety function of TS LCO 3.7.5, Auxiliary Feedwater System, was intended to be limited to supply water to the steam generators for heat removal and that this should not be changed in favor of any UFSAR design analysis. The IR concluded that Operability per the TS was not applicable, and operations did not need to place the unit in any TS condition statement with the AF005 valves failed open with no instrument air supply during the associated instrument calibrations. From the time the licensee received the measurement uncertainty recapture license amendment on February 7, 2014, through March 22, 2016, the licensee had failed open all four AF005 valves in each train of auxiliary feedwater using BISR 3.4.2200 at least five times per train, and has not entered a TS LCO during most of these time periods. The regulations stated in 10 CFR 50.26(c)(2)(ii)(C) that a TS LCO of a nuclear reactor must be established for each SSC that is part of the primary success path and which functions or actuates to mitigate a design basis accident or transient that assumes the failure of/or presents a challenge to the integrity of a fission product barrier. The inspectors were concerned that when all air is isolated to the auxiliary feedwater flow control valve actuators, operators may not be able to throttle or isolate flow to a ruptured steam generator quickly enough to prevent overfill of the steam generator, assuming the motor-operated containment isolation valve fails to close, which could challenge the integrity of containment. As such, the inspectors were concerned that the licensee failed to enter a TS LCO action requirement when the air to the actuator was isolated. To determine whether a performance deficiency or violation exists, the inspectors need to determine if a TS LCO should have been established for the ability of the AF005 valves to close to mitigate a steam generator tube rupture event, and if the licensees modifications and license amendment requests properly addressed the establishment of an LCO for this function of the SSC. (URI 05000454/201600101, 05000455/201600101; Failure to Enter Technical Specification Limiting Condition for Operation Action Requirement with Auxiliary Feedwater Flow Control Valves Failed Open) |
| Site: | Byron  |
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| Report | IR 05000454/2016001 Section 1R15 |
| Date counted | Mar 31, 2016 (2016Q1) |
| Type: | URI: |
| cornerstone | Mitigating Systems |
| Identified by: | NRC identified |
| Inspection Procedure: | IP 71111.15 |
| Inspectors (proximate) | C Thompson E Duncan I Khan J Cassidy J Draper J Mcghee |
| INPO aspect | |
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Finding - Byron - IR 05000454/2016001 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Finding List (Byron) @ 2016Q1
Self-Identified List (Byron)
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