05000461/LER-2014-002
| Clinton Power Station, Unit 1 | |
| Event date: | 03-25-2014 |
|---|---|
| Report date: | 05-22-2014 |
| 4612014002R00 - NRC Website | |
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PLANT AND SYSTEM IDENTIFICATION
General Electric -- Boiling Water Reactor, 3473 Megawatts Thermal Rated Core Power Energy Industry' Identification System (EIIS) codes, are identified in text as [XX].
EVENT IDENTIFICATION
Lowering Condenser Vacuum due to B Train Steam Jet Air Ejector Instability Results in Manual Reactor Scram A. Plant Operating Conditions Before the Event ' Event Time: 19:42 CDT
B. DESCRIPTION OF EVENT
On March 25, 2014, at 15:00, Clinton Power Station (CPS) was in Mode 1 (Power Operation) at 85 percent reactor [RCT] power and operators were proceeding with restoring the plant to full power following maintenance outage C1M15. ' The B train Steam Jet Air Ejector (SJAE) [EJR], Condenser Vacuum system [SH] was in service, and Operators in the Main Control Room (MCR) observed that Off gas (OG) system [WF] dilution steam flow was lower than desired (92% versus 104%). In response, the MCR performed a heightened level of awareness brief for increasing the dilution flow, which is controlled by air operated valve (AOV) [PDCV] 1621F435B via pressure controller [PDC] 1621N544. The system utilizes pressure control downstream of the AOV to set desired flow.
The as-found setting of the pressure controller was 98 pounds per square inch gage (psig) (the controller input range is 30 inches mercury (Hg) to 300 psig).
At 16:30, an initial adjustment was made to 99 psig with no changes noted.
At 16:45, a second adjustment was made to 100 psig with minimal change noted.
At 17:00, a third adjustment was made from 100 psig to 101 psig.
Following the third adjustment the pressure began oscillating between 70 and 110 psig. Operators restored the controller setpoint to the as-found setpoint of 98 psig at 17:20 and the oscillations reduced slightly (30 pounds per square inch swings) and remained constant. At this time Operators decided to leave the work site and monitor the dilution flow on an hourly basis.
At 18:42, as condenser vacuum lowered from 29 inches Hg to 27.4 inches Hg Operators entered the off-normal procedure for Loss of Vacuum.
- Unit: 1 Mode: 1 Event Date: 3/25/14 ' Mode Name: Power Operation Reactor Power: 46 percent Clinton Power Station, Unit 1 05000461 At 19:39, Operations initiated a rapid plant shutdown due to main condenser vacuum being 24 inches Hg and lowering. While reducing power, the MCR dispatched operators to begin preparations for plabing the A SJAE in service: The initiator of the vacuum reduction was unstable pressure control of the 'B' train SJAE.
At 19:42, with the plant at 46 percent reactor power, Operators initiated a manual reactor Scram by placing the reactor mode switch [HS] in the Shutdown position.
C. CAUSE OF EVENT
The cause of the event has been determined to be unstable pressure control of `B' SJAE. The most probable cause of unstable pressure control is a system resonance or instability in the 'B' SJAE system that has caused the station to be unsuccessful in tuning the 1B21N544 controller. The root cause of the system resonance is indeterminate at this time pending additional testing.
D. SAFETY CONSEQUENCES
This event had no actual nuclear safety consequences. Operators appropriately responded to lowering condenser vacuum by initiating a manual reactor Scram prior to the automatic Scram as directed by procedure. All control rods fully inserted in response to the manual reactor Scram and no Engineered Safety Feature (ESF) actuations occurred or were required. No safety/relief valve(s) lifted and all systems responded as expected in response to the Scram.
There was no unusual plant response and no complications resulting from the Scram.
The affected steam jet air ejector equipment is non-safety related. No loss of safety function occurred during this event.
E. CORRECTIVE ACTIONS
Corrective actions include replacement of the original controller with a new model featuring a manual mode of operation, and development of a comprehensive test plan that will isolate the instability region and create a final solution to dampen cif. eliminate the system resonance.
F. PREVIOUS OCCURRENCES
There have been previous issues at CPS related to the equipment problems (SJAE instability). The License Event Reports 1991-006 and 1993-007 from Clinton Power Station were associated with Steam Jet Air Ejector and Reactor Scrams.
Clinton Power Station, Unit 1 05000461
G. COMPONENT FAILURE DATA
Component Description: SJAE 1B Second Stage Main Steam Inlet Pressure Controller Manufacturer: Fisher Controls Model: 4160K