05000250/LER-2012-004
| Turkey Point Unit 3 | |
| Event date: | 9-6-2012 |
|---|---|
| Report date: | 11-5-2012 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 2502012004R00 - NRC Website | |
DESCRIPTION OF THE EVENT
On September 6, 2012 at approximately 1659 hours0.0192 days <br />0.461 hours <br />0.00274 weeks <br />6.312495e-4 months <br />, Turkey Point Unit 3 entered Mode 1. At approximately 2300 on September 6, 2012, the Outage Control Center initiated Action Request (AR) 1800833 and Work Request 94056749 identifying that indication associated with feedwater flow transmitter FT-3-476, Channel IV Steam Generator 3A Main Feedwater Flow, was reading lower than expected compared to other channels.
After further assessment, on September 7, 2012 at approximately 0540 the associated Reactor Protection System (RPS) channel [JB:FT] was declared inoperable, and the off-normal procedure and Action 6 for Technical Specification (TS) Limiting Condition for Operation (LCO) 3.3.1, Table 3.3-1, Functional Unit 12 were entered. Action 6 allows continued operation "...provided the inoperable channel is placed in the tripped condition within 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />." On September 7, 2012 at approximately 0837, the channel was placed in the tripped condition.
Subsequently on September 7, 2012, Maintenance personnel discovered that the high and low sides of the process tubing for feedwater flow transmitter FT-3-476 were reversed. The process tubing was repaired under WO 40181434. Feedwater flow transmitter FT-3-476 was returned to service, Action 6 of TS Table 3.3-1, Functional Unit 12 was exited, and the channel trip bistables were restored at approximately 1100 on September 7, 2012. AR 1800993 was initiated to document the reversed process tubing.
The process tubing for FT-3-476 was reversed during the recent refueling outage with work complete on May 19, 2012.
This report is submitted in accordance with 10 CFR 50.73(a)(2)(i)(B) as a condition which was prohibited by the plant's TS.
CAUSES OF THE EVENT
The Work Order Task Description (WOTD) specified "Skill-of-the-Craft", leading to a failure to use or ineffective use of human error prevention tools.
The post maintenance test (PMT) did not provide for a positive method of tubing orientation verification after replacement. The specified channel check was not effective without process flow.
ANALYSIS
System Description The function of the Feedwater System is to provide preheated, high pressure feedwater to the steam generators at a flow rate to match steam flow and a pressure sufficiently greater than steam generator pressure to make up for losses due to flow through the feedwater regulating valves, feedwater heaters, and associated piping.
As a part of the RPS there is a Steam Generator (SG) Low Level concurrent with SG Steam Flow/Feedwater Flow mismatch reactor trip. The SG Low Level Steam Flow/Feedwater Flow trip is provided to protect the reactor from steamline break protection.
There are two SG level channels and two SG feedwater/steam flow mismatch channels associated with each SG. The steam flow mismatch channels compare the feedwater flow with the steam flow from the SGs to determine if there is sufficient feedwater flow to maintain level for the measured steam flow. If one of the two SG level channels indicates a low level coincident with one of the two steam flow/feedwater flow mismatch channels, a reactor trip occurs.
Feedwater flow transmitter FT-3-476 provides the safety related input to the anticipatory reactor trip signal for steamline break protection logic for SG 3A. FT-3-476 is required to be operable in Modes 1 and 2 by TS LCO 3.3.1, Table 3.3-1, Functional Unit 12 for low SG level coincident with feedwater flow less than steam flow. With FT-3-476 inoperable in Modes 1 or 2, TS Table 3.3-1 Action 6 requires applicable bistables be tripped within 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />. FT-3-476 also provides a NRC Regulatory Guide 1.97 monitoring function in post accident circumstances.
Reportability With FT-3-476 inoperable in Modes 1 or 2, TS LCO 3.3.1, Table 3.3-1, Action 6 requires applicable bistables be tripped within six hours or the plant placed in Mode 3 within an additional seven hours as required by TS 3.0.3. Unit 3 was operated in Modes 1 and 2 in excess of the 13 hour1.50463e-4 days <br />0.00361 hours <br />2.149471e-5 weeks <br />4.9465e-6 months <br /> completion time allowed by TS (six hours to trip the bistables with seven additional hours to place the unit in Mode 3 if the bistables were not tripped) during certain periods of time between August 15, 2012 and September 7, 2012. Because the TS were not met during those periods, the condition is reportable in accordance with 10 CFR 50.73(a)(2)(i)(B).
ANALYSIS OF SAFETY SIGNIFICANCE
The 3A SG feedwater flow transmitter FT-3-476 provides input into the steam flow/feedwater flow mismatch coincident with 3A SG low level reactor trip signal. FT-3-476 utilizes a differential pressure type flow transmitter. With the high and low sides of the FT-3-476 process tubing reversed, the FT-3-476 indication was failed low and would have caused the reactor bistable to have failed to properly actuate (i.e., actuated early) when steam flow was increased above the steam/feed flow mismatch value coincident with low SG level. As a result, FT-3-476 could have performed its intended TS Table 3.3-1 function (i.e., early) of providing the reactor trip signal for the safety related anticipatory reactor trip for steamline break protection due to the inaccurate signal. However, the condition affected only a single RPS trip initiator, and redundant trips and diverse methods of reactor shutdown were not affected. Therefore, the safety significance is very low.
CORRECTIVE ACTIONS
Corrective actions are documented in AR 1800833 and include the following:
1. Include Operating Experience (OE) from this event, a previous Unit 4 occurrence in 2008, and other industry OE relating the missing/inadequate human error prevention tool usage that contributed or caused the events into the Instrumentation and Control technician continuing and apprentice training programs.
2. Minimize usage of "Skill-of-the-Craft" for completion of work in WOTDs for in-house and contract maintenance personnel. WOTDs will be revised to ensure the orientation of replaced instrumentation tubing via independent or continuous verification as appropriate.
3. A review of work package PMTs will be conducted to ensure the tubing is properly connected.
FAILED COMPONENTS IDENTIFIED: None feedwater flow transmitter FT-4-476 (the same transmitter that is the subject of this report but on Unit 4). An Apparent Cause Evaluation was conducted that determined human error prevention tools were not used to verify proper configuration on completion of tubing replacement. Corrective action consisted of coaching personnel involved with the activity on the use of human error prevention tools which was not effective in preventing recurrence.