05000259/LER-2007-006
| Browns Ferry Unit 1 | |
| Event date: | 08-07-2007 |
|---|---|
| Report date: | 10-09-2007 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 2592007006R00 - NRC Website | |
I. PLANT CONDITION(S)
Prior to the event, Unit 1 was operating in Mode 1 at approximately 100 percent of rated thermal power (approximately 3458 megawatts thermal). Units 2 and 3 were operating in Mode 1 at 100 percent rated thermal power (approximately 3458 megawatts thermal) and were not affected by the event.
II. DESCRIPTION OF EVENT
A. Event:
On August 7, 2007, at approximately 1100 hours0.0127 days <br />0.306 hours <br />0.00182 weeks <br />4.1855e-4 months <br /> central daylight time (CDT) TVA determined that BFN Unit 1 was operating in a condition prohibited by the plants' Technical Specifications (TS) when the Reactor Core Isolation Cooling (RCIC) [BN] steam high flow primary containment isolation instrument (1-PDT-071-001B) was found inoperable.
Previously, on August 6, 2007, at 1315 hours0.0152 days <br />0.365 hours <br />0.00217 weeks <br />5.003575e-4 months <br /> CDT maintenance personnel installed a temporary gauge parallel with the RCIC inlet steam flow transmitter (1-FT-071-001B) to measure steam flow during the scheduled performance of the surveillance, RCIC System Rated Flow at Normal Operating Pressure (1-SR-3.5.3.3.(COMP)). During a previous performance of 1-SR-3.5.3.3(COMP) in May of 2007, operations noted that 1-FI-071-001B was down scale. The installation of the temporary gauge was part of the trouble shooting activities from the previous performance of 1-SR-3.5.3.3(COMP). Flow indicator 1-FI-071-001B is not a TS instrument and is not needed to successfully complete the surveillance. Either 1-FI-071-001A or 1-FI-071-001B is acceptable. On August 7, 2007, during the trouble shooting activities for 1-FI-071-001B, maintenance personnel noted that 1-PDIS-071-001B was also down scale. It was subsequently determined that the RCIC steam line flow high transmitter (1-PDT-071-001B) was inoperable.
On August 7, 2007, at approximately 1100 hours0.0127 days <br />0.306 hours <br />0.00182 weeks <br />4.1855e-4 months <br /> CDT, Unit 1 entered TS Limiting Condition for Operation (LCO) for inoperable primary containment isolation instrument under TS 3.3.6.1, Action A.1. TS 3.3.6.1 states: The primary containment isolation instrumentation for each Function in Table 3.3.6.1-1, Primary Containment Isolation Instrumentation, shall be operable when the reactor is in Modes 1, 2, or 3. TS 3.3.6.1. Action A.1, also requires, with one or more channels inoperable: Place the channel in trip within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />. The TS further requires that if the associated completion time for Action A.1 cannot be met, under action F4, within 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br />, isolate the affected penetration flow path(s). On August 8, 2007, at 0935 hours0.0108 days <br />0.26 hours <br />0.00155 weeks <br />3.557675e-4 months <br /> the RCIC steam line was isolated per the TSs.
On August 12, 2007, at 1435 hours0.0166 days <br />0.399 hours <br />0.00237 weeks <br />5.460175e-4 months <br /> CDT, following satisfactory completion of maintenance activities on 1-PDT-071-001B, the RCIC steam high flow primary containment isolation function was declared operable.
Unit 1 commenced start-up activities in late May 2007, following an extended outage. There is firm evidence this condition existed prior to startup and was not identified until August 7, 2007; therefore, the completion time for the LCO action was not met and WA exceeded the LCO action time limit. TVA is submitting this report according to 10 CFR 50.73(a)(2)(i)(B), as any operation or condition prohibited by the plant's Technical Specifications.
B. Inoperable Structures, Components, or Systems that Contributed to the Event:
None.
C. Dates and Approximate Times of Major Occurrences:
May 2007 � TVA commences Unit 1 startup activities following an extended outage.
August 7, 2007�1100 hours CDT�TVA determined Unit 1 operated outside TS.
August 12, 2007 1435 hours0.0166 days <br />0.399 hours <br />0.00237 weeks <br />5.460175e-4 months <br /> CDT The RCIC steam high flow primary containment isolation function was declared operable.
D. Other Systems or Secondary Functions Affected
None.
E. Method of Discovery
Maintenance personnel discovered the reversed sense lines during trouble shooting activities for 1-FI-071-001B.
F. Operator Actions
None.
G. Safety System Responses
None.
III. CAUSE OF THE EVENT
A. Immediate Cause
The sense lines for 1-PDT-071-001B were installed reversed. The high pressure sense line was connected to the low pressure port on the transmitter and the low pressure sense was line connected to the high pressure port on the transmitter.
B. Root Cause
TVA postulates that poor verification techniques were used in the installation of 1-PDT-071-001B sense lines by both the Craftsmen and Quality Control (QC) Inspectors.
Those involved in the installation failed to verify proper sense line alignment to the instrument panel. They assumed the sense lines for 1-PDT-071-001B was the same as 1-PDT-071-001A and routed with the low side process sense line on the right side of transmitter and the high pressure sense line on the left side of the transmitter. The sense lines were routed from the flow element to the instrument panel with the high side process sense line on the right side of transmitter and the low pressure sense line on the left side of the transmitter. Pressure transmitter 1-PDT-071-001A was replaced under the same work order as 1-PDT-071-001B.
C. Contributing Factors
Contractor personnel preparing the post modification testing requirements assumed that the RCIC surveillance testing under 1-SR-3.5.3.3.(COMP) would adequately test the process functions of 1-PDT-071-001B.
IV. ANALYSIS OF THE EVENT
The Unit 1 RCIC system was tested for plant acceptability under the Unit 1 Startup Test Program.
Pressure differential transmitter 1-PDT-071-001B which was installed as part of Unit 1 recovery was calibrated as part of Unit 1 startup testing. The calibration procedure inputs a milliamp signal into the analog trip unit and verifies the analog trip unit actuates at the proper setpoint. It appears there was no opportunity to recognize that the instrument was connected to the sensing lines incorrectly until 1-SR-3.5.3.3(COMP) was initially performed in May of 2007. Operations recognized that 1-FI-071-001B was down scale during pump operation and issued a work order to correct the deficiency. Flow indicator 1-FI-071-001B is not a TS instrument and is not needed to successfully complete the surveillance. Either 1-FI-071-001A or 1-FI-071-001B could be used during the surveillance. Operations did not realize that the flow indicator used a common sense line with a TS instrument, 1-PDT-071-001B. As such, the work order priority did not require scheduling until the next performance of 1-SR-3.5.3.3(COMP) which was on August 6, 2007.
V. ASSESSMENT OF SAFETY CONSEQUENCES
The safety consequences of this event were not significant. High steam flow functions are provided to detect a break in the RCIC steam line and initiate closure of the steam line containment isolation valves. The RCIC Steam Line Flow - High signal is initiated from two transmitters; 1-PDT-071-001A and 1-PDT-071-001B that are connected to the RCIC steam line to ensure no single instrument failure can preclude the isolation function. During the time 1-PDT-071-001B was inoperable; 1-PDT-071-001A remained operable and, if needed, would have performed the containment isolation function. Therefore, the failure to meet the TSs did not adversely affect the safety of plant personnel or the public.
VI.� CORRECTIVE ACTIONS
A. Immediate Corrective Actions
TVA declared 1-PDT-071-001B inoperable and entered the appropriate LCO.
B. Corrective Actions to Prevent Recurrence (1) The individuals involved in the installation of 1-PDT-071-001B were part of the Unit 1 recovery workforce and on longer employed by TVA. However, to prevent recurrence of this event, TVA will revise the indoctrination training for modifications personnel, to reflect lessons learned from this event including the use of sound verification techniques.
TVA will develop an operator aid that lists non-TS instruments that share a common sense lines with TS instruments.
TVA recently completed enhanced training on PMT requirements for WA engineers. However, TVA will review training for WA task engineers responsible for contractor oversight to ensure adequate contractor oversight relative to applicable training and PMT requirements. Additional training will be performed as needed.
VII.� ADDITIONAL INFORMATION
A. Failed Components
None.
(1) TVA does not consider these corrective actions as regulatory requirements. The completion of these actions will be tracked in TVA's Corrective Action Program.
B. Previous LERs on Similar Events None.
C. Additional Information
Browns Ferry Corrective action document PER 128556.
D. Safety System Functional Failure Consideration:
This event is not considered a safety system functional failure in accordance with NEI 99-02.
E. Scram With Complications Consideration:
This event did not result in a complicated scram as defined in NEI 99-02.
VIII.COMMITMENTS None.