05000424/LER-2006-002
| Vogtle Electric Generating Plant - Unit 1 | |
| Event date: | 07-26-2006 |
|---|---|
| Report date: | 9-22-2006 |
| 4242006002R00 - NRC Website | |
A) REQUIREMENT FOR REPORT This report is required per 10 CFR 50.73 (a)(2)(i)(B), any operation or condition which was prohibited by Technical Specifications (TS), because flow transmitter 1FT-5152 and pressure transmitters 2PT-0455 and 1PT-0456 were inoperable for longer than allowed by the TS. Transmitter 1FT-5152 is one of the two channels that provides Auxiliary Feedwater flow indication for Steam Generator 1 as required by TS 3.3.3, Post Accident Monitoring Instrumentation. With one channel of flow indication inoperable, TS 3.3.3 requires the inoperable channel to be restored within 30 days. Since the electronics housing was apparently rotated during initial installation or a subsequent calibration, 1FT-5152 had been inoperable for longer than allowed by the TS. 2PT-0455 and 1PT-0456 are one of four channels per unit providing Pressurizer Pressure indication required by TS 3.3.1, Reactor Trip System Instrumentation. With one channel of pressure indication inoperable, TS 3.3.1 requires placing the channel in trip within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />. Since the electronics housing was apparently rotated during initial installation or a subsequent calibration, 2PT-0455 and 1PT-0456 had been inoperable for longer than allowed by the TS.
B) UNIT STATUS AT TIME OF EVENT 1FT-5152 was determined to have been inoperable on July 26, 2006. 2PT-0455 was determined to have been inoperable on August 21, 2006. 1PT-0456 was determined to have been inoperable on August 30, 2006. At the time of the events, the affected units were in Mode 1 (Power Operation) at 100% rated thermal power.
C) DESCRIPTION OF EVENT Transmitters 2PT-0455, 1FT-5152, and 1PT-0456 were discovered with the electronics housing rotated with respect to the sensor module during walk downs on December 12, 2005, July 14, 2006, and August 7, 2006 respectively. The electronics housing on these transmitters (Rosemount model 1153 Series B and model 1154) cannot be rotated at all, because the connection between the sensor module and electronics housing is hermetically sealed before shipment. Rotating the electronics housing with respect to the sensor module could break the seal causing a moisture path to the electronics. On July 26, 2006, an engineering evaluation determined that the integrity of this seal is necessary for reliable operation of 1FT-5152 during accident conditions. The transmitter was declared inoperable on July 26, 2006 and replaced with an operable transmitter on July 28, 2006. On August 21 and 30, 2006, engineering evaluations determined that the integrity of this seal is necessary for reliable operation of 2PT-0455 and 1PT-0456 respectively. Transmitter 2PT-0455 was replaced with an operable transmitter on December 22, 2005, and transmitter 1PT-0456 was replaced with an operable transmitter on August 9, 2006.
The issue of rotating these transmitter electronic housings with respect to the sensor modules was first identified during a Vogtle Equipment Self-assessment the week of June 6, 2005. An Equipment Engineer from another utility company was aware that the transmitter vendor manual cautioned, "Be careful not to break the neck seal between the sensor module and the electronics housing. The threaded interface between the sensor module and the electronics housing is hermetically sealed before shipment.
The integrity of this seal is necessary for the safe operation of the transmitter during accident conditions." The neck seal is assumed to be broken when the electronics housing (head) is rotated. This resulted in an inspection plan to walk down these transmitters to determine if this condition applied to Vogtle. The inspection plan was initiated in June 2005 and completed during August 2006. As a result of the inspection, three Technical Specification (TS) instruments were found to have been rendered inoperable per the TS.
Flow transmitter 1FT-5152, Steam Generator (SG) 1 Auxiliary Feedwater Flow, was discovered as having the head rotated after initial installation in the plant such that the seal which protects the transmitter electronics from moisture intrusion may have been damaged or degraded. In addition, pressure transmitters 2PT-0455, Pressurizer Channel 1 Pressure, and 1PT-0456, Pressurizer Channel 2 Pressure, were also discovered as having the heads rotated after initial installation in the plant such that the seal which protects the transmitter electronics from moisture intrusion may have been damaged or degraded. This rotation appears to have been to allow connection of the loop wiring to the transmitter in the field or during calibration. An engineering evaluation determined that the integrity of this seal is necessary for reliable operation of the transmitter during accident conditions. 1FT-5152 is one of two transmitters for SG 1 required by Technical Specification (TS) 3.3.3, Post Accident Monitoring Instrumentation. With one channel inoperable, TS 3.3.3 requires restoration within 30 days. 2PT-0455 and 1PT-0456 are one of four channels per unit providing Pressurizer Pressure indication required by TS 3.3.1, Reactor Trip System Instrumentation. With one channel inoperable, TS 3.3.1 requires placing the channel in trip within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />. 1FT-5152 was found rotated on July 14, 2006 and replaced on July 28, 2006. 2PT-0455 was found rotated on December 12, 2005 and was replaced on December 22, 2005. 1PT-0456 was found rotated on August 7, 2006 and was replaced on August 9, 2006.
D. CAUSE OF EVENT
Transmitters 1FT-5152, SG 1 Auxiliary Feedwater Flow, 2PT-0455, Pressurizer Channel 1 Pressure, and 1PT-0456, Pressurizer Channel 2 Pressure, were discovered as having the head rotated after initial installation in the plant. This rotation appears to have been to allow connection of the loop wiring to the transmitter in the field or during calibration. The cause of the event was a result of inadequate installation and calibration procedure guidance in that a caution statement from the vendor manual not to break the neck seal between the sensor module and the electronics housing was not included.
E. ANALYSIS OF EVENT
Flow transmitter 1FT-5152 is one of two transmitters that provide auxiliary feedwater (AFW) flow indication for SG 1. Auxiliary feedwater flow instrumentation loops 5152, 15152, 5153, 15153, 5151, 15151, 5150, and 15150 are Regulatory Guide 1.97, Type A instrumentation loops that provide information required by control room operators to perform certain manual actions specified in the Emergency Operating Procedures. The other instrument loop that provides AFW flow indication for SG 1, 1FT-15152, was operable with its electronics housing in the proper orientation with respect to the sensor module. A review of maintenance work orders for the last 3 years has indicated that there were approximately 3 instances where 1FT-15152 was out of service for maintenance. However, had an event occurred while 1FT-15152 was out of service, this would not have prevented delivery of AFW flow to SG 1. In addition, the AFW flow indication for the other three SGs was not affected by this condition. Pressure transmitters 2PT-0455 and 1PT-0456 are one of 4 transmitters per unit that provide Pressurizer Pressure indication. The Pressurizer Pressure instruments are part of the Reactor Trip System (RTS) and Engineered Safety Feature Actuation System (ESFAS). Signals from these transmitters are processed by the RTS and ESFAS actuation logic to provide reactor trip and safety injection actuation signals which protects the core fuel design limits and Reactor Coolant System (RCS) pressure boundary during Anticipated Operational Occurrences (AOOs) and mitigates accidents. The other instruments that provide Pressurizer Pressure indication, 2PT-0456, 2PT-0457, 2PT-0458, 1PT 0455, 1PT-0457, and 1PT-0458, were operable with the electronics housing in the proper orientation with respect to the sensor module. Therefore, Pressurizer Pressure indication would have been available on both units to make up the required actuation logic in the event of an A00 or an accident even with another channel out of service for maintenance. Furthermore, no event occurred while 1FT 5152, 2PT-0455, and 1PT-0456 were in this condition that would have challenged their ability to perform their function. Therefore there was no adverse impact to the health and safety of the public.
F. CORRECTIVE ACTIONS
1) Transmitters 1FT-5152, 2PT-0455, and 1PT-0456 have been replaced.
2) The maintenance installation and calibration procedures for the affected model transmitters has been updated to reflect the vendor manual caution about not breaking the neck seal. This information has also been incorporated into the Equipment Qualification Data Package for these transmitters.
3) The Root Cause evaluation and supporting documentation will be included as part of the I&C personnel continuing training. Estimated completion date is January 19, 2007.
4) The plant "Vendor Document Control" and "Procedures Review and Approval" procedures will be revised to add a requirement to consider Equipment Qualification (EQ) impacts in the procedure review process for EQ identified equipment. Estimated completion date is November 15, 2006.
5) The corporate "Vendor Document Review, Update, and Transmittal" procedure will be revised to specifically require a documented review for Environmental Qualification impacts during the preparation of a new vendor document. Estimated completion date is November 15, 2006.
G. ADDITIONAL INFORMATION
1) Failed Components:
Flow Transmitter, Pressure Transmitter 2) Previous Similar Events:
None 3) Energy Industry Identification System Codes:
Auxiliary Feedwater System — BA Reactor Coolant System - AB