05000498/LER-2017-002
| South Texas Unit 1 | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 4982017002R00 - NRC Website | |
| ML18022A786 | |
| Person / Time | |
|---|---|
| Site: | South Texas  |
| Issue date: | 01/22/2018 |
| From: | Connolly J South Texas |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| NOC-AE-18003546, STl 34591589 LER 17-002-00 | |
| Download: ML18022A786 (8) | |
comments regarding burden estimate to the Information Services Branch (T-2 F43), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by e-mall to Infocollects Resource@nrc gov, and to the Desk Officer, Office of Information and Regulatory Affairs, used to impose an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
I. Description of Reportable Event
A. Reportable event classification
This event is reportable under 10 CFR 50.73(a)(2)(i)(B) as an operation or condition prohibited by the plant's Technical Specifications.
B. Plant operating conditions prior to event
Prior to the event on November 23, 2017, South Texas Unit 1 was operating in Mode 1 at 100 percent power.
C Status of structures, systems, and components that were inoperable at the start of the event and that contributed to the event Unbeknownst to the Control Room operators at the start of the event, the Train "C" Control Room Makeup and Cleanup Filtration System was inoperable due to a misconfigured jumper on the circuit board associated with the Train "C" control room makeup filtration unit outlet low flow switch. The switch provides an input to energize/de-energize the associated filtration unit heater.
D. Narrative summary of the event NOTE: When known, approximate times for all major occurrences are provided below.
March 2, 2017 STP Nuclear Operating Company (STPNOC) issued a purchase order to Fluid Components International (FCI) for four circuit boards. The circuit boards are configured with a set of jumper pins that can be configured in either position J12 or J13. In the purchase order, the specified circuit board model indicated that all four circuit boards were to be procured with a standard option of "ENERGIZED AT FLOW OR WET", which corresponds to the J12 jumper position. The J13 position corresponds to the option of "ENERGIZED AT NO FLOW OR DRY.
April 1, 2017 STPNOC received the four circuit boards from FCI (Serial Numbers 624755, 624756, 624757, 624758).
May 30, 2017 The circuit board with serial number 624756 was installed in Unit 1 Train "B" Fuel Handling Building (FHB) exhaust.
June 1, 2017 A scheduled monthly surveillance on Unit 1 Train "B" FHB exhaust was performed During the surveillance, the associated FHB exhaust heater function was tested by measuring heater coil current. Based on the successful completion of this surveillance, the jumper on the circuit board with serial number 624756 was configured in the correct J12 position. Note that the FHB exhaust air system is not governed by Technical Specifications but is required in the Technical Requirement Manual during the movement of fuel within the spent fuel pool or when conducting crane operation with loads over the spent fuel pool.
comments regarding burden estimate to the Information Services Branch (T-2 F43), U S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by e-mail to Infocollects.Resource@nrc gov, and to the Desk Officer, Office of Information and Regulatory Affairs, used to impose an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person Is not required to respond to, the information collection.
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3. LER NUMBER
September 7, 2017 At 1036 hours0.012 days <br />0.288 hours <br />0.00171 weeks <br />3.94198e-4 months <br />, the quarterly surveillance was completed satisfactorily for Unit 1 Train "C" Control Room Makeup and Cleanup Filtration System.
September 27, 2017 The circuit board with serial number 624757 was installed in the Unit 1 Train "C" control room makeup filtration unit. Installation of the new circuit board was due to a planned periodic replacement and not because of a component failure. Following installation of the new circuit board, a post-maintenance test was performed to verify circuit board setpoints. However, a post-maintenance test to verify heater operability was not performed.
The as-found configuration of the removed circuit board was configured with the jumper in the J12 position (correct position); the new circuit board was installed with the jumper in the J13 position (incorrect position).
At 1445 hours0.0167 days <br />0.401 hours <br />0.00239 weeks <br />5.498225e-4 months <br />, Unit 1 Train "C" Control Room Makeup and Cleanup Filtration System was declared Operable following planned maintenance.
November 23, 2017 At 0940 hours0.0109 days <br />0.261 hours <br />0.00155 weeks <br />3.5767e-4 months <br />, the scheduled quarterly surveillance on Unit 1 Train "C" Control Room Makeup and Cleanup Filtration System was commenced (Unit 1 was in Mode 1 at 100% power).
At 1544 hours0.0179 days <br />0.429 hours <br />0.00255 weeks <br />5.87492e-4 months <br />, a manual actuation of the Unit 1 Train "C" control room emergency ventilation system was initiated per surveillance procedure.
At 1545 hours0.0179 days <br />0.429 hours <br />0.00255 weeks <br />5.878725e-4 months <br />, Unit 1 Train "C" Control Room Makeup and Cleanup Filtration System associated heater de-energized. The train was declared inoperable and Technical Specification 3.7.7 Action a was entered:
a. With one Control Room Makeup and Cleanup Filtration System inoperable for reasons other than condition b or condition e, within 7 days restore the inoperable system to OPERABLE status, or be in at least HOT STANDBY within the next 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and in COLD SHUTDOWN within the following 30 hours3.472222e-4 days <br />0.00833 hours <br />4.960317e-5 weeks <br />1.1415e-5 months <br />.
November 24, 2017 At 1202 hours0.0139 days <br />0.334 hours <br />0.00199 weeks <br />4.57361e-4 months <br />, after corrective maintenance was performed, the quarterly surveillance on Unit 1 Train "C" Control Room Makeup and Cleanup Filtration System was re-performed. The jumper configuration for the installed circuit board with serial number 624757 was corrected in the field and the circuit board was returned to service.
At 2305 hours0.0267 days <br />0.64 hours <br />0.00381 weeks <br />8.770525e-4 months <br />, following successful surveillance test performance, Unit 1 Train "C" Control Room Makeup and Cleanup Filtration System declared Operable.
Time unknown: The circuit board with serial number 624758, which was never installed in the plant, was verified to have the jumper in the correct J12 position.
December 14, 2017 The circuit board with serial number 624755 was inspected and the jumper was found to be misconfigured (i.e., jumper was in the J13 position). The circuit board was located in the warehouse and had never been installed in the plant. A "discrepant hold" was placed on the circuit board with serial number 624755 to ensure that the card is not installed in the plant until the jumper is properly configured.
Infocollects Resource@nrc goy, and to the Desk Officer, Office of Information and Regulatory Affairs, used to impose an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection 17
NO
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3. LER NUMBER
January 10, 2018 The circuit board with serial number 624755 was reconfigured to place the jumper in the correct configuration and the "discrepant hold" was removed.
E. Method of discovery The event was discovered when the scheduled quarterly surveillance on Train "C" Control Room Makeup and Cleanup Filtration System failed on November 23, 2017.
II. Component failures
A. Failure mode, mechanism, and effects of failed component
The affected circuit board did not fail but was improperly configured. The system is designed to de-energize the heaters based on low air flow. As a result of the misconfigured jumper, the system operated in the opposite manner (i.e., the heaters energized during low flow conditions). The heaters are required to maintain desired makeup filtration effectiveness because without the heater energized, the humid ambient air would saturate the filters with moisture and reduce the filter efficiency from approximately 90% to approximately 30%.
B. Cause of component failure
The cause of the component failure was due to an improperly configured circuit board jumper. The jumper changed the output of the circuit board such that the associated heaters were energized (versus de-energized) at system low flow conditions.
C. Systems of secondary functions that were affected by failure of components with multiple functions The affected circuit board does not provide any secondary functions nor does it provide inputs to other systems.
D. Failed component information (Energy Industry Identification System (EIIS) designators provided in {brackets}) Control Room HVAC System (Control Building/Control Complex Environmental Control System) {VI} Flow Switch {80} Fluid Components International {F132}
III. Analysis of the event
A. Safety system responses that occurred
No safety systems were required to respond as a result of this event.
B. Duration of safety system inoperability Unit 1 Train "C" Control Room Makeup and Cleanup Filtration System was inoperable for a period of 58 days, 10 hours1.157407e-4 days <br />0.00278 hours <br />1.653439e-5 weeks <br />3.805e-6 months <br />, 20 minutes from 1445 hours0.0167 days <br />0.401 hours <br />0.00239 weeks <br />5.498225e-4 months <br /> on September 27, 2017 until 2305 hours0.0267 days <br />0.64 hours <br />0.00381 weeks <br />8.770525e-4 months <br /> on November 24, 2017.
comments regarding burden estimate to the Information Services Branch (T-2 F43), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by e-mail to used to impose an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the informafion collection.
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C. Safety consequences and implications
When STPNOC reanalyzed the UFSAR Chapter 15 Accident Analyses for Alternate Source Term, Control Room makeup filtration was not credited in any accident analyses. Only recirculation filtration was credited in the design bases calculations. Therefore, reduced makeup filtration effectiveness, due to loss of heater function in a makeup train heater, would have no effect on the plant design basis assumptions.
Control Room makeup filtration is only credited for use as a compensatory action if tracer gas testing fails the inleakage measurement limit. The presence of uncredited makeup filtration would provide margin until the measured inleakage problem is resolved. During the time period of this event, no tracer gas testing was performed in Unit 1, so makeup filtration was not credited as a compensatory measure while the Train "C" Control Room Makeup and Cleanup Filtration System was inoperable.
In the STP PRA model, the system function of the Control Room Makeup and Cleanup Filtration System is to provide outside air for cooling of plant equipment located in the Control Room Envelope The heaters in the makeup filtration portion of the system are not modeled in the STP PRA model and have no impact on core damage frequency or large early release frequency. The heaters would become important after a core damage event followed by a radiological release to provide clean air to the Control Room Envelope for habitability; however, this is beyond the scope of the STP PRA model, which is a Levels I and II PRA model.
From a Technical Specification perspective, during the time period of this event, the other two trains of the Control Room Makeup and Cleanup Filtration System were Operable and capable of performing their required functions. Note that the Control Room Makeup and Cleanup Filtration System trains are 50% capacity trains (i.e., two trains are required to meet the design bases function).
IV. Cause of the event
The cause of the event is the applicable maintenance work instructions did not include steps to: (1) ensure that the circuit board jumper is in the correct position, and (2) conduct a post-maintenance test to ensure proper operation of the heaters.
V. Corrective actions
The applicable maintenance work instructions will be revised to (1) ensure that the circuit board jumper is in the correct position, and (2) conduct a post-maintenance test to ensure proper operation of the heaters.
VI. Previous similar events
An operating experience review was conducted to find similar events regarding improperly configured jumpers. One event in the past ten years was discovered (reference STP Condition Report 09-16821). This event did not result in an LER because the incorrectly installed jumper was discovered prior to the component being placed into service. No changes to written instructions were made as a result of this event.