ENS 49117
ENS Event | |
|---|---|
20:39 Jun 13, 2013 | |
| Title | Failure of In-Core Thermocouple |
| Event Description | Description of Event:
During operations at full power (500 kWth), the Senior Reactor Operator (SRO) on duty noticed that the fuel temperature thermocouple reader indicated a temperature of 202 [degrees] C, approximately 60 - 70 [degrees] C below the expected value. The SRO recognized that the problem was likely caused by a fuel thermocouple wire grounding to its conduit. A trainee was instructed to move the wires to avoid grounding. Following this action, the thermocouple reader indicated the proper value. Upon review of the log book, the SRO noticed that the faulty fuel temperature reading had been logged for several days without corrective action. The facility Technical Specifications (TS) require at least one fuel temperature indication to be operable during operation, and define a system as 'operable' when it is capable of performing its intended function in a normal manner. Therefore the fuel temperature indication was not operable as defined in the TS. Since the reactor was not immediately secured nor was the indication immediately fixed, the event constitutes a Reportable Occurrence per facility TS 6.9.2. Background: For the four days of reactor operations during which the problem with the thermocouple existed, the reactor was operated for short amounts of time (approximately 10 -15 minutes) at various power levels in order to characterize a new beam port configuration and test an experimental apparatus. The total time above 100 kWth was 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> and 51 minutes. The reactor was typically staffed by a trainee at the panel, supervised by a licensed reactor operator (RO). The indicated temperature is the average reading of three thermocouples. One thermocouple is at the fuel midplane, one is 2 [inches] above the midplane, and one is 2 [inches] below the midplane. The fuel temperature indication, when partially grounded, is approximately correct below the point of adding heat (approximately 10 kWth). It differs from the expected value by approximately 15 [degrees] C at 100 kWth, and by approximately 65 [degrees] C at 500 kWth. The fuel temperature readout at the control panel is used to provide an automatic scram at 400 [degrees] C. This setpoint is set well below the Safety Limit of 750 [degrees] C fuel temperature during steady state reactor operations. The fuel temperature scram is NOT required by TS. Normal operations at the reactor do not approach this scram setpoint or the Safety Limit. The logbooks are reviewed daily as part of the pre-operation reactor checkout procedure. The staff is trained to review logs back to the most recent time they were on duty, to check for changes to the reactor, problems with instruments, etc. The staff is not trained to audit the previous days' logs for anomalous readings. Timeline: The following timeline of operations is taken from the reactor logbook. Only operations at or above 100 kWth are listed, because the difference between measured and expected temperature is small at lower power levels. All times are local (Central Daylight Time). Date Time Power T (Measured, [degrees] C) T (Expected, [degrees] C) 6/7/2013 0946-1001 500kW 200 265 6/7/2013 1037 - 1050 500kW 202 265 6/7/2013 1441 - 1446 500kW 202 265 6/10/2013 0937 - 0950 100kW 83 100 6/10/2013 1005 - 1015 100kW 87 100 6/10/2013 1029-1041 100kW 84 100 6/12/2013 0906 - 0919 100kW 84 100 6/12/2013 0934 - 0959 530kW 217 270 6/12/2013 1611 - 1633 100kW 74* 100 6/13/2013 1103 - 1143 500kW 201 265 6/13/2013 1352 - 1406 530kW 209 270
6/13/2013 - 1559 - Problem observed and corrected by repositioning thermocouple wires. 6/14/2013 - 1020 - Reportable occurrence reported to NRC Headquarters Operations Center. Causes: The facility has identified the following as contributing causes to the event. 1. Licensed operators were not sufficiently attentive when supervising trainees at the control panel. The licensed operators were focused on reactor power indications and did not pay sufficient attention to other TS related indications. 2. The log book review required prior to daily operations was not conducted with sufficient rigor to detect the improper thermocouple readings logged the previous day. The review was instead focused on noting changes to the reactor facility and problems with instrumentation since the operators' previous duty at the panel. 3. Only one functioning instrumented fuel element was used to provide the required fuel temperature indication channel. Therefore no redundant readout was available to check against the indicated fuel temperature. 4. The sharp edge on the instrumented fuel element conduit can cut through the insulation on the thermocouple wires, causing grounding. Corrective Actions: The facility will perform the following corrective actions. All changes to the reactor systems, such as thermocouple wire insulation, are subject to review per the requirements of 10CFR50.59. Time: Prior to operation; Action: Attempt to improve insulation on thermocouple wires, using electrical tape, shrink tubing, or spray-on insulation. Time: Prior to operation; Action: Attempt to repair thermocouple wires for a currently installed but non-functional instrumented fuel element to provide an independent fuel temperature indication channel. Time: Prior to operation; Action: Install a new instrumented fuel element. This will bring the total number of independent channels of fuel temperature indication to 2 - 3. Time: Prior to operation and as part of requalification training program; Action: Train reactor staff on the importance of vigilance when supervising trainees and the importance of attentiveness to all channels of information at the control console, as opposed to focusing on a few specific indicators, such as reactor power channels. Time: Prior to operation and as part of requalification training program; Action: Train reactor staff to check for anomalous values in the prior days' log entries during the daily reactor checkout. Time: Upon approval by Reactor Safeguards Committee, but not necessarily prior to operation; Action: Append Procedure 15 - Reactor Startup with a list of observed instrument values for different reactor power levels to be used as a reference by trainees and licensed staff. A copy of this report will be provided to the Kansas State University Reactor Safeguards Committee for review. |
| Where | |
|---|---|
| Kansas State University Manhattan, Kansas (NRC Region 4) | |
| License number: | R-88 |
| Reporting | |
| Non | |
| Time - Person (Reporting Time:+14.68 h0.612 days <br />0.0874 weeks <br />0.0201 months <br />) | |
| Opened: | Jeffrey Geuther 11:20 Jun 14, 2013 |
| NRC Officer: | Charles Teal |
| Last Updated: | Jun 14, 2013 |
| 49117 - NRC Website
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Kansas State University with Non | |
WEEKMONTHYEARENS 544212019-12-05T00:00:0005 December 2019 00:00:00
[Table view]Non Annual Surveillance Not Completed ENS 538052018-12-22T06:00:00022 December 2018 06:00:00 Non Surveillance Not Done Due to Inadequate Procedure ENS 529802017-09-19T19:49:00019 September 2017 19:49:00 Non Reactor Bay Ventilation Inoperable ENS 491172013-06-13T20:39:00013 June 2013 20:39:00 Non Failure of In-Core Thermocouple ENS 462832010-09-22T12:40:00022 September 2010 12:40:00 Non Unexpected Changes in Restricted Area Dose Rates 2019-12-05T00:00:00 | |