ENS 47625
ENS Event | |
|---|---|
17:16 Jan 27, 2012 | |
| Title | Technical Specification Violation Discovered |
| Event Description | The licensee has determined that technical specification 6.5.2 was violated.
The annual maintenance outage was conducted during the first two weeks in January 2012, with the biennial fuel inspection occupying most of the effort during the outage. On January 11th, the instrumented fuel elements were disconnected from the safety system for routine biennial surveillance which tests for unacceptable changes in fuel element length and bend. The surveillance was completed and the safety system restored on the same day. Maintenance was completed and normal operations resumed on January 23rd. Two non-routine maintenance items remain to be completed, installation of a 3rd safety channel calibrated to provide indication in the range where the safety limit is challenged, and replacement of an instrument rack in the control room to accommodate additional equipment supporting a facility security upgrade. On Monday January 23rd, the reactor was operated to support experiment operations coincident with reactor operator training. The preoperational checkout indicated satisfactory operation of the safety system, including the fuel temperature channels. Shutdown fuel temperatures were within tolerance for ambient conditions. Preoperational checks were completed at 9:32, with startup to 50 watts initiated at 09:33. Critical checks at 50 watts were accomplished at 9:33, followed by ascension to 100 kW at 10:00. Records of 100 kW operating data (status window print files) indicated 18?C on fuel temperature channel 1 and 83?C on fuel temperature channel 2; the senior reactor operator who performed the operation did not recognize the difference in temperature. The reactor was shutdown on completion of the experiment at 10:40. The next operation occurred on January 27th. Shutdown fuel temperatures were within tolerance for ambient conditions. Preoperational checks were completed at 9:09 with 50 watt critical data obtained at 9:13. Reactor power of 100 kW was achieved at 9:21, and 500 kW at 9:54. Records (status window print files) show fuel temperature channel 1 did not change from approximately 18?C at 100 kW and 500 kW. The senior reactor operator who performed the operation did not recognize the difference in temperature between fuel channel 1 and fuel channel 2. The reactor was shutdown at 11:16. Prior to a planned startup, the minor deviation between fuel temperatures at shutdown was noted to be unusual which prompted recognition of the previous 500 kW operating temperature. A preoperational check was performed, with no indication of abnormalities. Operations were terminated for investigation. INVESTIGATION The output of the thermocouple at fuel temperature channel 1, and was noted to be erratic when the wires at the pool side terminal were moved. It was noted that the nylon braid insulation was frayed and the black electricians tape around the lead wire was degraded. Resistance readings confirmed that perturbing the thermocouple lead wire causes the resistance of the detector loop to vary erratically, and that an alternate thermocouple loop is stable when the wires are moved. A functional response test was performed using the chill water system to cool the pool below ambient, and fuel temperature 2 was observed to fall significantly below ambient (about 13?C ) while fuel temperature channel 1 dropped slightly, to about 17?C. There are three thermocouples in each instrumented fuel element, although the fuel temperature monitoring channel uses only one of the three. Fuel channel 1 temperature monitoring channel was connected to an alternate thermocouple and the indication came into agreement with fuel temperature channel 2 and the pool water temperature channel. The plug and socket connector for fuel channel 1 was inspected, and it was noted that the wires entering the plug were frayed, facilitating a short circuit and an alternate thermocouple junction. It is not possible to unambiguously identify the short circuit path, but there is a metal identification tag, and a metal strain relief device that are in contact with the thermocouple lead wire assembly. Therefore the thermocouple junction being sensed by fuel temperature channel 1 was an inadvertent connection at the plug, sensing ambient air temperature. The wires at the fuel temperature channel 2 plugs were fabricated with sleeves over the wires, preserving the insulation, providing additional electrical isolation between the wires, and preventing sharp bends in the wires. At this point, an alternate thermocouple has been connected to fuel temperature channel 1, resistance readings indicate no short circuits, and the laboratory Director is preparing a restart letter with compensatory measures to be implemented pending development of permanent corrective action. |
| Where | |
|---|---|
| Univ Of Texas Austin, Texas (NRC Region 4) | |
| License number: | R-129 |
| Reporting | |
| Non | |
| Time - Person (Reporting Time:+70.77 h2.949 days <br />0.421 weeks <br />0.0969 months <br />) | |
| Opened: | Paul Whaley 16:02 Jan 30, 2012 |
| NRC Officer: | John Knoke |
| Last Updated: | Jan 30, 2012 |
| 47625 - NRC Website | |
Univ Of Texas with Non | |
WEEKMONTHYEARENS 499922014-04-02T16:25:0002 April 2014 16:25:00
[Table view]Non Console Key Left Unattended ENS 476252012-01-27T17:16:00027 January 2012 17:16:00 Non Technical Specification Violation Discovered 2014-04-02T16:25:00 | |