05000285/FIN-2010005-04
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Finding | |
|---|---|
| Title | Calibration Failures of RPS Trip Units 6 and 7 |
| Description | The inspectors identified an unresolved item concerning calibration of steam generator low-pressure trip unit A/TU-6 and asymmetrical steam generator transient (ASGT) trip unit A/TU-7. Further investigation is required to determine whether multiple performance deficiencies exist and if they are more than minor. On November 8, 2010, the licensee performed Surveillance Test IC-ST-RPS-0044, calibration of steam generator low-pressure trip unit A/TU-6 and asymmetrical steam generator transient (ASGT) trip unit A/TU-7. During the performance of this test out of tolerance as found values were recorded at approximately 10:30 a.m. Specifically, on Attachment 9.1 - Data Sheet 1, terminal 73 and terminal 75 were elevated out of tolerance by 0.0001 Vdc and 0.0002 Vdc respectively. These values normally correspond to RC-2A and RC-2B steam generator pressure. RC-2A and RC-2B pressure transmitters scale from 1-4 volts corresponding to 0 - 1000 psi. The condition observed was nonconservative, in that, increased voltage would mask a low pressure condition to the reactor protection system (RPS) by a linear amount. The intent of gathering this data is to ensure that there is minimal degradation of the signals by the circuitry prior to trip unit input. The remaining as found data required by the surveillance test was recorded by the instrumentation and controls (I&C) technician. The remaining values including trip unit A/TU-6 and trip unit A/TU-7 input values were in specification. The out-of-tolerance values failed the surveillance test. Work Request 157517 was generated to troubleshoot and repair. Condition Report 2010-5645 documented the out of tolerance values. During troubleshooting efforts it was determined the issue resided with the circuit. Specifically, terminal 74 is connected to common and should have a value of zero Vdc. Instead, this terminal was reading greater than zero Vdc by a few millivolts. Common to all three terminals is AI-31A-AW12 B2 contact module, which is part of the ASGT test circuit and should not affect the circuits. Instrumentation and controls technicians knew this module had previously been an issue. Condition Reports 200302822 and 2009- 2317 document past out of tolerance results. Cycling the contact module or replacing it had cleared out of tolerances values in the past, therefore part of the FC-1212 troubleshooting plan was to cycle the contact module. The FC-1212 was executed and no maintenance activities were performed. Surveillance Test IC-ST-RPS-0044 was performed again to check the required values for change. The out of tolerance values were now in tolerance. The on-shift I&C technician did not intend to complete the surveillance test. Instead, the trip units were left in bypass and the results were discussed with the shift manager including a safety concern regarding the contact module. This concern was documented in Condition Report 2010-5667 on November 8, 2010, at 3:00 p.m. The condition report questioned the problem with the contact module and stated that if the problem occurred again there would be no indication to the control room. It also stated that the ASGT test relay was exercised during troubleshooting specifically to make a better connection to pass the IC-ST-RPS-0044 surveillance test. At approximately 5:06 p.m., the night shift I&C technician completed the last three steps of IC-ST-RPS-0044 with the day shift operations crew based on the data recorded by the day shift I&C technician. This consisted of ensuring the trip units were reset, removing the bypass keys, and informing the shift manager. The trip units were returned to service and an operability determination was requested by the shift manager to evaluate the ASGT test circuit during normal operation for operability. Based on discussions with I&C personnel and the shift manager, as well as review of condition reports, the inspectors questioned if the surveillance test used to declare operability had been compromised due to potential preconditioning. The inspectors also asked what corrective actions were taken to correct the problem. The inspectors brought these questions to the licensing department. These questions were documented by the licensee in Condition Report 2010-5733, on November 10, 2010. Based on discussions with licensing and I&C personnel the operating crew declared trip units A/TU-6 and A/TU-7 inoperable, replaced the contact module, performed Surveillance Test IC-ST-RPS-0044 again, and then returned the trip units to service. On November 16, 2010, operability determination associated with Condition Report 2010-5667 was completed. This determination concluded that the out of tolerance values on November 8, 2010, were not outside the design basis as the values do not account for 4 psi of margin not built into the tolerances based on Calculation FC05733. Therefore, the values could be out of tolerance +/- 16-millivolt dc before they are outside of their design basis. In addition, the increase in voltage does not affect trip unit A/TU-7 as the voltage is added to each signal, which are then subtracted to determine a difference. To address the concern regarding the ASGT test circuit effect on trip unit operability additional actions were required to confirm operability in the current calibration cycle. Specifically Work Order 396853 was generated to monitor the voltage of the relay contact on all channels to confirm operability. Surveillance Test IC-ST-RPS-0044 test frequency was increased for the next six weeks. On November 29, 2010, voltage at terminal 74 was elevated 39-millivolt dc, thus rendering trip unit A/TU-6 inoperable. This is documented in the operator logs as well as Condition Report 2010-6190. Trip Unit A/TU-6 was declared inoperable. Subsequent trouble shooting determined a bad wire in the circuit. The wire was replaced, post maintenance testing was performed, and the trip unit was returned to service. Condition Reports 200302822 and 2009-2317 documents prior out of tolerance readings, for the same values in Surveillance test IC-ST-RPS-0044, which rendered the trip unit inoperable. These events were not determined by the licensee to be functional failures. After reviewing the condition reports, the inspectors believe these particular events to be functional failures of trip unit A/TU-6. Not fixing a condition adverse to quality is a performance deficiency. The events on November 8, 2010, show that the corrective actions taken in response to Condition Report 2009-2317 were inadequate. These actions consisted of replacing the AI-31A-AW12 B2 contact module. These same actions were taken in response to Condition Report 200302822 and therefore, were within the licensees ability to foresee and correct. The actions taken in response to the events on November 8 and November 10, 2010, were inadequate as demonstrated when trip unit A/TU-6 was declared inoperable on November 29, 2010, documented in Condition Report 2010-6190. To determine if there is more than one performance deficiency, the inspectors intend to investigate the actions taken on November 8 and November 10, 2010, as well as review the licensees apparent cause analysis regarding Condition Report 2010-6190. In accordance with the guidance in Inspection Manual Chapter 0612, an unresolved item is warranted if more information is required to determine if the performance deficiency is more than minor. URI 05000285/2010005-04, Calibration Failures of RPS Trip Units 6 and 7. |
| Site: | Fort Calhoun  |
|---|---|
| Report | IR 05000285/2010005 Section 1R22 |
| Date counted | Dec 31, 2010 (2010Q4) |
| Type: | URI: |
| cornerstone | Mitigating Systems |
| Identified by: | NRC identified |
| Inspection Procedure: | IP 71111.22 |
| Inspectors (proximate) | K Clayton J Kirkland P Elkmann J Clark T Farina J Wingebach |
| INPO aspect | |
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Finding - Fort Calhoun - IR 05000285/2010005 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Finding List (Fort Calhoun) @ 2010Q4
Self-Identified List (Fort Calhoun)
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