L-MT-08-007, Supplemental Information Related to Nmc'S Response to Generic Letter 2007-01, Inaccessible or Underground Power Cable Failures That Disable Accident Mitigation Systems or Cause Plant Transients.
| ML080380369 | |
| Person / Time | |
|---|---|
| Site: | Monticello  |
| Issue date: | 02/06/2008 |
| From: | O'Connor T Nuclear Management Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| GL-07-001, L-MT-08-007 | |
| Download: ML080380369 (4) | |
Text
Committed to Monticello Nuclear Generatinq Plant Operated by Nuclear Management Company, LLC February 6,2008 L-MT-08-007 GL 2007-01 10 CFR 50.54 (9 US Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 Monticello Nuclear Generating Plant Docket 50-263 License No. DPR-22 SUPPLEMENTAL INFORMATION RELATED TO NMC'S RESPONSE TO GENERIC LETTER 2007-01, "INACCESSIBLE OR UNDERGROUND POWER CABLE FAILURES THAT DISABLE ACCIDENT MITIGATION SYSTEMS OR CAUSE PLANT TRANSIENTS".
References:
- 1) NRC Generic Letter (GL) 2007-01 issued February 7,2007.
- 2) NMC Response to NRC Generic Letter 2007-01, dated May 7, 2007.
On February 7, 2007, the Nuclear Regulatory Commission (NRC) issued Generic Letter 2007-01 with a 90-day required response (Reference 1). On May 7, 2007, Nuclear Management Co. (NMC) provided the NRC the required response (Reference 2).
During a conference call held on December 18,2007, between NMC and the NRC, two additional questions were discussed. The questions were satisfactorily responded to by NMC and at the conclusion of the conference call; NMC was requested to submit the responses in writing.
NMC response to the questions is included as Enclosure 1.
Summaw of Commitments This letter contains no, w or revised commitments.
/T of perjury that the foregoing is true and correct.
Nuclear Management Company, LLC 2807 West County Road 75 Monticello, Minnesota 55362-9637 Telephone: 763.295.5151
US Nuclear Regulatory Commission ATTN: Document Control Desk Page 2 Enclosure (1) cc: Administrator, Region Ill, USNRC NRR Project Manager, Monticello, USNRC Resident Inspector, Monticello, USNRC Minnesota Department of Commerce
ENCLOSURE 1 Generic Letter 2007-01 Supplemental Information NRC Question No. 1 The NRC staff has received the cable failure history for Monticello in response to Generic Letter (GL) 2007-01, "Inaccessible or Underground Power Cable Failures that Disable Accident Mitigation Systems or Cause Plant Transients."
The licensee found a power cable failure within the scope of Title 10 of the Code of Federal Regulations (10 CFR), Section 50.65, Requirements for Monitoring the Effectiveness of Maintenance at Nuclear Power Plants (Maintenance Rule(MR)).
Specifically, the licensee found a power cable failure that occurred in 1997 in the 480V feeders to off-gas storage Motor Control Centers. In addition, NRC Inspection Report 50-263198-09 discussed a previous failure of the cables feeding the off-gas storage building that occurred in 1994. Please provide the information requested in GL 2007-01 for the 1994 cable failure, or justify why it is not within the scope of the GL.
NMC Response Failure of the cables feeding the off-gas storage building that occurred in 1994 were reported in Work Request Authorization 94-50049 to have resulted from damage by previous construction activities in the area. Specifically, it was reported that the practice of driving a bobcat upslope to backfill dirt washed out by rain damaged the cable and caused the failure. As the failure mechanism was not associated with insulation degradation or cable aging, Nuclear Management Co. (NMC) did not conclude that it should be included in the failed cable history being requested in GL 2007-01. However, the additional information requested is provided below:
Description Type1 Manufacturer Insulation Year of Type of Voltage Years of Reason for Part No. Jacket Replacement Service Class Service Replacement Material 480V 358007 General Electric Butyl 1994 480VAC 480 V A C 23 Damaged by Feeders to Rubber1 Power Construction Off Gas Neoprene Equipment Storage MCCs
ENCLOSURE 1 Generic Letter 2007-01 Supplemental Information NRC Question No. 2 In Corrective Action Program document CAP037776 and Condition Evaluation CE12033 for Monticello, the licensee discussed the testing failure of a recirculation motor generator set cable that was routed below the turbine building. Please provide the information requested in GL 2007 01 if the cable failure is within the scope of the GL, or justify why the failure is not within the scope of the GL.
NMC Response:
The GL says to provide a history of failures and in particular those failures from insulation degradation or aging. When testing is performed and the acceptance criterion is not met, the cable is replaced so that we do not have failures. This is the intent of having criteria so that we know when to pre-emptively replace cable prior to failure. We will in the future continue to replace cable based on acceptance criteria. This is called condition-based maintenance.
With regard to the recirculation motor generator set cable, as stated in CE12033, Our initial meggering of the cable indicated unacceptably low Insulation Resistance (IR) readings which prompted NMC to implement the UtilX Cable Cure polymer injection process at Monticello Nuclear Generating Plant (MNGP) in the belief that the cables were wicking up moisture from the spring thaw while the load was de-energized during the refueling outage. The circuit had operated acceptably right up until it was taken out of service in the refueling outage.
Meggering following the injection initially indicated the good results. However, validation meggering concluded the following day at higher voltage indicated the cable had failed. NMC could not discern if the injection of the polymer caused the failure vice the actual cable condition. It is clear from the Condition Evaluation that water intrusion was strongly suspected as the failure mechanism.
The cable could not be removed for failure analysis. A temporary replacement cable was installed at the time and it and the remaining cables in the 4160 V recirculation motor generator set circuit were recently replaced during RF023 (spring of 2007). However, the additional information requested is provided below:
Description Type1 Manufacturer Insulation Year of Type of Voltage Years of Reason for Part No. Jacket Replacement Service Class Service Replacement Material 4KV Power RHWlS158042 General Butyl Rubber1 2007 4160VAC 4160V 36 Unknown.
Cables for Electric Neoprene Power AC Possibly Reactor Jacket Damaged by Recirc Injection Pump MG Process Sets
Text
Committed to Monticello Nuclear Generatinq Plant Operated by Nuclear Management Company, LLC February 6,2008 L-MT-08-007 GL 2007-01 10 CFR 50.54 (9 US Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 Monticello Nuclear Generating Plant Docket 50-263 License No. DPR-22 SUPPLEMENTAL INFORMATION RELATED TO NMC'S RESPONSE TO GENERIC LETTER 2007-01, "INACCESSIBLE OR UNDERGROUND POWER CABLE FAILURES THAT DISABLE ACCIDENT MITIGATION SYSTEMS OR CAUSE PLANT TRANSIENTS".
References:
- 1) NRC Generic Letter (GL) 2007-01 issued February 7,2007.
- 2) NMC Response to NRC Generic Letter 2007-01, dated May 7, 2007.
On February 7, 2007, the Nuclear Regulatory Commission (NRC) issued Generic Letter 2007-01 with a 90-day required response (Reference 1). On May 7, 2007, Nuclear Management Co. (NMC) provided the NRC the required response (Reference 2).
During a conference call held on December 18,2007, between NMC and the NRC, two additional questions were discussed. The questions were satisfactorily responded to by NMC and at the conclusion of the conference call; NMC was requested to submit the responses in writing.
NMC response to the questions is included as Enclosure 1.
Summaw of Commitments This letter contains no, w or revised commitments.
/T of perjury that the foregoing is true and correct.
Nuclear Management Company, LLC 2807 West County Road 75 Monticello, Minnesota 55362-9637 Telephone: 763.295.5151
US Nuclear Regulatory Commission ATTN: Document Control Desk Page 2 Enclosure (1) cc: Administrator, Region Ill, USNRC NRR Project Manager, Monticello, USNRC Resident Inspector, Monticello, USNRC Minnesota Department of Commerce
ENCLOSURE 1 Generic Letter 2007-01 Supplemental Information NRC Question No. 1 The NRC staff has received the cable failure history for Monticello in response to Generic Letter (GL) 2007-01, "Inaccessible or Underground Power Cable Failures that Disable Accident Mitigation Systems or Cause Plant Transients."
The licensee found a power cable failure within the scope of Title 10 of the Code of Federal Regulations (10 CFR), Section 50.65, Requirements for Monitoring the Effectiveness of Maintenance at Nuclear Power Plants (Maintenance Rule(MR)).
Specifically, the licensee found a power cable failure that occurred in 1997 in the 480V feeders to off-gas storage Motor Control Centers. In addition, NRC Inspection Report 50-263198-09 discussed a previous failure of the cables feeding the off-gas storage building that occurred in 1994. Please provide the information requested in GL 2007-01 for the 1994 cable failure, or justify why it is not within the scope of the GL.
NMC Response Failure of the cables feeding the off-gas storage building that occurred in 1994 were reported in Work Request Authorization 94-50049 to have resulted from damage by previous construction activities in the area. Specifically, it was reported that the practice of driving a bobcat upslope to backfill dirt washed out by rain damaged the cable and caused the failure. As the failure mechanism was not associated with insulation degradation or cable aging, Nuclear Management Co. (NMC) did not conclude that it should be included in the failed cable history being requested in GL 2007-01. However, the additional information requested is provided below:
Description Type1 Manufacturer Insulation Year of Type of Voltage Years of Reason for Part No. Jacket Replacement Service Class Service Replacement Material 480V 358007 General Electric Butyl 1994 480VAC 480 V A C 23 Damaged by Feeders to Rubber1 Power Construction Off Gas Neoprene Equipment Storage MCCs
ENCLOSURE 1 Generic Letter 2007-01 Supplemental Information NRC Question No. 2 In Corrective Action Program document CAP037776 and Condition Evaluation CE12033 for Monticello, the licensee discussed the testing failure of a recirculation motor generator set cable that was routed below the turbine building. Please provide the information requested in GL 2007 01 if the cable failure is within the scope of the GL, or justify why the failure is not within the scope of the GL.
NMC Response:
The GL says to provide a history of failures and in particular those failures from insulation degradation or aging. When testing is performed and the acceptance criterion is not met, the cable is replaced so that we do not have failures. This is the intent of having criteria so that we know when to pre-emptively replace cable prior to failure. We will in the future continue to replace cable based on acceptance criteria. This is called condition-based maintenance.
With regard to the recirculation motor generator set cable, as stated in CE12033, Our initial meggering of the cable indicated unacceptably low Insulation Resistance (IR) readings which prompted NMC to implement the UtilX Cable Cure polymer injection process at Monticello Nuclear Generating Plant (MNGP) in the belief that the cables were wicking up moisture from the spring thaw while the load was de-energized during the refueling outage. The circuit had operated acceptably right up until it was taken out of service in the refueling outage.
Meggering following the injection initially indicated the good results. However, validation meggering concluded the following day at higher voltage indicated the cable had failed. NMC could not discern if the injection of the polymer caused the failure vice the actual cable condition. It is clear from the Condition Evaluation that water intrusion was strongly suspected as the failure mechanism.
The cable could not be removed for failure analysis. A temporary replacement cable was installed at the time and it and the remaining cables in the 4160 V recirculation motor generator set circuit were recently replaced during RF023 (spring of 2007). However, the additional information requested is provided below:
Description Type1 Manufacturer Insulation Year of Type of Voltage Years of Reason for Part No. Jacket Replacement Service Class Service Replacement Material 4KV Power RHWlS158042 General Butyl Rubber1 2007 4160VAC 4160V 36 Unknown.
Cables for Electric Neoprene Power AC Possibly Reactor Jacket Damaged by Recirc Injection Pump MG Process Sets