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| Entered date | Event description | |
|---|---|---|
| ENS 43562 | 13 August 2007 17:04:00 | At 0900 on July 30 2007, an Engineer noted during the review of a revision to the Comanche Peak Fire Safe Shutdown Analysis that a cable associated with the control circuitry for Train B of the Safety Chilled Water System may not be adequately protected from a potential fire. By design, electrical control cables for Trains A and B of the Safety Chilled Water System are located in the same fire zone. The original design specified that the Train B electrical control cables in this zone were to be protected with fire barrier material (thermolag). However, in this case the fire barrier material was found to be missing from the Train B electrical control cables. Upon discovery of this condition, a fire impairment was implemented for the affected fire zone. Engineering performed an evaluation of this condition and at 0900 on August 13, 2007 concluded that if a fire occurred in the affected fire zone, the required degree of separation for redundant safe shutdown trains was inadequate (i.e. both A and B trains were affected) and this would adversely affect the control circuitry and potentially prevent the Unit 1 Safety Chilled Water System from performing its intended safety function. The Unit 1 Safety Chilled Water Systems safety function at Comanche Peak is to remove heat dissipated from engineering safety features equipment and to maintain ambient temperatures in rooms containing safety related equipment below maximum design temperatures. This condition is similar to an example given in NUREG 1022, Rev. 2, Section 3.2.4 for an unanalyzed condition that significantly affects plant safety (fire barrier missing such that the required degree of separation for redundant safe shutdown trains is lacking). Therefore, this condition is reportable per 10CFR50.72(b)(3)(ii)(B), 'The nuclear power plant being in an unanalyzed condition that significantly degrades plant safety.' The licensee notified the NRC Resident Inspector.
CPNPP is retracting Event Notification 43562 based on the following: Further review of this issue by Engineering has determined that the required degree of separation for redundant safe shutdown trains was adequate and the Unit 1 Safety Chilled Water System was capable of performing its intended safety function. Therefore, this condition is not reportable per 10CFR50.72(b)(3)(ii)(B), 'The nuclear power plant being in an unanalyzed condition that significantly degrades plant safety.' CPNPP has informed the NRC Resident Inspector. R4DO (R. Nease) notified. |
| ENS 42945 | 29 October 2006 18:02:00 | Unit 2 was operating in Mode 1 at 80% power following refueling holding for stabilization xenon in preparation for incore - excore calibration. An alarm condition for steam generator 2-03 indicating Steam - Feedwater flow mismatch was observed. Manual control of the feed regulating valve was taken, but operators were unable to control feed flow while steam generator 2-03 level continued to decrease. A manual reactor trip was initiated and the reactor was tripped. Auxiliary feedwater automatically started on low-low level in steam generators. All systems responded normally during and following the trip. Unit 2 is being maintained in Mode 3 pending the event investigation. All control rods fully inserted. RCPs are in operation transferring decay heat to the steam generators. The MSIV's are open with the steam generators discharging steam to the main condensers using the steam dumps. AFW is maintaining steam generator water levels. Unit 1 was not affected. The licensee notified the NRC Resident Inspector. |
| ENS 41134 | 19 October 2004 12:35:00 | Unit 2 experienced an autostart of Auxiliary Feedwater System (AFW) and Emergency Diesel Generator 'B' following transfer of the '2E' Switchgear to Alternate Power Supply. Normal Power Supply (XST1) experienced a loss of power, causing the '2E' Switchgear to slow transfer to the -2 Breakers from the Alternate Power Supply (XST2). The AFW (MDAFWP (Motor-driven Auxiliary Feedwater Pumps) 'A' and 'B' and TDAFWP (Turbine-driven Auxiliary Feedwater Pump)) autostarted due to Sequencer Operations. The EDG 'B' autostarted on low voltage condition but did not supply power to the affected '2E' bus. The EDG 'B' cooling water was provided by the service water system. Power was restored to XST1 at 0606 CDT. The cause of the EDG 'B' autostart is under investigation. The cause of the loss of power to XST1 is under investigation. Power was reduced to 98.2% to ensure Nuclear Power <100%. All other systems functioned as required. Local NRC Resident was informed. |