Headquarters Daily report OCTOBER 11, 1994 *************************************************************************** REPORT NEGATIVE NO INPUT ATTACHED INPUT RECEIVED RECEIVED HEADQUARTERS X REGION I X REGION II X REGION III X REGION IV X *************************************************************************** PRIORITY ATTENTION REQUIRED MORNING REPORT - HEADQUARTERS OCTOBER 11, 1994 MR Number: H-94-0093 NRR DAILY REPORT ITEM GENERIC COMMUNICATIONS BRANCH/EVENTS ASSESSMENT BRANCH DIVISION OF OPERATING REACTOR SUPPORT OFFICE OF NUCLEAR REACTOR REGULATION Subject: N/A NRC Information Notice 94-75, "Minimum Temperature for Criticality," will be issued October 14, 1994. The NRC is issuing this information notice to alert addressees to potentially non-conservative initial conditions that were used in the analysis of some design-basis transients. Technical contact: George A. Schwenk, NRR (301) 504-2814 PRIORITY ATTENTION REQUIRED MORNING REPORT - REGION III OCTOBER 11, 1994 Licensee/Facility: Notification: Commonwealth Edison Co. MR Number: 3-94-0180 Braidwood 2 Date: 10/11/94 Braceville,Illinois SRI VIA PC Dockets: 50-457 PWR/W-4-LP Subject: UNIT 2 SCHEDULED REFUELING OUTAGE Reportable Event Number: N/A Discussion: On October 8, 1994, Braidwood Unit 2 shut down for a scheduled 45- day refueling outage. In addition to core refueling, major activities to be accomplished during the outage include safety-related battery replacements, steam generator eddy current testing, 2A/2B diesel generator 18-month inspections, 2B/2C reactor coolant pump inspections and seal replacements, and a containment integrated leak rate test (ILRT). Regional Action: The resident staff will monitor outage activities. Contact: L. MILLER (708)829-9629 PRIORITY ATTENTION REQUIRED MORNING REPORT - REGION IV OCTOBER 11, 1994 Licensee/Facility: Notification: Wolf Creek Nuclear Oper. Corp. MR Number: 4-94-0117 Wolf Creek 1 Date: 10/11/94 Burlington,Kansas LICENSEE PHONE CALL TO THE SRI Dockets: 50-482 PWR/W-4-LP Subject: COMMON MODE FAILURE OF EDG VOLTAGE REGULATOR TRANSFORMER Reportable Event Number: N/A Discussion: On September 30, 1994, with EDG A declared inoperable, a fire occurred in the EDG A voltage regulator potential transformer. The licensee was performing the post maintenance EDG test and engine balance. The fire was extinguished quickly by deenergizing the transformer and by use of a portable carbon dioxide fire extinguisher. The transformer was replaced and the diesel was declared operable on October 2, 1994. On October 11, 1994, with EDG B declared inoperable, a fire occurred in the EDG B voltage regulator potential transformer. The licensee was performing the same post maintenance EDG test and engine balance. The licensee had performed electrical checks on this transformer following the failure on EDG A and found no problems. The fire was again quickly extinguished by deenergizing the transformer and by use of a portable carbon dioxide fire extinguisher. The EDG is a Colt Pielstick engine coupled to a generator manufactured by Beloit Power Systems. The voltage regulator was manufactured by Westinghouse. The transformer which failed during both fires has a nameplate stating that it was manufactured by NWL Transformer in Bordentown, N.J., and has a model number of 26616. The nameplate ratings show it to be a step down 4160 vac to 480 vac, 45 kva, 3 phase, 60 cycle transformer. The inspector observed that the windings were clearly charred and the primary and secondary cables were blistered from the terminal lug back approximately six inches. The secondary side of the transformer supplies the voltage regulator firing circuits through three fuses (one for each phase). After each test and fire the licensee found that one of the fuses had blown. There is some speculation that after the fuse opened, the circuitry caused the other two phases to compensate which may have overloaded the transformer. Additional speculation is focusing on the licensee's discovery, prior to these maintenance tests, that some of these fuses were not the fuses shown on the controlled drawings. The licensee replaced these fuses with fuses matching the controlled drawing specifications. The licensee formed an investigation team to determine the root cause, and evaluate the potential for a common mode failure of the EDG. The licensee is giving this investigation the highest priority. EDG A is currently still considered to be operable. The licensee plans to continue loading the remaining approximately 15 fuel assemblies, but not drain the refueling cavity until the cause of the transformer failure is understood and management has additional assurance that EDG A is indeed operable. With the cavity flooded up to 23 feet above the reactor vessel flange, the time to boil on a loss of all cooling is conservatively estimated to be approximately 18 hours. Regional Action: The resident inspector and regional staff will monitor licensee actions. Contact: J. F. Ringwald (316)364-8653