DIABLO CANYON 2 27921 10-18-94 POW LICENSEE: PACIFIC GAS & ELECTRIC CO. SITE: DIABLO CANYON 2 EN NUMBER:27921 DOCKET: 05000323 EVENT DATE: 10-18-94 RX TYPE: PWR EVENT TIME: 23:35 VENDORS: W-4-LP NOTIFY DATE: 10-19-94 EMERGENCY CLASS: N/A REGION: 4 STATE: CA TIME: 04:41 OPS OFFICER: CHAUNCEY GOULD 10 CFR SECTION: AINB 50.72(b)(2)(iii)(B) POT RHR INOP NLCO TECH SPEC LCO A/S UNIT SCRAM RX INIT INITIAL MODE CURR CURRENT MODE CODE CRIT PWR PWR 2 N N 0 COLD SHUTDOWN 0 COLD SHUTDOWN THE PLANT LOST RHR DURING A DIESEL GENERATOR TEST DUE TO PERSONNEL ERROR. THIS OCCURRED DURING THE PERFORMANCE OF A DIESEL GENERATOR TEST WHICH REQUIRED THEM TO LOAD SHED. WHEN THEY STARTED LOAD SHEDDING, ONE OF THE PIECES OF EQUIPMENT DROPPED WAS THE OPERATING RHR PUMP. THEY BELIEVE THE CAUSE WAS DUE TO PERSONNEL ERROR, BECAUSE THEY HAD THE WRONG RHR PUMP RUNNING. THE PUMP WAS RETURNED TO SERVICE WITHIN 6 MINS AND RCS TEMPERATURE INCREASED FROM 96 DEGREES TO 102 DEGREES. THEY ENTERED TS 3.4.1.4.2 WHICH REQUIRES AN RHR PUMP TO BE IMMEDIATELY STARTED WHEN THEY NO RHR PUMPS RUNNING. THE RI WAS INFORMED. BRAIDWOOD 1 27922 10-19-94 POW LICENSEE: COMMONWEALTH EDISON CO. SITE: BRAIDWOOD 1 EN NUMBER:27922 DOCKET: 05000456 EVENT DATE: 10-19-94 RX TYPE: PWR EVENT TIME: 07:45 VENDORS: W-4-LP NOTIFY DATE: 10-19-94 EMERGENCY CLASS: N/A REGION: 3 STATE: IL TIME: 09:44 OPS OFFICER: DOUG WEAVER 10 CFR SECTION: DDDD 73.71 UNSPECIFIED PARAGRAPH UNIT SCRAM RX INIT INITIAL MODE CURR CURRENT MODE CODE CRIT PWR PWR 1 N Y 100 POWER OPERATION 100 POWER OPERATION SAFEGUARDS SYSTEM DEGRADATION RELATED TO AREA BOUNDARY DUE TO IMPROPER COMPENSATORY MEASURES. ALTERNATE COMPENSATORY ACTIONS WERE TAKEN UPON DISCOVERY. LICENSEE BELIEVES THERE WERE NO ADVERSE CONSEQUENCES DUE TO THE FAILED COMPENSATORY MEASURE BASED ON INSPECTION AND RECORDS REVIEW. THE LICENSEE WILL INFORM THE NRC RESIDENT INSPECTOR. DETAILS OF THIS EVENT ARE AVAILABLE IN THE HOO LOG. GRAND GULF 1 27923 10-19-94 POW LICENSEE: ENTERGY OPERATIONS INC. SITE: GRAND GULF 1 EN NUMBER:27923 DOCKET: 05000416 EVENT DATE: 10-19-94 RX TYPE: BWR EVENT TIME: 09:45 VENDORS: GE-6 NOTIFY DATE: 10-19-94 EMERGENCY CLASS: N/A REGION: 2 STATE: MS TIME: 10:54 OPS OFFICER: CHAUNCEY GOULD 10 CFR SECTION: AARC 50.72(b)(1)(v) OTHER ASMT/COMM INOP UNIT SCRAM RX INIT INITIAL MODE CURR CURRENT MODE CODE CRIT PWR PWR 1 N Y 100 POWER OPERATION 100 POWER OPERATION THE PLANT HAS COMPLETE LOSS OF POST ACCIDENT SAMPLE SYSTEMS DUE TO A PREPLANNED INSTRUMENT CALIBRATION. PRIOR TO TAKING THE LIQUID POST ACCIDENT SAMPLE SYSTEM OUT OF SERVICE FOR CALIBRATION, THE GASEOUS SYSTEM HAD BEEN OUT OF SERVICE AND CAPPED DUE TO A BROKEN LINE. SINCE THE GASEOUS SYSTEM WAS ALREADY OUT OF SERVICE AND THE LIQUID SYSTEM WAS BEING TAKEN OUT OF SERVICE, IT RESULTED IN A COMPLETE LOSS OF POST ACCIDENT SAMPLE SYSTEMS. THE LIQUID SYSTEM SHOULD BE BACK IN SERVICE WITHIN 1 DAY. THE RI WAS INFORMED. WESTINGHOUSE ELECTRIC CORP 27924 08-15-94 OTH LICENSEE: WESTINGHOUSE ELECTRIC CORP SITE: WESTINGHOUSE ELECTRIC CORP EN NUMBER:27924 DOCKET: EVENT DATE: 08-15-94 RX TYPE: EVENT TIME: 00:00 VENDORS: NOTIFY DATE: 10-19-94 EMERGENCY CLASS: N/A REGION: 1 STATE: PA TIME: 11:00 OPS OFFICER: CHAUNCEY GOULD 10 CFR SECTION: NINF INFORMATION ONLY CCCC 21.21 UNSPECIFIED PARAGRAPH WESTINGHOUSE HAS IDENTIFIED A DEFECT THAT COULD CREATE A SUBSTANTIAL SAFETY HAZARD IF THE DEFECT REMAINS UNCORRECTED. INGERSOLL-DRESSER PUMP COMPANY NOTIFIED WESTINGHOUSE ABOUT A POTENTIAL DEFECT REGARDING THE "JHF" MODEL SAFETY INJECTION PUMPS THAT INGERSOLL-DRESSER & WESTINGHOUSE SUPPLIED TO SEVERAL NUCLEAR POWER PLANTS. THE DEFECT IS THAT SEVERAL AXIAL CRACKS WERE DISCOVERED IN THE PRESSURE REDUCING SLEEVE LOCKNUT (ITEM #D042) FOR THE "JHF" MODEL SAFETY INJECTION PUMP. TWO KNOWN DISCOVERIES WERE REPORTED BY DUKE POWER COMPANY TO INGERSOLL-DRESSER PUMPS. DUKE POWER CO PERFORMED FAILURE ANALYSES OF THE TWO CRACKED PRESSURE REDUCING SLEEVE LOCKNUTS, WHICH ARE MADE OF 416SS, AND ATTRIBUTED THE FAILURE TO STRESS CORROSION CRACKING. THE PRIMARY CONTRIBUTOR TO THE STRESS CORROSION CRACKING WAS DETERMINED BY DUKE POWER TO BE MARTENSITE PHASE HARDNESS OF 47Rc. IT IS KNOWN THAT 400 SERIES SS WITH A HARDNESS IN EXCESS OF 40 Rc IS HIGHLY SUSCEPTIBLE TO INTERGRANULAR STRESS-CORROSION CRACKING IN AQUEOUS ENVIRONMENTS. LIMERICK 2 27925 10-19-94 POW LICENSEE: PHILADELPHIA ELECTRIC CO. SITE: LIMERICK 2 EN NUMBER:27925 DOCKET: 05000353 EVENT DATE: 10-19-94 RX TYPE: BWR EVENT TIME: 12:19 VENDORS: GE-4 NOTIFY DATE: 10-19-94 EMERGENCY CLASS: N/A REGION: 1 STATE: PA TIME: 13:14 OPS OFFICER: WILLIAM HUFFMAN 10 CFR SECTION: ACCS 50.72(b)(1)(iv) ECCS INJECTION ARPS 50.72(b)(2)(ii) RPS ACTUATION AESF 50.72(b)(2)(ii) ESF ACTUATION UNIT SCRAM RX INIT INITIAL MODE CURR CURRENT MODE CODE CRIT PWR PWR 2 A/R Y 92 POWER OPERATION 0 HOT SHUTDOWN REACTOR SCRAM ON LOW REACTOR VESSEL WATER LEVEL. WHILE PERFORMING AN EMERGENCY DIESEL GENERATOR SURVEILLANCE, THE DIVISION IV 4160 VOLT SAFEGUARDS BUS D24 WAS DE-ENERGIZED DUE TO SOME KIND OF ELECTRICAL FAULT. THIS CAUSED A FEEDWATER LEVEL CONTROL PROBLEM WHICH RESULTED IN A LOW REACTOR VESSEL WATER LEVEL SCRAM (AT +12.5 INCHES). ALL RODS FULLY INSERTED AND THE REACTOR IS STABLE IN CONDITION 3 AT 920 PSIG. DECAY HEAT IS BEING DISCHARGED TO THE MAIN CONDENSER VIA THE TURBINE BYPASS VALVES. AFTER THE SCRAM, WATER LEVEL CONTINUED TO DECREASE TO APPROXIMATELY -38 INCHES. THE REACTOR CORE ISOLATION COOLING (RCIC) SYSTEM STARTED AND INJECTED TO MAINTAIN LEVEL. HIGH PRESSURE COOLANT INJECTION (HPCI) STARTED BUT WAS SECURED BEFORE THE INJECTION VALVE OPENED. WATER LEVEL WAS QUICKLY RETURNED TO A NORMAL BAND OF 30 TO 40 INCHES USING THE FEEDWATER SYSTEM. ALL APPROPRIATE ISOLATIONS OCCURRED, INCLUDING RWCU AND REACTOR BUILDING HVAC. THERE WERE NO COMPLICATIONS FROM THE SCRAM. NO SAFETY/RELIEF VALVES LIFTED DURING THE TRANSIENT. THE D24 BUS HAS BEEN RE-ENERGIZED USING OFFSITE POWER. ALL SYSTEMS FUNCTIONED AS REQUIRED. INVESTIGATION INTO THE CAUSE OF THE D24 ELECTRICAL FAULT IS ONGOING. THE LICENSEE PRESENTLY PLANS TO REMAIN IN MODE 3. THE NRC RESIDENT INSPECTOR HAS BEEN INFORMED. *** UPDATE FROM LICENSEE:NEFF TO NRC:HUFFMAN AT 1836 EDT ON 10/19/94 *** THE CAUSE OF THE DE-ENERGIZED D24 BUS WAS OPERATOR ERROR. THE DIESEL SURVEILLANCE PROCEDURE CALLED FOR THE OPERATOR TO OPEN THE EDG OUTPUT BREAKER AND THEN QUICKLY SHUTDOWN THE DIESEL. THE OPERATOR INADVERTENTLY OPENED THE OFFSITE FEEDER BREAKER AND THEN SHUTDOWN THE DIESEL. R1DO(MEYER) HAS BEEN INFORMED. LASALLE 2 27926 10-19-94 POW LICENSEE: COMMONWEALTH EDISON CO. SITE: LASALLE 2 EN NUMBER:27926 DOCKET: 05000374 EVENT DATE: 10-19-94 RX TYPE: BWR EVENT TIME: 10:57 VENDORS: GE-5 NOTIFY DATE: 10-19-94 EMERGENCY CLASS: N/A REGION: 3 STATE: IL TIME: 14:03 OPS OFFICER: WILLIAM HUFFMAN 10 CFR SECTION: ARPS 50.72(b)(2)(ii) RPS ACTUATION AESF 50.72(b)(2)(ii) ESF ACTUATION UNIT SCRAM RX INIT INITIAL MODE CURR CURRENT MODE CODE CRIT PWR PWR 2 A/R Y 100 POWER OPERATION 0 HOT SHUTDOWN REACTOR SCRAM FOLLOWING MAIN TURBINE TRIP. A REACTOR SCRAM FROM FULL POWER OCCURRED FOLLOWING A MAIN TURBINE TRIP. ALL RODS FULLY INSERTED AND THE REACTOR IS STABLE AT 720 PSIG. DURING THE TRANSIENT, TURBINE BYPASS VALVES CAPABILITY WAS LOST. CONSEQUENTLY, SIX SAFETY/RELIEF VALVES OPENED (3 OF THEM WERE ADS VALVES) IN THE RELIEF MODE. ALL SIX SRVs RESEATED WITHOUT DIFFICULTY. DECAY HEAT IS CURRENTLY BEING DISCHARGED TO THE MAIN CONDENSER VIA THE STEAM LINE DRAINS. THE TURBINE TRIP RESULTED FROM A LOSS OF ELECTRO-HYDRAULIC CONTROL (EHC) SYSTEM PRESSURE DUE TO AN EHC LEAK. OPERATORS NOTICED THAT TURBINE CONTROL VALVES WERE OSCILLATING SLIGHTLY. TROUBLESHOOTING CONCLUDED THAT THE OSCILLATION WAS DUE TO FLUCTUATIONS IN A CONTROL SYSTEM DC POWER SUPPLY. PERSONNEL STATIONED AT THE EHC SYSTEM ALSO REPORTED UNUSUAL VIBRATIONS OF THE EHC SYSTEM PIPING WHICH APPEARED TO BE RELATED TO THE CONTROL SYSTEM OSCILLATIONS. A LEAK EVENTUALLY DEVELOPED FROM THE VIBRATING EHC PIPING. THE LEAK DEPRESSURIZED THE EHC SYSTEM AND CAUSED THE MAIN TURBINE TO TRIP. BECAUSE THE MOTIVE FORCE FOR THE TURBINE BYPASS VALVES IS EHC FLUID, THE BYPASS VALVES WERE ALSO RENDERED INOPERABLE. ALL FIVE BYPASS VALVES OPENED MOMENTARILY TO RELIEVE PRESSURE FROM THE TRANSIENT USING PRESSURE STORED IN LOCAL EHC ACCUMULATORS. HOWEVER, THE PRESSURE IN THE ACCUMULATORS WAS QUICKLY DEPLETED RESULTING IN THE EVENTUAL LOSS OF BYPASS CAPABILITY. THE EHC SYSTEM WAS IMMEDIATELY SHUT DOWN. THE LICENSEE STATES THAT THE EHC FLUID SPRAYED FROM THE PIPE LEAK DID NOT CONSTITUTE A FIRE HAZARD. DURING THE TRANSIENT, SOME ANOMALIES WERE OBSERVED. THE REACTOR RECIRCULATION PUMPS TRIPPED AND ALTERNATE ROD INSERTION WAS INITIATED. IN ADDITION, REACTOR CORE ISOLATION COOLING AUTO INITIATED AND INJECTED TO THE REACTOR VESSEL. CONTROL ROOM INDICATIONS SHOW THAT THE LOWEST REACTOR VESSEL WATER LEVEL REACHED WAS +6 INCHES. THE HIGHEST PRESSURE REACHED WAS 1080 PSIG. ARI, RCIC INITIATION, AND RECIRC PUMP TRIPS SHOULD NOT HAVE OCCURRED UNLESS REACTOR VESSEL WATER LEVEL DROPPED BELOW -50 INCHES OR PRESSURE EXCEEDED 1135 PSIG. THE CAUSE OF THESE INITIATIONS IN NOT KNOWN AND STILL UNDER INVESTIGATION. THE LICENSEE ALSO NOTED THAT TWO CIRCULATING WATER PUMPS TRIPPED DURING THE FAST BUS TRANSFER OF ONE OF THE NON-SAFETY RELATED ELECTRICAL BUSES. A STANDBY CIRC WATER PUMP WAS STARTED WITHOUT DIFFICULTY. OTHER THAN THE UNEXPLAINED ESF ACTUATIONS, ALL SYSTEMS FUNCTIONED AS REQUIRED. THE LICENSEE PRESENTLY PLANS TO REMAIN IN CONDITION 3 UNTIL FURTHER ASSESSMENT OF THE REPAIRS REQUIRED FOR THE EHC SYSTEM ARE MADE. THE NRC RESIDENT INSPECTOR HAS BEEN INFORMED. PALO VERDE 2 27927 10-19-94 POW LICENSEE: ARIZONA PUBLIC SERVICE CO. SITE: PALO VERDE 2 EN NUMBER:27927 DOCKET: 05000529 EVENT DATE: 10-19-94 RX TYPE: PWR EVENT TIME: 15:26 VENDORS: CE80 NOTIFY DATE: 10-19-94 EMERGENCY CLASS: N/A REGION: 4 STATE: AZ TIME: 18:43 OPS OFFICER: WILLIAM HUFFMAN 10 CFR SECTION: ASHU 50.72(b)(1)(i)(A) PLANT S/D REQD BY TS UNIT SCRAM RX INIT INITIAL MODE CURR CURRENT MODE CODE CRIT PWR PWR 2 N Y 1 STARTUP 0 HOT STANDBY PLANT SHUTDOWN REQUIRED BY TECHNICAL SPECIFICATIONS DUE TO INOPERABLE SAFETY INJECTION VALVE. ON 10/16/94 AT 1535 MST, THE HIGH PRESSURE SAFETY INJECTION THROTTLE VALVE (SIA-UV-627) FAILED TO OPEN DURING ASME SECTION XI TESTING. THE LICENSEE HAS DETERMINED THAT THE NECESSARY REPAIRS TO RESTORE THE VALVE TO OPERABILITY WILL TAKE LONGER THAN THE 72 HOUR LCO ACTION TIME LIMIT. CONSEQUENTLY, THE PLANT HAS SHUTDOWN TO HOT STANDBY. THE LICENSEE PLANS TO REMAIN IN MODE 3 UNTIL VALVE REPAIRS ARE COMPLETED. THE NRC RESIDENT INSPECTOR HAS BEEN INFORMED. QUAD CITIES 1 2 27928 10-19-94 POW LICENSEE: COMMONWEALTH EDISON CO. SITE: QUAD CITIES 1 2 EN NUMBER:27928 DOCKET: 05000254 05000265 EVENT DATE: 10-19-94 RX TYPE: BWR BWR EVENT TIME: 16:20 VENDORS: GE-3 GE-3 NOTIFY DATE: 10-19-94 EMERGENCY CLASS: N/A REGION: 3 STATE: IL TIME: 20:43 OPS OFFICER: WILLIAM HUFFMAN 10 CFR SECTION: ADAS 50.72(b)(2)(i) DEG/UNANALYZED COND UNIT SCRAM RX INIT INITIAL MODE CURR CURRENT MODE CODE CRIT PWR PWR 1 N N 0 COLD SHUTDOWN 0 COLD SHUTDOWN 2 N N 0 COLD SHUTDOWN 0 COLD SHUTDOWN LACK OF DOUBLE BARRIER ISOLATION OF REACTOR COOLANT SYSTEM ON CONTROL ROD DRIVE (CRD) VENT LINES. THE LICENSEE FOUND THAT THE CRD UNDER AND OVER PISTON VENT VALVES (1&2-0301-117 AND 118) ARE MISSING STEM PORT PLUGS ON ALL THE CRD'S ON BOTH UNITS. THE PLUGS ARE NEEDED TO PROVIDE A SECOND ISOLATION BARRIER FOR ANY REACTOR COOLANT SYSTEM LEAKAGE WHICH MAY DEVELOP AT THE STEM OF THESE VALVES. IT IS CURRENTLY UNKNOWN WHEN THESE STEM PORT PLUGS WERE REMOVED. THE CONDITION WAS DISCOVERED FOLLOWING NOTIFICATION OF A SIMILAR CONDITION AT DRESDEN. RESOLUTION OF THIS ISSUE WILL BE ACCOMPLISHED PRIOR TO STARTUP. THE NRC RESIDENT INSPECTOR WILL BE NOTIFIED. HOO NOTE: DRESDEN DID NOT REPORT THIS CONDITION VIA A 50.72 REPORT. BYRON 1 2 27929 10-19-94 POW LICENSEE: COMMONWEALTH EDISON CO. SITE: BYRON 1 2 EN NUMBER:27929 DOCKET: 05000454 05000455 EVENT DATE: 10-19-94 RX TYPE: PWR PWR EVENT TIME: 19:15 VENDORS: W-4-LP W-4-LP NOTIFY DATE: 10-19-94 EMERGENCY CLASS: N/A REGION: 3 STATE: IL TIME: 23:00 OPS OFFICER: WILLIAM HUFFMAN 10 CFR SECTION: APRE 50.72(b)(2)(vi) OFFSITE NOTIFICATION UNIT SCRAM RX INIT INITIAL MODE CURR CURRENT MODE CODE CRIT PWR PWR 1 N N 0 COLD SHUTDOWN 0 COLD SHUTDOWN 2 N Y 99 POWER OPERATION 99 POWER OPERATION UNISOLABLE SULFURIC ACID TANK SPILL. AN UNISOLABLE LEAK DEVELOPED WHILE ATTEMPTING TO REPAIR A VALVE ON A SULFURIC ACID STORAGE TANK. THE TANK CONTAINED APPROXIMATELY 5000 GALLONS OF SULFURIC ACID WHEN THE LEAK OCCURRED. THE SULFURIC ACID LEAKED INTO A BERM SURROUNDING THE TANK AND ALSO LEAKED DIRECTLY INTO THE CIRCULATING WATER SYSTEM FLUME. THE LEAK STOPPED AT 2203 CDT WHEN MOST OF THE CONTENTS OF THE TANK DRAINED OUT. TWO CONTRACTORS WORKING ON THE TANK VALVE REPAIR WERE INJURED AND TRANSPORTED TO THE SAINT ANTHONY MEDICAL CENTER IN ROCKFORD, ILLINOIS. ABOUT 200 GALLONS OF SULFURIC ACID LEAKED PAST A FLANGE IN THE BERM ONTO THE GROUND COVERING ABOUT 70 SQUARE FEET OF AREA. THE REMAINING 4800 GALLONS LEAKED INTO THE CIRC WATER SYSTEM. CIRC WATER BLOWDOWN WAS SECURED AT 1940 CDT AND THE LICENSEE BELIEVES THAT THERE HAS BEEN NO RELEASE TO THE ENVIRONMENT. A HAZARDOUS MATERIAL EMERGENCY WAS DECLARED AT 2020 CDT AND THE SITE'S HAZARDOUS MATERIALS TEAM RESPONDED TO THE SCENE. ASSESSMENT AND CLEANUP OPERATIONS ARE BEING COORDINATED BY THE HAZMAT TEAM LEADER AND THE SITE CHEMIST. THE SPILL HAS HAD NO AFFECT ON PLANT OPERATIONS. NO SIGNIFICANT FUMES HAVE BEEN REPORTED AND THE REDUCED pH OF THE CIRC WATER SYSTEM WILL NOT CAUSE ANY CIRC WATER SYSTEM CONCERNS. OFFSITE NOTIFICATIONS TO FEDERAL(NATIONAL RESPONSE CENTER), STATE, AND LOCAL AUTHORITIES HAVE BEEN MADE. THE LICENSEE ANTICIPATES A PRESS RELEASE. THE NRC RESIDENT INSPECTOR HAS BEEN INFORMED. MILLSTONE 2 27930 10-20-94 POW LICENSEE: NORTHEAST UTILITIES SITE: MILLSTONE 2 EN NUMBER:27930 DOCKET: 05000336 EVENT DATE: 10-20-94 RX TYPE: PWR EVENT TIME: 03:23 VENDORS: CE NOTIFY DATE: 10-20-94 EMERGENCY CLASS: UNU REGION: 1 STATE: CT TIME: 03:41 OPS OFFICER: CHAUNCEY GOULD 10 CFR SECTION: AAEC 50.72(a)(1)(i) EMERGENCY DECLARED UNIT SCRAM RX INIT INITIAL MODE CURR CURRENT MODE CODE CRIT PWR PWR 2 N N 0 REFUELING 0 REFUELING THE PLANT DECLARED AN NOUE DUE TO HEIGHTENED AWARENESS BECAUSE OF A SERVICE WATER LEAK AFFECTING THEIR 120 VOLT DC. A SERVICE WATER LEAK ONTO THE ELECTRICAL SWITCHGEAR HAS CAUSED A GROUND ON A 120VDC VITAL BUS, WHICH THE LICENSEE IS PRESENTLY SEARCHING IN ORDER TO LOCATE AND ISOLATE. THE LEAK WAS ONTO A NON VITAL 4160 BUS WHICH HAS SINCE BEEN DE-ENERGIZED, BUT THIS DID NOT CLEAR THE GROUND ON THE 120VDC BUS. THE LEAK OCCURRED WHILE THE LICENSEE WAS SETTING UP AND DRAINING THE SERVICE WATER HEADER IN PREPARATION FOR SOME WORK. THE PLANT IS CURRENTLY STABLE AND HAS NO VITAL AC OUT OF SERVICE. THE RI WAS INFORMED ALONG WITH STATE AND LOCAL AGENCIES. ***UPDATE AT 05:28 ON 10/20/94 TO GOULD FROM BONNER*** THE VITAL DC BUS GROUND HAS BEEN ISOLATED. CAUSE OF GROUND IS STILL UNKNOWN.