Jyh-Tzong Hwang Section Chief Department of Nuclear Regulation Atomic Energy Council Follow Up Measures for Maanshan Unit 1 Station Blackout Incident

Table of Contents 1. Maanshan Baseline Information 2. Major Causes of the Incident 3. Root Cause Analyses for the Breaker Failure 4. Root Cause of the Electric Magnet Valve Failure 5. Other Follow Up Measures

Locations of the Nuclear Power Plants in Taiwan MS (951*2) LM (1350*2) CS (636*2) KS (985*2)

Maanshan Baseline Information 。 Two units PWR plant; rated electric power: 951MWe per unit 。 NSSS Vendor: Westinghouse 。 Architect Engineer: Bechtel 。 Commercial Operation: (unit 1); (unit 2)

Front View of Maanshan Nuclear Power Plant

。 Degradation of the breaker No 17 incoming side insulation induced arching fire at the essential bus A. After the arcing occurred, there was a problem of grounding in the bus and caused the loss of offsite power to both of the essential buses. 。 Train A of the EDG was successfully started, but can not supply power to essential bus A because of the bus grounding failure. Train B of the EDG had problem of loss of excitation and can not generate power. Major Causes of the Incident

Emergency Startup XTR VVVVVV VV VVVVVV VV 4.16 KV Nonessential Bus KV Essential Bus A 4.16 KV Essential Bus B X3 EDG A Swing EDG X3 VVVV VV Gas Turbine × KV Bus C 13.8 KV Bus B13.8 KV Bus A Startup XTR Main XTR X3 To Unit 2 Aux XFR VV VVVV X3 VVVVVV VV VVVVVV VV Unit 1 Main Gen To Unit 2 VVVVVV Darpeng 1 Darpeng 2 Lungchi (sea-side) Lungchi (mountain-side) Bus 1 Bus KengtingFengkang KV Bus 25 EDG B 00 ： 08 Trip 00 ： 41 大鵬 一路 跳脫 00 ： 41 Trip Switching from 345KV to 161KV ： 41 大鵬 一路 跳脫 00 ： 45 Re- covered 00 ： 、 3510 Trip X KV Nonessential Bus Aux XFR Emergency Startup XTR 161 KV Transmission Line 345 KV Transmission Line

1. Possible reasons for the breaker insulation degradation are : 。 Ferro-Resonance of 345 KV transmission line induced voltage shock. 。 Instability of the offsite 345 KV power system induced voltage shock. 2. The reason for EDG B loss of excitation was judged to be the sluggish actuation of the electric magnet valve. Major Causes of the Incident (Continued)

345 KV Start-up Transformer 4.16 KV Bus Breaker No.17 Maanshan Plant 345 KV Lungchi Line SwitchyardLungchi End RCP 4.16 KV 13.8 KV Ferro-Resonance of 345 KV Transmission Line

Offsite Power Situation before the Incident

Insulator Maanshan 345 KV Offsite Power Transmission Line

Root Cause Analyses for the Breaker Failure 。 A simulation of the Ferro-Resonance of the 345 KV transmission line is under going to evaluate its effects to the breaker insulation. 。 The flywheel motion of the reactor coolant pumps induced reverse power to the 345KV system will also be included in the Ferro-Resonance simulation.

Root Cause Analyses for the Breaker Failure (Continued) 。 Early analysis by using Electro Magnetic Transient Program (BMTP) indicated that the 345 KV transmission line breaker switching effect would induce a voltage shock ranging from 7 KV to 9 KV to the Maanshan 4.16 KV essential bus. 。 However, recent analysis by refining the input conditions showed that the voltage shock induced by switching effect is below 7 KV. 。 An independent simulation is under going to evaluate the transmission line breaker switching effects.

Root Cause of the Electric Magnet Valve Failure 1. Electric Magnet Valve141-2A 。 Aging induced degradation of the rubber seat and O- ring of the plunger 2. Electric Magnet Valve142-2B 。 Aging induced open circuit of the coil 3. Corrective Action 。 Replace the electric magnetic valves every 5 years

PS-32A1PS-32B 142-2B 141-2A 60 PSI Air Control Air 142-2B failed before the incident 141-2A sluggish actuation during the incident EDG B Emergency Startup Control Circuit

Plunger Deformation of the Rubber Gasket at the Air Inlet O-Ring Oily Gasket Oily Internal Components Dusty Air Outlet Root Cause of Electric Magnet Valve 141-2A Failure

Open Circuit of the Coil Hardening of the Lead Root Cause of Electric Magnet Valve 142-2B Failure

Other Follow Up Measures 1. Prevention for the Occurrence of the Ferro-Resonance 。 Automatic Trip Function of the Switch Yard Offsite Power Supply Breaker 。 Protection Relay for RCP Flywheel Motion Induced Reverse Power 2. Re-Evaluation of Electrical System Coordination Study 3. Replacement of Potential Degraded Insulation Breakers 4. Shorten Swing EDG Connection Time to Essential Bus

Other Follow Up Measures (Continued) 5. Alternatives to Supply Electrical Power to Plant Systems under Abnormal Conditions 6. Re-evaluation of Turbine Driven Auxiliary Feed Water Pump Startup Logic 7. Evaluation of the Capability of Fire Door to Cope with the Arcing Fire Induced Pressure Wave 8. Simulation of the Incident for Experience Feedback and Operator Training