This document summarizes the timeline and root cause analysis of an accident at a nuclear power plant. Turbine blades failed due to accumulated stress, rupturing hydrogen seals and lubricating oil lines. This caused a fire that spread through generator bus ducts and power cables, damaging the control equipment room over several minutes. The complete loss of Class I and II power supply required emergency procedures including manual reactor shutdown, boron injection, and use of diesel generators to power secondary systems and remove decay heat. The root causes were identified as lack of consideration for turbine blade dynamics, inadequate backup power systems, and lack of fire-resistant cabling and barriers.

1. By-DIVYA DEEPAK M.Engg-Mechanical Engg(University of Windsor)

8. TIME EVENT 0 Turbine trip 72 ms UT-1 breaker trip 105 ms Generator Tranformer-1 breaker trip 117ms Main generator-1 field breaker trip 140 ms 6.6kv bus section breaker trip 38.512s Reactor trip manually 38.592s PSS got actuated 3M 0.247s Power MG-2 breaker trip 4M 54.552s Control MG-1 breaker trip 5M 47.942s Manual crash cool down initiated 5M 47.957s SSS got actuated 6M 47.862s All PHT pumps tripped-complete loss Of class-IV supply 7M 4.347s Complete MG-3 breaker trip, Complete loss of control power supply

9. 7M.39.228 SEC Control MG3 breaker trip (complete loss of Control Power Supply) About 8 Min PLANT EMERGENCY DECLARED 10 Min Two diesel driven fire water pumps started 1 Hr. 30 Min Fire was extinguished in ground and mezzanine floors on TB 2 Hr. 10 Min Boron poison added through GRABS ABOUT 3 Hr. 50 Min Both diesel driven fire water pumps tripped 4Hr. 25 Min First entry to reactor building by the operating staff 4 Hr. 25 Min PHT pressure noted as 42 Kg/cm 2 from master gauge at E1.103M 4 Hr. 35 Min Fire water hose connected to the end shield system 5Hr. 35Min One fire water pump restarted at T=5hrs.35mins , cooling to end shields provided in addition to putting water to steam generators. 5Hr. 35Min D.G #3 was started 6Hr. 00Min Class Bus Q was charged 7Hr. 00Min End shield metal temp 70-80 deg C 7Hr. 30Min End shield metal temp. 70-80 deg C

10. 9Hr. 10Min PHT pressure noted to be 2 KG/cm2 9Hr. 30Min Active HPPW started 3335-MW-15 &16 (D2O accumulator outlet valves) found in nearly closed position 10Hr. 00Min Instrumented IRVs closed manually 13Hr. 10Min control room made habitable 13Hr. 30Min 5.5 Te of D2O from accumulator was taken into PHT system. (System pressure increased to 5 Kg/cm2) 15Hr. 50Min Environmental survey showed normal radiation fields 17Hr. 05Min Shutdown cooling pump #2 was started 17Hr . 45Min FM supply pump #2 was started and PHT system pressure increased to 31 Kg/cm2 19Hr. 15Min Plant Emergency Lifted 20Hr and beyond Moderator pump, end shield recirculation pump, PC ventilation fan, Purge dryer fan started

15. TIME LINE EVENT CAUSE REASON FOR OCCURANCE OF THE EVENT 0 m.s Rupture of turbine blades ROOT CAUSE Accumulated Stress 38 sec Rupturing of hydrogen Seals CONTRIBUTING CAUSE Vibrations in the Generator Unit 40 sec Rupturing of lube oil lines CONTRIBUTING CAUSE Vibrations in the Generator Unit 1M 20sec Fire spread through the generator bus duct in the Turbine Building (TB) and through cables into the Control Equipment Room (CER) DIRECT CAUSE Lubricating oil as a medium of transport 3M 24sec Power cables Burning ROOT CAUSE Lack of fire resistant insulation Negligence of the organization ROOT CAUSE …………………… ..