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Three Mile Island

Three Mile Island. Events Briefing and Results. General Information. Most serious nuclear accident in U.S. History No deaths or injuries to plant workers or member of nearby communities Caused shutdown of nuclear power plant construction in the U.S. Schedule of Events.

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Three Mile Island

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  1. Three Mile Island Events Briefing and Results

  2. General Information • Most serious nuclear accident in U.S. History • No deaths or injuries to plant workers or member of nearby communities • Caused shutdown of nuclear power plant construction in the U.S.

  3. Schedule of Events • It’s 4:00 a.m. on 28 March 1979 at TMI # 2 • Main feedwater pumps stop • Steam generator cannot remove heat from the reactor • The turbine, then then reactor shut down • Pressure in reactor vessel increases • Pilot-operated relief valve (PORV) opens

  4. Schedule of Events • Continued …. • PORV does not close when pressure decreases • Instruments showed valve still open • Cooling water pours out and core begins to overheat • Instruments provide confusing information

  5. Schedule of Events • Continued …. • Technicians shut off cooling water to the reactor • Nuclear fuel begins to overheat • Zirconium cladding ruptures on control rods • Nuclear fuel pellets begin to melt • Zirc-water reaction begins to occur, causing hydrogen bubble to form at top of reactor vessel

  6. What Caused this Event? • A combination of • Personnel error • Design deficiencies • Component failures

  7. Major Changes After TMI • Upgrading and strengthening of plant design and equipment requirements • Identifying human performance as critical; improved operator training • Improved instruction to avoid confusing signals

  8. Major Changes After TMI • Immediate NRC notification of all events 24/7/365 • Improved NRC licensing requirements • Expansion of NRC inspector program

  9. Major Changes After TMI • Expansion of performance and safety inspections • Separate enforcement office in NRC • Established Institute of Nuclear Power Operations (INPO), the nuclear powers “policing” group.

  10. Major Changes After TMI • Installation of additional safety and radiation equipment • Identification and sharing of all safety related problems • Expansion of NRC’s international activities to share knowledge

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