Actinide Behaviour during Severe Nuclear Accident Three Mile - - PowerPoint PPT Presentation

Actinide Behaviour during Severe Nuclear Accident – Three Mile Island

Andriy Sizov, PhD, Senior researcher/Technical Expert Institute for Safety Problems of NPPs/ENCO

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TMI

• Middletown, Pennsylvania
• May 1968 Three Mile Island (TMI) Unit 1

Construction began

• November 1969 TMI Unit 2 Construction began
• Unit 1 began operation in September 1974
• Unit 2 started up in December 1978
• Within 90 days, on March 28, 1979, a nuclear meltdown
• ccurred in TMI 2
• A non-nuclear failure led to a nuclear meltdown
• Worst accident at a nuclear power plant in the

history of U.S. commercial power plants

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Location

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Three Mile Island NPP

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Reactor

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Sequence

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Sequence 2

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Sequence 3

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Sequence 4

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Sequence 5

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Sequence 6

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Sequence 7

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Actions

Physical and Chemical processes during the accident

• Phase 1 of the accident: LOCA (estimated duration 100 minutes)
• Phase 2 of the accident: core heating with the RCS and high-

pressure SIS shut down (from 100 minutes to 174 minutes)

• Phase 3 of the accident: partial reflooding of the core - formation of

a debris bed (between 174 and 180 minutes)

• Phase 4 of the accident: heating of the debris bed – development of

the corium pool (between 180 and 200 minutes)

• Phase 5 of the accident: total reflooding of the core - continued

development of the corium pool (between 200 and 224 minutes)

• Phase 6 of the accident: movement of core materials towards the

reactor vessel’s lower plenum (between 224 and 226 minutes)

• End of the accident: restoration of stable cooling (to 16 hours after

the start of the accident)

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Phase 1.

Phase 1 of the accident: LOCA (estimated duration 100 minutes). Assumed state of the core after lower crust formation.

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Phase 2.

Phase 2 of the accident: core heating with the RCS and high- pressure SIS shut down (from 100 minutes to 174 minutes). Dose rate alarm. Relief valve is closed. Assumed state of the core 174 minutes after the start of the accident.

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Phase 3.

Phase 3 of the accident: partial reflooding of the core (23 m3)- formation of a debris bed (between 174 and 180 minutes).

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Phase 4 and 5.

Phase 4 of the accident: heating of the debris bed – development of the corium pool (between 180 and 200 minutes). Reopening pressurizer relief valve. Emergency situation declared. Phase 5 of the accident: total reflooding of the core

• continued development of

the corium pool (between 200 and 224 minutes) SIS is restarted.

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Phase 6.

Phase 6 of the accident: movement of core materials towards the reactor vessel’s lower plenum (between 224 and 226 minutes). Crust rupture.

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End state.

End of the accident: restoration of stable cooling (to 16 hours after the start of the accident). Hydrogen combustion occurred 9 hours 30 minutes after the start of the accident.

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Decontamination and Defueling

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Why can it be dangerous? China syndrome

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Environmental/Public Health Consequences

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• No fatalities or injuries
• Radiation exposure ~ 0.3 - 0.6 rem
• No conclusive evidence for an increase in

cancer cases

• Unit 2 not allowed to resume operation
• Unit 1 not allowed to resume operations until 1985
• General Public Utilities paid $82 million as compensation
• Negative media coverage
• Property values dropped
• Mistrust of Nuclear Industry
• Loss of income for surrounding farms

Environmental/Public Health Consequences

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Consequences of the accident: comparison with Chornobyl and Fukushima

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• New Regulations
• Inherently Safer Design and Operation
• Emphasis on Training and Transparency
• Expect the Unexpected (PSA). More

severe accidents than a LOCA

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Lessons Learned

The PHEBUS FP programme

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References / Useful Links

• Missouri University of Science and Technology

http://web.mst.edu/~dludlow/classes/ChE%20285%20S p12/Three%20Mile%20Island.pptx

• Nuclear Power Reactor Core Melt Accidents. Current

State of Knowledge. IRSN 2015

• Three Mile Island Nuclear Accident. March 28, 1979 at

Three Mile Island, Pennsylvania, USA. Failure Knowledge Database

• Three Mile Island Accident of 1979 Knowledge

Management Digest. Overview. NUREG/KM-0001, Revision 1. Office of Nuclear Regulatory Research

• Backgrounder on the Three Mile Island Accident

https://www.nrc.gov/reading-rm/doc-collections/fact- sheets/3mile-isle.html

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Thank you for your attention.

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