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Nuclear Power as a High Risk System And the Accident at Three Mile Island

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Nuclear Power as a High Risk System And the Accident at Three Mile Island Discussing Perrow Chapters 1 and 2 Presented by Gus Scheidt Friday the Thirteenth – PowerPoint PPT presentation

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Title: Nuclear Power as a High Risk System And the Accident at Three Mile Island


1
Nuclear Power as a High Risk System And the
Accident at Three Mile Island
  • Discussing Perrow Chapters 1 and 2
  • Presented by Gus Scheidt
  • Friday the Thirteenth
  • September 2002

2
Three Mile Island
  • Nuclear Plant near Harrisburg, Pennsylvania
  • March 28, 1979 -- Unit 2 near meltdown
  • U.S. most serious nuclear accident to date (1984)
  • Presented "to convey... the interconnectedness of
    the system, and the occasion for baffling
    interactions."

3
TMI Summary of Events
  • (Failure) condensate polisher system, part of
    secondary cooling system, leaked some water
  • (ASD) Feedwater pumps shut down
  • (ASD) Turbines stopped
  • (ASD) Emergency feedwater pumps started
  • Normally, problem would have been solved, but...

4
TMI Summary of Events
  1. (Failure) Valves in Emergency Feedwater system
    left closed by maintenance
  2. (Operator Error?) No one noticed the indicator
    signaling that the valves were closed
  3. (ASD) Reactor Scrammed
  4. (ASD) PORV (Pilot-Operated Relief Valve) briefly
    opened

5
TMI Summary of Events
  • (Failure) PORV failed to close
  • (Failure) PORV indicator malfunctioned
    operators thought PORV had closed
  • NOTE We are now only 13 seconds into the
    accident

6
TMI Summary of Events
  1. (ASD) Two reactor coolant pumps started
  2. Steam bubbles that resulted from loss of
    pressure caused false readings
  3. Pressure readings in core dropped sharply
  4. (ASD) HPI (High Pressure Injection) turned on
  5. (Operator Error?) After 2 minutes, operators cut
    back HPI

7
TMI as a System Failure
  • Pieces of TMI accident occur elsewhere in the
    industry just not all at once
  • Reactor (new/complex) engineered by one company
    system for drawing off heat (old/unsophisticated)
    by another
  • Tolerance for some components frighteningly small
  • Technology was new process not well understood

8
TMI as a System Failure
  • Parts of the reactor are interdependent
  • But not in direct operational sequence
  • The situation was incomprehensible to the
    operators working during the accident
  • So much known about failures of TMI Unit 2 only
    because of the accident
  • Why is this called a "Normal" Accident?

9
Nuclear Power as a High Risk System
  • We have not given nuclear power enough time to
    disclose its disastrous potential
  • We don't have enough experience to make a
    reasonable assessment of the risks

10
Tools for Examining High-Risk Systems
  • Operating Experience
  • The Construction Problem
  • Safer Designs?
  • "Defense in Depth"
  • Trivial Events in Nontrivial Systems
  • Learning from Our Mistakes
  • Fermi
  • The Fuel Cycle as a System

11
Operating Experience
  • Varying sizes and types of plants
  • Different manufacturers with different designs
  • Little industry learning time
  • Slow maturation of the industry

12
The Construction Problem
  • Lack of NRC engineers on site
  • "The builders can't pour concrete"
  • Intimidation of federal inspectors
  • Falsified safety inspection documents
  • Diablo Canyon -- Wrong diagrams

13
Safer Designs?
  • Government push for nuclear power adoption
  • There are other designs, but not significantly
    less complex, interactive, tightly coupled
  • We likely will not see safer designs in the near
    future
  • Under-utilization of current reactors
  • 10 years to design/build new facility

14
"Defense in Depth"
  • Containment buildings
  • Semi-Remote locations
  • ECCS (Emergency Core Cooling System)
  • Helpful, but the possibility of accidents that
    evade these defenses exist

15
Trivial Events in Nontrivial Systems
  • Everyday failures are significant if we add
    catastrophic potential
  • Shirt trips breaker -gt scram
  • Complex plumbing -gt radioactive water to drinking
    systems
  • Dropped light bulb -gt scram, almost cracked
    vessel meltdown
  • Faulty indicator -gt 9 feet of river water in
    containment building

16
Learning from Our Mistakes
  • We Don't
  • Nuclear Safety
  • Reports dozens of accidents, many near meltdown,
    to show how an excellent safety record... has
    been maintained
  • Two-thirds of the problems... are strikingly
    similar to ones previously reported.

17
Fermi
  • A safety device (piece of metal) dislodged by the
    coolant and blocked the flow of the coolant
  • Illustrates some of the principles in the book
  • Problem originated with a safety device
  • Poor design and negligent construction
  • No clear procedure to follow
  • Those attached to high-risk systems can be
    uncommonly cheerful about failures

18
The Fuel Cycle as a System
  • Mining uranium ore
  • Processing ore into fuel
  • Burning it in reactors
  • Disposing the many kinds of waste
  • All involve serious hazards

19
Conclusion
  • Design, construction, and operating problems do
    not, in themselves, cause system accidents
  • Rather, it is the potential of unexpected
    interactions of small failures that make the
    system prone to accident

20
Discussion
  • How do software systems, or software components
    of systems, compare to TMI?
  • How does TMI compare to Guam?
  • Given Guam and TMI, can we hypothesize some
    failure paradigms?
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