Nuclear Power Plants

1
Nuclear Power Plants

• A Brief Overview

2
What We Use Them For

• Most Significant Current Use
• Nuclear Power (Generation of Electrical Power)
• Others Uses
• Nuclear Propulsion (in devices such as rockets)
• Transmutation of Elements (production/creation of
  Plutonium/other radioactive isotopes for uses
  such as radiation therapy)
• Research/Technology (neutron and positron
  radiation)

3
Nuclear Power Plants Around The World
4
Map of Site
5
Nuclear Reactor Designs

• Thermal (slow) Reactors
• Use slow neutrons b/c they have higher
  probability of fissioning U-235
• Have moderator, fuel, containments, pressure
  vessels, shielding, instrumentation to
  monitor/control systems of reactor
• Three Types
• pressurized fuel channels, large pressure
  vessel, gas cooling

• Fast Reactors
• Use fast neutrons to sustain chain reaction
• Do not have moderating material
• Require heavily enriched fuel/ Plutonium to
  reduce amount of U-238 that would normally absorb
  fast neatrons

6
Various Types of Nuclear Reactors

• Pool-type Reactor
• Pressurized Water Reactor
• Boiling Water Reactor
• Fast Breeder Reactor
• Pressurized Heavy Water Reactor
• Magnox Reactor
• Advanced Gas-Cooled Reactor
• Light-Water Cooled Graphite Moderated Reactor
  (RBMK)
• Aqueous Homogenous Reactor
• Liquid Fluoride Reactor

7
The General Nuclear Fuel Cycle

• NUCLEAR FISSION
• Heavy Atom? Splits?Total Mass of Smaller
  Productslt Mass of Original Atom
• Where is the mass that is unaccounted for?
• Einsteins EMC2
• mass difference ? converted to ? energy

8
Nuclear Fission
9
Nuclear Fission in Reactors and Generation of
Electricity

• Fuel (type of Uranium or sometimes Plutonium)
• Nuclear fission occurs when a heavy nucleus is
  struck by a neutron and is divided into two
  smaller nucleuses as well as extra neutron
• This starts the chain reaction of nuclear fission
  and is the basis for nuclear energy

10
Nuclear Fission (Cont.)

• If the stable atom of Uranium-235 is converted to
  the unstable U-236 by adding a neutron, it
  immediately begins to decay by splitting into
  smaller atoms and it releases energy.
• Chain Reaction
• Each time an atom breaks apart and gives off
  neutrons, those neutrons fly into other U-235
  atoms and cause them to decay
• Most neutrons move too quickly and simply bounce
  off the heavier atoms, so a coolant is introduced
  to slow them down and continue the chain reaction

11
Chernobyl Nuclear Power Station When, Where, and
Why Was it Built?
http//video.google.com/videoplay?docid-401766423
4059701260qchaes
12
V.I. Lenin Memorial Chernobyl Nuclear Power
Station

• Located in Prypiat, Ukraine, 18 kilometers
  Northwest of Chernobyl, very lose to border of
  Ukraine/Belarus
• Increase in electricity demand? generation of new
  power plants
• Construction began in 1970s
• Four Reactors up and running by 1986

13
The Specifics Chernobyls Reactor Design, the
Meltdown, and Why it Occurred
14
The Reactors

• Four RBMK-1000 reactors in use that each produced
  1 GW of electric power, Two more under
  construction
• RBMK-1000 Reactor Design
• reaktor bolshoy moshchnosti kanalniy
• Type of graphite-moderated nuclear power reactor
• Built only in Soviet Union

15
RBMK-1000 Design
16
What Makes the RBMK Reactor Unlike ANY Other
Fission Reactor?

• It uses neutron-absorbing light water (as
  opposed to hard water for cooling and fixed
  graphite for moderating (combination of graphite
  moderator and water coolant is not found in any
  other reactors)
• Based on design intended to produce plutonium
  (for weapons)
• Ability to refuel without shutting down reactor
• Positive void coefficient
• Can use natural Uranium for fuel as opposed to
  enriched Uranium
• These factors make a large reactor possible,
  however, they also make it very unstable,
  especially at low power levels

17
RBMK Reactor How it Functions

• Powered by slightly enriched uranium dioxide fuel
  pellets (U-235)
• Uses solid graphite to slow down neutrons
• Fuel rods arranged cylindrically to form fuel
  assembly, and two fuel assemblies are stacked on
  top of each other and placed in individual
  pressure tubes (allows reactor to be refueled
  while running)
• Graphite blocks between pressure tubes act as
  moderators

18
RBMK Reactor How it Functions (Cont.)

• Boron Carbide Control Rods control reaction
• Water is pumped through each pressure tube,
  allowed to boil, and drives the turbines

19
The Meltdown

• What Happened?

20

• Reactor Number 4 was scheduled to be shut down
  for maintenance which gave rise to
• Opportunity to test ability of reactors turbine
  to generate enough electricity to power reactors
  safety systems in case outside electric power was
  lost
• AIM/ GOAL OF TEST ? TO DETERMINE WHETHER THE
  TURBINES IN THE RUNDOWN PHASE COULD POWER PUMPS
  WHILE GENERATORS WERE STARTING UP
• Test not able to be carried out during day, so it
  was left for underqualified night crew

21

• Electricity to water pumps shut off
• ? Water flow rate decreased
• 2. Turbine disconnected from reactor
• ?Increased level of steam in reactor core
• Coolant heated, steam formed voids in coolant
  lines
• ?Power of Reactor Increased Rapidly
• All control rods fully inserted to shutdown the
  reactor
• ?Slow speed of control rod insertion mechanism
  caused reaction rate to increase
• ?Deformation of Control Rod Channels
• ? Control Rods stuck, reaction unable to be
  stopped

22
5. Fuel Rods melted, steam pressure
increased ?HUGE steam explosion 6. Steam
travelled up control rod channels ?displaced and
destroyed reactor lied, ruptured tubes, blew
HOLE in roof 7. Oxygen rushing in high
temperature of reactor fuel and graphite
moderator ?graphite fire
23
A Scram

• In an emergency, a set of control rods that can
  be inserted into the core to absorb the neutrons
  are dropped to stop the reaction completely
• Coolant is circulated around core to extract heat
  and becomes highly radioactive
• In the RBMK reactor, the primary coolant is
  boiled within the reactor to produce steam
  directly
• Assembly housed in concrete containment building
  (only PARTIAL containment)

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WHY?
25

• Design Theory (Flaws in Design)
• Large positive void coefficient (produces more
  energy as it gets hotter, unlike most reactor
  designs which are exact opposite)
• Graphite tipped control rods (at time of initial
  insertion, graphite ends displace coolant, which
  greatly increases rate of fission reaction)
• Temperature gradient in core (uneven temperature
  distribution, not all parts of core temp, being
  evenly moderated)
• Only Partial Containment

26

• Operator Theory
• Operators careless and violated plant procedures
• Operators not informed by designers of dangerous
  conditions for reactor
• Operators lacked proper experience/training
  (Non-RBMK-qualified personnel on duty at time of
  test)
• Insufficient communication between safety
  officers and operators (in charge of experiment
  being run that night)