1. Nuclear Power Plants
A Brief Overview

2. What We Use Them For Most Significant Current Use: Others Uses
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 Products< Mass of Original Atom
* Where is the mass that is unaccounted for?
Einstein’s E=MC2:
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?

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 1970’s
Four Reactors up and running by 1986

13. Chernobyl’s Reactor Design, the Meltdown, and Why it Occurred
The Specifics:
Chernobyl’s 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 reactor’s turbine to generate enough electricity to power reactor’s 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)

24. 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)