1. What are fission and fusion? What fuels a nuclear reaction?
Nuclear Powerplants
What are fission and fusion?
What fuels a nuclear reaction?

2. So how do we use the heat of fission to boil water, make steam, spin a generator, and make electricity?
The Harnessed Atom
Atoms and Isotopes

3. Today’s Topics Nuclear Reactors Using heat to generate electricity
Fueling the reaction
Controlling the reaction
Moderator and coolant
Pressure vessel
Using heat to generate electricity
Heat transfer
Types of nuclear powerplants
Safety is built in to nuclear powerplants
Layers of containment
Engineered safety systems
Monitoring system
Workers contribute to safety
Nuclear Regulatory Commission
The Harnessed Atom
Atoms and Isotopes

4. The Reactor The heart of the nuclear powerplant is the reactor.
The reactor is made up of 4 parts:
Fuel assemblies
Control rods
Coolant/moderator
Pressure Vessel
These 4 parts are all contained in the containment structure
The Harnessed Atom
Atoms and Isotopes

5. Fuel Assemblies Uranium pellets Fuel Rods Fuel assemblies
are stacked together into…
Fuel Rods
which are bundled together into…
Fuel assemblies
The Harnessed Atom
Atoms and Isotopes

6. Balancing the Reaction
Reproduction constant (K).
The average number of neutron released from each fission event (the splitting of one atom).
K = 1:
For a chain reaction to sustain itself, at least one neutron from each fission event must strike another nucleus and cause a new fission event.
The reactor is considered critical. The reaction rate and the temperature will remain stable.
The Harnessed Atom
Atoms and Isotopes

7. Balancing the Reaction
K < 1:
The chain reaction will fade out.
Reactor considered subcritical
K > 1:
More than 1 neutron per event are causing subsequent fission
The reactor is supercritical
The rate of reaction and the temperature in the core will increase
The Harnessed Atom
Atoms and Isotopes

8. Chain Reactions In a chain reaction, each uranium atom that splits
releases 2 or 3 additional neutrons.
The Harnessed Atom
Atoms and Isotopes

9. Chain Reactions
Inside a reactor, control rods capture the additional neutrons to control the reaction and maintain a steady rate of fission.
The Harnessed Atom
Atoms and Isotopes

10. Control Rods
Main purpose: to absorb neutron and slow down the chain reaction
Made of cadmium or boron
The atomic structure of these elements allow them to work like sponges to absorb neutrons
The Harnessed Atom
Atoms and Isotopes

11. Control Rods
Lowering the control rods into the reactor allows them to absorb more neutrons
Raising the control rods out of the reactor keeps them from absorbing as many neutrons
The Harnessed Atom
Atoms and Isotopes

12. Coolant and Moderator
Water slows down the neutron, so that they can be “caught” by other atoms or by control rods
Water also absorbs the heat generated by the reactions
The Harnessed Atom
Atoms and Isotopes

13. Pressure Vessel Encases fuel, control rods, and coolant/moderator
Massive steel walls 23 cm (9 in.) thick, and it often weighs more than 270,000 kg (300 tons).
Tremendous strength to withstand high temperature and high pressure
The Harnessed Atom
Atoms and Isotopes

14. Heat Transfer Heat produced by fission reaction is absorbed by water
Water has high specific heat
It can absorb more heat than other materials without its temperature changing as much
The Harnessed Atom
Atoms and Isotopes

15. Heat Transfer Heat absorbed in water is used to create steam
Steam is used to spin a turbine…
The Harnessed Atom
Atoms and Isotopes

16. Pressurized Water Reactor
Loop 2
Loop 3
Loop 1
PWRs keep water in the reactor under pressure so that it can not boil.
Three loops of water keep the water from the reactor and water in the steam generator from ever mixing.
The Harnessed Atom
Atoms and Isotopes

17. Boiling Water Reactor
In BWRs a single loop both delivers steam to the turbine and returns water to the reactor core to cool it.
Another loop contains the cooling water.
The Harnessed Atom
Atoms and Isotopes

18. Cooling the Water
Water is cooled so that it can be recycled through the powerplant to absorb heat again
The Harnessed Atom
Atoms and Isotopes

19. Cooling Towers
Not all cooling towers look like tall hyperbolic cylinders:
Mechanical Draft cooling towers:
The Harnessed Atom
Atoms and Isotopes

20. Layers of Safety
Ceramic fuel pellets provide a stable solid form for fuel.
Fuel rods made of strong “zircaloy.” This helps fission products from leaking.
Pressure vessel, with its 9-inch-thick steel walls, holds radioactive materials within the reactor core.
The Harnessed Atom
Atoms and Isotopes

21. Layers of Safety
Containment building, a massive concrete and steel structure that encases the reactor
Prevent radioactivity from being released into the environment if an accident should occur
Reactor containment buildings are among the strongest structures in the world
The Harnessed Atom
Atoms and Isotopes

22. Monitoring Systems
The Harnessed Atom
Atoms and Isotopes

23. NRC Nuclear Regulatory Commission
Regulates civilian use of nuclear materials
Nuclear powerplants
Medical and industrial uses
Research sites
Nuclear waste
All facilities must be licensed by this agency
The Harnessed Atom
Atoms and Isotopes

24. Other Types of Nuclear Powerplants
The Harnessed Atom
Atoms and Isotopes

25. Words to know Boiling‑water reactor Chain reaction Condenser
Control rods
Convective cooling
Coolant
Cooling tower
Critical
Fission
Fission event
Fuel assemblies
Fuel rods
Heat transfer
Heavy water
Laws of Thermodynamics
Light water
Moderator
Monitoring
Multiplication factor
Nuclear Regulatory Commission
Pressurized‑water reactor
Reactor vessel
Redundancy
Specific heat
Subcritical
Supercritical
The Harnessed Atom
Atoms and Isotopes

26. Reactor Designs

27. The Reactor The reactor is the heart of the nuclear powerplant.
These designs are innovative variations on fuel and coolant
Oddly, they aren’t new—they were developed in the 1940s and 50s by the clever young physicists who worked out the first designs

28. Light Water Reactors

29. Pressurized Water Reactor
Use light (regular) water as a moderator & coolant
Use slightly enriched uranium … 4% U-235

30. Boiling Water Reactor
Also a LWR (regular water), but with only 2 loops
Otherwise, pretty much the same technology

31. Breeder Reactors

32. Breeder Reactor U-238 Blanket
Blanket of U-238 surrounds U-235 or Pu-239 fuel to “breed” plutonium using neutrons
Coolant is liquid metal (sodium) so neutrons stay “fast”

33. High Temperature Gas-Cooled Reactors

34. High Temperature Gas Cooled Reactor
Uses U-235 or Pu-238 fuel in a graphite moderator
Instead of water for coolant, it uses helium gas

35. Very High Temperature Gas Cooled Reactor (Advanced Pebble Bed)
Uses U-235 dioxide or carbide fuel pebbles instead of rods
Uses helium gas as coolant at temperature of 1000°C
Can be designed as a breeder reactor

36. Heavy Water Reactors

37. CANDU
Canadian Deuterium reactor uses natural un-enriched uranium fuel (0.7%).
Sub-critical, so it needs heavy water Du2O to reflect neutrons to sustain reaction

38. Research and Special Purpose Reactors

39. MIT Research Reactor MITR-II
Actually a LWR, uses high-enriched uranium fuel
But also sub-critical, so it uses heavy water reflector around the outside to reflect neutrons back in to sustain reaction

40. Molten Salt Reactor
Uses dissolved UF4 in molten fluoride salt or sodium—the coolant and the fuel are mixed together
Circulates the “liquid” fuel to the graphite core where it becomes critical

41. Naval Propulsion Reactor
Miniature PWR
Uses high-enriched U-235 fuel

42. Production Reactor Hanford B Reactor Graphite core, breeds Pu-239
Weapons production for national defense

43. Graphite Reactor Graphite Reactor Oak Ridge 1943-60s
Built of blocks of graphite with U-235 fuel
Used for research and plutonium production

44. Swimming Pool Reactor Reactor sits in a pool of water
High Flux Isotope Reactor
HFIR
Oak Ridge
Reactor sits in a pool of water
Used for research and medical isotope production