1. 23.4 Nuclear energy NUCLEARNUCLEAR POWERPOWER Millstone Station

2. 23.4 Nuclear energy U.S. Nuclear Power Plant Locations

3. 23.4 Nuclear energy Nuclear fission heavy nuclei split into two smaller parts  Nuclear fission: heavy nuclei split into two smaller parts in order to become more stable  Releases a huge amount of energy proton neutron U-235 nucleus Kr-90 nucleus Ba-144 nucleus energy

4. 23.4 Nuclear energy Nuclear chain reaction- a reaction sustained by its products  Neutrons released in fission  Neutrons released in fission act as reactants to split more nuclei proton neutron U-235 nucleus

5. 23.4 Nuclear energy Critical Mass- minimum amount of fissionable material needed to maintain a chain reaction Sub-critical mass Above critical mass, chain reaction!

6. 23.4 Nuclear energy The chain reaction is not slowed down a huge amount of energy is released very quickly the rate of fission increases rapidly Nuclear bomb Uncontrolled nuclear reaction

7. 23.4 Nuclear energy Nuclear reactors  Nuclear power plant: rate of fission is controlled by artificial means to generate electricity  Only 3% of fuel rod uranium is fissionable  Enough for chain reaction; not enough to explode Millstone Nuclear Power Station located in Waterford, CT

8. 23.4 Nuclear energy Schematic diagram of a nuclear plant control rods fuel rods reactor pressure vessel water (cool) water (hot) water (high pressure) water (low pressure) coolant out coolant in steam condenser steam (low pressure) turbine electric power steam generator steam (high pressure) pump primary loop secondary loop generator reactor core pump

9. 23.4 Nuclear energy control rods reactor pressure vessel water (cool) water (hot) water (high pressure) water (low pressure) coolant out coolant in steam condenser steam (low pressure) turbine electric power steam generator steam (high pressure) pump primary loop secondary loop fuel rods  They contain the nuclear fuel: uranium (U-235) moderator (water or graphite) slow down the neutrons released.  They are surrounded by a moderator (water or graphite) to slow down the neutrons released.

10. 23.4 Nuclear energy

11. control rods reactor pressure vessel water (cool) water (hot) water (high pressure) water (low pressure) coolant out coolant in steam condenser steam (low pressure) turbine electric power steam generator steam (high pressure) pump primary loop secondary loop fuel rods  They control the rate of reaction by moving in and out of the reactor. Move in: rate of reaction  Move out: rate of reaction  All are moved in: the reactor is shut down absorb neutrons.  They are made of boron 硼 or cadmium 鎘 that can absorb neutrons.

12. 23.4 Nuclear energy control rods reactor pressure vessel water (high pressure) water (low pressure) coolant out coolant in steam condenser steam (low pressure) turbine electric power pump primary loop secondary loop fuel rods  The energy released in fissions heats up the water around the reactor.  The water in the secondary loop is boiled to steam  The water in the secondary loop is boiled to steam. water (hot) water (cool) steam generator steam (high pressure)

13. 23.4 Nuclear energy steam generator control rods reactor pressure vessel water (high pressure) water (low pressure) coolant out coolant in steam condenser steam (high pressure) pump primary loop secondary loop fuel rods  The steam drives a turbine, which turns the generator.  Electricity is produced by the generator. water (hot) water (cool) steam (low pressure) turbine electric power generator

14. 23.4 Nuclear energy control rods fuel rods reactor pressure vessel water (cool) water (hot) water (high pressure) water (low pressure) coolant out coolant in steam condenser steam (low pressure) turbine electric power steam generator steam (high pressure) pump primary loopsecondary loop  Two separate water systems  Two separate water systems are used to avoid radioactive substances to reach the turbine.

15. 23.4 Nuclear energy Nuclear wastes  highly radioactive  have very long half-lives (thousands of years)  Radioactive waste must be stored carefully. Radioactive Decay- spontaneous process of an atom changing into another atom by emitting a particle and/or energy Half Life- time needed for one-half of a sample to decay

16. 23.4 Nuclear energy Bismuth has a half-life of 5 days What % of bismuth is present after 5 days? 20 days? How many grams are present after 5 days? 10 days? With each half-life, what happens to the amount of radioactive material remaining? Decreases by ½

17. 23.4 Nuclear energy Low level radioactive waste  cooling water pipes, radiation suits, etc.  stored in storage facilities  radioactivity will fall to a safe level after 10 to 50 years.

18. 23.4 Nuclear energy  used nuclear fuel  highly radioactive  embedded in concrete and stored deep underground for several thousand years  Proposed storage sites in Yucca Mountain, Nevada High level radioactive waste:

19. 23.4 Nuclear energy

20. Nuclear fusion  Nuclear fusion: light nuclei fuse together to form a heavier nucleus proton neutron helium nucleus neutron energy deuterium nucleus tritium nucleus H-2 + H-3  He-4 + n + energy

21. 23.4 Nuclear energy  They must have enough kinetic energy to overcome the electrical repulsion.  Very high temperature (about 10 7 K) is required to start a nuclear fusion. Atomic nuclei are positively charged and repelled each other. How can two nuclei fuse together?

22. 23.4 Nuclear energy  The temperatures inside the Sun and the stars reach such high temperature.  Inside the Sun, 657 million tons of hydrogen undergo fusion to form helium each second.

23. 23.4 Nuclear energy  Man-made uncontrolled fusion was first achieved in 1952, during the explosion of the first hydrogen bomb.  Controlled fusion is still under investigated by scientists.  No one has succeeded in yielding a net surplus of energy from fusion reactors.

24. 23.4 Nuclear energy  Unlimited supply of fuel for fusion reactors. We can get hydrogen from water. We can get hydrogen from water.  Little problem on disposal of radioactive waste. The end products of fusion are generally stable and not radioactive. The end products of fusion are generally stable and not radioactive. What are the advantages of fusion power?