1. NUCLEAR ENERGY: FISSION CONVERSION OF MASS TO ENERGY = mc 2

2. Nuclear Fission (1) Neutron + Radioactive Heavy Nucleus  Stable Lighter Nuclei + ENERGY 1 0 n + 235 92 U  142 56 Ba + 91 36 Kr + 3 1 0 n This is one fission pathway for U-235. There are nearly 400 fission pathways for U-235. τ 1/2 = 7.04E+8 yrs. Sum of mass number and sum of atomic number must be conserved. Note Ex.17.4

3. Prentice Hall Slide

4. Nuclear Fission (2) 1 0 n + 235 92 U  142 56 Ba + 91 36 Kr + 3 1 0 n The 3 product neutrons can induce 3 more fission rxns. These 3 rxns can cause 9 more fission rxns. This is called a Chain Reaction If amt of U-235 is large enough (critical mass = 56 kg), the chain rxn can be self- sustaining. I.e. an external neutron source is not needed.

5. Nuclear Fission (3) U-235 is naturally occurring in UO 2 ores at 0.7% abundance level. It is the only isotope of U that can undergo fission. In a controlled fission rxn, the energy (1.68E+10 kJ/mol) produced can be captured and used for generating electricity. Nuclear power require fuel rods enriched to 3.0% U-235.

6. Nuclear Fission (4) If the amt of U-235 is in a small enough volume, the energy release is so rapid as to create a nuclear explosion or atomic bomb. Nuclear bombs require the fuel to be enriched to 90.0% U-235. Current world concern about Iran and North Korea’s ability to achieve this enrichment level.

7. Plutonium - 239 The most abundant isotope of uranium is U-238 (99.3%). It is not fissionable but is radioactive. U-238 in fuel rods absorbs neutrons to form highly radioactive U-239 which decays to give highly radioactive Pu-239. (p 639) Pu-239 has a long τ 1/2 = 2.4E+4 yrs, is radioactive (emits α particles) and is fissionable. Pu-239 is not naturally occurring. If enriched to 93%, Pu-239 can be used in an atomic bomb.

8. Nuclear Waste Nuclear plant waste is highly radioactive and must be secured, stored and monitored. The big challenges are: How, where, for how long? Recent news story about storing waste in Utah, but there are additional challenges including transporting waste to Utah.

9. Other Issues Reprocessing spent fuel to obtain Pu-239. The world supply of Pu-239 is growing. Breeder reactors maximize production of Pu-239 to be used for nuclear power plants instead of U-235. The last nuclear energy plant in the US was built in 1979. Public acceptance of nuclear energy is low Pres. Bush’s 4/29/05 press conference.

10. Prentice Hall Slide