April 29, 2013 Positive Attitude

1. April 29, 2013 Positive Attitude • Cognoscente: a connoisseur; a person of special knowledge in some field, esp. fine arts • Do Now: Write 3 complete sentences on the following topic. Nuclear Energy

2. Nuclear Power

3. Uranium was discovered in 1789 by Martin Klaproth, a German chemist, and named after the planet Uranus. • The science of atomic radiation, atomic change and nuclear fission was developed from 1895 to 1945, much of it in the last six of those years • Over 1939-45, most development was focused on the atomic bomb • From 1945 attention was given to harnessing this energy in a controlled fashion for naval propulsion and for making electricity • Since 1956 the prime focus has been on the technological evolution of reliable nuclear power plants.

4. First commercial power plant, England 1956 17% of world’s electricity is from nuclear power

5. Nuclear reactions deal with interactions between the nuclei of atoms including of nuclear fission and nuclear fusion • Both fission and fusion processes deal with matter and energy • Fission is the process of splitting of a nucleus into two "daughter" nuclei leading to energy being released • Fusion is the process of two "parent" nuclei fuse into one daughter nucleus leading to energy being released

6. 1. Nuclear fission nucleus of atom is split into parts, produces free neutrons and energy What is nuclear energy? Power plants use heat to produce electricity. Nuclear energy produces electricity from heat through a process called fission. Nuclear power plants use the heat produced by fission of certain atoms.

7. 2. Uranium-235 Fissionof U-235 splits nucleus in two pieces releases neutrons for chain reaction Nuclear fission chain reaction releases energy in the form ofheat http://www.ecolo.org/photos/uranium/uranium-black.jpg Nuclear Fuel: Uranium 92 U Uranium The fuel used in nuclear power plants is an isotope of the radioactive element uranium

8. Nuclear Fission • We convert mass into energy by breaking large atoms (usually Uranium) into smaller atoms. Note the increases in binding energy per nucleon.

9. A slow moving neutron induces fission in Uranium 235

11. Fission products • The fission products shown are just examples, there are a lot of different possibilities with varying probabilities

13. Expanding Chain Reaction • The fission reaction produces more neutrons which can then induce fission in other Uranium atoms. • Mouse Trap Chain Reaction

14. Linear Chain Reaction • Obviously, an expanding chain reaction cannot be sustained for long (bomb). For controlled nuclear power, once we reach our desired power level we want each fission to produce exactly one additional fission

15. 3. Nuclear Reactor device built to sustain a controlled nuclear fission chain reaction http://en.wikipedia.org/wiki/Image:Crocus-p1020491.jpg www.pbase.com/pbrakke/image/44279993 Nuclear Reactors • Main Components of Nuclear Reactor: • reactor vessel • tubes of uranium • control rods • - containment structure control rods control radioactivity, absorbs neutrons Containment structure contains the reaction in at least 3 feet of concrete!

16. Tricks of the trade • Slow moving (thermal) neutrons are more effective at inducing fission, but, fissions produce fast moving electron. We need to slow neutrons down. • Fissions typically produce several neutrons but a linear chain reaction only needs one. We need to get rid of a good fraction of our neutrons.

17. Moderator • Neutrons are slowed down by having them collide with light atoms (Water in US reactors). • Highest level of energy transfer occurs when the masses of the colliding particles are equal (ex: neutron and hydrogen)

18. Basic Ideas • The Uranium is both the fuel and the source of neutrons. • The neutrons induce the fissions • The Water acts as both the moderator and a heat transfer medium. • Control rods regulate the energy output by “sucking up” excess neutrons

19. Control Rods • Control rods are made of a material that absorbs excess neutrons (usually Boron or Cadmium). • By controlling the number of neutrons, we can control the rate of fissions

20. 4. Nuclear power plant consists of all the parts needed to create electricity by using nuclear energy The heat is used to heat water to create steam Fission occurs in the reactor vessel. Heat is produced. The steam is used to turn the turbine in the generator to produce electricity The steam is cooled in the condenser to return to the liquid phase. The Nuclear Power Plant

21. Practicalities • Processing of Uranium • Each ton of Uranium ore produces 3-5 lbs of Uranium compounds • Uranium ore is processed near the mine to produce “yellow cake”, a material rich in U3O8. • Only 0.7% of U in yellow cake is 235U. Most of the rest is 238U which does not work for fission power.

22. Enrichment • To be used in US reactors, fuel must be 3-5% 235U. • Yellow cake is converted into UF6 and this compound is enriched using gaseous diffusion and/or centrifuges. • There are some reactor designs that run on pure yellow cake.

23. NOTE: A nuclear bomb requires nearly 100% pure 235U or 239Pu. The 3% found in reactor grade Uranium CANNOT create a nuclear explosion!

24. Fuel Pellets • The enriched UF6 is converted into UO2 which is then made into fuel pellets. • The fuel pellets are collected into long tubes. (~12ft). • The fuel rods are collected into bundles (~200 rods per bundle • ~175 bundles in the core

25. Cladding • The material that the fuel rods are made out of is called cladding. • It must be permeable to neutrons and be able to withstand high heats. • Typically cladding is made of stainless steel or zircaloy.

27. Controlling the chain reaction depends on • Arrangement of the fuel/control rods • Quality of the moderator • Quality of the Uranium fuel • Neutron energy required for high probability of fission

28. Reactor is inside a large containment building

29. Two common US reactor types: Boiling Water Reactor and Pressurized Water Reactor. • BWR: P=1000 psi T=545F • PWR P=2250 psi T=600F • PWR is most common and is basis of marine nuclear power.

31. Other Options • Other countries use different reactor designs. • Some use heavy water (D2O) as a moderator. Some use Graphite as a moderator. • Some are designed to use pure yellow cake without further enrichment • Liquid metal such as sodium or gasses such as Helium are possibilities to use for coolants

32. Breeder Reactors • A big problem with nuclear power is the creation of Plutonium in the reactor core. • This is a long lived radioactive element that is difficult to store. • Q: Why not use it as a fuel too?

33. Basic Idea • Process that creates the Pu. • During fission use one of the extra neutrons to create a Pu atom

34. Video: How a pressurized water nuclear reactor (pwr) works http://www.youtube.com/watch?v=u0VjHg0juz4

35. 2. Uranium-235 1. nuclear fission 3. nuclear reactor 4. nuclear power plant Key Components of Nuclear Energy

36. US Uranium Deposits

37. World Distribution of Uranium

38. US Nuclear Power Plants

40. Nuclear Power in the US • We currently generate approximately 20% of our electricity using nuclear power. • No new nuclear power plants have been “ordered” since the late 1970’s. • Even “new” plants are nearing 20 years old and will start to need replacing.

42. Three Mile Island Pennsylvania, USA

43. The American Experience’s Meltdown at Three Mile Island http://www.youtube.com/watch?v=wBNM3GLzvzo

44. Chernobyl Accident- April 26, 1986 • World’s worst nuclear power plant accident • Chernobyl in Ukraine on Pripyat River • Population 12,500; 120,000 in 30 km radius • 4 reactors (2 built in 1970’s, 2 in 1980’s) • Combination of design and operator error during electrical power safety check resulted in cascade of events leading to core breach of Reactor 4 with subsequent chemical (not nuclear) explosion

45. Chernobyl- Reactor 4 Site http://www.greenfacts.org/en/chernobyl/ /UN Chernobyl Forum(2006) http://en.wikipedia.org/wiki/Chernobyl_disaster

46. Chernobyl Accident • Flow of coolant water interrupted, insufficient # control rods, core breach • Graphite used to slow neutrons in reactor caught fire. Water sprayed on graphite, resulting in hydrogen gas formation- chemical combustion reaction and explosion • Large amount of radioactive fission products dispersed into atmosphere for 10 days (about 100X greater than Hiroshima/Nagasaki) • 150,000 people in 60 km radius permanently evacuated • Toll: several workers immediately, about 30 firefighters/emergency workers from acute radiation exposure, and a smaller # from subacute effects (overall, about 60 deaths) • About 250 million people exposed to radiation levels which may reduce lifespan, including about 200,000 in the clean-up crew (“liquidators”) who buried the waste and built a concrete “sarcophagus” around Reactor 4

47. Chernobyl Accident • Initial radiation released primarily I-131 (half life= 8 days), later Cs-137 (half life= 30 years) • Children particularly susceptible to I-131. Thyroid takes up I- to produce the hormone thyroxine (T4, growth/metabolism). • I-131 decays be beta emission with accompanying gamma ray • If ingested, can cause thyroid cancer • About 4000 cases of thyroid cancer in exposed children (2000), nine related deaths in this group • Preliminary evidence (2006) suggests increased risk of leukemia and possibly other cancers in “liquidator” group and others with higher exposure in the first year- “Among some 600,000 workers exposed in the first year, the possible increase in cancer deaths due to this radiation exposure might be up to a few percent.” Chemistry in Context, Chapter 7 http://www.world-nuclear.org/info/chernobyl/inf07.htm

48. Chernobyl Accident • Otherwise, UN report (2000)- “there is no scientific evidence of any significant radiation-related health effects to most people exposed” • No evidence of increase in birth defects, abnormal pregnancies, or reduced fertility • Secondary effects- fatalism, mental health problems, smoking, alcohol abuse, general poor health and nutrition • Surrounding farmland (1000 square miles) not farmable due to high Cs-137 (exception, one small area in Belarus) • High levels of Cs-137 found down wind in reindeer meat in Scandinavia • Contamination effects on plants/animals within 30 km • Contamination of nearby water bodies and fish http://www.world-nuclear.org/info/chernobyl/inf07.htm http://www.greenfacts.org/en/chernobyl/

49. Pathways Of Exposure To Man From Release of Radioactive Materials http://www.greenfacts.org/en/chernobyl/, Chernobyl Forum(2006)

50. http://www.world-nuclear.org/info/chernobyl/inf07.htm