Nuclear Energy

1. Nuclear Energy

2. History of Nuclear Energy in the US During the 1940�s and 1950�s nuclear power was viewed as a solution to energy problems The Price-Anderson Act of 1957 exempted these companies from any �legal liabilities incurred�. By 1975 there were 53 plants operating in the US producing about 9% of the electricity. Similar nuclear development occurred in other industrialized nations (France, UK, USSR, etc.) By the end of the 1970�s, interest in nuclear power substantially waned. Interest in nuclear power dropped off, and the public perception of nuclear energy grew more suspicious

3. Figure 13-2

4. Nuclear Power, The US and Worldwide According to DOE, there are 104 nuclear power plants in operation in October of 2005. No applications for new nuclear power plants have been submitted. The last nuclear power plant constructed was in 1996 in Watts Bar, Tennessee http://www.eia.doe.gov/cneaf/nuclear/page/nuc_reactors/reactsum.html Worldwide = 441 operating nuclear power plants. Nuclear power is restricted to those industrialized nations that have the technological know-how to enrich Uranium (described later)

6. What Happened to the Promise of Nuclear Energy? The public became (and still is) suspicious of nuclear energy. Actual accidents like Three-Mile Island (1979) and Chernobyl (1986) Cinema, TV, and science fiction novels (e.g. The China Syndrome and Them) Better awareness of what a nuclear meltdown will do.

7. Nuclear-Related Movies

8. Nuclear Energy Nuclear reactions; Fission = one large atom splits into smaller daughter atoms Fusion = two smaller atoms fuse to form a larger atom

9. Fission and Fusion Fission or fusion of an atom produces energy as the conversion from one large into many small (fission) or many small into one large (fusion) doesn�t occur cleanly.

10. Note that both reactions produce energy, neutrons, alpha particles, beta particles, gamma rays, etc.

11. Fission Fission: the weight of the large atom (parent) prior to splitting does not equal the combined weights of the daughter atoms.

12. Fusion, similar process The weight of the two initial atoms weighs different from the daughter atom

13. Fission and Fusion An example of such a radioactive isotope is uranium 235. Uranium 238 is the more stable and more abundant isotope. Fusion occurs within the sun where hydrogen atoms fuse to form helium.

14. Radioactive Isotopes Some Isotopes are unstable and will decay to more stable forms (via fission). For example, carbon-14 will decay into carbon-12 at a fixed rate (known as a half-life). Unstable isotopes are called radioisotopes and the process of breaking down into more stable atoms is called radioactive decay. Radioactive decay releases energy.

15. Uranium One of the most common atoms used in nuclear reactors is uranium. Uranium is found abundantly in nature, with the majority of uranium being the more stable isotope U-238. Uranium also has a radioactive isotope U-235, which is very rare. In nature the percent of U-235 of all uranium isotopes is < 0.05% to 0.3%. Raw uranium (mostly U-238) is mined The radioactive uranium (U-235) has to be distilled from the raw uranium (U-238) through a process called enrichment. For uranium to be used in nuclear power plants, the goal is to increase the abundance of U-235 via enrichment to about 4%. Enrichment has to be much higher for nuclear weapons

16. Uranium to Fuel Rod Uranium processing and enrichment: First the raw uranium is mined, then it is chemically leached to form a uranium oxide powder known as �yellowcake� The yellowcake is converted to uranium hexafloride, then it is enriched The enriched uranium exists as a powder = uranium dioxide The powder is pressed into pellets and the pellets are stuffed into hollow tubes and sealed. This tube filled with enriched uranium pellets is a fuel rod. The fuel rod is used within a nuclear power plant.

17. Fuel Rods, Full of Enriched Uranium

18. Uranium Fission within Fuel Rods The U-235 in fuel rods will undergo fission through a chain reaction. Enriching the uranium is one of the most technologically difficult operations to master.. Currently Iran is in the processes of developing uranium enrichment; this has been very controversial (later in the lecture we will come back to this point). Also North Korea has learned how to enrich uranium � both for nuclear power plants and for nuclear weapons.

19. Uranium-235 Fission, a Chain Reaction (Figure 13-6 Fission of U-235 can occur through a chain reaction. When a U-235 is bombarded by a neutron, it forms U-236 U-236 instantaneously breaks down Part of the fission process releases more neutrons, which bombard additional U-235 atoms. This occurs numerous times in a �chain reaction� This is what is going on inside a fuel rod

20. Nuclear Reactor �A nuclear reactor for a power plant is designed to sustain a continuous chain reaction but not allow it to amplify into a nuclear explosion�. A chain reaction can be achieved using a moderator, which �slows down the neutrons that produce fission, so that they are traveling at the right speed to trigger another fission�. Moderators in US nuclear reactor plants = water. Graphite is used as a moderator in former Soviet plants. Nuclear power plants, like those in the US, have to be located near a water source to have access to water. Water is both a moderator and a coolant.

21. Fuel Rods and Energy Groups of fuel rods are placed close together to form a reactor core. The reactor core is contained within a fortified reactor vessel that holds moderator, reactor core, coolant, safety equipment, control rods, etc . Heat given off from the reactor core is used to boil water and generate steam. The steam is used to turn turbines to generate nuclear power. �Spent Fuel Rods� have to be replaced (after about 10 years) with fresh new ones.

22. Control Rods Control rods are used to regulate the fission reaction. They absorb neutrons When inserted in between the fuel rods they slow down the chain reaction.

25. Cooling Towers

26. Reactor Core: Fuel Rods Plus Control Rods

27. Advantages of Nuclear Energy Well-run nuclear power plants produce very minute amounts of pollution. As a matter of fact, radiation levels near coal-burning power plants are significantly higher (100 times more!) than around nuclear power plants Nuclear fuel produces no greenhouse gases no need to be reliant on foreign oil. The amount of uranium needed is relatively small compared to coal-burning power plants. No sulfur dioxides or other acid-rain progenitors are released, whereas coal �plants produce over 300,000 tons of sulfur dioxide. The coal plant produces 600,000 tons of ash requiring land disposal; nuclear power produces only 250 tons of radioactive waste requiring safe storage.

29. The Dark Side!

30. Radiation Exposure People exposed to radiation can become very sick Radioactive decay produces direct products and indirect products Direct products = daughter elements (30 possible ones, such as radioactive isotopes of iodine, strontium, cesium, cobalt, etc.) Indirect products = alpha particles, beta particles, gamma rays, errant neutrons. Any material in and around radioactivity will absorb these indirect radioactive emissions. These radioactive byproducts cause significant harm to the body.

32. Possible Biological Effect of Radiation Immediate Death: radiation destroys cells and burns tissues Stops cell division: organic tissues that absorb radioactive emissions will cease cell division, which leads to radiation sickness. Red blood cells (RBC) are continuously being produced, for example, and if a person is exposed to too much radiation this will stop the production of new RBC�s. Without new RBC�s a person will die. Skin and hair cells will also stop dividing. Long-term effect = mutation of DNA and higher risk of cancer. Birth defects are also possible.

33. Radioactive Waste Radioactive materials can cause substantial harm. Moreover, spent fuel rods have to be replaced with new ones. How do we dispose of the spent fuel rods without exposing people to radioactivity? Traditionally, spent fuel rods are placed within containers and then stored on-site within containment ponds or containment-pools. The immersed containers are surrounded by water, which absorbs the radioactive emissions. How long will the waste be radioactive? It depends on the �half-life� of the material. The next table (Table 13-1) shows radiation levels for various substances. Read the textbook explanation of measuring radioactivity �Radioactive Emissions� pg 358.

35. Half-life The half-life of carbon 14 is approximately 5700 years. By knowing the rate of decay, which is a fixed value, scientists are able to radiocarbon date objects from the past. By knowing the ratio of C14 to C12 in organic matter and by knowing the half-life, you can backtrack the age of the organic material to determine when it was alive and when it was incorporating both C12 and C14 within similar amounts. Plutonium has a half life of 24,000 years The following table (Table 13-2) reports the half-lives of some of the uranium fission daughter products. Note how some, like plutonium, take a long time to decompose � and that�s just half of the radioactive material! The complete decomposition takes 10,000�s of years.

37. Where are the spent fuel rods stored? Again, most fuel rods are stored on-site at the nuclear power plants. But available storage is rapidly diminishing. Some nuclear power plants have been operating for decades, and the amount of storage space is running out. Some nuclear power plants are researching how to reuse spent fuel rods. The following slide is an excerpt form a �Morning Edition� report on recycling fuel rods.

38. Storing Spent Fuel Rods The US Government has invested billions of dollars to build a long-term nuclear waste disposal site, Yucca Mountain in Nevada (discussed a little later). The Yucca Mountain site will be used to safeguard nuclear waste from nuclear reactors, and it will start accepting the spent fuel rods by 2017 (11 years). One major concern regarding this is that fuel rods from across the country will have to be shipped to Nevada along America�s roadways.

39. Nuclear Meltdown Perhaps the biggest fear of nuclear energy is a meltdown of the reactor and the contamination of the environment by radioactive waste. Nuclear plants generate a lot of internal heat to be converted into power. As stated, a coolant is used to convert the heat energy into steam to turn a turbogenerator. Reactors in the US use water as a coolant and as a moderator. If there is a loss of the coolant (it leaks out of the double-loop structures), the heat within the reactor will continue to rise. Because the water also acts as a moderator to slow the neutrons, the loss of the coolant will result in the nuclear reaction continuing unabated. The reactions start to occur way too fast and cannot be controlled. The internal heat of the reactor core (physical location of where the fuel rods, control rods are within a nuclear reactor) will heat up to such a degree that the whole system will melt. This is the actual �meltdown�. Examine Figure 13-8, all those things in the containment building basically overheat and melt.

40. Meltdown (continued) The melting of the reactor core from the loss of coolant will accomplish several things: melt away and destroy all the safety features. The melting reactor core will collapse into the remaining pool of water and will cause an explosion of steam. The worst case scenario of a meltdown is termed a �China Syndrome�.

41. Nuclear Disasters There have been two major nuclear disasters to date: 1979 = Three-Mile Island in Pennsylvania Partial meltdown, no major release of radiation, no one got really hurt, but it scared the �you-know-what� out of the public 1986 = Chernobyl, Ukraine (former USSR) Meltdown, conflagration and radiation killed 100�s of people directly The release of a radioactive cloud of fission products across much northern Central Europe forced the evacuation of 150,000 people Long-term affects on the population are still being monitored and increased cancer risk and birth defects are a major concern.

42. Three Mile Island

43. Three-Mile Island Worst nuclear disaster in the US 25,000 people live within 5 miles of the plant The partial meltdown occurred from a loss of coolant (LOCA). Complicating factors associated with this disaster (Synopsis) Many safety features were not working properly The reactor core did melt, but the containment building that holds the reactor core never fully melted and the meltdown never breached the outer walls.

44. Three-Mile Island (continued) No one was really hurt from the accident There was a release of radioactive cloud from the reactor. The public within a 10 mile radius was exposed to about 1 millirem, far less radiation then normal background exposure. The accident didn�t result in a worst-case scenario, it actually was pretty minor considering what could have happened. Public perception of nuclear power, however, changed forever! There was a major loss of confidence in nuclear power in the country after Three-Mile Island.

45. Chernobyl THE WORST NUCLEAR DISASTER, EVER The meltdown at Chernobyl (April 26, 1986) was a worst-case scenario and the molten reactor core and ensuing steam explosions breached the reactor vessel and contaminated the environment. Making matters even worse, was that the reaction was due to human error. A planned experiment to run the generator without coolant was conducted late at night. The experiment was run by a nightshift skeleton crew that didn�t know what they were doing. The experiment was to see if they could generate enough power to fuel the safety systems without using external electricity.

46. Chernobyl

48. The World Finds Out The USSR didn�t immediately admit to the accident. A Swedish nuclear plant started picking up high radiation levels. They shut down their plant thinking that they had a leak. Once the determined that there was no leak, they looked at the upper level wind patterns. Global attention then turned to the USSR as being the culprit for higher radiation levels. They finally admitted to it several days after the accident.

49. Result of Meltdown 31 people died immediately, mostly firefighters exposed to the radiation and fire Residents had to be evacuated leaving behind all possessions and pets. In order for the evacuation to occur more quickly the USSR government told the citizens that the evacuation was only temporary (a lie). 135,000 had to be evacuated. The reactor was encased in a �sarcophagus of concrete and steel. A barbed-wire fence now surrounds a 1000- square-mile exclusion zone around the reactor site.� More than 4000 workers that participated in the cleanup have since died. Concerns of elevated cancer will be a concern for the area for the next 70 years!! However to date there has been no significant rise in leukemia and only a slight rise in thyroid cancer. Long term estimates from 140,000 � 475,000 cancer deaths worldwide from the accident.

50. Synopsis of Three-Mile Island and Chernobyl The disasters were both related to human error and faulty designs. Also both disaster occurred late at night. From this it is easy to conclude that nuclear power is perfectly safe, IF: Workers are not tired nor otherwise in a bad mood Everyone is properly trained and knows exactly what to do All gauges read correctly and all systems are working properly, never breaking down of needing repair Security is tight and security screening is 100% No guerilla warfare or terrorism No natural or human disasters occur, e.g. earthquakes, tornadoes, plane crashes, So, you have nothing to worry about

51. Nuclear Power Today? Energy Policy Act 2005 (EPACT) Section 1306, Credit for Production from Advanced Nuclear Power Facilities under Title XIII - Energy Policy Tax Incentives

52. Dream or Delusion? Questions to think about (just think about them, you don�t have to turn answers in or debate them) Is nuclear power the solution to our energy problems? Does the promise of cheap, clean energy outweigh the costs of a meltdown? Will public perception of nuclear energy ever change? Can we make nuclear energy safer? Where do you stand on nuclear energy?