Chapter 7: The Fires of Nuclear Fission
Transcription
Chapter 7: The Fires of Nuclear Fission
Chapter 7: The Fires of Nuclear Fission What is nuclear fission? Is using nuclear energy safe for humans and the environment? Is nuclear energy better to use than electric generated energy? What happens to the waste of nuclear fission? Would you prefer to purchase electricity being generated from a nuclear power plant or a traditional coal-burning plant? Which would you choose and why? What do you think of when you hear “nuclear energy”? Is the U.S. doing everything it can to conserve energy? How does it compare to other countries? Name some ways that energy can be conserved. 20% of the electricity in the U.S. is produced by 103 nuelear reactors The Nuclear Regulatory Commission (NRC) oversees and licenses these power plants. No new nuclear plants have been licensed since 1978, but several have received extensions on their operating licenses. Energy and matter are related by Einstein’s famous equation: E = mc2 Atomic Particle Mass (g/mole or amu) Electron 0.0005486 Proton 1.007277 Neutron 1.008665 1 1.007825 H Binding Energy – the difference in energy between an atom’s nucleus and the individual subatomic particles that make it up The energy equivalent of the mass defect is the binding energy. What is Fission and How Does it Produce Energy? Nuclear fission is the splitting of a large nucleus into smaller ones with the release of energy. Energy is released because the sum of the masses of these fragments is less than the original mass. This 'missing' mass (about 0.1 percent of the original mass) has been converted into energy according to Einstein's E=mc2 equation. 7.2 What is Fission and How Does it Produce Energy? E = mc2 This equation dates from the early years of the 20th century and is one of the many contributions of Albert Einstein (1879–1955). It summarizes the equivalence of energy, E, and mass, m. The symbol c represents the speed of light, 3.0 x 10 8 m/s. 7.2 What is Fission and How Does it Produce Energy? E = mc2 Consider this: c2 is equal to 9.0 x 1016 m2/ s2 When mass is in kg, the energy units are kg x m2/s2, which is equivalent to 1 Joule. The large value of c2 means that it should be possible to obtain a tremendous amount of energy from a small amount of matter - whether in a power plant or in a weapon. 7.2 What is Fission and How Does it Produce Energy? E = mc2 For 1.0 g of U-235: E = (1.0 x 10-3 kg)(3 x 108 m/s)2 E = (1.0 x 10-3 kg)(9.0 x 1016 m2/s2) E = 9.0 x 1013 kg m2/s2 = 9.0 x 1013 J Don’t forget to cube or square where needed This is equivalent to 33,000 tons of TNT 7.2 TNT, or trinitrotoluene (discovered in 1863 by Alfred Nobel) became the standard of explosive power as a result of the birth of nuclear weapons-they needed to be compared to some substance of known explosiveness. CH3 NO2 O2N TNT NO2 The TNT molecule is very unstable and when explodes, 2 moles of TNT rearrange to form 15 moles of hot gas (3 mol N2, 7 mol CO, 5 mol H2O) plus some carbon. About 1 g of TNT will produce about 1 L of hot gas – a 1000 times increase in volume. 1 kg of U-235, where only about 0.1% mass is converted to energy is equivalent to 33,000 tons of TNT 7.2 What is special about the mass number of U-235? When a massive nucleus like U-235 undergoes fission, the net yield of energy is a result of the sum of the fragments being slightly less than the mass of the uranium nucleus. If the mass of the fragments is equal to or greater than that of iron (element 26) at the peak of its binding energy curve, the nuclear particles (daughters) will be more tightly bound than the uranium nucleus was, and that mass decrease is converted to energy according to E = mc2. For elements with lower mass numbers than iron, fusion may lead to energy release 7.5 Discovery of Nuclear Fission Nuclear reactions involve changes in the atomic nuclei (where the protons and neutrons are). Ordinary chemical reactions involve bond making and breaking with the valence (outermost) electrons. In 1938, Otto Hahn and Fritz Strassmann, two German chemists, were attempting to make heavier-than-uranium elements by bombarding uranium (the heaviest naturally-occurring element) with neutrons. Instead of the heavier elements they hoped to synthesize, they discovered barium-139, a lighter element. Hahn and Strassmann sent a copy of their results to Lise Meitner, a colleague of theirs, now living in Sweden. Meitner published a paper with her nephew, Otto Frisch, in which they explained that barium and other light elements were formed by the cleavage of the uranium nucleus, a process they named nuclear fission. Nuclear Fission – the splitting of a large atomic nucleus into smaller ones with the release of energy Chain Reaction – a self-sustaining fission reaction; sufficient fissionable atomic nuclei are necessary for this condition to be reached Critical Mass – the amount of fissionable material required to sustain a chain reaction; the critical mass of U-235 is about 15 kg or 33 lb. A Chain Reaction with U-235 Visit Figures Alive! For more information on nuclear fission and chain reactions! 7.5 Schematic of a Nuclear Reactor A nuclear reactor is a device in which nuclear chain reactions are initiated, controlled, and sustained at a steady rate (as opposed to a nuclear explosion, where the chain reaction occurs in a split second). 7.3 Primary Coolant – a liquid that comes into direct contact with the nuclear reactor to carry away heat (e.g. aqueous solution of H3BO3) Moderator – substance that slows the speed of the neutrons and makes them more effective at causing fission Secondary Coolant – water in the steam generators that never comes in direct contact with the reactor Basics of a Nuclear Reactor Actual size of fuel pellet An awesome source of electrical energy— but what to do with the spent nuclear fuel? Reactor core Cooling tower 7.3 Two cooling towers at the Byron nuclear plant in Illinois This image shows a fuel assembly submerged in an active reactor core 7.6 Still, the only person to win two unshared Nobel Prizes was Linus Pauling, the American chemist who won for his chemistry work and also a Nobel Peace Prize for his objection to nuclear testing. Marie Sklodowska Curie won two Nobel Prizes—one in chemistry, the other in physics—for her research on radioactive elements. 7.5 Discovery of Radioactivity In 1896, Henri Becquerel left a sample of K2UO2(SO4)2 on top of a sealed photographic plate in a drawer. After several days, he discovered the plate was fully exposed as if it had been exposed to light. He realized that the uranium salt must be emitting some type of radiation. Pierre and Marie Curie investigated further to show that the uranium and not the potassium or sulfur was the source of the radiation. All uranium-containing compounds behaved the same way. The Curies and Henri Becquerel shared the 1903 Nobel Prize in Physics for the discovery of radioactivity. Neutron/Proton Ratio for Isotopes Types of Radioactivity Ernest Rutherford discovered alpha and beta radiation, and gamma radiation was later discovered. Alpha particles – Helium nuclei (He2+) are bundles of two protons and two neutrons. By losing two protons, alpha emitters decrease their atomic number by two. This is nature’s method of reducing an isotope atomic number. Beta particles – Electrons that increase the atomic number by one. Beta emitters have too high of a neutron/proton ratio and loss of a beta particle improves this ratio. Gamma rays – This type of radioactivity does not consist of matter at all. It is simply electromagnetic radiation of a very high frequency. Gamma rays are usually emitted along with alpha or beta particles. All radioactive isotopes undergo a radioactive decay (or a series of radioactive decays) until they form a stable isotope. Each radioisotope has its own unique half-life (the amount of time it takes for half of the radioisotope to undergo its radioactive decay reaction). This half-life is a physical characteristic of the particular isotope and cannot be changed. Radioactivity Include alpha, beta, and gamma rays. 7.5 Three Types of Radioactivity Neutron Source Alpha Emitter 238 94 Pu Gamma Emitter 4 2 He 234 92 U + 9 4 Be 12 6 + 4 2 He C + 1 n 0 + 0γ 0 Control Rods Typically made of cadium; the control rods are interspersed with the fuel rods and can be raised and lowered into the fuel rod bundle. 112 48 Cd + 1n 0 113 48 Cd Uranium consists of approximately 99.3% of U-238 and 0.7% U-235. U-238 does not undergo fission, but U-235 does. 1n 0 + [ 236 92 U] 235 92 U 141 56 Ba + 92 36 Kr + 3 10 n U-238 absorbs neutrons. For this reason, unenriched uranium cannot sustain a chain reaction. 1n 0 + 238 92 U 239 92 U (half-life = 23.5 min) 239 92 U 239 93 Np + 0e –1 239 93 Np 239 94 Pu + 0e –1 (half-life = 2.35 days) (half-life = 24,400 yr) U-238 Radioactive Decay Series Radioactive isotopes undergo decay until they reach a stable species. All isotopes of all elements with atomic number 84 (Po) and higher are radioactive. 7.5 Halflives for the U235 Decay Series Half-life: the time required for the level of radioactivity to fall to one-half of its value. 7.8 Half-life: the time required for the level of radioactivity to fall to one-half of its value. 7.8 Writing Nuclear Equations 14 6C 14 6C 210 84 210 84 Po is a beta emitter. 14 7N + 0 –1 e Po is an alpha emitter. 206 82 Pb + 4 2 He Writing Nuclear Equations Fission of 235 92 U + Fission of 235 92 U 1n 0 235 92 U with a fast-moving neutron produces144 55 Cs and two neutrons 144 55 Cs + 90 37 Rb + 2 10 n with a fast-moving neutron produces139 52 Te , an isotope with a mass number of 94 and some number of neutrons 235 92 U + 1n 0 139 52 Te + 94 40 Zr + 3 10 n A nuclear power plant cannot undergo a nuclear explosion because it uses uranium ore that contains only 4-5% U-235. Nuclear weapons use fuel that is typically 80-90% U235. Gaseous Diffusion – a process in which a gas is forced through a series of permeable membranes; lighter mass materials of the same type move through the membranes more quickly UF6 is a solid that vaporizes at 56°C. A 235UF6 molecule moves about 0.4% faster than 238UF6. Diffusion through a very long series of permeable membranes results in separation of the isotopes. Depleted uranium is almost entirely U-238 since it has been depleted of most of the small amount of U-235 it once had. Nuclear fuel can be diverted to make nuclear weapons. 1n 0 + 238 92 U 239 93 Np 239 92 U + 0 –1 e (half-life = 2.35 days) 239 93 Np 239 94 Pu + 0e –1 (half-life = 24,400 yr) Spent nuclear fuel (SNF) is the radioactive material remaining in fuel rods after they have been used to generate power in a nuclear reactor. Pu-239, like U-235, is a fissionable radioisotope. During WWII, a breeder reactor was built on the Columbia River in Hanford, Washington. It was designed to convert U-238 to Pu-239 by neutron capture. The plutonium was then chemically separated from the uranium. Plutonium was used in the first atom bomb exploded in New Mexico in July, 1945 as a proof of concept. The bomb dropped on Nagasaki a few weeks later was also fueled by plutonium. Pu-239 reacts easily with oxygen to form PuO2, one of the most toxic compounds known. It is a powdery substance which is easily inhaled. It causes lung cancer in minute quantities and accumulates in the liver and bones where its radioactivity does serious damage. Nuclear Weapons The isotopes U-235 and U-238 behave essentially the same in all chemical reactions, so the separation of these two isotopes is extremely difficult and relies on advanced technology that is not readily available. Building and deploying a nuclear weapon is a very difficult operation to carry out. 7.10 The Three Mile Island Accident The accident began about 4 a.m. on March 28, 1979 in the non-nuclear portion of the plant, when the main feedwater pumps stopped running due to either a mechanical or electrical failure. Pressure in the nuclear portion of the plant increased and a relief valve opened. The valve should have closed when pressure decreased by a certain amount, but did not. Cooling water poured out of the stuck-open valve and the reactor core overheated. Nuclear operators had no instrument to show the level of coolant in the reactor core (a design flaw) and no signal that the relief valve was open. As alarms rang and warning lights flashed, they did not realize the plant was experiencing a loss-of-coolant accident. Conditions worsened when they reduced the flow of coolant through the core (human error). Some of the fuel rods ruptured and the fuel pellets spilled out and melted. When federal and state authorities were notified, they took steps to gain control of the reactor by ensuring adequate cooling. It is estimated that 2 million people received an average dose of one millirem. The average person receives 100-125 millirems per year from natural sources. Monitoring of thousands of samples of air, water, milk, soil and foodstuffs in the years following the accident indicates that most of the radiation was contained and the actual release of radioactive materials had negligible effects on the physical health of individuals or the environment. July, 1 982: Und er water cam er a survey s the i nside o f t he re ac tor vessel for the first t im e, re vealing t hat t he ext ent of t he core m eltdown was far greater t ha n ex pe cte d. Current Status The reactor is permanently shut down and defueled, with the reactor coolant system drained, the radioactive water decontaminated and evaporated, radioactive waste shipped offsite to an appropriate disposal facility, and reactor fuel and core debris shipped off-site to a Dept. of Energy facility. Impact of the Accident The U.S. Nuclear Regulatory Commission’s (NRC) oversight of its licensees has increased since the Three Mile Island incident. Plant design and equipment requirements were upgraded and strengthened. Operator training was revamped since human performance was identified as a critical part of plant safety. Drills and response plans are now tested several times a year by licensees. Two NRC inspectors live nearby and work exclusively at each plant to provide daily surveillance of licensee adherence to NRC regulations. Chernobyl – Causes of the Accident Lack of a “Safety Culture” Violation of Procedures: 1) Only 6-8 control rods (normally a minimum of 30 are required) were used by the end of a test to see if the turbines could produce sufficient energy to keep the coolant pumps running until an emergency diesel generator was activated 2) The reactor’s emergency cooling system was disabled Design Fault in the RBMK Reactor In this type of reactor, the neutrons released by the fission of U-235 nuclei are slowed down (moderated) by graphite and water so as to maintain a chain reaction. Nuclear experts have criticized this type of reactor primarily because it lacks a containment structure and requires large quantities of combustible graphite within its core. The RMBK reactor type suffers from instability at low power and may experience a rapid, uncontrollable power increase. The cause of this instability is: 1) Water is a better coolant than steam 2) The water acts as a moderator and neutron absorber (slowing down the reaction) while steam is much less effective. Excess steam pockets in the RBMK design lead to increased power generation. The additional heat produces more steam and means less neutron absorption, which causes the problem to escalate. Timeline On April 25, 1986, Chernobyl reactor #4 is powered down to 1600 MW (about half power) in preparation for the test. At 2 p.m., an electricity grid controller requested that Chernobyl stay online till 11:10 p.m. The test was therefore delayed, but the emergency core cooling system was not switched back on. At 11:10 p.m. power reduction resumed in order to reach the designated range of 700-1000 MW. Due to operator error, the power fell to about 30 MW at 12:28 a.m. on April 26. The reactor control engineer tries to raise the power by removing control rods and at 1:00 a.m. power had stabilized at about 200 MW. Although far below the desired range, Chernobyl engineers decide to continue with the experiment. The water level in the steam drums drops below emergency levels. At 1:19 a.m., engineers override an emergency signal and keep the reactor running. Water in the cooling circuit nears the boiling point. In order to keep power at 200 MW, all 12 automatic control rods and some manual control rods are withdrawn from the core. Computer printouts at 1:22 a.m. indicate an immediate shutdown of the reactor is required, but the experiment begins at 200 MW. The generator and turbines are shut down. Steam quantities begin to increase spontaneously and uncontrollably. Water flow through the core declines as the water temperature increases. A steep rise in power occurs and a full emergency shutdown is ordered. Control rods do not fully descend into the core due to damage or malfunction. Power reaches 530 MW in 3 seconds and continues to increase exponentially. Fuel rods rupture and fuel particles react with water creating a large steam explosion. The graphite ignited and in the ensuing inferno, the radioactive fission products and burning graphite were sucked up and released into the air. A second explosion shortly thereafter adds to the destruction. Fires start in over 30 places. In the first ten hours after the explosion, firefighters pumped cooling water into the reactor core. 31 members of this group died of radiation sickness shortly afterwards. After this attempt was abandoned, military helicopters dropped 2400 tons of lead and 1800 tons of sand in an attempt to smother the fire. This made matters worse as heat accumulated under the dumped materials and more radiation was released. In the final phase of firefighting, the reactor core was cooled with liquid nitrogen. Not until May 6 were the fire and radioactive emissions under control. Of the 800,000 firefighters and soldiers (liquidators) involved in the clean-up operations until 1989, a total of 25,000 have died according to government agencies. Estimates provided by the liquidator associations are far in excess of official figures. Today, the surviving liquidators are still suffering from the damage to their health. 36 hours after the explosion, the 45,000 inhabitants of Pripyat, 4 km away, were permanently evacuated by bus. Within 10 days, 130,000 people who lived within 30 km, were also evacuated. Within seven months, the ruined reactor building was enclosed in a reinforced concrete casing. A second shelter is scheduled to be completed by 2011 and is intended to safely confine radioactive material for at least 100 years. After prolonged international negotiations, the entire Chernobyl complex was closed in Dec. 2000. Types of Radiation Released More than 40 different radionuclides escaped into the atmosphere in the first ten days following the accident. Most significant are iodine (I-131, half-life = 8 days), cesium (Cs137, half-life = 30 years), strontium (Sr-90, halflife = 29 years) and plutonium (Pu-241, half-life = 24,400 years) and its decay products. Variable weather conditions in the days following the accident, spread the radiation in a very uneven pattern. Severely contaminated “hot spots” often lie close to only mildly contaminated areas. These radionuclides can enter the food chain through livestock and crops, wind erosion, forest fires, and transport by rivers. QuickTime™ and a Photo - JPEG decompressor are needed to see this picture. Environmental Damage There are 600 to 800 unsecured burial pits of radioactive debris in the 30 km zone around Chernobyl. These dumps were never precisely mapped and still pose a threat to groundwater. Contamination via river water in Ukraine is still a major problem. Measurements in Belarus and Ukraine show that radiation has concentrated in the sediments at the bottom of water bodies, particularly standing waters such as lakes or ponds. Some people continue to fish these waters and receive contamination via the food chain. The severe radioactive contamination of mushrooms, berries, game and fish, as well as of grass and hay used as feed for dairy cattle, are the main pathways whereby food is contaminated. Belarus The official Chernobyl Committee in Minsk estimates the total damage to Belarus at USD 235 billion. The nuclear disaster effectively deprived the country of 22 percent of its agricultural land and 21% of its forests. Ukraine By 2015, Ukrainian experts estimate the disaster will have cost the country USD 201 billion. 40% of Ukraine’s forested area is contaminated. Russia Russian costs were about USD 3.8 billion between 1992 and 1998. 2 million people still live in the contaminated westernmost area. Chernobyl: Social and Environmental Consequences Over 1,000 injuries and thirty-one deaths of firefighters and others who reported to scene of accident. 150,000 people evacuated from their Ukraine homes. Radioactive cloud released over a large part of Europe. Health threatening levels of radioactive materials were found in at least twenty nations, and as far away as 2,000 km from Chernobyl. Estimated 250 million people were exposed to unhealthy amounts of radiation. Estimates of future cancers from the accident range anywhere from 7,500 to 1 million. Radioactive particles in the environment and in the food chain. Large amount of uncertainty and fear in the population. 7.6 Chernobyl: Political Consequences Distrust of government. Soviet Union cover up: Sweden and Poland were the first nations to bring attention to the accident. Other nations attempted to downplay the health effects of the accident in their own nations. Public opposition to building additional nuclear power plants increased significantly worldwide. 7.6 Nuclear Energy Pros Cons No greenhouse gas emissions Nuclear fission generates a number of radioactive isotopes, some of which have long halflives No air pollutants (e.g. sulfur or nitrogen oxides, mercury emissions) Uranium ore, although not limitless, is relatively abundant Remote possibility o f a nuclear accident If there are approximately 50 years of easy-to-extract oil and petroleum available and 75 years of domestically produced natural gas, it can be safely predicted that the prices of these nonrenewable fuels will drift upward as the supplies decrease and energy demand increases. For the future, what energy sources should the US invest in? Nuclear energy? Expensive-to-extract oil? Renewables such as wind, solar or ethanol? Measures of radioactivity: 1 Curie = 1 Ci = 3.7 x 1010 decays/second = number of radioactive decays from one gram of radium 1 rad (radiation absorbed dose) = 0.01 joule of radiant energy absorbed per kg of tissue The rem is a measure of radioactivity adjusted for the type of radiation and the rate at which it is delivered. # of rems = Q x (# of rads) The sievert (Sv) is an international unit and equals 100 rems. rad = “radiation absorbed dose” – absorption of 0.01 J of radiant energy/kg tissue rem = “roentgen equivalent man” = Q x (number of rads) where Q is a relative biological effectiveness factor 1 Sv = 100 rem 7.7 Hazards of Radioactivity Rapidly dividing cells are particularly suspectible to damage from radioactivity. In adults, rapidly dividing cells are found in the bone marrow, skin, hair follicles, and the lining of the stomach and intestines. Radiation sickness is the illness produced by exposure to large amounts of radiation. The immune system is suppressed and anemia results from loss of red blood cell production. Disposal of Nuclear Waste High-Level radioactive waste (HLW) – the mixture of radioactive material from spent nuclear fuel (SNF) or from the reprocessing of SNF; because of the very long half-lives of some of the radioisotopes, it must be permanently isolated HLW also contains heavy metals, which are toxic. It poses a hazard both chemically and because of the high levels of radioactivity. HLW comes from both military facilities and commercial nuclear plants. Most of this waste is stored under water in pools at the site where it was generated. 7.9 Since 1977 there has been a moratorium on spent fuel reprocessing in which plutonium and uranium are separated from the other fission byproducts and used to generate additional energy. By 2010, the US will have more than 100,000 tons of HLW. 99.9% of radioactivity dissipates after ten halflives. For fission byproducts such as Sr-90 and Cs-137, this would mean storing the waste for 300 years. For Pu-239 (half-life = 24,400 yr), the waste needs to be sequestered from the environment for a much longer time period. Congress has approved the Yucca Mountain site in Nevada as the nation’s first high-level nuclear waste repository. If completed, it would have a capacity to hold 78,000 tons of HLW. Proposed High Level Nuclear Waste Storage in Yucca Mountain, Nevada 7.9 A worker in one of the Yucca mountain tunnels 7.9 Energy Secretary Steven Chu stated at a Senate hearing in March 2009 that the Yucca Mountain site is no longer viewed as an option to store reactor waste. The Obama Administration proposed to eliminate almost all funding in the FY2009 budget while it devised a new strategy for nuclear waste disposal. In July 2009, the House of Representatives voted 388 to 30 not to defund the Yucca Mountain repository in the FY2010 budget. This project is widely opposed in Nevada and is a hotly debated topic. Polls indicate that most Nevadans are against the repository. There is also general resentment felt by many Nevada residents over the fact that 87% of the land in Nevada is federal property. Although about 15% of their electricity comes from the Palo Verde nuclear station in Arizona, many Nevadans feel it is unfair for their state to have to store nuclear waste when there are no nuclear power plants in Nevada. The nuclear waste is planned to be shipped to the site by rail and/or truck in robust containers approved by the Nuclear Regulatory Commission. The transport of spent fuel in Europe and Asia is routine with few safety or security issues. Globally, over 70,000 MTU (metric tons of uranium) of spent fuel have already been transported by train, truck, and ship. In addition, the Nevada Test Site which encompasses Yucca Mountain, is the location where over 900 nuclear weapons have been detonated and continues to serve as primary location for any future nuclear weapons tests if needed. The likelihood that this land area would be used for any other purpose is remote. Is the Nevadans’ opposition merely a knee-jerk NIMBY (not in my backyard) reaction or is it unfair to force them to accept the nuclear waste repository in their state? What about concerns about transporting HLW from the sites where it is generated to Yucca Mountain? Low-level radioactive waste (LLW) – waste contaminated with smaller quantities of radioactive material than HLW; excludes spent nuclear fuel. It consists of a variety of materials: Lab clothing, gloves and instruments from hospitals and research facilities that use radioisotopes Waste from facilities that manufacture enriched uranium fuel pellets Waste from mining operations LLW comes military sites, commercial power plants and medical facilities. Currently it is placed in sealed containers and buried in trenches at three LLW disposal sites (Barnwell, SC; Clive, UT; Richland, WA). Costs of HLW waste disposal Cleanup of the Department of Energy’s Hanford Site in southeastern Washington is estimated at $90 billion. This is the most complex cleanup project for DOE, which is responsible for cleaning up some 100 other contaminated weapons sites. The cleanup plan calls for the production reactors to be dismantled and their highly radioactive cores to be encased in concrete cubes designed to last 75 years while radiation levels drop and scientists figure out a solution for their ultimate disposal. The Hanford Reservation – The Nation’s Most Contaminated Nuclear Site 53 million gal of high-level radioactive and chemical waste liquids and sludge are stored in 177 underground tanks. Some tanks have leaked and there is a plume of contaminated groundwater stretching from the tanks towards the Columbia River. There is no technological solution for this problem at the present time. Current plans are to vitrify this tank waste into glass logs, which could create 39,000 tons (13,000 canisters) of high-level radioactive waste and 600,000 of low-activity radioactive and chemical waste. The vitrification facility is currently under construction. Storage of nuclear waste Thousands of canisters of spent nuclear fuel rods submerged in water Encapsulating reprocessed HLW in glass canisters (vitrification). There is 2100 tons of spent nuclear fuel in aging, broken canisters in pools near the Columbia river. This material is being cleaned, repackaged, and loaded into special steel baskets by remotely-controlled equipment that works underwater. The baskets are loaded into 14-ft tubular canisters, the water drained and replaced with pressurized helium, and the canisters trucked to a storage building on the central plateau. About 85% of the site will be cleaned the radioactive and chemically hazardous soil, tank waste, spent nuclear fuel, surplus plutonium, and other dangerous material will be concentrated and isolated from human contact on the central plateau disposal area. The Canister Storage Building holds three underground vaults of SNF and vitrified waste Nuclear Power Globally Currently 441 nuclear reactors operate in 31 countries, producing 363 billion W of electricity. Another 30 reactors are under construction and an additional 100+ are in the planning stage. New generations of nuclear reactors are designed to have “passive” safety systems that do not require human intervention in the case of an accident. Some new designs feature a closed fuel cycle. Deleted uranium is used as a fuel source and after bombardment with neutrons, Pu-239 (a fissionable radioisotope) is produced. The heavy nuclides – such as neptunium, areicium, plutonium and curium – are removed from the spent fuel and returned to the reactor. Nuclear Reactors by Continent Nuclear Energy in France (http://www.world-nuclear.org) * France derives over 75% of its electricity from nuclear energy. This is due to a long-standing policy based on energy security. * France is the world's largest net exporter of electricity due to its v ery low cost of generation, and gains over EUR 3 billion per year from this. * France has been very active in developing nuclear technology. R eactors and fuel products and services are a major export. The present situation is due to the French government deciding in 1974, just after the first oil shock, to expand rapidly the country's nuclear power capacity. This decision was taken in the context of France having substantial heavy engineering expertise, but few indigenous energy resources. Nuclear energy, with the fuel cost being a relatively small part of the overall cost, made good sense in minimizing imports and achieving greater energy security. As a result of the 1974 decision, France now claims a substantial level of energy independence and almost the lowest cost electricity in Europe. It also has an extremely low level of CO2 emissions per capita from electricity generation, since over 90% of its electricity is nuclear or hydro. Highly radioactive materials, such as spent fuel rods, are stored in The Hague (a reprocessing facility) and at the Marcoule nuclear facility, on the Rhone River near the southern city of Orange. Waste disposal is being pursued under France's 1991 Waste Management Act (updated 2006) which established ANDRA as the national radioactive waste management agency. Research is being undertaken on partitioning and transmutation, and long-term surface storage of wastes following conditioning. Wastes disposed of are to be retrievable. After strong support in the National Assembly and Senate, the Nuclear Materials and Waste Management Program Act was passed in June 2006 to apply for 15 y ears. This formally declares deep geological disposal as the preferred solution for highlevel and long-lived radioactive wastes, and sets 2015 as the target date for licensing a repository and 2025 for op ening it. It also affirms the principle of reprocessing used fuel and using recycled plutonium and uranium "in order to reduce the quantity and toxicity" of final wastes, and calls for construction of a prototype fourthgeneration reactor by 2020 to test transmutation of long-lived actinides. The cost of the repository is expected to be around EUR 15 billion: 40% construction, 40% operation for 100 years, and 20% ancillary (taxes and insurance). Risks and Benefits of Nuclear Power How would you compare its safety with coal power generation? 7.11