Megawatts and Megatons

Megawatts and Megatons
by Richard L. Garwin and Georges Charpak

Main Points:

• Georges Charpak won the 1992 Nobel Prize in Physics "for his invention and development of particle detectors, in particular the multiwire proportional chamber". 
• Richard L. Garwin is the author of the first hydrogen bomb design.
• Purpose of the book: indicate where we are and where we might be in the case of nuclear power supplying power to society. Taking into account other sources of energy and taking into account safety, economy, etc.
• History:  1934, Enrico Fermi found radioactivity when they investigated uranium with slow neutron capture. In 1938 they had discovered fission of uranium, with energy 30x that of regular radioactive decay. The dream of Leo Szilard of 1932 was in sight when they realized that an absorption of a neutron resulted into the emission of several neutrons. You could have a neutron chain reaction. 
• First application of nuclear fission was achieved in 1945 when they destroyed 10kg of U-235 in the time of a few milliseconds. Every 10 nanoseconds you had 4 neutrons released. 
• Nuclear power plants - the idea is to have a perfectly steady rate of fissions/ emission of neutrons. Hiroshima bomb fissioned a 1kg of uranium in less than a microsecond. A large scale uranium 1Million KW plant fissions about 1 ton of uranium a year (1000x Hiroshima bombs ~ equivalent to an ordinary power plant in a year). Total 300 nuclear power plants around the world have 90% capacity factor with the downtime for planned maintenance/refueling and provide 15% of the electrical energy of the world (5% of the world's energy use). 
• The Numbers: In the United States, 103 plants produce 20% of the electrical power. The plant is connected to power transmission lines and needs nuclear fuel (25 tons of uranium with 4.4% U-235 in contrast to the 0.7% U-235 in naturally occurring uranium). The usual power reactor sustains about 0.6 million US residents. 25 tons of uranium could fit into a single railroad car, while the spent fuel (1 kg lighter) has released mass into electrical energy (1 Million kW for 8,000 hours) and heat that has been dissipated to cooling water. The 25 tons of uranium (4.4% U-235) is derived from 200 tons of natural uranium, which is also derived from 200,000 tons of ore mined from Canada, Russia, etc. from a substance called "yellow cake." In contrast, a coal fired power plant requires 3 million tons of coal/yr delivered to the power plant and results in 10 millions tons in CO2 ejected to the atmosphere each year. Transport of nuclear fuel is less of a burden than transport of coal. The disposition of ash from coal fired power plants constitutes 10% of the annual feed. In feed is 3 Megatons, but the ash is 0.3 Megatons. The ash of the coal plant is inert at room temperature. The ash of a nuclear plant (at 25 tons/yr) is 10,000 times less voluminous. Fresh fuel for a nuclear reactor is thin walled metal tubes, the size of a pen filled with pellets of uranium oxide and ceramic containing (4% U-235 and 96% U-238) while spent fuel (after four years in a reactor) has about 4% fission products, 0.9% residual U-235, 1% plutonium, 65% fissile plutonium, 0.1% non-plutonium (transuranic products). Plutonium 239 is formed by non fission capture of neutrons. Uranium from spent fuel costs less than naturally occurring uranium because of residual U-236 and U-234 contamination. Major problem with spent nuclear fuel is the radioactive components (Strontium-90 (pure beta emitter) and Cesium-137 (intense gamma ray)) with a half life of 30 years. Even after 2 years of cooling in a deep pool of water, it will still glow red hot after bringing it up to air within minutes.  10% of fission products have half lives of 1 million years.
• Storing Nuclear Waste: Tall casks about 8 meters tall. Two casks contain the spent uranium for the course of a year. Other methods are to micro encapsulate the fuel (about 0.5 mm in diameter) and working at lower output power. They result in improved safety. 
• Reprocessing Nuclear Waste: uranium, plutonium, and residual components of spent fuel is separated. The recovered uranium is stored with little radioactivity. The plutonium is separated and to be mixed into mixed oxide (MOX fuel) in which 5% plutonium is diluted with plutonium from the enrichment process to form fuel elements that are equivalent to the enriched uranium elements used in reactors. The fission products (transuranic) are vitrified with appropriate glass forming material and casked into stainless steel materials that can be mined into a geological repository. The maximum saving of uranium is 20% (~$700 /kg of uranium while today's cost of uranium is about $30-100/ kg). 
• Reactors: light water reactors, heavy water and graphite reactors. One type of light water reactor (pressurized water reactor) in which uranium is fissioned in a thick pressure vessel that produces 3,000 megawatts of heat that is converted at a rate of 30% efficiency in a turbine into 1,000 megawatts of electrical output. A PWR costs about $6-10 billion due to unnecessary government loan guarantees. With the requirement of 200 tons/yr of natural uranium per reactor, then 9,000 reactors would require almost 2 million tons of raw uranium a year and the world's reserve is about 4 million tons (so only 2 years of supply). However you can recover uranium from seawater where there are 4,500 megatons of uranium (enough to power the 10,000 reactor world for 2,000 years). Another type of reactor is the breeder reactor where neutron absorbing water is replaced by heat transfer fluid called a coolant (molten sodium, lead, lead-bismuth alloy) that absorbs few neutrons so that not only is there neutron left over to maintain fissions/power output, but there is an additional neutron to be captured by in a fertile element like thorium and U-238 to replace the fissile material. In a fast breeder reactor can use up the transuranic elements of fission material, while in the LWR these transuranics are not burned and pose high toxicity, spontaneous neutron generation, etc. 
• Expansions: expanding the present 20% from nuclear energy to all electrical power. About 2,000 reactors would provide all of the electrical needs currently. About 6,000 nuclear reactors would provide all of the world's energy needs. So 9,000 nuclear reactors will satisfy all energy needs in the world of 2050. 
• Carbon Dioxide Emitted (C) = Population (P) x Economic Activity per Person (GDP/P) x Energy Intensity of Economic Activity (E/GDP) x Carbon Intensity of Energy Supply (C/E). 
• Is it economically feasible to dilute the highly enriched uranium of the world's arsenal for peaceful energy generation/uses? The United States in 1992 contracted to buy 500 tons of Russian highly enriched uranium and convert it into nuclear power plant fuel. This is done at a lower price than mining uranium, however there is still another 500-700 tons available. 
• In the extrapolation of the next 50 years (2000-2050) Garwin says we need strong measures to offset the emission of CO2 into the atmosphere. What is the probability that these drastic measures be implemented? What is the relationships between the nuclear power stations and nuclear weapons? The United States and individual states (like California) have introduced laws to implement nuclear. People complain that India/ China were exempted from the Kyoto accords and they need to be included. In fact some of the cheapest reduction in carbon outputs will come from investments in the developing countries to improve the nature of the coal fired plants over there to reduce CO2 introduced into the atmosphere. Very little relation between having a nuclear power plant and nuclear weapon proliferation due to the difference in quality of enriched uranium. A country does not need an enrichment plant to have a nuclear power industry (buying in advance several years is possible). 
• Interested in knowing with new technologies, if a nation were to build a nuclear power plant, how much time would it take to build a new kind of power station? The only types of nuclear power plants are the light water reactors and the evolutionary plants. They are currently built in China and South Korea. This would take 5-6 years to build, by which time you can train the reactor operators. Another development can be in the micro-encapsulated prototype reactors that are currently being developed over the next 20 years. 
• How can we convince our public opinion that has built an opposition to nuclear power, that a new generation of power stations are intrinsically safe? In 1977 Garwin wrote Nuclear Power and in 1997  he wrote Unrealized Fears of Nuclear Power, and more recently, Megawatts and Megatons. These plants (light water reactors) are only safe if they are built properly, managed properly, and reviewed very closely by a competent reviewing organization. In 1979, the US had an accident which did not spew radioactivity into the environment, but loss much of its core. When one makes a decision to have nuclear power, one makes the commitment to reveal the vulnerability of these reactors and means to prevent such risks. 

Liquid Fluoride Thorium Reactors:

• Following the advice of Alvin Weinberg, former director of Oak Ridge National Lab (1955-1972) some teams tried to build thorium nuclear reactors. 
• There were 3 options for Nuclear Energy at the dawn of the nuclear era:
• U-235 (fissile form)
• U-238 (which needed to be transformed into plutonium)
• Two neutrons needed to be consumed, but you needed to know if they would emit more than two neutrons upon fission. Plutonium 239 would emit 3 neutrons when it would fission.
• Thorium (needed to be transformed into U-233)
• Plutonium doesn't emit enough neutrons if it isn't fissioned by fast neutrons.
• Thorium and U-233 has enough fast neutrons to do fission. So the assumption is that we just need a fast reactor. However, there is a disincentive called cross sections or how likely a nuclear reaction will proceed (10^(-24) sq. cm). This describes how probable a nuclear reaction is (U-233 thermal neutron is more likely (larger cross section) than a U-233 fast neutron (smaller cross section)). Similarly, Plutonium is more likely to have a reaction with a slow neutron versus a fast neutron. 
• Fast reactor: smaller cross section, higher probability if neutron is absorbed there is fission.
• Thermal reactor: large cross section, lower probability if neutron is absorbed there is fission.
• In 1951, the United States built the fast breeder reactor in Idaho (EBR-I) it would use fast neutrons to convert uranium into plutonium. Main Problem: unless you can rapidly reprocess nuclear fuel, you don't see the benefits of the fast breeder reactor. You would need to simplify the entire recycle step or achieve extremely long burns. 
• It was followed by the EBR-II (62 MW of power). 
• In 1969, Alvin Weinberg was working on molten salt reactors at Oak Ridge National Lab because he believed they could achieve a simpler recycling step to the spent fuel. 
• However in March 16, 1972 President Nixon mentioned the fast breeder reactor in his State of the Union address and in a call with Rep. Craig Hosmer mentioned that it would create economic wealth in Southern California and millions of jobs. Meanwhile the Atomic Energy Commission (AEC) did an investigation of the molten salt breeder reactor technology. 
• Why molten salt? It can run at high temperature and low pressure. In the event of an emergency, the fuel can be put into a passively cooled configuration. 
• Challenges: need special materials that are not corroded by the high temperature salts, technology base has stagnated for 40 years, and LFTR is very different from the water-cooled LWR reactors. 

Watch Richard L. Garwin as the invited lecturer at the first Lezione Felice Ippolito on the May 22nd, 2008 as part of his 9 part youtube series "Nuclear Energy in the Future of the World."

Watch an interesting talk by Kirk Sorensen, Founder of Flibe Energy, on what could be the optimal thorium nuclear reactor?

Watch Pandora's Promise (recommendation by David Hess from WNA) and take a listen to the Titans of Nuclear podcast for the latest news from experts on nuclear energy !