But what is missing in this picture of a modern, efficient coal-fired power plant? Is this the “clean coal” that the industry likes to talk about? The Platte River Power Authority (PRPA) non-profit utility is justifiably proud of its efforts and expense to make this coal-fired power plant as clean as it can be. But it is not clean! It suffers from the Achilles’ heel that all coal plants suffer from—the production of invisible carbon dioxide (CO2) that is coming out of the smokestack. When pure hydrocarbon (the type of carbon in fossil fuels) burns, it produces CO2 and water. When coal burns, it produces CO2 and water, as well as various other pollutants. Coal is delivered to Rawhide every other day by an 80-car coal train from the Antelope mine in the Powder River Basin south of Gillette, Wyoming. The Powder River Basin provides about one-third of all the coal used in coal-fired plants in the United States because it has low sulfur content and ash, which reduces emissions, but also because it is close to the surface so it can be pit-mined with gargantuan machines. About 80 trains—each a mile long—are needed daily to carry the coal from the mine to the various coal plants throughout the country that depend on it. Transportation of these huge amounts of coal also produces a lot of CO2. The coal from the Powder River Basin is sub-bituminous, so its energy density is less than that of the bituminous coal that is predominant in Appalachia and Illinois. Sub-bituminous coal contains 35-45% carbon; bituminous coal contains 45-86% carbon (2). This means that more of it has to be burned to give the same amount of electricity. About a million tons of coal are burned in the Rawhide power plant every year.

I talked to Dave Ussery, the Environmental Services Manager for PRPA, to find out about the pollutants coming from the plant. The so-called criteria pollutants that have to be monitored are sulfur oxides that cause acid rain; nitrogen oxides that cause acid rain, ozone, and smog; and particulates that cause haze (3). The emis­sions of these pollutants from Rawhide are much lower than required by state and EPA standards and are among the lowest for coal plants in the country. Emissions of toxic hazardous air pollutants such as mercury are also low, and Rawhide has imple­mented technology to reduce mercury emissions even further. But the 800-pound gorilla in the room is CO2. The plant emits over two million tons of CO2 annu­ally (4)! And this is for a relatively small power plant. A more typical coal-fired power plant would produce about 1,000 MWe, or nearly four times as much as Rawhide with correspondingly more CO2 emitted (about 8 million tons). The larg­est coal-fired power plant, Plant Scherer in Georgia, produces over 3,000 MWe and generates about 23 million tons of CO2 annually (4). When you multiply this by the approximately 600 coal plants in the United States, you can begin to see the magni­tude of the CO2 problem! Altogether, coal-fired power plants in the United States contribute 2 billion tons (gigatons or Gt) of CO2 to the atmosphere annually (5), about one-third of total CO2 emissions in the United States.

Furthermore, while the Rawhide power plant uses the latest and best technol­ogy to reduce pollutants, many power plants do not. The 1970 Clean Air Act was passed by Congress to reduce the problem of acid rain caused by sulfur oxides by requiring scrubbers on new coal-fired power plants. Because of lobbying from coal states, coal-fired plants existing or licensed before 1973 were grandfathered in so they would not have to meet the standards. The idea was that as they made modifications, they would then have to meet modern standards. However, many of them simply decided to remain as they were so they would not have to add on scrubbers. More recent regulations, such as the 2005 Clean Air Interstate Rule by the EPA, requires that sulfur dioxide emissions be reduced by 57% by 2015, so some older plants are being phased out or are adding scrubbers. Still, about 60% of coal plants still do not have scrubbers (6, 7).

Niels Bohr was 19 years old in 1905 when Einstein had his miracle year. The Danish scientist would be second only to Einstein in his scientific contribu­tions in the twentieth century, and he became an unmatched scientist-statesman. He founded the Institute of Theoretical Physics in Copenhagen, which was the breeding ground for most of the ideas that became the new physics of quantum mechanics. Everyone wanted to run their ideas past Bohr to see what he thought. But that is getting ahead of the story. Bohr went to Cambridge in 1911 to study under J. J. Thomson, but he soon became disenchanted with the work going on there, and Thomson was not particularly interested in him. Rutherford was in Manchester by then and he came to Cambridge to speak. Bohr was immediately impressed by Rutherford and wanted to study with him. In the spring of 1912, Bohr moved to Manchester and began studying radioactivity with Rutherford’s group. He also began thinking deeply about the problem of the nuclear atom that Rutherford had just published (7).

Bohr was familiar with the idea of the quantum that had been developed by Planck and Einstein in which nature became discontinuous and only certain dis­crete or quantized values could exist. He began thinking of stable orbits of an elec­tron around the nucleus as being quantized, that is, having only certain discrete values, but he had no theory to explain why they should. Then he heard about work on atomic spectra that had actually been done decades before. Since the mid-1800s it had been known that if you heated an element such as hydrogen or carbon or oxygen, it emitted light that was not continuous but rather consisted of very specific, discrete frequencies. It was possible to identify a specific element by measuring its atomic spectrum—the specific frequencies of light it emitted—but the cause of the spectrum was not understood. In 1885 the Swiss physicist and mathematician Johann Balmer developed a formula that precisely matched the atomic spectrum of hydrogen gas. The frequency of the emitted light in cycles per second was proportional to the difference of the ratios of two integer numbers squared. Mathematically,

f = 3.29 X1015 ( -1 —l— I V n m )

By setting n = 2 and letting m be 3, 4, or higher, this formula precisely agreed with the actual observed frequencies of light from the hydrogen atom (7). And Balmer predicted that n could also be any integer and m could be any integer larger than n, which turned out to be true also. But no one had a clue why the formula worked.

Bohr had gotten married and returned to Copenhagen in 1912 while he was thinking about the problem of the stable atom. A spectroscopy expert there asked Bohr to explain the Balmer formula. Bohr had never heard of it, but as soon as he saw the formula “the whole thing was immediately clear to me” (7). Bohr reasoned that there must be only certain orbits allowed for an electron as it revolved around the nucleus. These orbits are represented by the integers. He postulated that these orbits are stable and are not able to emit radiation, thus solving the problem of Rutherford’s atom, where the electron should collapse into the nucleus. In his quantum view of the hydrogen atom, the electron is most stable in the lowest orbit with n = 1. It can only exist in orbits with n = 1, 2, 3, and so on (Figure 6.2).

When the electron is in its lowest orbit, it is most tightly bound to the nucleus. The electron can be “excited” with a collision or absorption of a photon to move up to a higher orbit (a higher value of n). His critical insight was that when an electron is excited to a higher orbit m, it is unstable and will drop down to a lower orbit n. In the process it will emit a quantum of light (a photon) with an energy hf equal to the difference in energy between the two orbits. This is the same energy formula that Einstein discovered in his theory of the photoelectric effect.

A different way of thinking about the electron orbiting a nucleus is that the electron is trapped in an energy well and has negative energy (Figure 6.3). An electron with negative energy is bound to a nucleus. The energy well has differ­ent energy levels that are also quantized—that is the electron can only have spe­cific energies that vary by the integer n—so the inner orbit has the most negative energy. An electron is normally in the lowest (most negative) energy level with n = 1, which is also the innermost orbit and is called the “ground state” When the electron is given energy by a collision or by absorbing a photon, it moves up to another discrete energy level with n equal to 2 or 3 or higher. It can never be between energy levels, only in one or another of them.

After an electron has been excited to a higher level, it will then jump back down to the lower level and emit a quantum of energy in the form of a photon of light (the wave packets shown in Figure 6.3) that has an energy exactly equal to the difference between the two energy levels and is equal to hf. The larger the jump (e. g., from n = 3 to n = 1), the higher the frequency of the photon and the more

energy it has. This is, in fact, where some X-rays come from. If the electron is given enough energy, it can completely leave the energy well, and it is then a free electron with positive energy. In this case, the atom is ionized.

These two different pictures of the Bohr atom completely account for the light spectrum formula given by Balmer, where the values for n and m are the initial and final integer values for the energy levels of the electron. Bohr’s model also predicted spectra that had not yet been seen but were later measured exactly as predicted. It also fits in very well with Einstein’s photoelectric theory that photons can kick electrons out of the atom. This is the reverse situation to that shown in Figure 6.3; in the photoelectric effect, a photon of light with energy hf can give its energy to an electron and kick it up into a higher orbit or kick it completely out of the energy well.

Bohr understood that he had to make some assumptions that were clearly in violation of classical physics: namely, that the electron could have stable, quan­tized orbits in which it would not radiate energy, and that it emitted photons of light with energy hf when it jumped from one energy level to a lower one. These assumptions explained the observations and allowed predictions, but he did not have an underlying theory of why this should be. That would have to wait.

In 1922, the year in which Bohr received the Nobel Prize for his theory of atomic spectra, he made another great theoretical triumph. He developed a more general theory of atoms that explained the chemical properties of elements in the peri­odical table. By then, Rutherford had shown that the nucleus is made up of pro­tons—the nucleus of the hydrogen atom—with a positive charge. Bohr proposed that the electrons in atoms are arranged in concentric shells, as in Figure 6.2, with only a certain number of electrons allowed in each shell. Once a shell was filled, electrons would have to go into the next shell until the total number of electrons was the same as the number of protons in the nucleus. The electrons in any shell are associated with four different quantum numbers (n, l, m, and s), and Wolfgang Pauli proposed that no two electrons can have the same values for all four quan­tum numbers. This was known as the Pauli Exclusion Principle, and it explained why only a certain number of electrons can exist in any given shell (2). Bohr showed that only the electrons in the outer occupied shell determined the chemi­cal properties of elements; this explained the ordering of chemical properties that Mendeleev first outlined in his periodic table of the elements (12).

Werner Heisenberg was a young German from Bavaria who became captivated by Bohr’s ideas when he heard him lecture in Gottingen, Germany, one of the great scientific centers in Europe where numerous Nobel Prizes were hatched. Heisenberg went to Copenhagen to work with Bohr on the atom. However, Heisenberg was not enamored with the semi-classical model of orbits envisioned by Bohr. After returning to Gottingen in 1925, he focused entirely on a mathemat — ical—rather than physical—approach to the atom and developed a new theory based on arrays of numbers that were multiplied together by certain rules. This form of mathematics is known as matrix algebra; using it, he was able to develop a coherent theory that completely described the Bohr atom but had no physical model associated with it. In 1926 another student of Bohr’s, the Austrian Erwin

Schrodinger, developed another mathematical approach to describing the atom that was based on probability waves rather than jumping electrons. Schrodinger’s wave equations described the probability that an electron could be in a particu­lar orbit. Together, the contrasting mathematical approaches of Heisenberg and Schrodinger were called “quantum mechanics" and Schrodinger proved that they were mathematically equivalent (9, 10). Quantum mechanics, not the Bohr the­ory, provides the true self-consistent description of atoms.

Heisenberg made another great theoretical contribution to quantum mechan­ics, known as the Uncertainty Principle. Fundamentally, Heisenberg did not believe in the reality of objects but only in the reality of measurements. If you cannot measure something, then it does not exist. Classical physics described by Newton assumes that you can know to any degree of certainty where an object is and what momentum it has. But Heisenberg said that this is true only if you can measure it. If you were trying to measure where an electron is, you would try to shine light on it to see it, but you can only see something if it is larger than the wavelength of light used to observe it, so to see an electron you would have to use short wavelength light. Recall that the frequency of light is inversely related to the wavelength, so a short wavelength has a high frequency, which has a high energy (hf). So, in the very process of trying to determine exactly where an electron is, you have to use high frequency light with energy that then moves the electron so you no longer know its momentum (which is its mass times its velocity). The more accurately you try to determine where the electron is, the less accurately you can know how fast it is moving (13). According to Heisenberg, you can only simultaneously determine the momentum and location of an object to an accuracy given by Planck’s constant. Mathematically, the uncertainty (Д) in momentum (Ap) times the uncertainty in position (Ax) is greater than or equal to h, or ДpДx > h (9). Philosophically, the uncertainty principle means that we cannot know the precise details of the world to infinite precision and can therefore not predict future events precisely. It also means that it is impossible to state precisely where an electron’s orbit is around the nucleus. The Heisenberg Uncertainty Principle transformed our way of thinking about what we can know about reality.

Quantum mechanics describes a world that is very hard to think about in visual terms, and it is a world that seems contrary to all our experience. Electrons are not really hard charged balls that circulate around a solid nucleus but are prob­ability waves that can amplify or interfere with each other. In a quantum world, positions and energies of electrons are quantized, so they have a maximum prob­ability of existing in certain places but not in other places. Depending on how you measure them, objects can have properties of waves or properties of particles. Furthermore, there are fundamental limits to how accurately you can measure anything. The world of Newton and Galileo simply does not work in the realm of the atom. Fortunately, we don’t have to worry about it in our macroscopic world.

The semi-classical, semi-quantum picture of an atom developed by Bohr is not really an accurate picture for complex atoms. Quantum mechanics provides the true picture, but it is mathematically complex and difficult to think about.

However, it is easy to conceptualize Bohr’s atom, and it is good enough for our purposes. A specific atom is characterized by a certain number of electrons, which exactly matches the number of protons in the nucleus. All of chemistry is based on the electrons in the outer shell. It is possible to kick an electron out of its orbit and completely out of the atom. In this case, you have a free electron and an atom that has a net positive charge. These are called ions and the process is called ionization. Most of the effects of radiation on cells are determined by the ionization of atoms and molecules. We will look at this in more detail in Chapter 7.

At the beginning of the chapter, I posed the question of whether spent nuclear fuel is really waste or a resource. In fact, it is both, but in the United States we only con­sider the waste part of it. How can it be a resource? Recall that there is still about 1% of 235U in the spent nuclear fuel that could potentially be enriched and used for new nuclear fuel. But there are also several isotopes of plutonium present in the spent nuclear fuel, including 239Pu, 240Pu, 241Pu, 242Pu, and 238Pu, in decreasing order of abundance (1). Of those, 239Pu and 241Pu are fissile,7 meaning that they can be induced to fission with slow (or fast) neutrons, the essential condition for sus­taining a chain reaction in a standard nuclear reactor. And of course there are also a lot of fission products. Suppose it were possible to extract the fissile uranium and plutonium and recycle it into new fuel to burn in a reactor. Actually, it is possible, and it is currently being done in several countries, including France, England, Russia, and Japan. The United States is the sole holdout of major countries with large nuclear power production that does not reprocess its spent nuclear fuel. The United States actually developed the technology to reprocess8 spent nuclear fuel and was building a commercial reprocessing plant in South Carolina when President Carter halted the whole program. Are we making a big mistake?

France is a special case when it comes to nuclear power. The reason is that France lacks indigenous energy resources—“no oil, no gas, no coal, no choice.” Its coal deposits are poor quality and mining ceased in 2004; France imports 98% of its natural gas and 99% of its crude oil (33). In 1973, during the OPEC oil embargo that cut oil exports to consumer countries, France realized that it was too depen­dent on foreign countries for its energy. As a result, the French government, led by Prime Minister Pierre Messmer, pushed for a rapid expansion in nuclear power capability to make France more energy secure. France now has 58 nuclear power reactors, which produce slightly over 75% of its electricity. It has nearly the cheap­est electricity in Europe and has extremely low emissions of CO2, all because of its large nuclear power portfolio (34).

AREVA is a French company, owned primarily by the French government, that is the world leader in nuclear power. It is involved in all aspects of nuclear power, from mining to building reactors to recycling spent nuclear fuel. It operates what is known as a closed fuel cycle in which uranium is enriched and made into fuel pellets that are burned in a reactor, then the spent fuel is reprocessed to extract the plutonium and uranium, which is made into new fuel that is burned in a reactor again. The result is a large reduction in the waste storage problem and the creation of new fuel. In the United States, in contrast, we use an open fuel cycle in which uranium is enriched and made into fuel pellets that are burned in a reactor; but then, instead of recycling the spent nuclear fuel, it is to be stored in some perma­nent repository such as Yucca Mountain.

I went to France to see how spent nuclear fuel is recycled and made into new fuel. The La Hague recycling plant sits on the tip of the Cotentin peninsula west of Cherbourg in the Normandy region of France. It is a beautiful drive from the coastal resort town of Barneville-Carteret, where I stayed, through the Normandy countryside to La Hague (Figure 9.4). Farmers are busy tending their dairy herds and sheep and raising crops around the recycling plant while a wide diversity of seafood is caught in the nearby ocean. You would not guess that this idyllic spot would house a facility that recycles all of France’s spent nuclear fuel and that from other countries too.

After arriving at the highly secure recycling plant, I was met by Michael McMahon, a former US Navy officer on a nuclear submarine—excellent train­ing for workers in the nuclear power industry. The deputy general manager, Jean-Christophe Varin, gave an overview of the facility and described how the uranium and plutonium are removed from the fuel rods to eventually be made into new fuel, while the fission products are separated out and made into a glass. He told me that for many years Japan has shipped their spent nuclear fuel to La Hague to be recycled and then shipped back. Japan recently built a new recycling plant at Rokkasho-Mura that began operation in 2008, so they can now do their own recycling instead of shipping spent nuclear fuel across the ocean. France also recycles fuel from several European countries, including Germany and Italy.

Michael took me on a tour of the facility after we got decked out in white jump­suits and shoes and clipped on our radiation monitors. The first place we went was the receiving area, where spent fuel is delivered from France or other countries in special casks that weigh 110 tons. They are checked for contamination, then the casks are opened under remote control and the fuel assemblies are removed and placed in cooling pools, similar to the ones at a nuclear reactor. There are four pools that can hold all of the used fuel that can be processed. The used fuel rods are held for several years to cool down, depending on where they come from. Some countries store them for years before sending them to La Hague.

When the time is right, fuel assemblies are taken from the pools and go into a shearing facility that cuts off the ends of the assemblies and shears the pellets into small pieces. They go into a nitric acid bath to dissolve the uranium, plutonium, and fission products, then the hulls are separated, washed, and crushed into casks for long-term storage. Because of the high radioactivity of the fission products, all operations are done behind thick leaded glass with remote robotic arms. The uranium, plutonium, and fission products are separated by various chemical pro­cesses and then processed in different ways. First, the uranium and plutonium are removed from the fission products in a solution. They are then further separated into different processing streams. The uranium remains in a uranyl nitrate solu­tion, which is stored until it is needed; it can then be made into uranium oxide for nuclear fuel. It is about 1% 235U and 99% 238U, so it has to be enriched in the same way that mined uranium is enriched (see Chapter 11) before being made into nuclear fuel.

The plutonium is transformed into a plutonium oxide powder and put into can­isters about a foot long and 4 inches in diameter. These are welded shut, packed into longer tubes that are screwed or bolted shut, then put into larger containers for shipping to another plant called Melox, where they will be made into new fuel pellets. Michael told me that the reason the Melox plant is not here but is near Avignon in southern France is because of a political decision years ago based on creating hundreds of jobs in Avignon. As a result, the plutonium has to be shipped across France instead of being made into fuel at the same plant. Politics intrudes into these kinds of decisions everywhere!

The fission products are fed into a calcinator, where they are heated to a high temperature and turned into a dried material called calcine. This is fed into a machine with glass frit, where the calcine is mixed and vitrified under high heat. The resulting melted glass is poured into special stainless steel casks, where it solidifies and can then be safely stored for thousands of years. According to French government rules, all of the uranium, plutonium, and fission products are returned to the nation that contracted for their recycling. France stores all of its own vitrified waste in three areas that are about the size of a basketball court, and a fourth one is being built. The casks are stacked in underground storage with air circulation to allow for cooling. It is amazing to walk around the room where the waste is stored and realize that safely stored under my feet is the total waste generated by 58 reactors, and there is capacity for storage of 50 years worth of recycled spent nuclear fuel. The waste storage problem is vastly simplified because the fission products are primarily Cs-137 and Sr-90, which will decay away, so they are less radioactive than uranium ore after about 500 years (see Figure 9.2). There are also some transuranics such as americium in the vitrified waste, which will remain radioactive for thousands of years.

The final area of the tour was the environmental monitoring area. There are some emissions that are released to the air and to the ocean. A pipe takes low level radioactive liquid effluent from the plant and releases it 5 km into the English Channel in compliance with strict regulations. Local plants, foods, fish, seawa­ter, freshwater streams, aquifers, and air are frequently sampled and analyzed for radioactivity to make sure that there are no hazards to the people or the environ­ment in the surrounding area. Twenty thousand samples are taken each year for analysis. There are two main areas that are carefully monitored—one is a fishing village where currents would likely deliver the most radiation from the effluent, and one is a farming village downwind of the plant. There have never been any problems with radioactive contamination of more than a fraction of a percent of normal background radiation. The results of the tests are summarized daily and posted on the Internet for all to see.9 Before leaving the facility, my radiation badge was checked. I had no measurable exposure to radiation during my tour.

After the tour, my hosts took me to a restaurant the facility owns that is on the coast a few km away in a stunning site. From the restaurant you can see the pipe that gently slides into the ocean to release the low level liquid waste, and if you look down the coast you can see the newest Generation III+ EPR nuclear plant that France is building at Flamanville. We had a very good lunch (it is France, after all!) and talked about nuclear issues and how recycling is a very good solution for greatly reducing the problems with spent nuclear fuel and reusing fuel.

One of the most effective uses of solar energy is to heat energy-efficient houses and to heat water for residential use. Since it is not necessary to convert the sun­light into electricity, it is a much more efficient process. It is likely that this will

be one of the largest uses of solar energy, reducing the demand for electricity or natural gas to heat water.

Limitations of Solar Power

What are the limitations of solar that make it unlikely to be a large part of the overall energy portfolio? Remember that it currently only provides 0.04% of our electricity and the EIA projects that it will only be 5% of the renewable energy mix—excluding hydropower, the largest component now—by 2035. The biggest limitations are location, intermittency, footprint, and high cost.

Now that you are a member of the cognoscenti for your knowledge of radiation doses, it is time to explore what radiation does to cells and to DNA. The relative

damage depends on the kind of radiation because the density of ionizations varies greatly for a у ray compared to an a particle (Figure 7.5). A p particle or у ray has a low density of ionizations, so they may well pass through a strand of DNA and cause no damage whatsoever, but an a particle causes a lot of damage. In particular, the ionizations may cause breakage of molecular bonds that hold the strands of DNA together.

Radiation can cause ionizations in many molecules in a cell, but numerous experiments over the years have shown that it is the damage to DNA that causes the biological effects. Alpha particles mainly break both strands of the DNA in what is called a double strand break (DSB) (Figure 7.5). Beta particles and у rays, which are the main types of radiation from fission products in spent nuclear fuel (see Chapter 9), can cause a variety of types of damage to DNA. They can cause DSBs if the cluster of ionization occurs in just the right place. More commonly, they can break just a single strand of the DNA, forming a single strand break (SSB). In addition, they can cause various kinds of damage to the bases in DNA or can cause linkages to form between DNA and proteins.

Of all of these types of damage, the main one that causes problems is the for­mation of DSBs. DNA that is broken in this way forms what are sometimes called “sticky ends” and they can be stuck back together with special repair enzymes. But they don’t always get stuck back together properly. Sometimes a piece of DNA is just lost from the end of a chromosome, in what is called a terminal dele­tion. Sometimes two DSBs are formed, and a piece in the middle of a chromo­some can be deleted (an interstitial deletion) or inverted (an inversion). Pieces of DNA from different chromosomes can also get stuck together, forming what
is known as a reciprocal translocation, which is not lethal, or a dicentric (a chro­mosome with two centromeres), which is lethal to the cell. These various possi­bilities for sticking broken pieces of DNA back together form what are known as chromosomal aberrations, many of which are visible through a light microscope when you look at chromosomes in mitosis. Some of these chromosomal aber­rations are lethal to cells and some of them are benign, having no effects what­soever. And some of them may cause mutations that can cause a cell to become cancerous later (7).

So how much damage are we talking about? Now it is important to talk about a specific dose of radiation. A dose of 1 Gy of p or у radiation causes a rather large amount of damage in the DNA of a cell: about 20-40 DSBs, 1000 SSBs, 1,000 dam­aged bases, and 150 DNA-protein crosslinks (8, 9). The number of DSBs from the same dose of a particles is about three times as much as for у rays (9). Amazingly, the majority of cells that receive 1 Gy of у rays are not killed. How is that possible?

There are several factors that allow our cells to sustain so much damage from radiation without being killed. One factor is that we are diploid organisms—that is, we have two copies of our chromosomes—so damage to one copy can often be overcome by undamaged DNA on the other chromosome. Another factor is that the vast majority (about 98%) of our DNA does not code for anything. Genes contain coding DNA (exons) and long stretches of DNA known as introns that are spliced out before RNA and proteins are made, so much of the damage from radiation may be in regions of DNA that have no effect on the resulting proteins. There are also regions of DNA consisting of highly repetitive short sequences that do not code for anything. Finally, our cells have very sophisticated enzymatic repair machines that can fix most of the damage caused by DNA. This might be very surprising to you, and it apparently is unknown to Helen Caldicott and many anti-nuclear activists, who seem to believe that any radiation is going to cause cancer. In fact, the vast majority of damage to DNA caused by radiation is in DNA that has no apparent function or is repaired.

What does this mean for nuclear power? Only time will tell, but initial responses indicate that the consequences will vary dramatically in different places. In the United States, there are only two reactors that sit on a site that could conceiv­ably suffer a similar accident—Diablo Canyon, 12 miles southwest of San Luis Obispo, and San Onofre near San Diego, California. Both sit near faults and near the ocean. However, both are designed for worst-case earthquakes and neither is subject to a tsunami, since Diablo Canyon sits 85 feet above sea level and San Onofre sits 50 feet above sea level and also has a sea wall 30 feet tall. Both have cooling water reservoirs that sit above the reactor, so in the event of complete power failure, gravity would keep the water flowing (58). Thus, neither of these could suffer the same sequence of events that happened in Japan. There does not seem to be a groundswell against nuclear power, though it may impact the licens­ing of new reactors. However, a recent poll indicated that 80% of residents living within 10 miles of a nuclear power reactor supported the use of nuclear power to provide electricity in the United States and 83% thought the US nuclear industry was safe (59). US nuclear utility leaders are still interested in moving forward with nuclear, but how rapidly they move depends more on economic conditions than the accident in Fukushima (60).

The reaction in Europe varies. Germany and Switzerland have taken the extreme positions of deciding to end nuclear power. Switzerland has five reactors that provide 40% of its electricity and was planning to build two more, but the Parliament decided to phase out nuclear power by 2034 (61). Germany has long been somewhat paranoid about nuclear power, with a strong Green party that has vociferously opposed it since Chernobyl. Chancellor Angela Merkel had been supportive of nuclear power and just months previously had pushed through an agreement to extend the life of many of the existing 17 nuclear reactors that pro­vided 23% of Germany’s electricity. In an abrupt reversal in the face of public angst and anti-nuclear demonstrations, she decided to end nuclear power by 2022. This is in spite of the fact that Germany sits on no known fault lines and could not be subject to a tsunami and has never had a serious nuclear accident (62, 63). What it means is that Germany will buy more nuclear power from France, will burn more of its lignite “brown coal”—the poorest quality coal, which generates a lot of car­bon dioxide when burned—and will be more dependent on Russia for natural gas (64). It is highly unlikely that wind and solar can make up for the loss of nuclear power. Other European countries do not plan to reduce their nuclear power in response to Fukushima (62). Russia plans to continue its growth of nuclear power also, with 34 reactors being built or planned (65).

The most rapid growth of nuclear power is in Asia—China is building or plans to build 81 reactors, India 25, South Korea 10, and Japan had planned to build 14 in addition to the 54 it had before the accident (65). Except for Japan, it is not likely that these countries will greatly curtail their nuclear plans, since their needs for electricity are growing rapidly. Japan had 4 reactors destroyed, and shut down all but 19 of its 54 commercial reactors after the accident. By early 2012 it had shut down all of its reactors. Japan has few natural energy resources, so it depended on nuclear power for 30% of its electricity and is unlikely to permanently shut down a large number of its nuclear reactors. It is doing stress tests of the existing reactors to see how they would cope with a similar disaster (66). Most likely the undam­aged reactors will need to begin operating again.

The contrasts between a nuclear reactor such as Wolf Creek and a solar plant or a wind farm are stark. Nuclear power provides the constant baseload power that is essential to a power grid. Nuclear reactors are independent of when the wind blows or when the sun shines—they operate 24/7—so they have a 90% capacity factor on average (5) instead of 25% for solar or 33% for wind. Since the Wolf Creek nuclear reactor is rated at 1,200 MWe, the long-term average output will actually be about 1,100 MWe. The capacity factor would be even higher if it were not necessary to shut down the reactor every 12 to 18 months to change the fuel, a process that takes a month or more. This down time is scheduled ahead of time so a utility can plan around it—quite different from the intermittency of solar or wind. Except for the fuel change, the reactor is usually running at 100% capac­ity. Nuclear power doesn’t really compete with wind and solar, though. Instead, it reduces the need for coal or natural gas to provide baseload power. Of the CO2-free energy sources (renewable and nuclear), only nuclear can scale up suf­ficiently to displace our huge dependence on coal for baseload power.

“How many of you who moved to Colorado from Texas or Florida took into account that you were nearly tripling your annual dose of natural radiation by studying here?” That is the first question I ask students in my radiation biology class at Colorado State University, and of course none of the students considered that they were increasing their exposure to radiation by a large factor simply by moving here to live. And none of them would have used that as a reason to not study here. In contrast, if they were moving near a nuclear power plant in their state, they might have had second thoughts, even though they would be exposed to far less radiation than by coming to Fort Collins, Colorado.

There is no place on earth where you are not exposed to radiation. As I said in the previous chapter, life evolved in a radiation environment. But where does the radiation come from, and why is it higher in Colorado than elsewhere in the United States? Are there other areas in the world where it is even higher? Do we get a lot more cancer in Colorado than in other lower radiation states because we are exposed to more radiation? These are important questions—they help us to understand the risk from a particular dose of radiation and put into perspective the exposure to radiation from the nuclear fuel cycle.

We are exposed to radiation that comes from the skies, from the earth, and from our food. These are all natural sources, and there is not much we can do about it except decide where we want to live. But our decisions as to where we want to live almost certainly do not take into account the exposure to background levels of radiation from natural sources. The other main not-so-natural source of radiation exposure comes from medical procedures, a source that is increasing rapidly.

The National Council on Radiation Protection and Measurements (NCRP) publishes scientific information on radiation and its hazards, as well as protec­tion guidelines to assure that workers in radiation environments and the general public are safe. One of the NCRP reports details the exposure of the average US citizen to background radiation. In 1987, 83% of the exposure came from natu­ral sources of radiation, with only 15% coming from medical treatments (NCRP

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Report 93). By 2006, however, medical exposures were 48% of the average dose to an individual in the United States (Figure 8.1) (1). The average US citizen gets 6.2 mSv (620 mrem) of radiation every year, but of course the dose any individual gets varies from that because of where the person lives and the number and kind of medical radiation procedures the person has.

There is one more possibility for the future of nuclear power based on another natural material that is three times more common on earth than uranium—the element thorium. The Red Book estimates there are over 2.3 million tonnes of identified thorium resources, and over 6 million tonnes are likely available (47).

There has been little interest in mining thorium because it is not currently used in reactors, so there is undoubtedly far more available than is known. Natural tho­rium consists of a single isotope, 232Th. The problem is that it is not fissile itself— that is it cannot be used directly in a reactor—but it has to be converted into 233U in a reactor by capturing a neutron and undergoing a couple of rapid p decays. This is analogous to the process in which 238U—which is not fissile—absorbs a neutron in a fast neutron reactor and produces 239Pu. The 233U that is produced is fissile and can then be burned in the reactor or recycled and formed into fuel pellets for a new reactor.

There are several advantages to using thorium compared to uranium in reac­tors. A major advantage is that essentially all of it can be converted to fissile 233U, whereas only 0.7% of uranium is used (the fraction of 235U in natural uranium). It does not require enrichment—a major cost in producing uranium fuel. The nuclear waste produced is also more manageable, since little 239Pu is produced (it takes seven sequential neutron absorption events to transmute 232Th into 239Pu). That makes it much easier to deal with the shorter-lived fission products.

Several types of reactors can be used to convert thorium to 233U, including widely available boiling water reactors and CANDU reactors, made in Canada, which use heavy water as a moderator. Generation III high temperature gas reac­tors (HTGR), which use helium gas both as a coolant and to drive the turbine, are well-suited for incorporating thorium as a fuel. A novel new type of reactor—the molten salt reactor—is in the design stage. Both thorium and uranium would be incorporated in molten salt that would provide both the fuel and also the heat transfer to the turbine. The 233U that is produced from the thorium would be con­tinually extracted from the molten salt as the reactor is operating (59).

In reality, the design for a molten salt reactor was accomplished early in the history of nuclear power (in 1959) at Oak Ridge National Laboratory under the leadership of Alvin Weinberg. Since water is a moderator that slows down neu­trons and 233U requires fast neutrons to fission, a molten salt was used for cooling the reactor and boiling water to run a turbine. Lithium fluoride and beryllium fluoride had excellent properties as carrier salts into which thorium fluoride and uranium fluoride could be dissolved. An experimental reactor was built by 1965 and was operated for several years, though it used only uranium as a fuel, not tho­rium. But Weinberg lost the political and technological battle for reactor design to Admiral Rickover’s pressurized water reactor, and the thorium reactor design faded into obscurity. It is now being resuscitated by a dedicated band of true believers led by Kirk Sorensen who believe that liquid fluoride thorium reactors (LFTR) can solve the world’s energy problems (60).

While no reactors are currently operating on a thorium cycle, several have oper­ated for a number of years in the past. In the United States, the first experimental Peach Bottom reactor near Harrisburg, Pennsylvania, was a high temperature gas reactor using thorium and highly enriched uranium (HEU). It had a capacity of 40 MWe and ran from 1967 until 1974. It served as the precursor to a more ambi­tious 330 MWe HTGR near where I live—the Fort St. Vrain reactor—the first and only reactor to be built in Colorado. The Fort St. Vrain reactor operated from 1976 to 1989 but was shut down because of numerous operational problems that made it too expensive for the utility to manage. Germany operated a thorium high temperature reactor from 1983 to 1989. Its fuel consisted of small “pebbles” of thorium and HEU that constantly moved through the reactor. It is the precur­sor of the pebble-bed reactor that Germany was building in South Africa until construction halted recently. India is the country that is most vigorously pursuing thorium as a reactor fuel because it has little uranium but substantial resources of thorium (59, 61, 62).

SUMMARY

The quest for uranium began with little regard for safety of miners or the general public. However, in spite of the reality that underground miners were exposed to high levels of radon and many did develop lung cancer, modern rules for mining have greatly diminished the dangers to the public. Even the tailings from mining and milling had few if any actual health effects on the public. The shift toward ISR mining in recent years—for those sandstone deposits that are amenable to this type of min­ing—has greatly reduced the environmental issues associated with uranium mining.

The uranium fuel cycle includes mining, milling, enrichment, making fuel pellets that are burned in a reactor, and then dealing with the spent nuclear fuel. Much of the expense (and CO2 production) in the fuel cycle comes from the energy-intensive process of enrichment using the old gaseous diffusion technol­ogy. The new gas centrifuge technology dramatically reduces the energy neces­sary to get enriched uranium, however. In an open nuclear fuel cycle, such as that used in the United States, the spent nuclear fuel is simply stored, but in a closed nuclear fuel cycle, the plutonium and even the remaining 2 35U can be reused in reactors to get much more power out of the fuel. A number of other countries already do that, including France, Russia, Japan, Great Britain, and Germany.

Plenty of uranium exists to power the current 432 operating reactors world­wide for at least another century. Even if there is a dramatic expansion to more than double the number of reactors in a nuclear renaissance, there are still ade­quate known resources for powering these reactors for their design lifetime. With the future (but already proven) technology of fast neutron reactors, new fuel can be “bred” that would give adequate fuel for a thousand years or more. Not only that, but these reactors could be used to burn up plutonium and actinides to reduce the potential for nuclear terrorism. And the possibility exists to develop a thorium-based nuclear reactor economy that could coexist with the uranium-based nuclear reactors.

Clearly, there are adequate resources and technology for nuclear power to end the world’s reliance on coal and reduce greenhouse gas emissions from electric power generation. The question is, will we do so?

The sulfur oxides are not the only problem with emissions from coal-fired power plants. The EPA lists 189 hazardous air pollutants (HAPs) in the 1990 Clean Air Act Amendments. “Of these, 15 occur in coals: antimony, arsenic, beryllium, cad­mium, chlorine, chromium, cobalt, fluorine, lead, manganese, mercury, nickel, selenium, thorium, and uranium"(3) Not all coal contains all of these, and mer­cury is the main health hazard. The form of mercury that is hazardous is called methyl mercury, which is a potent neurotoxin. The largest source of mercury is coal plants, accounting for about one-third of mercury emissions in the United States, or about 48 tons per year. Mercury is emitted as elemental mercury, which is non-hazardous. When mercury settles out of the air, it gets deposited in streams and lakes and is converted to methyl mercury. From there it is taken up by plants, algae, and small organisms. Small fish eat these, and large fish eat the smaller fish, concentrating the mercury in body tissues. Finally, humans eat the fish and get the bioaccumulated mercury. It is because of this bioaccumulation that the Inuit people (Eskimos) of Siberia and Greenland have the highest blood levels of mercury in the world (8), even though they have no power plants. The EPA issued the Clean Air Mercury Rule in 2005 that sets a cap of 38 tons of mercury in 2010 and 15 tons by 2018, which will help reduce the problem but will add large costs to coal power plants (3). On December 21, 2011, the EPA ruled that coal- and oil-fired plants must reduce their mercury emissions by 90%. About 40% are not yet in compliance, and about 1% of them are expected to shut down rather than meet the requirement (9).