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Nuclear energy: Splitting the atom
Andreas Feininger/Time Life Pictures/Getty Images
FISSION: THE BASICS Nuclear fission is the formal name for the splitting of an atom. In self-sustained fission, a neutron causes an atomic nucleus to split, and this gives off more neutrons that cause nearby atoms to break apart, giving off yet more neutrons, in a chain reaction (see diagram, below). Heat from this process can be used to generate electrical energy. Atoms of many elements can be split to release a small amount of energy, but only uranium or plutonium can generate the neutrons necessary for a self-sustaining fission reaction. Plutonium is not found in nature, but mined uranium has three naturally occurring isotopes with atomic masses 234, 235 and 238. The latter is the most abundant of these, but cannot sustain a fission reaction. When a neutron hits a uranium-238 nucleus, it gets absorbed and the nucleus stays intact as uranium-239; in a couple
of days it decays to plutonium-239, “breeding” fissile fuel. Only uranium-235 is fissile, and it makes up just 0.7 per cent of natural uranium. The vast majority of nuclear reactors therefore use a uranium blend in which the proportion of uranium-235 has been boosted, or enriched, to between 3.5 and 5 per cent. The first step in enrichment involves converting refined uranium ore into uranium hexafluoride gas by a complex process. Because molecules of the gas containing uranium-238 are heavier than those containing the lighter isotope, a gas centrifuge can separate them, concentrating
the uranium-235 in stages. After enrichment, the uranium is made into pellets which are placed into long fuel rods. These rods are bundled inside the water-filled core of a light water reactor, a much-used design. The water is heated by nuclear fission, and turned into steam that drives a turbine. A typical nuclear plant can power about 1 million homes. Only a small fraction of the world’s uranium is found in concentrations high enough to be worth extracting. Some 90 per cent of supplies comes from seven countries: Canada, Australia, Kazakhstan, Russia, Namibia, Niger and Uzbekistan.
URANIUM-235 NEUTRON
VIRTUAL NUCLEAR ENERGY Some countries, such as Russia, China and India, are expanding their nuclear programmes. Together, these three countries plan to build nearly 30 new reactors over the next two decades, seven of which are already under construction (see graph, far right). Other countries are moving away from nuclear in the wake of the disaster at the Fukushima Daiichi plant in Japan in 2011. Germany, for example, will phase out its nuclear power plants by the end of 2022 in favour of energy sources such as solar and wind. However, with national power grids now integrated into larger networks, there is no guarantee that non-nuclear countries will never draw on nuclear power. Italy, for example, has no nuclear power stations of its own but obtains 14 per cent of its electricity from France, which has a vibrant nuclear sector. This indirect reliance on imported nuclear energy is described as virtual nuclear energy.
ii | NewScientist | 1 June 2013
FISSION PRODUCTS CAESIUM-137 STRONTIUM-90
Nuclear reactors bombard uranium atoms with neutrons. When the atoms split they release energy and more neutrons
SPLITTING THE ATOM The protons and neutrons in an atom’s nucleus are bound together by the strong nuclear force. By fusing together the nuclei of two light atoms, or by splitting a heavy atom in a process called fission, we can release some of this binding energy. After more than half a century of research, fusion remains technologically elusive. Here we focus on fission, exploited in hundreds of reactors around the world; in 2011, it provided about 13.5 per cent of the world’s electrical energy
250
A BRIEF HISTORY OF FISSION
200
150
In December 1942 Enrico Fermi achieved the first self-sustaining nuclear chain reaction, harnessing the process that would be used to lay waste to the Japanese cities of Nagasaki and Hiroshima in August 1945. In the aftermath of this destruction, proponents of nuclear power made the case that splitting the atom could also be used for benevolent ends, supplying clean energy for all. When that same nuclear chain reaction is channelled into electricity generation, a single gram of uranium can provide 1 kilowatt of power for a year. To put this into context, that is roughly the rate at which the average UK resident used electricity in 2011. Enthusiasts proclaimed that electricity from a nuclear plant would be “too cheap to meter”. In the 1950s, nuclear power began to be used for commercial electricity generation as well as to drive submarines, navy ships and icebreakers, and people spoke glowingly of future nuclear-powered trains and aircraft. By the 1960s, nuclear power was seen as the answer to space travel and just about anything else. Former weapons scientist Edward Teller argued that nuclear bombs should be used in massive civil
engineering projects, blasting canals and flattening mountains as part of a programme called Project Plowshare. Articles in The New York Times enthused about the possibility of “nuplexes” – shopping malls or small cities built around the nuclear plants that provided their electricity. But growing awareness of the potential health effects of any nuclear accidents – and the high costs of building massively shielded facilities that would keep the population safe from harmful radiation – curbed this enthusiasm somewhat. Still, nuclear reactors generate electricity without producing greenhouse emissions or pollutants such as oxides and nitrogen, sulphur, and carbon. Today, 31 countries rely on nuclear for some of their power.
Proposed
Specific programme and site proposals. Expected operation in 15 years
Planned
Approvals, funding in place. Expected operation in 8 to 10 years
Nuclear power’s profile varies greatly from country to country: France relies on it for up to 80 per cent of its electrical energy, the US for 20 per cent and China just 1.9 per cent at the moment
0
Under construction
437
TOTAL NUCLEAR POWER REACTORS OPERATING IN THE WORLD TODAY
However, these numbers are set to change; most of the over 60 reactors now being built are in Russia, China and India China will lead the world in nuclear power generation within 15 years if all its proposed reactors are built
Ch in a US In d Ru ia ss Ja ia p So Fr an ut an h ce Ko re a Uk UK ra Sa Ca ine ud na i A da ra bi a UA E I Vi tal et y Sw nam Ge ede n Cz rma So ech ny ut re Sw h A p. itz fric er a la Tu nd Be rke lg y iu Br m Fi azi n l Pa lan ki d Sl sta ov n ak ia Ar Sp ge ain n H tin u a In nga do ry ne Po sia Ro lan m d Th an ai ia l Be and la ru Ch s ile Ka za Ira kh n s M tan ex Bu ic lg o A a Ba rm ria ng en la ia de s Eg h M Ne al ypt th ay er sia l Sl and ov s en Is ia r No Jo ael rt rda h n Li Kor th ea ua ni a
50
SOURCE: INTERNATIONAL ATOMIC ENERGY AGENCY
100
1 June 2013 | NewScientist | iii
FISSION: THE BASICS Nuclear fission is the formal name for the splitting of an atom. In self-sustained fission, a neutron causes an atomic nucleus to split, and this gives off more neutrons that cause nearby atoms to break apart, giving off yet more neutrons, in a chain reaction (see diagram, below). Heat from this process can be used to generate electrical energy. Atoms of many elements can be split to release a small amount of energy, but only uranium or plutonium can generate the neutrons necessary for a self-sustaining fission reaction. Plutonium is not found in nature, but mined uranium has three naturally occurring isotopes with atomic masses 234, 235 and 238. The latter is the most abundant of these, but cannot sustain a fission reaction. When a neutron hits a uranium-238 nucleus, it gets absorbed and the nucleus stays intact as uranium-239; in a couple
of days it decays to plutonium-239, “breeding” fissile fuel. Only uranium-235 is fissile, and it makes up just 0.7 per cent of natural uranium. The vast majority of nuclear reactors therefore use a uranium blend in which the proportion of uranium-235 has been boosted, or enriched, to between 3.5 and 5 per cent. The first step in enrichment involves converting refined uranium ore into uranium hexafluoride gas by a complex process. Because molecules of the gas containing uranium-238 are heavier than those containing the lighter isotope, a gas centrifuge can separate them, concentrating
the uranium-235 in stages. After enrichment, the uranium is made into pellets which are placed into long fuel rods. These rods are bundled inside the water-filled core of a light water reactor, a much-used design. The water is heated by nuclear fission, and turned into steam that drives a turbine. A typical nuclear plant can power about 1 million homes. Only a small fraction of the world’s uranium is found in concentrations high enough to be worth extracting. Some 90 per cent of supplies comes from seven countries: Canada, Australia, Kazakhstan, Russia, Namibia, Niger and Uzbekistan.
URANIUM-235 NEUTRON
VIRTUAL NUCLEAR ENERGY Some countries, such as Russia, China and India, are expanding their nuclear programmes. Together, these three countries plan to build nearly 30 new reactors over the next two decades, seven of which are already under construction (see graph, far right). Other countries are moving away from nuclear in the wake of the disaster at the Fukushima Daiichi plant in Japan in 2011. Germany, for example, will phase out its nuclear power plants by the end of 2022 in favour of energy sources such as solar and wind. However, with national power grids now integrated into larger networks, there is no guarantee that non-nuclear countries will never draw on nuclear power. Italy, for example, has no nuclear power stations of its own but obtains 14 per cent of its electricity from France, which has a vibrant nuclear sector. This indirect reliance on imported nuclear energy is described as virtual nuclear energy.
ii | NewScientist | 1 June 2013
FISSION PRODUCTS CAESIUM-137 STRONTIUM-90
Nuclear reactors bombard uranium atoms with neutrons. When the atoms split they release energy and more neutrons
SPLITTING THE ATOM The protons and neutrons in an atom’s nucleus are bound together by the strong nuclear force. By fusing together the nuclei of two light atoms, or by splitting a heavy atom in a process called fission, we can release some of this binding energy. After more than half a century of research, fusion remains technologically elusive. Here we focus on fission, exploited in hundreds of reactors around the world; in 2011, it provided about 13.5 per cent of the world’s electrical energy
250
A BRIEF HISTORY OF FISSION
200
150
In December 1942 Enrico Fermi achieved the first self-sustaining nuclear chain reaction, harnessing the process that would be used to lay waste to the Japanese cities of Nagasaki and Hiroshima in August 1945. In the aftermath of this destruction, proponents of nuclear power made the case that splitting the atom could also be used for benevolent ends, supplying clean energy for all. When that same nuclear chain reaction is channelled into electricity generation, a single gram of uranium can provide 1 kilowatt of power for a year. To put this into context, that is roughly the rate at which the average UK resident used electricity in 2011. Enthusiasts proclaimed that electricity from a nuclear plant would be “too cheap to meter”. In the 1950s, nuclear power began to be used for commercial electricity generation as well as to drive submarines, navy ships and icebreakers, and people spoke glowingly of future nuclear-powered trains and aircraft. By the 1960s, nuclear power was seen as the answer to space travel and just about anything else. Former weapons scientist Edward Teller argued that nuclear bombs should be used in massive civil
engineering projects, blasting canals and flattening mountains as part of a programme called Project Plowshare. Articles in The New York Times enthused about the possibility of “nuplexes” – shopping malls or small cities built around the nuclear plants that provided their electricity. But growing awareness of the potential health effects of any nuclear accidents – and the high costs of building massively shielded facilities that would keep the population safe from harmful radiation – curbed this enthusiasm somewhat. Still, nuclear reactors generate electricity without producing greenhouse emissions or pollutants such as oxides and nitrogen, sulphur, and carbon. Today, 31 countries rely on nuclear for some of their power.
Proposed
Specific programme and site proposals. Expected operation in 15 years
Planned
Approvals, funding in place. Expected operation in 8 to 10 years
Nuclear power’s profile varies greatly from country to country: France relies on it for up to 80 per cent of its electrical energy, the US for 20 per cent and China just 1.9 per cent at the moment
0
Under construction
437
TOTAL NUCLEAR POWER REACTORS OPERATING IN THE WORLD TODAY
However, these numbers are set to change; most of the over 60 reactors now being built are in Russia, China and India China will lead the world in nuclear power generation within 15 years if all its proposed reactors are built
Ch in a US In d Ru ia ss Ja ia p So Fr an ut an h ce Ko re a Uk UK ra Sa Ca ine ud na i A da ra bi a UA E I Vi tal et y Sw nam Ge ede n Cz rma So ech ny ut re Sw h A p. itz fric er a la Tu nd Be rke lg y iu Br m Fi azi n l Pa lan ki d Sl sta ov n ak ia Ar Sp ge ain n H tin u a In nga do ry ne Po sia Ro lan m d Th an ai ia l Be and la ru Ch s ile Ka za Ira kh n s M tan ex Bu ic lg o A a Ba rm ria ng en la ia de s Eg h M Ne al ypt th ay er sia l Sl and ov s en Is ia r No Jo ael rt rda h n Li Kor th ea ua ni a
50
SOURCE: INTERNATIONAL ATOMIC ENERGY AGENCY
100
1 June 2013 | NewScientist | iii