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i08

Unique features of nuclear power

Man-made radioactivity

An operating nuclear reactor produces heat and radioactivity, simultaneously, inextricably and irreversibly. The potential energy embedded in the nuclei of uranium atoms is converted into heat and nuclear radiation by fission of the nuclei. During the fission process tremendous amounts of radioactivity are generated. The amount of man-made radioactivity is a billion times the radioactivity of the fresh uranium entering the reactor. One reactor of 1 GWe generates each year as much radioactivity as 1000 exploded nuclear bombs of about 15 kilotonnes, the yield of the Hiroshima bomb.

All radioactive wastes ever generated during the nuclear era are still stored in temporary storage facilities. These facilities are leaking all kinds of radioactivity into the environment at an increasing rate, due to the unavoidable deterioration of the materials and structures of the containing facilities. The temporary storage facilities are vulnerable to accidents, terroristic attacks and natural disasters, as happened at Fukushima Daiichi.

Once generated, radioactivity cannot be influenced by any means. The radioactivity resulting from nuclear power decreases by natural decay only. For some components of the man-made radioactivity the decay rate can be measured in seconds to hours, for other components time scales of years to hundreds of thousands of years are involved.

Mobilisation of radioactivity

Uranium is a radioactive metal found in nature in various chemical forms in uranium ore. In uranium ore strata, uranium and its many radioactive decay daughters are bound in chemically stable minerals. This is not to say uranium-bearing rock is harmless to man, not at all. When uranium ores are disturbed to extract the uranium, the element is brought out of its geologic confinement into the environment and is chemically mobilised. The uranium isotopes are chemically separated from the separated radioactive daughters, containing about 85% of the radioactivity in uranium ore, which are dumped as mill tailings in huge ponds and spoil heaps. From then on the radioactivity from the uranium ore is mobile.

The man-made radioactivity is also mobile: without active and dedicated precautions it will enter the human environment at some time [more i39, i43].

Metal as energy source

Uranium, the source of nuclear power is a metal, contrary to fossil fuels, which consist of burnable hydrocarbons. Fossil fuels can be used as found in nature. Uranium has to be extracted from rocks (ores) in the earth's crust and purified to high degree by means of a sequence of technical and chemical processes. From the pure uranium nuclear fuel is produced in another sequence of chemical and physical processes. Uranium is almost exclusively used as energy source and has no other industrial applications.

Time frame

The time frame of a nuclear project is extremely long. The construction of a nuclear power plant takes usually some 10 years. The nominal operational lifetime of a nuclear power plant is about 40 years. Once a nuclear reactor has started operating, society is committed to a long sequence of causally related and very demanding processes. Completion of this sequence may take 100 years. The complete time frame of a nuclear project, called the cradle-to-grave period, is estimated at some 150 years [more i12].

Complexity

The nuclear energy system is the most complex energy system ever, not only in technical sense, but also in economic, societal and political senses. The complexity has a profound negative effect on the controllability of nuclear power.

Irreversible consequences

The nuclear process chain encompasses several vulnerable phases with the potential of disasters of unheard magnitude, such as Chernobyl and Fukushima. The effects of nuclear disasters are irreversible because radioactivity cannot be destroyed nor made harmless to man. The health effects with people will remain visible for centuries to come. A disaster of the size of Chernobyl or Fukushima in Western Europe would have unimaginable consequences and does not need the explosion of a reactor. A large accident by whatever cause at a reprocessing plant or spent fuel storage facility could have even worse consequences [more i21].

The chances of occurence of large disasters are unkown. There are too many and too large technical uncertainties and variables regarding the processes in which highly radioactive materials are involved, to do a sound risk analysis. In addition the human factor in the broad sense of the word plays an important part. Practice is not encouraging: during the past 60 years two very large accidentsand a number of less grave accidents occurred, not counting the accidents which may have happened in the former Sovietunion before Chernobyl. If the après nous le dŽéluge paradigma keeps dominating the nuclear world, Fukushima will not be the last disaster of that kind.

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reactorsimple45

Figure 08-1. Heat and radioactivity, inextricably

An operating nuclear reactor produces heat and radioactivity, simultaneously, inextricably and irreversibly. The reactor is fueled by enriched uranium, produced from uranium ore in the well-established front end processes of the nuclear chain. The heat is partially converted into electricity. What to do with the man-made radioactivity is still an open-ended question.

mobileradioactyv3

Figure 08-2. Mobilisation and generation of radioactivity

Symbolic presentation of the radioactivity flow through the nuclear system. The flow starts with the mobilisation of natural radioactivity and multiplies a billionfold by generation of radioactivity in the reactor. Unavoidably a part of the mobilised radioactivity will be released into the human environment. A safe immobilised end of the nuclear chain still exists only in cyberspace. What quantities of the radioactive materials leaving the reactor will end up in the environment?

radbolv4

Figure 08-3. Man-made radioactivity

By fission of uranium in an operating nuclear reactor the radioacivity increases a billionfold. If the pea on the foreground (diameter 1 cm) represents the radioactivity of fresh nuclear fuel, then the balloon at a diameter of 10 meters represents the radioactivity of the spent nuclear fuel.

cumulative

Figure 08-4. World radioactivity inventory.

All man-made radioactivity still exists in a mobile form in the human environment. The world inventory of man-made radioactivity passed the 10 million nuclear bomb equivalent mark in 2010 and is rising nearly linearly with 370 000 nuclear bomb equivalents a year. These amounts of radioactivity are stored in temporary facilities, deteriorating with time, vulnerable to economic cutbacks, natural disasters, accidents and terroristic attacks. A nuclear bomb equivalent is the amount of radioactivity generated at the explosion of a nuclear bomb of 15 kilotonnes, about the yield of the Hiroshima bomb.

c2gperiod

Figure 08-5. Cradle-to-grave (c2g) period

Cradle-to-grave (c2g) period of fossil-fuelled and nuclear electricity generation. Assumed operational lifetime of noth systems is 40 years. Construction period fossil: 5 years, nuclear: 10 years. Back end (waste handling, decommissioning + dismantling) fossil: 5 years, nuclear: unknown, at least 60 years, possibly more than a century.