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Nuclear power plants are closely regulated by national and international agencies which provide rigorous oversight of the operation and maintenance of these plants. The safety record of nuclear power plants has been exemplary over the years. This was achieved through improved plant designs, high-quality construction, regular staff training, safe operation, and careful emergency planning. Diverse and redundant systems prevent accidents from occurring, and multiple safety barriers are placed to mitigate the effect of accidents in the highly unlikely event they occur. The safety of the nuclear industry has been significantly im-

Figure 8.20 United States electricity production costs (in 2004 cents kWh-1). Costs include fuel, operation and maintenance. Based on data from NEI.
Figure 8.21 Electricity production costs in France (€ kWh 1). Based on data from CEA.

proved since the Three Mile Island incident in 1979 which, although it was the most serious nuclear accident in the Western World, did not lead to any casualties.

The Chernobyl disaster was on a completely different scale. It was a consequence of human error, lack of safety measures, poor construction and design. The power plant had no reactor containment building preventing radioactivity from escaping to the atmosphere, and would never have been licensed and allowed to operate in any Western country. The explosion that occurred in Chernobyl however was not nuclear, but chemical. When the reactor went out of control, huge amounts of heat generated by nuclear fission evaporated virtually instantaneously the water used under normal conditions to cool the fuel rods. The steam produced reacted with extremely hot zirconium to produce hydrogen, and with the graphite used as moderator to form carbon monoxide and hydrogen. The pressure increased dramatically and blew off the 2200-ton concrete lid of the reactor pressure vessel. The remaining graphite then ignited, with flames carrying, in the absence of any containment, highly radioactive material into the atmosphere. Thirty-five persons who tried to extinguish the fire died shortly after the accident from the direct effects of radiation. According to the latest and most comprehensive study from the United Nations, 20 years after the accident, fewer than 50 deaths have been directly attributed to radiation from the disaster [84]. Over time, however, a total of up to 4000 people could eventually die from radiation exposure from the Chernobyl accident. Poverty and "lifestyle" diseases, rampant in the former Soviet Union, pose far greater threat to local communities than the exposure to radiations resulting from the accident. Although this was the most serious nuclear accident, it should also be compared with other energy-related losses of life such as coal mining accidents which draw much less public attention but nevertheless cause thousands - if not tens of thousands - of deaths every year. The Chernobyl accident is considered as the archetype of the worst conceivable civilian nuclear disaster. The probability for a disaster of this magnitude to occur in the Western World has been estimated by nuclear safety experts in the order of one millionth per reactor per year of operation in currently used reactors, and even less in the next generation of reactors with advanced safety features. Other potential accidents such as a dam rupture or the explosion of a LNG tanker have a much larger probability to cause large casualties. It is also important to point out that, contrary to widespread belief, it is impossible for a civilian nuclear reactor to undergo a nuclear explosion of the kind generated by nuclear bombs. Nuclear fuel used in commercial units contains at most 5% 235U, whereas for nuclear bombs the uranium used must contain at least 90% 235U and be contained in specifically designed devices before a nuclear explosion can occur.

124 | Chapter 8 Renewable Energy Sources and Atomic Energy Radiation Hazards

Unstable atomic nuclei can split to form other particles, ejecting at the same time different types of radiation (alpha, beta, gamma, and X-ray) in a process called radioactivity, discovered by Henri Becquerel in 1896. These radiations are able to penetrate matter and can disrupt biological systems and thus essential processes in human body cells. The degree of penetration will depend on the energy of the radiation, with gamma and X-rays being the most energetic. Today, radioactivity is a part of our daily life, and is present everywhere from various natural sources: cosmic rays, uranium and thorium contained in the Earth's crust, granite used as a construction material, radon gas produced by the natural decay of uranium, potassium in fertilizers and food, etc. The average natural irradiation to which a human is exposed in a year is around 2.4 millisieverts (mSv, the unit which quantifies the biological effect of radiation in our body).

Besides natural radioactivity, populations in developed countries are also exposed to artificial sources of radiation amounting less than 1 mSv, essentially for medical purposes (X-rays) but also daily activities such as watching television (0.015 mSv) or taking an airplane trip (0.05 mSv for a Paris to New York round trip) (Table 8.4; Fig. 8.22).

Nuclear power plants are responsible for emissions of around 0.0002 mSv per year, similar to the commonly used smoke detector containing americium, but 10 000 times less than naturally occurring radiation. Thus, they present no risk in terms of radiation in normal operation. Nuclear power plants de facto are even emitting less radiation than coal-burning power plants! A part of the radioactive contaminants in coal, uranium and thorium pass up the chimney stack and

Table 8.4 Radiation exposure (mSv year) from different activities.

Natural background radiation

2.4

Working at a nuclear power plant

1.15

One diagnostic X-ray

0.2

Living in a stone, brick or concrete building

0.07

One round-trip flight Paris-New York

0.05

Living at the gate of a nuclear power plant

0.03

Watching television

0.015

Luminous wrist watch

0.0006

Coal-fired power plant, average within 80 km

0.0003

Average radiation from nuclear power production

0.0002

Smoke detector

0.00008

Source: UNSCEAR, NEI and the environmental case for nuclear power, R. Morris 2000.

Source: UNSCEAR, NEI and the environmental case for nuclear power, R. Morris 2000.

Figure 8.22 Average radiation dose to the public (in mSv per year). Based on data from UNSCEAR, Sources and effects of ionizing radiation (New York, 2000).

are released to the atmosphere, while another part stays in the ashes. In fact, it has been calculated that that about 13 000 t thorium and 5000 t uranium are presently released yearly into the environment as a result of coal combustion [85].

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