® ®
|
|
A Desirable Energy Source?
Sten Hedegård Nielsen, ED 95
1 Preface
2 How does a nuclear power plant work?
3 Handling the waste
4 Alternatives to nuclear power
5 Economic aspects 6 Conclusion 7 Literature Annex (tables)
 1 Preface I have chosen nuclear power as the topic of my special paper as I find this energy source desirable for a number of reasons: It does not cause pollution, it has no negative impact on the health of people, and, contrary to renewable energy sources, it gives a high certainty of supply. In chapter 2, I shall describe how nuclear power plants work. I shall start with nuclear power plants in general and then explain the differences between the various reactor types. The last part of this chapter is about safety. I shall concentrate on the most common types already in use and on what some believe is the type of the future:
The boiling water reactorIn chapter 3, I shall describe the problems with handling the waste. This seems to worry the public a lot, but I believe the problems are overestimated and that they are of a political rather than a technical nature. I shall concentrate on the following questions:
How dangerous is it?In chapter 4, I shall examine the alternatives to nuclear power and their merits and demerits as regards certainty of supply and impacts on the environment. The alternatives are:
Fossil fuelIn chapter 5, I shall go into the economic aspects of nuclear power compared with the alternatives, which tend to be more or less ignored in the public debate. I shall concentrate on the following questions:
What are the costs per produced kWh?In my conclusion (chapter 6), I shall summarize the answers to the above questions in order to see if nuclear power is really as desirable as I — presently — believe.
2 How does a nuclear power plant work? 2.1 Generally To a wide extent, a nuclear power plant works exactly like a power plant using fossil fuel: The process in the "oven" heats a coolant, e.g. water, which transfers the energy to a turbine, and the turbine drives a generator which produces electricity. The difference is that the heat in the "oven" of a nuclear power plant is not created by mixing the fuel with air and burning it, but by dividing the atoms of the fuel into lighter atoms. The fuel used in most nuclear reactor types is the fissile uranium isotope 235U, the nucleus of which comprises 92 protons and 143 neutrons. If one neutron is added to the nucleus, the nuclear binding energy can no longer hold it together and it will be divided into 89Kr and 144Ba, thus releasing 3 free neutrons which can each start a similar process (the so-called chain reaction). However, it is necessary to slow down the neutrons so that they can be captured by the 235U nucleus; this is done by use of a "moderator". The energy released by the fission process is converted into heat, which is transported away from the fuel by the coolant. In some reactor types, the coolant also acts as a moderator; in other types, the moderator is a part of the reactor block or of the fuel elements. Control rods of a material that absorbs free neutrons, e.g. boron, cadmium, indium or silver, are pushed in and out between the fuel elements in order to increase or reduce — or, if necessary, stop — the chain process.
2.2 Specific types The boiling water reactor is the simplest of the water moderated reactor types. The reactor "swims" in a water-filled vessel, and the heat from the fuel rods makes the water boil. The steam, which typically has a temperature of app. 290° C and a pressure of app. 70 bar, is led directly to the turbines. From here, it is led to a condenser where it is converted into water, and the water is then led back to the reactor vessel.
In the pressurized water reactor, the water does not boil; at a pressure of app. 150 bar, it remains liquid even at temperatures above 300° C. The water is circulated between the reactor vessel and a heat exchanger in the reactor housing. In the secondary circuit of the heat exchanger, the pressure is only app. 50 bar, which causes the water in it to boil. The steam created hereby, which has a temperature of app. 280° C, drives the turbine as described above.
The graphite moderated reactor mainly differs from the other types due to the so-called pressure pipes: More than 1,600 pipes, each containing two fuel elements on top of each other, run vertically through a block of graphite. The water is pumped through each single pipe separately, where it is heated to steam by the 18 fuel rods of each element and led directly to a turbine. Both the water and the graphite are moderators in this reactor type. The safety problems caused hereby will be dealt with in paragraph 2.3 Safety.
In the fast breeder reactor, contrary to all other reactor types, the fuel is plutonium and not uranium, and the fission process is caused by fast and not slow neutrons. Therefore, no moderator is used in this type. The reactor core does not only contain fuel for the fission process; the 239Pu in the fission zone is surrounded by a breeding zone containing the non-fissile isotope 238U. Some of the neutrons released by the fission process convert the 238U into the fissile isotope 239Pu, which can then be used as fuel. Thus FBRs can use the 99.3% of natural uranium which cannot be used in other reactor types. The high energy density in the core of a fast breeder reactor requires the use of a special coolant. The metal sodium (melting point: 97.5° C) has the merits of a high thermal conductivity and of not being a moderator, but it has the demerits of becoming radioactive and of reacting violently with water. The radioactive sodium in the primary circuit is circulated between the reactor and a heat exchanger in the reactor containment. In the secondary circuit, non-radioactive sodium is circulated between this heat exchanger and one outside the containment. In the secondary circuit of the latter, water is heated to steam which drives a turbine. As the reactor is not under pressure, it need not be stopped for exchange of fuel elements.
Despite its name, the high temperature reactor works at a lower core temperature than do the other types described in this paper. The core temperature in the fuel rods of water-cooled reactors is app. 2,200° C, but the temperature in an HTR is only 1,000° C. However, the coolant used in this type is helium, which is heated to app. 900° C, whereas the temperature of the steam in a water-moderated reactor cannot exceed 540° C. Another important difference is the shape of the fuel elements: In all the above types, the fuel elements consist of several 4 m long pipes of a zirconium alloy containing pellets of uranium or plutonium. In a high temperature reactor, the fuel elements are balls of graphite with a diameter of 6 cm containing several thousand particles of coated 235U which are only 0.5 - 0.7 mm in size. The graphite in the balls and on the inside of the reactor is the only moderator. The helium, which is not under pressure, is circulated between the reactor core and heat exchangers where water is heated to steam. Like the fast breeder reactor, the high temperature reactor need not be stopped for exchange of fuel elements.
Of the reactor types described above, the boiling water reactor and the pressurized water reactor are most commonly used. The latter, being the most modern of the two types, is the one which is most often chosen for new power plants. The fast breeder reactor is less common, but I believe it has a large market potential, being able to use the 99.3% of natural uranium which is indigestible for the other types. The graphite moderated reactor is only used in the former Soviet Union and its vassal states. Due to its poor safety standard, it would never be commissioned in a non-communist country, and it is not likely to be used for new plants. The high temperature reactor technique has been known since the early 1950s, but only a handful of reactors have been built and they have all run into severe difficulties. Still, its advocates believe it could be the type of the future due to its high safety.
2.3 Safety
I shall start with settling a very wide-spread misunderstanding: A nuclear power plant can not explode like a nuclear bomb. This is mainly due to the low concentration of 235U in the fuel. Natural uranium consists of 0.7% fissile 235U and 99.3% non-fissile 238U. In order for the charge of a nuclear bomb to be explosive, the concentration of 235U must be increased to more than 30%, but the concentration in nuclear fuel is only 3 - 4%. Therefore, such an explosion is physically impossible. The explosion in the Chernobyl reactor was a steam explosion due to over-pressure in some of the pressure pipes, followed by a hydrogen explosion in the reactor building, which, contrary to western plants, did not have a containment capable of withstanding high pressure.
Under normal operation, a reactor produces radioactive nuclides which pose a potential danger to the surroundings and the personnel. Therefore, the reactor is constructed with a number of barriers which prevent the nuclides from leaking. Firstly, the fuel has a chemical form which ensures that the fission products stay in it. Secondly, the fuel is enclosed in pipes which hold back any gaseous fission products. The third barrier is the reactor vessel, which surrounds the reactor. Furthermore, all western and a few eastern reactors are surrounded by a several metres thick housing of concrete, called the containment. (Unfortunately, the Chernobyl reactor did not have a containment.) The containment of western reactors has never failed. Nevertheless, some Swedish and French reactors have been equipped with a stone filter through which the containment can be relieved in case of over-pressure. Another safety precaution is constructing the reactor with several parallel, independent cooling and control systems in order to protect it against technical faults, poor operators, and sabotage. If one system falls out, another will start and take over automatically.
In a boiling water reactor, the water is the only moderator. If the temperature in the core rises, a larger percentage of the water will be converted to steam which displaces the water. This reduction of the moderator will also reduce the fission process, which will cause the temperature to fall again. If all the water is removed from the core, the fission process will stop. Furthermore, the fission process can be reduced by increasing the content of boron in the water. If all cooling systems fail, the control rods will be pushed in automatically, which will stop the fission process within four seconds. However, the temperature in the fuel rods will still be high enough to cause a partial melt-down if no emergency cooling is established. The steam contains the radioactive nitrogen isotope 15N, which, in case of a leakage, will escape to the surroundings. However, 15N has a half-period of only 7 seconds, so being scalded by the hot steam must be considered a higher risk for the personnel than any radiation effects.
The pressurized water reactor is, to a wide extent, similar to the boiling water reactor, and most of what has been mentioned above can be transferred to this reactor type. However, there are a couple of differences. In a boiling water reactor, there is a steam separator above the core, so the control rods must be pushed up from below. This can be done by electrical motors or by gas pressure. In a pressurized water reactor, they are operated from above and, if necessary, they can fall down by themselves. As mentioned in point 1.2, the steam is produced in a heat exchanger and is therefore is not radioactive.
The graphite moderated reactor is also a boiling water reactor as the steam is produced in the reactor core, but contrary to the water-moderated types mentioned above, the main moderator is the graphite; the water in the pressure pipes only has very little moderating effect and mainly acts as a coolant. Normally, a loss of water would stop the fission process, but this is not the case here. Furthermore, as water also absorbs neutrons, the fission process in a graphite moderated reactor will be increased if the water is removed from the core due to a leakage or increased steam production. The only way to reduce the fission process is to push in the control rods. Therefore, a graphite moderated reactor is unstable. The water supply is another weak point: In the two other water-moderated reactor types, the core "swims" in a vessel filled with water, and the same water cools all fuel elements. In a graphite moderated reactor, each pressure pipe is cooled separately, so if the water supply for one pipe falls out, the two fuel elements in it will inevitably overheat. Furthermore, graphite moderated reactors do not have a containment which can withstand high pressure. Should a part of the core explode due to over-pressure, which happened at Chernobyl, the content will spread to the surroundings. Another weak point is the fact that graphite can burn if it is exposed to atmospheric air. This caused an additional problem at the Chernobyl accident.
The fast breeder reactor uses sodium as a coolant. If sodium is mixed with water in case of a leakage, there will be a chemical explosion. In order to prevent the explosion from happening in the reactor, it is necessary to have an extra coolant circuit between the reactor and heat exchanger where the steam is produced. The use of fast neutrons in the fission process makes this type technically more difficult to operate than other types, but as regards stability, it can be compared to water moderated reactors. Due to the high boiling point of sodium, 883° C, the reactor core need not be under pressure to avoid boiling, even at a temperature of 560° C.
The high temperature reactor has an advantage to all other types as a core melt-down is impossible. The core temperature in the uranium pellets in a conventional fuel rod is 2,210° C. The pellets are contained in a pipe of a zirconium alloy, the melting point of which is 80° lower: 2,130° C. Therefore, a sudden lack of coolant will inevitably cause a melt-down of the fuel rod. Due to the small size of the uranium particles in an HTR, the core temperature is only app. 1,000° C. The ceramic coating of the particles remains tight at temperatures up to 1,600° C. The graphite ball cannot melt and does not vaporize until the temperature reaches 3,600° C. A loss of coolant will only cause the temperature to rise a few hundred degrees. However, it is necessary to prevent the hot graphite balls from getting in contact with air; otherwise they will burn.
As regards safety, I find the high temperature reactor the most recommendable type as a melt-down is impossible. The relatively simple construction makes it easy to operate, and keeping air away from the fuel is no problem. The boiling water reactor and the pressurized water reactor do not vary much from each other as regards safety. Both are stable types as a loss of coolant will stop the fission process, and the accident on Three Mile Island in 1979 showed that even a severe accident with a partial melt-down can be handled without casualties or radioactive pollution. The fast breeder reactor is not a stable type as the fission process will continue after a loss of coolant, and the use of sodium and water as coolants entails the risk of a chemical explosion. However, several reactors of this type have operated for 30 years without any problems. The graphite moderated reactor is not recommendable as it is a de-stable type: As described above, a loss of coolant will lead to a melt-down. The reactor has no containment and is placed in direct contact with atmospheric air, which is the reason for the extent of the Chernobyl accident.
3 Handling the waste 3.1 How dangerous is it?
An objection very often raised against nuclear power is that the huge amounts of waste will remain radioactive for tens of thousands of years and thus pose a threat to the health of innumerable future generations. Radioactivity is actually harmful, and a high dose can even kill people. It should, however, be remembered that we are constantly exposed to radioactivity from cosmic radiation, from the ground, and from isotopes in the human body. This background radiation varies for numerous reasons: It is higher in some geographical areas, inside houses, and high in the atmosphere where planes travel. There is no place in the entire universe where there is no radioactivity. Based on examinations of people who have been exposed to high doses of radioactivity (mainly survivors from Hiroshima and Nagasaki, and patients treated with radiation), the International Commission on Radiological Protection has set a limit to the radiation people should be exposed to in order to avoid health impacts. The recommended limit for people who work with radioactive material is 20 mSv per year. (This does not mean that an annual dose of 21 mSv is harmful, but that annual doses up to 20 mSv are definitely not.) In Denmark, the average background radiation exposes people to an annual dose of 0.1 mSv, and the Chernobyl accident has exposed us to an additional dose of 0.05 mSv. Since 1985, only 3 out of 10,000 persons working with radiation have received a dose of more than 20 mSv, and none of them have exceeded 50 mSv [SIS]
Contrary to what many environmental groups claim, the waste will not remain radioactive for tens of thousands of years: One-year old spent fuel from a water-cooled reactor contains more than 20 different isotopes, including 4 different isotopes of plutonium, and the radioactivity level is 40 PBq per ton. However, isotopes with half-periods of more than 100 years only account for 0.14 PBq whereas e.g. 241Pu with a half-period of 13 years accounts for 5.9 PBq [H & SK]. After app. 10 half-periods, the radiation from any material is so weak that it cannot be distinguished from the background radiation, and the isotope has — per definition — vanished. »Within 800 years even high-level waste will be less radioactive than it was when the natural uranium was dug out of the ground« [BNIF 1]. It should also be noticed that e.g. normal coffee beans are just as radioactive as much of the low level waste.
3.2 How much is there?
Radioactive waste is divided into 3 groups depending on how radioactive it is:
Low-level waste, such as used protective clothing or air filters. This group also comprises waste from hospitals, industry and research.I have not managed to find the exact figures for the total amount of radioactive waste in the whole world, but the numbers for the United Kingdom, where nuclear power provides 27% of the electricity [BNIF 2], can be used as an example. In 1994, the total amount of solid and liquid waste was app. 117 million m3. Only 35,100 m3 (0.04%) of it was radioactive waste. 30,000 m3 was low-level waste, which can be disposed of in shallow land. There was 5,000 m3 intermediate level and 70 - 100 m3 high level radioactive waste, which will have to be encapsulated and disposed of in geological formations (table 1). The figures include the waste from all British nuclear power stations and all industrial and medical use of radioactive material. These figures should be compared with the amounts of waste from British coal power stations: Each year a single British coal power station produces 10 million tonnes of the greenhouse gas carbon dioxide, 200,000 tonnes of sulphur dioxide and 4,000 tonnes of ash. Among other things, the ash contains arsenic and cadmium, which do not have any half-periods but will remain toxic literally for all eternity. It should also be observed that the ash is radioactive: The level in one tonne is 2m Bq. [BNIF 1 and 2]. When spent fuel is reprocessed, 96% of the constituents are recovered and recycled. This allows selective conditioning of the waste and reduces the volume of the intermediate and high level fuel to one third. The plutonium which has been separated during reprocessing can be mixed with uranium in mixed oxide fuel, the use of which converts the plutonium to a form in which it cannot proliferate and be used for nuclear weapons. MOX fuel is presently used in 15 reactors in Switzerland, France and Germany [Goldsmidt].
3.3 How can it be disposed of safely?
Low-level waste is e.g. used protective clothing, paper towels and air filters. Much of it could be disposed of on a normal rubbish dump, but government policies in many European countries and the USA recommend it be disposed of deep underground together with intermediate-level waste. In other countries, e.g. Sweden, it is either burnt, declassified or deposited at the power plant for a few years until it is no longer radioactive.
Intermediate-level waste (e.g. contaminated material and parts from power stations or fuel reprocessing plants) is mixed with cement and packaged in steel drums. These are temporarily stored at various sites (most often at the plant) for a some years, and they are then deposited in underground vaults in stable geological formations.
High-level waste is either spent fuel or the four percent that remains when the useful uranium and plutonium has been extracted from the spent fuel during reprocessing. Contrary to low and intermediate level waste, it must be handled and deposited very carefully due to the radioactivity level. The normal procedure is turning the waste from reprocessing into glass by a so-called vitrification process and filling it into stainless steel vessels. Spent fuel which is not to be reprocessed is temporarily stored under water for app. 30 years until it has stopped generating heat and becomes more manageable. Both types of waste are then deposited in a repository deep underground in a stable geological formation, e.g. at Gorleben in Germany, Oskarshamn in Sweden, or Yucca Mountain in Nevada, USA. »Although alternatives, such as disposing of radioactive waste beneath the ocean floor or even in outer space, have been considered, the U. S. and all other countries with high-level waste disposal programmes have chosen to pursue deep geological repositories...« [Whipple]. However, no underground repository has yet come into use. At Gorleben and Oskarshamn, the waste is still cooling off, and the repository under Yucca Mountain is not expected to be ready to receive waste until 2015. So presently all intermediate and high-level waste is stored temporarily above ground. This is cheaper than underground repositories, but not advisable in the long term as the waste must be secured and maintained.
4 Alternatives to nuclear power
4.1 Fossil fuel
Fossil fuels are coal, oil and gas. The resources are large (though limited), the techniques for recovery and use are well-known, elaborate distribution systems already exist, and prices are low and stable. However, the use of fossil fuel pollutes the air with carbon dioxide, sulphur dioxide and nitrous gases. Furthermore, the use of coal and oil entails emissions of e.g. mercury, cadmium, lead, zinc, and arsenic, all of which are harmful to health. CO2 is a greenhouse gas and contributes to global warming. It does not in itself have as strong a greenhouse effect as the other gases, but it is the most important due to the large amounts of it. The content of greenhouse gases in the atmosphere is believed to have remained constant for millions of years, but since the industrial revolution outlets caused by human activities have increased the content of CO2 by app. 30%. Throughout the 1980s, the annual increase has been 0.5%. All fossil fuels contain carbon which is converted to CO2 when the fuel is burnt. (However, burning gas emits far less CO2 than burning coal and oil.) No operational method has yet been found to extract the CO2 from the smoke and deposit it in such a way that it is not released to the environment. The main problem is the vast amount of it: In 1994, the total emission from power plants in Denmark, where 96,6% of the electricity was produced by use of fossil fuel [DEF], was 31.4 million tonnes [DS]. SO2 contributes to acidification and forest withering. The content of sulphur in coal and oil varies depending on the location of the mine or the oilfield, and gas contains practically no sulphur. The sulphur can be extracted from the oil in refineries and from the smoke on coal-fired power plants. »In some systems the SO2 is converted into a waste product, while in others a useful by-product such as gypsum, sulphuric acid or sulphur is produced. (...) More than a hundred different processes have been developed but only a few are in large scale proven commercial operation« [EA 1, No. 10]. NOX contributes to over-fertilising and to the forming of photochemical oxidants such as ozone, which — at the surface of the earth — is harmful to plant growth and to people's health. It comes partly from the nitrogen in the fuel and partly from the air used for burning the fuel. The emissions can be minimised by use of carefully designed burners, lower flame temperature and by optimising the fuel and air mix.
During recovery and transport of fossil fuel, when large amounts are concentrated and handled in a small space, there is a risk of disasters: Mines may collapse, oil rigs may burst into fire (123 died on Alexander Kjelland, 165 on Piper Alpha), pipelines and wrecking tankers leak oil (Exxon Valdez). This should also be taken into consideration. As can be seen in table 2, uranium contains more than 10,000 times as much energy as even the best fossil fuel, which means that equally smaller amounts need to be recovered and transported.
As mentioned above, the resources of fossil fuel are large but not unlimited. In 1990, the total global consumption of fossil fuel was 7 Gtoe. The estimated reserves which can be recovered profitably are 1,200 Gtoe, enough for 180 years. The consumption of uranium was 0.5 Gtoe and the estimated reserves are 57 Gtoe, enough for 110 years. However, the use of FBRs will increase the reserves to 3,400 Gtoe, enough for more than 6,000 years [WEC, the numbers are rounded]. As nuclear power presently accounts for 17% of the world's electricity production, FBRs could — theoretically — provide the whole world with electricity for a thousand years.
4.2 Renewable energy sources
Renewable energy sources for electricity production are hydro, wind and solar power. Their advantages are that the resources are unlimited, the "fuel" is free of charge, it transports itself to the plant, and the use of it does not cause emission of pollutants. Except for large scale hydro power plants, however, they all have some characteristics which make it impossible to use them as the main source. Their output capacity varies regardless of the energy demand and it is not possible to concentrate the production in a small geographical area according to the demand.
Hydro power is produced by damming rivers where there is a sufficient water flow and difference of height. For instance, the shape and the placing of Norway has made it possible to base practically the entire Norwegian electricity production on hydro power, and in Sweden half of the electricity is produced by hydro power plants — in years with sufficient precipitation, that is. Drought, such as this year, reduces the capacity by up to one third, which makes it necessary to use other energy sources and/or import electricity. Hydro power is not without environmental impacts: China's Three Gorges project will displace 14 million people [BNIF 3], and in many cases large agricultural areas or habitats for animals are flooded. The dams also hinder the migrations of fish, and in many countries environmental groups insist fish ladders be constructed, which reduces the water flow to the turbines.
Wind power is the most developed of the renewable energy sources and is often considered the most promising technology for pollution-free electricity production. However, there must be a fixed constant voltage on the grid and the electricity supply must meet the varying demand exactly, but any production planning for windmills is literally blowing in the wind. As no technique has yet been developed which can make the wind blow harder during working days from 7 to 4 than it does in weekends, wind power can only be a supplement to the main production. »Studies have shown that the variable output of wind plants could be absorbed as a base load in the UK, provided that no more than 20% of generating capacity is derived from the wind« [EA 1, No. 7]. Furthermore, in some countries the distribution companies are legally obliged to buy the entire production of the windmills, which forces other suppliers to adapt their production not only to the varying demand of the customers but also to the varying production of their competitors. As even the biggest wind mills have a maximum capacity of app. 0.5 MW under ideal conditions, it is not possible to concentrate a large scale production of wind power in a small area. For example, producing the electricity needed in Toronto (3.9m inhabitants) by wind power would require 23,000 km² of land with 40,000 windmills. Furthermore, a reserve capacity using other energy sources would be necessary for periods with little or no wind. »By contrast, the Pickering nuclear station occupies two square kilometres of land surrounded by a one-kilometre radius exclusion zone ...« and supplies more than the city of Toronto [AECL 2]. The area of Denmark (5.1 m inhabitants) is 43,000 km². However, much of the land on windmill farms can also be used for other purposes such as agriculture. Windmills also have environmental impacts: As mentioned above, they require large areas of land in proportion to their electrical capacity, and neighbours complain that they are noisy and disfigure the landscape. Birdwatchers are concerned about the impact of thousands of windmills on migrating birds.
Solar energy is mainly used for electricity production in countries near the Equator where the solar energy input is often twice as high as in the developed countries and where elaborate (and expensive) national grids for electricity supply are not at hand. In Kenya, for instance, »more households now get their electricity from the sun than from the national grid« [Economist]. Solar energy can be used for heating and lighting up houses if they are constructed with large windows on the south side or by use of solar heating units. Furthermore, (contrary to electricity) heat from the sunlight can be captured and stored in water-filled insulated tanks for later use. Solar energy has the same weaknesses as wind power: The sun does not always shine when the consumers need electricity, and it is not possible to concentrate large scale production in a small area. Still, as is the case with wind energy, national grids can manage the fluctuations in supply from solar energy if the supply is less than 20% of the total supply. As can be seen in table 3, the land use is not nearly as big a problem with solar energy as with wind power.
4.3 Biofuel
Biofuel has been used ever since man learned to make fire, but it has not yet been used for large scale electricity production; its main use is still for cooking in developing countries where no alternative is available. However, some industrialized countries have recently started using e.g. straw and wood in municipal power and heating plants. The use of biofuel is not believed to give a net increase of the content of CO2 or other greenhouse gases in the atmosphere as the emission will be balanced by the consumption through photosynthesis by the next "generation" of biomass. This balance can be kept whether the biomass is burnt or reduced to vegetable mould. However, nitrogen and minerals which should have served as nourishment for the new biomass are removed from the earth and must be replaced in the form of fertiliser. The ash from the power plants can be used for this purpose, which also solves the problem of depositing it. Biofuel is not likely to become a main energy source for large scale electricity production as vast amounts of land would be needed for growing the biomass (see table 3), and as the electricity prices of such plants are not competitive. As a matter of curiosity, it can be mentioned that two power plants in the U.K., Eye in Suffolk (12.5 MW) and Glanford in South Humbershire (14 MW), use chicken litter as fuel [EA 1].
5 Economic aspects
5.1 Production costs per kWh
In order to be able to decide which energy source should be preferred, one must not only consider safety, environmental impacts and accessibility. On a free market, the price is a (if not the) main criterion. The costs for the various energy sources vary a lot, not only from country to country but also from plant to plant. Therefore, the prices stated in this chapter are only estimated and/or average prices, and one should not transfer them to other countries uncritically. However, there are some obvious trends which are common for all four countries from which I have been able to obtain such information.
In Sweden (table 4), hydro power is by far the cheapest of the energy sources presently used; as the "fuel" is free of charge, even the least profitable hydro power plants can easily compete with the cheapest competitor. That is nuclear power, by use of which electricity can be produced at about half the price of fossil fuel. The variations between the costs for the various fossil fuels are negligible. However, the production costs for hydro power will increase drastically if new plants are to be built: Unexploited capacity is mainly placed in remote areas, which will increase the distribution costs, and in most cases the water flow is low, which reduces the electrical capacity more than the operation and maintenance costs. The costs have not been estimated for new nuclear power plants as it has been decided politically that no such plants are to be constructed in Sweden. If, however, we assume that the costs would rise by approximately the same percentage as the costs for fossil fuel plants, not even hydro power could compete with nuclear power.
In the U.K. (table 5), the electricity sector is presently being privatized. According to the Financial Privatization Act of 1986, all information which might affect the share prices is confidential. I have, however, managed to obtain some figures from the British Wind Energy Association, but they only include present plants using coal, nuclear power, gas and wind energy. There are also several hydro-power plants in Britain, but their production costs are not included. Due to the easy access to gas from the North Sea, this is the cheapest of the "non-hydro" energy sources for British power plants. Contrary to all other sources of information which I have found, BWEA state that wind energy is a bit cheaper than coal and nuclear power. It should, however, be noted that the price spans for these three energy sources to a wide extent overlap each other; the lowest cost per kWh for wind energy is only 5% lower than that for nuclear power, which again is 7% lower than that for coal. Therefore, one should be careful making conclusions only on the basis of these figures.
Contrary to what the name indicates, Bangor Hydro Electric Company in Maine, USA, does not only run hydro-electric power plants. Except for wind power, all the prices in table 6 are the production costs on their own plants. Here, too, hydro power has the lowest production costs per kWh, closely followed by gas as No. 2 and nuclear power as No. 3. It is a close race, though: The cheapest gas-fuelled plant produces at 12% higher costs than the cheapest hydro power plant but exactly the same costs as the most expensive one. The costs per kWh for nuclear power is 28% and 14% higher than those of the cheapest and the most expensive hydro power plant respectively. Plants using fossil fuel are twice as expensive as the cheapest hydro power plant, and the costs for using biofuel is 3 times those of using hydro power. Bangor Hydro Electric Company does not deal in wind power. It has considered it but gave up the project, having found that it would be too expensive.
The German "price list" does not include gas and oil; on the other hand, it is the only one that includes solar energy. As can be seen in table 7, hydro power is also the cheapest energy source in Germany, followed by nuclear power, fossil fuel (coal) and wind energy. The exorbitant production costs of solar energy could be the reason why the other countries have not even included it on their "price lists".
Generally, it can be concluded that hydro power, where accessible, is the cheapest energy source, well ahead of the field consisting of nuclear energy and fossil fuels. Nuclear energy and gas compete for leading the field with coal in the rear. After the field comes wind energy, and biofuel is the most expensive of all energy sources being used in the industrialized countries. Solar energy, being ten times as expensive as its nearest competitor, is nowhere near being profitable for large scale electricity production. Fluctuations in fuel prices may affect the above placings in the field. Prices for uranium and fossil fuel are low and stable, but they may rise or fall unexpectedly like the oil prices did in the 1970s. As can be seen in table 4, fuel costs account for one third of the total costs on coal-fired power plants and half the costs on gas-fired plants, whereas it is less than 10% on nuclear power plants. Therefore, nuclear power is less sensitive to fluctuations in fuel prices than are plants using fossil fuel. (Of course, hydro power plants and windmills do not have this problem.) It should also be noted that the costs for fossil fuels described in this paper do not include external costs associated with environmental impacts and countermeasures against them. Including such costs would enhance the competitiveness of nuclear power and renewable energy sources against fossil fuels.
5.2 Amortizing time
The total costs of constructing and using any type of power plant comprise construction costs, fuel costs, and operation and maintenance costs. For nuclear power, contrary to all other energy sources, they also comprise the costs for disposing of the waste and dismantling the power plant after the end of its service life. These costs must all be offset by the electricity revenues within the service life of the plant. Nuclear power plants typically have a lifetime of 40 years but they are usually paid back over 30 years. Coal-fired plants have a lifetime of 25 - 30 years, which is also their normal amortizing time. Also gas-fired plants have a lifetime of 20 - 30 years, but, according to Bangor, they should be amortized within only 10 years, partly due to the short lifetime of the gas turbines, partly because uncertainties in gas prices and availability are greater than they are as regards coal and uranium. Hydro power plants usually have a lifetime of 60 years, but they, too, should be paid back over 30 years. This long lifetime also contributes to the low price per kWh described above. Windmills are expected to have a lifetime of 20 years, and the lifetime of a power plant using biofuel varies between 15 and 20 years.
It is not only necessary to invest a sum of money in a power plant; constructing it also requires an amount of energy. When comparing the various energy sources, one should therefore also consider how fast (or if) they can deliver the amount of energy that has been used for constructing them. I have only managed to find one single source of information which shows the amortizing time for various power plants [VDEW 3]. Here a coal-fired plant, a nuclear power plant, a wind power plant and three different types of photovoltaic plants are compared. The analysis does not comprise hydro power or plants using gas or biofuel. As can be seen in table 8, a nuclear power plant can deliver the amount of energy used for constructing it in 2.2 months, a coal-fired plant in 3.4 months, and a windmill in 8 months. The amortizing time for photovoltaic plants vary between 4 years and 25 years, depending on which technique is used. It should be noted, however, that the figures for wind and solar energy are based on ideal climatic conditions. As many owners of windmills have found, the conditions are rarely ideal in reality, and placing a solar energy plant in Northern Europe will double its amortizing time. Throughout its lifetime, a nuclear power plant can thus deliver more than a hundred times the energy used for constructing it. Again, we find a coal-fired plant in second place, delivering 70 times its own accumulated energy consumption, and a windmill can deliver the energy back 30 times. A photovoltaic plant based on amorphous cells can do it 5 times, and a multi-crystalline type twice. As all photovoltaic power plants have a lifetime of 20 years, a mono-crystalline type cannot deliver as much energy throughout its lifetime, even under ideal climatic conditions, as has been used for constructing it.
6 Conclusion
Except for the graphite moderated reactor, all types of nuclear power plants described in this paper must be considered safe. Only a small part of the waste is dangerous, handling it causes no problems, and repositories have been found. Construction of such repositories is possible partly because the amounts of waste are negligible compared with the amounts of other dangerous types of waste. The use of fossil fuels pollutes the environment with greenhouse gases, heavy metals and other toxic materials. The electrical capacity of renewable energy sources cannot be controlled and varies regardless of the demand, and they, too, have environmental impacts. Except for hydro power, their prices are not competitive. Biofuel, adding extreme land requirements to its high costs, can only play a marginal role. Nuclear power prices compete well with those of fossil fuel and are less liable to fluctuate. Hydro power is the cheapest of all energy sources but only accessible in few places. Other renewable energy sources and biofuel are not competitive. Nuclear power also has the shortest energetic amortizing time and the highest energy yield of the energy sources compared in this respect.
The uncontrollable capacity fluctuations of renewable energy sources make it impossible to let them account for more than 20% of the electricity production, and their unfortunate characteristics described in this paper make it questionable if they will even get near this market share. On the other hand, the higher prices for wind power could also be considered an investment in a clean environment, and I believe that hydro power should be exploited wherever possible and profitable. However, the vast majority of electricity must still be produced by use of fossil fuels and/or nuclear power. Considering all environmental and economic aspects, safety and certainty of supply, it must be concluded that nuclear power is the most recommendable energy source.
7 Literature
Atomic Energy of Canada Limited, Chalk River Laboratories, Chalk River, Ontario, Canada:
Letter from Dr. Gary van DrunenAll received by fax on 26th July 1996.
Australian Nuclear Science & Technology Organisation, Lucas Heights, Sydney, NSW, Australia:
Letter from M. J. McMillanAll received by fax on 9th August 1996.
Bangor Hydro Electric Company, Bangor, Maine, USA: Interview (by telephone) with Mr Morrell on 29th July 1996.
British Nuclear Industry Forum:
Fission, Fusion and Safety — and Nuclear Power. AEA Technology, Didcot, U.K., 1994.British Wind Energy Association, 89 Kingsway, London WC2B 6RH, U.K.:
Fact Sheets No. 1, 16 and 19. Updated April/May 1996.Danmarks Statistik, Sejrøgade 11, 2100 København Ø, Denmark: Nyt fra D. S. 1995 vol. 206.
Danske Elværkers Forening, Rosenørns Allé 9, 1970 Frederiksberg, Denmark: Copies of tables from Dansk Elforsyning Statistik 1995. Received by fax on 31st July 1996.
Department of Energy, Energy Information Administration, Washington DC, USA:
Letter from Mr William JeffersAll received by fax on 1st August 1996.
Economist, The (Unknown Author): The Future of Energy. Article in The Economist, 7th October 1995.
Electricity Association, 30 Millbank, London SW1P 4RD, U.K.:
UK Electricity '94 (Yearbook). 30 Millbank, London SW1P 4RD, U.K.Goldschmidt, Pierre: Managing used nuclear fuel: reprocessing vs direct disposal. Article in Nuclear Europe Worldscan, 1994 vol. 11/12.
Hoe, Steen and Sarholt-Kristensen, Leif: Stråling og miljø. Borgens Forlag, Copenhagen, Denmark, 1989.
Isotopcentralen/ATV: Noter til kursus Stråling og Sikkerhed. Copenhagen, Denmark, 1984. (Not published)
Kirchner, Ulrich: Der Hochtemperaturreaktor — Konflikte, Interessen, Entscheidungen. Campus Verlag GmbH, Frankfurt a. M., Germany, 1991.
Kraftverksföreningen, Olof Palmes Gata 31, 101 53 Stockholm, Sweden: Interview with Mr Bo Lexmark, Informationsavdelningen, on 1st April 1996.
Seidel, Jürgen: Kernenergie, Fragen und Antworten. ECON Verlag GmbH, Düsseldorf, Germany, 1990.
Statens Institut for Strålehygiejne: Revision af de grundlæggende strålebeskyttelsesprincipper. Brønshøj, Denmark, 1991.
Statens Offentliga Utredningar 1995:139. Omställning av energisystemet. Slutbetänkande av Energikommisionen. Stockholm, Sweden, 1995.
Vereinigung Deutscher Elektrizitätswerke, Stresemannallee 23, 60596 Frankfurt a. M., Germany
Interview with Mr Matthias Peter on 5th August 1996.Whipple, Chris G.: Can Nuclear Waste Be Stored Safely at Yucca Mountain? Article in Scientific American, June 1996.
World Energy Council: Global Energy Perspectives to 2050 and Beyond, Report 1995. World Energy Council, 34 St. James's Street, London SW1A 1HD, U. K., 1995.
Zorpette, Glenn: Return of the Breeder. Article in Scientific American, January 1996.
8 Annex (tables)
Table 1
Composition of annual waste in the U.K.
Amounts of waste types in m³ are adapted from BNIF 1. Total and percentages are calculated by me.
Table 2
How much energy is released by the use of kg fuel?
Based on BNIF 1.
Table 3
Required land use for various energy options, supplying 40 GW
Site-specific considerations dominate. The wide ranges indicated are illustrative of small and large scale hydro developments.(Based on AECL 2)
Table 4
Production costs per kWh on present and future power plants in Sweden. The construction of future plants is to be financed by loans which are to be paid back over 25 years. The prices are stated in SEK per kWh.
No estimate has been made as it has been decided politically that no new nuclear power plant is to be built in Sweden.(Based on Kraftverksföreningen)
Table 5
Costs per kWh on new power plants in the U.K., 1995 prices in GBP or pence per kWh.
*: 3.8 pence per kilowatt hour is the lowest price paid for projects with Scottish Renewable Order contracts. 4.8 pence per kilowatt hour is the highest price paid for project with a NNF03 contract.
(Adapted from BWEA 2)
Table 6
Production costs on power plants in the USA. the prices are stated in U.S. cent per kWh.
*: The cost for wind energy is estimated for a future plant. (The project was given up due to the high cost and low security of supply connected with wind power.) All other costs are average costs on existing plants.
(Based on Bangor)
Table 7 Production costs on existing power plants in Germany. The prices are stated in DEM per kWh.
Based on VDEW 2.
Table 8
Energetic amortization of various power plants.
*: The numbers for wind power and photovoltaic plants are based on ideal climatic conditions.AEC: Accumulated energy consumption during the construction of the plant and for producing the fuel, measured in MWh per installed MW capacity.
(Based on VDEW 3)
| |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Danish
Deutsch