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Several critiques from the nuclear world on this study have been published. For the nuclear industry the divergent results are reason to dismiss a priori this study at all, ignoring scientific arguments. Often physical and chemical observations are refuted on economic arguments. To scientists and decision makers who are not well introduced in this matter it may be difficult to judge these critiques on their scientific value, due to complexity and opacity of the nuclear energy system.

For that reason this section briefly addresses a number of factors that might explain differences between the results of this and other studies:

• perspective: scientific or economic

• complexity of the nuclear energy system

• methodology: defining the system boundaries and time horizon

• database: empirical data and proved technology, or paper concepts and wishful thinking

• data: paucity and secrecy

• inherent uncertaintities

• attitude: long-term sustainability or a stance of aprs nous le dluge

• thermodynamic assessment of uranium resources

• other arguments.

Different approaches may lead to divergent results of analyses by researchers with different backgrounds, views and interests.

Scientific or economic approach

This assessment is based on scientific insights and conserved quantities, such as energy and mass. The units kilogram and joule do not depend on the place and/or time of an observed phenomenon. For that reason an energy analysis can have a long-term forecasting value. Especially in the case of nuclear energy this is an important feature, because the completion of a nuclear project may take 100-150 years, an unprecedented timescale.

The value of money is unpredictable beyond a short time horizon. In an economic approach unquantifiable variables and implicite assumptions may play a part. Typical of the economically oriented approach are, for instance, the ways the availabilty of material resources and the energy debt are treated. The price of commodities, e.g. uranium, are pivotal in the economic approach and debts are discounted at an assumed rate. The price of uranium is not an unambiguous quantity, but depends on several unquantifiable and unpredictable variables.

Each nuclear power plant leaves behind an energy debt. The time at which the debt must be paid is irrelevant, quite differently than monetary debts. The latter are, in economic calculations, discounted at an assumed interest rate, and are further subject to the variations in the value of money. Energy debts cannot just be written off as uncollectable. A given physical task will take a given amount of energy, whenever and wherever.

Assessments based on the market mechanism and commodity prices have little forcasting value beyond a time horizon of a couple of years.

An economic paradigm may also be a clue to the systematic postponement of the back end processes by the nuclear industry. These processes will require enormous sums of money, measured in tens of billions of euros, without any return on investment. Indeed, the sole purpose of the back end processes is to let disappear the radioactive waste and its casings forever. Massive amounts of ordered materials have to disappear from the biosphere.

Conclusions of the scientific assessment are often at odds with conclusions based on economic considerations, see also below.

Complexity of the nuclear energy system

The nuclear energy system comprises an complex chain of some 14 industrial processes, some of which have extremely long time schedules of a 100 years. In fact the nuclear energy system is the most complex energy system ever designed. The distance in space and/or time between two consecutive processes may be very large, e.g. mining of uranium in Australia and conversion and enrichment in Europe. In time: if construction starts in 2012, commissioning may follow in 2022 and the first spent fuel may be removed from the reactor in 2024. The final disposal of the resulting radiaoctive waste may occur not before 2100.

The complexity and wide spread in time and place are rendering the nuclear process chain not very accessible and transparent The opacity is exacerbated by the paucity of vital data on processes of the nuclear chain.

A full energy analysis of the nuclear chain is complicated, not only because of the multitude of processes, but also because of the multitude of variables involved.

Methodology: system boundaries and time horizon

When comparing LCAs and energy analyses of the nuclear system the first look should be at the system boundaries and time horizon in each study. Which processes of the nuclear chain are included in a given LCA and which are not? What time horizon has the analysis? Does it end at the closedown of the reactor or does it extent to the moment of placing the last radioactive originating from the analyzed reactor in a safe and permanent repository? How exhaustive is a given LCA?

As pointed out above, the nuclear system comprises a large number of industrial processes. Each of these process consumes materials, chemicals, equipment and energy, electricity and fossil fuels. The processes can be divided into upstream processes, also called the front end, and the downstream processes (back end). The upstream processes comprise the activities needed to produce nuclear fuel from uranium ore. These all are well-known and mature operational processes. The downstream processes comprise the activities after the nuclear fuel has been spent and the nuclear power plant has been closed down. A number of the downstream processes exist only on paper.

• In regard of the choice of the system boundaries of the life cycle assessment (LCA) and energy analysis the known studies vary widely: which processes are included in the LCA and which are not. This study takes the full nuclear process chain into account, from cradle to grave. Consequently the time horizon of this study lies at 100-150 years. Other studies omit one or more of the downstream processes from their analysis, however unavoidable in the long run. Usually the omitted processes, would occur in the future beyond a time horizon of, say, 10 years.

• A second aspect of the system boundaries is the choice: which energy flows are accounted for and which are not. This study takes into account all energy inputs of each process, not only the direct energy inputs, but also the indirect inputs. The latter encompass the embodied energy in chemicals, materials, equipment, construction and dismantling. Other studies are not consequent in this respect.

• A third special methodologic feature of this study is the global perpective of nuclear power in a steady state. Climate change and energy security are global issues. Radioactive releases and emissions do not stop at the borders of a country.

In a steady state the number of reactors each year connected to the grid equals the number of reactors dismantled and permanantly disposed off in a geologic repository, including the spent fuel removed from the reactor during its operational lifetime. In the steady state all electric inputs of the nuclear process chain are assumed to be produced by nuclear power plants and are subtracted from the gross nuclear electricity production. This convention renders the energy analysis independent of the fuel mix of the local electricity generation and of time-dependent variables.

The CO2 emitted by the nuclear system originates from the burning of fossil fuels, mostly diesel, and from some CO2 producing chemical reactions, such as the production of cement and steel.

Proven technology versus paper concepts, empirical data versus wishful thinking

The available information on nuclear power originates almost exclusively from institutes with vested interests in nuclear power and from the nuclear industry. Understandably these sources tend to highlight the favourable aspects. Their public relations are usually charactized by a technical optimism, which is not always backed by emprical facts. Not seldom concepts existing in cyberspace only are presented with the same aplomb as if it were operational processes.

The complexity of the nuclear system, combined with its inherent uncertainties, gives room for different approaches in analyzing the energy balance and CO2 emissions of the nuclear system. An analysis started from a technically optimistic viewpoint invariably will end up in more favourable results than an analysis from a pragmatic and empirical starting point.

A number of processes needed to safely wind up any particular nuclear power project are still not operational and are existing only on paper, for example the dismantling of nuclear power stations and the permanent safe storage of radioactive waste in a geologically stable repository. Therefore no empirical data on the still-to-be developed processes are available. The nuclear establishment shows a tendency to delete the still-to-be developed processes, however unavoidable, from the analysis of the nuclear system.

Wherever possible this study is based on empirical data on energy and material inputs of the processes of the nuclear chain, as functioning at the current state of technology. All technical data come from the nuclear industry.

A number of processes downstream of the reactor operation are still in the design stage and therefore no operational data of such processes are available. The energy input and CO2 emissions of the yet-to-be developed processes are estimated in this study by comparison with analogous processes. For example, the construction of a deep geologic repository can be compared with convential underground mining.

The author is aware of introducing uncertainties by this method. However, in our view the results of an LCA including this kind of estimates will be much more reliable and realistic than when the yet-to-be developed processes are deleted at all. As it turns out, the input of energy and materials and the accompanying CO2 emissions of those processes might be far from negligible. Though, this observation may be a major reason why these processes are still being passed on to the future generations. Moreover, the numerical values of data of proven processes exhibit often a considerable spread, e.g. of the construction of a nuclear power plant.

Secrecy and paucity of data

The nuclear world is well organised. Due to its strong connection with military nuclear technology, the civil nuclear technology has many secrets to outsiders. For example it hardly possible to obtain the real construction cost of nuclear power plants in France, because the vendor and the operating utility both are state-owned companies.

An independent researcher has access only to the data the nuclear industry wants to be published. Understandably these publications are favourable to the own performance and policy.

Variables and uncertainties

The results of the energy analysis are presented as function of two main variables of the nuclear energy system, being the operational lifetime of the reactor and the grade of the uranium ore feeding the nuclear system.

In addition the spread in the numerical outcome resulting from the spread of the input data and uncertainties of the nuclear chain is given. Several important processes of the nuclear chain are not operational, so the energy input of these have to be estimated. Even the data of operational processes, as published by the nuclear industry, exhibit often a considerable numerical spread. There is no such thing as one correct value of the nuclear CO2 emission or operational lifetime of a nuclear power plant.

Long-term sustainability versus aprs nous le dluge

This analysis covers the entire nuclear chain, comprising all processes which are causally related with the generation of nuclear power today, regardless of place and time. In our view nuclear power should be applied in the safest and least unsustainable way, not only in the regions where nuclear power plants are operating, but also in the regions housing other parts of the nuclear chain, such as uranium mining and waste repositories.

The immense quantities of radioacivity produced by nuclear reactors – one 1 GWe reactor produces 1000 Hiroshima bomb equivalents of radioactivity each year – are stored in more or less unsafe locations. The downstream processes are indispensable to pack the radioactive waste and to store it in permanently safe locations, the so-called geologic repositories. All waste from nearly 60 years of nuclear power is still waiting for treatment in unsafe interim storage facilities, that will irrevocably deteriorate with time. The radioactive wastes pose an ever increasing risk to health, safety and societal stability. Accidents that will dwarf the Chernobyl disaster may happen every day in Europe, USA and other countries with nuclear power plants.

The nuclear industry systematically passes on the downstream processes to the future. Omitting these processes from LCAs and energy analyses enhances the suspicion that the nuclear industry does not intent to perform these unavoidable processes: an attitude of 'aprs nous le dluge'.

Thermodynamic vs economic assessment of uranium resources

Uranium is almost exclusively used as an energy source. The energy required to extract 1 kg of uranium from a given deposit in the earths crust is set by the physical and chemical properties of the uranium-bearing rock, such as the ore grade and minerology. As the amount of energy which can be generated from 1 kg of uranium has a fixed value, the net energy content of a given uranium occurrence in the earths crust depends on the ore grade and other parameters. This study assesses the world known uranium resources on thermodynamic criteria and classifies them according to their net energy potential, measured in joule/kg uranium.

The nuclear industry tests the world uranium resources by an economic criterion and classifies these resources into price ranges, measured in $/kg uranium.

In regard of the outlook of nuclear power in the world energy supply, the conclusions based on the thermodynamic classification are at odds with the conclusions based on the price classification. In the thermodynamic view the future role of nuclear power in a global context will remain small (less than 2% of the world demand). In the economic view the uranium resources, hence nuclear energy potential, are almost limitless.

Other arguments

Governments may have a hidden agenda. Civil nuclear technology is a step to a military nuclear programme, as one may observe in some countries of the world. Moreover, political decisions may be based on other than scientific arguments. The financial interests in the nuclear industry are very large. Institutes such as WNA (World Nucear Association), UIC (Uranium Information Centre), OECD/NEA (Nuclear Eenergy Agency), NEI (Nuclear Energy Institute) and IAEA (International Atomic Energy Agency) have vested interests in nuclear power and are not necessarily independent scientific institutes.