Nuclear: is there any net energy addition?

15 September 2004

Whether or not nuclear power plants are built and whether they keep operating for many years after commencing operation is these days essentially an economic decision. The financial costs of construction and operation are compared with the revenues which will flow from selling the electricity generated and a decision can then be made. There are usually alternative options for power available which can be taken up and these can be assessed in a similar way before a generation mix is established.

There are, however, alternatives to financial measures in assessing different modes of electricity generation. One is to use energy itself as a unit of accounting and to attempt to measure the balance between inputs and outputs in the power production process. This is a major element of what is now known as lifecycle analysis (LCA) for generating plants. Such assessments have been made for many years and some have concluded that the nuclear fuel cycle requires very heavy energy inputs to operate, even to the extent that the net energy production will be very low or, in extreme cases, even negative. Such a conclusion would mean that nuclear energy is not sustainable and should therefore not form part of future world energy supply. But how are such conclusions reached?

The first point to make is that analysing energy balances is a complex process because the inputs are so diverse and there is always a question of how far one should go back. It is clear that the energy used in enriching uranium should be included but what about the energy required to construct the enrichment plant in the first place? Clearly we must include the energy requirement for waste management and plant decommissioning. Also the energy it takes to transport materials from A to B. This may be relatively low in the case of nuclear, but coal transportation takes up a huge amount of energy while even natural gas transportation by pipeline is also surprisingly energy intensive. There are clearly going to be some measurement difficulties – it is easy to measure the energy used in operating an enrichment plant but much harder to estimate what is bound up in plant construction or in transporting gas. Finally, it is necessary to establish comparable measuring rods, so kilowatt hours have to be converted into kilojoules and vice versa, which requires assumptions about thermal efficiencies and the like.

Where nuclear has come out badly in energy balance studies, it is invariably the assessments made for uranium mining and enrichment which are at the source. Such studies have invariably been very pessimistic about the magnitude and quality of uranium resources, such that it is necessary to exploit low grade and inaccessible deposits in the near future, which will inevitably involve a greater energy input. In fact, higher grade resources have been discovered and these (particularly in Canada) are the foundation of today’s industry. Additionally, in situ leaching (ISL) has become a common technique for exploiting certain low grade uranium resources and this involves a relatively low energy input.

It is, however, the uranium enrichment stage which can potentially involve a very high energy input. Gas diffusion enrichment, the dominant technology until Urenco and the Russians perfected gas centrifuges in the 1980s, uses a huge amount of electricity. If this is supplied by fossil fuel plants, the energy input is very significant, as was the case with the three huge enrichment facilities in the USA (Oak Ridge, Paducah and Portsmouth). It can amount to more than half the lifetime energy input into the fuel cycle. This can, however, be reduced significantly if the electricity is provided by a nuclear power plant, as is the case at the largest gas diffusion plant in the world, Georges Besse in France. Centrifuge enrichment, however, is very economical in energy terms and only uses about 2% of that consumed by a gas diffusion facility taking its electricity from a coal-fired generating plant. In this case, the total energy input into the entire nuclear fuel cycle will only be about one third of what it will be if coal-fired gas diffusion enrichment is used.

Even with gas diffusion enrichment, it is clear that the studies which attempt to show that there is little or no net energy gain from nuclear are absurd, relying on unrealistic assumptions about key elements of the fuel cycle. In fact, best estimates of the energy inputs in each area, backed up by a thorough study from Vattenfall of the Forsmark plant, show that the energy inputs in nuclear are at most only 5-10% of the output. Only hydropower can beat this, with both coal and gas lagging well behind. Waste management within the nuclear fuel cycle involves very little use of energy, either in spent fuel ponds, dry cask storage or repositories, although construction of the latter will be relatively energy-intensive.


The impact of global warming is still hard to quantify and so some studies ignore this factor

Renewables are not necessarily so favourable in energy input-output terms. Some studies have even showed wind to be less efficient than nuclear, because of the energy bound up in the steel and concrete for the rotors and the low capacity factors. Similarly, the production of pure silicon for solar photovoltaics requires large energy inputs and accounts for most resource consumption in solar cell manufacture.

The other important area in LCA, in addition to the measurement of energy inputs and outputs, is the assessment of the external costs of power generation, which are the environmental and health consequences which do not appear in the financial accounts. An emerging issue today is the likely contribution of each power generation technology to global warming. It is clear that nuclear does very well on this measure, along with hydro and renewables, but the fossil fuels all emit significant quantities of carbon dioxide. The impact of global warming is, however, still hard to quantify and so some studies ignore this factor.

The ExternE study (1995), launched by the EU, attempted to provide an expert assessment of lifecycle external costs for European electricity generation. These external costs are those incurred in relation to health and the environment which are quantifiable but are not built into the cost paid by the customer and so are borne by society as a whole. They include the effects of air pollution on human health, crop yields and buildings as well as occupational disease and accidents. The impact of global warming was excluded, on the basis that it is not quantifiable yet.

The report shows that nuclear incurs only about one tenth of the external costs of coal. This is because the waste costs of nuclear are already internalised, which has the effect of reducing the competitiveness of nuclear when only internal costs are considered, as in conventional financial analyses. The average cost of electricity throughout the EU averages 4¢ per kWh without external costs. The externalities of nuclear would add only 0.4¢/kWh to this, whereas coal’s add more than 4¢/kWh (in other words, the external costs are above the internal cost), and those of gas add 1.3-2.3¢/kWh. Only wind shows up better than nuclear, adding only 0.1-0.2¢/kWh. So if the external costs could be incorporated, the cost of coal-fired electricity would double and gas-fired rise by around 50%. If the potential impact of fossil fuels on global warming was to be added, the impact would be considerably greater.

Economists would argue that these external costs should be incorporated in the electricity price paid by consumers or else there is a misallocation of resources. This could ideally be achieved by imposing appropriate taxes to reflect the external costs with the revenues from these sufficient to compensate society. This would considerably alter the mix of electricity generating capacity in favour of those with low external costs, essentially nuclear, hydro and the renewables. However, there are substantial political barriers to this being achieved.

Nuclear power therefore comes out very favourably from LCA, whether this is on the basis of merely looking at energy inputs and outputs or also incorporating external costs. The analyses which purport to show the opposite can easily be shown to be misguided. The only possible cloud on the nuclear horizon is spent fuel management. Critics would argue (with some justification) that until further management decisions have been made and repositories are in operation, the long-term costs of various solutions are hard to calculate. The industry can counter by producing various estimates, but it will take time for the true picture to emerge.

Author Info:

Steve Kidd is Head of Strategy & Research at the World Nuclear Association, where he has worked since 1995 (when it was the Uranium Institute). Any views expressed are not necessarily those of the World Nuclear Association and/or its members.

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