Why consider nuclear power in a book about
the transition to renewable energy? In my
view, because nuclear is complementary to
renewables in moving to a sustainable and
largely carbon-free energy future. The reason I
say this is that in most countries, the demand
for electricity has a very large continuous
component - see Figure 1D1. This requires a
reliable supply of electricity which cannot be
readily met from intermittent wind or solar
sources since their electricity cannot be stored
on a large scale.
Nuclear is simply the most appropriate technology for the job of providing clean baseload power. (Hydrogen may one day be made on a large scale from electricity, or directly from nuclear energy by thermochemical means and then stored on a large scale for turning back to electricity, but such developments are many years away. Even then the hydrogen will be in higher demand for transport.)
ENERGY BALANCE
The economics of electricity generation are important. If the costs of building and operating a power plant cannot profitably be recouped by selling the electricity, it is not financially viable. But as energy itself can be a more fundamental unit of accounting than money, it is also essential to know which generating systems produce the best return on the energy rather than the money invested in them. Determing this involves Life Cycle Analysis (LCA).
Analysing the energy balance between inputs and outputs, however, is complex because the inputs are diverse, and it is not always clear how far back they should be taken. For instance, oil expended to move coal to a power station, or electricity used to enrich uranium for nuclear fuel, are generally included in the calculations. But what about the energy required to build the train or the enrichment plant? And can the electricity consumed during enrichment be compared with the fossil fuel needed for the train? Many analysts convert kilowatt-hours (kWh) to kilojoules (kJ), or vice versa, but this requires them to make assumptions about the thermal efficiency of the electricity production.
Some inputs are easily quantified, such as the energy required to produce a tonne of uranium oxide concentrate at a particular mine, or to produce a tonne of particular grade of uranium hexfluoride at a uranium enrichment plant. Similarly, the energy required to move a tonne of coal by ship or rail can be identified, although this will vary considerably depending on the location of the mine and the power plant. Moving gas long distances by pipeline is surprisingly energy-intensive.
Other inputs are less straightforward such as the energy required to build a 1000 MWe power plant of a particular kind, or even that to construct and erect a wind turbine. But all such energy inputs need to be amortised over the life of the plant and added to the operational inputs such as fuel. Also the post-operational energy requirements for waste management and decommissioning plants must be included. There is no such thing as a free kilowatt-hour! As well as energy costs, the environmental and health consequences of energy production that do not appear in the financial accounts need to be considered as well. Recent studies have plausibly quantified them in financial terms, and I will comment on those at the end.
Many energy analysis studies done in the 1970s seem to have assumed that if nuclear generating capacity was expanded very rapidly, it would require so much energy for fuel production and construction that, for a few years, inputs would exceed overall outputs. To determine whether or not this would happen requires the dynamic analysis of the whole energy system and is not attempted here. The 1970s studies were also driven by a perception that primary energy sources including uranium would become increasingly difficult and expensive to recover, and would thus require undue amounts of energy to access them. This notion has since re-surfaced.
The figures in Figure 1D2 are based as far as
possible on current assumptions and current
data for enrichment, mining and milling, etc.
Where current data are unavailable, that from
earlier studies is used. For nuclear power,
enrichment is clearly the key energy input
where the older diffusion technology is used - it
comprises more than half of all the energy used
in the lifetime of the plant. However, with centrifuge
technology, enrichment takes far less
energy than the construction of the plant itself.
Indeed, the difference between the two processes
is so great that, overall, an input of only a
third of the energy is required to build and operate
a nuclear plant using centrifuge technology
than one fuelled by the older diffusion method.
| (Figure 1D2) Life Cycle Energy Requirements for a Nuclear Power Plant | |||
| GWh (e) | TJ (th) Annual | PJ (th) 30 year | |
| Inputs | |||
| Mining & Milling (180 t/yr U308 at Ranger) | 37 | 1.26 | |
| Conversion (ConverDyn data) | 5.63 | ||
| Initial enrichment diffusion @ 2400 kWh/SWU | 576 | 6.23 | |
| Urenco centrifuge @ 63 kWh/SWU | 15 | 0.16 | |
| Reload enrichment diffusion @ 2400 kWh/SWU | 201 | 2175 | 65.25 |
| Urenco centrifuge @ 63 kWh/SWU | 5.3 | 57 | 1.71 |
| Fuel Fabrication (ERDA 76/1) | 4.32 | ||
| Construction & Operation (ERDA 76/1) | 24.69 | ||
| Fuel storage, Waste storage, Transport (ERDA 76/1, Perry 1977), Decommissioning allow | 1.0 | ||
| Total (diffusion enrichment) | 108 | ||
| Total (centrifuge enrichment) | 39 | ||
| Output: 7 TWh/yr | 7000 | 75.670 | 2 270 PJ |
| Input percentage of lifetime output, thermal | (diffusion) | 4.8% | |
| (centrifuge) | 1.7% | ||
| Energy ratio (output/input), thermal | (diffusion) | 21 | |
| (centrifuge) | 59 | ||
Assumptions:
Fuel Cycle: 1000 MWe, 30-year life, 80% capacity factor, enrichment with 0.30% tails (3.0 SWU/kg for initial 80 t fuel load @ 2.3% U-235, 4.3 SWU/kg for 3.5% fresh fuel @ 19.5 t/yr), 45,000 MWd/t burn-up, 33% thermal efficiency.
Calculations: Electrical inputs converted to thermal @ 33% efficiency (x 10 800, kWh to kJ)
Other figures for front end: Cameco mines in Saskatchewan input 32 TJ per 180 t U3O8 over 1992-2001 including some capital works. Urenco enrichment at Capenhurst input 62.3 kWh/SWU for whole plant in 2001- 02, including infrastructure and capital works.
Other figures for construction (but not operation) of 1000 MWe PWR power plant are: 13.6 PJ (Chapman 1975, recalculated), 14.76 PJ (Held 1977, if converted direct), 24.1 PJ (Perry et al 1977).
Energy payback period. If 30 PJ or 25 PJ is taken for diffusion and centrifuge enrichment respectively as the energy capital cost of setting up, then at 75 PJ/yr output the initial energy investment is repaid in 5 months or 4 months respectively at full power. Construction time for nuclear plants is 4-5 years.
The only data available for storage and disposal of radioactive wastes, notably spent fuel, suggests that this is a minor contribution to the energy picture. This is borne out by personal observation in several countries - spent fuel sitting quietly in pool storage or underground is about as passive as you can imagine. Decommissioning energy requirements may be considered with wastes, or (as Vattenfall) with plant construction.
As yet, no energy-input figures seem to have been published for the fuel cycle that the UK has been using - the closed cycle involving reprocessing at Sellafield, a point that some Irish observers find upsetting. However, this probably uses less energy overall because, although reprocessing requires extra energy, 25% less enrichment will be required. It is also important to recognise that precise energy figures for plant construction are not readily available, although several studies use a factor converting monetary inputs to energy.
Recent studies have compared different means
of generating electricity in energy and greenhouse
terms. Here are some of their results,
together with earlier data. The energy ratio is
simply output divided by input for the full life
cycle. Unlike some others in use, the R3 energy
ratio employs a convention which converts
between electrical and thermal energy, including
a thermal efficiency factor, so is used here.
Nevertheless the reciprocal percentage, the
input as a percentage of a plant's lifetime output,
may be more meaningful.
| (Figure 1D3) Life Cycle Energy Ratios for Various Technologies | |||
| R3 Energy
Ratio. (output/input) |
Input % of
lifetime output | ||
| Hydro | Uchiyama 1996 | 50 | 2.0 |
| Held et al 1977 | 43 | 2.3 | |
| Quebec | Gagnon et al 2002 | 205 | 0.5 |
| Nuclear (centrifuge enrichment) | see Table 1D2. | 59 | 1.7 |
| PWR/BWR | Kivisto 2000 | 59 | 1.7 |
| PWR | Inst. Policy Science 1977* | 46 | 2.2 |
| BWR | Inst. Policy Science 1977* | 43 | 2.3 |
| BWR | Uchiyama et al 1991* | 47 | 2.1 |
| Nuclear (diffusion enrichment) | see Table 1d. | 21 | 4.8 |
| PWR/ BWR | Held et al 1977 | 20 | 5.0 |
| PWR/BWR | Kivisto 2000 | 17 | 5.8 |
| Uchiyama 1996 | 24 | 4.2 | |
| PWR | Oak Ridge Assoc.Univ. 1976* | 15.4 | 6.5 |
| BWR | Oak Ridge Assoc.Univ. 1976* | 16.4 | 6.1 |
| BWR | Uchiyama et al 1991* | 10.5 | 9.5 |
| Coal | Kivisto 2000 | 29 | 3.5 |
| Uchiyama 1996 | 17 | 5.9 | |
| Uchiyama et al 1991* | 16.8 | 6.0 | |
| Inst. Policy Science 1977* | 14.2 | 7.0 | |
| unscrubbed | Gagnon et al 2002 | 7 | 14 |
| Natural gas- piped | Kivisto 2000 | 26 | 3.8 |
| piped 2000 km | Gagnon et al 2002 | 5 | 20 |
| LNG | Uchiyama et al 1991* | 5.6 | 17.9 |
| LNG (57% capacity factor) | Uchiyama 1996 | 6 | 16.7 |
| Solar | Held et al 1997 | 10.6 | 9.4 |
| Solar PV rooftop | Uchiyama 1996 | 9 | 11.1 |
| utility | Uchiyama 1996 | 5 | 20.0 |
| amorphous silicon | Kivisto 2000 | 3.7 | 27 |
| Wind | Resource Research Inst. 1983* | 12 | 8.3 |
| Uchiyama 1996 | 6 | 16.7 | |
| Kivisto 2000 | 34 | 2.9 | |
| Gagnon et al 2002 | 80 | 1.3 | |
| Biomass forestry waste | Gagnon et al 2002 | 27 | 3.7 |
| plantation | Gagnon et al 2002 | 5 | 20 |
* In IAEA 1994, TecDoc 753.
These figures show that energy ratios are clearly sensitive not only to the amount of energy used to build the power source and supply it with whatever it needs to run, but also to the proportion of the time at which it is delivering power - in other words, its capacity factor.
This is particularly true where a significant amount of energy is required to build the power plant. The higher the energy input to build the plant, the more output is needed to amortise it. With technologies such as wind, where a turbine will only be producing whenever the wind blows, and then at a rate dependent on the wind speed, a longer period is required to cover the inputs due to lower capacity factors. Energy payback period for the construction of a nuclear power plant is 3-4 months, which compares favourably with all except gas combined cycle.
The Liquid Natural Gas (LNG) figures quoted are for natural gas compressed cryogenically and shipped to Japan and used largely for peak loads. The solar and wind figures relate to intermittent inputs of primary energy, with inevitably low capacity utilisation and relatively high energy costs in the plant (for silicon manufacture in the case of solar cells, or steel and concrete for wind turbines).
The Swedish utility Vattenfall has undertaken a
thorough life cycle assessment of its Forsmark
nuclear power station, which has three boiling
water reactors totalling 3100 MWe net. These
started up in 1980-84 and run at 86.4% capacity.
The energy analysis figures (input as % of
output, transport included, 40 yr plant life, with
PJ figures calculated from % on basis of 3272
PJ output) are shown in figure 1D4 below.
| (Figure 1D4) Energy analysis of a Swedish nuclear power station | ||
| input as % of output | PJ (calculated) | |
| Mine | 0.44 | 14 |
| Refining & conversion | 3.18 | 104 |
| Enrichment (80:20 centrifuge:diffusion) | 3.00 | 98 |
| Fuel fabrication | 1.34 | 44 |
| Plant operation | 0.28 | 9.2 |
| Plant build & decommission | 0.27 | 8.8 |
| Waste management | 0.11 | 3.6 |
| Waste build & decommission | 0.01 | |
| Total life cycle: | 8.70% | 285 PJ |
The Vattenfall Life Cycle Analysis study tracks energy inputs further back than others, and so is only comparable with data based on similar methodology. Even so, some major variances are unexplained - notably refining and conversion.
Uchiyama (1996) points out that hydro, nuclear and fossil fuel plants have high energy ratios of output over inputs because of their higher energy density as well as capacity factors. Wind and solar, however, are under 10 because of their lower energy density, or output in relation to plant volume and hence materials used.
LIFE CYCLE ANALYSIS: GREENHOUSE GASES
A principal concern of life cycle analysis for energy systems today is their likely contribution to global warming. This is a major external cost.
If all energy inputs are assumed to be from coal-fired plants that release about one tonne of carbon dioxide per MWh, it is possible to derive a greenhouse contribution from the energy ratio. With major inputs, this is worth investigating further.
Uranium enrichment in USA is by diffusion and some of this capacity is supplied by coal-fired plants. If a national average, allowing for different sources of power, is applied, this input has a value of around 650 kg CO2/MWh. This gives a greenhouse contribution for nuclear power of about 40kg/MWh overall. In France, however, which has the world's largest diffusion enrichment plant, electricity is supplied by on-site nuclear reactors (which also supply the grid). Because of this, the greenhouse contribution from any nuclear reactor using Frenchenriched uranium is similar to a reactor using centrifuge-enriched uranium -- less than 1kg /MWh for the enrichment input, and less than 20 kg/MWh overall.
Rashad and Hammad conclude that the life cycle CO2emission coefficient for nuclear power, on the basis of centrifuge enrichment, is 2.7% of that for coal-fired generation. This is consistent with other figures based on fossil fuel inputs.
Adding further confirmation to figures already published from Scandinavia, Japan's Central Research Institute of the Electric Power Industry has published life cycle carbon dioxide emission figures for various generation technologies. Vattenfall (1999) has published a popular account of life cycle studies based on the previous few years experience and its certified Environmental Product Declarations (EPDs) for Forsmark and Ringhals nuclear power stations in Sweden, and Kivisto in 2000 reports a similar exercise for Finland. They show the CO2 emissions in the table below.
The Japanese gas figures include shipping LNG
from overseas, and the nuclear figure is for
boiling water reactors, with enrichment 70% in
USA, 30% France & Japan, and one third of the
fuel to be MOX. The Finnish nuclear figures
are for centrifuge and diffusion enrichment
respectively, the Swedish one is for 80%
centrifuge.
| (Figure 1D5) Relative carbon dioxide emissions from different energy sources | |||
| g/kWh CO2 | Japan | Sweden | Finland |
| coal | 975 | 980 | 894 |
| gas thermal | 608 | 1170 (peak-load, reserve) | - |
| gas combined cycle | 519 | 450 | 472 |
| solar photovoltaic | 53 | 50 | 95 |
| wind | 29 | 5.5 | 14 |
| nuclear | 22 | 6 | 10 - 26 |
| hydro | 11 | 3 | - |
OTHER EXTERNAL COSTS
The report of ExternE, a major European study of the external costs of various fuel cycles, focusing on coal and nuclear, was released in 2001. The European Commission launched the project in 1991 in collaboration with the US Dept of Energy (which subsequently dropped out), and it was the first research project of its kind "to put plausible financial figures against damage resulting from different forms of electricity production for the entire EU".
The external costs are defined as those actually incurred in relation to health and the environment and quantifiable but not built into the cost of the electricity to the consumer and therefore which are borne by society at large. They include particularly the effects of air pollution on human health, crop yields and buildings, as well as occupational disease and accidents. In ExternE they exclude effects on ecosystems and the impact of global warming, which could not adequately be quantified and evaluated economically.
The methodology measures emissions, their dispersion and ultimate impact. With nuclear energy the (low) risk of accidents is factored in along with high estimates of radiological impacts from mine tailings and carbon-14 emissions from reprocessing (waste management and decommissioning being already within the cost to the consumer).
The report shows that in clear cash terms nuclear energy incurs about one tenth of the costs of coal. In particular, the external costs for coal-fired power were a very high proportion (50-70%) of the internal costs, while the external costs for nuclear energy were a very small proportion of internal costs, even after factoring in hypothetical nuclear catastrophes. This is because all waste costs in the nuclear fuel cycle are internalised, which reduces the competitiveness of nuclear power when only internal costs are considered. The external costs of nuclear energy averages 0.4 euro cents/kWh, much the same as hydro, coal is over 4.0 cents (4.1 - 7.3 cent averages in different countries), gas ranges 1.3-2.3 cents and only wind shows up better than nuclear, at 0.1-0.2 cents/kWh average.
The EU cost of electricity generation without these external costs averages about 4 cents/kWh. If these external costs were in fact included, the EU price of electricity from coal would double and that from gas would increase 30%. These particular estimates are without attempting to include possible impacts of fossil fuels on global warming. See also web: http://externe.jrc.es/
Another European treatment of production and external costs, specifically of power generation in Switzerland, has recently been done by the Paul Scherrer Institut and shows that the damage costs from fossil fuels range from 10% (gas) to 350% (coal) of the production costs, while those for nuclear are very small. A summary is accessible on the web: http://gabe.web.psi.ch/
An earlier European study (Krewitt et al, 1999) quantified environmental damage costs from fossil fuel electricity generation in the EU for 1990 as US$ 70 billion, about 1% of GDP. This included impacts on human health, building materials and crop production, but not global warming.
The ExternE report proposes two ways of incorporating external costs: taxing the costs or subsidising alternatives. Due to the difficulty of taxing in an EU context, the subsidy route is favoured. EC guidelines published in February 2001 encourage member states to subsidise "new plants producing renewable energy ... on the basis of external costs avoided", up to 5 c/kWh. However, this provision does not extend to nuclear power, despite the comparable external costs avoided. EU member countries have pledged to have renewables (including hydro) provide 12% of total energy and 22% of electricity by 2010, a target that appears unlikely to be met. The case for extending the subsidy to nuclear energy is obvious, particularly if climate change is to be taken seriously.
Consideration of external costs leads to the conclusion that the public health benefits associated with reducing greenhouse gas emissions from fossil fuel burning could be the strongest reason for pursuing them. Considering four cities - New York, Mexico, Santiago and Sao Paulo - with total 45 million people, a 2001 paper in Science presents calculations showing that some 64,000 deaths would be avoided in the two decades to 2020 by reducing fossil fuel combustion in line with greenhouse abatement targets. This is consistent with a 1995 WHO estimate of 460,000 avoidable deaths annually from suspended particulates, largely due to outdoor urban exposure.
The World Health Organisation in 1997 presented two estimates, of 2.7 or 3 million deaths occurring each year as a result of air pollution. In the latter estimate: 2.8 million deaths were due to indoor exposures and 200,000 to outdoor exposure. The lower estimate comprised 1.85 million deaths from rural indoor pollution, 363,000 from urban indoor pollution and 511,000 from urban ambient pollution. The WHO report points out that these totals are about 6% of all deaths, and the uncertainty of the estimates means that the range should be taken as 1.4 to 6 million deaths annually attributable to air pollution.
OTHER CONCERNS ABOUT NUCLEAR POWER
In discussions of the relative merits of different means of producing electricity, several concerns are commonly raised regarding nuclear power. This is not the place to treat them comprehensively, but I will attempt a paragraph on each of four:
RESOURCES
Uranium is abundant. The world's present measured resources of uranium in the IAEANEA lower cost category (3.1 million tonnes) and used only in conventional reactors, are enough to last for almost 50 years. This represents a higher level of assured resources than is normal for most minerals. Further exploration and higher prices will certainly, on the basis of present geological knowledge, yield further resources as present ones are used up. This is indicated in the figures if those covering estimates of all conventional resources are considered 15.4 million tonnes, which is 240 years' supply at today's rate of consumption. This figure still ignores unconventional resources such as phosphate deposits (22 Mt) and seawater (up to 4000 Mt). But before recourse to them, widespread use of the fast breeder reactor could increase the utilisation of uranium sixty-fold or more. It is well-proven but currently uneconomic due to low uranium prices. Using uranium for electricity is responsible in relation to allowing for the needs of future generations.
WASTES
Virtually all wastes from the civil nuclear fuel cycle are contained and managed. Certainly none cause any harm to people or the environment, nor pose any significant credible threat, with the possible exception of reprocessing where high-level wastes are in liquid form for a time. High-level wastes mainly comprise, or are derived from, spent fuel. They must be shielded and cooled, neither of which is difficult or complex. As spent fuel, they are in stable ceramic form, and if reprocessed they end up thus. Storage under water or in shielded concrete structures is simple and safe. For final disposal some 50 years ex reactor, they will be encapsulated and placed in deep repositories, well down towards where radiogenic decay of uranium already heats the earth. The distinguishing feature of radioactive wastes is that their toxicity decays, unlike most other industrial wastes - after 40 years from reactor, the radioactivity of spent fuel has decayed to one thousandth of its original level, and it is producing less than one kilowatt of heat per tonne. Apart from renewables, nuclear power is the only energy-producing industry which takes full responsibility for all its wastes, and fully costs this into the product.
SAFETY
From the outset, the safety of nuclear reactors (where one has a very high energy density) has been a high priority in their design and engineering. About one third of the cost of a typical reactor is due to safety systems and structures. The Chernobyl accident in 1986 was a reminder of the need for this (normal safety provisions being largely absent there), whereas the comparable Three Mile Island accident in 1979 showed that such safety measures work - noone was harmed. In fact, and despite Chernobyl, the safety record of nuclear power is better than for any other major industrial technology. And it is improving with newer reactors.
WEAPONS PROLIFERATION
An early concern as nuclear technology
emerged from its military chrysalis was that
civil nuclear power should not enable more
countries to acquire nuclear weapons. Under
the Nuclear Non-Proliferation Treaty a safeguards
system was set up to detect and deter
any diversion of fissile material from civil to
military use. It is arguably the UN's most successful
program, and early prospects of 20-30
countries with nuclear weapons have been
averted. Today, the flow of material is from
weapons stockpiles to civil use, filling about
one fifth of world uranium demand. One in ten
light globes in the USA are now lit by ex-
Russian military uranium.
The WNA web site www.world-nuclear.org has
information papers on all these issues and many
more.
This is one of almost 50
chapters and articles in the 336-page large format book, Before the Wells
Run Dry. Copies of the book are available for £9.95 from Green Books. Continue to Section A of Part Two: A Sustainable Future - the Limits to Renewables
