by David Fleming, April 2006
It takes a lot of fossil energy to mine uranium, and then to extract and prepare the right isotope for use in a nuclear reactor. It takes even more fossil energy to build the reactor, and, when its life is over, to decommission it and look after its radioactive waste.
As a result, with current technology, there is only a limited amount of uranium ore in the world that is rich enough to allow more energy to be produced by the whole nuclear process than the process itself consumes. This amount of ore might be enough to supply the world's total current electricity demand for about six years.
Moreover, because of the amount of fossil fuel and fluorine used in the enrichment process, significant quantities of greenhouse gases are released. As a result, nuclear energy is by no means a 'climate-friendly' technology.
Nuclear power promises much. It is based on a process which does not produce carbon dioxide. It is produced in a relatively small number of very large plants, so that it fits easily onto the national grid. And there is even the theoretical prospect of it being able to breed its own fuel. So, what's the problem?
The form of nuclear power available to us at present comes from nuclear fission, fuelled by uranium. Uranium-235 is an isotope of uranium with the rare and useful property that, when struck by a neutron, it splits into two and, in the process, produces more neutrons which then proceed to split more atoms of uranium-235 in a chain of events which produces a huge amount of energy. We can get an idea of how much energy it produces, by looking at Einstein's famous equation, E=mc2, which says that the energy produced is the mass multiplied by the square of the speed of light. A little bit of mass disappears in the process - we can think of this as the material weighing slightly less at the end of the process than at the beginning - and it is that "missing" mass which turns into energy which can be used to make steam to drive turbines and produce electricity. Neutrons from the reaction which strike one of the other isotopes of uranium: uranium-238, are more likely to be absorbed by the atom which transforms it into plutonium-239. Plutonium-239 shares with uranium-235 the property that it, too, splits when struck by neutrons, so that the plutonium-239 then begins to act as a fuel as well.2
The process has to be controlled; otherwise, it would be a bomb. The control is provided by a "moderator", in the form of large quantities of, for instance, water or graphite, whose presence means that the neutrons cannot so easily find the next link in the chain, so the sequence slows down or stops. Eventually, however, the uranium gets clogged with radioactive impurities such as the barium and krypton produced when uranium-235 decays, along with "transuranic" elements such as americium and neptunium, and a lot of the uranium-235 gets used up. It takes a year or two for this to happen, but eventually the fuel elements have to be removed, and a fresh ones inserted.
The used fuel elements are very hot and radioactive (stand close to one for a second or two and you are dead), so there are some tricky questions about what to do with them. Sometimes they are recycled (reprocessed), to extract some of the remaining uranium and plutonium to use again, although you don't get as much fuel back as you started with, and the bulk of the impurities remains. Alternatively, the whole lot is disposed-of - but there is more to this than just dumping it somewhere, for it never really goes away. The half-life of an element is the time it takes for half of it to decay; the half-life of uranium-238, which is the largest constituent of the waste, and which keeps the whole thing radioactive, is about the same as the age of the earth: 4.5 billion years.3
Those are the principles. Now for a closer look at what nuclear power means. It is quite important that we should do this, because nuclear power cannot be sensibly discussed on the basis of popular misconceptions such as the one about nuclear energy producing almost no carbon dioxide.
The principal source for the discussion that follows is the work of Jan Willem Storm van Leeuwen and Philip Smith, but the interpretation of their work, and its application in the context of current energy options, is the author's. The paper relies centrally, but not exclusively, on work from this one source, and the implications of this are discussed in the concluding section.4
1. WHAT IS REALLY INVOLVED IN NUCLEAR POWER?
Mining and milling
Uranium is widely distributed in the earth's crust but only in minute quantities, with the exception of a few places where it has accumulated in concentrations rich enough to be uses as an ore. The main deposits of ore, in order of size, are in Australia, Kazakhstan, Canada, South Africa, Namibia, Brazil, the Russian Federation, the USA, and Uzbekistan. There are some very rich ores; concentrations as high as 1 percent have been found, but 0.1 percent (one part per thousand) or less is usual. Most of the usable "soft" (sandstone) uranium ore has a concentration in the range between 0.2 and 0.01 percent; in the case of "hard" (granite) ore, the usable lower limit is 0.02 percent. The mines are usually open-cast pits which may be up to 250m deep. The deeper deposits require underground workings and some uranium is mined by "in situ leaching", where hundreds of tonnes of sulphuric acid, nitric acid, ammonia and other chemicals are injected into the strata and then pumped up again after some 5- 25 years, yielding about a quarter of the uranium from the treated rocks and depositing unquantifiable amounts of radioactive and toxic metals into the local environment and aquifers.5
When it has been mined, the ore is milled to extract the uranium oxide. In the case of ores with a concentration of 0.1 percent, the milling must grind up approximately 1,000 tonnes of rock to extract just one tonne of the bright yellow uranium oxide, called "yellowcake". Both the oxide and the tailings (that is, the 999 tonnes of rock that remain) are kept radioactive indefinitely by, for instance, uranium-238, and they contain all thirteen of its radioactive decay products, each one changing its identity as it decays into the next, and together forming a cascade of heavy metals, with spectacularly varied half-lives.
The decay sequence of uranium-238
The sequence starts with uranium-238. Half of it decays in 4.5 billion years, turning as it does so into thorium-234 (24 days), protactinium-234 (one minute), uranium-234 (245,000 years), thorium-230 (76,000 years), radium-226 (1,600 years), radon-222 (3.8 days), polonium-218 (3 minutes), lead-214 (27 minutes), bismuth-214 (20 minutes), polonium-214 (180 microseconds), lead-210 (22 years), bismuth-210 (5 days), polonium-210 (138 days) and, at the end of the line, lead-206 (non-radioactive).
Once these radioactive rocks have been disturbed and milled, they stay around to cause trouble. They take up much more space than they did in their undisturbed state, and their radioactive products are free to be washed and blown away into the environment by rain and wind. These tailings ought therefore to be treated: the acids should be neutralised with limestone and made insoluble with phosphates; the mine floor should be sealed with clay before the treated tailings are put back into it; the overburden should be replaced and the area should be replanted with indigenous vegetation. In practice, all this is hardly ever done. It is expensive, and it also requires approximately four times the amount of energy that was needed to extract the ore in the first place.6Preparing the fuel
The uranium oxide then has to be enriched. Yellowcake contains only about 0.7 percent uranium-235; the rest is mainly uranium-234 and -238, neither of which directly support the needed chain reaction. In order to bring the concentration of uranium-235 up to the concentration of uranium-235 up to the required 3.5 percent, the oxide is reacted with fluorine to form uranium hexafluoride (UF6), or "hex", a substance with the useful property that it changes - "sublimes" - from a solid to a gas at 56.5°C, and it is as a gas that it is fed into an enrichment plant. About 85 percent of it promptly comes out again as waste in the form of depleted uranium hexafluoride. Some of that waste is chemically converted into depleted uranium metal, which is then in due course distributed back into the environment via its use in armour-piercing shells, but most of it is kept as uranium hexafluoride in its solid form. It ought then to be placed in sealed containers for final disposal in a geological depositary; however, owing to the cost of doing this, and the scarcity of suitable places for it, much of it is put on hold: in the United States, during the last fifty years, 500,000 tonnes of depleted uranium have accumulated in cool storage (to stop it subliming), designated as "temporary".7
The enriched uranium is then converted into ceramic pellets of uranium dioxide (UO2) and packed in zirconium alloy tubes which are finally bundled together to form fuel elements for reactors.8Generation
The fuel can now be used to produce heat to raise the steam to generate electricity. In due course the process generates waste in the form of spent fuel elements and, whether these are then reprocessed and re-used or not, eventually they have to be disposed of. But first they must be allowed to cool off, as the various isotopes present decay, in ponds for between 10 and 100 years - sixty years may be taken as typical. Various ideas about how to deal with them finally are current, but there is no standard, routinely-implemented practice. One option is to pack them, using remotely-controlled robots, into very secure containers lined with lead, steel and pure electrolytic copper, in which they must lie buried for millions of years in secure geological depositaries. It may turn out in due course that there is one best solution, but there will never be an ideal way to store waste which will be radioactive for millions of years and, whatever leastbad option is chosen, it will require a lot of energy: it is estimated that the energy cost of making the lead-steel-copper containers needed to package the spent fuel produced by a reactor is about the same as the energy needed to construct the reactor.9
A second form of waste produced in the generation process consists of the routine release of very small amounts of radioactive isotopes such as hydrogen-3 (tritium), carbon-14, plutonium-239 and many others into the local air and water. The significance of this has only recently started to be recognised and investigated.10
A third, less predictable form of waste occurs in the form of accidental emissions and catastrophic releases in the event of accident. The nuclear industry has good safety systems in place; it has to have them, because the consequences of an accident are so extreme. However, it is not immune to accident. The work is routine, and the staff at some reactors have been described by a nuclear engineer as "asleep at the wheel". There is also the prospect, rising to certainty with the increase in numbers and the passage of time, of sabotage by staff, of the flooding of reactors by rising sealevels, and poor training and systems, particularly if a nuclear programme were to be developed in haste by governments eager to produce energy as fast as possible to make up for the depletion of oil and gas. Every technology has its accidents. The risk never goes away; society bears the pain and carries on but, in the case of nuclear power, there is a difference: the consequences of a serious accident - another accident on the scale of Chernobyl, or greater, or much greater. It is accepted that the damage could be so great that it was far beyond the capacity of the world's insurance industry to cover. It has therefore been agreed that governments should step in and meet the costs of a nuclear accident once the damage goes beyond a certain limit. In Britain, the Nuclear Installations Act of 1965 requires a plant's operator to pay a maximum of £150 million in the ten years after the incident. The government would cover any excess and pay for any damage that arose between ten and thirty years afterwards. Under international conventions, the government would also cover any cross-border liabilities up to a maximum of about £300 million. These figures seem to grossly understate the problem. If Bradwell power station in Essex blew up and there was an east wind, London would have to be evacuated. Perhaps even the whole of southern England. The potential costs of a nuclear accident could be closer to £300 trillion rather than £300 million, six orders of magnitude greater.
A fourth type of "waste" is the plutonium itself which, when isolated and purified in a reprocessing plant, can be brought up to weapons-grade, making it the fuel needed for nuclear proliferation. This is one of two ways in which the nuclear industry is used as the platform from which the proliferation of nuclear weapons can be developed; the other one is by enriching the uranium-235 to around 90 percent, rather than the mere 3.5 percent required by a nuclear reactor.The reactor
The maximum full-power lifetime is 24 years, but most reactors fall short of that. During that time, they require regular maintenance and at least one major refurbishing; towards the end of their lives, corrosion and intense radioactivity make reliable maintenance impossible. Eventually, they must be dismantled, but experience of this, particularly in the case of large reactors, is limited. As a first step, the fuel elements must be removed and put into storage; the cooling system must be cleaned to reduce radioactive CRUD (Corrosion Residuals and Unidentified Deposits). These operations, together, produce about 1,000 m3 of high-level waste. At the end of the period, the reactor has to be dismantled and cut into small pieces to be packed in containers for final disposal. The total energy required for decommissioning has been estimated at about double the energy needed in the original construction.11
2. GREENHOUSE GASES AND ORE QUALITY
Every stage in the process of supporting nuclear fission uses energy, and most of this energy is derived from fossils fuels. Nuclear power is therefore a massive user of energy and a very substantial source of greenhouse gases. In fact, the delivery of electricity into the grid from nuclear power produces, on average, roughly one third as much carbon dioxide as the delivery of the same quantity of electricity from gas...12
... or, rather, it should do so, because the calculation of the energy cost of nuclear energy is based on the assumption that the high standards of waste management outlined above, including the energy used in decommissioning, are actually carried out. Unfortunately, that is not the case: the nuclear power industry is living on borrowed time in the sense that it is has not yet had to find either the money or the energy to reinstate its mines, bury its wastes and decommission its reactors; if those commitments are simply left out of account, the quantity of fossil fuels needed by nuclear power to produce a unit of electricity would be, on average, only 16 percent of that needed by gas. However, these are commitments which must eventually be met. The only reasonable way to include that energy cost in estimating the performance of nuclear power is to build them into the costs of electricity that is being generated by nuclear power now.13
Another assumption contained in the calculation of the carbon emissions of nuclear power is that the reactors last for the practical maximum of 24 full-power years. For shorter-lived reactors, the quantity of carbon dioxide emissions per unit of electricity is higher; when the energy costs of construction and decommissioning are taken into account, nuclear reactors, averaged over their lifetimes, produce more carbon dioxide than gas-fired power stations (per unit of electricity generated), until they have been in full-power operation for about seven years.
These estimates of carbon dioxide emissions understate the actual contribution of nuclear energy to greenhouse gas emissions, because they do not take into account the releases of other greenhouse gases which are used in the fuel cycle. The stage in the cycle in which other greenhouse gases are particularly implicated is enrichment. As explained above, enrichment depends on the production of uranium hexafluoride, which of course requires fluorine - along with its halogenated compounds - not all of which can by any means be prevented from escaping into the atmosphere. As a guide to the scale of problem: the conversion of one tonne of uranium into an enriched form requires the use of about half a tonne of fluorine; at the end of the process, only the enriched fraction of uranium is actually used in the reactor: the remainder, which contains the great majority of the fluorine that was used in the process, is left as waste, mainly in the form of depleted uranium. It is worth remembering here, first, that to supply enough enriched fuel for a standard 1GW reactor for one full-power year, about 160 tonnes of natural uranium has to be processed; secondly, that the global warming potential of halogenated compounds is many times that of carbon dioxide: that of freon-114, for instance, is nearly 10,000 times greater than that of the same mass of carbon dioxide. Moreover, other halogens, such as chlorine, whose compounds are potent greenhouse gases, along with a range of solvents, are extensively used at various other stages in the nuclear cycle, notably in reprocessing.14
There is no readily-available data on the quantity of these hyperpotent greenhouse gases regularly released into the atmosphere by the nuclear power industry, nor on the actual, presumably variable, standards of management of halogen compounds among the various nuclear power industries around the world. There has to be a suspicion that this source of climate-changing gases substantially reduces any advantage which the nuclear power industry has at present in the production of emissions of carbon dioxide, but no well-founded claim can be made about this. It is essential that reliable research data on the quantity of freons and other greenhouse gases released from the nuclear fuel cycle should be researched and made available as a priority.The future
The advantage of nuclear power in producing lower carbon emissions holds true only as long as supplies of rich uranium last. When the leaner ores are used - that is, ores consisting of less than 0.01 percent (for soft rocks such as sandstone) and 0.02 percent (for hard rocks such as granite), so much energy is required by the milling process that the total quantity of fossil fuels needed for nuclear fission is greater than would be needed if those fuels were used directly to generate electricity. In other words, when it is forced to use ore of around this quality or worse, nuclear power begins to slip into a negative energy balance: more energy goes in than comes out, and more carbon dioxide is produced by nuclear power than by the fossil-fuel alternatives.15
The world's annual production of uranium oxide has been lagging behind its use in nuclear reactors for the past twenty years. The shortfall has been made up from military stockpiles.
There is doubtless some rich uranium ore still to be discovered, and yet exhaustive worldwide exploration has been done, and the evaluation by Storm van Leeuwen and Smith of the energy balances at every stage of the nuclear cycle has given us a summary. There is enough usable uranium ore in the ground to sustain the present trivial rate of consumption - a mere 2 1/2 percent of all the world's final energy demand - and to fulfil its waste-management obligations, for around 45 years. However, to make a difference - to make a real contribution to postponing or mitigating the coming energy winter - nuclear energy would have to supply the energy needed for (say) the whole of the world's electricity supply. It could do so - but there are deep uncertainties as to how long this could be sustained. The best estimate (pretending for a moment that all the needed nuclear power stations could be built at the same time and without delay) is that the global demand for electricity could be supplied from nuclear power for about six years, with margins for error of about two years either way. Or perhaps it could be more ambitious than that: it could supply all the energy needed for an entire (hydrogen- fuelled) transport system. It could keep this up for some three years (with the same margin for error) before it ran out of rich ore and the energy balance turned negative.16
If, as an economy measure, all the energy-consuming waste-management and clean-up practices described above were to be put on hold while stocks of rich ore last, then the energy needed by nuclear energy might be roughly halved, so that global electricity could be supplied for a decade or so. At the end of that period, there would be giant stocks of untreated, uncontained waste, but there would be no prospect of the energy being available to deal with it. At the extreme, there might not even be the energy to cool the storage ponds needed to prevent the waste from being released from its temporary containers.
But it is worse than that. There is already a backlog of high-level waste, accumulated for the last sixty years, and now distributed around the world in cooling ponds, in deteriorating containers, in decommissioned reactors and heaps of radioactive mill-tailings. Some 1/4 million tonnes of spent fuel is already being stored in ponds, where the temporary canisters are so densely packed that they have to be separated by boron panels to prevent chain reactions. The task of clearing up this lethal detritus will require a great deal of energy. How much? That is not known, but here is a very rough guideline. Energy equivalent to about one third of the total quantity of nuclear power produced - in the past and future - will be required to clear up past and future wastes. And the whole of this requirement will have to come from the usable uranium ore that remains, which is not much more than half the entire original endowment of usable ore.17
This means that, if the industry were to clear up its wastes, only about one third of the present stock of uranium would be left over as a source of electricity for distribution in national grids. To put it another way, the electricity that the industry would have available for sale in the second half of its life - if at the same time it were to meet its obligation to clear up the whole of its past and present wastes - would be approximately 70 percent less than it had available for sale in the first half of its life. On that calculation, the estimates given earlier for the useful contribution that nuclear power could make in the future must be revised: nuclear energy, if it cleared up all its wastes, could supply enough power to provide the world with all the electricity it needed for some three years. And remember that this is no mere thoughtexperiment: those wastes do have to be cleared up; the energy required for this will reduce the contribution that can be expected from nuclear power from the trivial to the negligible.
And we should not forget the cost of this. If the nuclear industry in the second part of its life were to commit itself to clearing up its current and future wastes, the cost would make the electricity it produced virtually unsaleable. Bankruptcy would follow, but the waste would remain. Governments would have to keep the clearup programme going, whatever the other priorities. They would also have to keep training programmes going in a College of Nuclear Waste Disposal so that, a century after the nuclear industry has died, the skills they will require to dispose of our waste will still exist. And yet, Government itself, in an energy-strapped society, would lack the funds. The disturbing prospect is already opening up of massive stores of unstable wastes which no one can afford to clear up.
The implication of this is that nuclear power is caught in a depletion trap - the depletion of rich uranium ore - at least as imminent as that of oil and gas. So the question to be asked is: as the conventional uranium sources run low, are there alternative sources of fuel for nuclear energy?
3. ALTERNATIVE SOURCES OF FUEL
Earlier this year, James Lovelock, the originator of the Gaia Hypothesis, argued in his book The Revenge of Gaia that the threat of climate change is so real, so advanced and potentially so catastrophic that the risks associated with nuclear power are trivial by comparison - and that there really is no alternative to its widespread use. Nuclear power, he insisted, is the only large-scale option: it is feasible and practical; a nuclear renaissance is needed without delay. He robustly dismissed the idea that the growth of nuclear power was likely to be constrained by depletion of its raw material. This is how he put it:
"Another flawed idea now circulating is that the world supply of uranium is so small that its use for energy would last only a few years. It is true that if the whole world chose to use uranium as its sole fuel, supplies of easily-mined uranium would soon be exhausted. But there is a superabundance of low-grade uranium ore: most granite, for example, contains enough uranium to make its fuel capacity five times that of an equal mass of coal. India is already preparing to use its abundant supplies of thorium, an alternative fuel, in place of uranium.18 "
Lovelock added that we have a readily-available stock of fuel in the plutonium that has been accumulated from the reactors that are shortly to be decommissioned. And he might also have added that another candidate as a source of nuclear fuel is seawater. So, if we put the supposed alternatives to uranium ore in order, this is what we have: (1) granite; (2) fast-breeder reactors using (a) plutonium and (b) thorium; and (3) seawater.
It has already been explained above that granite with a uranium content of less than 200 parts per million (0.02%) cannot be used as a source of nuclear energy, because that is the borderline at which the energy needed to mill it and to separate the uranium oxide for enrichment is greater - and in the case of even poorer ores, much greater - than the energy that you get back. But Lovelock is so insistent and confident on this point that it is worth revisiting.
Storm van Leeuwen, basing his calculations on his joint published work with Smith on the extraction of uranium from granite, considers how much granite would be needed to supply a 1 GW nuclear reactor with the 160 tonnes of natural uranium it would need for a year's full-power electricity production. Ordinary granite contains roughly 4 grams of uranium per tonne of granite. That's four parts per million. One year's supply of uranium extracted from this granite would require 40 million tonnes of granite. So, Lovelock's granite could indeed be used to provide power for a nuclear reactor, but there are snags. The minor one is that it would leave a heap of granite tailings (if neatly stacked) 100 metres high, 100 metres wide and 3 kilometres long. The major snag is that the extraction process would require some 530 PJ (petajoules = 1,000,000 billion joules) energy to produce the 26 PJ electricity provided by the reactor. That is, it would use up some 20 times more energy that the reactor produced.19
- Fast breeder reactors
Lovelock's proposal that we should use plutonium as the fuel for the nuclear power stations of the future can be taken in either of two ways. He might be proposing that we could simply run the reactors on plutonium on the conventional "once-through" system which is standard, using light-water reactors. This can certainly be done, but it cannot be done on a very large scale. Plutonium does not exist in nature; it is a by-product of the use of uranium in reactors and, when uranium is no longer used, then in the normal course of things no more plutonium will be produced. There is enough reactor-grade plutonium in the world to provide fuel for about 80 reactors. That is just about realistic, but there are another two theoretical but highly unrealistic possibilities. The first is that all weapons-grade plutonium could be converted into enough fuel for about 60 more reactors; the second is that all the spent fuel produced by all nuclear power stations in the world could be successfully reprocessed (despite the substantial failure and redundancy of reprocessing technology at present) and used to provide the fuel for the reactors of the future. That would provide fuel for another 600 reactors - making a total of 740 operating with plutonium alone.20
But since we're trying to be realistic here, let us concentrate on what could actually be done, and stay as close as we can to what Lovelock seems to be suggesting: we could, using the plutonium that we actually have, build 80 reactors worldwide. At the end of their life (say, 24 full-power years), the plutonium would have been used up, though supplemented by a little bit over from the final generation of ordinary uranium-fuelled reactors, but soon all reactors would be closed down and not replaced, because at that time there will be no uranium to fuel them with, either. This would scarcely be a useful strategy, so it is more sensible to suppose that Lovelock has in mind the second possibility: that the plutonium reactors should be breeder reactors, designed not just to produce electricity now, but to breed more plutonium for the future.
Breeders are in principle a very attractive technology. In uranium ore, a mere 0.7 percent of the uranium it contains consists of the useful isotope - the one that is fissile and produces energy - uranium-235. Most of the uranium consists of uranium-238, and most of that simply gets in the way and has to be dumped at the end; it is uranium-238 which is responsible for much of the awesome mixture of radioactive materials that causes the waste problem. And yet, uranium-238 does also have the property of being fertile. When bombarded by neutrons from a "start-up" fuel like uranium-235 or plutonium-239, it can absorb a neutron and eject an electron, becoming plutonium-239. That is, plutonium-239 can be used as a start-up fuel to produce more plutonium-239, more-or-less indefinitely. That's where the claim that nuclear power would one day be too cheap to meter comes from.
But there is a catch. It is a complicated technology. It consists of three operations: breeding, reprocessing and fuel fabrication, all of which have to work concurrently and smoothly. First, breeding: this does not simply convert uranium-238 to plutonium-239; at the same time, it produces plutonium-241, americium, curium, rhodium, technetium, palladium and much else. This mixture tends to clog up and corrode the equipment. There are in principle ways round these problems, but a smoothly-running breeding process on a commercial scale has never yet been achieved.21
Secondly, reprocessing. The mixture of radioactive products that comes out of the breeding process has to be sorted, with the plutonium-239 being extracted. The mixture itself is highly radioactive, and tends to degrade the solvent, tributyl phosphate. Here, too, insoluble compounds form, clogging up the equipment; there is the danger of plutonium accumulating into a critical mass, setting off a nuclear explosion. The mixture gets hot and releases radioactive gases; and significant quantities of the plutonium and uranium are lost as waste. As in the case of the breeder operation itself, a smoothly-running reprocessing process on a commercial scale has never yet been achieved.
The third operation is to fabricate the recovered plutonium as fuel. The mixture gives off a great deal of gamma and alpha radiation, so the whole process of forming the fuel into rods which can then be put back into a reactor has to be done by remote control. This, too has yet to be achieved as a smoothly-running commercial operation.
And, of course, it follows from this, that the whole fast-breeder cycle, consisting of three processes none of which have ever worked as intended, has itself never worked. There are three fastbreeder rectors in the world: Beloyarsk-3 in Russia, Monju in Japan and Ph´nix in France; Monju and Ph´nix have long been out of operation; Beloyarsk is still operating, but it has never bred. But let us look on the bright side of all this. Suppose that, with 30 years of intensive research and development, the world nuclear power industry could find a use for all the reactor-grade plutonium in existence, fabricate it into fuel rods and insert it into newly-built fast-breeder reactors - 80 of them, plus a few more, perhaps, to soak up some of the plutonium that is being produced by the ordinary reactors now in operation. So: they start breeding in 2035. But the process is not as fast as the name suggests ("fast" refers to the speeds needed at the subatomic level, rather than to the speed of the process). Forty years later, each breeder reactor would have bred enough plutonium to replace itself and to start up another one. By 2075, we would have 160 breeder reactors in place. And that is all we would have, because the ordinary, uranium-235-based reactors would by then be out of fuel.22The safety/cost trap
The complexity of in-depth defence against accident can make the system impossible
There is a systemic problem with the design of breeder reactors. The consequences of accidents are so severe that the possibility has to be practically ruled out under all circumstances. This means that the defence-in-depth systems have to be extremely complex, and this in turn means that the installation has to be large enough to derive economies of scale - otherwise it would be hopelessly uneconomic. However, that means that no confinement dome, on any acceptable design criterion, can be built on a scale and structural strength to withstand a major accident. And that in turn means that the defence-in-depth systems have to be even more complex, which in turn means that they becomes even more problem-prone than the device they were meant to protect. A study for the nuclear industry in Japan concludes: "A successful commercial breeder reactor must have three attributes: it must breed, it must be economical, and it must be safe. Although any one or two of these attributes can be achieved in isolation by proper design, the laws of physics apparently make it impossible to achieve all three simultaneously, no matter how clever the design."23
The other way of breeding fuel is to use thorium. Thorium is a metal found in most rocks and soils, and there are some rich ores bearing as much as 10 percent thorium oxide. The relevant isotope is the slightly radioactive thorium-232. It has a half-life three times that of the earth, so that makes it useless as a direct source of energy, but it can be used as the starting-point from which to breed an efficient nuclear fuel. Here's how:
- Start by irradiating the thorium-232, using a start-up fuel - plutonium-239 will do. Thorium-232 is slightly fertile, and absorbs a neutron to become thorium 233.
- The thorium-233, with a half-life of 22.2 minutes, decays to protactinium-233.
- The protactinium-233, with a half-life of 27 days, decays into uranium-233.
- The uranium-233 is highly fissile, and can be used not just as nuclear fuel, but as the start-up source of irradiation for a blanket of thorium-232, to keep the whole cycle going indefinitely.24
But, as is so often the case with nuclear power, it is not as good as it looks. The two-step sequence of plutonium breeding is, as we have seen, hard enough. The four-step sequence of thorium-breeding is worse. The uranium-233 which you get at the end of the process is contaminated with uranium-232 and with highlyradioactive thorium-228, both of which are neutron-emitters, reducing its effectiveness as a fuel; it also has the disadvantage that it can be used in nuclear weapons. The comparatively long half-life of protactinium-233 (27 days) makes for problems in the reactor, since substantial quantities linger on for up to a year. Some reactors - including Kakrapar-1 and -2 in India - have both achieved full power using some thorium in their operation, and it may well be that, if there is to be a very long-term future for nuclear fission, it will be thorium that drives it along. However, the full thorium breeding cycle, working on a scale which is largeenough and reliable-enough to be commercial, is a long way away.25
For the foreseeable future, its contribution will be tiny. This is because the cycle needs some source of neutrons to begin. Plutonium could provide this but (a) there isn't very much of it around; (b) what there is (especially if we are going to do what Lovelock urges) is going to be busy as the fuel for once-through reactors and/or or fast-breeder reactors, as explained above; and (c) it is advisable, wherever there is an alternative, to keep plutonium-239 and uranium-233 - an unpredictable and potentially incredibly dangerous mixture - as separate as possible. It follows that thorium reactors must breed their own start-up fuel from uranium-233. The problem here is that there is practically no uranum-233 anywhere in the world, and the only way to get it is to start with (say) plutonium-239 toget one reactor going. At the end of forty years, it will have bred enough uranium-233 both to get another reactor going, and to replace the fuel in the original reactor. So, as in the case of fastbreeders, we have an estimated 30 years before we can perfect the process enough to get it going on a commercial scale, followed by 40 years of breeding. Result: in 2075, we could have just two thorium reactors up and running.26
Seawater contains uranium in a concentration of about thirty parts per billion, and advocates of nuclear power are right to say that, if this could be used, then nuclear power could in principle supply us with the energy we need for a long time to come. Ways of extracting those minute quantities of uranium from seawater and concentrating them into uranium oxide have been worked out in some detail. First of all, uranium ions are attracted - "adsorbed" - onto adsorption attracted - "adsorbed" - onto adsorption beds consisting of a suitable material such as titanium hydroxide, and there are also some polymers with the right properties. These beds must be suspended in the sea in huge arrays, many kilometres in length, in places where there is a current to wash the seawater through them, and where the sea is sufficiently warm - at least 20°C. They must then be lifted out of the sea and taken on-shore, where, in the first stage of the process, they are cleansed to remove organic materials and organisms. Stage two consists of "desorption" - separating the adsorbed uranium ions from the beds. Thirdly, the solution that results form this must be purified, removing the other compounds that have accumulated in much higher concentration than the uranium ions. Fourthly, the solution is concentrated, and fifthly, a solvent is used to extract the uranium. The sixth stage is to concentrate the uranium and purify it into uranium oxide yellowcake, ready for enrichment in the usual way.27
But the operation is massive and takes a lot of energy. Very roughly, two cubic kilometres of sea water is needed to yield enough uranium to supply one tonne, prepared and ready for action in a reactor. A 1 GW reactor needs about 160 tonnes of natural uranium per annum, so each reactor requires some 324 cubic kilometres of seawater to be processed - that is, some 32,000 cubic kilometres of seawater being processed in order to keep a useful fleet of 100 nuclear reactors in business for one (full-power) year.28
And what is the energy balance of all this? One tonne of uranium, installed in a light water reactor, is taken as a rule-of-thumb also to produce approximately 162 TJ (1 terajoule = 1,000 billion joules), less the roughly 60-90 TJ needed for the whole of the remainder of the fuel cycle - enrichment, fuel fabrication, waste disposal, and the deconstruction and decommissioning of the reactor - giving a net electricity yield of some 70-90 TJ. The energy needed to supply the uranium from seawater, ready for entry into that fuel cycle, is in the region of 195-250 TJ. In other words, the energy required to operate a nuclear reactor using uranium derived from seawater would require some three times as much energy as it produced.