A modern uranium-fuelled PWR contains 400-600 tonnes of uranium in fuel, of which about a third is replaced on average each year. To support a global reactor fleet of 440, annual fuel production, at a typical enrichment of 3.5% 235U, will need to be about 8-10000 tonnes, implying uranium production of 60-70000 tonnes yr-1. Currently, about 25% of this need is being met by ‘‘blending down’’ surplus high enriched uranium from military programmes, but this will not continue over the long term.

Uranium is not a particularly rare element (crustal abundance 2.8 ppm) and in 2007, global uranium reserves were estimated at 5.5 x 106 tonnes.11 There is a "‘‘Resources’’ are the total quantity estimated to be available; ‘‘reserves’’ are that proportion of the resources which can be extracted economically. Clearly, the balance between resources and reserves varies with the uranium price. As price increases, more resources can be exploited eco­nomically and therefore become reserves. Also, a higher price prompts exploration and the identification of additional resources and reserves. Resources and reserves can also change as a result of better definition of deposits, or successful exploration. The data presented here are based on a uranium price of $130 kg-1. The uranium price in October 2010 was $138 kg-1.

comparable quantity of uranium in seawater (4.5 x 106 tonnes; mean seawater concentration 3 ppb) but it is presently difficult to envisage a cost effective, large scale process for extracting it. The current position is therefore that global reserves would provide about 100 years’ fuel at current consumption rates, but expansion even at the lower end of the scale projected will reduce this to a few decades, comparable to the lifetime of a modern reactor. However, there is a complex relationship between demand, price, exploration activity and size of reserves, so it is difficult to draw firm conclusions about the long term avail­ability of uranium.

Even so, given the very long lead times associated with nuclear technology, a debate about alternatives has to be conducted at some point over the next decades. An open uranium fuel cycle is arguably wasteful and appears not to be sustainable over more than a century or two. A closed fuel cycle, particularly if combined with fast reactors, offers a vast increase in energy availability, but at the cost of industrial scale fuel reprocessing, which is a difficult and costly technology, and the large scale creation of plutonium or other fissile materials, which brings with it major ethical and security issues. Other fission technolo­gies, such as thorium-fuelled reactors, would raise similar technical and ethical questions. Probably the most far-reaching question is therefore the role we see for nuclear fission? Is it a stopgap, lasting a few decades and bridging from a fossil fuel era to a renewable — or fusion-powered era, or is it a resource we will need to exploit over centuries? The answer to this question has substantial implications for the fuel cycle(s) we choose to develop, and the associated environmental impacts.

5 Conclusions

Nuclear fission potentially offers the prospect of very substantial amounts of energy from a low carbon source. However, all steps in the nuclear fuel cycle create wastes and have potentially major environmental impacts. The open fuel cycle creates smaller waste volumes and, at first sight wastes which are easier to manage, than a closed fuel cycle, but involves the dis­posal as waste of large quantities of potentially reusable material. The technology required for closed fuel cycles, for fast reactors, or for parti­tioning of long-lived waste components is particularly demanding and fast reactors, separations beyond Purex, and partitioning and transmutation in particular are far from mature. Likewise, many aspects of the conditioning and disposal of higher activity wastes remain challenging. In addition, the proliferation risks associated with the widespread production and use of fissile materials must be addressed. While the demand for nuclear energy appears to be growing substantially at present and is expected to do so in future, this raises complex questions for the long term, to which there are currently few clear answers.

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