How GREEN is Tomorrow's Nuclear Energy

I. Introduction

There's been quite a lot of talk about a resurgent nuclear power industry, especially in light of the present discussion about global warming and the reduction of carbon-dioxide emissions. On paper at least, the argument against the usual fossil fuels seems to be valid, even more so when considering many plants are fueled with low-grade coals. Yet there are some facts/truths out there that many proponents won't mention, and some people, like me, would consider them to be a skeleton in nuclear energy's closet.

II. The Raw Materials

Everything starts with the uranium ore. And don't kid yourself, the extraction, benefaction and purification of uranium as any other metal, requires vast amounts of resources, especially energy. But uranium isn't just an ordinary metal like tin, copper or iron, to be useful in a reactor. Besides the fact that the metal must be extremely purified and free of even slight impurities, another extremely intensive energetic phase follows, the enrichment cycle. In this case, the normal metal, which consists, depending upon the source of the ore, of three or more isotopes, needs to be treated to increase the relative amount of the fissile 235 in relation to the 238. Normally, today's ores contain about 0.7% of the 235 isotope. To be used in most of the current reactors, this needs to be boosted to about 2.5%. There are several means for doing this technologically, ranging form the initial historic gas diffusion process (the most energy intensive) to today's much discussed gas centrifuges (still very energy intensive, but less so than the former). Not just the current and spent fuel elements of all the reactors up to now have gone through this process, but also all the uranium metal used in atomic bombs and as triggers in nuclear bombs have also gone this route. The latter statement will be of extreme relevance in the discussion that follows.

One very interesting aspect about the energy discussion is the argument that with nuclear power, the world would less dependent on fossil fuels like crude oil, and such organizations such as OPEC. Yet, when you take a look that the world's uranium reserves, nuclear energy would create a new “OUEC”, a club of uranium produces that include mainly Australia, Canada, South Africa and Kazakhstan, with a few additional minor players. If lots of new reactors are to be built (reports are that alone China will build several 10's of reactors in the next few years and consider the recent uranium deal China made with Australia), these suppliers will reap a windfall.

Here is where the main nasty little secret starts. Over the past months, several publications, here in Europe, as diverse as the magazine Der Spiegel, the financial magazine Borse Online and even the newspaper The International Herald Tribune have run articles about nuclear energy and the fact that the current consumption of uranium, for the existing reactors, is about double what the mines currently produce. That being the case, where is the uranium for the projected new reactors to come from? Basically, at the moment, the missing half is being covered much as one does in the gold and silver industry, by recycling. In this case it means using the uranium one has from reprocessing old fuel rods. This factor explains two aspects, why some countries actively pursing nuclear energy are also proponents of reprocessing and many are advocating using so-called MOX (mixed oxide – uranium and plutonium) fuel elements. The argument by MOX is that this way plutonium gets “burned”, but mainly it helps stretch the uranium too. The next escalation level would be reigniting the discussion about breeder reactors that would produce more fuel than they consume – but mainly plutonium. Besides that, though, another source is used, highly enriched uranium out or scrapped warheads is diluted down to nuclear fuel concentrations, by mixing it with either normal, freshly mined uranium or perhaps even using the DU (depleted uranium) left around after the initial enrichment of years past. DU has been in the news in recent years, as a part of armor piercing munitions used by tanks and aircraft. DU litters vast areas in regions and countries where the US and the UK have fought in the last couple of wars and campaigns (e. g. Iraq).

III. The Enriched Dilution

Most of the uranium enriched by the USA was done by the old energy intensive gaseous diffusion method. But to be fair, most of the energy came from the Tennessee Valley Authority, which consists mainly of hydroelectric energy. But still, this “cleaner” energy being thus used, meant it wasn't available for other users and they in turn got most of their energy demand covered by coal powered plants. So whether direct or indirectly the question of how much energy in terms of carbon-dioxide created was used for enrichment is valid.

The numbers you will see in the following analysis are just using some characteristic number for each process, the result obtained could differ by +/- 10 to 20% depending upon differing conditions. But this little example is mainly meant to serve as an indication of the magnitude of the produced gas. To produce a single kilogram of uranium enriched to the level of a weapon requires roughly 225 SWUs (Separative Work Unit). Each SWU is the equivalent of 2400 kWh (kilowatt-hours). Thus, to get one kilogram of bomb material, you need about 550,000 kWh.

One pound of coal, when totally burned, produces 120,000 BTUs (British Thermal Units) and each BTU is 0.0003 kWh. Thus, 1 lb. of coal produces 3.6 kWh. To produce the kilogram of enriched uranium thus requires approximately 150,000 lbs of coal, or 75 tons of pure carbon. When completely burned, that represents 275 tons of carbon-dioxide gas. Since a warhead requires, roughly, 5 kilograms, that means 1275 tons of carbon-dioxide per warhead, just due to the enrichment stage. Consider now the thousands of warheads in all the arsenals of the world powers, and you can see the sheer mass of gas produced.

Although a magazine such as New Scientist often complains about people creating crazy units or comparisons to make a point, I will indulge in this case, this urge. Imagine you have a 100 Watt bulb, burning 24/7, year after year. The energy of one SWU would keep this bulb lit for 24,000 hours. There are 8760 hours in a year. In other words, almost 3 years. since 225 SWUs are required for a kilogram and 5 kilograms for a bomb, a single bomb's energy requirement would keep that 100 Watt bulb lit for about 3 millennia!

IV. Conclusion

As long as weapons grade uranium is used to boost newly mined natural uranium to reactor grade, thereby eliminating an additional enrichment step, then the carbon-dioxide account will be balanced/neutral. If though the uranium supply problem becomes so acute that it is actually remixed with DU, then the account is highly negative, all the energy used and gas created during the enrichment procedure got blow for nothing at all. When new plants are being contemplated, let's have a true, holistic comparison, including everything form the mine head to the repository for waste material considered, including any eventually wasted energy and excess carbon-dioxide due to any possible mixture of weapons grade enriched uranium.