Young Australian Skeptics

Well, by popular demand, here’s a bit more of a primer on nuclear power.

It’s often said by its opponents that nuclear energy is somehow exceptionally dangerous, and therefore should not be used. However, my response to that is simple — where are the injuries? Where are the deaths?

The disaster at Chernobyl was really something very exceptional, and entire volumes can and have been written about the details of exactly what happened at Chernobyl and how it happened. The short story about Chernobyl is that it is simply absolutely irrelevant to any discussion of any power reactors that ever have been built or will be built in the Western world. It’s just not relevant.

It’s often pointed out that according to credible, fact-​​based scientific research, only 56 people died as a result of the Chernobyl accident. In response to this, anti-​​nuclear activists usually kick and scream and say, no, it was tens of thousands, hundreds of thousands, millions, or whatever figure they feel like making up at the time.

Sure, the overall number of people injured was likely to be greater than 56. But we don’t have access to the information needed to study those numbers and make any conclusion about them in a credible scientific way. The only figure that can be pinned down in a scientifically credible fashion is 56 deaths. Perhaps more, but we cannot know anything about them in a scientifically credible way; credible data does not exist.

In the late 1940s, nuclear scientists and engineers in the United States founded what was known as the Reactor Safety Council, to ensure that the fledgling development of nuclear power technology was done in a very safe way. The council was chaired by the infamous Edward Teller, the man who inspired Dr. Strangelove, who despite his notorious political views was really a very good physicist.

To consider just how far departed from nuclear power in the Western world Chernobyl was, consider this. In the 1940s, Edward Teller realized that the primitive graphite pile natural uranium reactors used for weapons production at the Hanford site were potentially dangerous – they were graphite-​​moderated, water-​​cooled, and had significant positive void coefficients of reactivity. This means that if the water coolant within the pile becomes excessively hot, it expands, some of the water boils off, and bubbles of steam form within the water. All these factors mean that less neutrons are absorbed within the water, and reactivity within the reactor increases, in a way that is subject to positive feedback.

The Hanford piles had no real containment structures, and could suffer dangerous, explosive power excursions if they were operated at a very low power level and forcibly restarted from a condition of xenon-​​135 poisoning. That’s what people like Teller predicted could happen in the late 1940s, and that’s what happened nearly four decades later at Chernobyl in a very similar water-​​cooled graphite-​​pile reactor.

Teller took reactor safety very seriously, and studied it very carefully. He ruffled a lot of feathers, as he carried on about the things that were not safe. Some derisively called him “the reactor opposer”. But thanks to his lobbying, no more such graphite piles were built ever again in the United States, aside from those very first few graphite reactors at Hanford, even though if building plutonium bombs is your goal, they’re the easiest and cheapest way to do it.

In short, everything that happened in the dangerous reactor at Chernobyl in 1986 was completely understood… nearly 40 years before the disaster.

To consider just how dangerous nuclear power is, ask yourself this. Aside from Chernobyl, how many examples can you find where anyone has actually been injured or killed by nuclear power? There are simply no such examples. Perhaps I should specifically say radioactivity or ionising radiation in relation to nuclear power, because the odd example of a person falling off a ladder at a nuclear power plant, for example, doesn’t count. It’s less likely at a a nuclear power plant than it is at, say, a coal-​​fired plant, due to the rigorous safety culture demanded of nuclear power.

The deaths simply do not exist, except for the deaths at Chernobyl, which are completely irrelevant to nuclear energy outside the Soviet Union, and are impossible to accurately quantify without stirring up a hornet’s nest of emotional debate. There were a couple of fatalities in the US in the 1950s involving the SL-​​1 reactor, an experimental prototype reactor being developed for the US Army, but that was back in the ‘50s, and isn’t relevant to today’s commercial power generation. There were also a few fatalities in Japan a few years ago involving a criticality accident during the mishandling of a solution of highly enriched uranium which was being prepared for an experimental prototype research reactor — but again, this is not relevant to the nuclear power industry. The risk of a criticality accident when handling highly enriched uranium is far greater than the risk when handling low-​​enriched uranium. Even if you somehow took those cases to be relevant, the overall rate of injuries or deaths for a large-​​scale industrial enterprise is exceptionally small. The empirically demonstrated fact is that nuclear energy is very safe.

So, how safe is nuclear power, compared to say, wind power? Wind power is pretty safe, right? The rate of accidental deaths associated with wind power today is approximately 0.15 deaths per TWh, according to this source.

A typical nuclear power plant might have two 1000 MW reactors, and might operate with a typical capacity factor of 95%. Therefore, in one year it will generate 16.7 TWh of energy, and if nuclear power was equally as dangerous as wind power, we’d expect to see about 2.5 fatalities per year on average, at every such nuclear power plant. But of course all those fatalities don’t exist — maybe nuclear power is less dangerous than wind power?

Of course, coal and natural gas really are dangerous — they kill people all the time. Seven coal miners were killed earlier this month in a mine explosion in southern Poland, and 35 were killed in a coal mine explosion in China earlier this month. Nine were killed in a natural gas explosion in the Ukraine in December last year. Twenty were killed in a coal mine explosion in Slovakia in August, and 74 were killed in a coal mine explosion in China in Febuary. And those are just a few examples I could find quickly. It’s estimated that particulates and air pollution kill over two million people prematurely each year, and a large portion of that vast public health impact is due to the dangerous waste from coal-​​fired power stations being pumped into the atmosphere.

But what about that dreaded nuclear waste?

For an existing, established, nuclear power plant using conventional light-​​water reactors, approximately 160 tonnes of natural uranium needs to be mined to supply the nuclear fuel for one year’s operation for an output of 1 gigawatt of electrical power, for a single nuclear reactor. This assumes that the nuclear fuel is used relatively inefficiently in a “once-​​through” way, and that the irradiated nuclear fuel is simply declared “waste”, without any efficient re-​​use or reprocessing of the nuclear fuel, no high-​​efficiency utilisation of the nuclear fuel in advanced reactors, and no supply of nuclear fuel materials from existing stockpiles, from recycled fuels, or from the downblending of high-​​grade fissile materials from decommissioned nuclear weapons.

So this is the conservatively inefficient, low-​​technology, comparatively wasteful scenario, only using presently widely established nuclear fuel practices.

When this 160 tonnes of natural uranium is enriched, approximately 140 tonnes of it is put aside as the seperated uranium which is mostly uranium-​​238 and almost no uranium-​​235; this is the so-​​called depleted uranium. However, this uranium-​​238 is perfectly useful as fuel in fast-​​spectrum reactors, and it can simply be stored and put to work, tomorrow, in fast reactors and more advanced reactors, even if it is not being used extensively today. This uranium can also be used to blend down very highly enriched uranium from decommissioned nuclear weapons stockpiles, or to blend with plutonium which has been extracted from nuclear fuels, or from nuclear weapons. The resulting low-​​enriched uranium or mixed-​​oxide fuels can be used perfectly well in light-​​water reactors and other presently well established types of power reactors; advanced reactors are not required to use these fuels.

With superior approaches to the nuclear fuel cycle, however, uranium enrichment is not required at all — in a fast reactor, you can simply take natural uranium and throw that in the reactor. Uranium enrichment is in fact completely unnecessary, if nuclear energy is to be utilised in a truly more efficient way.

After uranium enrichment for light-​​water reactor fuel, approximately 20 tonnes of low-​​enriched uranium is obtained, and this is manufactured into fuel for the reactors.
This fuel is made of uranium dioxide, and the fuel for one gigawatt-​​year of energy generation weighs about 23 tonnes, due to the small amount of additional mass of the oxygen in that compound compared to pure uranium. This low-​​enriched uranium is approximately 4% uranium-​​235, and 96% U-​​238.

Later, when the used nuclear fuel has been removed from the reactor, it still weighs approximately 23 tonnes, and has not experienced any significant change in its mass.
This is what many people call the so-​​called nuclear “waste”. But even if you call this so-​​called “waste”, there isn’t even that much of it. Given the very high density of uranium dioxide, 23 tonnes fits into the volume of a cube measuring less than 1.3 meters on each side.

To put this into context, the emissions into the atmosphere from Loy Yang Power in 2008 were 18,389,935 tonnes of carbon dioxide, 66,327 tonnes of sulfur dioxide, 37,642 tonnes of nitrogen dioxide, 3643 tonnes of carbon monoxide and 1840 tonnes of dust particulates.

(I’m not picking on that particular company specifically, they’re just the first example of a coal-​​fired generator in Victoria that came to my mind, and you do have to give them some credit for their candor in making those statistics all publically available.)

The total amount of electrical energy sent to the grid from Loy Yang in 2006 was 15,206 GWh, or 1.73 gigawatt years. Therefore, so that we’re making a sensible comparison, we need to scale up all the above quantities for uranium by a factor of 1.73 — so we’ve got approximately 40 tonnes of uranium oxide fuel, containing approximately 35 tonnes of uranium itself, to generate the same amount of energy as a Loy Yang scale plant over one year. A cube approximately 1.5 meters on a side.

Don’t you think that it’s possible that just maybe this 40 tonnes of used uranium oxide fuel is just a little bit less of a problem than 18.5 million tonnes of toxic and environmentally dangerous crap being pumped into the atmosphere from the coal-​​fired power station?

That used nuclear fuel is all stored, and kept isolated from the environment. It takes up a small amount of volume, since it’s so dense. If it’s being stored, you can actually go and see it, and it’s far more visible than that 18.5 million tonnes of carbon dioxide and other stuff being dumped out into the atmosphere, which you can never really see the magnitude of. It’s for this reason, that it seems to be more visible, that nuclear fuel “waste” seems to have this totally nonsensical reputation amongst some people as some sort of grave, intractable problem.

But what is this so-​​called waste? What are its properties? What’s it made of? You can’t just go and label it “waste” and make such a dilemma of it without answering these questions.

Of that 35 tonnes of uranium (we’re not interested in the mass of the oxygen in the oxide, which hasn’t really changed), about 96% of the mass of this used fuel, from an existing light-​​water reactor, is uranium. It’s uranium which is almost entirely unchanged within the nuclear reactor, and it’s approximately 1% uranium-​​235, with the remainder being uranium-​​238.

So if we separate off that uranium, which is easy enough to do, you’re left with only 1400 kilograms of material, from 1.73 gigawatt-​​years of electrical energy generation. Why would you call all that uranium “waste”, when it’s exactly the same uranium that you started with, uranium that you would otherwise have to go and mine?
Containing approximately 1% U-​​235, this uranium still contains a higher ratio of uranium-​​235 to uranium-​​238 than occurs in natural uranium, meaning that less separative work is required to enrich it, compared to natural uranium. Even if you ignore the useful applications of the materials other than uranium in the irradiated fuel, seperate the uranium and then declare all of what’s left over to be “waste”, you only have 1400 kilograms of so-​​called “waste”.

Of the remaining mass of the used fuel, approximately 1%, or 350 kg, is made up of transuranic actinides, such as plutonium, neptunium, americium and californium.
About half of that, approximately, might be plutonium-​​239, mixed with other more radioactive plutonium nuclides such as plutonium-​​238 and Pu-​​240, along with smaller amounts of more exotic nuclides such as neptunium-​​237, americium-​​241, curium and californium.

All these nuclides can be burned as fuel in a fast reactor — but many of these nuclides have valuable technological applications. Neptunium-​​237 is a highly valuable nuclide produced in nuclear reactors, since it is the precursor to the production of plutonium-​​238. Plutonium-​​238 is a highly valuable radionuclide, with uniquely favourable characteristics as a radiothermal heat source for energy generation, of both heat and electricity, on spacecraft, in pacemakers, and in other applications where highly reliable solid-​​state generation of small amounts of energy is needed for application in inaccessible areas where other forms of energy aren’t useful. At the moment the Department of Energy is stuffing around working out how many millions of dollars they need to spend to restore the capability to manufacture Pu-​​238 in the United States, since there is a severe shortage of it and it is needed for use in NASA’s spacecraft.

Americium-​​241 has valuable technological applications, in portable low-​​energy gamma ray sources for portable X-​​ray fluorescence spectroscopy, in neutron sources for research, chemical composition analysis, smoke detectors, nuclear gauges, moisture gauges used in civil engineering, and nuclear sensors for borehole logging of the geochemical composition of the surrounding rock in the oil exploration industry. At the moment, all the Am-​​241 produced in the world for radioactive sources for these kinds of applications is produced by only one organisation, in Russia. If an americium-​​based source is wanted, say, in the oilfield industry for a down-​​hole logging tool, they need to spend several years on a waiting list to get such a device, which contains perhaps milligrams of the material. And this is so-​​called waste?

Californium-​​252 is wonderfully valuable stuff in neutron sources, with similar applications in research, neutron-​​based sensors for chemical analysis, sensors for the detection of explosives and munitions such as landmines and geochemical analysis of petroleum exploration boreholes, amongst other applications. The Advanced Test Reactor in the US is one of the only reactors in the world currently set up for the production of the stuff, and lack of availability and supply security is a real concern.

Many of these materials comprising your so-​​called nuclear “waste” are materials so technologically valuable we’re often concerned about their lack of availability and supply security.

The remaining 3% or so, or approximately 1050 kg, is made up of the fission products. These are nuclides which are approximately half as massive as the uranium or plutonium nucleus that was fissioned — for example, nuclides of krypton, barium, iodine, palladium, or elements in that mass range — left behind after the heavy nucleus has fissioned, or split. Not all these fission products are radioactive, and some are very short lived, with others having moderately long half lives, and less radioactivity for a given amount of material. Energy can’t be generated by nuclear fission from fission products, but many of these radioactive nuclides generate significant amounts of heat as they decay, and this heat could be harnessed under the right conditions for valuable work. Some short-​​lived fission products are important as radioactive tracers, in research and in medicine — similar shortages and lack of supply security exist for many short-​​lived fission products such as molybdenum-​​99 and iodine-​​131 used in nuclear medicine and medical imaging as they do for some of the actinide elements mentioned above for industrial applications. Many of the longer-​​lived radioactive fission products, such as caesium-​​137 with a half-​​life of 30 years, have valuable industrial and technological applications, too.

The overwhelming majority of all the radioactivity in used nuclear fuel of this type is due to radioactive fission products with moderately long lifetimes, such as caesium-​​137 with a half-​​life of 30 years, and strontium-​​90 with a half-​​life of 29 years. Therefore, scary-​​sounding statements such as “the waste lasts for 100,000 years!” are not at all particularly accurate, in terms of an honest scientific assessment as to what the radionuclides actually are in this material, what their half-​​lives are, and how much overall radioactivity they contribute to the radioactivity of the material.

Of course, even if this efficient processing and utilisation of this material, via old-​​fashioned reprocessing or via integrally efficient use in advanced reactors, isn’t happening right now, that’s OK. This used nuclear fuel from existing reactors can simply be stored for a while. Since it’s such a small amount of dense, solid, stable material, it’s easy to store on site where it’s generated, and that’s what’s happening now. Used nuclear fuel which is being stored has never hurt anybody. It’s entirely practical that such fuel continues to be stored on the sites of nuclear power plants where it is being used for the foreseeable future, for years or even decades, and a little bit later, when the desire and political momentum exists to use it more efficiently, then we simply take this large resource of stored energy and interesting materials, and put it to use.

I think I really better keep this post under 3000 words, so I’ll wrap this up. Feel free to leave some comments, tell me what you think, argue politely and intelligently if you like, and tell me if you’d like to see any other aspects of the issue discussed in future.

This entry was posted on Friday, October 2nd, 2009 at 6:00 pm and is filed under Luke Weston, Politics, Science, Skeptic. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.