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Archive for the ‘nuclear energy’ Category

Thermodynamics, stars, uranium, life and everything: Part II

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The amount of time necessary to exhaust nuclear energy provided by existing uranium deposits, unused energy in current reserves of used radioactive “waste”, heat produced by the radioactive decay of uranium, thorium and potassium deep inside the Earth (in other words, geothermal energy), and uranium in seawater could indeed last billions of years – approaching the evolution of the sun off the main sequence, and with that, the end of life on this world.

If the energy from the Sun is “renewable”, so too is nuclear energy equally every bit as renewable.

The concentration of uranium in seawater in the world ocean is about 3.3 parts per billion. The total mass of Earth’s hydrosphere is about 1.4×1021 kilograms, therefore putting the total mass of uranium in the world ocean at 4.62 billion tonnes.

Current total world demand for electricity stands at 16,330 TWh per year. Let’s conservatively suppose that, over the millennia to come, the average total world demand for electricity is four times what it is at present, or 65,320 TWh. Conventional LEU fueled light-water reactors and inefficient once-through fuel use in these reactors consume about 200 tonnes of uranium mined per gigawatt-year of electric power generation.

Hence, if we make the assumption that all the nuclear energy generation over these coming millenia is performed with this inefficient once-though LEU fuel chain and no recycling or reprocessing of nuclear fuels is performed, then the world demand for uranium can be expected to be 1.49 million tonnes per year.

Hence, consuming 1.49 million tonnes of uranium per year to supply all the world’s electricity, the 4.62 billion tonnes of uranium presently dissolved in the ocean will supply the world’s electricity for 3100 years.

\mathrm{\frac{4.62 \times 10^{9}\ tonnes}{(200\ tonnes\ per\ GW\cdot year) \cdot (65320\ TWh/year)}\ =\ 3100\ years}

Here we have assumed that no use is made of efficient, advanced reactors or breeder reactors and no use is made of the excess “depleted” uranium-238 or natural thorium, no deuterium is used for nuclear fusion, and no uranium is mined on land. Such assumptions are of course ridiculous, but let’s just be as conservative as possible, for argument’s sake for the purposes of this baseline, worst-case scenario.

If we considered a truly efficient efficient use of nuclear fuel, we may consider an efficient, advanced reactor such as a molten-salt reactor, efficiently transmuting uranium-238 into plutonium-239 in situ to generate energy. We may assume that 200 MeV of energy is released per fission event, and that the efficiency of the 238U transmutation and liberation of useful energy output from these nuclear processes within the reactor is, say, 75% overall. If we assume that this thermal energy is converted in a Brayton-cycle power plant with a thermodynamic efficiency of 50%, then hence we know the amount of natural uranium required to fuel the reactor.

\mathrm{\frac{1\ GW\ \cdot\ 1\ year\ \cdot\ 238\ u\ \cdot\ 1.66 \times 10^{-24}\ grams/u}{200\ MeV\ \cdot\ 75\% \cdot\ 50\%}\ =\ 1.04\ tonnes}

Just over one tonne of natural uranium is required, to generate one gigawatt-year of energy. (That number is basically the same if we’re looking at efficiently burning thorium in a MSR, incidentally, also.) If we utilised nuclear energy efficiently, like this, then the 4.62 billion tonnes of uranium presently dissolved in the ocean would supply the energy we discussed above, 65,320 TWh, for (just under) an astonishing 600,000 years!

\mathrm{\frac{4.62 \times 10^{9}\ tonnes}{(1.038\ tonnes\ per\ GW\cdot year) \cdot (65320\ TWh/year)}\ =\ 597,558\ years}

However, we are not finished yet. Elution of the uranium in the Earth’s crust into the ocean occurs on an ongoing basis, adding 3.24×104 tonnes of uranium to the ocean annually.

It was motivated by Cohen* that we could recover uranium from seawater at perhaps half of that rate; 16,000 tonnes of uranium from seawater per year. This quantity of uranium would supply 15.4 TW of electric power, if used efficiently as outlined above. In order to supply 65,320 TWh of electricity per year, four times the current worldwide demand for electricity, we only require 7750 tonnes of uranium per year, less than half that figure of 16,000 tonnes.

[* Many of you will be familiar with Cohen’s work, but if you are not, that book is highly recommended.]

Cohen argues that given the geophysical cycles of erosion, subduction and uplift, the uranium elution into the oceans would last for five billion years, at a rate of withdrawal of 6500 tonnes per year. At a rate of consumption of 7750 tonnes per year, in the absence of the use of any uranium and thorium mined on the crust, or the use of deuterium for nuclear fusion, the uranium from the oceans alone can be expected to meet world demand for electricity, at 65,320 TWh of electricity per year, for 4.2 billion years. Over a timeframe on the order of 109 years, of course, some non-trivial fraction will be lost, simply due to radioactive decay – however, at the same time, we have not even begun to consider the use of uranium and thorium reserves in the crust, or the use of the vast supply of deuterium as an energy source.

Clearly nuclear energy remains a viable resource on the Earth for a time scale of approximately five billion years – these nuclear fuels will not be consumed or depleted over a timeframe comparable to the life of the sun on the main sequence. Just as the finite hydrogen within the core of the Sun is a “renewable” energy resource, so too is the finite resource of terrestrial nuclear energy an equally renewable energy resource.

However, there is one final point we have overlooked. Even during its life in the main sequence, the Sun is evolving, as with all such stars. The Sun is gradually increasing in luminosity, by about 10% every one billion years, and its surface temperature is correspondingly slowly rising. This increase in the luminosity of the sun is such that in about one billion years, the surface temperature of the Earth will permanently have become too high for liquid water to exist, the oceans will evaporate and a catastrophe of the most immense proportions imaginable will overtake our planet. The Aztecs foretold a time `when the Earth has become tired… when the seed of Earth has ended’. All life on Earth will be extinguished, billions of years before all the nuclear fuels will be depleted.

In the meantime, our descendants will have evolved into something quite different, as far divergent from us in evolutionary terms as we are from the simplest one-celled organisms to have existed on the Earth. If they still inhabit the Earth, our descendants will leave, perhaps to Mars, or to the moons of the gas giants, Europa, perhaps, rich in water and perhaps not dissimilar to Earth if warmed up a little, or perhaps to a younger, more distant world, orbiting a younger star, around which their civilization will flourish once more.

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Written by Luke Weston

October 12, 2008 at 1:12 pm

Green Heretic: environmentalist Mark Lynas investigates nuclear energy.

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“Card carrying” UK Green and climate change expert Mark Lynas has been scorned by eco-colleagues for that greatest of big-G Green heresies: Daring to investigate and discuss nuclear energy, in any rational fact-motivated way.

“Except, well, I don’t believe that any more. Just a month ago I had a Damascene conversion: the Green case against nuclear power is based largely on myth and dogma.”

This investigation of what Lynas has learned, how he’s thought about it, how his views have changed, and how people have responded to him for it, is very much worth reading.

I was going to back up Lynas’ positions by posting this on the discussion thread on his website – but it’s a bit long and I don’t think they will post it, so I’ll post the following here instead.

I will cite or respond to a number of previous comment posts, in chronological order as you read down through the thread:

Read the rest of this entry »

Written by Luke Weston

October 3, 2008 at 12:55 am

Nuclear fuel recycling in the United States

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Earlier this month an editorial was posted on GreenvilleOnline.com titled Nuclear reprocessing is risky and impractical, laying out the case against recycling of nuclear fuels (or at least the case against conventional methods for recycling of conventional nuclear fuels). (Thanks to Atomic Insights for the story tip.)

The editorial states:

Nuclear reprocessing separates plutonium from radioactive waste so that it can be reused to generate additional energy. However, reprocessing also has an unfortunate side effect: It dramatically increases the volume of radioactive waste.

Of course, if the alternative to nuclear fuel recycling is to take all the used fuel and label it as supposed “waste” material, and of course that is the alternative, then it’s a universally accepted fact that of course recycling of the nuclear fuel reduces the volume of material that is considered “waste”.

Typical used fuel from a typical LWR with a LEU fuel consists of approximately 96% uranium-238 and 235, which is completely unchanged in the reactor from the original fuel, about 3% of fission product nuclides, about 1% of plutonium, about half of which is plutonium-239 and half of which is comprised of other plutonium nuclides, and small trace quantities of other actinides, including a little U-236, U-232, Np-237, Am-241 and what have you.

Even if nuclear reprocessing involves only taking the uranium from that nuclear fuel, then immediately, with uranium separation alone, you’ve removed 96% of the mass of the radioactive “waste” that you need to deal with – and that’s without any consideration of the valuable, useful materials which constitute the other four percent.

If “nuclear waste” is such a terrible concern, the the first thing that should be done is to make sure we’re not wasting it.

The separation of plutonium is not necessary in any way for the use of nuclear energy, nor is it required at any point for the efficient recycling of used uranium fuels. The separation of plutonium, contrary to popular belief, is not the point of nuclear recycling. Separation of plutonium is an integral part of nuclear weapon building, and it is certain technologies which were developed for this latter purpose which have, historically, been applied to the recycling of power reactors fuels.

To construct a nuclear fission weapon from plutonium does indeed require the chemical separation of pure plutonium from uranium irradiated within a nuclear reactor – but that’s the only thing that requires separation of plutonium. This is why separation of plutonium, or the possibility of it, seems to be viewed with distrust and suspicion, especially at the Savannah River Site, perhaps, given its historical mission of the production of weaponisable plutonium via nuclear reactors and PUREX extraction.

Even if you want to use plutonium from used civilian reactor fuel efficiently, and recycle it back into the recycled nuclear fuel, where it serves as a potent, valuable energy source, chemical separation of plutonium is not needed. Even though most established, mature efforts for the recycling of nuclear fuels at the industrial scale involve the PUREX process, which was designed and established specifically to support the production of separated plutonium for nuclear weapons, there is no reason why this process is essential at all. It’s quite straightforward to modify the chemistry of the solvent extraction process so that the plutonium is kept combined with the other actinides, so that this material can be recycled into new nuclear fuel without any material being produced that presents any proliferation risk. That is what is done with the COEX or DIAMEX chemical processes, and what can be done even better via pyroprocessing or in-situ separation of nuclear poisons in a molten salt reactor.

Even if the potential for diversion and weaponisable plutonium was considered so grave that we were insistent of taking the plutonium and disposing of it in some kind of deep geological repository, this would only constitute 1% of the fuel – so, we wouldn’t be losing much of the fuel, really. However, plutonium-239 is a moderately long lived nuclide – with a half-life of 24,400 years, it doesn’t just go away overnight if put in a geological repository. So, in decades to come, the material could still be removed, and weaponised.

The only proper way to get rid of plutonium, if you’re really concerned about nuclear weapons proliferation, is to fission it in a nuclear reactor – and, lo and behold, you get plenty of clean, safe energy to boot, at the same time.

According to the Union of Concerned Scientists, “After reprocessing … the total volume of nuclear waste will have been increased by a factor of twenty or more ….”

Of course, that’s simply absurd. What sort of definition of reprocessing are they using? What evidence is provided for such a claim?

For instance, discharges of iodine-129, a very long-lived carcinogen, have contaminated the shores of Denmark and Norway at levels 1,000 times higher than nuclear weapons fallout.

Well, does that tell us anything? What is the background dose rate to the public as a result of the nuclear weapons fallout, and what is the contribution added to the dose rate to the public as a result of nuclear fuel reprocessing?

Health studies indicate that significant excess childhood cancers have occurred near French and English reprocessing plants.

Is there any peer-reviewed, scientifically motivated, literature which demonstrates the existence of such excess childhood cancers, and demonstrates, or even reasonably motivates, a causal connection between the two?

In 2003, for example, researchers from Harvard’s Kennedy School of Government said that reprocessing costs more than twice as much as safe, on-site interim storage of nuclear waste.

The report cited, from the Belfer Center for Science & International Affairs at Harvard University, The Economics of Reprocessing vs. Direct Disposal of Spent Nuclear Fuel, states:

At a uranium price of $40/kgU (comparable to current prices), reprocessing and recycling at a reprocessing price of $1000/kgHM would increase the cost of nuclear electricity by 1.3 mills/kWh. Since the total back-end cost for the direct disposal is in the range of 1.5 mills/kgWh, this represents more than an 80% increase in the costs attributable to spent fuel management (after taking account of appropriate credits or charges for recovered plutonium and uranium from reprocessing).

Furthermore, the editorial’s authors continue with much the same assertion:

In 2007, the National Academies of Science (NAS) noted that no reprocessing technology currently on the table “is at a stage of reliability and understanding that would justify commercial-scale construction” and the report therefore concluded “there is no economic justification for going forward with this program at anything approaching a commercial scale.”

The nuclear industry has reached a similar conclusion. A 2007 report by the Keystone Center, underwritten by various utility companies, said “reprocessing of spent fuel will not be cost-effective in the foreseeable future.”

The “reprocessing is not economically competitive” argument basically boils down to the idea that recycling the used fuel is more expensive than the inefficient, once-through use of newly mined uranium.

People are frequently concerned about the environmental intensiveness of uranium mining and the handling of radioactive wastes from nuclear power – and yet recycling and efficient re-use of nuclear fuels minimise the requirement for both of these things. To me, the argument against recycling because recycling costs more is ridiculous, and it’s essentially equivalent to eschewing the use of alternative energy systems in favor of more coal, because coal is cheaper.

Written by Luke Weston

September 16, 2008 at 11:49 am

ScienceDebate 2008: Presidential candidate’s answers to the science questions facing America

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http://www.sciencedebate2008.com/www/index.php?id=40

The presidential candidates provide their responses to the most important science questions facing the United States.

Unfortunately, they have not yet posted Senator McCain’s responses yet, hopefully they do so at some point in the near future. So, at the moment, all they’re really presenting are Obama’s responses to the questions. It still makes for interesting reading, though.

Interestingly, although not specifically asked about nuclear energy at all, Obama specifically mentions “A new generation of nuclear electric technologies” as one of his policy goals. Such bipartisan support, even to a slight degree, is a promising sign.

Written by Luke Weston

September 5, 2008 at 9:07 am

“Nuclear Power Will Kill the Coal Industry”

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Many reader’s will be familiar with Australia’s Construction, Forestry, Mining and Energy Union (CFMEU) and their now-slightly-infamous “nuclear energy threatens coal jobs!” position.

But could nuclear power really “kill the coal industry” in Australia? I don’t think so.

Total production of raw black coal in Australia in 2006 was 405 Mt (million tonnes). This production represented a small increase of 1.6% over the 2005 figure of 399 Mt. After processing, a total of 317 Mt of metallurgical and thermal black coal were available for both domestic use and export in 2006.
(I’ve taken these statistics from the Australian Coal Association website.)

In 2006, Australia’s domestic consumption of black coal for electricity generation amounted to 62.4 million tonnes of black coal. Hence, domestic electricity generators consume only about 20% of Australia’s output of processed black coal. Other domestic industrial uses of coal, such as steel production, account for about three percent, with the entire remaining 77% being exported.

(The ACA’s statistics refer exclusively to black coal – however, brown coal is a much smaller resource, relatively, and since we have the statistics for black coal, I’ll limit the discussion to black coal.)

Hence, under the worst case scenario (or best case scenario), we may envisage a future in which every coal-fired generator in Australia is closed down and replaced by nuclear power plants. This would result in cutting Australia’s greenhouse gas emissions in half – at the cost of a 20% reduction in coal demand. If we were to see half of Australia’s coal fired plants closed down and replaced by nuclear energy, we will see a 10% reduction in coal revenue.

I don’t think a 10% to 20% downturn in revenue constitutes “killing the coal industry” – and I really don’t think that the coal industry has anything to worry about for the foreseeable future.

Written by Luke Weston

August 31, 2008 at 8:48 am

Embarrassingly predictable?

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Here’s a powerpoint presentation from an excellent presentation given by Kirk Sorensen about the use of thorium as a nuclear energy resource.

Of course, the Powerpoint slides themselves are not as good as the whole presentation, and in and of themselves they can be a little hard to follow, without the presenter, but unfortunately you have to deal with that with any presentation where you’ve only had a chance to pick up the slides after the fact.

This presentation was prepared over a year ago – but I was only reading it last week. As for the title of this post – there was something, on a related note, that I found a little amusing.

Check out the 6th slide, in Kirk Sorensen’s presentation, and compare it to the oh-so-factual and educational graphics used in Joseph Romm’s recent post on GristMill. Isn’t it uncanny – just when you thought that nobody trying to construct a coherent (?) argument of some kind against the use of nuclear energy could actually be that silly.

Joe Romm has got another post up recently that’s worth looking at as well, in which he attempts to reinforce the notion that the linear-non-threshold hypothesis is somehow factually motivated, and that every little contribution to low doses of ionising radiation is dangerous. I’m sure some readers will be interested in going and leaving a comment in response to that.

Still, Romm deserves some credit for correctly pointing out that on the grounds of ionising radiation dose, as well as numerous other ecological and health impacts, coal-fired electricity generators are far more dangerous than nuclear power plants.

Also, in one final note, congratulations to Rod Adams on the momumental 100th episode of The Atomic Show podcast. That’s a monumental effort, producing 100 episodes of interesting, unique high-quality podcasting, interviews and commentary, and I look forward to the next 100 episodes to come.

Australian support for consideration of nuclear energy continues to grow.

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Paul Howes, national secretary of the Australian Workers’ Union, is continuing to advocate taking a reasonable look at the role of nuclear energy as a means to achieve anthropogenic GHG emissions reductions. As you might expect from Australia’s largest trade union, their chief area of concern is the mitigation of GHG emissions, and the introduction of GHG emissions trading, without damage to Australian industries and industrial employment.

THE Rudd Government is being urged to embrace nuclear power as a source of clean energy, amid warnings its emissions trading scheme could result in desolating Australian mineral and metallurgy industries.

Just days before the Government releases a discussion paper on carbon trading, a new report shows Australia’s aluminium industry – employing 35,000 people – could be devastated.

Challenging Professor Ross Garnaut’s preferred model, the Australian Workers’ Union wants the key metals sector to receive a partial reprieve from carbon trading.

The union has a powerful ally: respected business figure and Commonwealth Bank chairman John Schubert.

Mr Schubert, who also chairs the Great Barrier Reef Foundation, says Canberra should “definitely look at” nuclear power.

It needs to be a real option… should absolutely be on the table“, Mr Schubert said.

Howes has just released a report from Per Capita consulting on the effects of the emissions trading scheme on Australian industry – specifically the aluminium industry, in this case.

It says the future for the aluminium industry is grim if the Government gets the design of an ETS wrong.

Union and business leaders fear an ETS will cause job losses and send investment offshore, with the aluminium industry particularly vulnerable.

The Per Capita report says jobs could be lost to Brazil, China and India if Canberra imposes tough new laws.

The study recommends the Government give the aluminium industry a “partial exemption” from carbon trading for up to five years and embrace nuclear power.

Mr Howes said the report would bring a “bit of level-headedness” to the debate over emissions trading and climate change.

Mr Howes said he was sick of hearing claims that workers in “heavy-polluting” industries, such as steel and aluminium, could be re-trained in “green” industries.

Instead, workers could be “left on the scrapheap of history” and enter the ranks of the long-term unemployed, Howes claims.

Personally, I don’t agree with the popular conception that aluminium production is an especially highly GHG emissions intensive industry.

Direct GHG emissions intensity for aluminium production in Australia was 2.0 tonnes CO2-e per tonne of aluminium production in 2007 — down from 2.1 in 2006 and 5.0 in 1990 — an improvement over the 1990 level of 60 per cent.

Indirect GHG emissions intensity from electricity consumption for aluminium production remained at the same level as 2006 at 14.1 tonnes CO2-e per tonne of aluminium production — down from 16.1 in 1990 — an improvement of 12%. This reflects both energy efficiency and changes in greenhouse grid factors.

Australian aluminium production in 2007 (i.e. aluminium smelting, not alumina production) contributed 31.6 mt (million tonnes) of GHG emissions (CO2-e), comprising 3.95 mt CO2-e of direct PFC emissions, direct carbon dioxide process emissions and other site-level emissions, and 27.69 mt CO2-e of indirect emissions from electricity consumption.

The Australian aluminium smelting industry consumed 29,500 GWh of electricity in 2007, corresponding to an average GHG emissions intensity of 939 g/kWhe for the electricity consumed by Australia’s aluminium smelters – consistent with Australia’s extremely GHG intensive, overwhelmingly coal based electricity generation capacity.

[These statistics are taken from the Australian Aluminium Council’s 2007 Sustainability Report.]

Indirect GHG emissions from fossil fuel electricity generation – which aren’t really emissions from the aluminium production industry at all – hence comprise 88 percent of the GHG emissions intensity ascribed to the aluminium smelting industry.

If the overall GHG emissions intensity of the electricity supply of 939 g/kWhe was cut to, say, 100 g/kWhe through the replacement of coal fired generators with nuclear energy, geothermal, solar thermal, hydroelectricity or what have you, then the greenhouse gas emissions of aluminium production in Australia can be cut from 31.6 mt to 6.9 mt – 3.52 tonnes CO2-e per tonne Al, compared with 16.1 tonnes CO2-e per tonne Al at present – a 78% reduction in greenhouse gas emissions intensity, and that’s on top of any further improvement in energy efficiency and/or process efficiency, PFC emissions reduction and so forth, in the industry.

Aluminium smelters are not at all the cause for concern here. The burning of coal and fossil fuel for essentially all the country’s electricity generation is by far the foremost concern that we need to address.

The AWU’s press release, and the 32 page analysis commissioned by the AWU from Per Capita, are available here.

Also, in Canberra today, economist Professor Jeffrey Sachs warns that the world must embrace nuclear power as one of its options if it is going to win the fight against the potentially catastrophic damage of anthropogenic greenhouse effect forcing.

Professor Sachs, director of the Earth Institute at Columbia University and author of the book The End of Poverty, warned that global warming had the potential to undo the progress being made in the war on global poverty, making the tropics hotter and arid regions even more arid.

In Canberra to give a keynote speech today at the Australian National University’s annual China Update, he said the world would need to use every available technology – and develop some more – to reduce anthropogenic greenhouse forcing at the same time as rapidly expanding its output.

Professor Sachs, who has not supported nuclear power in the past, said better technology was the key to breaking the link between economic growth and carbon dioxide emissions, and the world could not afford to do without either nuclear power or cleaner coal.

“I support the reintroduction of nuclear power”, he said. “It’s hard to see how we’re going to get enough energy with low carbon emissions without nuclear playing a significant role.

If Australia chooses not to go that way, it’s going to have to go even more aggressively towards solar energy and carbon capture and storage. My own feeling is that nuclear is safe and cost-effective.

Professor Sachs, 52, played a key role in drawing up the Millennium Development Goals that are the targets for reducing global poverty.

Yesterday he said climate change was one cause of the steep rise in world food prices, which is making food unaffordable in some poorer areas.

If the world can not afford to do without either nuclear power or “cleaner coal”, and nuclear power is already a developed, mature, proven technology across the world, and “cleaner coal” is far from it, then it’s not much of a contest, is it?

Written by Luke Weston

July 14, 2008 at 5:12 pm