A Friend’s Path to Nuclear Power

Here’s a very thoughtful piece, written by the author of A Musing Environment. Certainly an article that is worth reading.

The October 2008 Friends Journal focuses on Energy, Climate, and Building Community, and includes my article, A Friend’s Path to Nuclear Power.

I’m not going to pretend to know much of anything about Quakerism, but of course they certainly care deeply about peace, human welfare and environmental sustainability, like we all do, really. This is a very thoughtful, well researched, well argued and passionate article on one person’s investigation of the importance of nuclear energy in improving human welfare.

The Bomb That Fell On Niagara: The Sphere

Feel like reading something really, really stupid? This seems appropriate.

It’s pretty obvious that if it looks like an ammonia gas tank, quacks like a gas tank, and they say it’s a gas tank, then it’s probably a gas tank.

It certainly doesn’t look like any early prototype of any nuclear reactor design I’ve ever heard of.

Almost 4,000 tons of radioactive radium-226, the largest repository in the western hemisphere, representing a staggering quantity of radiation.

4000 tons of radium!? In 1937, radium cost $25,000 per gram. That’s, uh, 91 trillion dollars, in 1937 US dollars, anyway.

There is also polonium-210 on site. According to Bob Nichols, a San Francisco-based researcher and writer who reviewed the same documents as Weyman, polonium was used as a trigger in nuclear weapons. Its presence in quantities sufficient to detect all these years and half-lives later is not easily explained by the KAPL wastes.

It ought to be obvious where any Po-210 comes from – it’s a daughter product of radium, and it’s present in secular equilibrium where ever there is radium present. In fact, given the quite short 138-day half-life of Po-210, the decay of radium is indeed the only possible source of any Po-210 detectable on the site today.

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

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.

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.

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!

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.

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

We hear a lot about this phrase “renewable energy” these days. But what exactly is “renewable energy”?

Why are certain energy systems considered “renewable”, whilst others are not? What makes, say, solar power “renewable” energy, but nuclear power not, supposedly, “renewable energy”? These questions bear thinking about.

Now, uranium is technically a finite mineral resource, just like the bauxite used to construct wind turbines is a finite resource and the silica used to construct silicon photovoltaic devices is a finite mineral resource from the Earth.

Five billion or so years from now, the hydrogen within the Sun’s interior will be exhausted, and it will begin to use that in its less dense upper layers. It will expand to eighty times its current diameter, about 7.5 billion years from now, to become a red giant, cooled and dulled as a result of its vastly increased surface area. As the Sun expands, it will swallow up the planet Mercury. However, Earth and Venus can be expected to survive, since the Sun will lose about 28 percent of its mass, and its lower gravity will send them into higher orbits. The Earth will be left scorched, its land surface reduced to the consistency of hot clay by a flux of solar heat a thousand times more powerful than that today, and our atmosphere will be stripped away into space by a now-ferocious solar wind. Not one living cell on this planet will remain alive.

Eventually, the helium produced in hydrogen fusion in the Sun’s outer regions will fall back into the core, increasing the density until it reaches the levels needed to fuse helium into carbon. A “helium flash” will then occur; the Sun will shrink abruptly to slightly larger than its original radius, as its energy source has fallen back to its core. Due to the increase in the reaction rates, due to the increased temperature and pressure at the stellar core, and the smaller amount of helium compared to hydrogen, the complete helium-burning stage will last only 100 million years. Eventually it will have to again resort to its reserves in its outer layers, and will again attain a red giant form. This phase lasts a further 100 million years, after which, over the course of a further 100,000 years, the Sun’s outer layers will fall away, ejecting a vast stream of matter into space and forming a planetary nebula.

Eventually, all that will remain of the Sun is a white dwarf, a hot, dim and extraordinarily dense object; half its original mass but only the size of the Earth. Were it viewed from Earth’s surface, it would be a point of light the size of Venus with 100 times its current apparent luminosity. Eventually, after trillions of years, it will fade and die, finally ceasing to shine altogether.

Why is geothermal energy produced by the of uranium in the ground considered as “renewable” when that produced by fissioning those same atoms in a reactor is not?

The answer, of course, is that that’s not the point. The point is that “renewable”, as we hear the term used in society today, doesn’t have any rigorous physical meaning. Loosely, the popular definition of “renewable” means “not fossil fuels and not nuclear energy”, and fossil fuels do not meet the above definition when used at today’s consumption rates (if oil use were cut by a factor of 100,000, it would also be renewable). More correctly, “renewable” energy has come to refer to anything that the Green lobby hasn’t chosen to oppose – anything except fossil fuels or nuclear reactor-derived energy. (Nuclear geothermal energy seems to be OK, though.)

When something does meet the definition that the environmentalist lobby doesn’t like, they amend the mysterious unwritten non-scientific definition to exclude it.

For example, whale oil could produced by farming whales, constituting “renewable biofuel”, in exactly the same way that sugarcane-derived ethanol is in principle a “renewable” fuel. I can’t see the capital-G Green lobby being too keen about the idea, though.

Now, it seems reasonable to argue that, for example, wind energy or solar energy are not in fact consuming any significant finite resources at all during their ongoing operation, the raw materials such as aluminium, silicon or concrete used in the construction of their infrastructure not withstanding.

Opponents of nuclear energy often seem keen to point out that nuclear fuels are what they often describe as “finite, nonrenewable” resources. However, there’s no such thing as a source of energy that we can use without consuming any finite resource, because the energy that we can extract from any isolated system is in itself a finite resource. When the free energy of the universe is expended, the “heat death” of the entire universe is the result. This is the end of all that is, all that was, and all that ever will be, and this is going to happen.

There’s no such thing as “renewable energy”.

The free energy of any isolated system, for any reasonably literal, sensible definition of the word renewable, is not “renewable”.

“Renewable energy” does not exist. That’s the second law of thermodynamics.