OFC Meeting 17

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13 Aug 2019: Jess on

ENERGY in the FUTURE

No matter how determined we are to "use it up; wear it out; make it do; do without", if we are going to have a future we are going to need a lot of power (energy per unit time) to solve the problems that must be solved -- like transportation of people and goods, provision of clean water and air, communication and computation. (Alphabet, Google's parent company, used an average of 0.65 billion watts of power in 2015. That's the output of a good-sized nuke.) We need more power, not less. So where are we going to get it? Here (below Philip's comments) are a few possible topics; we certainly won't get to them all.

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Philip: To avoid the worst effects of global heating, the extraction and burning of all fossil fuels must be phased out (unless the CO₂ is captured) over the next few decades starting ASAP. This means for example that all new tar sands development needs to be halted and production steadily cut back - fortunately investors are already acknowledging this. Also on the demand side, vehicles using fossil fuels need to be phased out (perhaps using high taxes) and replaced by battery electric and fuel cell powered vehicles, and buildings upgraded to zero net energy standards. Also of course coal and gas power plants (that do not capture CO₂) must be replaced by renewable or nuclear power. Note that the Canadian government will require all coal power plants that do not capture CO₂ to shut down by 2030.

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NUCLEAR POWER

Fusion

Let's start at the beginning: all the energy we presently have access to comes from gravity and fusion. First gravity drew hydrogen together into stars and compressed it until it began to fuse into deuterium, helium, lithium and so on, up to iron, where fusion stops being exothermic. The older stars eventually burned out and collapsed under gravity until the electrons of atoms were pushed into the nuclei, turning protons into neutrons and electron neutrinos in catastrophic explosions called supernovas, in which the plentiful extra neutrons made even heavier nuclei, including unstable elements like uranium. The clouds of debris drifted around for a while until gravity again caused them to collect into new stars like the Sun and planets like the Earth, where that stored fusion and gravitational energy is still being released in the Earth's core (and, incidentally, in human-made reactors).

Will we eventually be able to "harness" fusion directly to make electric power? Probably, someday; but IMNERHO it will not be a significant improvement over fission. Ask me why if you are interested; I won't use up space here on that issue.

Fission Reactor Designs

American nuclear reactors have been scaled-up versions of Admiral Hyman G. Rickover's design for the US Navy's submarines since 1955. The fission of U-235 or Pu-239 releases energy as (mainly) fast neutrons, which slow down by scattering in the pressurized water surrounding the reactor core and thereby deposit their energy as heat (disordered energy) in the water, which boils to make steam, which runs turbines to make electricity. Most of the energy produced is lost as waste heat. This basic process (fission --> neutrons --> heat --> heat engine --> electricity) is common to all nuclear power plants; the last 3 steps are the same in fossil-fuel-burning power plants, as is the waste of most of the heat.

In recent decades there have been many new reactor designs developed and tested, including thorium reactors (thorium has the pleasant features of being lavishly abundant and unusable for bombs), liquid salt reactors (where the heat is absorbed and the neutrons moderated by liquid salt that must be continuously pumped up from a reservoir in the basement; if the system fails, the moderation and the chain reaction stop) and "pebble bed" reactors, in which the fissionable "fuel" is in small "pebbles" rather than fuel "rods", making cooling simpler and allowing smaller local reactors, perhaps one per small town or neighbourhood. I am fond of a design which uses "extra" neutrons from a spallation source to keep an otherwise subcritical reaction going, because it incorporates a big accelerator that would also make lots of muons!   :-)

Safety

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