America's Nuclear Waste

Nuclear power can be made safer, cleaner, and more sustainable than any other energy technology.
At present, its chief hindrance is the ban upon reprocessing. It is already safer and cleaner than any fossil fuel technology is or even can be. We get 20% of our electrical energy production from reactors that require a mere 25,000 tons of uranium oxide, containing about 21,000 tons of uranium, to be supplied annually. But they only consume about a third of 0.7 percent of that. There is a reactor design that can be refueled using natural or even depleted uranium, and consumes about 4/5 of a ton of it per gigawatt-year. A typical base load generator, coal or nuclear, is rated at about 1000 megawatts, which is of course a gigawatt. But the ARC100 is rated at 100 MW, so ten of them can produce a gigawatt. It is designed to be factory built and thus more flexible than a big reactor. If you want to power a remote island, one of these would be enough, and it needs no refueling for 20 years! The fuel core weighs 20 tonnes, and the reactor vessel is less than 60 ft high and 30 ft diameter. It is designed to be buried in the ground. It is also quite good at load-following, because the feedback from the demand following heat transfer circuit to the power-collecting circuit automatically varies the rate of the fission reaction, which is suitably temperature sensitive.

The fissile isotope, 235U, is 0.7% of natural uranium. To make fuel grade uranium, an energy-expensive process called enrichment concentrates about half of the 235U into about one-eighth of the total uranium, which is then 3.6% fissile. It is false to attribute a carbon cost to the energy thus consumed, because it need not have been generated by coal burning. It should simply be subtracted from the electrical energy produced by the reactors. Depending upon what enrichment process is used, it costs between 0.1% and 4% of the energy which the fuel will produce.

About one-third of the energy produced by thermal-neutron reactors comes from fission of plutonium created by neutron bombardment of the otherwise inert 238U.
Note that when we split a nucleus in two, the mass of the fragments, i.e. the fission products, is just less than the mass of the fuel fissioned. Suppose that the definition of 50% burnup is that the 235U has gone from 3.6% to 1.8%. Then for 100 tons of fuel rod uranium, we now have 1.8 tons of fissile 235U and 239Pu. But the one-third implies that half as much 239Pu as 235U has been produced and fissioned. Presumably 1.8 tons of the original 238U became 239Pu. Half of it is fissioned. Some of the remainder becomes 240Pu. Since "burnup" refers to quantity of fissile material, at 50% burnup there cannot be as much as 1.8 tons of fissile plutonium left. Maybe as much as a ton of plutonium, per hundred tons of spent fuel.

So the fission-product waste from 100 tons of fuel is 2.7 tons of uranium- and plutonium- fission products.
Note that radioactivity is inversely proportional to half-life, and most fission products have half lives measured in seconds, hours, or days.

Per 100 Tons

new rods spent rodsradioactivity per kg.half-life in years
238U 96.4 94.5 negligible, 4.2 billion
235U 3.6 1.8trifling, 700 million
239Pu 0.0 1.0 slight, 25 thousand
fission products 0.0 2.7 intenseup to 30
Total100 100

Total US Civilian Consumption

So if we start with one eighth of 24,000 tons, that's 3,000 tons of fuel rods at 3.6% enrichment, we get
235U consumed 1.8 x 30 54 tons
239Pu consumed 0.9 x 30 27 tons
fission products 2.7 x 3081 tons

There is less than 90 tons of actual unusable waste, chemically very different from the uranium-like remainder, and in principle easily separated.
But the USA treats all 3,000 tons as "waste" and the other part, 21 thousand tons, is left lying about in canisters as the hexafluoride of "depleted" uranium.
So instead of having 81 tons a year of waste that is harmless in a few centuries, and needs only some shielding that is impervious to alpha particles, beta particles, and gamma radiation, we have chosen to burden ourselves with 3,000 tons a year of waste, most of which is less radioactive than what we put in as fuel.

The US government has already developed a technology that could use all three thousand tons! The class of technology is called "fast breeder reactor" and the specific project was the "Integral Fast Reactor" (IFR), canceled in a fit of monumental ignorance in 1994.

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