Global Warming Examiner

COGEMA La Hague nuclear fuel reprocessing plant

Physically, the fuel is made into pellets which are cladded with zirconium. The pellets are put into rods with are inserted into the reactor. Most of the fuel is made up of uranium-238 isotope. This isotope makes up over 99% of the uranium found in nature. It has a half-life of 4.46 billion years. The half-life measures how long it takes uranium to break down through radioactive decay. A half-life of 4.46 billion years means that it takes that long for one-half of the uranium 238 to decay into lead 206. Lead 206 is not radioactive and does not decay. (There are a number of intermediate decay products, but the end result is lead.)

Uranium has such a long half-life and does not emit enough neutrons to sustain a nuclear chain-reaction by itself. To increase the production of neutrons necessary for a chain-reaction, the fuel is enriched by either increasing the percentage of uranium 235 isotope or adding plutonium 239. Natural uranium contains about 0.72% Uranium 235, which has a half-life of 704 million years. Enriching is a process where the natural uranium is processed through a centrifuge (like Iran is building) which removes some of the uranium 238 on each pass, leaving a higher percentage of uranium 235. The uranium is enriched to 3% to 4% uranium 235. If plutonium is added to the fuel, it is called MOX.

The nuclear fuel in the reactor is bombarded with neutrons, which cause the uranium to break down into long-lived transuranic elements like Plutonium, and medium-lived fission byproducts like strontium-90 and caesium-137. Caesium-137 has a half-life of 30.23 years and strontium-90 has a half-life of 28.8 years. For every 1000 lbs of fuel that is put into a reactor, 960 lbs is uranium-238 and 40 lbs is uranium-235. After a fuel cycle in the reactor of 1 to 3 years, the fuel will contain about 940 lbs of uranium-238, 8 pounds of uranium-235, 8 pounds of plutonium and 44 lbs of fission byproducts (mostly strontium-90 and caesium-137).

Reprocessing is the process of breaking the fuel down into its component parts and removing the fission byproducts. The long-lived byproducts can be used as fuel again in the reactor. This material has half-lives measured in the hundred thousand or millions of years. They are not very dangerous because their long half-lives mean they release energy very slowly. The medium-lived byproducts release their energy over a very short time and exposure to their radiation will cause injury. But the high rate of decay means that every 30 years approximately half of the material will decay out of existence.

By reprocessing, 97% of the fuel can be reused. 3% of the fuel is waste, but it only has a half-life of 30 years. This makes this material a candidate for storage instead of burial as in about 200 to 250 years (7 half-lives), all of the medium term waste will have decayed out of existence.

Reprocessing fuel is more expensive than just burying used fuel. This may change as the price of nuclear fuel rises over time. The reason for reprocessing is not economic, but political. People just do not trust the nuclear energy companies or the government to bury radioactive waste. I think there is the image of someone coming into your yard with a shovel, digging a hole, and leaving a nasty buried in your yard. Not their problem anymore. Out of sight, out of mind!

Storage, at least in France, has been a politically acceptable solution. The owner of the waste retains responsibility for it. The separated waste is typically put into steel storage containers and then stored in an underground facility. Storage is fairly simple as the containers give off some heat from the decay process and just need to be left alone for about 250 years. There are a lot of businesses, governments and churches that have been storing things for long periods of time. It is fairly easy to set up a trust fund to pay for the long term management and storage of these fairly small amounts of material.

Reprocessing and storage of waste may be the political answer to allowing nuclear plants to again be constructed in this country. Nuclear energy has the benefits of using locally sourced fuel and not emitting any carbon dioxide. We have the technology now. We are going to have to invest trillions of dollars in a new energy infrastructure in this country. Nuclear energy would be a great place to put some of this investment as it has a high return of energy on invested dollars.