Plutonium is fuel and "seed corn", not waste

A number of years ago, I had the opportunity to spend tens of hours each week in the library. It may seem a little weird, but I decided to spent a few of those weeks in an intensive effort to learn a little more about the nuclear non-proliferation “community”.

I just spent some time going back through my notebooks from that era in my life – unfortunately I could not find the specific references I was looking for. Where was Google in 1992-93? Of course, to be of use, it would have to be able to index my chicken scratch.

Instead, I am going to have to work from memory and simply describe some of the things I found out during that research. One thing that became abundantly clear to me is that a major cannon of the nuclear non proliferation catechism is that the world must never be allowed to think of plutonium as a valuable fuel source. In their belief system, allowing plutonium to become an accepted material for commerce is a fatal step toward nuclear annihilation of the earth.

In order to enforce this belief on the rest of us, the nuclear non proliferation community fights very hard to portray plutonium as a dangerous waste material that must be expensively stored and guarded until methods can be developed for its permanent disposal.

I am under a different set of guidelines. The factual nature of the world is that there is an inventory of plutonium 239 that is a legacy of nuclear weapons programs. Between the United States and Russia, that inventory is in excess of 100 tons – some sources indicate that the excess is significant. Another part of my understanding of the world is that each gram of that plutonium can be fissioned to release heat – the general rule of thumb is that a gram of plutonium releases a megawatt-day of heat energy.

If that heat energy is converted to electricity in a moderately efficient engine, it would produce enough electricity to supply approximately 3,000 homes all the power that they need for a full day. It could also be used in a propulsion engine – it would supply enough energy for a 400 horsepower machine to run for a day.

I live in Annapolis and often see 30-35 foot pleasure boats with two large, 200 HP outboard motors dashing around the Chesapeake Bay. Of course, in the past few years, the overall quantity of dashing has been greatly reduced; those boats consume dozens of gallons of fuel per hour at high speed.

According to some bulletin board chatter that I found here, you can use a rule of thumb of 1/10 gallon per hour per HP. Let’s see how that compares with some of my other thumb rules. If the rule is 1/10th of a gallon per hour per HP, 400 HP consumes 40 gallons per hour or 960 gallons per day. (Of course, we are talking about an open throttle here where the engines produce their full rated power continuously.) At about 75 F, gasoline weighs about 6.2 pounds per gallon, so 960 gallons is almost 6000 pounds. Converting pounds to grams, multiply that 6000 times 454 and you get 2,700,000 grams of gasoline.

That compares pretty well to my normal rule of thumb that plutonium or uranium fission releases 2 million times more energy than the same weight of oil. Gasoline is less energy dense than oil and there is some rounding inherent in all rules of thumb. Anyway, my point, in case you have forgotten, is that 100 Tons of plutonium contains a whole bunch of energy. It is comparable to 270,000,000 tons of gasoline. At about 8 barrels per ton, that is 2.2 billion barrels. At 43 gallons per barrel, that is 93 billion gallons of gasoline worth about $190 billion at wholesale (using $2.03 from bloomberg.com energy prices as of August 4, 2007.)

Now I happen to work for an organization (the US government) with a pretty large overall budget, but if you slice off just the service I work for (USN), $190 billion would pay all of our bills for a full year with a pretty good down payment left for the next year. In other words, considering 100 tons of plutonium as a waste product that needs to be isolated and buried permanently seems to be pretty wasteful to me.

That is even more true when you consider the fact that it is not outside of the realm of known technology to arrange to fission plutonium in such a way as to convert at least two different isotopes that are normally considered to be kind of useless from an energy perspective into something that also fissions readily. Also maintained in inventory in the US and Russia are enormous stocks (tens of thousands of tons) of one of those isotopes – U-238 – also known as depleted uranium.

This is the “seed corn” aspect of plutonium. If a reactor is designed correctly, it can convert fertile isotopes like U-238 and Th-232 into fissile isotopes like Pu-239 and U-233. In other words, as it operates and consumes fuel to produce valuable electricity or motive power, it can be building fuel out of what are often considered waste products – excess neutrons and fertile isotopes. This can yield nuclear reactors that operate for a very long time without the need for new fuel to be added; all of the conversion can take place inside the original core boundaries.

I like to think of it like a well built, overnight fire. You stoke it with sufficient small stuff to get the fire going, but you also have to put in some large, slow-burning logs that will sustain the fire while you are sleeping.

This concept is not original; it was demonstrated in one of many possible configurations in the last core of the Shippingport reactor, which used U-233 as the seed corn and Th-232 as the fertile material. The core operated for five years and could have gone a lot longer, but the experiment was halted in order to allow the results to be analyzed. According to the abstract of a paper produced in 1987 titled Proof of self-sustaining breeding in the light water breeder reactor the core had more fissile material in it after five years of operation than it did when it started.

The impetus for writing this rather meandering post – other than the fact that I am beginning to occasionally adopt the posting style of a friend named NNadir – was an article by Matthew Wald published by the International Herald Tribune on August 3, 2007 titled US. starting plant work to convert plutonium.

Instead of celebrating the fact that we are finally beginning to take action to stop wasting money just guarding plutonium that has been removed from decommissioned bombs, the non proliferation priesthood is back to its old tricks. Here is a quote from the article:

Ultimately, the plant, as well as the plants that Moscow wants to build, could help pave the way for more use of plutonium in civil commerce. The Russians, who see the plutonium as an asset, want to use it in a new reactor that could be set up to consume plutonium faster than it creates it or that could be set up to “breed,” making more material than it consumes.

As a result, some private weapons-control specialists have soured on the project. “There is not a lot of reduction in national security risk associated with this program,” said Thomas Cochran, a weapons expert at the Natural Resources Defense Council. “The U.S. might just as well store the stuff.”

What do you think? Should we just store the stuff or should we use it to produce valuable energy, reduce the stockpiles of weapons useable material, and produce additional fuel material? Is plutonium waste or is it something that should be introduced into commerce – using due care and protection, of course.