Thorium Fuel for Nuclear Energy
An unconventional tactic might one day ease concerns that spent fuel could be used to make a bomb
In light of the potential advantages for reducing the quantity of nuclear waste and preventing the dissemination of bomb-making materials, it is not surprising that interest in thorium-based fuels has recently undergone something of a renaissance. The U.S. Department of Energy has been particularly eager to foster research activities in this area. In addition to funding Radkowsky's company and its partners in their tests with Russian reactors, the DOE has lent support to three other recent efforts. One involves a consortium made up of two national labs (the Idaho National Engineering and Environmental Laboratory, and Argonne National Laboratory), two private companies in the business of fabricating nuclear fuels (Framatome Technologies and Westinghouse) and three universities (the University of Florida, Purdue University and my own institution, the Massachusetts Institute of Technology). The goal has been to come up with a scheme for using thorium in reactors without the added complication of dealing with separate types of fuel arrays (from the seed and blanket units), as is required in Radkowsky's design.
In another program that brought investigators at Brookhaven National Laboratory together with the Center for Advanced Nuclear Energy Systems (CANES) at MIT, the objective is to look at practical ways to simplify the design of the separated seed and blanket units. This could be done by assigning entire fuel assemblies to be either seeds or blankets. Although the terminology of "seeds" and "blankets" has been kept (we name this arrangement the whole-assembly seed-and-blanket core), the metaphor is less applicable in this case, which calls for these assemblies to be arranged, more or less, in a checkerboard array within the core of a reactor.
In a third research thrust, nuclear engineers at Brookhaven and Purdue University examined the use of plutonium-primed thorium as fuel for boiling-water reactors: These designs are distinct from the more common pressurized-water variety, which keep the cooling water under high pressure so that it always remains a liquid. The idea behind this program is that it may provide an economical means to consume surplus weapons plutonium—without producing yet another generation of plutonium waste, as would happen with the leading plan currently being contemplated, something known as the mixed oxide option. In this respect, the Brookhaven-Purdue research on plutonium-seeded thorium fuel is similar to some of the work that Thorium Power and its Russian partners are hoping soon to engage in.
My CANES colleagues and I have devoted considerable effort over the past few years to evaluating the details of various designs, including ways of combining uranium and thorium within individual fuel rods. As might be expected, our conclusions about the technical and economic feasibility vary depending on the particular design under consideration. Here I would like to describe just a few of our results for the seed-and-blanket arrangements, the strategy that in my view has the best chances of commercial success.
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