Sunday, November 16, 2008

Revisiting the thorium-uranium nuclear fuel cycle

From: Revisiting the thorium-uranium nuclear fuel cycle
by Elisabeth Huffer, Hervé Nifenecker, Sylvain David
Europhysics News 38 2 (2007) 24-27

Today’s MOX fuels are comprised of approximately 5% pluto-Thorium-uranium breeder reactors with slow neutrons need only a small uranium 233 inventory, on the order of 1 metric ton. Their theoretical doubling time is similar to that of uranium-plutonium fast neutron breeder reactors. However, fission products are much more efficient in poisoning slow neutron reactors than fast neutron reactors. Thus, to maintain a low doubling time, neutron capture in the fission products and other elements of the structure and coolant have to be minimized. An elegant theoretical solution to this problem was proposed in the 1960’s, namely, a reactor in which the fuel is a molten salt which also ser ves as the coolant. Neutron capture on the fission products would be limited thanks to on-line salt recycling, at the cost of additional complexity since the reactor becomes also a chemistry factory. Giving up the low doubling time objective opens the way to molten salt
reactors with drastically simplified on-line fuel processing or to other reactor types, such as those with in-operation fuel loading/unloading such as heavy water reactors (CANDU) or gas-cooled pebble-bed reactors. A particularly interesting scheme would consist in complementing a thorium-uranium reactor f leet with fast neutron reactors with a uranium- plutonium core surrounded with a thorium blanket that could produce the uranium 233 needed in excess to extend an
existing thorium-based reactor fleet.

It would be unfortunate if orientations were to be decided on the basis of fast decisions made without true scientific and technological debates concerning future reactors and fuel cycles,
using the argument that different orientations would break away too radically from currently accepted procedures. There is no real hurry for the definition of the systems of the future and the
times lend themselves to open and thorough reflection. Granting, however, that pencil and paper designs are not sufficient, small scale prototypes of the more promising reactors will have
to be built within the frame of international collaborations.

It would thus be worthwhile to resume the molten salt reactor program that was started in the 1960s at the Oak Ridge National Laboratory in the US, with the construction of a reactor prototype with a power capacity of a few ten MW.

A Hat Tip to Robert Hargraves and Bill from "Energy from Thorium"

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