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IAEA-TECDOC--1349: Potential of thorium-based fuel cycles to constrain plutonium and to reduce the long-lived waste toxicity

International Atomic Energy Agency, Vienna (Austria)

Abstract

Large stockpiles of civil plutonium have accumulated worldwide from nuclear power programs in different countries. There is a serious public and political concern in the world about misuse of this plutonium and about accidental release of highly radiotoxic material into the environment. It is therefore necessary to safeguard the plutonium under strong security. One alternative for the management of plutonium is to incinerate it in reactors. However, if the reactors are fuelled with plutonium in the form of U-Pu-mixed oxide (MOX), secondgeneration plutonium is produced. A possible solution to this problem is to incinerate plutonium in combination with thorium. The thorium cycle produces 233U that, from a nonproliferation point of view, is preferable to plutonium for two reasons. Firstly, it is contaminated with 232U, which decays to give highly active daughter products. This would make handling and diversion difficult. Secondly, in case this is not sufficient a deterrent, the 233U could be denatured by adding some 238U to the thorium. The quantity of 238U could be fine-tuned so as to be sufficient to denature the 233U, but not so much as to produce a significant quantity of plutonium. The thorium option not only produces electricity, but also replaces the plutonium with denatured 233U, which can be used in other reactors at a later date. All this can be done in existing reactors.

This CRP examined the different fuel cycle options in which plutonium can be recycled with thorium to incinerate plutonium. The potential of the thorium-matrix has been examined through computer simulations. Each participant has chosen his own cycle, and the different cycles are compared through certain predefined parameters (e.g., annual reduction of plutonium stockpiles). The radio-toxicity accumulation and the transmutation potential of thorium-based cycles for current, advanced and innovative nuclear power reactors are investigated. The research program was divided into three stages:

Benchmark calculations,
Optimization of the incineration of plutonium in various reactor types,
Assessment of the resulting impact on the waste radio-toxicity.

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