Advantages and limitations of thorium fuelled energy amplifiers

The recently proposed energy amplifier rector concept, based on the use of an accelerator driven sub-critical assembly with thorium as the breeding fuel, offers potentially significant advantages over conventional reactors in the nuclear fuel cycle. The main advantages stated are, in addition to providing a reactor which is essentially sub-critical, that much less transuranic actinide waste is generated and the risk of nuclear proliferation is substantially reduced. In this paper, we analyse the proliferation and radiotoxicity problems associated with the various energy amplifiers using 232Th and 238U as breeding fuels. It is shown that there are major advantages to be obtained in radiotoxicity using 232Th especially if the bred 233U and additional uranium isotopes are recycled. In addition, the fuel can be rendered proliferation resistant through mixing with the isotopic denaturant 238U. This is in contrast to uranium fuelled reactors where there is no natural denaturant for plutonium isotopes. It is also shown, however, that through the use of this isotopic denaturant for proliferation resistance of thorium fuel, a new source of radiotoxicity arises. The proliferation and radiotoxicity problems are now coupled together and this leads to limitation in the overall advantages to be gained. This is the proliferation/toxicity dilemma of a thorium cycle. Nevertheless, depending on which aspects have priority i.e. proliferation resistance, radiotoxicity of the spent fuel, or combined proliferation - radiotoxicity, a thorium fuelled energy amplifier can have clear advantages over conventional reactors in the nuclear fuel cycle. (author). 11 refs, 11 figs, 4 tabs