Minimizing the Integrated Collective Radiation Dose and the Transmutation of Long-lived Nuclear Waste

For more than a year, ECN is engaged in a research programme on transmutation of actinides as well as of fission products by means of respectively fission and neutron capture. It is intended to contribute to international efforts, which evaluate recycling options of the nuclear waste problem. Besides studies on strategy and scenarios, efforts are made to demonstrate possibilities for transmutation of long-lived fission products as Tc-99 and 1-129. Global scenario studies on light water power reactors show that in principle such reactors could consume their own technetium production by means of neutron capture only in case that some surplus of technetium is being situated in the core. If the Tc would be homogeneously mixed through the LWR fuel, the inventory of Tc (a few hundred kg) would be too high to be practical in present scenarios for reprocessing this fuel. For inhomogeneous combinations of waste and fuel, the inventory would have to be even higher, and in general it can be stated that problems with reactor based incineration are complicated whereas only marginal advantages are to be expected. Therefore incineration schedules have been studied, which use an inventory as low as possible, and which would involve a high flux thermal neutron field for example at accelerator based reactor systems. Such hybrid systems are being considered as they may reduce the risk possibly without too high energy cost. Finally an experimental programrne is presented, in which the Petten High Flux Reactor may be used to support comparative studies on targets for incineration. 1. Motivation for a study of transmutation of nuclear waste There are various arguments in favour of nuclear transmutation of waste, each of which deserve examination. Here the discussion will be aimed towards the reduction of human exposure to leakage of waste repositories by removing long-lived components from the waste. This study is motivated by the wish to minimize the time integrated collective radiation dose due to nuclear waste. There is a growing tendency to extend the time interval of integration to infinity and consequently the interest in incineration of very long-lived waste (half lives from 10.000 years up to millions of