Plutonium Utilization in Boiling-Water Power Reactors

The status of plutonium utilization in boiling-water reactors is described in this paper, with emphasis on evaluations of alternate fuel designs and fabrication concepts. The boiling-water reactor offers unique opportunities for taking advantage of the characteristics of plutonium in a predominantly thermal spectrum and it is concluded that plutonium can be effectively utilized as a fuel in thermal power reactors prior to the build-up of a large-scale fast reactor demand. Nuclear characteristics of plutonium with isotopic compositions typical of water-moderated power reactors can influence design decisions regarding its utilization in a BWR. For example, the resonance capture in 240Pu tends to reduce the rate of reactivity loss, increase the negative void coefficient, and reduce the excess reactivity in the core. The increase in the capture to fission ratio in plutonium-239 in the neighbourhood of the 0.3 eV resonance favours designs with some self-shielding of this resonance as well as a 'colder' incident thermal neutron spectrum. A number of alternate techniques have been employed for both the preparation and final fabrication of PuO2-UO2, fuels. Both dry powder and aqueous processing routes can be used to obtain the basic mixed oxide. Finally, either pellets or compacted powder can be considered for the fabrication form. Economically, a compacted powder in which the PuO2 is added at a late stage in the process has decided advantages. Considerable experience has been gained in the fabrication and irradiation of this type of fuel at Hanford (BNW), In present studies, however, a pelletized fuel is favoured in which greater homogeneity of the plutonium and uranium can be ensured with current starting materials and uncertainties in the response to rapid accidental excursions can be reduced. The additional cost of fabricating the plutonium relative to uranium fuel does not appear to be excessive for any of the fabrication concepts. It is concluded that several feasible alternates exist for both the design and fabrication of plutonium fuel for utilization in boiling-water reactors. Greater experience is needed in designing, fabricating and irradiating fuel in operating power reactors before establishing large-volume plutonium utilization. Experience gained and capabilities developed in the utilization of plutonium in thermal reactors should be valuable in the eventual utilization of plutonium in fast reactors. (author)