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Neutronic and Safety Aspects of a Gas-Cooled Subcritical Core for Minor Actinide Transmutation

Daniel Westlén, Janne Wallenius

Nuclear Technology / Volume 154 / Number 1 / April 2006 / Pages 41-51

Technical Paper / Thermal Hydraulics /

We have designed a gas-cooled accelerator-driven system dedicated to transmutation of minor actinides. Thanks to the excellent neutron economy of the uranium-free fuel employed, the pin pitch to diameter ratio (P/D) could be increased to 1.8. The increased coolant fraction allows for decay heat removal at ambient pressure. The large coolant fraction further results in a low pressure loss - 26 kPa over the core, 35 kPa in total. Thanks to the large P/D, the elevation of the heat exchanger necessary to remove decay heat by natural circulation is just more than 1 m. The absence of uranium in conjunction with the presence of 35% (heavy atom) americium in the fuel results in a low effective delayed neutron fraction and a vanishing Doppler feedback, making subcritical operation mandatory.

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