Converting HIFAR to low enriched uranium fuel
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Date
2007-11-07
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International Atomic Energy Agency
Abstract
The Australian Nuclear Science and Technology Organisation (ANSTO) began operating the High Flux Australian Reactor (HIFAR) in 1958, a DIDO-class research reactor operated at a thermal power of 10 MW. On 30th January 2007, after more than 49 years of successful and safe operation HIFAR was finally shutdown. Since that time all the fuel has been successfully removed from the reactor containment building. HIFAR was primarily used for neutron scattering science, service irradiations and isotope production. Over the nearly 50-year operating life of HIFAR a variety of fuel designs have been used. After the 1970s fuel enrichment was reduced in stages from over 90 percent to 19.75% in 2006. The reactor core consisted of 25 fuel elements with uranium-aluminium alloy fuel sections, arranged in concentric tubes. HIFAR was moderated and cooled by heavy water, and the coolant contained within an aluminium tank, which in turn was surrounded by a graphite reflector and concrete biological shielding. Reactor control and shutdown were achieved with six europium tipped cadmium control blades, which moved as a bank between the rows of fuel elements. Two cadmium shutdown rods provided additional shutdown capacity. In May 2006 the HIFAR reactor was fully converted to Low Enriched Uranium fuel. The conversion commenced in October 2004. The LEU fuel was procured from Risoe National Laboratory in Denmark, was originally made for use in the DR3 reactor, and was modified to be compatible with HIFAR. This type of fuel was used safely in DR3 before its closure. A safety analysis report for the approval and use of the LEU fuel which was prepared well in advance of loading the fuel into HIFAR, provided detailed analyses of issues important to reactor and general fuel safety, including, criticality safety outside the reactor, reactor physics, eversafe times, thermal hydraulics and accident analyses. Many of the issues studied for LEU fuel reanalysed operational and accident conditions that had been previously analysed for HEU fuel. In most cases the conclusions provided in each analysis demonstrated there was little difference in behaviour between HEU fuel and LEU fuel in HIFAR under operational and accident conditions. However, there was one significant difference between HEU and LEU fuel as it was shown that in general eversafe times for LEU fuel are greater than for HEU fuel. Consequently, procedures were modified for some operations to ensure compliance with safe heat limits. The paper will present the process undertaken for the conversion of HIFAR, including the development of the safety case, requirements for regulatory approvals, and results from the conversion program. © The Authors
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Keywords
Aluminium alloys, Cadmium, DIDO Reactor, Fuel elements, Graphite, HIFAR Reactor, Highly enriched uranium, Neutron diffraction, Nuclear fuels, Reactor cores, Risoe National Laboratory, Safety analysis, Thermal hydraulics
Citation
Storr, G., Vittorio, D., & hall, R. (2007). Converting HIFAR to low enriched uranium fuel. Paper presented to International conference on research reactors "Safe management and effective utilization", Sydney, 5-9 November 2007. Retrieved from: https://inis.iaea.org/collection/NCLCollectionStore/_Public/39/043/39043136.pdf?r=1