Design of Fission Neutron Converter in HFETR

In order to increase local fast neutron fluence rate in High Flux Engineering Test Reactor (HFETR), the fission neutron converter adopted the crisscross fuel rod whose fuel pellet was made of high fission density alloy UMo with 7%Mo. 62 fuel rods in the converter were arranged with triangle dot-matrix between outer tube with diameter of 63 mm and inner tube with diameter of 24 mm. And the converter has an irradiation hole with diameter of 20 mm in the center. The calculation result with MCNP shows that fast neutron （E>1 MeV） fluence rate of irradiated samples in the converter can achieve up to 3.34×10¹⁴cm^-2•s^-1, which is about 40% higher than that in the HFETR core at the same position without converter. On the other hand, under the condition of design flow velocity and pressure, the analysis results with ANSYS/CFX show that the maximum permission power can reach 2.4 MW and the maximum power density of fuel pellet is 8.007 kW/cm³. Here, the cladding temperature of the fuel rod is 193.6 ℃, and the converter can fulfill the requirement of thermal-hydraulic design criteria of HFETR and flow instability will not occur.