Effects of high density dispersion fuel loading on the control rod worth of a low enriched uranium fueled material test research reactor

The effects of using high density low enriched uranium on the worth of the control rods of a material test research reactor were studied. For this purpose, the low density LEU fuel of an MTR was replaced with high density U–Mo (9 w/o) LEU fuels, having uranium densities of 6.57 g/cm3, 7.74 g/cm3 and 8.90 g/cm3. Simulations were carried out to calculate the worth of the control rods at beginning of life. Three control rod materials were investigated: Ag–In–Cd alloy, B4C and Hf. Nuclear reactor analysis codes WIMS-D4 and CITATION were employed to carry out these calculations. It was seen that the control rod worth decreased as the uranium density of fuel increased from 6.57 g/cm3 to 8.90 g/cm3. The decrease was 10.58%, 9.39% and 9.74% for Ag–Cd–In alloy, B4C and Hf respectively. Even the increase in control rod thickness could not compensate for the decreased worth.

► Change in uranium density of fuel affects different parameters of an LEU fuelled MTR.
► The change in the worth of control rods as uranium density increases has been analyzed.
► Reactor under study is the IAEA’s 10 MW benchmark reactor.
► Codes used include WIMS-D4 and CITATION.