A preliminary feasibility study of control disks for a compact thermionic space reactor

Results of a preliminary feasibility study of control disks are presented. These results show improved performance in compact space reactor systems through a more even fuel burnup due to improved core power profiles. Reactivity worth and axial power profile calculations have been performed for a fully reflected epithermal core typical of a compact thermionic reactor. Similar calculations were performed for the same reactor employing control rods for performance comparison. The neutronics calculations were performed in three dimensions utilizing the MCNP computer code due to the axial power dependance on rotational geometry changes. The analysis shows that control disks would provide enough worth to compensate for the built in excess reactivity for an estimated 10 year lifetime and still can take the system subcritical at end of life. Axial flux profiles show the advantages over the same system employing control rods in the form of a more even fuel burnup.