Spallation Target Design for Converting the Isfahan MNSR Reactor to an Accelerator Driven Subcritical System

There are many research reactors around the world that have been installed from many years ago and must be decommissioned sooner or later. Most of these reactors were fuelled with high enriched uranium and substantial amount of initial loaded fuel has not been exploited yet. The reactor conversion to an accelerator driven system (ADS) is one of the novel ideas for minor actinide utilization and reducing the spent fuel radio toxicity. The main objective of this study is dedicated to spallation target design in miniature neutron source reactor (MNSR) core conversion to an ADS one. The MNSR is a pool type research reactor, which was developed by China. After more than 25 years, the fuel burn-up could not be compensated more by adding shimming plates. The subcriticality in MNSR reactor was attained by entirely removing the top plate shims as well as control rod and installing the spallation target in interior space of guide thimble. Different state of the art targets such as tungsten, lead, bismuth, and LBE (lead-bismuth eutectic) have been investigated and target neutronic parameters including the spallation yield, neutron energy spectrum, deposited energy and the angular distribution of spallation neutrons were evaluated using MCNPX2.6 code. The results showed that the neutronic performance of tungsten is somewhat greater than its competitors. On the other hand the maximum power density in tungsten is about two times greater than lead and LBE targets.