Neutronic analysis of the fuel loaded irradiation loop device of the RMB Multipurpose Brazilian Reactor

The structuring project of the Brazilian Multipurpose Reactor (RMB) is responsible for meeting the capacity to develop and test materials and nuclear fuel for the Brazilian Nuclear Program. An irradiation test device (Loop) capable of performing fuel test for power reactor rods is being conceived for RMB reflector. In this work neutronic calculations have been carried out in order to determine parameters to the Loop basic design. Safe position determined to be 52.7 cm displaced from the core, where linear heat rate (q') < 1 W/cm fission power is released in the rig loading fissile sample. Since irradiation rig moves during normal operation of the reactor, displacement of the samples must be investigated in terms of perturbation in the core. Results confirmed efficacy of the 12 cm heavy water layer designed to suppress reactivity effects in the core. Linear heat rate in the fissile sample was calculated in order to estimate predefined power ramps of 50-350 W/cm, information necessary to the project of the displacement device. Ramp lengths of 9.59 cm-13.22 cm were found depending on the peak factor considered for the sample rod and the number of beryllium rows arranged in the reflector.