Monte Calrlo Modelling of Void Coefficient of Reactivity Experiment

The Atominstitute (ATI) of the Vienna University of Technology utilizes a TRIGA Mark II research reactor for last fourty eight years at a nominal reactor power of 250 kW (thermal). It has a completely mixed core and employing three different types of fuels i.e. aluminium clad fuel with 20% enrichment, stainless steel (SS) clad fuel with 20% enrichment and SS clad FLIP fuel with 70% enrichment. The current core loading is 83 fuel elements. The reactor core is equipped with many irradiation facilities inside the core to irradiate samples at different flux levels. These irradiation facilities include the Central Channel (CC which is used to irradiate samples at maximum flux. This paper presents the calculations and measurements of the void coefficient of reactivity in CC. For this purpose, a cylindrical void of 66.47 cm was inserted into the CC and moved from bottom to top of the core along the axial length of the channel in steps of 5 cm. For each step, the effect of void sample on the core reactivity was measured by the regulating control rod position. This experiment was performed at 10W in automatic mode of operation. Monte Carlo neutronics simulating code, equipped with the cross sections library JEFF 3.1, was employed to perform these calculations. For each 5 cm step in the central irradiation channel, a separate model was executed. To see the influence of the control rods, the MCNP calculations were performed. In theses calculations, the control rods were set to the reactor operating conditions. Both the simulated and measured results were compared. Fairly good agreement was observed between calculations and experimental results.