Effect of high density dispersion fuels on transient behavior of MTR type research reactor under multiple reactivity transients

The effect of fuel on transient behavior under simultaneous multiple reactivity insertion in a typical MTR type research reactor have been studied. The PARET code was used for three different high density fueled cores. The fuels included oxide (U3O8-Al), silicide (U3Si2-Al) and aluminide (UAlx-Al) respectively. In first part single ramp reactivity insertions were done and results were found in good agreement with already published data. Then simultaneous multiple reactivity insertion transients were investigated with totally disabled control systems. Multiple reactivities were inserted in the IAEA benchmarked MTR type research reactor and effects on reactor power and temperatures (fuel, clad and coolant) were studied. The simultaneous accidents included ramp reactivity (large and small) plus beam tube flooding, a ramp reactivity plus a core movement and a ramp reactivity plus a sample ejection accident respectively. In all cases, the reactivity rises to peak values and then starts decreasing slowly; however when the ramp is large the peak values also become high and power also shows multiple peaks. The core having oxide fuel has slightly higher power peak values while core with silicide and aluminide fuels show similar behavior. The fuel temperatures in all cases were much higher for the core having oxide fuel as compared to other two cores.