Abstract Safety assessment for simultaneous multiple reactivity insertions in a typical research reactor having low enriched, high density (U 3 Si 2 –Al) fuel has been done using modified PARET code. As a first step, the effect of single reactivity ramps on power and temperatures during transients showed good agreement with already published data. Then simulation of transients for multiple reactivity insertions were carried out and the effects on reactor power, net reactivity of the system, and temperatures (fuel, clad and coolant) were studied. The simultaneous reactivity insertions included ramp reactivity (large and small) and beam tube flooding, a ramp reactivity and a core movement and a ramp reactivity and a sample ejection accident respectively. When simultaneously two different reactivity insertion transients are coupled in the reactor under uncontrolled conditions, the self-control of the reactor decreases. The power and temperatures show several peaks and it oscillates along with the net reactivity of the system within the first second of the accident.