Study of successive ramp reactivity insertions in typical pool-type research reactors

• A comparative safety assessment three different research reactor cores was done.
• Single and double ramps at low power start-up have been studied using PARET code.
• The HEU core with single reactivity ramps has good agreements with previous work.
• It was done for double reactivity ramps up to $2.2/0.5 s for all three cores.
• The peak power, fuel & clad temperature values remain within safe limits.

A comparative safety assessment of both HEU and the proposed LEU1 & LEU2 cores having UAlx–Al, U3O8–Al and U3Si2–Al fuels respectively in a typical MTR system has been carried out using the PARET code. Super prompt-critical transients initiated with the insertion of single as well as double ramps at low power start-up have been studied in this work. The results for the standard HEU core with single reactivity ramps up to $2.2/0.5 s show excellent agreement with the already published data. According to these simulations, for large time gap values (ΔtΔt = 1 s) between double ramps, the first peak power dominates for all three cores and each system remains safe up to $2.2/0.5 s ramp rates. However, for closely spaced double ramps (ΔtΔt = 0.1 s), for both HEU and the LEU2 cores, the simulations indicate clad melting for $2.4/0.5 s ramp rates. The peak power, fuel centerline & clad surface temperature values remain within safe limits for single as well as for double reactivity ramps up to $2.2/0.5 s for all three cores.