wseas-12093-20260924112343-21e061 20260924112343244 wseas/wseas wseas.group@gmail.com WSEAS WSEAS Transactions on Heat and Mass Transfer 1790-5044 2224-3461 05 25 2026 05 25 2026 21 Sangida Akter Department of Nuclear Science and Engineering, Military Institute of Science and Technology, Dhaka-1216, BANGLADESH Abdus Sattar Mollah Department of Nuclear Science and Engineering, Military Institute of Science and Technology, Dhaka-1216, BANGLADESH The type of inert gas utilised for spent fuel storage at the Rooppur Nuclear Power Plant (RNPP) has a significant impact on the thermal performance and safety of the TN-32B dry cask storage system. To determine the suitable gas, this study used fuzzy TOPSIS decision-making, Monte Carlo sensitivity analysis, and CFD simulations with ANSYS Fluent. Under a 34 kW decay heat load, the effects of air, nitrogen, argon, and helium were assessed for a single fuel assembly. The estimated peak temperatures were below the 649 K statutory safety limit: 635 K for helium, 621 K for argon, 591 K for nitrogen, and 589 K for air. For estimating uncertainties in decision-making criteria, fuzzy TOPSIS was applied using 10,000 Monte Carlo simulations, which accounted for a ±20% variation in criteria weights. The outcomes consistently pointed to argon as the most favorable option, showing the highest mean closeness coefficient of 0.681 and ranking first in 79.6% of the simulations. Nitrogen was identified as a strong alternative, with a mean closeness coefficient of 0.647 and securing a second-place position in 20.4% of the simulations. However, neither helium nor air reached the top rank in any simulation, and their mean closeness factors were 0.418 and 0.582, respectively, making them less advantageous. 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