Safety assessment of a loss-of-pool-water accident in the spent fuel storage of a high-power research reactor

Abstract

Abstract

As research reactors undergo power uprates to enhance medical isotope production and materials testing, higher fuel burnup and elevated decay-heat levels significantly reduce the thermal margins of spent fuel storage facilities under postulated accident conditions, necessitating a systematic reevaluation of their safety limits. This study presents a safety analysis of the spent fuel storage system of a 10 MW research reactor under a postulated loss-of-pool-water accident. A multiphysics framework combining neutronic analysis, transient thermal–hydraulic modeling, and radiation transport calculations is employed to evaluate the safety limits of a high-density two-tier rack configuration. The results show that the effective multiplication factor remains well below unity for all investigated configurations, indicating preserved subcriticality. However, thermal–hydraulic margins are significantly reduced for fuel with only 24 h of post-irradiation cooling, resulting in cladding blistering after approximately 5 h of air exposure. In contrast, a decay period of 144 h provides sufficient passive cooling to prevent cladding degradation under complete loss of pool water. Radiation shielding analysis further indicates that a water column of approximately 300 cm above the top of the spent fuel assembly rack is required to reduce the personnel dose rate below the adopted criterion of 10 μSv/h for the pool geometry and radiation source considered in this study. These findings provide quantitative guidance for safety evaluation and operational planning in high-power research reactor spent fuel storage systems.