Spalling effect on gamma-ray shielding performance in MACSTOR-400 (Korean CANDU spent fuel storage module)

The saturation of South Korea's at-reactor (AR) spent fuel storage pools has created a need for additional spent fuel storage capacity. The Korea Hydro & Nuclear Power Company is planning to construct a MACSTOR-400 facility composed of reinforced concrete.In concrete structures, cracks occur due to thermal stress, hydration heat, weather, load and other reasons, and shielding performance changes according to the event by crack. However, there are no researches providing the allowable crack for shielding. This paper presents estimating the effect of concrete spalling on gamma-ray shielding performance in MACSTOR-400 based on an FEM simulation. When the cover thickness is under 10 cm, it is estimated that spalling will be formed. Generally, because cover thickness is under 10 cm in the concrete structure, it is estimated that spalling will be formed in MACSTOR-400. If the thickness of wall in MACSTOR-400 is over 100 cm, it is estimated that surface dose rate will be maintained within the radiation safety standards under any conditions related to crack effect. The results of this study may be used for developing standards for radiological safety in shielding structures, especially in relation to the shielding margin.