Effects of the concrete crack on radiation shielding in spent fuel dry storage facility

Abstract

The saturation of South Korea\`s at-reactor (AR) spent fuel storage pools has created necessity for additional spent fuel storage capacity. The Korea Hydro & Nuclear Power Company is planning to construct a MACSTOR-400 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 crack width. However, there are no design criteria providing the allowable crack size for shielding. This research presents to estimate the effect of concrete cracking on gamma-ray shielding performance in MACSTOR-400. In order to estimate the crack effect on spent fuel storage facility, this research assume the two cases ; crack effect on surface dose rate and crack effect on dose rate in site boundary. For estimating the surface dose rate according to the event by crack, two cases were assumed. One is a “Normal State,” which is based upon the assumption that crack is formed. The other is a “Abnormal State,” which assumes that spalling by reinforcement corrosion occurs. Normal state is based on deduction of a correlation between intensity and crack width through experiments. For the experiment, the measuring system is designed and fabricated. With this system, test is carried out and the accuracy is estimated through comparing result of simulation with result of experiment. It is confirmed that result of simulation and experiment has a similar trend with 5% error. The surface dose rate increased logarithmically according to the increase in crack width. According to the results, if the thickness of shield is over 30cm and the crack width is 0.4mm, crack effect is under 10%. If the thickness of wall is 90cm and the crack width is 0.4mm in MACSTOR-400, because it is estimated that surface dose rate exceed the design criteria, the proper measures are demanded. The present results are used to formulate an attenuation equation for gamma rays in a concrete st...