According to increase of operating nuclear power plants and ages of them, effective management for large amount of spent nuclear fuel became a important issue in the nuclear society of Korea. After 2016, spent nuclear fuel will be transported vigorously for permanent disposal or interim storage. And nowadays, because of lack of storage capacities, spent nuclear fuel assemblies discharged from nuclear reactors that had been operated long time transported to near unit facilities.
Spent nuclear fuel emits a lot of radiations and decay heat. For safe transport of them, radiation shielding performance, decay heat, containment, nuclear criticality and structural stability should be considered and sufficiently prepared for them.
CASTOR KN-12 is the third spent nuclear fuel transport cask that designed and manufactured in Korea. The cask had been designed to be able to contain 12 spent nuclear fuel assemblies of pressurized water reactor (PWR) and transport with dry or wet condition. Characteristics of transportable nuclear fuel assemblies should be lower initial enrichment than 5 weight percents, lower burn-up than 50,000 mega watt day per metric ton of uranium (MWd/MTU) and longer cooling time than 7 years.
In this study, it was considered that spent nuclear fuels with various burn-up were transported with CASTOR KN-12 in wet condition. Through the study, it was estimated that radiation shielding performance and minimum cooling time for transport with various burn-up conditions.
The study was conducted two stages. The first was a comparison between Monte carlo simulation results and measured data to verify modeling and simulation methods. The last was to calculate surface dose rates with various source terms. The results showed that CASTOR KN-12 had good performance of radiation shielding. The minimum cooling time for transport was 3.9 years for low burn-up (32,000 MWd/MTU) and 23 years for high burn-up (58,000 MWd/MTU) spent nuclear fuel assemblies.