CFD SIMULATION OF NATURAL VENTILATION PERFORMANCE OF THE INTERIM REGION IN SPENT FUEL DRY-STORAGE SYSTEM OF HTR-PM

The spent fuel dry-storage system of High Temperature Reactor-Pebble bed Modules (HTR-PM) in China is designed to consist of 3 separate regions, with each composed of multiple storage wells. Cold air is distributed to 8 parallel wells in the interim region from a bifurcation chamber, and then heated by vertical placed canisters in each well before gathering in a mixture chamber. In accident condition, the decay heat in interim region will be discharged by open-cycle natural ventilation. In this paper, thermal performance of the interim region by natural ventilation was investigated by a step-by-step scheme. Firstly, the resistance characteristics of wells loaded with different numbers of canisters and bifurcation chamber were studied with CFD code, and were formulated into momentum sources of porous media. Then, equivalent model of the system with porous media regions was employed to simulate the flow distribution of the system. Two different operation conditions (half-loaded condition and full-loaded condition) were studied in this step and hottest well were located. Finally, a refined' model of the hottest well with minimized and necessary assumption was employed to investigate the conjugate heat transfer coupled with thermal radiation process, and to obtain the internal temperature profile of the hottest well. The results showed that the total mass flow of natural ventilation is 5.53 kg/s under half-loaded condition (20 canisters, 156.72 kW of decay heat) and 4.83 kg/s under full-loaded condition (40 canisters, 192.37 kW of decay heat). Hottest well was the well-1th under half-loaded condition, where maximal temperatures of concrete walls, steel barrel, canisters and spent fuel pebble bed inside the canister were 86.5, 142.2 degrees C, 279.5 degrees C, 484.9 degrees C, respectively. The results demonstrate that the interim region of dry-storage system satisfies the temperature limitation of component materials in accident condition.