Session: 08-11: Computational Fluid Dynamics (CFD) and Applications - XI

Paper Number: 136361

136361 - A Eulerian-Lagrangian Investigation on Graphite Aerosol Transport in the Containment During a Water-Ingress Accident of Htgr 

Abstract: 

As a special problem of high temperature gas-cooled reactors (HTGR), the graphite dust is an important concern for the accident analysis of HTRG, due to its coupling with fission products. A large fraction of graphite particles deposit on the tube bundles of steam generator (SG) due to the particle-vortex interaction and thermophoresis effect. Once a water-ingress accident occurs, the graphite dust may resuspend due to the rapid change of flow field. A certain fraction of resuspended dust, together with some fission products, could be discharged to the containment if the overpressure protection of the primary circuit is triggered. The distributions of deposited and airborne particles in the containment are crucial for the safety analysis and source term evaluation. Especially, the fragmentation effect during the overpressure discharge shifts the size distribution of graphite dust to the smaller end, which is an important factor to consider for the graphite aerosol behaviors in the containment. In this work, we use a Eulerian-Lagrangian method to numerically study the transport and deposition behaviors of graphite aerosol in the full-scale containment during a water-ingress accident. Particularly, the effects of highly irregular shape of graphite particles on the particle-wall and particle-fluid interactions are incorporated. The statistical results show that as the tracking time increases, the deposition rate first exponentially decreases and then becomes stable. About 68.7% of particles are finally deposited on the shell of the containment, and less than 1% on other surfaces. As the particle size increases, the deposition fraction increases first and then decreases, reaching a maximum value at 1 μm. The rebound behavior dominates the deposition of particles above 3 μm and the deposition fraction is significantly overestimated if the hit-and-stick assumption is adopted. The total deposition fraction is 4.43% for discharge tube and 9.89% for the steam generator, and largely increases to 42.17% for containment shell due to the strong thermophoresis effect. Less than 1% of particle are deposited on the bottom and top surfaces. Large particles prefer to deposition the bottom and SG top surfaces due to the gravity. The angular distribution of the discharge tube is uniform especially for small particles, while that of the steam generator side surface is fairly non-uniform, showing a deep valley at-45°, 0° and 45°and high peak at -90°,-15, 15° and 90°.Our preliminary investigation demonstrates that the containment of HTR-PM has a good capability to retain a large fraction of graphite dust particles and thus may reduce the releasing fraction of fission products in a real water-ingress accident scenario.

Presenting Author: Yiyang Zhang Institute of Nuclear and New Energy Technology

Presenting Author Biography: Prof. Yiyang Zhang got his PhD degree from Tsinghua University in 2013. He is now an associate professor in the Institute of Nuclear and New Energy Technology (INET), Tsinghua University. His research insterets are aerosol dyanmics, non-spherical particles, and gas-solid flows.

Authors:

Yiyang Zhang Institute of Nuclear and New Energy Technology
Zhu Fang Institute of Nuclear and New Energy Technology
Xinxin Wu Institute of Nuclear and New Energy Technology
Libin Sun Institute of Nuclear and New Energy Technology