Graphite aerosol release to the containment in a water ingress accident of high temperature gas-cooled reactor (HTGR)

• Published in: Nuclear engineering and design Vol. 342; pp. 170 - 175
• Main Authors: Wei, Mingzhe, Zhang, Yiyang, Fang, Zhu, Wu, Xinxin, Sun, Libin
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01.02.2019; Elsevier BV
• Subjects: Accidents; Aerodynamics; Aerosol; Aerosols; Boilers; CFD; Compressive strength; Computational fluid dynamics; Computer applications; Computer simulation; Containment; Discharge; FEM; Finite element method; Fission products; Fluid dynamics; Fragmentation; Graphite; High temperature; High temperature gas cooled reactors; High temperature gas-cooled reactor; High temperature gases; Hydrodynamics; Impact velocity; Mathematical models; Nuclear engineering; Nuclear safety; Particle impact; Particle size distribution; Pressure; Reactors; Safety; Safety valve; Safety valves; Size distribution; Steam; Stress concentration; Velocity; CFD; Aerosol; Safety valve; High temperature gas-cooled reactor; FEM
• ISSN: 0029-5493; 1872-759X
• DOI: 10.1016/j.nucengdes.2018.11.037

•Multiphase computational fluid dynamics (CFD) is used to obtain the particle trajectories and impact velocities during pressure relief in the water ingress accident of HTGR. Driven by the high velocity flow, even submicron particles show a high impact rate during the pressure relief.•FEM is used to obtain the fragment results when particles hitting the wall.•The possibility of particle fragmentation is given by combining CFD and FEM. As a design-basis accident, the water ingress due to the rupture of a single steam generator tube is a major threat for high-temperature gas-cooled reactors (HTGR). The rapid rise of primary pressure could reach the set pressure of safety valve and trigger the relief to the containment. For HTGR, the graphite dust particles, which usually carries fission product condensations, are also discharged to the containment during the pressure relief. The size distribution of the aerosol is crucial for the safety analysis of the containment in this accident scenario. Particularly, the high velocity flow in the safety valve may greatly change the size distribution of the graphite aerosol, due to the possible impact and fragmentation. In the present work we study graphite particle impact and fragment during pressure relief in the water ingress accident of HTGR by combining multiphase computational fluid dynamics (CFD) and finite element method (FEM). An Eulerian-Lagrangian scheme is employed to calculate the trajectory and instantaneous impact velocity of different sized particles. Then FEM with Hertz contact model is used to evaluate the outcome of the impact. CFD results show that the impact rate increases from 22% to nearly 100% as particle size increases from 0.1 μm to 1.9 μm. The critical fragment velocity is larger for smaller particle because the compressive strength limit increases due to Hall-Petch effect. By combining CFD and FEM simulation, it is shown that the possibility of fragmentation reaches 80% for particles larger than 1.5 μm. Our work suggests that this fragmentation effect needs to be considered for the initial size distribution of graphite aerosol that is discharged to the containment.