Analysis on the amount of graphite dust deposited on steam generator of HTGR

1. Analysis on the amount of graphite dust deposited on steam generator of HTGR Wei Peng1, Tian-qi Zhang1, Su-yuan Yu2* 1Institute of Nuclear and new Energy Technology (INET), Tsinghua University, China 2Center for Combustion Energy, Tsinghua University, China

2. Outline • Background • Physical Model • Simulation model • Result • Conclusion

3. Background Gen III/III+ units represent the current level of BAT (Best Available Techniques). Gen-IV aims: more efficiency and more safety VHTGR: Very High Temperature Gas-cooled Reactor

4. Background Carbonaceous dust is suspected to be a hidden problem for HTGR. It comes from abrasion between pebbles/ pebbles and the fuel handling pipe. Dusts finally deposit on the primary surface and influence the surface’s feature

5. Combined with FP (fission products) released by fuel elements • Radioactive source of HTR in depressurization accidents • Hamper operation and maintenance in normal operation. • steam generator is an important component for the dust deposition. 5

6. Physical Model • Heat transfer component between the hot helium and the cool water→ great temperature gradient→thermophoretic deposition • Spiral heat exchange tube→complex flow field→ turbulent deposition

7. the amount of graphite dust coated on steam generator is the dynamic equilibrium between deposition of graphite dust and resuspension of deposited dust.

8. Deposition model The total deposition mass depends on the deposition velocity • thermophoretic deposition • turbulent deposition Model of Fan, F. G., & Ahmadi, G. Model of Brock-Talbot

9. Resuspension model • The revised Rock’n’Roll model (Reeks and Hall, 2001) by Biasi et al. (2001) • Particle Resuspension: caused by the coupled effects of aerodynamic lift and drag; particles detach from the substrate when it receives enough energy from the turbulent flow. F is the aerodynamic force couple acting on the particle FLis the lift force and FD is the drag force on the particle fa is the adhesive force which is assumed to be a log-normal distribution:

10. Conditions Diameter of graphite dust

11. Velocity and temperature distribution The heat flux of the tube in steam generator can be divided into four parts: friction velocity distribution heat flux distribution Distribution of temperature gradient

12. Deposition Vacuum tank Collect bag thermophoretic deposition turbulent deposition Link to the sonic nozzle • the thermophoretic deposition velocity is larger than turbulent deposition velocity. Average deposition velocity is 0.0013m/s total deposition velocity

13. Resuspension Vacuum tank Collect bag Link to the sonic nozzle resuspension rate • The resuspension rate is associated with the time: in the beginning stage, the resuspension rate is high, it decreases rapidly as the time increasing, and then it decline slower. • the resuspension rate after a long sufficient time is used to analyze the graphite dust behavior in present study, ​​is of about 10-5 s-1

14. Distribution of dust in the steam generator the amount of the graphite dust on the tube surface depends on the rate of the deposition and resuspension. Vacuum tank The result indicated that the amount of the graphite dust loading on the tube surface will tend to 6,760mg/m2.

15. Conclusion The deposition and resuspension of graphite dust in the steam generator was studied numerically: Vacuum tank • The turbulent deposition and thermophoretic deposition are the two mechanisms that make the graphite dust deposit on the heat transfer tube surface in SG, and thermophoretic deposition is the main depositional mechanism; • The preliminary calculations result showed that the amount of the graphite dust loading on the tube surface will tend to 6,760mg/m2. Collect bag Link to the sonic nozzle

16. Thanks for your attention ！