Chapter 7
Applications: Pebble Flow Optimizations
7.1 Introduction
This chapter will show two categories of optimization: the geometric optimization,
including the optimizations of wall structure, flow-corrective insert, conical base,
discharging silo, and the mechanical optimization, including the optimizations of
friction and flow dynamics.
7.2 Wall Structure Optimization
Crystallization of pebbles in a pebble bed is a crucial problem in high-temperature
gas-cooled pebble-bed reactors. This phenomenon usually happens along the internal
surface and leads to a large number of stagnated pebbles, which poses a threat to
reactor safety. In real reactor engineering, wall structures have been utilized to avoid
this problem. The wall structures of the pebble bed have not been given enough
emphasis yet. In the pebble-bed reactor HTR-10 built by Institute of Nuclear and
New Energy Technology, Tsinghua University, the wall structures have been adopted,
as shown in Fig. 7.1. These structures can give an obvious effect to the overall flow
field by influencing pebble motions in the near-wall region. Specifically, with the
help of the unsmooth internal surface, blocking or crystallization of a pebble flow
that often happens along the wall would be eliminated to some extent. This definitely
contributes to the elimination of the stagnant region and improves the reactor’s safety
capacity by reducing the probability of radiation leakage. Moreover, such structures
enhance the dispersion of pebbles in the peripheral core so that these fuel pebbles are
more likely to move to the relatively central region and be exposed to more neutron
flux, which would narrow the burn-up level in the radial direction.
This chapter verifies the crystallization phenomenon through the discrete element
method simulation. It also explains how wall structures work in preventing crystallization. Moreover, several kinematic parameters have been adopted to evaluate wall
© Tsinghua University Press 2021
S. Jiang et al., Multiphase Flow and Heat Transfer in Pebble Bed Reactor Core,
https://doi.org/10.1007/978-981-15-9565-3_7
443
Applications: Pebble Flow Optimizations
7.1 Introduction
This chapter will show two categories of optimization: the geometric optimization,
including the optimizations of wall structure, flow-corrective insert, conical base,
discharging silo, and the mechanical optimization, including the optimizations of
friction and flow dynamics.
7.2 Wall Structure Optimization
Crystallization of pebbles in a pebble bed is a crucial problem in high-temperature
gas-cooled pebble-bed reactors. This phenomenon usually happens along the internal
surface and leads to a large number of stagnated pebbles, which poses a threat to
reactor safety. In real reactor engineering, wall structures have been utilized to avoid
this problem. The wall structures of the pebble bed have not been given enough
emphasis yet. In the pebble-bed reactor HTR-10 built by Institute of Nuclear and
New Energy Technology, Tsinghua University, the wall structures have been adopted,
as shown in Fig. 7.1. These structures can give an obvious effect to the overall flow
field by influencing pebble motions in the near-wall region. Specifically, with the
help of the unsmooth internal surface, blocking or crystallization of a pebble flow
that often happens along the wall would be eliminated to some extent. This definitely
contributes to the elimination of the stagnant region and improves the reactor’s safety
capacity by reducing the probability of radiation leakage. Moreover, such structures
enhance the dispersion of pebbles in the peripheral core so that these fuel pebbles are
more likely to move to the relatively central region and be exposed to more neutron
flux, which would narrow the burn-up level in the radial direction.
This chapter verifies the crystallization phenomenon through the discrete element
method simulation. It also explains how wall structures work in preventing crystallization. Moreover, several kinematic parameters have been adopted to evaluate wall
© Tsinghua University Press 2021
S. Jiang et al., Multiphase Flow and Heat Transfer in Pebble Bed Reactor Core,
https://doi.org/10.1007/978-981-15-9565-3_7
443