Nuclear iconReactor Components

Pebble Bed Reactor (Generation 2)

The Pebble Bed Reactor element (Generation 2) is a simplified model of the pebble bed nuclear reactor. The purpose of the model is not to do detail reactor design, but rather to allow for the integrated simulation of the reactor together with the rest of the main power system within acceptable computer simulation times.



Advanced Pebble Bed Reactor (Generation 3)

The Advanced Pebble Bed Reactor model (third generation reactor model) is based on the fundamental equations for the conservation of mass, momentum and energy for the compressible fluid flowing through a fixed bed, as well as the equations for the conservation of energy for the pebbles and core structures. The equations are in a form that is suitable for incorporation in an integrated systems CFD code. This formulation of the equations results in a collection of one-dimensional elements (models) that can be used to construct a comprehensive multi-dimensional model of the reactor (two-dimensional axi-symmetrical model).

The elements account for the pressure drop through the reactor; the convective heat transport by the gas; the convection heat transfer between the gas and the solids; the radiative, contact and convection heat transfer between the pebbles and the heat conduction in the pebbles. Despite the increased complexity, it retains the simplicity of the network approach.




The phenomena that cannot be simulated in the previous pebble bed reactor model (second generation) include the following:

  • The presence of a central reflector column that implies that the core itself does not extend outward from the center but has an inner and outer diameter.
  • The addition and extraction of gas via purpose provided channels and/or leak flow paths along the inner or outer perimeters of the core.
  • The simulation of heat transfer and fluid flow through porous and solid core structures surrounding the core.
  • The simulation of fluid flow and heat transfer, including radiation and natural convection, in purpose, provided cavities between core structures with a two-dimensional rather than one-dimensional nature.
  • The ability to specify normalized radial power distribution profiles within the different axial layers in the core.
  • The ability to take into account heat generation that may occur in any of the core structures.