Motivation

1
Advancing the Fundamental Understanding and
Scale-up of Spouted Bed TRISO Coaters Vesna
Havran, Josh Grimes, Fadha Ahmed, and Muthanna
Al-Dahhan

• Experimental Setup
• A small scale fluidized spouted bed column with 6
  inches diameter
• Solid particles glass beads 2 mm diameter, 2.5
  g/cc density
• Gas phase air
• Distributor inlet orifice of 0.5 inch i.d. and
  20 open area
• Bed height of 32.5 cm and an inlet pressure of 80
  psig
• Operating gas velocity Ug1.09 m/s
• Ten axial positions where an optical probe can be
  inserted into the column, in order to determine
  the solid concentration
• Axial positions are separated by 47.24 mm in
  order to create a complete concentration profile
  in the spouted bed
• Measure at six radial positions at each axial
  position

• Motivation
• Advanced Gas Reactors (AGRs)
• The advancement and commercialization of nuclear
  energy produced by advanced gas reactors (AGRs)
  (spouted bed) is dependent on Tri-isotropic
  (TRISO) fuel particle coating step via chemical
  vapor deposition in gas-solid fluidized spouted
  beds
• The acceptable level of defective coated
  particles is essentially zero
• The quality of nuclear fuel particles produced is
  strongly impacted by the hydrodynamics of the
  spouted bed, solids flow field and flow regime
  characteristics
• Unfortunately, the current spouted fluidized bed
  coating technology and scale-up relies on
  trial and error and is based on empirical
  approaches
• Accordingly, fundamental understanding of the
  underlying phenomena of the spouted bed TRISO
  coater using advanced diagnostic techniques is
  essential

• Objectives
• Hydrodynamic investigation of solid particles
  and gas holdup distribution
• Assessing and comparison of results obtained by
  different advanced measurement techniques
  optical probe and ?-ray computational tomography
  (CT)
• Identification of match and mismatch hydrodynamic
  conditions
• Evaluation of reported dimensionless groups for
  scale-up of spouted bed reactors
• Investigation of the effects of scale, design and
  operating conditions on dimensionless groups,
  cross-sectional solid and gas holdup profiles

Nuclear power is the most environmentally benign
way of producing electricity on a large scale.
Therefore the increasing importance of nuclear
power in meeting energy needs while achieving
security of supply and minimizing carbon dioxide
emissions.

• Optical probe
• Local solid and gas holdup measurements based on
  backscattering of light
• Three fibers, one receiver and two detectors
  aligned in a straight line
• 1/8 inch diameter tubing, 600 microns fiber
  diameter
• Distance between detectors 2mm

• Computational Tomography
• Time averaged solid and gas holdup
  cross-sectional distribution
• Measure attenuation coefficient on the basis of
  Beer Lamberts law
• 7 out of 11 NaI- detectors were used
• Source Cs-137 of 187 mCi

TRISO particle
Fuel kernel -provide fission energy Buffer
layer - attenuates fission product recoils from
kernel - provides space for
the fission gases Inner pyrocarbon (IPyC) -
traps the fission gases inside the particle
- protects kernel from
clorine- during SiC deposition
- provides support for SiC Silicon
carbide (SiC)- the primary component, the
strongest layer -
impervious to gaseous fission products Outer
pyrocarbon (OPyC) - protects SiC from
surroundings
- holds SiC in compression

• Background
• Spouted fluidized beds are very efficient in
  contacting gases and coarser particles.
  Therefore, they have been applied to a wide
  variety of processes including coating,
  granulation, drying, coal gasification, catalytic
  reactions, and more.
• A jet of air penetrates the bed of particles,
  creating a central spout zone, a fountain about
  the spout, and an annulus surrounding the spout.
• Different flow regimes and characteristics can be
  obtained with minor variations in geometry or
  operating conditions
• Existing scale-up approaches based on
  hydrodynamic and geometrical similarity do not
  take into account two additional non-dimensional
  terms
• - interfacial angle
  of particle (?), or internal friction angle
• - loose packed voidage (?)
• that need to be considered in order to achieve
  mechanical similarity.

• Future plan
• Performing of further experiments in order to
  validate the conditions of hydrodynamic
  similarity and dissimilarity, by changing the
  size of reactor, inlet gas velocity, solid
  material and other parameters
• Implementation of the new optical system that
  will enable not only measurement of solid holdup
  distribution but also measurement of solid
  particle velocity
• Complementing the investigation and measurement
  with pressure transducers measurement
• Investigation of the effect of the selected
  conditions (match and mismatch) on the pressure
  signals and compare the findings with the results
  obtained by optical probe technique and
  computational tomography
• Evaluating the approach for the development of
  the on-line measurement technique based on
  nuclear gauge densitometry (NGD)

CHEMICAL REACTION ENGINEERING LABORATORY (CREL)