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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

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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 Ug=1.09 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 γ-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 Lambert’s 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)