Motivation Advanced Gas Reactors (AGRs)

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 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) CHEMICAL REACTION ENGINEERING LABORATORY (CREL)