Broadway, Jeramie

Hickman, Robert

Mireles, Omar R.

NASA Technical Reports Server

National Aeronautics and  
Space Administration
Development of a Fluidized Bed CVD 
System for Coating UO2 Particles with 
Tungsten
NASA Advanced Exploration System (AES) Project:
Nuclear Cryogenic Propulsion Stage
O. Mireles, J. Broadway, R. Hickman
NASA Marshall Space Flight Center
omar.r.mireles@nasa.gov
NETS 2012
22 March 2012
https://ntrs.nasa.gov/search.jsp?R=20120014215 2019-08-30T22:01:37+00:00Z
National Aeronautics and  
Space Administration
• NTP fuels under development
− W-60vol%UO2 CERMET
• Minimize erosion
− Prevent H2 propellant at ~3000 K from reducing UO2 
fuel kernels
− Requires each fuel kernel to be clad in tungsten
• Coat spherical dUO2 powders with 40 vol% W
• Coated spherical powders                
advantageous for HIP
− Higher powder packing %TD
− Minimize powder segregation
National Aeronautics and  
Space Administration• WF6 process
− Residual F exacerbates fuel loss
− HF bi-product
• WCl6 process
− Minimal Cl contamination
− More complex than WF6 process (solid-to-
vapor vs. gaseous reagent)
• Vendor cost to coat dUO2 excessive
• Develop a lab-scale prototype that 
utilizes the WCl6 process that 
enables cost effective coating of 
spherical dUO2 powders
SEM Micrograph of spherical 
uncoated particles
SEM micrographs of spherical 
coated particles 
National Aeronautics and  
Space Administration
• WCl6 process
• Fluidized bed reactor (H2/Ar 10:1 ratio)
• Raining feed system (fill and drain powder hoppers)
• 3rd generation system (25 g quantities)
CVD System
HClWHWCl
C
63
930
26 

National Aeronautics and  
Space Administration
National Aeronautics and  
Space Administration
Reactor Design Evolution
Sublimer Design Evolution
National Aeronautics and  
Space Administration
• Minimum fluidization flow rate
− Fluidization flow rate varies as particle density                           
increases with increasing coating thickness
• Fluidization as a function of powder size
• Fluidization as a function of furnace temperature
• Powder column height as a function of flow rate and 
temperature
• Reactor temperature profile as a function of flow rate
• Sublimer temperature profile as a function of flow rate
• Coated Al2O3 substrates and ZrO2 spherical powders Pre-CVD Al2O3Substrate
National Aeronautics and  
Space Administration
National Aeronautics and  
Space Administration
New reactor set-
point increased to 
930 °C
National Aeronautics and  
Space Administration
National Aeronautics and  
Space Administration
EDS Phase Maps
SEM micrographs of W coating on  ZrO2 substrate (a) 150x (b) 2000x (c) 7000x
EDS spectra
National Aeronautics and  
Space Administration
All Pyrex-Quartz CVD System Design Concept
Spherical ZrO2 Powder (-53/+45 μm)  before and 
after fluidization at room temperature
National Aeronautics and  
Space Administration
• Demonstrated viability and utilization of:
− Fluidized powder bed
− WCl6 CVD process
− Coated spherical particles with tungsten
• The highly corrosive nature of the WCl6 solid 
reagent limits material of construction
• Indications that identifying optimized process 
variables with require substantial effort and will 
likely vary with changes in fuel requirements
National Aeronautics and  
Space Administration
• Optimize process variables in order to produce 
coating properties that meet requirements
• Characterize coatings as a function of substrate 
microstructure and process variables
• Design next-generation system to process 
larger quantities of power required for engine 
scale fuel fabrication
National Aeronautics and  
Space Administration
• Funding was provided by the “Advanced 
Exploration Systems – Nuclear Cryogenic 
Propulsion Stage” project.
• The authors would like to thank Grace Belancik, 
Mike Houts, Roger Harper, Jeff Quick, Gabriel 
Putnam, Jim Martin of NASA MSFC and Gene 
Nelson of AG Scientific Glass, Inc.
• The opinions expressed in this presentation are 
those of the author and do not necessary reflect 
the views of NASA or any NASA Project.


Development of a Fluidized Bed CVD System for Coating UO2 Particles with Tungsten

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