Presentation on theme: "Raymond S. Troy, Robert V. Tompson, Jr., Tushar K. Ghosh and Sudarshan K.Loylalka Particulate Systems Research Center & Nuclear Science and Engineering."— Presentation transcript:
Raymond S. Troy, Robert V. Tompson, Jr., Tushar K. Ghosh and Sudarshan K.Loylalka Particulate Systems Research Center & Nuclear Science and Engineering Institute, University of Missouri, Columbia, MO 65211
Made up of about 400,000 pebbles Online refueling Fission potential measured when removed from reactor Remain in cycle up to 6 years (~10 trips)
As the reactor operates, the pebbles are in contact with each other, the fuel handling system, and reactor components (pressure vessel, etc.) and graphite dust is produced. For many reasons, information about this dust must be collected. Our goal is to characterize graphite particles generated by fuel pebble abrasion
Safety Modeling ▪ “the production of dust by fuel element abrasion and its effect on fission product transport…would complete a comprehensive model for the core release behavior under normal operating conditions 1.” ▪ Data provided to codes Accident mitigation ▪ Amount of dust Inhalation ▪ Cancer/dose calculations 1. http://www.iaea.org/inisnkm/nkm/aws/htgr/fulltext/29009817.pdf
Operation Radioactivity levels ▪ Estimate radioactivity levels in the loop Mechanical ▪ Clogs ▪ Length of pebble life Re-suspension ▪ Depressurization of the loop may cause re-suspension of dust Modeling of thermophoresis ▪ Uneven distribution of particles along loop 1. http://www.iaea.org/inisnkm/nkm/aws/htgr/fulltext/29009817.pdf
Size Distribution Mean, Standard Deviation and Median calculated Loading and rotational speed measured SEM images of sample and abraded particles Unbraded Surface roughness BET surface area, pore analysis Humidity and temperature in room
Our experimental apparatus allows us to control loading, atmosphere, rotation speed, graphite type and the shape of the graphite interface.
Measures particle size distributions in the diameter range 2.5 nm to 1000 nm Pulls vacuum of 2.4 L/min and particles are drawn into the machine http://www.tsi.com/Scanning-Mobility-Particle-Sizer-Spectrometer-3936/
http://www.tsi.com/Aerodynamic-Particle-Sizer-Spectrometer-3321/ Measures particle size distributions in the diameter range 500 nm to 20,000 nm Pulls vacuum of 5 L/min and particles are drawn into the machine
The loading between the two hemispheres is measured by a Mettler Toledo Scale, model number PBA 430, with an IND 560 readout having accuracy to 0.001 kg. The rotational speed is determined by the machine’s preset speeds.
Samples were prepared Machined inserts The assembly was dismantled and cleaned Background samples were taken With graphite samples in cylinder Machine was started Loading set Collection of data
Diameter of most of the pores is in the range of 10 to 60 Å.
Total cumulative pore volume was found to be 1.213 cm 3 gm −1. Porosity of the generated particle is about 68%.
Measured with a atomic force microscope (AFM) Average Ra of pre abraded samples was 0.96 µm The AFM did not have capability to measure post abrasion surface roughness (too rough) We have a new method to measure surface roughness and this will not be an issue for future tests
The size distribution and the concentrations change with time wear has a strong effect on particle generation rate as well as size, and physical/mathematical models for particle generation should account for the aging of the pebbles. Time changes at what size particles are generated
Certainly, with different loadings, graphites, atmospheres, and rotational speeds the particle size distributions will change models for particle generation will need to account for abrasive effects
Dry Air (to produce dusting effect) Reactor grade graphite Shape of interface (disk, point) Sliding abrasion Wear Rate Statistical Fit of size distribution Temperature and Humidity measurements inside chamber Surface roughness before and after test