GRAPHITE-MATRIX NUCLEAR FUEL SYSTEMS FOR THE PEACH BOTTOM HTGR

Technical Report · Wed Feb 20 00:00:00 EST 1963

OSTI ID:4675616

Ragone, D V; Goeddel, W V; Zumwalt, L R

A summary of the development and evaluation of pyrolytic-carbon-coated carbide fuel particles and graphite matrix fuel compacts is presented. A process that was developed for the preparatlon of particles of thorium -uranium dicarbide is described. Granulated particles composed of powdered UO/sub 2/, ThO/sub 2/, and carbon were suspended in- a bed of graphite fiour and heated to convert the oxides to dicarbides. The particles were then melted to densify and spheroidize them, while the graphite flour kept them separated so they would not flow together. Coating the (Th, U)C/sub 2/ particles with pyrolytic carbon was accomplished in a fluidized-bed apparatus using a methane --helium mixture at a temperature of approximates 1400 deg C. Data are presented on the properties of coatings. Graphite - matrix fuel compacts of high density were prepared by a hot- pressing process. Graphite flour was used as the filler and pitch as the binder; the use of graphite flour, rather than coke, permitted the attainment of good thermal properties in the compacts without the necessity for high processing temperatures. The hot-pressing process is described and the properties of the compacts are given. The thermal stability of coated fuel particles was evaluated at temperatures to 2000 deg C and for times up to one year. Some coated particles were found to fail in thermal gradient tests because of the movement of the particle through the coating on the hightemperature side; this was named the amoeba effect.'' Tests of coated particles prepared by the techniques described showed that there should be no thermal instability at temperatures up to 1500 deg C for periods of at least three years. Results of extensive irradiation tests of graphitematrix fuel compacts prepared by the hot-pressing process are presented. The compacts containing uncoated (Th,U)C/sub 2/ particles were dimensionally stable after burnups of 6.9 x 10/sup 19/ fissions/cm/sup 3/ at 1100 to 1500 deg C. Compacts containing coated particles were tested to burnups of 1.2 x 10/sup 20/ cent of the particle coatings were found to be broken after these tests. Possible explanations for these failures are presented. (Th,U)C/sub 2/ fuel particles coated with pyrolytic carbon had good xenon retention at first, but degradation occurred as high fuel burnup was achieved. Barium was found to permeate pyrolytic-carbon coatings which were impermeable to xenon, particularly at temperatures above 1400 deg C. Retention of iodine and tellurium by carbon coatings, although not quite as good as xenon retention, was much better than iodine and tellurium retention by uncoated rate of release of Xe/sup 133/ from coated and uncoated (Th,U)C/sub 2/ fuels was measured at 1000 to 1700 deg C. The release of Ba/sup 140/, Te/sup 132/, and I/sup 133/ was also determined for lightly irradiated samples. Xe/sup 133/ release was interpreted in terms of the equivalent spheres'' approach. Release rates for shorthalf-life xenon predicted by this treatment were in approximate agreement with steady-state Xe/sup 138/ and Xe/sup 139/ release rates obtained out-of-pile for uncoated (Th,U)C/sub 2/ particles by using an electron linear accelerator to produce a steady rate of photo fissions. Data for Kr/sup 85m/, Kr/sup 87/, Kr/sup 88/, and Kr/s up 89/ were also obtained in these out-of-pile experiments. Inpile experiments on samples of coated particles were performed to determine the effects of high fuel burnup and temperature on the retention of krypton and xenon fissionproduct nuclides. Activation energies for release were found to be about 29 kcal/mole for krypton and 39 kcal/ mole for xenon. The results of these studies show that hotpressed graphite - matrix fuel compacts containing pyro lytic-carbon-coated (Th,U)C/sub 2/ fuel particles will perform satisfactorily at the conditions to be encountered in the Peach Bottom HTGR (maximum temperature less than 1500 deg C in a purged fuel element). (auth)

• Research Organization: General Atomic Div. General Dynamics Corp., San Diego, Calif.
• DOE Contract Number: AT(04-3)-314
• NSA Number: NSA-17-031727
• OSTI ID: 4675616
• Report Number(s): GA-4002
• Resource Relation: Other Information: Orig. Receipt Date: 31-DEC-63
• Country of Publication: United States
• Language: English

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REACTOR TECHNOLOGY
ANNEALING
BARIUM
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BURNUP
CARBIDES
CARBON
COATING
COMPACTING
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ENERGY
FABRICATION
FAILURES
FISSION PRODUCTS
FUEL ELEMENTS
FUELS
GRAPHITE
GRAPHITE MODERATOR
HALF-LIFE
HEAT TREATMENTS
HELIUM
HIGH TEMPERATURE
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IODINE
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KRYPTON
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LINEAR ACCELERATORS
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METHANE
MIXING
PARTICLES
PHOTOFISSION
POWDERS
PREPARATION
PRESSING
PRESSURE
PYROLYSIS
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TELLURIUM
TELLURIUM 132
TESTING
THORIUM CARBIDES
THORIUM OXIDES
URANIUM CARBIDES
URANIUM DIOXIDE
XENON
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XENON 139