Irradiation of Metal-Fiber-Reinforced Thoria-Urania

Autor: J. H. Kittel, C. L. Hoenig, L. A. Neimark
Rok vydání: 1963
Předmět:
Zdroj: Journal of the American Ceramic Society. 46:219-224
ISSN: 1551-2916
0002-7820
Popis: Randomly oriented fibers of either molybdenum or niobium were incorporated into hot-pressed pellets of 10, 30, and 50 wt% UO2 in ThO2 to improve the thermal conductivity and the thermalshock resistance. Pellets 3/8 in. in diameter and about 3/8 in. long were irradiated in NaK capsules either bare or jacketed in Zircaloy-2 with the annulus between pellet and jacket filled with lead or helium. The pellets were irradiated to burnups ranging up to 34,500 Mwd per ton of oxide (1.0 × 1021 fissions per cm3) at central temperatures of the order of 3000°C. Fracture and metallographic sections of the irradiated specimens confirmed out-of-pile measurements that the molybdenum fibers increased the effective thermal conductivity of the mixed oxides. It was possible to give the fibered pellets higher heat ratings than the unfibered pellets before comparable thermal effects occurred. The fibers tended to reduce central-void formation, to retard columnar recrystallization, and to maintain the integrity of the pellet. In some heliumbonded specimens, the molybdenum fibers coalesced into a central sphere after melting. The coalescence did not occur in lead-bonded specimens. The niobium fibers were found to react with the oxides. Fission gas release from unclad fibered pellets was a maximum of 15.3% of theoretical at a burnup of 31,500 Mwd per ton of oxide (8.3 × 1020 fissions per cm3) and aκdθ value of 57 watts per cm. Gas release from similarly irradiated unfibered pellets was a maximum of 6.3% at 21,800 Mwd per ton of oxide (6.6 × 1020fissions per cm3) and an initial κdθ value of 92 watts per cm. The disparity in gas release was attributed to the breaking into pieces of the unfibered pellets early in the irradiation and their consequent operation at significantly lower temperatures than the fibered pellets.
Databáze: OpenAIRE
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