Randomly oriented fibers of either molybdenum or niobium were incorporated into hot-pressed pellets of 10, 30, and 50 wt% UO/sub 2/ in ThO/sub 2/ to improve thermal conductivity and thermal shock resistance. Pellets, 9.5 mm in diameter and 9.5 mm in length, were irradiated in NaK capsules, both bare and jacketed with Zircaloy-2, with the annulus between pellet and jacket filled with lead or helium. They were irradiated to burnups ranging up to 34 500 Mwd/T (1 0 x 10/sup 21/ fiss/cc) at central temperatures of the order of 3000 deg C. Integral kd theta values ranged from 34 to …
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Randomly oriented fibers of either molybdenum or niobium were incorporated into hot-pressed pellets of 10, 30, and 50 wt% UO/sub 2/ in ThO/sub 2/ to improve thermal conductivity and thermal shock resistance. Pellets, 9.5 mm in diameter and 9.5 mm in length, were irradiated in NaK capsules, both bare and jacketed with Zircaloy-2, with the annulus between pellet and jacket filled with lead or helium. They were irradiated to burnups ranging up to 34 500 Mwd/T (1 0 x 10/sup 21/ fiss/cc) at central temperatures of the order of 3000 deg C. Integral kd theta values ranged from 34 to 129 w/cm. Fracture and metallographic sections of the irradiated specimens confirmed out-of-pile measurements that the molybdenum fibers increased the effective thermal conductivlty of the mixed oxides. It was possible to give the fibered pellets higher heat ratings than unfibered pellets before comparable thermal effects occurred. The fibers tended to reduce central void formation, retard recrystallization, and maintain the integrlty of the pellet. In some helium- bonded specimens, the molybdenum fibers coalesced into a central sphere after melting during irradiation. The coalescence did not occur in lead-bonded specimens. The niobium fibers were found to react with the oxide. Fission gas release from unclad fibered pellets was a maximum of 15.3% of theoretical at a burnup of 3l,500 Mwd/T (8.3 x l0/0 fiss/cc) and an integral kd theta value of 57 w/cm. Gas release from similarly irradiated unfibered pellets was a maximum of 6.3% at 21,800 Mwd/T 16.6 x 10/0 fiss/cc) and an integral kd theta value of 92 w/ cm. The disparity in gas release is 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. (auth)
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Neimark, L. A.; Kittel, J. H. & Hoenig, C. L.Irradiation of Metal-Fiber-Reinforced Thoria-Urania. Final Report- Metallurgy Program 6.2.4,
report,
December 1, 1961;
Illinois.
(https://digital.library.unt.edu/ark:/67531/metadc1061347/:
accessed September 13, 2026),
University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu;
crediting UNT Libraries Government Documents Department.