BREAK-UP TIME OF FRAGMENTING - SOLIDIFYING UO-2 SPHERES WHEN QUENCHED IN SODIUM
In this contribution the solid shell of a breezing UO-2 drop is continuously subdivided in a plastic or ductile layer for 1300**oC<T<2850**oC and a brittle one for 945 < T < 1300 degrees C. Cracking occurs in the brittle layer only. In the present model a layer of a predescribed depth is assumed to ablate instantaneously, when the temperature reaches the transition point of elastic or ductile behavior (T=1300 degrees C) at its inner boundary. A new layer is formed within a time step, governed by the heat conduction equation. The discontinuous ablation process is thus related to the continuous progression of the solidification front. A calculation of the fragmentation time is possible: in principle it comprehends the summation of a large number of time steps for the formation of brittle layers. The parametrizing of the thickness of the cracked brittle layer, the concept of instantaneous ablation are minor changes that make the thermal stress model more realistic: it can explain, why UO-2 does not fragment in argon and water. The fragmentation time assessed for a UO-2 drop of certain specifications is given.
Bibliographic Reference: NUCLEAR ENGINEERING AND DESIGN, VOL. 80 (1984), PP. 19-25
Record Number: 1989123081400 / Last updated on: 1987-01-01
Available languages: en