A thermal stress mechanism for the fragmentation of molten UO2 upon contact with sodium coolant

Thermal stress initiated fracture as a fragmentation mechanism in the UO2-sodium fuel-coolant interaction

“…In contrast to the molten drop models, recent efforts to take into account the possibility of solidification of the hot material have resulted in solid shell theories of fragmentation (76)(77)(78)(79) (80) was used.…”

“…However, further experimental and analytical work is necessary to establish firm verification of this model. The velocity of the liquid-solid interface versus time determined from the heat transfer process (77) 45 3.3…”

“…Several other parametric evaluations were carried out by Cronenberg, as well (77) . A comparison of the transient numerical solution with the steady-state approximation of London and Seban (80) used by Hsiao (76) was made (Figure 3.5 It is this potential energy, as ascertained by…”

“…Net rate of solid growth versus temperature as determined from crystallization theory (77) .... 47 3.4 Comparison between the solidification rates for a convective heat transfer boundary condition and a constant surface temperature (76) The outer surface tangential stress components versus time; U0 9 in Na (a (0~) = 0.0; a t Kinetic energy versus half crack length (89) ... Tensile stress to sustain crack velocity versus propagation velocity (92) 68 4.5 Crack length versus elapsed time after initiation of crack 70 4. 6 Crack propagation velocity versus crack length (89) 71 4.7…”

“…Incorporation of the erf X term results from the movement of the solidification front in the UCU and its value is determined from the transcendental equation (77) (82) with the temperature in the solidified shell given as The selection of the nucleate boiling coefficient for use was based on the prediction of Henry's correlation (86) which required a temperature of 9500°C for Na film boiling. Several other parametric evaluations were carried out by Cronenberg, as well (77) .…”