Void collapse

Plastic strain localization and mixing due to void collapse in porous materials works in the same way, with perhaps an even greater degree of actual mixing due to jetting, and other extreme conditions that can occur at internal free surfaces in shock-loaded solids. 

K. Solanki et al Multiscale study of dynamic void collapse in single crystals. Mech. Matls. 

Figure 12. Initiation of chemical reactions due to void collapse in a REBO 2D diatomic (AB) solid.

The basic questions concerning shock void collapse are outlined in Fig. 

In an explosive compact voids exist between the grains, and during shock or impact the voids collapse rapidly. Any plastic flow of material may also aid in sealing the gases in the spaces. The adiabatic heating process is, therefore, likely to be of major importance in providing hot spots and initiating fast decomposition in explosives of less than theoretical density. 

To identify the probable cause of the transients, 20 postulates were studied and 14 of them were tested during reactor operation. Based on recorded observations, calculations, tests and analysis, inadvertent raising of CR by operator just before the incident was ruled out. The postulates studied can be broadly classified into the following five categories viz. process parameter changes, absorber movement, voids collapse and sodium filling, fuel movement and moderator ingress ... 

Coagulation in the spin bath produces filaments that are extremely porous for reasons to be discussed later. Even after orientational drawing of the fiber, the void volume fraction can be over 50%. The wet-porous fiber is taken over two pairs of steam-heated rolls, where the voids collapse and the porosity is eliminated in the course of drying. At this point, the fiber density approaches the polymer density of 1.17 g/cm. ... 

Operator increased feed flow. Automatic rods withdrawn to maximum extent. Further withdrawal of manual rods to compensate for loss of reactivity due to void collapse with channel inlet temperature reduction. Drum level started to rise again. Steam pressure fell... 

Why does not the void collapse unto itself The architecture of the void is shaped by the behavior of this tiny entity called electron. In general, all chemical matter and its various interaction modes abide by the rules of the electronic behavior. In this sense, chemical matter is unique because the electron is an elementary particle and hence chemical patterns cannot be further reduced or reconstructed from bottom up (i.e. from more elementary constituents). 

High reactor vessel pressure which can happen due to MSIV closure, void collapse, or failure to open pressure relief valve... 

Lundstrom, T.S. Bubble transport through constricted capillary tubes with application to resin transfer molding. Polym. Compos. 1996, 17, 770-779. Lundstrom, T.S. Void collapse in resin transfer molding. Composites A 1997, 28A, 201-214. 

The limiting ATWS events differ among PWRs, BWRs, and the Super LWR due to their design differences. Loss of the heat sink at the secondary system is the most important event for PWRs because it is accompanied by an increase in the coolant temperature and then rapid pressurization at the primary system. Pressurization is the most important event for BWRs because it is accompanied by considerable increases in the reactivity and power caused by void collapse. Loss of flow is the... 

Although two phase flow exists in the core at pressurization phase, the increase in the power is very small at pressurization events unlike BWRs. It is because the quality or void fraction is very small during the pressurization phase, and hence the increase in the coolant density by void collapse is also small. 

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