Void condition

Void coefficients were measured through the use of thln-wall aluminum tubes. The reactivity differential between the void and no-void condition was evaluated by a measurement of the change in t e reactor period between the two conditions with the core fully reflected. 

Figure 6.4 Thermal Flux for Varying Temperature and Void conditions in Undermoderated and Overmoderated Fuel...

Fig. 7.6 Relative changes in neutron production and absorption in homogeneous cores with and without ZrHi.7 layer at complete void condition...

Fig. 7.7 Neutron spectra of homogeneous Super FR core at complete void condition (1)...

This equation shows that there are three options for reducing the local void reactivity of a seed assembly decreasing the fission rate, increasing the neutron leakage rate, or increasing the neutron absorption at the void condition. Two of them are realized by inserting the ZrHj 7 layer between the seed and blanket assemblies. This layer slows down the fast neutrons leaked from the seed assemblies at void condition and decreases the fast fission at blanket assemblies. More neutrons moderated by the layer will be absorbed in blanket assemblies this increases the neutron absorption at the void condition. Therefore, the fuel assembly... 

Similar behaviour occurs when trying to locate voids in concrete cast behind steel plates, e g. the steel liner in nuclear containment walls. Our own experience has shown that in the case of a steel liner (encast at depth 250 mm) the reflected compression waves are dominant regardless of the condition of the concrete behind the plate. 

In extensively deionized suspensions, tliere are experimental indications for effective attractions between particles, such as long-lived void stmctures [89] and attractions between particles confined between charged walls [90]. Nevertlieless, under tliese conditions tire DLVO tlieory does seem to describe interactions of isolated particles at tire pair level correctly [90]. It may be possible to explain tire experimental observations by taking into account explicitly tire degrees of freedom of botli tire colloidal particles and tire small ions [91, 92]. 

Maintenance of conditions ia the culture environment that keep stress to a minimum is one of the best methods of a voiding diseases. Vacciaes have beea developed agaiast several diseases and more are under development. Selective breeding of animals with disease resistance has met with only limited success. Good sanitation and disiafection of contaminated faciUties are important avoidance and control measure. Some disiafectants are Hsted ia Table 6. Poad soils can be sterilized with burnt lime (CaO), hydrated lime [Ca(OH)2], or chlorine compounds (12). 

Gases and vapors permeate FEP resin at a rate that is considerably lower than that of most plastics. Because FEP resins are melt processed, they are void-free and permeation occurs only by molecular diffusion. Variation in crystallinity and density is limited, except in unusual melt-processing conditions. 

Dielectric Strength. Dielectric failure may be thermal or dismptive. In thermal breakdown, appHed voltage heats the sample and thus lowers its electrical resistance. The lower resistance causes still greater heating and a vicious circle, leading to dielectric failure, occurs. However, if appHed voltage is below a critical value, a stabilized condition may exist where heat iaput rate equals heat loss rate. In dismptive dielectric failure, the sample temperature does not iacrease. This type of failure is usually associated with voids and defects ia the materials. 

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