Contamination time behavior

Another study (Marble, 1985) showed that the time behavior of the contamination buildup in different BWR plants may exhibit significant differences. Usually, the buildup is a logarithmic or parabolic function of time, possibly indicating that the incorporation of dissolved radioactive cobalt species into the oxide layers on the surfaces of the materials is the responsible mechanism. In individual cases, however, pronounced increases in the radiation levels were observed in the first... 

Skaret presents a general air and contaminant mass flow model for a space where the air volume, ventilation, filtration, and contaminant emission have been divided for both the zones and the turbulent mixing (diffusion) between the zones is included. A time-dependent behavior of the concentration in the zones with constant pollutant flow rate is presented. 

On the contaminated and slightly hydrophobic surface, the spherical droplets grow continuously with time, as shown in the sequence of images in Figure 11. This behavior is... 

These tests can also be used to evaluate the induction time for the start of an exothermic decomposition, and the compatibility with metals, additives, and contaminants. The initial part of the runaway behavior can also be investigated by Dewar tests and adiabatic storage tests. To record the complete runaway behavior and often the adibatic temperature rise, that is, the consequences of a runaway, the accelerating rate calorimeter (ARC) can be used, although it is a smaller scale test. 

Explanation of Principal Application Codes 1 = screening 6 = reaction due to oxidation 2 = thermal stability 7 = runaway behavior (initial phase) 3 = sensitive thermal stability 8 = complete runaway behavior and 4 = very sensitive thermal stability simultaneous pressure measurements 5 = study autocatalysis, contaminations, 9 = time to maximum rate of reaction inhibitor depletion ... 

Figure 10.1b shows spatial concentration profiles within the column, at different snapshots in time. Note that the profile spreads with increasing travel distance (and thus with increasing time). The positions (distances) noted by the points and correspond to the times and shown in Fig. 10.1a. The effect of retardation, caused by the additional mechanism of chemical adsorption, is shown in Fig. 10.1c both the average velocity of the contaminant (corresponding to the point dc = 0.5) and the degree of spreading around this value are reduced. This behavior is discussed further in Sect. 11.1.

Fig. 10.1 Effect of different mechanisms on behavior of contaminants advancing through a column of porous material the relative concentration is given by c/c. (a) temporal breakthrough curves at the column outlet, showing effects of diffusion and dispersion (b) spatial concentration profiles along the column, at different times (c) spatial concentration profiles illustrating effects of retardation caused by contaminant absorption.

To account for the effect of a sufficiently broad, statistical distribution of heterogeneities on the overall transport, we can consider a probabilistic approach that will generate a probability density function in space (5) and time (t), /(i, t), describing key features of the transport. The effects of multiscale heterogeneities on contaminant transport patterns are significant, and consideration only of the mean transport behavior, such as the spatial moments of the concentration distribution, is not sufficient. The continuous time random walk (CTRW) approach is a physically based method that has been advanced recently as an effective means to quantify contaminant transport. The interested reader is referred to a detailed review of this approach (Berkowitz et al. 2006). 

The behavior of nonaqueous phase liquids (NAPLs) as they enter the partially saturated subsurface from a land surface source follows two well-defined scenarios in one case, the physical properties of the NAPL remain unchanged, while in the second case, NAPL properties are altered during transport. In the case of dense NAPLs, the contaminant plume reaches the aquifer and is subject to longterm, continuous, slow local redistribution due to groundwater flushing-dissolution processes. These plumes become contamination source zones that evolve over time, often with major negative impacts on groundwater quality. 

---