Overall Corrosion Scenario

It is possible to surmise, based on the foregoing discussion, that either one or all the following processes of corrosive attack may be involved  

In order to suggest preventive measures it is necessary to identify the corrosive mode in the system. The following outline of laboratory studies should help to identify the major corrosive mode. 

Measure potential-time curves for steel/Al couple in solutions of interest (tanks 3,4,5 compositions)  

Simulated laboratory corrosion rates of steel/Al in solutions of interest both with added copper and without copper  

---

Mass-transport (i.e., diffusion or electromigration) effects are particularly acute in the cases of cracking, pitting, and crevice corrosion, whereby occlusion effects can create highly concentrated solutions that move an otherwise stable system into regions of thermodynamic instability at the local level [13,14,41 3, 79-82]. When porous films or particular solution flow conditions exist, mass-transport effects should also be taken into account [83, 84]. Molecular dynamics and Monte Carlo simulations of interfaces over the past few decades have provided some insight into the concentration gradients that occur close to the electrochemical interface [85-91], and these, coupled with computational fluid dynamics simulations, can indicate the extent to which mass-transport effects can dominate an overall corrosion scenario [92]. 

Overall Scenario A release rates are shown in Figure 26. From the dumping in 1981, initially, no active material is expected to appear due to the hull and bitumen barriers. When it does start, the initial fission product and actinide release is less than 0.0001 GBq-a at the year 2105 when the fission product and actinide inventory in the corroded left board SG starts to appear. Corrosion of the outer surfaces of the activated RPVs by that time contributes about 8 GBq-a. ... 

Mixed Control In the previous two sections we have examined the kinetics of active gas corrosion from the standpoint of two limiting scenarios (1) surface reaction control and (2) diffusion control. Under many conditions, it is quite likely that one of these two processes will limit the overall rate of corrosion, and hence one of these two limiting models can be used to calculate the corrosion rate. Under certain conditions, however, the surface reaction and diffusion rates may be comparable, in which case both will influence the overall rate of corrosion. When two series processes both affect the overall rate, they essentially act as two series resistances. Like electronic resistors, these two kinetic resistances will add in series. However, it is important to keep in mind one key point the resistance of each process is effectively given by the inverse of its rate thus. 

---