First-order point process deposition

Taking into account that development of a comprehensive model is not feasible given the current state of knowledge, a simple kinetic model Actranf has been elaborated by Harper et al. (1992). In this model, the primary circuit is divided into three main sections the coolant, the in-core surfaces and the out-of-core surfaces. Cobalt is introduced into the system by release from circuit materials, either as Co from any point in the circuit or as Co from activated materials in the neutron field. Both isotopes are removed from the coolant to the purification system by a first-order process, and are also removed from the circuit when they have been deposited on fuel assembUes that are withdrawn from the reactor in the course of refuelling. Co is converted to Co by neutron activation when it is deposited on fuel surfaces or when it is contained in the internals of the reactor pressure vessel. Thus, unlike the models described above, Actranf considers both possible Co sources the calculations showed that activation of Co which is temporarily deposited in the reactor core is only a small contributor when compared with the direct release of Co from in-core sources, in particular in plants equipped with Stellites inside the reactor pressure vessel. Distribution of cobalt isotopes around the surfaces of the primary circuit proceeds by exchange of dissolved species with the coolant deposition and re-release are assumed to be first-order processes. The first applications of the model to operating plants with and without Stellite materials in the primary circuit have yielded encouraging results. 

In processing VGO it has been argued that the heavy poly-aromatic structures characterised by the Ramsbottom Carbon Residue (RCR, Table 1) can be considered as coke precursors [8]. An increase of the boiling point of those structures via condensation reactions or dehydrogenation reactions is responsible for coke deposition onto the catalyst. In order to increase our level of understanding of these processes we consider first the effects of catalyst parameters on the coke formation. 

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