30 Containment systems Deterministic method

Risk Assessment Systems. Most of the techniques, design methods and applications in this book are deterministic. That is, some worst-case accident is assumed to happen, its effects are calculated to the best of our ability, and systems or structures are then designed to contain, suppress or mitigate the explosion accident effect. 

Investigating the behaviour of small systems , i.e. the case when the number of particles is small , fluctuation phenomena are very important. More precisely they cannot be interpreted as the superposition of certain deterministic behaviours, as they are the very phenomena under observation. A thermodynamic description of small systems was attempted by Hill (1969). Under the traditional conditions of chemists, small systems are rather rare e.g. 10 molecules (which are considerably less than Avogadro s number) are contained in the volume of 10 ml of a 10 mol dm" solution. Such small volumes are availabe to experimentalists using optical or sometimes electrical methods. 

The kinetics for catalytic systems can be modeled by one of two general methods. The first is based on continuum concentrations and uses deterministic kinetics whereas the second approach follows the temporal fate of individual molecules over the smface via stochastic kinetics. Both approaches have known advantages and disadvantages, as will be discussed. B These methods provide the constructs for simulating the elementary kinetics. However, in order to do so, they require an accurate and comprehensive initial kinetic database that contains parameters for the full spectra of elementary surface processes that make up the catalytic cycle. The ultimate goal for both approaches would be to call upon quantum mechanics calculations in situ in order to establish the potential energy surface as the simulation proceeds. This, however, is still well beyond our computational capabilities. 

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