5.38. Scenarios represent structured combinations of features, events and processes relevant to the performance of the disposal system. Different types of scenario are usually considered, including a ‘base case scenario’ and ‘alternate evolution scenarios’ (which will include disturbing processes and events). The various alternate scenarios considered in an assessment will have most features, events and processes in common with the base case scenario (also called the ‘reference scenario’, ‘expected evolution’, ‘normal evolution’ or ‘undisturbed performance’). However, some particular features, events and processes will differ between the scenarios, and these will characterize each particular scenario.