In some situations the regulator can ask to suspend manoeuvring, for example if the physic-chemical characteristics of the core indicate a leak of a fuel element or another malfunction. Load following operation is implicitly permitted by the licenses, and has been practised since many years, in fact from the beginning of operation. License conditions describe the permitted rates of power change, the maximum frequency of power variation and further operational details. Requirements due to “conditions of safe operation’’ give additional constraints on load following operation, i.e. conditions arising from measures on fatigue safety.