Regulatory oversight consists of 4 main instruments: licensing, inspection, assessment and enforcement.
Licensing is the regulatory instrument used prior to the commencement activity: the authority judges before the commencement of the activity whether its implementation will comply with the requirements, and if necessary specifies additional conditions and respective tasks.
Inspection typically takes places during the realization of the activity; it reveals the facts and circumstances of the activities and, in addition, it gives opportunity for intervention in the implementation phase.
The authority performs the assessment typically after termination of an activity or a process, so the conclusions are drawn subsequent to the completion of the activity or the process, the feedback therefore is an essential part of this regulatory instrument, by which the failures revealed can be avoided next time.
Licensing, inspection and assessment are not fully separate instruments: they may and frequently must supplement each other for the appropriate oversight of a certain case.
Enforcement means fine for most of us, however in the nuclear field the fine is the ultimate instrument. The authority has a lot of opportunities for the intervention before imposing a fine to enforce the compliance with a legal requirement or regulatory decision.