The stress tests were conducted according to a common methodology along two parallel tracks:
- A Safety Track to assess how individual nuclear power plants can withstand the consequences of various unexpected events, ranging from natural disasters to human error or technical failure and other accidental impacts.
- A Security Track to analyse security threats and a methodology for the prevention of, and response to, incidents due to malevolent or terrorist acts. For the assessments under this second track, the Council set up the Ad-hoc Group on Nuclear Security (AHGNS).
Specifications on the safety track of the stress tests defined three main areas to be assessed: extreme natural events (earthquake, flooding, extreme weather conditions), response of the plants to prolonged loss of electric power and/or loss of the ultimate heat sink (irrespective of the initiating cause) and severe accident management.