The "stress tests" are a set of additional safety criteria drawn up in the light of the nuclear accident in Fukushima. In addition to safety standards already being in place at national level, the EU will start nuclear stress tests. Their aim is to assess whether the safety margins used in the licensing of nuclear power plants were sufficient to cover unexpected events.

The criteria are defined and approved by both the European Commission and the European Nuclear Safety Regulators' Group (ENSREG), which represents the 27 independent national authorities responsible for nuclear safety in their country. This was decided by the European Council on 23 and 24 March 2011. Commissioner Günther Oettinger, responsible for Energy, is making the decision on behalf of the European Commission.

In addition, the test will be carried on by the independent national authorities and through peer review according to the European Council. This means that the national authorities responsible for nuclear safety are involved, they will produce reports which will be examined by a group of peers for consistency.

Each and every nuclear power plant in the EU has undergone an extensive authorisation process before starting to operate. If a nuclear power plant is operating in a region where there is a risk of earthquakes, operators needed to prove that the specific design of a power plant can withstand the magnitude of an earthquake that could be expected in the region. To assess the risk of an earthquake, past experiences are normally taken into account.

Member States will take decisions on how to follow up the outcome of the assessments on the basis of the national reports and the peer reviews' outcome. However, decisions on individual installations remain a national responsibility. In case an upgrade is technically or economically not feasible, reactors shall be shut down and decommissioned.

The Commission will make a proposal for revised legislation on nuclear safety in the light of the stress tests results in 2012. The existing nuclear safety directive gives legal force to some safety principles drawn up by the International Atomic Energy Agency (IAEA) and it leaves the competence for enforcement of nuclear safety to Member States.