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Nuclear Stress Tests - guide

11 May 2011
by eub2 -- last modified 11 May 2011

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


The aim is to learn from what happened in Japan and prevent that a similar accident can happen in Europe. One of the most important lessons to be drawn is that the unthinkable can happen – that two natural disaster can hit at the same time and knock out the power supply system completely. The power plant withstood the earthquake but the tsunami interrupted the power supply which is necessary to cool down fuel elements. If they are not cooled down, there is a risk of a core meltdown with leakage of radioactivity and radiation getting into the soil and the water.

What will be tested? Are we checking for the first time, whether EU nuclear power plants can withstand natural catastrophes?

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. If in a given region, earthquakes of a magnitude of Richter scale 6 took place, it was assumed that such an earthquake could happen again. Power plants constructed in this area therefore need to be built in a way that they can operate or shut down automatically if an earthquake of this scale occurs. The same is true for floods and other disasters.

As Fukushima has taught us that the magnitudes of earthquakes can be much higher than what we experienced in a region in the past, the stress tests include a higher safety margin. If a power plant was built to withstand a magnitude of Richter scale 6, it needs now to prove that it can withstand a higher magnitude. The same is with floods and other natural disasters.

In addition to this, irrespective of the cause, power plants have to prove that they have enough back-up power systems in place in case the power supply is interrupted. That includes batteries, diesel-generators. They have to describe what happens when the first back-up-system does not work, the second, thus describing a chain reaction.

Will man-made hazards also be included in the stress tests?

The European Council says that a "comprehensive" risk and safety assessment should be done. This could include also man made disasters.

Who sets the criteria?

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. No formal decision of the European Commission nor on minister level is needed.

Is there a deadline for the decision to be taken?

There is no deadline for adopting the stress tests.

What is WENRA? Why did they come up with draft proposals for a stress test?

The Western European Nuclear Regulators Association (WENRA) is the organisation of those EU Member States which had or have nuclear power. The European Council says that ENSREG and the Commission shall take use of "available expertise, notably WENRA". The decision is taken by ENSREG and the Commission.

Will all the nuclear power plants be tested?

Yes. All plants in the EU will need to be reassessed using the agreed common criteria and methodology.

How will the test be carried out? Is the EU sending experts to all 143 nuclear power plants in the EU?

It was never the intention that the EU would send its own experts to the nuclear power plants. The European Council says that the assessment is done by "independent national authorities and through peer review". 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.

Will there be also tests on the spot?

Whether this will be the case, and which nuclear power plants will be controlled on the spot, will be decided by the peer review team.

Is this credible, if the national regulators check what they already have checked?

They are not checking again what they have checked in the past. The stress tests will be a set of questions and criteria which are new. They include a higher safety margin for natural disasters and back-up systems for power supply. In addition, the international peer-reviews guarantee the credibility and accountability of the whole process. This is even more so the case, as out of the 27 national regulators only 14 have nuclear power and 13 have not.

What is the timetable for the stress tests?

The assessments will be launched as soon as possible. Based on the national reports and drawing from the available peer-reviews' outcomes, the Commission will present its views in an interim report to the European Council on 9 December 2011.

What will happen if a plant fails the tests?

On the basis of the national reports and the peer reviews' outcome, Member States will take decisions on how to follow up the outcome of the assessments. 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.

What happens, if a country does not shut down a plant which fails the tests?

The Commission will publish the report of the national authority and also the peer review. This means that the results are known to the public and a government has explain to its public why it has taken a decision or failed to act.

Given that disasters know no borders will the EU neighbours also implement these tests?"

The Commission is working to extend the assessments to other countries, in particular those neighbours operating nuclear installations: Switzerland, the Russian Federation, Ukraine and Armenia. The initial reactions have been positive. Russia has already made concrete proposals for improving the international nuclear safety framework.

The Commission is also ready to provide expertise to the IAEA and to third countries, both for carrying out safety reviews and for further developing the international legal framework and regulatory capacities in specific countries. It can also consider providing additional financial assistance to third countries.

What happens after the report is made?

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 (25/06/2009) gives legal force to some safety principles drawn up by the International Atomic Energy Agency (IAEA). It leaves the competence for enforcement of nuclear safety to Member States.

Source: European Commission