Nuclear stress tests: Q&A
What are nuclear stress
"stress tests" are a set of additional safety
criteria drawn up in the light of the nuclear
accident in Fukushima. These EU wide tests will
be in addition to safety standards already 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
The aim is to learn from what happened in Japan
and help 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 disasters can hit at
the same time and knock out the electrical power
supply system completely. In Japan, 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 assessed in the stress tests?
be assessed whether the nuclear power plant can
withstand the effects of the following events:
1. Natural disasters: earthquakes, flooding,
extreme cold, extreme heat, snow, ice, storms,
tornados, heavy rain and other extreme natural
2. All man-made failures and actions. These
accidents can be: air plan crashes and
explosions close to nuclear power plants,
whether caused by a gas container or an oil
tanker approaching the plant, fire. Comparable
damaging effects from terrorist attacks (air
plan crash, explosives) are also covered.
3. Preventive and other terrorist and malevolent
Preventive measures for terrorist attacks –
meaning all measures which should stop an attack
from happening in the first place - will be
dealt with separately, involving experts such as
anti-terrorism experts, officials of ministries
for national security. The reason is that these
concerns are issues of national security.
Measures taken to counter terroristic acts
cannot be made public – while the stress tests
will be published. On these issues, the
Commission will work together with Member
An example of preventive measures which have
been mentioned in the public are fog systems
which produce fog when an airplane is getting
close to the nuclear power plant. The fog
impairs the view of pilot thus making it
virtually impossible to target the nuclear power
What about the power cuts?
Irrespective of the cause (natural disaster or
whatever), power plants have to prove that they
have enough back-up power systems in place in
case the power supply is interrupted. They
should assume that power is completely lost for
several days. They also have to describe what
happens when the first back-up-system – the
battery - does not work, the second, thus
describing a chain reaction.
What will be assessed in detail? How do you
assess natural disasters?
Earthquakes already reviewed in the past: 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. Higher safety margin in stress
test: 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.
In practice, this means that at this magnitude
all the safety functions are working – that the
reactor can be shut down safely, that there is
still supply of electricity and that radioactive
materials are confined to prevent releases. The
same is with floods and other natural disasters.
Is there an EU definition of this "higher
No. It would not make sense to say that all 143
nuclear power plants have to withstand an
earthquake of Richter Scale 8 or so, as this
would put an unnecessary burden to those plants
which are not in a zone with earthquake risks or
where risk are much lower. For this reasons, it
is the national regulator which has to define
this additional safety margin.
How do you assess airplane crash? And
terrorist attacks? Explosions?
From the way a power plant is constructed, it is
possible to say whether a crash will seriously
damage the containment of the nuclear power
plant or not. Engineers take the following data
to make their calculations: the materials used (beton,
steel), the thickness of the walls and the data
of the airplane – the weight of the plane and
the speed with which the plane apporaches the
plant. As the effect on the plant is measured –
whether it damages the containment and/or sets
it on fire – it does not make a difference
whether it was an accident or a deliberate act
The same is true for explosions or fire. Experts
can tell from the design of the plant whether a
power plan can withstand a fire or an explosions
happening close to the plant. Whether it was
caused by accident by a gas container or an oil
tanker, or whether terrorists did use
explosives, does not make a difference.
How will the test be carried out?
Tests will be carried out at three levels:
1. Pre-Assessment: The plant operators have to
answer all the questions in the stress tests
questionnaire and describe how the plant would
react in different situations. To support what
they say, they have to submit engineering
2. National Report: In the second step, the
national regulator will look at the
pre-assessments and check whether the
assumptions are credible. As they know the
particular design of the plants and have made
controls on the spot, they are best placed to do
3. Peer Reviews: In a third step, the national
report of the regulator will be reviewed by
other regulators within European Nuclear Safety
Regulators' Group (ENSREG), which represents the
27 independent national authorities responsible
for nuclear safety in their country. This will
be done by peer teams consisting of seven people
- one European Commission representative
- two permanent ENSREG members. They will be
part of all the peer review teams cross-checking
the 14 national reports of all the Member states
having nuclear power). This is to guarantee the
consistency of the tests.
- four non-permanent ENSREG members.
The composition of each of the teams will be
decided together by the EU Commission and ENSREG.
Are you also going inside the plants to make
Yes. Peer Reviews teams are explicitly allowed
to go into the plants. Member States have to
give them access to power plants and help them
in any way to do their controls on the spot.
Are their independent experts in the teams?
National regulators are by definition
independent from their governments and industry.
Scientists, NGOs and experts from nuclear fields
will be able to discuss the results of the
stress tests as they will be made public and
also discussed in seminars.
Is this credible, if the national regulators
check what they already have checked?
New criteria: 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, air plane crashes and back-up
systems for power supply.
Peer Reviews: The 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.
Transparency: All national reports and the
results of the peer reviews will be made public.
Results should be discussed both in seminars
where independent experts, non governmental
organizations and experts from the field should
When will the tests start?
On 1 June at the latest.
When will we have the final results of the
By the end of April 2012.
Some Member States already conducted their
national stress tests. Does this mean they do
are not taking part in the EU tests?
Some Member Stats have started early on the
basis of what was discussed in ENSREG. We expect
that any addition made in the course of the
definition of the EU wide process will be taken
Will all the nuclear power plants be tested?
Yes. All existing and planned plants in the EU
will need to be reassessed using the agreed
common criteria and methodology.
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, we believe 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 to explain to its
public why it has taken a decision or failed to
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
What happens after the report is made?
The European Council called on the Commission to
review the existing EU nuclear safety framework.
The Commission's proposals will take fully into
account the results of the stress tests. 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.