ARE NUCLEAR POWER PLANTS
SAFE?
7.1

Design: ASN and IRSN Communications Departments - May 2022
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ARE NUCLEAR POWER PLANTSSAFE?

NUCLEAR POWERIN FRANCEWorldwide, more than 440 nuclear reactors
generate around 10% of the world's electricity.
This figure reaches 30% in Europe and over 75%
in France, which has 56 pressurised water nuclear
reactors commissioned between the late 1970s
and early 2000s.

NUCLEAR SAFETY

MAP OF POWER PLANTS
IN OPERATION IN FRANCE

As with any high-risk activity,
the safe operation anddismantling of our facilities
is regulated, assessed andmonitored rigorously
and independently.

Gravelines

Commissioned: 1980
Reactors: 6

Chooz

Commissioned: 2000
Reactors: 2

PaluelCommissioned: 1985
Reactors: 4

Penly

Commissioned: 1990
Reactors: 2

Cattenom

FlamanvilleCommissioned: 1987
Reactors: 4

Commissioned: 1986
Reactors: 2

Nogent-sur-Seine
DampierreCommissioned: 1980
Reactors: 4

ChinonCommissioned: 1984
Reactors: 4

St-Laurentdes-EauxCommissioned: 1983
Reactors: 2

Commissioned: 1988
Reactors: 2

BellevilleCommissioned: 1988
Reactors: 2

Civaux

Bugey

Commissioned: 2002
Reactors: 2

in 2022
Nuclearpower

Le Blayais

900 MWe
reactorCommissioned: 1981
Reactors: 4

Commissioned: 1979
Reactors: 4

St-AlbanCommissioned: 1986
Reactors: 21300 MWereactorCruas

1450 MWereactor

Tricastin

GolfechCommissioned: 1991
Reactors: 2

DEBATE

Commissioned: 1980
Reactors: 4

Commissioned: 1980
Reactors: 4

Those in favour of nuclear power put forward the following arguments:

FOR OR AGAINST• It ensures that the electricity produced is competitively priced;

NUCLEAR
POWER
PLANTS?

• It is an energy source that emits virtually no CO2;
• The safety of nuclear facilities is subject to strict requirements;• Incidents are reported and analysed so that lessons can be learned.

Opponents respond as follows:• Nuclear operations have already caused serious accidents despite
the controls in place;• These accidents have contaminated the environment and led tohealth hazards;• The cost of decommissioning facilities and disposing of nuclear
waste is a cause for concern;• Some waste will have to be stored for thousands of years, raising
the question of safety and of the transmission of knowledge andskills to future generations.

7.2

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ARE NUCLEAR POWER PLANTSSAFE?

NUCLEARFISSION 

AND ITS RISKS
The word atom comes from the Greek atomos,
meaning "cannot be divided". However, atoms can be
broken. This phenomenon, known as nuclear fission,
produces intense heat that can be converted into
electricity in a nuclear power station! But this process
involves risks: the chain reaction could become arunaway reaction, dispersing radioactive atoms
known as fission products, for example.

THE CASE OF
URANIUM-235
When a uranium-235 nucleus is bombarded
by a neutron, it can break. Nuclear fission of an atomalways generates three phenomena:

EQUIVALENCE
10 gramsof enriched uranium
produce as much energy
as 1 tonne of coal.

1. HEAT IS PRODUCEDHeat is captured andconverted into electricity.
At the atomic level,fission releases energythat is incomparable
to other sources of energy.

Xenon-143

Barium-141

89 neutrons,
54 protons

85 neutrons,
56 protons

Uranium-235
143 neutrons,
92 protons

Strontium-90
52 neutrons,
38 protons

Krypton-92
56 neutrons,
36 protons

Yttrium-94
55 neutrons,
39 protons

Iodine-131

78 neutrons,
53 protons

Rubidium-98

2. TWO OR THREE NEUTRONSARE RELEASEDThey are projected with suchenergy that they can in turn breakother nuclei, releasing otherneutrons: a chain reaction canoccur that must be controlled.

Caesium-137

37 protons,
61 neutrons

55 protons,
82 neutrons

3. THE DEBRIS OF THE ORIGINALATOM REMAINS
All sorts of new radioactive bodies are
created. Their chemical nature is random:
it depends on the way in which the
92 protons contained in the nucleus of
the uranium atom are divided between
the two pieces resulting from the break.
These "fission products" are radioactive
because their number of neutrons isunlikely to be the same as that of natural
bodies. Moreover, because they radiate,
they can heat up the material they are an
integral part of, and must be cooled. They
constitute radioactive waste that will haveto be stored. It is essential to containthem so that they do not escape into
the environment.

In the caseof an atomic bomb,
the aim is to set off an
uncontrolled chain reaction
to produce maximum damage.
In a nuclear power plant, however,control rods and borated water
absorb neutrons to control
the chain reaction.

A LITTLE HISTORY
1938

Discovery of nuclear fission by German chemist
Otto Hahn and his assistant Fritz Strassmann, with thecontribution of an Austrian physicist, Lise Meitner.

1948

Commissioning of the Zoé installation,
France's first experimental reactor.

1956

In France, at Marcoule, commissioningof the first French reactor (G1)
to experimentally produce electricity.
Natural uranium graphite gas reactor (UNGG).

1977

Commissioning of reactor No.1
at the Fessenheim power plant in Alsace, the firstpressurised water reactor (PWR) in a vast
programme that would include
58 reactors.

7.3

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ARE NUCLEAR POWER PLANTS
SAFE?

HOW
A NUCLEAR
POWER PLANT
WORKS
In principle, a nuclear reactor can be compared toa gigantic pressure cooker. The steam created by
the heat of nuclear fission drives a turbine which,thanks to the alternator, produces electricity.

THE PEOPLEIN CONTROLCOOLING 
EVEN DURING SHUTDOWN

Operators control the plant's operation using
thousands of sensors. They activate valvesand pumps.

The fission products continue to release a lot of heat,even when the reactor is shut down and the chain
reaction has almost completely stopped.

NUCLEAR FUELThe fuel is placed in asteel pressure vessel filled withwater. Every second, billions ofatoms break, releasing enormous
amounts of energy. This heat
energy heats up the water in thereactor coolant system to atemperature of over 300°C
and a pressure of 150 bars.

REGULATION
The heat producedby the fuel is regulated
notably by the control
rods. This makes it
possible to adapt
electricity production
to consumer demand.

STEAM
GENERATOR
The hot water in the
coolant system heats
the water in the secondary
system, which istransformed into steam.

THE REACTOR PRESSURE
VESSELWith its 20-cm thick steel,it confines the 40 tonnesof nuclear fuel contained inmetal tube assemblies filledwith uranium oxide pellets.

REACTOR COOLANT
PUMPS
They circulate the water inthe reactor coolant system.

COOLING TOWER
This large tower helps
to cool the water. It is notnecessary for power
stations located by the sea
or near high-flow rivers.

THE TURBINE AND ALTERNATOR
The pressure of the steam turns theturbine that drives the alternator,
producing the electricity that istransported by very high-voltage lines.
Steam

Steam

REACTORCOOLANTSYSTEM
The water in thissystem neverleaves the reactor.

TERTIARY COOLING SYSTEM
This system takes water from a riveror the sea to cool the condenser.

Water
Water

SECONDARYCOOLING SYSTEM
The water in this systemchanges state, passing
successively between
liquid and gaseous
forms.

7.4

THE CONDENSER
After passing throughthe turbine, the steam
is cooled, transformed
back into liquid andreturned to the steam
generator for a new cycle.

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ARE NUCLEAR POWER PLANTS
SAFE?

THE SAFETY 
OF A NUCLEAR
POWER PLANT

Numerous mandatory safety systems are installed
in a power plant to reduce the risk of a severe
accident and limit its consequences.

CONTAINING RADIOACTIVEFISSION PRODUCTS
The metal cladding surrounding
the fuel and the reactor coolant
system (including the reactor
pressure vessel) form two
containment barriers.
In addition, the reactor building
itself acts as a third barrier.
On 900 MWe reactors, this barrier
consists of a prestressed concrete
enclosure with a steel shell.
On more powerful reactors,
a double wall of prestressed
concrete provides a containment
barrier.

REDUCING PRESSURE
IN THE EVENT OF AN ACCIDENT
In operation, the water is pressurised to 155 bar.
If there is a leak, the pressure rises in the reactor
building and could lead to loss of leaktightness.
In this case, a cold water circuit is triggered,lowering the pressure by spraying fine dropletsin the reactor building.

CONTROLLINGTHE CHAIN REACTION
Control rods and borated
water are used to control
the chain reaction.
The rods immediately shut
down the reactor in the eventof a malfunction orearthquake, for example.

DEPRESSURISING IN THE
EVENT OF AN ACCIDENT
If too much pressure threatens
the leaktightness of thebuilding, it is depressurisedby opening this circuit.
This is the last resort, as it
releases fission products
into the environment througha stack after filtering them.

COOLINGTO PREVENT CORE MELTDOWN
The plant is equipped to ensure continuous coolingof the fuel during operation, shutdown, and during
an accident.
There are redundant safety systems; injection
circuits can add water in the event of a leak, sothat the fuel is always cooled.
Even when shut down, circuits cool the reactor
core, which is heated by fission products.

Steam

Steam

REACTORCOOLANT SYSTEM
The water in thissystem never leaves
the reactor.

Water
Water

TERTIARY COOLINGSYSTEM
This system takes water froma river or the sea to cool thecondenser.

SECONDARY COOLINGSYSTEM
The water in this systemchanges state, passing
successively between
liquid and gaseous forms.

POWERING ALL
SAFETY SYSTEMS
Emergency generators keep pumps, measuring
instruments and valves running in the event ofa power failure.

SINCE THE
FUKUSHIMA ACCIDENTIn France, IRSN experts
have recommended the addition of
new safety systems: the "hard core".
On the basis of these recommendations,
ASN has imposed the installation of new equipmentin the power plants: "bunkerised" emergency
management centres, additional emergency
generators, etc.
In addition, EDF has set up a Nuclear Rapid
Action Force (FARN) to intervene at a site
in the event of an accident to restore
water, air and electricity supplies
in less than 24 hours.

7.5

Design: ASN and IRSN Communications Departments - May 2022
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ARE NUCLEAR POWER PLANTS
SAFE?

POWER PLANTS

AND PEOPLE

Nearly 30,000 people work in nuclear power plants
in France. In addition, 300,000 jobs are directly or
indirectly linked to power plants.

PEOPLE
AT THE HEART OF SAFETY
All kinds of professions are involved: valve makers,
engineers, electricians, control operators, etc.
Taking into consideration the organisational,social and human factors is therefore of crucial
importance.
Management, training, documents and working
methods are at the heart of industry concerns.
For example, each operator is trained for two years
to operate the reactors, and each year they return toa training course where they revise the conduct to be
adopted in the event of an accident.
ASN is responsible for labour inspections at nuclear
power plants.

PROTECTING
NUCLEAR WORKERS
Nuclear workers are more exposed to radiation than othercitizens. The legal limit on the dose of radioactivity they
can receive each year is set at 20 millisieverts instead of
1 millisievert for the general public.
They wear dosimeters to warn them of ambient doses andcalculate the dose they receive. They have regular medical
check-ups.
Epidemiological studies carried out on the health of CEA,
EDF and Orano staff show that their health is equivalent tothat of staff in large French companies.

SUBCONTRACTING

THE RISKS ASSOCIATED WITH
MALICIOUS INTENT
Nuclear facilities and the transport of radioactive substances
could be the target of malicious acts. Facilities are protected by:

80% of the work carried out on nuclear sites is carriedout by contractors. For example, during maintenancework on a power plant, known as "unit shutdowns",
when the reactors are temporarily shut down,around a thousand people carry out more than
10,000 operations, organised and planned by EDF.
Subcontractors are trained in radiation protection.
Checks and verifications are part of the quality rules.

• anti-terrorism measures, air traffic control, bans on flying overnuclear sites;• strengthening infrastructure and buildings;• implementation of procedures and resources to limit thepossible consequences of an attack.
These topics are examined by the Ministry of Energy's Senior
Defence and Security Official, with the support of IRSN.

DEBATESUBCONTRACTING

AND OPERATION
Subcontractors say that they are exposed to 80% of the doses
received during maintenance, even though they do not receive
the same medical monitoring because they travel so much, nor
the same benefits as the employees of the nuclear operators
for whom they work.
The number of levels of subcontracting worried the Frenchauthorities: up to 7 tiers of subcontractors were used in somecases.

ANNUAL REVIEW
of occupational exposure
to ionising radiationin France.

Operators consider that when it comes to work on pumps, valves,automated systems, etc., the expertise of subcontractors isessential.
Since then, regulations have been imposed. In particular,
subcontracting has been limited to 3 levels, maximum. In addition,
the operator must retain control of the operations it subcontracts.

7.6

Design: ASN and IRSN Communications Departments - May 2022
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ARE NUCLEAR POWER PLANTSSAFE?

CHECKS AT
EVERY STAGE
IN THE LIFE OF
A POWER PLANT
From design to decommissioning, the life of a power
plant is governed by a set of strict procedures.

STEP 1:
CONSTRUCTIONSTEP 2:
OPERATION

As soon as the facility is designed, ASN and IRSN
check that all possible accident scenarios are taken into
account (pipe rupture, valve or pump failure, loss ofelectricity, etc.), including those linked to external
hazards (earthquake, flood, etc.).

When the facility is commissioned, ASN and IRSN
check that the operation and maintenance comply
with procedures. They analyse the operator's
activities and reported incidents.

They check that the emergency systems and equipment
provided for in the safety demonstration are capable ofavoiding the consequences of accidents.
When the facility is built, ASN and IRSN check that thework carried out complies with the safety demonstrationand that the tests before commissioning are conclusive.

The facilities are subject to regular inspections by
ASN. Every 10 years, during periodic reviews, ASN
and IRSN also ensure that the facility complies
with safety requirements by imposing numerous
checks, such as pressurising the reactor building
to check that it is leaktight. At the same time,safety requirements are revised to integrate thelatest knowledge and practices.

Construction of the EPR
reactor in Flamanville.

Inspection of the
Tricastin power plant.

REGULARCHECKSAt any time, new work may be required by
ASN to improve the level of safety, taking into
account national and international lessons learned.
For example, new devices have been installed tolimit the risk of hydrogen explosion or to trap the
caesium atoms released in the event of an
accident.

STEP 3:
DECOMMISSIONING
Once the operating period is over, a closely monitoreddeconstruction process follows, lasting around thirty years:

Under normal operating conditions, releases fromthe facilities into the environment are strictly
controlled by ASN.

1. the fuel elements are removed and the water circuits
drained;
2. the installations are partially dismantled: the main
components of the reactor coolant system are isolated,cut and enclosed in concrete structures;

IRSN carries out measurements in theenvironment near the facility in the air, waterand agricultural products to check the levelof radioactivity.

3. around 10 years later, once its radioactivity has been
reduced, the facility is completely dismantled. Radioactive
materials and equipment are removed. The site is returned
to its original state or used for another installation.

EVERYONE HAS A ROLE
THE OPERATOR(Orano, CEA, EDF, etc.)
The operator remains primarily responsible
for the safety of its facility.

ASN(French Nuclear Safety Authority)
ASN is responsible for controlling, authorisingand regulating the safety of installations.

IRSN(Institute for Radiation Protection
and Nuclear Safety)
IRSN is responsible for the scientific and technicalassessment of safety implemented byoperators. In particular, it provides
technical support to ASN.

7.7

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ARE NUCLEAR POWER PLANTSSAFE?

PROTECTION GAINSTA
NATURAL HAZARDS
A nuclear power plant has safety systems
to deal with natural hazards.

NATURAL HAZARDS
Nuclear power plants have to withstand a wide range of natural hazards.
For each of them, we need to assess the levels of exceptional stressand check that the facility will be able to withstand them without causing
a nuclear accident or releasing radioactivity into the environment.
SNOW

WIND
High winds,
tornadoes, etc.

EXTREME HEAT
Heat waves, hightemperatures of thewater needed forcooling.

EXTREME COLD
Cold snaps,
freezing weather,etc.

FLOODING
Floods, heavy rain,
dam burst, etc.

EARTHQUAKEAPPROPRIATE PROTECTION
Natural phenomena can damage equipment important for plant safety or thebuildings that protect this equipment. For example, flooding can cause water toenter the plant buildings, leading to the failure of equipment located there. It canalso make access to the site difficult and damage the plant's external power
supplies. Or, during extreme winds, projectiles can damage structures, buildings
or equipment located outdoors.
Power plants are protected against these risks by physical measures (dykes,
reinforced structures, anti-projectile screens or nets, etc.) or organisational
measures (weather warning systems, surveillance rounds, etc.).
Plant protection measures against natural hazards are reassessed every 10 years
during periodic reviews.

OTHER NATURAL HAZARDSOther natural hazards (snow, hail,lightning, etc.) are also taken into account,by checking the strength of structures andbuildings and the availability of theequipment needed to ensure the safetyof the facility and, if necessary, byimplementing dedicated protection
measures.
The pumping station, which extracts thewater needed to cool the reactor, is also
protected against phenomena that could
obstruct transit or degrade water quality,
such as freezing, silting or clogging byplants, fish, jellyfish, etc.

HOW ARE LESSONSLEARNED INTEGRATED?
National and international events are systematicallytaken into account. The Fukushima Daiichi accident inJapan, for example, led to the definition of additional
seismic and flooding threshold levels, which are now
higher than those existing in 2011.
More recently in France, the Le Teil earthquake
in the Ardèche in 2019 led to the shutdown of reactors
at the Cruas power plant as a precautionary measure.
After checks, ASN authorised their restart. Analysis of
the data and research into this event will enable scientificlessons to be learned to improve plant safety in theyears to come.

Filter drums are installed upstream of power
station cooling systems, to filter out any
elements that might clog the water intakes.

More information

CLIMATE CHANGE 
The effects of climate change are already being felt and will continue
to be in the years to come, potentially altering the frequency andintensity of natural phenomena.
Where scientific knowledge permits, the effects of climate change
on meteorological and hydrological phenomena are taken into account.
This is particularly true of rising sea levels and heat waves.
Climate change can also have an effect on the flow of rivers that supply
water to power stations. The risk of low flow is assessed at the design stage
to ensure that, even in the event of prolonged heatwaves, there will still beenough water to cool the reactors. In addition to the safety risk, which isassessed by IRSN, this issue also touches on other questions, such as theprotection of the flora and fauna of the waterways, which can lead toreactors being shut down when they cause water temperature to rise
too high, and the sharing of water for various uses.

Concrete blocks fitted with earthquake-resistantpads. The pads are made of rubber and metal.
They can limit the accelerations and shear forces
associated with ground movements during anearthquake.

FIND OUT MORE • EARTHQUAKE
Accounting for seismic
risk at nuclear facility sites(irsn.fr)• FLOODING AND
CLIMATIC VARIATIONSClimate-related
hazards (irsn.fr)

7.8

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ARE NUCLEAR POWER PLANTS
SAFE?

THE AGEINGOF INSTALLATIONS
Like any other industrial installation,
nuclear power plants are subject toageing. We need to control the risks.

DEBATETHE GENERAL STATE
Reactor number and power ratingx

900 MWe     x1300 MWe     xYear ofcommissioning

1450 MWeAgein 2022(years)1999 > 232
Civaux1997 > 25

2

1

Chooz

Civaux1996 > 26

1
Chooz

OF FRENCH NUCLEAR
POWER PLANTS
After each periodic review, ASN sets the conditions requiredfor continued operation for an additional 10 years. A plant canbe shut down for safety reasons, for example if the operator
detects a serious problem or considers that the work required
is too costly.

Most French reactors were built between 1977 and 1984.
The appearance of serious generic anomalies in equipment
could cause a series of shutdowns of many power plants ina relatively short period of time.

1993 > 292
Golfech1992 > 30

2
Penly1991 >

4

31

Cattenom

1990 > 32

3

1

1

Cattenom

Golfech

Penly

2

2

NogentBelleville sur-Seine

1

2

4

1

Belleville

Cattenom

ChinonNogentsur-Seine

1

3

2

4

2

Cattenom

ChinonFlamanville

Paluel

St-Alban

1

6

3

1

Paluel

St-Alban

1

2

1984 > 38

2

11983 > 39

Chinon

Cruas

2

1

BlayaisChinon3

4

Flamanville Gravelines

2

3

4

5

Cruas

Gravelines

3

4
Blayais1

3
Blayais4

4Dampierre Gravelines

1

2
Dampierre

1988 > 34

1

1

2

3

1986 > 36

1985 > 37

OF A POWER PLANT?
In some countries, operating licences for nuclear power plants
are granted for a limited period of time. In the United States,for example, this period used to be 40 years, then it was
extended to 60 years for the majority of reactors and to
80 years for some.
In other countries, such as France, the authorisation to operate
a nuclear facility does not specify a time limit. In exchange, theplants are subject to an in-depth periodic review every 10 years.
The purpose of this review is to verify the level of safety andmake technical improvements.
However, ASN considers that the continued operation of EDF'sreactors beyond the age of 40 is only conceivable if it isassociated with an ambitious improvement programme. It insiststhat safety targets should be aligned with those for new reactors,
such as the EPR.

PaluelSt-Laurent-des-Eaux2

1987 > 35

WHAT IS THE LIFESPAN

1982 > 40

1981 >

41

Tricastin

1

Gravelines

1980 > 422
Tricastin

4

5

1979 > 43

31978 > 44

Bugey

2

CAN WE CONTROLWEAR AND TEAR
OF MATERIALS?
In a nuclear reactor, the reactor vessel, the containment vessel
and certain electrical cables are components that cannot be
replaced. The effects of their ageing are therefore closely
examined.
IRSN is studying the main degradation mechanisms: deteriorationof the concrete of the containment, development of defects inthe steel of the reactor vessel, oxidation of the cable sheaths.
These mechanisms are taken into account at the design andmanufacturing stages and then in a preventive maintenanceprogramme. The aim is to keep an accurate picture of the stateof the materials and to remain in control of the risks associatedwith ageing.

Bugey

CAN EQUIPMENTEXPIRE?

Safety-critical equipment is subject to qualification:
its performance and operation are checked under accident
conditions. They are subject to regular maintenance to ensurethat parts are replaced and their reliability maintained.
The cessation of production of certain components or thedisappearance of their manufacturer can lead to difficulties,
which is why the operator must be able to replace them.
However, replacement with a new model or a new suppliermust be subject to prior qualification.

7.9

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ARE NUCLEAR POWER PLANTS
SAFE?

DECOMMISSIONING
Even when shut down definitively, a nuclear power plantcontinues to present risks. It has to be decommissioned
according to a very precise scenario.

THE SPECIFIC CHALLENGESOF DECOMMISSIONING
A NUCLEAR POWER PLANT

Why not wait until theradioactivity disappears?
ASN recommends that the nuclear
operator dismantle its facility as soon
as possible after shutdown.

During the decommissioning of a nuclear power plant,
ASN pays particular attention to:

A waiting period certainly contributes
to a reduction in radioactivity through decay,
but it has its drawbacks: ageing structures,
possible loss of containment, loss of technicalknowledge, burden of decommissioning
on future generations.

PROTECTION OF WORKERS
Scenarios are designed to protect workers.
If the risk of exposure is too great, the workis carried out remotely using robots.

RADIOACTIVE WASTE MANAGEMENT
Waste is produced in greater quantities thanduring the operating phase and is of a different nature
because the equipment and structures are activated orcontaminated. When the time comes, the appropriate
disposal facilities must be available.

AVAILABILITY OF
FINANCIAL RESOURCES
It must be ensured that the budget requiredfor decommissioning is available.

The duration and costof decommissioning
The total decommissioning time
for a power plant is estimated ataround twenty years.
Due to a lack of experience,
costs are still poorly estimated.
What's more, the calculation
methods can be very different.

SCENARIO AND TIMESCALESFOR THE UNDERWATER DISMANTLING OF A REACTOR(strategy chosen for the Chooz A reactor)
1. PERMANENT SHUTDOWN
1

2

The fuel is unloaded from the reactor core.
It will cool for a few years in the storage pool.

3

2. ABOUT 2 YEARS LATER
The fuel is sent to the La Hague plant for processing.
The water in the reactor coolant system is drained.
The steam system and turbine are dismantled.

3. ABOUT 5 YEARS LATER
4

Dismantling operations begin in the reactor building,
except for the reactor vessel.

4

4. ABOUT 10 YEARS LATER
The reactor vessel is flooded to limit radiation during
its dismantling. The reactor vessel and internal structures
are then dismantled.

5. 20 TO 30 YEARS LATER
The site is cleaned up: either the buildings are kept fora possible identified future use, or they are demolished.

5

DECOMMISSIONINGUNDER WAY

Map of current decommissioning
operations.

Decommissioning operations differ
depending on the type of reactor.

THE COST OF
DECOMMISSIONING
A recent report by the French Court of
Auditors shows that the actual cost ofdecommissioning exceeds the initial
forecasts.
Some organisations are concerned about
the final cost of decommissioning
and how it will be financed.

Despite the experience gained during
the decommissioning of the Chooz A
pressurised water reactor (PWR),
France does not yet have the experienceof complete decommissioning ofpressurised water reactors (PWRs).
However, EDF includes the estimatedcost of decommissioning in the priceper kilowatt-hour.

7.10 Design: ASN and IRSN Communications Departments - May 2022
Graphic design and production: www.kazoar.fr - Pictograms: Freepik, Kazoar - Illustrations: B2 infographie
Reproduction prohibited without the agreement of ASN/IRSN. For further information: contact@irsn.fr

ARE NUCLEAR POWER PLANTSSAFE?

TOMORROW’SPOWER PLANTS

In order to achieve more ambitious objectives in termsof safety, security and resource savings, the range of
nuclear power plants on offer is set to diversify
worldwide. While some technologies are alreadyavailable, others are still being studied and could makean appearance in the coming years.

DIFFERENT TECHNOLOGIES 
ON DIFFERENT TIMESCALES...

4TH GENERATIONREACTORS

Around the world, there have been several generations (technologies
and versions) of nuclear reactors over the years. In France, forexample, the first generation of UNGG (graphite-moderated, gascooled natural uranium) nuclear reactors were designed in the 1950s
and 1960s. They are all currently being decommissioned.

Fast neutron reactors,
high temperature reactors(HTR-PM), even very hightemperature reactors (VHTR),
molten salt fast reactors...
there are many different
concepts for 4th generation
reactors!

The second generation corresponds to the fleet of pressurised water
reactors currently in operation in France.
The EPR reactor under construction in Flamanville is known as a"third-generation" reactor.
Prototypes are already being built, foreshadowing the power plants
of tomorrow. Other technologies are still in the research phase:they are sometimes referred to as the fourth generation.
Side view of the core catcher of an EPR reactor

Spreadingcompartment

IRWST(safety injection
system pool)

EPR
The EPR (European Pressurized Reactor) is a powerful"evolutionary" reactor (1650 MWe) that does not represent
a major technological breakthrough compared with existing
facilities. Nevertheless, this 3rd generation reactor offers significant
improvements to safety systems, in particular four channels forthe safety-critical water systems (compared with two in reactors
currently in operation) capable of operating independently
and spread across four different buildings.
It is the first French reactor to benefit from the lessons
learned from the nuclear accidents at Three Mile Island (USA),
Chernobyl (Ukraine) and Fukushima (Japan), as well as fromlessons learned from the reactors in operation.
Cooling plates

CoriumSacrificial
concrete

Discharge
channelProtectivelayer

It is equipped with a core catcher to cool the molten core in
the event of a severe accident, and its design has taken into
account increased requirements in terms of radiation
protection for humans.
Finally, the buildings housing the reactor, control roomand fuel storage are covered by a concrete structurethat can withstand aircraft crashes.

... AND OF DIFFERENT SIZES
Nuclear reactors for electricity production come in a wide
range of sizes and power ratings, from the EPR (1650 MWe) tothe SMR (10 to 300 MWe), and even the micro-reactor (10 MWe)!

SMALL MODULAR REACTORS
Compact nuclear reactors have been used for naval propulsion
for decades. However, a new generation of small reactors has
been gaining popularity around the world in recent years:
Small Modular Reactors (SMR). These reactors have an outputof less than 300 MWe (1650 MWe for an EPR).
Built from elementary modules manufactured in dedicatedfactories and transported by road or river, the SMRs areassembled on the operating site. There are many different
concepts (over 70) based on different technologies andgenerations of reactors.
Their small size and low power give them greater safety.
In the event of an incident or accident, they should enable thereactor to be brought to a safe shutdown state and kept there
for a long period without human intervention.
NUWARDTM reactor
vessel and containment
in the overall view of themain nuclear building.

900 MWe PWR
Containment≈35 x 58 m
40 m

20 m
170 MWe NUWARD™ SMR
Containment≈15 x 16 m
10 MWe microreactor
Containment≈3 x 6 m

Even smaller than SMRs, microreactors have an output of less than
10 MWe (the equivalent of 1 tonne of petroleum per hour). Extremelycompact, they can be easily moved and integrated into very limited spaces
and used in very specific situations (supplying power to isolated areas,
space modules or military bases in operation, crisis intervention, etc.).

And beyond
domestic electricity...
The heat produced by nuclear reactors
can be used for purposes other thanelectricity generation: desalination ofseawater, district heating, energy-intensive
industrial processes (chemicals,
paper, steelworks).
They can also be used to provide
solutions to growing local electricity needs,
such as powering the ever-increasing
number of data centres!

7.11 Design: ASN and IRSN Communications Departments - May 2022
Graphic design and production: www.kazoar.fr - Pictograms: Freepik, Kazoar - Illustrations: Georges Goué/Médiathèque IRSN, Nuward/EDF, Kazoar
Reproduction prohibited without the agreement of ASN/IRSN. For further information: contact@irsn.fr

ARE NUCLEAR POWER PLANTSSAFE?

NUCLEARFUSION
Fusion is the phenomenon at workin stars like our sun.

HOW DOES,FUSION WORK?

Deuterium

NeutronIn the fission process, heavy atoms are broken into several pieces bybombarding them with neutrons.

EnergyIn the fusion process, the opposite occurs: matter is compressedwith such force that two light atoms come together to form a single
heavier atom.
Both physical processes release energy, but the fusion reaction
has a dual theoretical advantage:• It does not generate high-level, long-lived radioactive by-products;• It uses a fuel that can be extracted from water, a very
abundant resource. However, as the tritium extraction process is very
costly, systems that produce tritium under neutron bombardment(such as "tritium breeding blankets") are being studied.

PRODUCING
THE FUSION REACTION

Tritium

Helium-4

Fusion process

THE LONG ROADTO INDUSTRIALISATION

Nuclear fusion reactions naturally take place at the core of stars,
as in the sun, at extreme pressures and temperatures (around200 billion times the Earth's atmospheric pressure and 150 million
degrees Celsius). Under these conditions, matter takes the form ofplasma: the nuclei and electrons surrounding them are no longer
bound together.

Large-scale electricity generation using nuclear fusion
still presents major technological hurdles:• the balance between energy released and energy
supplied must be positive. Unlike fission, which issustained by a chain reaction, fusion requires anenormous amount of energy to bring the atoms
together;To reproduce and control this fusion process on Earth, it istherefore necessary to be able to reach high pressures andtemperatures. There are two possible technologies:• magnetic confinement: inside a tokamak, the plasma, createdby a very powerful current and additional heating systems, is"trapped" in a magnetic field created by electromagnetic coils.
The fuel used is a mixture of hydrogen isotopes;• fusion must continue. Plasma has many intrinsic
instabilities: so far, the positive balance has been
maintained for just a few minutes.

• inertial confinement: very high temperature and pressure
conditions are provided by lasers placed around the fuel,confined in a very small volume.
The pressure exerted by the lasers and the heat produced
enable the fuel to become plasma.

TOKAMAK FOR THE ITER PROJECTMAGNETS
The magnetic field generated
by 10,000 tonnes of superconducting
magnets will be needed to confine
and shape the plasma inside thevacuum chamber.

ITER, THE
INTERNATIONAL THERMONUCLEAR
EXPERIMENTAL REACTORCRYOSTATThe cryostat is a large stainlesssteel structure (29 m x 29 m)
enclosing the vacuum chamberand superconducting magnets,
creating an extremely cold
vacuum environment.

ITER is an international project for a civil nuclear fusion
research reactor of the tokamak type, located in theimmediate vicinity of the Cadarache nuclear research
centre in Saint-Paul-lez-Durance (Bouches-du-Rhône,France). It operates on the principle of thermonuclear
fusion, whereas current reactors use fission.
The ITER project aims to verify the scientific and technicalfeasibility of nuclear fusion as a new source of energy,
with a view to building commercial fusion reactors that
produce electricity in the future. Researchers are currently
working on various fusion reactor projects (such as theEuropean DEMO project).
The project involves a number of countries: those of theEuropean Union, as well as India, Japan, China, Russia,
South Korea, the United States, Switzerland and theUnited Kingdom.

TOROIDALVACUUM CHAMBER
The vacuum chamber
is a sealed stainlesssteel enclosure in which
the fusion reactions takeplace.

DIVERTOR
The divertor, which is located on the'floor' of the vacuum chamber, extracts
the gaseous effluents and impurities
from the machine, and must be capableof withstanding very high surface
thermal loads.

BLANKET
The blanket modules protect
the vacuum chamber andsuperconducting magnets
from the very high-energy
neutrons produced by thefusion reaction.

A fusion reactor would not produce the same nuclear waste as current
power plants (fission products, actinides, etc.) but rather tritiated wastewith a lower level of activity and a shorter lifespan.

DEBATEIS FUSION

CLEAN?

The fusion reaction requires tritium, a radioactive substance.
Although the fusion reaction requires little fuel (a few grams of tritium),around 4 kg of tritium will be present in the ITER installation. Also
neutrons activate the tokamak's metal structures. These activatedstructures are a source of waste in addition to tritiated waste. The total
volume of waste will be greater than that of a current reactor, but will not
be high activity waste. In addition, these activated metal structures
produce dose rates that make human intervention impossible, whichmeans that maintenance operations must be automated.

7.12 Design: ASN and IRSN Communications Departments - May 2022
Graphic design and production: www.kazoar.fr - Pictograms: Freepik, Kazoar - Illustration: La-fabrique-créative/Bruno Bourgeois, @iter.org
Reproduction prohibited without the agreement of ASN/IRSN. For further information: contact@irsn.fr