Enhancing nuclear safety

Chernobyl 25 years on
In late April 1986,
a major nuclear accident
released a large quantityof radioactive material
into the atmosphere…

Collection of topics

UnitsSome sources of radiation
exposure for humans		

An introduction to the Chernobyl accident		What is radioactivity? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

p. 2

1 n	 The accident . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

p. 4

2 n Radioactive releases.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

p. 7

3 n	Spread of the radioactive plume over Europe . . . . . . .

p. 8

4 n	Radioactive deposits in Europe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

p. 125 n	Contamination of various environments
and the food chain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

p. 17

6 n	Health impact in the most contaminated areas ..

p. 24

7 n	Doses received in France and theirassociated risks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

p. 31

8 n	The site today . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

p. 35

9 n	Lessons learned from Chernobyl. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

p. 38

Becquerel
The becquerel (Bq) is the unit ofmeasurement of radioactivity.
It corresponds to one decay persecond, for all types of radiation
emitted (a, b, g).

Gray
The gray (Gy) is the unit ofabsorbed dose. It corresponds
to the quantity of energy(measured in Joules – J)transferred by ionising radiation
to the mass through which it
passes (expressed in
kilograms – kg).
1 Gy = 1 J.kg-1.

SievertThe sievert (Sv) is the unit ofequivalent dose received bya specific organ or tissue, andthe unit of effective (wholebody) dose. The equivalent doseis determined from the doseabsorbed, taking into accountdifferences in the ability ofdifferent kinds of radiation todamage organs or tissues. The
effective dose is determinedfrom the equivalent dosesdelivered to the various bodyorgans or tissues, taking into
account their relative sensitivity
to the effects of ionisingradiation. These sievert doses
can be used to estimate the riskof stochastic effects (cancers or
hereditary effects) which may
affect the exposed organism.

Naturalradioactivity

Artificial
radioactivity
AbdomenCT scanSome partsof Brazil andSouth-West India

La Paz (Bolivia),
altitude3660 mRadon*
in France*Naturally
occurringradioactive gas

Paris-New York 0.06
return flight

Average annual dose (mSv)“One-off” dose (mSv)

Average medical
exposure in France(CT scan,
X-rays, etc.)

Dentalpanoramic
X-ray

0.006
0.002

Release of radioactive
elements into theenvironment from
nuclear power plants.

Note
The average individual effective dose due to naturalradioactivity in France is 2.4 millisieverts a year.

1What is radioactivity?
Radioactivity is a natural phenomenon which has existed eversince atoms were formed billions of years ago.
Chemical elements present in matter are made up of atoms with anucleus of protons and neutrons, surrounded by a cloud of electrons.
Atoms of the same element all have the same number of protons(e.g. uranium has 92) but different isotopes of the element can havedifferent numbers of neutrons.
Most isotopes have a stable nucleus and stay the same indefinitely.
Others have an unstable nucleus because they have too many or too
few neutrons. They spontaneously decay into more stable atoms and,in the process, they release energy in the form of ionising radiation.
This is the phenomenon known as radioactivity.
A source consisting of radioactive isotopes is characterised by its
activity, expressed in becquerels (Bq): 1 Bq corresponds to one
radioactive decay per second. The higher the activity of a source,
the more radiation it emits. As the radioactive nuclei contained ina source decay, its activity decreases. The half-life is the time taken
for a source’s activity to decrease by half.
The radiation emitted by a radioactive source carries a great deal ofenergy that is gradually absorbed by the matter it passes through.
The absorbed dose, expressed in grays (Gy), measures this transfer
of energy.
When a person is exposed to radiation emitted by a radioactive
source, the dose absorbed by the tissues through which the radiation
passes can cause biological damage. The risk of harmful effects on
health is evaluated on the basis of the effective dose (whole body)or the equivalent dose received by a specific organ or tissue, both
expressed in sieverts (Sv), depending on the nature of the radiationand the sensitivity of the irradiated organs.
We are constantly exposed to natural sources of radioactivity, in
our environment, in the air we breathe, in the food we eat andeven inside our bodies.

2

We are also exposed to radiation from man-made sources (such as
medical X-rays, fallout from atmospheric nuclear weapons tests,
nuclear facilities, etc.). The average individual effective dose due tonatural radioactivity in France is 2.4 millisieverts a year.

Power
grid

Steam
generator

Containmentbuilding
Nuclear fuel(radioactive
elements)

River

Steam

Water

Power generator
TurbineTransformer

Operation of a power plant
Thermal, hydroelectric and nuclear power plants are all based on the same principle.
A turbine drives a generator which produces electricity. In conventional thermal
power plants, fossil fuels (coal, natural gas or oil) are used to produce the heat
which turns water into steam to drive the turbine. In nuclear power plants, fossil
fuels are replaced by nuclear fuel made up of fissile uranium or plutonium atoms.
Fuel assemblies are placed in the nuclear reactor and produce heat by fission of theuranium and plutonium nuclei. They break up under the impact of neutrons andproduce radioactive fission products that must be contained in the reactor, andneutrons which maintain the fission reaction.

3

The accident
Combined causes of the accident
The initial design of the RBMK
reactors had some significant
weaknesses from a safety standpoint. In particular, they werehighly unstable at certain power
ranges, the emergency shutdown
system had too long a responsetime and there was no containment around the reactor. In addition, the lack of sufficient prepa-

ration for the conditions required
for the planned test, and the lackof time to complete it, meantthat operators did not follow all
the operating rules. They also
violated them by suppressing
some important safety systems.

Spiral to disaster

There were four reactors on the Chernobyl power plant. On 26th April 1986, reactor no. 4
exploded. The 2000 tonne reactor vessel head destroyed the roof (reconstructed) and ended
up on its end (model of destroyed reactor 4).

The Chernobyl power plant
On 26 th April 1986 at 01:24,
reactor 4 at the Chernobyl
power plant, which had been
in service since 1983, exploded
in an accident during a technical test.
It was a RBMK type reactor, a Soviet model designed in the 1960s.
The reactor core was made up ofa huge block of graphite containing vertical channels in which

4pressure tubes were placed, eachof which contained several nuclear fuel assemblies. The graphite functioned as a moderator –neutrons had to be slowed down
to maintain the chain reaction.
Cooling was provided by boiling water flowing through thepressure tubes in contact withthe fuel.

In the morning of 25 th April,
operators began the power reduction procedure.
Between 13:00 and 23:00, thereactor was held at half-power,
contrary to the initial test schedule, at the request of the electric
power distribution centre.
At about 23:00, power reduction
was resumed. However, the reactor state was now inappropriate
for the test to be performed. The
core was very difficult to control
with the systems available. The
reactor should have been stabilised at this stage. However, operators were in a hurry to catchup the delay in the schedule, anddecided to perform the test regardless.

On 26th April at 01:23:04, thetest was launched, and the turbine steam supply valves wereclosed. The temperature rose in
the core, causing reactivity toincrease.
The reactor started to go criticaland out of control. At this point,
the operators realised the seriousness of the situation.
At 01:23:40, the chief operator ordered an emergency shutdown. All control rods began toenter the core, but did not havetime to stop a runaway chain
reaction.
At 01:23:44, power peaked, exceeding the reactor’s nominal
power by a factor of more than100.
5

Radioactive releases
An explosion followed by a fire
The high pressures reached in
the pressure tubes caused themto rupture. An explosion lifted
the upper reactor cover, weighing about 2000 tonnes, off thereactor.
The top of the reactor core was
exposed to the open air. The
graphite ignited, and a numberof fires broke out in the facility. It

took fire-fighters three hours to
extinguish the fires. The graphite
fire reignited. It was not fully
extinguished until 9 May.
Between 27th April and 10th May,
5000 tonnes of material (sand,boron, clay, lead, etc.) were poured
onto the reactor by helicopter tocover it.

Most of the radioactive material released was discharged at thetime of the reactor’s explosion.
All together, nearly 12 billionbillion becquerels were ejected
into the environment in 10 days,
that is 30,000 times the radioactive emissions released into theatmosphere by all the nuclear
facilities operating in the world
at that time in one year. The vast
majority (84% of the total activity released) of the radioactive
elements had a half-life of lessthan one month.

The energy of the explosion
propelled radioactive materials
contained in the nuclear reactor core into the atmosphere, toaltitudes of over 1200 metres.
These materials continued to bereleased until 5th May as a resultof the fire that followed the accident and then the residual heatreleased by the remains of thecore destroyed by the accident.

0.60

Radioactive materials (excluding noble gases) released daily into the atmosphere
after the explosion of Chernobyl reactor no.4 (INSAG estimate 1986)

0.40

0.30

0.20
0.002 - 0.006 Ebqd

The fuel rods in the core broke up. The overheated uranium oxide pellets exploded.

Release rate in exabecquerels (1018 Bq) per day.

0.50

0.10

0.00
26th April 27th April 28th April 29th April 30th April 1st May

6

2nd May

3rd May

4th May

5th May

6th May7

Spread of the radioactive
plume over Europe
Nuclear fuel debris and pieces of the reactor were thrown into
the environment around the power plant. Radioactive dust, fineparticles (aerosols) and gases rose to high altitudes and formed
a plume which was carried over great distances in air masses bychanging winds.

times and the various plumes
mixed to form a mass of contaminated air which covered
most of Europe in decreasing
concentrations. These radioactive elements then contin-

ued to be dispersed across thewhole of the northern hemisphere and were detected in
North America and Japan, in
extremely low concentrations.

Activity conc. at ground level on 28th Apr at 12:00 (Bq/m3)

Between 26th April and mid-May
1986, the radioactive plume
scattered radioactive elements
such as iodine-131, caesium-134
and caesium-137 over most of
the countries in Europe.
As time passed, this dispersion
resulted in the dilution of theradioactive elements in the air.
Some of the aerosols were deposited along the way, graduallydepleting the radioactive cloud.
Finally, the radioactive elementswith a very short half-life (a few
hours) disappeared quickly asa result of radioactive decay inthe plume. This meant that theconcentration of radioactive elements in the air, which was over
10 million becquerels per cubic
metre (Bq/m3) in the vicinityof the damaged reactor on 26th
April, decreased as it travelled
and was no more a few tens ofbecquerels per cubic metre overFrance on 1st May.

69N
66N
63N
60N
57N
54N
51N
48N
45N
42N
39N
36N
10W 5W

05E

10E 15E
0,01

20E 25E 30E 35E 40E 45E
0,1

1

10

50E

55E

60E

100 1000

Spread of caesium-137
released into the atmosphereby the Chernobyl accident:
situation at 12:00 on 28th
April 1986
(modelling: IRSN 2006).

Act. concentr. at ground level on 1st May at 12:00 (Bq/m3)
69N
66N
63N
60N
57N
54N
51N
48N

Plume paths
Initially, the wind carried the radioactive material released on
26th April in a north-westerly direction. The plume passed overthe Baltic countries and thenScandinavia on 28 th April, andwas then blown eastwards andthen south, carrying the contaminants towards central Europe
and the Balkans.
The plume of material releasedon 27th April travelled towards
western Europe - Germany,
8

45N
42N

France and Northern Italy which it reached between 30th
April and 5th May, before being
picked up by a south wind which
took it to the British Isles, avoiding Spain and Portugal. Emissions from the power plant from28th April were carried east andsouth, towards Russia, the Caucasus, the eastern Mediterraneanand central Europe.
Over time, the radioactive
materials released at different

39N
36N
10W 5W

05E

10E 15E
0,01

20E 25E 30E 35E 40E 45E
0,1

1

10

50E

55E

60E

100 1000

Air contamination bycaesium-137:
situation at 12:00
on 1st May 1986
(modelling: IRSN 2006).

Activity conc. at ground level on 3rd May at 12:00 (Bq/m3)
69N
66N
63N
60N
57N
54N
51N
48N
45N
42N
39N
36N
10W 5W

05E

10E 15E
0,01

20E 25E 30E 35E 40E 45E
0,1

1

10

100 1000

50E

55E

60E

Air contamination bycaesium-137: situation at
12:00 on 3rd May 1986
(modelling: IRSN 2006).

9

30th April 1986

1st May 1986

2nd May 1986

3rd May 1986

In France
The main radioactive elements
measured in the air in early May
1986 are given below, in decreasing order of concentration:

Radioactive elements

Half-lifen Iodine-131 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

n 8 days  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

n Tellurium-132 . . . . . . . . . . . . . . . . . . . . . . .

n 78 hours  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

n Tellurium-129m  . . . . . . . . . . . . . . . . . . . . . 

n 33 days  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

n Ruthenium-103  . . . . . . . . . . . . . . . . . . . . . 

n 39 days  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

n Caesium-137  . . . . . . . . . . . . . . . . . . . . . . . . 

n 30 years  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

n Caesium-134  . . . . . . . . . . . . . . . . . . . . . . . . 

n 2 years  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

n Barium-140  . . . . . . . . . . . . . . . . . . . . . . . . . . 

n 13 days  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

The air contamination lasted
until 5th May, but continued todecrease. It remained highest in
the east throughout this period.

After 6th May, it decreased considerably as the plume headed
back towards Eastern Europe.
.

(Maps drawn up by IRSN in 2004 based on measurements of daily aerosol samples taken by the SCPRI monitoring network).

In France, the concentrationof radioactive elements in the
air increased in the east of thecountry during 30th April 1986,
peaking on 1 May.

4th May 1986

5th May 1986

6th May 1986

Air contamination bycaesium-137 (Becquerels/m3)

0.5
0.1
0.05
0.025
0.01
0.0015

Mean concentration of caesium-137 in the air over France
between 30th April and 6th May 1986.

10

11

Radioactive deposits
in Europe
The radioactive particles carried in the air masses fell to the groundas dry deposition when the particles were near the ground and as
wet deposition with rain or snow.

Total activity deposited (Bq/m²)

WET DEPOSITION
Wet depositionon leaves

DRY DEPOSITION
Dry depositionon leavesareas where it rained, and theiractivity was up to 10 times higher
than dry deposits formed in thesame places. Contamination“patches” thus formed depending on when and where it rained.
n In mountainous areas, where
it rains more, the activity of deposits was greater. In forest areas,
the leaves on trees captured theradioactive dust in the air more
readily, which increased the ac-tivity of the radioactive deposits
compared with those in open
fields. This led to highly nonuniform radioactive deposits,with the greatest amounts being
distributed around the Chernobyl site and in the countries
neighbouring the power plant.
Caesium-137 is a good indicatorfor measuring the distributionof deposits on a European scale.

Deposits carried away
by runoff
Kilobecquerels/m2

Deposits carried inby runoff
Wet deposition Dry deposition
on soilon soil

Residual activity in the ground

These deposits covered plants,
soil and surface water but also
built-up areas and inhabited
locations. When deposits wereformed by rain, they were distributed across the surface orinto the ground by runoff.
The extent of deposits in Europe
varied according to many different factors.
n The biggest and heaviest particles, especially nuclear fuel debris,
fell in the immediate vicinity of
12

Wet and dry
deposition under
the radioactive
plume

the power plant, forming very
highly active deposits within
the 30-kilometre exclusion zone
around the power plant.
n The severity of the concentration of radioactive elements inthe air and the length of time
the surrounding air was contaminated resulted in highly active deposits in the three most
severely affected countries Ukraine, Belarus and Russia.
Deposits were much higher in

1 480
185
40
10
2
0
Data
unavailable

Map of caesium-137 deposits over Europe immediately after the Chernobyl accident(source: European Atlas EC/IGCE 1998 and IRSN). No data is available for the Balkans.

13

Contaminated areas in former Soviet Union countries
In Russia, Belarus and Ukraine,
vast areas were unevenly contaminated with radioactive
deposits that reached several
hundreds of thousands andsometimes exceeded a million

20© EC/IGCE, Roshydromet (Russie) / Minchernobyl (Ukraine) / Belhydromet(Bielorussie), 1998

Kilometres
Kilomètres
5 0
10becquerels per square metre.
In the area around the power
plant, varying deposits of strontium-90, plutonium, etc., wereformed along the paths of theradioactive plumes.

kBq/m2

FranceDue to the depletion of the radioactive plume and the shortamount of time that the air
over France was contaminated(about a week), deposits generally had low levels of activity,
which tended to be greater inthe east than in the west of thecountry.
Consequently, dry deposits of
caesium-137 were estimatedat around 1000 becquerels per
square metre in the east and approximately 100 becquerels per

square metre in the more westerly
départements of France.
However, heavy localised rainfall,especially between 2nd and 4th May,
resulted in greater wet deposition
to the east of an imaginary line
drawn between the Moselle riverand Corsica. Some areas received
deposits with activities exceeding 10,000 becquerels per square
metre and even, locally, 20,000
becquerels per square metre. Départements in the North-East ofFrance, the Franche-Comté region,

18 500
7 400
3 700
1 480

Caesium-137 deposits in 1986 around the Chernobyl power plant.
Cs
Bq/m2(values from May 1986)
137> 40,000

Central and Western Europe
Outside the former Soviet Union,
deposits exceeding 40,000 becquerels per square metre occurred in Scandinavia (southern
Finland, central and eastern Sweden, central Norway), in central
Europe - especially in southern
Romania, on the border between
14

the Czech Republic and Poland,in Austria and northern Greece,
as well as over smaller areas in
the UK, Switzerland, Bavaria and
Italy (Italian Lakes and the Dolomites).

20,000 to 40,000
10,000 to 20,000
5,000 to 10,000< 5,000

Reconstitution of caesium-137 fallout in May 1986 over France by modelling based on theamount of rainfall in early May 1986 (IRSN 2005).

15

the Southern Alps and Corsica
were the worst affected.
On a very local scale, severe
downpours led to even heavier
deposits over areas of a few
square kilometres.
In mountainous regions, theconcentration of deposits due
to melting snow, water drippingfrom trees and surface waterrunoff into basins at the baseof the slopes, resulted in highactivity patches over very small
surface areas (several becquerels
per kilogramme of soil over a few
square feet).

At a local level, widely varying
deposits were found within thesame department, with readings varying by a factor of 10
to 15. This made precise mapping impractical. Qualitatively,
iodine-131 deposits in the same
way as caesium-137, with an
initial activity approximately 10
times higher. However, its shorthalf-life (eight days) means that,
unlike caesium, it quickly disappears from soil (80 days after
the accident, iodine-131 activity
had reduced by a factor of 1000,
while that of caesium-137 waspractically unchanged).

Soil sample used tomeasure deposits.

16

Contaminationof various environments
and the food chain
Radioactive fallout from the atmosphere was distributed overvarious environmental contexts.

Plants were directly contaminated by leaf-capture of radioactive products suspended in theair (aerosols). This phenomenon,
which happens much more in dry
deposition than in wet deposition, led to contamination of agricultural and natural food products. The time of year at which
the accident occurred meantthat grass and leafy vegetables,
especially lettuces, spinach andleeks, were the plants most affected in May 1986. Livestock
which grazed on the contaminated fields were also affected.

This contamination extended torelated production, such as dairy
produce and meat.
Contamination reached a peak
immediately after the deposits
occurred and decreased considerably in the following weeks
due to the continuing growth ofplants and the disappearance ofshort-half-life radioactive elements (iodine-131). It was 100
times lower after three months.
The soil retained part of the radioactive elements depositedand a persistent inventory wasformed in the case of those witha long half-life and a tendency to
become fixed in soil components(e.g. clays), such as caesium-137.
From 1987, the transfer of radioactive elements via roots, whilemuch less efficient than direct
capture by leaves, contributed tomaintaining chronic contamination of plants and the rest of thefood chain in the most severely
affected areas.

17

Contaminated areas in Russia, Belarus and Ukraine
Agricultural produce
In the severely affected areas of
Russia, Belarus and Ukraine, highlevels of contamination were detected in agricultural products
both in 1986 and in the years
that followed. After 1986, formost soils, the contamination
was largely fixed in the upper
10 to 20 centimetres. Overall,the contamination of agricultural products decreased as theyears passed, to differing extents

depending on the initial characteristics of the deposits, soil
types and agricultural practices.
Until the beginning of the 1990s,
it was not unusual to find highconcentrations of caesium-137.
This was noted mainly in theGomel region of Belarus, wherecontamination levels reachedseveral thousand becquerels per
litre for cow’s milk, 1000 to 5000
becquerels per kilogramme ofbeef and 1000 to 2500 becquerels per kilogramme in cabbages.
In the same period, most of thecereals and potatoes produced
had an activity of less than 100
becquerels per kilogramme.
However, activity levels remained high in some areas, withseveral thousand becquerels per
kilogramme in natural grasses
and some fodder. After a sharp

reduction up until the beginningof the 1990s, contamination levels in agricultural produce havecontinued to reduce more gradually (3% to 7% per annum) and is
now largely due to caesium-137.
It is more significant in animal
products (meat, milk), especiallyfrom extensive farming, than invegetable products.

Forests
Leaves on trees are especiallyprone to capturing ambient
aerosols.
When these leaves fall, they contaminate forest litter and soil,

which thus constitutes a persistent inventory of radioactive
substances, that are recycled by
the trees and plants of the undergrowth, especially new growth.

Collective farms
Private farms

Months/years
Months/years

Caesium-137 activity (in becquerel/litre) measured from 1987 in cow’s milk collected fromfarms in contaminated areas. Contamination was extremely variable depending on the severityof the fallout and on rehabilitation measures on agricultural land..

18

Caesium-137 concentration measured in mushrooms gathered between 1986 and 2000 incontaminated areas of Russia, Belarus and Ukraine.

19

Twenty-five years after the accident, the caesium-137 contamination persisting in plant litterand forest soil has essentiallyonly reduced due to radioactive
decay (i.e. to 56% of the activity
initially deposited) and, via theroots, still contaminates woodand leaves, as well as mushrooms, berries and game. So,
unlike for agricultural produce
whose contamination has generally sharply decreased with pass-ing time, very high caesium-137
activity is still found in natural
products gathered in forests inthe most contaminated regions.
Levels as high as several tens of
thousands of becquerels per kilogramme may be found in mushrooms, game and wild berries.

Becquerels/lCaesium in the Dniepr
Caesium in the Pripyat
Caesium emissions

Graph showingchanges incaesium levels(1986 to 1994)
in the Pripyat andthe Dniepr.

River water
An impact on surface water was
mainly found in the first few
weeks following the accident inareas near the damaged power

plant, where it was directly contaminated by radioactive fallout.
After this, water contaminationlevels decreased rapidly, due to

Cargo port on the Pripyat (tributary of the Dniepr) and abandoned contaminated boats.

20

0.5

Years

the disappearance of short-lived
radio-isotopes and the absorption of radioactive substancesby sediments. Thus, the Pripyat
and the Dniepr which supply themain towns in Ukraine with drinking water were contaminated tosuch an extent that preventive
actions had to be taken during the first few months: dykes
were built, towns were suppliedwith water from uncontaminated areas and water use wasrestricted. In 1986 and the years
that followed, rainwater runoff,

melting snow and flood waterpromoted the leaching of somesurface-soil deposits into water
courses. Caesium-137 and strontium-90 are the main radioactive
elements that have been found in
the long term in the Pripyat, near
Chernobyl, in low concentrations(of the order of 0.1 Bq/l dissolvedin the water). Groundwater was
not affected, other than in theimmediate proximity of the site
due to infiltration into the soil
where contaminated debris had
been hastily buried.

21

In France
In France, the highest levels ofcontamination in agriculturaland natural products were
found in eastern regions.
The maximum levels measured
in cow’s milk and lettuces were
found during the first half of May
1986. In areas in the east of thecountry, which had received particularly substantial wet deposition, the reduced efficiencyof leaf-capture of radioactive
fallout due to heavy rainfall resulted in contamination of theseproducts that was only two or
three times higher than thatmeasured in areas of the same
regions less severely affected bythis type of deposit. In the weeks
following the initial deposition ofradioactive substances, the concentrations of iodine-131 andcaesium-137 in vegetables anddairy produce decreased very
rapidly due to plant growth andradioactive decay of iodine-131.
Some products are extremely
sensitive to the effects of radioactive fallout. In particular,
this is the case for goat’s andsheep’s milk as, in the Mediterranean area, these animals feedon plants with low water content scattered over large areas.
Immediately after deposition,
the contamination in this milkreached as high as 10,000 becquerels per litre for iodine-131
and 500 becquerels per litre for
caesium-137.
From 1987, contamination offarm produce was due to theroots of plants absorbing caesium-137 and caesium-134 present in soil.
At this point, contamination
was much lower and decreased
steadily as the years passed. Thisdecrease is explained by radioactive decay, especially that of
caesium-134 with a half-life of
2.1 years, and the reduced availability of caesium for plants.

Becquerel/kg fresh
iodine-131: < 100 Bq/lcaesium-137: < 10 Bq/l

iodine-131: 50-250 Bq/lcaesium-137: 20-50 Bq/l

iodine-131: 100-600 Bq/lcaesium-137: 30-100 Bq/l

iodine-131: 30-250 Bq/lcaesium-137: 10-20 Bq/l

iodine-131: 300-2700 Bq/kg fresh
caesium-137: 100-600 Bq/kg fresh

Cereals
caesium-137: < 200 Bq/kg

22

Ranges of
caesium-137
andiodine-131
contamination
values:measured in
the first halfof May 1986.

In 2010, contamination in farm
produce was between 10 and
30 times lower than in 1987
and between 1000 and 10,000
times lower than immediately
after deposition in May 1986.
It continues to decrease slowly
over time.
Some forest soils in the east ofFrance still contain nearly 55%of the caesium-137 initiallydeposited. This radioactive element can still be measured inconcentrations in the region of
100 becquerels per kilogramme
in some species of mushrooms
harvested from these soils.

Cereals
Beef
Cow’s milk
Leafy vegetables

0.1
0.01
Years

Changes incaesium-137
contaminationin various
foodstuffs inFrance since1986. From themid-1990s,
caesium-134
was no longer
detectable.

23

Health impact in the mostcontaminated areas
In the days following the accident, the population of most ofEurope was exposed to varying degrees of fallout from the
Chernobyl accident.

and Ukraine owing to the long
half-life of caesium-137 (30years).
The doses received by the people subjected to these various
types of exposure depended on
their relative intensity and eachindividual’s way of life. Theirintensity determined the riskof the occurrence of diseases

such as cancers in the exposed
populations. In situations involving very severe exposure, as
suffered by on-site personnel
and the first emergency workers, the absorbed doses were sohigh that some people’s exposure exceeded the thresholds at
which acute radiation symptoms
and radiation burns appear.

Fire-fighters and power plant personnel

Two elderly people
living in the exclusion
zone.

From 26th April 1986 onwards,
people present on the site orin its immediate vicinity wereseverely exposed to radiation
emitted by the reactor, to radioactive elements released into
the external environment andto deposits that formed on the
ground. These were mainly workers on the site and their families
who lived in the nearby town of
Pripyat.
First of all, these people were
exposed to the plume that was
highly charged with fine radioactive dust. The severity of this ex-

24

posure decreased with distancefrom the power plant. They werethen exposed to radiation emitted by the radioactive deposits
on the ground. Finally, they were
exposed through food contamination due to deposition onto
leaves (an important factor in
the months after the accident)
or to transfer via roots of residual contamination in the soil.
Although these last two sourcesof exposure have considerably
decreased over the years, they
still persist in the most contaminated areas of Russia, Belarus

Among the 600 emergency
workers involved on the firstday and who received the highest doses, two died immediately of burns and 28 others
died in the four months following the accident as a resultof their exposure to radiation.
Between 1987 and 2006, 19 moredied from various causes, most ofwhich were unrelated to expo-

sure to ionising radiation (cardiac
arrest, pulmonary tuberculosis,
cirrhosis of the liver, trauma, andcancer).
Among the survivors of the 134
who presented with acute radiation syndrome immediately after
the accident, skin lesions secondary to the radiation burns andcataracts are the main effects
seen today.

Monument inhonour of thefire-fighters.

25

Liquidators
The “liquidators”, approximately
600,000 civilian and military personnel, worked on the site in thefirst few years after the accident
to carry out various tasks: workon the reactor, site decontamination, construction of the sarcophagus, and burial of radioactive waste in the exclusion area.
Some of the personnel involvedin the first few weeks received
high effective doses (in somecases exceeding 1000 mSv).

However, for most liquidators
the effective doses received weremuch lower (on average 120 mSv,
with 85% of effective doses recorded being between 20 and
500 mSv), as they carried outtasks for limited periods and, insome cases, several years after
the accident. The doses received
by the liquidators were generally
estimated with a great deal of
uncertainty, except for those who
were carrying a dosimeter during
their work.

The rate of thyroid cancer seems
to be higher among liquidators
than among the general population, but this does not establish
a clear cause-and-effect link toradiation exposure. There does
not seem to be an overall excessof other types of solid cancer,
despite the apparently contradictory results of two Russianstudies that highlighted an increase in solid cancer mortality
in proportion to dose received.
Although they are not definitive,
recent reports suggest an excess
in cases of leukaemia amongliquidators in Belarus, Ukraine
and Russia and the Baltic states.
Additional studies are needed,in particular due to the numerous uncertainties surrounding
the “reconstruction” of dose
received.

Many studies also report on
diseases other than cancer; forexample, there is an excess ofcataracts among liquidators
who received doses over 0.7
Gray. Furthermore, a Russian
study demonstrated a link between the doses received by theliquidators and an increase in
cardiovascular disease mortality
and the incidence of cerebrovascular disease. However, theselatest results require confirmation because the study does nottake into account other risk factors, such as obesity or alcoholand tobacco consumption.
Currently, it is not yet possible
to reach a conclusion on theexistence of a cause-and-effectlink between radiation exposuredue to the Chernobyl accident
and the increases in cardiovascular and cerebrovascular mortality.

A funeral monument in honour of Chernobyl liquidators in Slavutych, 38 km from the
Chernobyl reactor.

26

27

Inhabitants of the three republics
The areas of Belarus, Ukraine
and Russia that received depositions of caesium-137 exceeding
37,000 becquerels per square
metre after the accident covera surface area of approximately
150,000 square kilometres withmore than 5 million inhabitants.

Gross annual incidence rate (per million)

The most severely affected
were children and adolescents
exposed at the time of the disaster.
Their thyroid glands, in particular, were irradiated by the radioactive iodine that they breathedin and ingested in milk.
In Belarus, where the first cases ofcancer were detected, the number of cases of thyroid cancer
in children aged under 15 years
was very low before the accident.
After a latency period of five
years, this number rapidly increased at the beginning of the
1990s, especially among children who were under 10 at thetime of the accident.
From 1991 to 2005, 6,848 thyroid cancers were observed inchildren who were under 18 in
1986, of which the majority(5,127 cases) were under 14 in
1986. Almost all of these cancers
were treatable (there were only
15 deaths recorded up to 2005).

Girls

Boys

1996-2000

2001-2005

140
120
100
80
60
40

A young girl undergoes a medical test to find traces of caesium-137 at school in
Novozybkov.

For children born after 1986,
no increase in thyroid cancers
has been observed, the rate
found among under 10s being
2 to 4 cases per million per year,
which is similar to what was
found before the Chernobyl accident.

The risk of thyroid cancer inpeople affected during theirchildhood or adolescence still
exists 25 years after the Chernobyl accident. Monitoring ofthese cancers must therefore
be continued. Similar results
were observed in adolescentsand young adults in Ukraine andsome highly contaminated areasof Russia.

2001986-1990

1991-1995

Rate of thyroid cancers among people exposed in Belarus during childhood andadolescence (under 18 in 1986).

28

29

Doses received
in France and theirassociated risks

Psychological consequences
People were affected by theshock of the accident and ofliving in contaminated areas.
Psychological problems (stress,
depression, anxiety and physical symptoms that could not be
explained medically) were foundamong people living in the contaminated areas.

In most cases, the symptoms
observed did not come frompsychiatric problems as such.
However, they probably playeda part in changing the eating,smoking and drinking habits ofthe people affected.

The effective (whole body) doses received by inhabitants of France
were low. The highest levels were received in the east of France.
In 1986, the effective doses received by people living in themost affected areas in the eastof the country were less than 1
mSv for the year. In subsequent

years, the doses received as aresult of persistent radioactive
elements in the environment
were much lower and continuously decreased.

Effective annual dosein mSv/year
10

1

0.01

0.01

0.001
1986

1989

1992

1995

1998

2001

2004

2007

2009

2.4 mSv/year: mean annual dose due to natural radioactivity
Most affected regions in the east of France
Least affected regions in the west of France

Changes in effective dose ranges received annually from 1986 to 2010 by inhabitants ofFrance exposed to Chernobyl-accident fallout. The mean annual dose received due tonatural sources of ionising radiation is also shown for comparison.

30

31

Contribution of various
entry routes to total dose(%), for all radioactive
elements

Ingestion
Exposure to radiation from deposits
Inhalation
Exposure to radiation from the air

2011

Contribution of various
foodstuffs to ingested
dose (%)

Fruit and vegetables
Cereals
Milk and dairy products
Meat

In 1986, doses received by locals
were mainly linked to the ingestion of contaminated foodstuffs,
especially milk and dairy products, leafy vegetables and beef.
From 1987, the food chain wasmuch less contaminated, so it
was exposure to radiation emitted by remaining deposits thatmade the largest contribution
to the annual dose.
Currently, the mean effective
dose received by inhabitantsof France due to residual contamination originating fromthe Chernobyl accident is lessthan 10 microsieverts per year.

32

However, some specific eating
habits, such as consuming large
quantities of forest mushrooms
and game from the east of thecountry, can result in higher doses(of the order of tens of microsieverts per year).

received by this organ were, in thegreat majority of cases, attributable to iodine-131 ingested byconsuming fresh produce (milk,
vegetables and meat) contaminated by this radioactive element.
Given the short half-life of iodine-131 (eight days), the vast
majority of thyroid-gland exposure occurred during the threemonths following the radioactive

deposition. In the table below,
the equivalent doses at the thyroid are the mean values by age
band. Thus, some children in thesame age band may have received
lower doses and others higher
doses, which, depending on lifestyle, could be of the order of ahundred millisieverts in extreme
cases.

Age of children

Dose received (half-life)n Infants  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

n between 1.3 and 2.5 mSv  . . . . . . . . . 

n Children aged 1  . . . . . . . . . . . . . . . . . . . . . 

n between 6.6 and 13 mSv  . . . . . . . . . 

n Children aged 5 . . . . . . . . . . . . . . . . . . . . . . 

n between 4 and 7.8 mSv  . . . . . . . . . . . . 

n Children aged 10  . . . . . . . . . . . . . . . . . . . 

n between 2.1 and 3.9 mSv  . . . . . . . . . 

Mean doses in the thyroid gland received by children living in the east of France in 1986. The
range of estimated values for each age band corresponds to the variability of eating habits, aparameter that greatly influenced the dose.

In France, investigation of the risks
associated with fallout from the
Chernobyl accident has focusedon thyroid cancers, due to the epidemic observed in the most contaminated regions of Belarus. On
average, the highest equivalentdoses in the thyroid gland werereceived by children living in theeast of France in 1986. The doses

33

The site today
In 2000, a study by IRSN and
Institut National de Veille Sanitaire (InVS, the French national
health monitoring institute) produced an estimate of the theoretical number of excess casesof thyroid cancer likely to occur
between 1991 and 2015 amongthe 2.3 million children aged
under 15 who were living in theeast of France in 1986.
It is very difficult to assess any
additional risk corresponding tofallout from the Chernobyl ac-

cident by means of an epidemiological study, as the estimatednumber of additional cases wasless than or similar to the uncertainties in the predicted number of “spontaneous” thyroid
cancers in this population (seetable below). The existence of
any additional risk is not certain
for the doses received in France,as these were of the order of
100 times smaller than thosereceived by Belarusian children
among whom an epidemic of
thyroid cancers was detected.

Forecast
periodNumber of
spontaneous
thyroid cancers

Number ofadditional cases
theoreticallyattributable to theaccidentn 1991-2015  . . . . . . . . . . . 

n 889 (± 60)  . . . . . . . . . . . . 

n 7 to 55 . . . . . . . . . . . . . . . . . 

Between 1986 and 2000, all the reactors at the power station
were shut down for decommissioning. Currently, there is intense
activity on the site to construct a new containment building and
to install a spent fuel storage facility.

The sarcophagus
The sarcophagus intended tocontain the reactor’s radioactive
material, which was built underparticularly difficult conditions inthe six months after the accident,
rapidly deteriorated.

Chernobyl power plant. If the sarcophagus
were to collapse, radioactive dust would
be placed in suspension and could
recontaminate the vicinity of the site.

Inside the sarcophagus. The corium willremain radioactive for thousands of years.

34

35

The new containment
A programme, jointly fundedby Ukraine and an international
fund administered by the European Bank for Reconstruction
and Development, was launched
in 1997 to reduce the risks posedby the sarcophagus.
In September 2007, a contract
for the construction of a newcontainment building to enclose the old sarcophagus was
signed with the Novarka (Vinci
and Bouygues) consortium. This
new arched structure will be verylarge: 250 m span, 150 m longand 105 m tall.

The metal framework will weighmore than 18,000 tonnes. This
structure should be completed
in 2014.
This new arch has multiple purposes: to protect the sarcophagus from external hazards, toprovide a perfect seal between
the radioactive ruins of the destroyed reactor and the environment, and to eventually allow for
the dismantling of the sarcophagus and the safe removal of theradioactive material.

International cooperation
There is still a great deal of international activity in Ukraine. At
present, it specifically concerns
assessing the safety of the arch
project and of the new facilities
for storing spent fuel which arebeing constructed on the Chernobyl site.
In addition, several specific safety
projects, funded by the European
Commission, are being pursued

36

on currently-operating nuclear
power stations in Ukraine.
In the near future, safety assessments should also begin for theconstruction of two new reactors at the Khmelnitsky power
station, the construction of a
new research reactor and theconstruction of a nuclear fuelproduction plant.
Contractors for the sarcophagus arch project (EDF, Novarka: Vinci and Bouygues Travaux
Publics).

37

Lessons learned from
Chernobyl
This accident profoundly changed the perception of theconsequences of a serious accident and how to manage them. It also
highlighted the importance of information for that management.

Protecting people
In addition to the deaths and theimmediate acute effects due toradiation that occurred shortly
after the accident, studies conducted since 1986 clearly show
an increase in the rate of occurrence of thyroid cancers, especially in children who inhaled oringested radioactive iodine.
Studies are being pursued todetect or assess other healthconsequences that could beconnected with the accident.
No definite conclusion has yet
been reached. In any event, living
conditions in the contaminatedareas continue to pose problems.
In particular, actions are being
taken to reduce the doses that
may result from the ingestion ofcontaminated produce.

Currently, crisis management
policy is that, in the event ofa reactor accident leading toradioactive releases and whenordered by the local authorities,
stable iodine tablets should betaken to prevent doses being
received in the thyroid gland byinhalation of radioactive iodine.
Tablets were distributed on a
preventive basis at the end of the
1990s around EDF power plants
and this action is periodicallyrepeated. Furthermore, orders
prohibiting the consumption
and sale of contaminated products would be issued with reference to the maximum permissible levels defined by European
regulations.

A stabilised iodine tablet, an effective means of reducing dose at the thyroid in the event of
exposure to radioactive iodine.

Transparency and information
An international convention
was signed in 1986. It statedthat immediate information
should be given by the countries concerned in the eventof an accident at one of their
nuclear facilities.
Furthermore, an International
Nuclear Event Scale (INES) was
defined to ensure clear understanding of the relative severity of the various incidents and38

accidents occurring at nuclear
facilities.
Since 1981, local informationcommissions have been created for French nuclear facilities
and, in particular, nuclear power
plants.
IRSN provides assistance forthese local information commissions either directly or
through their national association, ANCCLI.

39

The role assigned to these organisations has been strengthened by the French Transparency
and Nuclear Safety (TSN) Act
of 2006.
Other forms of dialogue are developing, such as multi-disci-

plinary expert groups, in which
technical topics can be discussed
on the basis of operator documentation and IRSN surveys,
with input from the various interested parties before decisions
are made.

Crisis management
Since 1986, there have been
important developments in the
resources available in the eventof a crisis. Operators, administrations and their technical agencies have all modernised theircrisis centres, including with regard to communications.
In this context, IRSN has gradually increased its technical capacities in the following areas:

monitoring of radioactivity inthe environment including, inparticular, the setting up of the
TELERAY network, which can detect any abnormal increase inambient radiation in real time;n methods and software forpredicting the possible consequences of a crisis on the environment and people, to help
decision-making for effective
protective actions;n field equipment that can bemobilised in emergencies tomeasure accidental contamination of the environment andpeople.
n

About 15 crisis drills are conducted every year to train thevarious parties. Organisation
for the emergency phase is now
considered well tested, althoughcare should be taken to maintainits effectiveness.
Studies are on-going to improve
preparation for handling situations that may arise as a resultof accidents: Chernobyl clearly
demonstrated the problems involved in managing such situations, especially on a large scale.

Power plant safety
Nuclear power plant safety has
been considerably improvedin Eastern European countries,
with international and, especially, European help.

TELERAY: a system for measuring ambient gamma radiation in real time and warning in theevent of an increase in radioactivity.

40

However, vigilance is required
due to the original design ofsome facilities and the economic
problems faced by many countries concerned.

In the West, the Chernobyl accident, coming on the back of
the Three Mile Island accident(in Pennsylvania, USA), led torenewed analysis of serious accidents involving core meltdownwith the aim of determining all
possible means of reducing releases in such events, both for existing facilities and for any futurefacilities. These analyses have led

41to significant improvements tonuclear facilities.
With regard to human intervention in the context of nuclear
power plant safety, the Chernobyl accident led to thoroughre-examination of the conceptof a safety culture and its implementation. This concerns not
only operators but also managers and organisations.

Economic and social consequences
This disaster had major humanitarian, environmental and economic
consequences in Ukraine, Russia
and Belarus. Between them, thesecountries received 70% of theradioactive fallout. In addition to
the 30-kilometre exclusion zone,
which is located mainly in Ukraine,
23% of Belarusian land was con-taminated by caesium-137. In thisrespect, Belarus is the most significantly affected country: with
1.6 million people living in thecontaminated areas (15% of the
population), the inhabitants of theworst-affected areas had to be permanently displaced; their originalvillages razed to the ground, andhomes and infrastructure rebuilt.
In Belarus alone, nearly 235,000
people have had to be resettled.
Several million people benefit fromhealth screening, including “liquidators” from the three countries
concerned. New healthcare centres have been established and actions have been taken to protect
children’s health, thus building
up health costs. People living incontaminated areas are exposedto specific difficulties, and theiraccompanying costs.
The three countries had to deal
with significant agricultural andforestry losses. Some production
was unfit for consumption andtherefore banned while products

not banned were sometimes nevertheless rejected resulting in a double blow to affected areas. In areas
contaminated but not evacuated,
agriculture is still handicapped andradioactive waste management
cannot be discontinued.
Work performed on the Chernobylsite itself has been very costly andthis will continue even more so
into the future. While Eastern Europe depended on nuclear power,
many reactors had to be upgraded
and the oldest ones shut down.
Overall, despite large gifts fromthe international community, thethree affected countries have beenburdened with costs amounting toseveral hundred billion dollars.

Chernobyl Museum in Kiev (Ukraine): the names of villages razed in the exclusion zone.

42

43

COLOPHON APRIL 2011
Photographs by: Sygma n Claude Cieutat n Campagne-Campagne n D.R.
n IRSN/Hôpital Cochin/Seignette-Lafontan n Pascal Landmannn Noak/Le bar Floréal/IRSN n Jean Robert/IRSN n Novarka n Chernobyl museum/Brice Mairen Illustrations: P. 3 Stéphane Jungers. n P. 12 Laurent Stéfano - P. 40 Chromatiques Éditions

IRSN
The French Institute for Radiological Protection and Nuclear Safety(IRSN) is responsible for the scientific assessment of nuclear and radiological risk.
It is an “EPIC” (a state-owned industrial and commercial enterprise)that carries out research and surveys for the French Government andthe general public. It is a reference body both in France and internationally, with a workforce of over 1,700 people who cover a diverse range of
disciplines ranging from life sciences to nuclear physics. It carries out
research and surveys in its areas of expertise as follows:n protection of people and the environment against the risks of ionisingradiation,n safety of facilities and transportation of radioactive material and its
protection against malicious acts,n monitoring of nuclear materials and products that may be used in the
manufacture of weapons,n crisis management.
It also contributes to providing the public with information.

Chernobyl

Head office31, avenue de la Division Leclerc
92260 Fontenay-aux-Roses
Registered at the Register of Commerceof Nanterre under No. B 440 546 018
Telephone+33 (0)1 58 35 88 88
Postal address
B.P. 1792262 Fontenay-aux-Roses Cedex
Websitewww.irsn.fr© 2011 IRSN n Communication department

The accident that occurred in 1986 at the Chernobyl nuclear power plant in Ukraine had a profound
impact on public opinion in Europe. Since then, IRSN
has worked constantly to improve understandingof that catastrophe and its consequences on publichealth and the environment and to act to improve
the safety of the sarcophagus built over the damaged
reactor in 1986.