Enhancing nuclear safety
Chernobyl 25 years on
In late April 1986, a major nuclear accident released a large quantity of radioactive material into the atmosphere…
Collection of topics Units Some sources of radiation An introduction to the Chernobyl accident exposure for humans Becquerel The becquerel (Bq) is the unit of Natural Artificial What is radioactivity? ...... p. 2 measurement of radioactivity. radioactivity radioactivity It corresponds to one decay per Abdomen second, for all types of radiation CT scan 1 n The accident ...... p. 4 emitted ( , , ). Some parts a b g of Brazil and South-West India Gray 2 n Radioactive releases...... p. 7 The gray (Gy) is the unit of absorbed dose. It corresponds to the quantity of energy La Paz (Bolivia), Average medical 3 n Spread of the radioactive plume over Europe ...... p. 8 (measured in Joules – J) altitude exposure in France transferred by ionising radiation 3660 m (CT scan, X-rays, etc.) to the mass through which it 4 n Radioactive deposits in Europe ...... p. 12 passes (expressed in kilograms – kg). -1 5 n Contamination of various environments 1 Gy = 1 J.kg . Radon* in France Dental and the food chain ...... p. 17 Sievert panoramic *Naturally X-ray The sievert (Sv) is the unit of occurring n .. equivalent dose received by radioactive gas 6 Health impact in the most contaminated areas p. 24 a specific organ or tissue, and the unit of effective (whole Paris-New York 0.06 return flight n body) dose. The equivalent dose 0.006 7 Doses received in France and their is determined from the dose 0.002 associated risks ...... p. 31 absorbed, taking into account differences in the ability of Release of radioactive 8 n The site today ...... p. 35 different kinds of radiation to Average annual dose (mSv) damage organs or tissues. The elements into the “One-off” dose (mSv) environment from effective dose is determined nuclear power plants. 9 n Lessons learned from Chernobyl...... p. 38 from the equivalent doses delivered to the various body organs or tissues, taking into account their relative sensitivity to the effects of ionising Note radiation. These sievert doses The average individual effective dose due to natural radioactivity in France is 2.4 millisieverts a year. can be used to estimate the risk of stochastic effects (cancers or hereditary effects) which may affect the exposed organism.
1 What is radioactivity?
Radioactivity is a natural phenomenon which has existed ever We are also exposed to radiation from man-made sources (such as since atoms were formed billions of years ago. medical X-rays, fallout from atmospheric nuclear weapons tests, Chemical elements present in matter are made up of atoms with a nuclear facilities, etc.). The average individual effective dose due to nucleus of protons and neutrons, surrounded by a cloud of electrons. natural radioactivity in France is 2.4 millisieverts a year. Atoms of the same element all have the same number of protons (e.g. uranium has 92) but different isotopes of the element can have different numbers of neutrons. Most isotopes have a stable nucleus and stay the same indefinitely. Containment Steam Power Others have an unstable nucleus because they have too many or too building generator grid few neutrons. They spontaneously decay into more stable atoms and, Nuclear fuel (radioactive River in the process, they release energy in the form of ionising radiation. elements) 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 Steam radioactive decay per second. The higher the activity of a source, the more radiation it emits. As the radioactive nuclei contained in
a source decay, its activity decreases. The half-life is the time taken Water for a source’s activity to decrease by half. The radiation emitted by a radioactive source carries a great deal of energy that is gradually absorbed by the matter it passes through. The absorbed dose, expressed in grays (Gy), measures this transfer Power generator of energy. Turbine Transformer When a person is exposed to radiation emitted by a radioactive source, the dose absorbed by the tissues through which the radiation Operation of a power plant passes can cause biological damage. The risk of harmful effects on Thermal, hydroelectric and nuclear power plants are all based on the same principle. health is evaluated on the basis of the effective dose (whole body) A turbine drives a generator which produces electricity. In conventional thermal or the equivalent dose received by a specific organ or tissue, both power plants, fossil fuels (coal, natural gas or oil) are used to produce the heat expressed in sieverts (Sv), depending on the nature of the radiation 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. and the sensitivity of the irradiated organs. Fuel assemblies are placed in the nuclear reactor and produce heat by fission of the We are constantly exposed to natural sources of radioactivity, in uranium and plutonium nuclei. They break up under the impact of neutrons and our environment, in the air we breathe, in the food we eat and produce radioactive fission products that must be contained in the reactor, and even inside our bodies. neutrons which maintain the fission reaction.
2 3 The accident
Combined causes of the accident The initial design of the RBMK ration for the conditions required reactors had some significant for the planned test, and the lack weaknesses from a safety stand- of time to complete it, meant point. In particular, they were that operators did not follow all highly unstable at certain power the operating rules. They also ranges, the emergency shutdown violated them by suppressing system had too long a response some important safety systems. time and there was no contain- ment around the reactor. In addi- tion, the lack of sufficient prepa-
Spiral to disaster In the morning of 25th April, On 26th April at 01:23:04, the operators began the power re- test was launched, and the tur- duction procedure. bine steam supply valves were 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 closed. The temperature rose in up on its end (model of destroyed reactor 4). Between 13:00 and 23:00, the the core, causing reactivity to reactor was held at half-power, increase. contrary to the initial test sched- The reactor started to go critical ule, at the request of the electric and out of control. At this point, The Chernobyl power plant power distribution centre. the operators realised the seri- ousness of the situation. On 26th April 1986 at 01:24, pressure tubes were placed, each At about 23:00, power reduction reactor 4 at the Chernobyl of which contained several nu- was resumed. However, the reac- At 01:23:40, the chief opera- power plant, which had been clear fuel assemblies. The graph- tor state was now inappropriate tor ordered an emergency shut- in service since 1983, exploded ite functioned as a moderator – for the test to be performed. The down. All control rods began to in an accident during a techni- neutrons had to be slowed down core was very difficult to control enter the core, but did not have cal test. to maintain the chain reaction. with the systems available. The time to stop a runaway chain It was a RBMK type reactor, a So- Cooling was provided by boil- reactor should have been stabi- reaction. viet model designed in the 1960s. ing water flowing through the lised at this stage. However, op- The reactor core was made up of pressure tubes in contact with erators were in a hurry to catch At 01:23:44, power peaked, ex- a huge block of graphite contain- the fuel. up the delay in the schedule, and ceeding the reactor’s nominal ing vertical channels in which decided to perform the test re- power by a factor of more than gardless. 100.
4 5 Radioactive releases
An explosion followed by a fire Most of the radioactive material released was discharged at the time of the reactor’s explosion. The high pressures reached in took fire-fighters three hours to the pressure tubes caused them extinguish the fires. The graphite to rupture. An explosion lifted fire reignited. It was not fully The energy of the explosion All together, nearly 12 billion- the upper reactor cover, weigh- extinguished until 9 May. propelled radioactive materials billion becquerels were ejected ing about 2000 tonnes, off the contained in the nuclear reac- into the environment in 10 days, reactor. Between 27th April and 10th May, tor core into the atmosphere, to that is 30,000 times the radioac- The top of the reactor core was 5000 tonnes of material (sand, altitudes of over 1200 metres. tive emissions released into the exposed to the open air. The boron, clay, lead, etc.) were poured These materials continued to be atmosphere by all the nuclear graphite ignited, and a number onto the reactor by helicopter to released until 5th May as a result facilities operating in the world of fires broke out in the facility. It cover it. of the fire that followed the ac- at that time in one year. The vast cident and then the residual heat majority (84% of the total activ- released by the remains of the ity released) of the radioactive core destroyed by the accident. elements had a half-life of less than one month.
Radioactive materials (excluding noble gases) released daily into the atmosphere after the explosion of Chernobyl reactor no.4 (INSAG estimate 1986) 0.60
The fuel rods in the core broke up. The overheated uranium oxide pellets exploded. 0.40 Bq) per day. 18 0.30
0.00 0.002 - 0.006 Ebqd Release rate in exabecquerels (10 in exabecquerels rate Release
26th April 27th April 28th April 29th April 30th April 1st May 2nd May 3rd May 4th May 5th May 6th May
6 7 Spread of the radioactive plume over Europe times and the various plumes ued to be dispersed across the mixed to form a mass of con- whole of the northern hemi- Nuclear fuel debris and pieces of the reactor were thrown into taminated air which covered sphere and were detected in the environment around the power plant. Radioactive dust, fine most of Europe in decreasing North America and Japan, in particles (aerosols) and gases rose to high altitudes and formed concentrations. These radio- extremely low concentrations. a plume which was carried over great distances in air masses by active elements then contin- changing winds.
Activity conc. at ground level on 28th Apr at 12:00 (Bq/m3) th 69N Between 26 April and mid-May with a very short half-life (a few 66N 63N 1986, the radioactive plume hours) disappeared quickly as 60N 57N scattered radioactive elements a result of radioactive decay in 54N such as iodine-131, caesium-134 the plume. This meant that the 51N 48N Spread of caesium-137 and caesium-137 over most of concentration of radioactive ele- 45N released into the atmosphere 42N by the Chernobyl accident: the countries in Europe. ments in the air, which was over 39N 36N situation at 12:00 on 28th As time passed, this dispersion 10 million becquerels per cubic 10W 5W 0 5E 10E 15E 20E 25E 30E 35E 40E 45E 50E 55E 60E April 1986 (modelling: IRSN 2006). resulted in the dilution of the metre (Bq/m3) in the vicinity 0,01 0,1 1 10 100 1000 radioactive elements in the air. of the damaged reactor on 26th Some of the aerosols were de- April, decreased as it travelled Act. concentr. at ground level on 1st May at 12:00 (Bq/m3) 69N posited along the way, gradually and was no more a few tens of 66N 63N depleting the radioactive cloud. becquerels per cubic metre over 60N st 57N Finally, the radioactive elements France on 1 May. 54N 51N 48N Plume paths 45N Air contamination by 42N caesium-137: 39N situation at 12:00 Initially, the wind carried the ra- France and Northern Italy - 36N st th 10W 5W 0 5E 10E 15E 20E 25E 30E 35E 40E 45E 50E 55E 60E on 1 May 1986 dioactive material released on which it reached between 30 (modelling: IRSN 2006). 26th April in a north-westerly di- April and 5th May, before being 0,01 0,1 1 10 100 1000 rection. The plume passed over picked up by a south wind which Activity conc. at ground level on 3rd May at 12:00 (Bq/m3) the Baltic countries and then took it to the British Isles, avoid- 69N th 66N Scandinavia on 28 April, and ing Spain and Portugal. Emis- 63N 60N was then blown eastwards and sions from the power plant from 57N th 54N then south, carrying the contam- 28 April were carried east and 51N inants towards central Europe south, towards Russia, the Cau- 48N 45N and the Balkans. casus, the eastern Mediterranean 42N Air contamination by 39N caesium-137: situation at The plume of material released and central Europe. 36N 10W 5W 0 5E 10E 15E 20E 25E 30E 35E 40E 45E 50E 55E 60E rd th 12:00 on 3 May 1986 on 27 April travelled towards Over time, the radioactive (modelling: IRSN 2006). 0,01 0,1 1 10 100 1000 western Europe - Germany, materials released at different
8 9 30th April 1986 1st May 1986 In France In France, the concentration The main radioactive elements of radioactive elements in the measured in the air in early May air increased in the east of the 1986 are given below, in decreas- country during 30th April 1986, ing order of concentration: peaking on 1 May.
2nd May 1986 3rd May 1986 Radioactive elements Half-life
n Iodine-131 ...... n 8 days ......
n Tellurium-132 ...... n 78 hours ......
n Tellurium-129m ...... n 33 days ......
n Ruthenium-103 ...... n 39 days ......
th n Caesium-137 ...... n 30 years ...... 4th May 1986 5 May 1986
n Caesium-134 ...... n 2 years ......
n Barium-140 ...... n 13 days ......
The air contamination lasted After 6th May, it decreased con- until 5th May, but continued to siderably as the plume headed decrease. It remained highest in back towards Eastern Europe. Air contamination by th the east throughout this period. . 6 May 1986 caesium-137 (Becquerels/m3)
0.5 0.1 0.05 0.025 0.01 0.0015 (Maps drawn up by IRSN in 2004 based on measurements of daily aerosol samples taken by the SCPRI monitoring network). by taken samples aerosol of daily based on measurements IRSN in 2004 up by (Mapsdrawn
Mean concentration of caesium-137 in the air over France between 30th April and 6th May 1986.
10 11 Radioactive deposits in Europe areas where it rained, and their tivity of the radioactive deposits activity was up to 10 times higher compared with those in open than dry deposits formed in the fields. This led to highly non- The radioactive particles carried in the air masses fell to the ground same places. Contamination uniform radioactive deposits, as dry deposition when the particles were near the ground and as “patches” thus formed depend- with the greatest amounts being wet deposition with rain or snow. ing on when and where it rained. distributed around the Cher- n In mountainous areas, where nobyl site and in the countries it rains more, the activity of de- neighbouring the power plant. Total activity deposited (Bq/m²) posits was greater. In forest areas, Caesium-137 is a good indicator WET DEPOSITION DRY DEPOSITION the leaves on trees captured the for measuring the distribution Wet deposition Dry deposition on leaves on leaves radioactive dust in the air more of deposits on a European scale. readily, which increased the ac-
Deposits carried away by runoff
Kilobecquerels/m2 Deposits carried in by runoff 1 480 185 Wet deposition Dry deposition 40 on soil on soil 10 Wet and dry 2 deposition under 0 Data Residual activity in the ground the radioactive unavailable plume
These deposits covered plants, the power plant, forming very soil and surface water but also highly active deposits within built-up areas and inhabited the 30-kilometre exclusion zone locations. When deposits were around the power plant. formed by rain, they were dis- n The severity of the concentra- tributed across the surface or tion of radioactive elements in into the ground by runoff. the air and the length of time The extent of deposits in Europe the surrounding air was con- varied according to many differ- taminated resulted in highly ac- ent factors. tive deposits in the three most n The biggest and heaviest parti- severely affected countries - Map of caesium-137 deposits over Europe immediately after the Chernobyl accident cles, especially nuclear fuel debris, Ukraine, Belarus and Russia. (source: European Atlas EC/IGCE 1998 and IRSN). No data is available for the Balkans. fell in the immediate vicinity of Deposits were much higher in
12 13 Contaminated areas in former Soviet Union countries France In Russia, Belarus and Ukraine, becquerels per square metre. Due to the depletion of the ra- square metre in the more westerly vast areas were unevenly con- In the area around the power dioactive plume and the short départements of France. taminated with radioactive plant, varying deposits of stron- amount of time that the air However, heavy localised rainfall, deposits that reached several tium-90, plutonium, etc., were over France was contaminated especially between 2nd and 4th May, hundreds of thousands and formed along the paths of the (about a week), deposits gener- resulted in greater wet deposition sometimes exceeded a million radioactive plumes. ally had low levels of activity, to the east of an imaginary line which tended to be greater in drawn between the Moselle river the east than in the west of the and Corsica. Some areas received KilometresKilomètres 510 020 country. deposits with activities exceed- Consequently, dry deposits of ing 10,000 becquerels per square
1998 caesium-137 were estimated metre and even, locally, 20,000 at around 1000 becquerels per becquerels per square metre. Dé- square metre in the east and ap- partements in the North-East of ydromet(Bielorussie), proximately 100 becquerels per France, the Franche-Comté region, 2 aine) / Belh kBq/m yl (Ukr
3 700 ydromet (Russie) / Minchernob osh R 1 480 © EC/IGCE,
Caesium-137 deposits in 1986 around the Chernobyl power plant. 137Cs Bq/m2 (values from May 1986)
> 40,000 20,000 to 40,000 Central and Western Europe 10,000 to 20,000 Outside the former Soviet Union, the Czech Republic and Poland, 5,000 to 10,000 < 5,000 deposits exceeding 40,000 bec- in Austria and northern Greece, querels per square metre oc- as well as over smaller areas in curred in Scandinavia (southern the UK, Switzerland, Bavaria and Finland, central and eastern Swe- Italy (Italian Lakes and the Do- den, central Norway), in central lomites). Reconstitution of caesium-137 fallout in May 1986 over France by modelling based on the amount of rainfall in early May 1986 (IRSN 2005). Europe - especially in southern Romania, on the border between
14 15 Contamination of various environments the Southern Alps and Corsica At a local level, widely varying were the worst affected. deposits were found within the and the food chain On a very local scale, severe same department, with read- downpours led to even heavier ings varying by a factor of 10 Radioactive fallout from the atmosphere was distributed over deposits over areas of a few to 15. This made precise map- various environmental contexts. square kilometres. ping impractical. Qualitatively, iodine-131 deposits in the same This contamination extended to In mountainous regions, the way as caesium-137, with an related production, such as dairy concentration of deposits due initial activity approximately 10 produce and meat. to melting snow, water dripping times higher. However, its short Contamination reached a peak from trees and surface water half-life (eight days) means that, immediately after the deposits runoff into basins at the base unlike caesium, it quickly disap- occurred and decreased consid- of the slopes, resulted in high- pears from soil (80 days after erably in the following weeks activity patches over very small the accident, iodine-131 activity due to the continuing growth of surface areas (several becquerels had reduced by a factor of 1000, plants and the disappearance of per kilogramme of soil over a few while that of caesium-137 was short-half-life radioactive ele- square feet). practically unchanged). ments (iodine-131). It was 100 Plants were directly contami- times lower after three months. nated by leaf-capture of radioac- The soil retained part of the ra- tive products suspended in the dioactive elements deposited air (aerosols). This phenomenon, and a persistent inventory was which happens much more in dry formed in the case of those with deposition than in wet deposi- a long half-life and a tendency to tion, led to contamination of ag- become fixed in soil components ricultural and natural food prod- (e.g. clays), such as caesium-137. ucts. The time of year at which From 1987, the transfer of radio- the accident occurred meant active elements via roots, while that grass and leafy vegetables, much less efficient than direct especially lettuces, spinach and capture by leaves, contributed to leeks, were the plants most af- maintaining chronic contamina- fected in May 1986. Livestock tion of plants and the rest of the which grazed on the contami- food chain in the most severely Soil sample used to measure deposits. nated fields were also affected. affected areas.
16 17 Contaminated areas in Russia, Belarus and Ukraine beef and 1000 to 2500 becque- reduction up until the beginning rels per kilogramme in cabbages. of the 1990s, contamination lev- In the same period, most of the els in agricultural produce have Agricultural produce cereals and potatoes produced continued to reduce more gradu- In the severely affected areas of depending on the initial char- had an activity of less than 100 ally (3% to 7% per annum) and is Russia, Belarus and Ukraine, high acteristics of the deposits, soil becquerels per kilogramme. now largely due to caesium-137. levels of contamination were de- types and agricultural practices. However, activity levels re- It is more significant in animal tected in agricultural products Until the beginning of the 1990s, mained high in some areas, with products (meat, milk), especially both in 1986 and in the years it was not unusual to find high several thousand becquerels per from extensive farming, than in that followed. After 1986, for concentrations of caesium-137. kilogramme in natural grasses vegetable products. most soils, the contamination This was noted mainly in the and some fodder. After a sharp was largely fixed in the upper Gomel region of Belarus, where 10 to 20 centimetres. Overall, contamination levels reached Forests the contamination of agricul- several thousand becquerels per tural products decreased as the litre for cow’s milk, 1000 to 5000 Leaves on trees are especially which thus constitutes a per- years passed, to differing extents becquerels per kilogramme of prone to capturing ambient sistent inventory of radioactive aerosols. substances, that are recycled by When these leaves fall, they con- the trees and plants of the under- taminate forest litter and soil, growth, especially new growth. Collective farms Private farms
Caesium-137 activity (in becquerel/litre) measured from 1987 in cow’s milk collected from farms in contaminated areas. Contamination was extremely variable depending on the severity Caesium-137 concentration measured in mushrooms gathered between 1986 and 2000 in of the fallout and on rehabilitation measures on agricultural land.. contaminated areas of Russia, Belarus and Ukraine.
18 19 Twenty-five years after the acci- ing time, very high caesium-137 Becquerels/l dent, the caesium-137 contami- activity is still found in natural Caesium in the Dniepr nation persisting in plant litter products gathered in forests in Caesium in the Pripyat and forest soil has essentially the most contaminated regions. only reduced due to radioactive Levels as high as several tens of Caesium emissions decay (i.e. to 56% of the activity thousands of becquerels per kilo- initially deposited) and, via the gramme may be found in mush- roots, still contaminates wood rooms, game and wild berries. and leaves, as well as mush- rooms, berries and game. So, unlike for agricultural produce whose contamination has gener- ally sharply decreased with pass- Graph showing changes in River water caesium levels 0.5 (1986 to 1994) An impact on surface water was plant, where it was directly con- in the Pripyat and the Dniepr. mainly found in the first few taminated by radioactive fallout. Years weeks following the accident in After this, water contamination areas near the damaged power levels decreased rapidly, due to the disappearance of short-lived melting snow and flood water radio-isotopes and the absorp- promoted the leaching of some tion of radioactive substances surface-soil deposits into water by sediments. Thus, the Pripyat courses. Caesium-137 and stron- and the Dniepr which supply the tium-90 are the main radioactive main towns in Ukraine with drink- elements that have been found in ing water were contaminated to the long term in the Pripyat, near such an extent that preventive Chernobyl, in low concentrations actions had to be taken dur- (of the order of 0.1 Bq/l dissolved ing the first few months: dykes in the water). Groundwater was were built, towns were supplied not affected, other than in the with water from uncontami- immediate proximity of the site nated areas and water use was due to infiltration into the soil restricted. In 1986 and the years where contaminated debris had that followed, rainwater runoff, been hastily buried. Cargo port on the Pripyat (tributary of the Dniepr) and abandoned contaminated boats.
20 21 In France reached as high as 10,000 bec- In 2010, contamination in farm querels per litre for iodine-131 produce was between 10 and In France, the highest levels of this type of deposit. In the weeks and 500 becquerels per litre for 30 times lower than in 1987 contamination in agricultural following the initial deposition of caesium-137. and between 1000 and 10,000 and natural products were radioactive substances, the con- times lower than immediately found in eastern regions. centrations of iodine-131 and From 1987, contamination of after deposition in May 1986. The maximum levels measured caesium-137 in vegetables and farm produce was due to the It continues to decrease slowly in cow’s milk and lettuces were dairy produce decreased very roots of plants absorbing cae- over time. found during the first half of May rapidly due to plant growth and sium-137 and caesium-134 pre- Some forest soils in the east of 1986. In areas in the east of the radioactive decay of iodine-131. sent in soil. France still contain nearly 55% country, which had received par- Some products are extremely At this point, contamination of the caesium-137 initially ticularly substantial wet depo- sensitive to the effects of ra- was much lower and decreased deposited. This radioactive ele- sition, the reduced efficiency dioactive fallout. In particular, steadily as the years passed. This ment can still be measured in of leaf-capture of radioactive this is the case for goat’s and decrease is explained by radio- concentrations in the region of fallout due to heavy rainfall re- sheep’s milk as, in the Mediter- active decay, especially that of 100 becquerels per kilogramme sulted in contamination of these ranean area, these animals feed caesium-134 with a half-life of in some species of mushrooms products that was only two or on plants with low water con- 2.1 years, and the reduced avail- harvested from these soils. three times higher than that tent scattered over large areas. ability of caesium for plants. measured in areas of the same Immediately after deposition, regions less severely affected by the contamination in this milk
Becquerel/kg fresh Cereals Beef iodine-131: < 100 Bq/l iodine-131: 50-250 Bq/l Cow’s milk caesium-137: < 10 Bq/l caesium-137: 20-50 Bq/l Leafy vegetables Changes in caesium-137
iodine-131: 100-600 Bq/l Ranges of contamination caesium-137: 30-100 Bq/l caesium-137 in various and foodstuffs in iodine-131: 30-250 Bq/l iodine-131 France since caesium-137: 10-20 Bq/l iodine-131: 300-2700 Bq/kg fresh caesium-137: 100-600 Bq/kg fresh contamination 0.1 1986. From the values: mid-1990s, measured in 0.01 caesium-134 the first half was no longer Cereals of May 1986. detectable. caesium-137: < 200 Bq/kg Years
22 23 Health impact in the most and Ukraine owing to the long such as cancers in the exposed contaminated areas half-life of caesium-137 (30 populations. In situations in- years). volving very severe exposure, as In the days following the accident, the population of most of The doses received by the peo- suffered by on-site personnel Europe was exposed to varying degrees of fallout from the ple subjected to these various and the first emergency work- Chernobyl accident. types of exposure depended on ers, the absorbed doses were so their relative intensity and each high that some people’s expo- individual’s way of life. Their sure exceeded the thresholds at intensity determined the risk which acute radiation symptoms of the occurrence of diseases and radiation burns appear.
Fire-fighters and power plant personnel Among the 600 emergency sure to ionising radiation (cardiac workers involved on the first arrest, pulmonary tuberculosis, day and who received the high- cirrhosis of the liver, trauma, and
Two elderly people est doses, two died immedi- cancer). living in the exclusion ately of burns and 28 others Among the survivors of the 134 zone. died in the four months fol- who presented with acute radia- lowing the accident as a result tion syndrome immediately after of their exposure to radiation. the accident, skin lesions second- From 26th April 1986 onwards, posure decreased with distance Between 1987 and 2006, 19 more ary to the radiation burns and people present on the site or from the power plant. They were died from various causes, most of cataracts are the main effects in its immediate vicinity were then exposed to radiation emit- which were unrelated to expo- seen today. severely exposed to radiation ted by the radioactive deposits emitted by the reactor, to ra- on the ground. Finally, they were dioactive elements released into exposed through food contami- the external environment and nation due to deposition onto to deposits that formed on the leaves (an important factor in ground. These were mainly work- the months after the accident) ers on the site and their families or to transfer via roots of re- who lived in the nearby town of sidual contamination in the soil. Pripyat. Although these last two sources First of all, these people were of exposure have considerably exposed to the plume that was decreased over the years, they highly charged with fine radioac- still persist in the most contami- Monument in honour of the tive dust. The severity of this ex- nated areas of Russia, Belarus fire-fighters.
24 25 Liquidators The “liquidators”, approximately However, for most liquidators The rate of thyroid cancer seems Many studies also report on 600,000 civilian and military per- the effective doses received were to be higher among liquidators diseases other than cancer; for sonnel, worked on the site in the much lower (on average 120 mSv, than among the general popula- example, there is an excess of first few years after the accident with 85% of effective doses re- tion, but this does not establish cataracts among liquidators to carry out various tasks: work corded being between 20 and a clear cause-and-effect link to who received doses over 0.7 on the reactor, site decontami- 500 mSv), as they carried out radiation exposure. There does Gray. Furthermore, a Russian nation, construction of the sar- tasks for limited periods and, in not seem to be an overall excess study demonstrated a link be- cophagus, and burial of radioac- some cases, several years after of other types of solid cancer, tween the doses received by the tive waste in the exclusion area. the accident. The doses received despite the apparently contra- liquidators and an increase in by the liquidators were generally dictory results of two Russian cardiovascular disease mortality Some of the personnel involved estimated with a great deal of studies that highlighted an in- and the incidence of cerebrovas- in the first few weeks received uncertainty, except for those who crease in solid cancer mortality cular disease. However, these high effective doses (in some were carrying a dosimeter during in proportion to dose received. latest results require confirma- cases exceeding 1000 mSv). their work. tion because the study does not Although they are not definitive, take into account other risk fac- recent reports suggest an excess tors, such as obesity or alcohol in cases of leukaemia among and tobacco consumption. liquidators in Belarus, Ukraine and Russia and the Baltic states. Currently, it is not yet possible Additional studies are needed, to reach a conclusion on the in particular due to the numer- existence of a cause-and-effect ous uncertainties surrounding link between radiation exposure the “reconstruction” of dose due to the Chernobyl accident received. and the increases in cardiovas- cular and cerebrovascular mor- tality.
26 27 Inhabitants of the three republics The areas of Belarus, Ukraine cancer were detected, the num- and Russia that received deposi- ber of cases of thyroid cancer tions of caesium-137 exceeding in children aged under 15 years 37,000 becquerels per square was very low before the accident. metre after the accident cover After a latency period of five a surface area of approximately years, this number rapidly in- 150,000 square kilometres with creased at the beginning of the more than 5 million inhabitants. 1990s, especially among chil- dren who were under 10 at the The most severely affected time of the accident. were children and adolescents From 1991 to 2005, 6,848 thy- exposed at the time of the dis- roid cancers were observed in aster. children who were under 18 in A young girl undergoes a medical test to find traces of caesium-137 at school in Their thyroid glands, in particu- 1986, of which the majority Novozybkov. lar, were irradiated by the radio- (5,127 cases) were under 14 in active iodine that they breathed 1986. Almost all of these cancers For children born after 1986, The risk of thyroid cancer in in and ingested in milk. were treatable (there were only no increase in thyroid cancers people affected during their In Belarus, where the first cases of 15 deaths recorded up to 2005). has been observed, the rate childhood or adolescence still found among under 10s being exists 25 years after the Cher- 2 to 4 cases per million per year, nobyl accident. Monitoring of Girls Boys 140 which is similar to what was these cancers must therefore
120 found before the Chernobyl ac- be continued. Similar results
100 cident. were observed in adolescents
80 and young adults in Ukraine and
60 some highly contaminated areas
40 of Russia.
0 Gross annual incidence rate (per million) incidence rate annual Gross 1986-1990 1991-1995 1996-2000 2001-2005
Rate of thyroid cancers among people exposed in Belarus during childhood and adolescence (under 18 in 1986).
28 29 Doses received in France and their Psychological consequences associated risks People were affected by the In most cases, the symptoms shock of the accident and of observed did not come from The effective (whole body) doses received by inhabitants of France living in contaminated areas. psychiatric problems as such. were low. The highest levels were received in the east of France. Psychological problems (stress, However, they probably played depression, anxiety and physi- a part in changing the eating, In 1986, the effective doses re- years, the doses received as a cal symptoms that could not be smoking and drinking habits of ceived by people living in the result of persistent radioactive explained medically) were found the people affected. most affected areas in the east elements in the environment among people living in the con- of the country were less than 1 were much lower and continu- taminated areas. mSv for the year. In subsequent ously decreased.
Effective annual dose in mSv/year 10
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 of France exposed to Chernobyl-accident fallout. The mean annual dose received due to natural sources of ionising radiation is also shown for comparison.
30 31 received by this organ were, in the deposition. In the table below, Contribution of various Ingestion great majority of cases, attribut- the equivalent doses at the thy- entry routes to total dose Exposure to radiation from deposits (%), for all radioactive Inhalation able to iodine-131 ingested by roid are the mean values by age elements Exposure to radiation from the air consuming fresh produce (milk, band. Thus, some children in the vegetables and meat) contami- same age band may have received nated by this radioactive element. lower doses and others higher Given the short half-life of io- doses, which, depending on life- 2011 dine-131 (eight days), the vast style, could be of the order of a majority of thyroid-gland expo- hundred millisieverts in extreme sure occurred during the three cases. months following the radioactive
Fruit and vegetables Contribution of various Cereals foodstuﬀs to ingested Milk and dairy products Age of children Dose received (half-life) dose (%) Meat n Infants ...... n between 1.3 and 2.5 mSv . . . . .
n Children aged 1 ...... n between 6.6 and 13 mSv . . . . . In 1986, doses received by locals However, some specific eating were mainly linked to the inges- habits, such as consuming large n Children aged 5 ...... n between 4 and 7.8 mSv ...... tion of contaminated foodstuffs, quantities of forest mushrooms n Children aged 10 ...... n between 2.1 and 3.9 mSv . . . . . especially milk and dairy prod- and game from the east of the ucts, leafy vegetables and beef. country, can result in higher doses Mean doses in the thyroid gland received by children living in the east of France in 1986. The From 1987, the food chain was (of the order of tens of microsiev- range of estimated values for each age band corresponds to the variability of eating habits, a much less contaminated, so it erts per year). parameter that greatly influenced the dose. was exposure to radiation emit- ted by remaining deposits that In France, investigation of the risks made the largest contribution associated with fallout from the to the annual dose. Chernobyl accident has focused on thyroid cancers, due to the epi- Currently, the mean effective demic observed in the most con- dose received by inhabitants taminated regions of Belarus. On of France due to residual con- average, the highest equivalent tamination originating from doses in the thyroid gland were the Chernobyl accident is less received by children living in the than 10 microsieverts per year. east of France in 1986. The doses
32 33 The site today
In 2000, a study by IRSN and cident by means of an epidemio- Between 1986 and 2000, all the reactors at the power station Institut National de Veille Sani- logical study, as the estimated were shut down for decommissioning. Currently, there is intense taire (InVS, the French national number of additional cases was activity on the site to construct a new containment building and health monitoring institute) pro- less than or similar to the uncer- to install a spent fuel storage facility. duced an estimate of the theo- tainties in the predicted num- retical number of excess cases ber of “spontaneous” thyroid The sarcophagus of thyroid cancer likely to occur cancers in this population (see between 1991 and 2015 among table below). The existence of The sarcophagus intended to particularly difficult conditions in the 2.3 million children aged any additional risk is not certain contain the reactor’s radioactive the six months after the accident, under 15 who were living in the for the doses received in France, material, which was built under rapidly deteriorated. east of France in 1986. as these were of the order of 100 times smaller than those It is very difficult to assess any received by Belarusian children additional risk corresponding to among whom an epidemic of fallout from the Chernobyl ac- thyroid cancers was detected.
Number of additional cases Number of theoretically Forecast spontaneous attributable to the period thyroid cancers accident n 1991-2015 ...... n 889 (± 60) ...... n 7 to 55 ......
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 will remain radioactive for thousands of years.
34 35 The new containment A programme, jointly funded The metal framework will weigh by Ukraine and an international more than 18,000 tonnes. This fund administered by the Euro- structure should be completed pean Bank for Reconstruction in 2014. and Development, was launched This new arch has multiple pur- in 1997 to reduce the risks posed poses: to protect the sarcopha- by the sarcophagus. gus from external hazards, to In September 2007, a contract provide a perfect seal between for the construction of a new the radioactive ruins of the de- containment building to en- stroyed reactor and the environ- close the old sarcophagus was ment, and to eventually allow for signed with the Novarka (Vinci the dismantling of the sarcopha- and Bouygues) consortium. This gus and the safe removal of the new arched structure will be very radioactive material. large: 250 m span, 150 m long and 105 m tall.
International cooperation There is still a great deal of in- on currently-operating nuclear ternational activity in Ukraine. At power stations in Ukraine. present, it specifically concerns In the near future, safety assess- assessing the safety of the arch ments should also begin for the project and of the new facilities construction of two new reac- for storing spent fuel which are tors at the Khmelnitsky power being constructed on the Cher- station, the construction of a nobyl site. new research reactor and the In addition, several specific safety construction of a nuclear fuel projects, funded by the European production plant. Commission, are being pursued Contractors for the sarcophagus arch project (EDF, Novarka: Vinci and Bouygues Travaux Publics).
36 37 Lessons learned from Chernobyl
This accident profoundly changed the perception of the consequences 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 the Currently, crisis management immediate acute effects due to policy is that, in the event of radiation that occurred shortly a reactor accident leading to after the accident, studies con- radioactive releases and when ducted since 1986 clearly show ordered by the local authorities, an increase in the rate of occur- stable iodine tablets should be rence of thyroid cancers, espe- taken to prevent doses being cially in children who inhaled or received in the thyroid gland by ingested radioactive iodine. inhalation of radioactive iodine. Studies are being pursued to Tablets were distributed on a detect or assess other health preventive basis at the end of the A stabilised iodine tablet, an effective means of reducing dose at the thyroid in the event of consequences that could be 1990s around EDF power plants exposure to radioactive iodine. connected with the accident. and this action is periodically No definite conclusion has yet repeated. Furthermore, orders been reached. In any event, living prohibiting the consumption Transparency and information conditions in the contaminated and sale of contaminated prod- An international convention accidents occurring at nuclear areas continue to pose problems. ucts would be issued with refer- was signed in 1986. It stated facilities. In particular, actions are being ence to the maximum permis- that immediate information Since 1981, local information taken to reduce the doses that sible levels defined by European should be given by the coun- commissions have been cre- may result from the ingestion of regulations. tries concerned in the event ated for French nuclear facilities contaminated produce. of an accident at one of their and, in particular, nuclear power nuclear facilities. plants. IRSN provides assistance for Furthermore, an International these local information com- Nuclear Event Scale (INES) was missions either directly or defined to ensure clear under- through their national associa- standing of the relative sever- tion, ANCCLI. ity of the various incidents and
38 39 The role assigned to these or- plinary expert groups, in which n monitoring of radioactivity in About 15 crisis drills are con- ganisations has been strength- technical topics can be discussed the environment including, in ducted every year to train the ened by the French Transparency on the basis of operator docu- particular, the setting up of the various parties. Organisation and Nuclear Safety (TSN) Act mentation and IRSN surveys, TELERAY network, which can de- for the emergency phase is now of 2006. with input from the various in- tect any abnormal increase in considered well tested, although terested parties before decisions ambient radiation in real time; care should be taken to maintain Other forms of dialogue are de- are made. n methods and software for its effectiveness. veloping, such as multi-disci- predicting the possible conse- Studies are on-going to improve quences of a crisis on the en- preparation for handling situa- vironment and people, to help tions that may arise as a result Crisis management decision-making for effective of accidents: Chernobyl clearly Since 1986, there have been crisis centres, including with re- protective actions; demonstrated the problems in- important developments in the gard to communications. n field equipment that can be volved in managing such situa- resources available in the event In this context, IRSN has gradu- mobilised in emergencies to tions, especially on a large scale. of a crisis. Operators, administra- ally increased its technical ca- measure accidental contami- tions and their technical agen- pacities in the following areas: nation of the environment and cies have all modernised their people.
Power plant safety Nuclear power plant safety has In the West, the Chernobyl ac- been considerably improved cident, coming on the back of in Eastern European countries, the Three Mile Island accident with international and, espe- (in Pennsylvania, USA), led to cially, European help. renewed analysis of serious ac- cidents involving core meltdown However, vigilance is required with the aim of determining all due to the original design of possible means of reducing re- some facilities and the economic leases in such events, both for ex- problems faced by many coun- isting facilities and for any future TELERAY: a system for measuring ambient gamma radiation in real time and warning in the tries concerned. facilities. These analyses have led event of an increase in radioactivity.
40 41 to significant improvements to re-examination of the concept homes and infrastructure rebuilt. not banned were sometimes never- nuclear facilities. of a safety culture and its im- In Belarus alone, nearly 235,000 theless rejected resulting in a dou- With regard to human interven- plementation. This concerns not people have had to be resettled. ble blow to affected areas. In areas tion in the context of nuclear only operators but also manag- contaminated but not evacuated, power plant safety, the Cher- ers and organisations. Several million people benefit from agriculture is still handicapped and nobyl accident led to thorough health screening, including “liqui- radioactive waste management dators” from the three countries cannot be discontinued. Economic and social consequences concerned. New healthcare cen- tres have been established and ac- Work performed on the Chernobyl This disaster had major humanitar- taminated by caesium-137. In this tions have been taken to protect site itself has been very costly and ian, environmental and economic respect, Belarus is the most sig- children’s health, thus building this will continue even more so consequences in Ukraine, Russia nificantly affected country: with up health costs. People living in into the future. While Eastern Eu- and Belarus. Between them, these 1.6 million people living in the contaminated areas are exposed rope depended on nuclear power, countries received 70% of the contaminated areas (15% of the to specific difficulties, and their many reactors had to be upgraded radioactive fallout. In addition to population), the inhabitants of the accompanying costs. and the oldest ones shut down. the 30-kilometre exclusion zone, worst-affected areas had to be per- The three countries had to deal Overall, despite large gifts from which is located mainly in Ukraine, manently displaced; their original with significant agricultural and the international community, the 23% of Belarusian land was con- villages razed to the ground, and forestry losses. Some production three affected countries have been was unfit for consumption and burdened with costs amounting to therefore banned while products several 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 Landmann n Noak/Le bar Floréal/IRSN n Jean Robert/IRSN n Novarka n Chernobyl museum/Brice Maire n 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 ra- diological risk. It is an “EPIC” (a state-owned industrial and commercial enterprise) that carries out research and surveys for the French Government and the general public. It is a reference body both in France and internation- ally, 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 ionising radiation, 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 The accident that occurred in 1986 at the Cherno- byl nuclear power plant in Ukraine had a profound impact on public opinion in Europe. Since then, IRSN has worked constantly to improve understanding of that catastrophe and its consequences on public health and the environment and to act to improve the safety of the sarcophagus built over the damaged reactor in 1986.
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