Radionuclide Concentrations in Foor and the Environment - Chapter 3 pdf

37 3 Radioactivity in the Air Peter Carny CONTENTS 3.1 Cosmic Rays 37 3.2 Cosmogenic Radionuclides 38 3.3 Terrestrial Radiation 38 3.3.1 Terrestrial Radiation: Radon and Decay Products in the Air and Other Radionuclides That Can Be Inhaled 38 3.3.2 Terrestrial Radionuclides in the Air Due to Industrial Activities (Other Than Nuclear Energy) 41 3.3.3 Summary: Airborne Activity Due to Natural Radiation Sources 42 3.4 Man-Made Radionuclides in the Air 43 3.4.1 Man-Made Radionuclides in the Air Due to Nuclear Weapons Tests and Production 43 3.4.2 Man-Made Radionuclides in the Air Due to Electricity Generation in Nuclear Power Plants: Fuel Production and Operation of Nuclear Power Plants 44 3.4.3 Man-Made Radioactivity in the Air in Case of Nuclear Accident 46 References 57 3.1 COSMIC RAYS Cosmic radiation contributes to a great extent to the total radiation exposure of human beings. This radiation has its origins in outer space; one component (protons with energies ~100 MeV) is generated by the Sun, all other components are primarily from our galaxy, and the origin of some high-energy protons (with energies ~10 19 eV) is probably extragalactic. Cosmic rays enter our atmosphere as protons, α particles, heavier nuclei, and electrons. These cosmic particles have an energy from 10 8 eV to greater than 10 20 eV. After their interaction with atoms and molecules in the atmosphere, a lot of secondary charged and uncharged particles are generated: protons, neutrons, pions, nuclei with lower Z values, and further nucleonic cascades, electrons, muons, and photons. Exposure from cosmic rays at ground level is primarily from muons, electrons, photons, and neutrons. This exposure is realized as external exposure. The intensity of cosmic rays and the dose absorbed depends on the layer of the atmosphere above the ground; in other words, it quite strongly depends on the DK594X_book.fm Page 37 Tuesday, June 6, 2006 9:53 AM © 2007 by Taylor & Francis Group, LLC 38 Radionuclide Concentrations in Food and the Environment altitude and on geographic latitude. The thicker the layer of atmosphere, the lower the absorbed dose. At sea level, the typical annual effective dose due to cosmic rays is about 350 µSv/year (from this, 80 µSv/year is typically due to neutrons). According to the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) [1], the world average (altitude and latitude averaged) annual effective dose due to cosmic rays is about 460 µSv/year (from this 120 µSv/year is due to neutrons). People living at altitudes of 2 to 3 km above the sea level could obtain an annual effective dose from cosmic rays of up to 2000 µSv/year. 3.2 COSMOGENIC RADIONUCLIDES Radioactivity in air due to cosmic radiation is a source of external irradiation of human beings as well as internal irradiation. Internal irradiation is caused by cosmogenic radionuclides present in the air. Cosmogenic radionuclides are products of cosmic ray interactions in the atmosphere. As a result of these interactions, many lower Z nuclei are created. The most important cosmogenic nuclei are 3 H and 14 C. Their importance is shown by their role in human body metabolism. They are contributors to the internal irradiation of human beings via inhalation and ingestion. Typical average volumes in air and average annual effective doses from these cosmogenic radionuclides are given in Table 3.1 (according to UNSCEAR [1]). The global inventory of 3 H is about 1275 × 10 15 Bq and the annual production rate is 72 × 10 15 Bq/year. The global inventory of 14 C is about 13 × 10 18 Bq and the annual production rate is 1.5 × 10 15 Bq/year. Both these cosmogenic nuclides ( 3 H and 14 C) are released to the environment as man-made nuclides from nuclear installations and have been released during nuclear weapons tests. 3.3 TERRESTRIAL RADIATION 3.3.1 T ERRESTRIAL R ADIATION : R ADON AND D ECAY P RODUCTS IN THE A IR AND O THER R ADIONUCLIDES T HAT C AN B E I NHALED Radionuclides that have a terrestrial origin (primordial radionuclides) are present at various levels in every kind of matter in nature. This means they are naturally present, even in the human body. TABLE 3.1 Typical Volume Activities of the Most Important Cosmogenic Radionuclides in the Air, Typical Annual Effective Dose Caused By These Nuclides Nuclide 3 H 14 C Average volume activity in air (Bq/m 3 ) 1.4 × 10 –3 56.3 × 10 –3 Annual effective dose (µSv/year) 0.01 12 DK594X_book.fm Page 38 Tuesday, June 6, 2006 9:53 AM © 2007 by Taylor & Francis Group, LLC Radioactivity in the Air 39 Terrestrial radiation is formed mainly by radionuclides from the 238 U and 232 Th series and from 40 K. These radionuclides irradiate our body with γ radiation (externally and internally) and β and α radiation (mainly internally). External irradiation is caused by radioactivity present in the soil and in any other material surrounding our bodies, including the air. Internal irradiation is caused by radio- nuclides that are inhaled or ingested. In this chapter we discuss radioactivity in the air; therefore, the most important exposure pathway is inhalation. Irradiation and effective doses caused by inhalation of terrestrial nuclides from the air result from the presence of dust particles containing radionuclides from the 238 U and 232 Th series. Typical amounts of 238 U and 232 Th in the air are about 1 µBq/m 3 . If the dust particles in air are formed by organic matter, then their uranium and thorium content is significantly lower. On the other hand, if dust particles are formed by fly ash (from the burning of coal), then the uranium and thorium content may be much higher. Typical volumes of uranium and thorium series radionuclides in air (according to UNSCEAR [1]) are shown in Table 3.2. The average annual effective dose from inhalation of uranium and thorium series radionuclides in air (without contributions of radon [ 222 Rn] and thoron [ 220 Rn]) is typically about 5 to 10 µSv/year. The most important and dominant contributors to inhalation dose are decay products of radon. Radon and its decay products in the air are the main natural sources of irradiation in human beings. Inhalation of radon (and its decay products) and thoron (so-called thoron) from the air causes their deposition on the lining of the lungs. These deposited radionuclides irradiate the lungs and other tissues, especially by α particles, as well as β and γ radiation. What is the mechanism by which radon and thoron enter the atmosphere? Both nuclides are the gaseous products of the decay of radium isotopes 226 Ra and 224 Ra, which belong to the uranium and thorium series and are present in any terrestrial materials (in solid matrix). Some radon atoms are released from the solid matrix and escape from the mineral grain into the pore space. These radon atoms are then transported by diffusion and advection, and are either decayed or released to the atmosphere. As a result, the volume activity of radon and its daughter products in the air is observed. The process of radon emanation (escape from the solid matrix) and transportation is influenced by many factors such as TABLE 3.2 Typical Volume Activities of Radionuclides From the Uranium and Thorium Series in Air (Bq/m 3 ), with the Exception of 222 Rn and 220 Rn Nuclide 238 U 230 Th 226 Ra 210 Pb 210 Po 232 Th 228 Ra 228 Th 235 U Average volume activity 1 × 10 –6 0.5 × 10 –6 1 × 10 –6 500 × 10 –6 50 × 10 –6 0.5 × 10 –6 1 × 10 –6 1 × 10 –6 0.05 × 10 –6 DK594X_book.fm Page 39 Tuesday, June 6, 2006 9:53 AM © 2007 by Taylor & Francis Group, LLC 40 Radionuclide Concentrations in Food and the Environment moisture, geological factors, and climate or meteorological conditions. Radon and its decay products are released not only from the soil or from the mineral grains, but can also be released from various building materials. Radon can penetrate from the ground around the foundations of buildings. Under some special conditions radon can be “withdrawn” from the ground to the atmosphere of buildings at higher entry rates. These phenomena can cause indoor radon activity to be higher than outdoor radon activity. The volume activity of radon in the air is therefore classified as “outdoor” activity and “indoor” activity. The typical outdoor volume activity of radon and thoron in the air is 10 Bq/m 3 . There are many places in the world with lower volume activities (from 1 Bq/m 3 ) and with higher average activities (more than 100 Bq/m 3 ) of radon and thoron in the air. Lower activities are typical for coastal regions and small islands. Higher activities are typical for sites with higher radon emanation and release to the atmosphere. The typical outdoor volume activity of radon results in a typical annual effective dose of about 100 µSv/year. Significant variations in radon volume activity in the air are usually observed in a given place during the day (solar radiation causes heating and transport of radon to higher layers of the atmosphere, thus expected air volume activity near the ground will be lower; at night and in the early morning, temperature inversions cause radon atoms to be closer to the ground, thus expected air volume activity near the ground will be higher), as a result of precipitation (rain can wash radon and its decay products from the higher air layers, causing an increase in radon levels near the ground), or as a result of winds. The typical indoor volume activity of radon is about 10 to 100 Bq/m 3 and thoron is about 2 to 20 Bq/m 3 . The typical indoor volume activity of radon produces a typical annual effective dose of about 1000 µSv/year (1 mSv/year) (Table 3.3). The indoor volume activity of radon varies significantly depending on geological conditions and the building materials used. Numerous surveys in many countries have been performed to determine the radon activity in dwellings. For example, the mean radon volume activity in dwellings in the Czech Republic TABLE 3.3 Typical Volume Activities of 222 Rn and 220 Rn in the Air (Outdoor and Indoor) and Typical Annual Effective Doses (Outdoor and Indoor) Nuclide 222 Rn 220 Rn Average volume activity in outdoor air (Bq/m 3 )10 10 Average volume activity in indoor air (Bq/m 3 ) 10–100 2–20 Annual effective dose (µSv/year), outdoor 100 ~10 Annual effective dose (µSv/year), indoor 1000 ~90 Note: Values are based on data from UNSCEAR [1]. DK594X_book.fm Page 40 Tuesday, June 6, 2006 9:53 AM © 2007 by Taylor & Francis Group, LLC Radioactivity in the Air 41 is about 140 Bq/m 3 , but buildings with values as high as 20,000 Bq/m 3 have been found. The mean radon volume activity in dwellings in Slovakia is about 90 Bq/m 3 and the highest values found have been about 4000 Bq/m 3 (see Table 3.4). On the other hand, the mean radon volume activity in dwellings in Egypt is about 9 Bq/m 3 and maximal values found have been about 20 Bq/m 3 . As was stated above, building materials (and the radioactivity of the uranium and thorium series in them) can affect indoor radon activities. Therefore in many countries there is legislation that defines the maximal permitted activity in build- ing materials. For example, in Slovakia, the maximal permitted mass activity of 226 Ra in building materials is 120 Bq/kg. 3.3.2 T ERRESTRIAL R ADIONUCLIDES IN THE A IR D UE TO I NDUSTRIAL A CTIVITIES (O THER T HAN N UCLEAR E NERGY ) Natural (terrestrial) radionuclides can be and are released to the atmosphere as a result of the industrial processing of various raw materials. Mineral processing and the combustion of fossil fuels are the most important processes that contribute to the emission of uranium and thorium series radionuclides to the environment, increasing their air volume activities and causing exposure of human beings. The main radionuclide released from industrial activities is radon. Radon is released in the process of burning natural gas, as well as in the phosphates and cement industry and gas and oil extraction. Iron and steel production processes and cement and phosphorus production result in the release of 210 Pb. Radionuclides released to the atmosphere can be transmitted over large dis- tances (especially if they are released as a result of a thermal process) or can be released in the form of dust or fly ash in the vicinity of the industrial plant. Radionuclides released to the atmosphere from industrial activities other than nuclear energy contribute mainly to the internal exposure of human beings via inhalation and ingestion. For example, in the case of coal-burning power plants, the annual effective dose from natural radionuclides present in emissions is assumed to be maximally 10 to 50 µSv/year. According to UNSCEAR [1], the overall average annual effective dose due to emissions from industrial activities TABLE 3.4 Typical Content of Radionuclides in Building Materials in Slovakia (According to Cabanekova [4]) and Typical Mass Activity (in Bq/kg) 40 K 226 Ra 232 Th Bricks 600 (varies from 100 to 1000) 60 (varies from 30 to 300) 70 (varies from 100 to 600) Concrete 300 (varies from 100 to 600) 50 (varies from 10 to 100) 30 (varies from 5 to 70) DK594X_book.fm Page 41 Tuesday, June 6, 2006 9:53 AM © 2007 by Taylor & Francis Group, LLC 42 Radionuclide Concentrations in Food and the Environment (other than nuclear) ranges between 0.001 and 20 µSv/year. The highest values for members of critical groups could be about 1000 µSv/year. Examples of typical releases of radon to the atmosphere from various industrial plants are shown in Table 3.5 (values are from UNSCEAR [1]). 3.3.3 SUMMARY: AIRBORNE ACTIVITY DUE TO NATURAL R ADIATION SOURCES Table 3.6 shows typical air volume activities (in Bq/m 3 ) of natural radionuclides in the environment. TABLE 3.5 Typical Annual Releases of 222 Rn from Various Industrial Plants Industrial Plant Release of 222 Rn (Bq/year) Coal-fired power plant 34 × 10 9 Gas-fired power plant 230 × 10 9 Oil extraction 540 × 10 9 Iron production 180 × 10 9 TABLE 3.6 Typical Air Volume Activities of Natural Radionuclides in the Environment Nuclide Average Volume Activity (Bq/m 3 ) 3 H 1.4 × 10 –3 14 C 56.3 × 10 –3 238 U1 × 10 –6 230 Th 0.5 × 10 –6 226 Ra 1 × 10 –6 210 Pb 500 × 10 –6 210 Po 50 × 10 –6 232 Th 0.5 × 10 –6 228 Ra 1 × 10 –6 228 Th 1 × 10 –6 235 U 0.05 × 10 –6 222 Rn outdoor 10 222 Rn indoor 10–100 220 Rn outdoor 10 220 Rn indoor 2–20 DK594X_book.fm Page 42 Tuesday, June 6, 2006 9:53 AM © 2007 by Taylor & Francis Group, LLC Radioactivity in the Air 43 3.4 MAN-MADE RADIONUCLIDES IN THE AIR 3.4.1 M AN-MADE RADIONUCLIDES IN THE AIR DUE TO N UCLEAR WEAPONS TESTS AND PRODUCTION Nuclear weapons tests in the atmosphere were performed between 1945 and 1980 by the U.S., the Soviet Union, the U.K., France, and China. During these tests (especially when performed in the atmosphere), many radioactive materials were released directly into the environment without any restrictions. As a result, the world’s population was exposed to these materials via exposure from the ground deposition, inhalation of airborne nuclides, and ingestion. According to UNSCEAR [1], the average annual effective dose resulting from atmospheric nuclear tests was highest in 1963, about 110 µSv/year. At the end of the 20th century it was less then 6 µSv/year. Many radionuclides were deposited as local or intermediate fallout and cre- ated deposits on the ground; however, large amounts of volatile radionuclides like 90 Sr, 137 Cs, and 131 I were dispersed in the world’s atmosphere (Table 3.7). In the 1960s, the highest average airborne volume activities of 90 Sr in the air near the ground were about 10 –3 Bq/m 3 , while in the 1980s they were only about 10 –7 to 10 –6 Bq/m 3 . The effective dose from the inhalation (total effective dose due to inhalation resulting from all tests) of radionuclides produced in atmospheric tests was about 150 µSv. The annual effective dose due to inhalation was highest in 1963, about 36 µSv. The most important contributors to this exposure pathway were 144 Ce, 106 Ru, 95 Zr, and 90 Sr. After the atmospheric tests ceased, airborne activity of these radionuclides decreased rapidly and inhalation as an exposure pathway due to nuclear tests became practically negligible (Table 3.8). There are still two other contributors to exposure that are widely dispersed in the atmosphere (and especially in the biosphere), namely 3 H and 14 C. However, their contribution to the inhalation dose is negligible and they contribute to effective dose via ingestion only. The estimated global release of 14 C in atmo- spheric tests was about 213 × 10 15 Bq. The global inventory of 14 C as a cosmogenic TABLE 3.7 Average Annual Airborne Volume Activity for the Northern Hemisphere of 90 Sr Due to Releases From Atmospheric Tests (According to UNSCEAR [1]) Year Average Annual Volume Activity in Air (Bq/m 3 ) 1957 0.23 × 10 –3 1963 2.17 × 10 –3 1970 0.12 × 10 –3 1983 0.001 × 10 –3 DK594X_book.fm Page 43 Tuesday, June 6, 2006 9:53 AM © 2007 by Taylor & Francis Group, LLC 44 Radionuclide Concentrations in Food and the Environment nuclide is about 13 × 10 18 Bq and the annual production rate due to cosmic radiation is 1.5 × 10 15 Bq/year. From this it can be seen that atmospheric tests quite significantly influenced the natural state. 3.4.2 MAN-MADE RADIONUCLIDES IN THE AIR DUE TO ELECTRICITY G ENERATION IN NUCLEAR POWER PLANTS: FUEL P RODUCTION AND OPERATION OF NUCLEAR POWER PLANTS Global radionuclides released from the nuclear fuel cycle are nuclides that are fairly long-lived and are dispersed in the atmosphere and biosphere and irradiate the world population as a whole. These nuclides are 3 H (half-life 12.26 years), 14 C (half-life 5,730 years), 85 Kr (half-life 10.7 years), and 129 I (half-life 1.6 × 10 7 years). Again it should be emphasized that 3 H and 14 C are cosmogenic nuclides; this means they are also present naturally in the environment. The total activity of global radionuclides released from the nuclear fuel cycle (nuclear power plants and reprocessing plants, release activity from the entire nuclear power industry at the end of 1997, according to UNSCEAR [1]), together with the average annual effective doses to individuals due to releases of global radionuclides (world average) are shown in Table 3.9. Common releases caused by normal long-term operation of nuclear power plants consist of not only global radionuclides, but many other radionuclides. As an example, Table 3.10 and Table 3.11 list common atmospheric discharges from a nuclear power plant (VVER-440 MW type). The activity of aerosols in normal effluents from power reactors is a function of the state of the fuel. If there is a problem with the tightness of the fuel in the reactor, contamination of the primary circuit is increased and consequently efflu- ents of aerosols can be higher. TABLE 3.8 Average Effective Dose Due to Inhalation (Total Effective Dose Due to Inhalation Resulting From All Tests) Caused By the Most Important Radionuclide Contributors Produced in Atmospheric Tests Nuclide Effective Dose Due to Inhalation (Total From All Atmospheric Tests) (µSv) 131 I 2.6 95 Zr 2.9 144 Ce 53 106 Ru 35 90 Sr 9.2 137 Cs 0.3 Pu, Am 38 DK594X_book.fm Page 44 Tuesday, June 6, 2006 9:53 AM © 2007 by Taylor & Francis Group, LLC Radioactivity in the Air 45 The reported annual effective dose in individuals living in the vicinity (up to 50 to 100 km from the site) of a nuclear power reactor is between 1 and 500 µSv/year. According to UNSCEAR [1], the typical annual effective dose to individuals resulting from nuclear reactor effluents to the atmosphere is between 0.04 µSv/year and 10 µSv/year (per reactor; this means that the dose is realized in human beings living up to approximately 50 km from the reactor). TABLE 3.9 Activity of Global Radionuclides Released to the Atmosphere From the Nuclear Fuel Cycle Through the End of 1997, According to UNSCEAR [1], and World Average Annual Effective Dose Due to These Releases Global Nuclide Activity in Effluents, Sum From the Whole Nuclear Fuel Cycle (Bq) Annual Effective Dose (World Average) 3 H ~300 × 10 15 ~0.005 µSv/year 14 C ~3 × 10 15 Maximally 1 µSv/year 85 Kr ~3.3 × 10 18 ~0.1 µSv/year TABLE 3.10 Common Activity of Noble Gasses Measured in Atmospheric Discharges From a Nuclear Power Plant VVER-440 (According to Tecl [8]) Nuclide Half-Life Typical Activity in Atmospheric Discharges From a Nuclear Power Plant VVER-440 41 Ar 110 minutes 500–700 Bq/m 3 133 Xe 5.2 days 70–80 Bq/m 3 85 Kr 10.7 years 20–30 Bq/m 3 TABLE 3.11 Atmospheric Effluents of Aerosols: Typical Values in Discharges From a Nuclear Power Plant VVER-440 (According to Rulik et al. [5]) Nuclide Common Discharge Activity Per Quarter (VVER-440) 137 Cs 1E+4 to 1E+5 Bq 242 Cm 1E+3 to 1E+5 Bq 238 Pu 1E+3 to 1E+4 Bq DK594X_book.fm Page 45 Tuesday, June 6, 2006 9:53 AM © 2007 by Taylor & Francis Group, LLC 46 Radionuclide Concentrations in Food and the Environment 3.4.3 MAN-MADE RADIOACTIVITY IN THE AIR IN CASE OF NUCLEAR ACCIDENT The operation of nuclear power plants is one human activity that, if a serious accident occurs, can lead to very significant radioactive pollution of the environment and can cause increased irradiation of the population, especially in the vicinity of the plant (up to 100 to 300 km from the site of release). The possible impacts of a serious accident are the main reason why the nuclear industry is under very strict and sophisticated controls. These controls cover the nuclear power plant (the phys- ical and chemical principles of the processes and the barriers preventing radio- nuclides from the reactor core from being released to the environment; one such barrier is modern containment, in which the reactor and all other systems that might be in contact with radioactivity from the core are covered and protected), training of the operators, safety procedures, etc. These controls have greatly improved because of the serious nuclear accidents that have taken place in the last 30 years. Two such accidents were Three Mile Island, in the U.S., and Chernobyl, in Ukraine (former USSR). The Three Mile Island accident occurred in 1979. The initial cause of the accident was the loss of primary coolant. Consequently partial core damage occurred (half of the reactor core melted). As a result, an increase in radioactivity in the air due to the release of radionuclides to the atmosphere was observed. Effective doses to the inhabitants in the vicinity of the plant were relatively low, about 10 µSv per individual. This dose was realized in about 2 million people living in the vicinity of the plant. The most catastrophic and severe nuclear accident happened in 1986 at the Chernobyl nuclear power plant. There was almost total damage of the core, with very high releases of radioactive substances from the reactor core to the atmo- sphere and the environment. Radioactive products were also emitted from the fires and explosions in the reactor. Released radionuclides were dispersed over long distances and pollution was measured all over Europe. The Chernobyl accident was the most severe accident that could be imaged in the context of the peaceful use of nuclear power. For a better understanding of what could be expected in case of such a severe nuclear accident (as an example), the radiological conditions of a Chernobyl-type release are shown in Table 3.12, based on computer model calculations. The source term (the total release of radionuclides to the atmosphere) applied in the model calculations was the same as that estimated for the Chernobyl accident. The mete- orological conditions applied were prepared (artificial) ones. The point of release assumed in the model calculations is identical with the former Chernobyl nuclear power plant site in Ukraine. It should be stated here that all three remaining reactors of the Chernobyl nuclear power plant have been shut down and decommissioned. The model calculations were performed using the este code — the computer code that is used by emergency response workers and crisis staff in case of a nuclear accident [2]. The results (the maps of radiological impacts calculated by este) are shown in Figure 3.1 and Figure 3.2. The estimated total release of radionuclides (the source term) in case of a Chernobyl-type accident is shown in Table 3.12. DK594X_book.fm Page 46 Tuesday, June 6, 2006 9:53 AM © 2007 by Taylor & Francis Group, LLC [...]... 11.99 23. 99 23. 99 23. 99 23. 99 23. 99 100.00 100.00 100.00 100.00 23. 99 23. 99 23. 99 23. 99 4.80 0.22 0.22 0.22 0.21 0.21 0.21 0.21 0.21 0.21 0.21 0.21 25–60 50–60 100 33 – 43 33 43 4.0–6.0 3. 5 3. 5 3. 5 3. 5 3. 5 3. 5 3. 5 49 © 2007 by Taylor & Francis Group, LLC DK594X_book.fm Page 49 Tuesday, June 6, 2006 9: 53 AM Te Te 131 I 132 I 133 I 134 I 135 I 133 mXe 133 Xe 135 Xe 138 Xe 134 Cs 136 Cs 137 Cs 138 Cs 140Ba 140La 143Pr... June 6, 2006 9: 53 AM 52 Radionuclide Concentrations in Food and the Environment FIGURE 3. 3 Example of the map of time integrals of air volume activity of 131 I in the vicinity of the point of release Predicted situation 24 hours from the beginning of the release The point of the release is the site of the Chernobyl nuclear power plant The source term applied is the estimated source term for the Chernobyl... demand protective measures (urgent or precautionary measures) are shown in Table 3. 13 [3] © 2007 by Taylor & Francis Group, LLC DK594X_book.fm Page 53 Tuesday, June 6, 2006 9: 53 AM Radioactivity in the Air 53 FIGURE 3. 4 Example of the map of ground deposition of 137 Cs in the vicinity of the point of release Predicted situation 24 hours from the beginning of the release The point of the release is the. .. Projected deposition in 3 h Projected deposition in 6 h Projected deposition in 9 h Example of expected ground deposition at chosen point in 9 h FIGURE 3. 2 Example of the maps of 137 Cs ground deposition in the vicinity of the point of release as a function of the time from the beginning of release The point of release is the site of the Chernobyl nuclear power plant The source term applied is the estimated... 143Ce 144Ce 239 Np 238 Pu 239 Pu 240Pu 241Pu 132 Radioactivity in the Air 131 m DK594X_book.fm Page 50 Tuesday, June 6, 2006 9: 53 AM 50 Radionuclide Concentrations in Food and the Environment Actual situation, cloud due to 4 h release Projected cloud in 3 h Projected cloud in 6 h Projected cloud in 9 h Example of air volume activities and time integrals of air volume activities at chosen point FIGURE 3. 1... activities of 131 I can be seen The radiotoxicity of 131 I occurs because iodine is inhaled with the air or ingested with food and causes irradiation of internal organs, especially irradiation of the thyroid gland During longer periods after the accidental release, other nuclides (due to their longer half-life and expected larger amounts in the release) are expected to take the role of the most radiotoxic... Concentrations in Food and the Environment Estimated Core Inventory of the RBMK 1000 Reactor T is the time from the end of the chain reaction (Bq) DK594X_book.fm Page 48 Tuesday, June 6, 2006 9: 53 AM 48 TABLE 3. 12 (continued) Estimated Total Release of Radionuclides (the Source Term) From the Core of a Chernobyl-Type Reactor in the Case of a Severe Accident with Total Melting of the Core (Core Damage) and Bypass... damage to the reactor building (Bq) Percent of the Core 1.2E+16 4.9E+15 9.2E+15 8.7E+15 8.0E+15 1.3E+14 1.8E+15 8.0E+15 2.7E+15 2.3E+16 3. 1E+15 2.1E+16 2.3E+16 3. 5E+15 0.22 0.22 0.20 0.20 0.20 0.20 0.20 0.20 0.20 11.99 11.99 11.99 11.99 11.99 Total Release to the Environment During the Chernobyl Accident, Estimation According to OECD [7] Percent of the Core >3. 5 >3. 5 >3. 5 Radionuclide Concentrations in Food... FIGURE 3. 1 Example of the maps of 131 I air volume activity in the vicinity of the point of release as a function of time from the beginning of release The point of release is the site of the Chernobyl nuclear power plant The source term applied is the estimated source term for the Chernobyl accident Meteorological conditions are modeled without relation to the real conditions during the accident at Chernobyl... 2006 9: 53 AM 54 Radionuclide Concentrations in Food and the Environment FIGURE 3. 5 Example of the map of avertable dose: the dose averted by evacuation of inhabitants before the cloud enters a given region on the map The intervention level for evacuation is usually the effective dose averted (= 50 mSv) (The value of the intervention level can vary country by country.) This means that evacuation of inhabitants . Radiation Sources 42 3. 4 Man-Made Radionuclides in the Air 43 3.4.1 Man-Made Radionuclides in the Air Due to Nuclear Weapons Tests and Production 43 3.4.2 Man-Made Radionuclides in the Air Due to. Decay Products in the Air and Other Radionuclides That Can Be Inhaled 38 3. 3.2 Terrestrial Radionuclides in the Air Due to Industrial Activities (Other Than Nuclear Energy) 41 3. 3 .3 Summary: Airborne. LLC Radioactivity in the Air 53 FIGURE 3. 4 Example of the map of ground deposition of 137 Cs in the vicinity of the point of release. Predicted situation 24 hours from the beginning of the release. The point of