3. Medico-tactical characteristic of failures on radiation dangerous objects.

In the world now works more than 400 NPP (nuclear power plants) and about 110 are still under construction. Besides the plenty of separate nuclear reactors works. In 1990 in USSR worked 46 energy-blocks of 15 NPP, in USA 111 reactors and 12 were under construction. By 1987 284 serious failures on NPP, accompanied by emission of radioactive substances were registered in the world. Largest of them were in Northern England (in Windscale, 1957), in USA (on Tri-Mile-Island, 1979) and in USSR (on Chernobyl NPP, 1986).

Manufacture, transportation, storage and use of radioactive materials is strictly kept by rules of technology, safety precautions and control of their application. However it does not exclude an opportunity of occurrence of failures. The failure with complete destruction of nuclear reactor can take place as a result of act of nature, influence of ordinary ammunition explosion, air-crashes etc. The break of pipelines with the heat-carrier, breakage of protection and management systems may result in RS emission with outflow of steams into environment. The amount of radioactive products on the ship reactors is many times less than the appropriate parameters on NPP. Therefore the distribution of a gas-aerosol mix at failures on them can result in an affect of the population on distance till 20-30 km, and the separate centers of pollution of district can be observed on large distances. There are various types of nuclear reactors, but the common principles of their arrangement and works are similar. In the reactors on thermal neutrons the delay element is the graphite, and the water serves as a heat-carrier. The reactor as the vertical cylinder is filled with graphite blocks of entire weight up to 2000 tons. At the center of each block there is a channel for accommodation of heat-producing elements, which are outside washed by water. Uranium-235 dioxide is used as a fuel(contents of uranium about 2%). The tablets of uranium-235 dioxide, with diameter of 1 cm and height of 1,5 cm, are gathered in the cylinder made of zirconium with an impurity 1 % of niobium, which is the heat-producing element. The whole weight of uranium in the block (like Chernobyl NPP) makes 190 tons. The water (in the closed system) around of heat-producing elements is heated up to 284 ˚С at the pressure of 70 atmospheres and acts as the steam on turbines for producing the electric power. Worked out steam in the form of water with temperature of 165 ˚C goes back in main circulation pumps. Around of the reactor there is a protective water cover, and also other protection against neutrons. At disintegration of uranium-235 there will be formed up to 400 various radionuclide.

The emission of RS outside the NER (NPP and AHEC) over the established norms, causing the increased radiation danger representing threat for life and health of the people, is called the radiation accident. At the accident on NPP there is a steam explosion with an outflow of radionuclides into the environment. Due to this, the station personnel may acquire burns and mechanical traumas.

By the limits of distribution of the allocated radioactive substances and radiating consequences the failures are divided into three types:

The local failure is a failure, which radiating consequences are limited to one building or structure and at which the radiation of the personnel and pollution of a building or structure above the levels estimated for normal operation is possible.

In local failure - the radioactive consequences are limited to buildings, NPP territory and at them the radiation of the personnel, the pollution of buildings and structures on the territory of station, is higher than levels, established for normal operation.

General accident - the radiating consequences are distributed out of the NPP territories and result in the radiation of the population and pollution of an environment of the above established levels.

As a result of general(common) radiating failures, as it was on Chernobyl NPP, from damaged NPP the RS are thrown into the environment as the heated gases and aerosols.

At failure on Chernobyl NPP the average throw out on the territory of the USSR was 3,5% of the total quantity of product division, theoretically accumulated in the 4^th block of the reactor for its working period (namely the product division, but not the nuclear fuel). The throw out equals approximately 1 kt. As МАГАТЭ points out, the total activity was equal to 30-50 Mki not taking into account inert steams.

The emissions are not the same and are distributed on different directions under influence of a movement of ground air layers. Accumulated RS are chemically clean, small disperse products, having ability of dense coupling with surfaces of subjects, especially metal, and also sorb on clothes and skin of the man, penetrating deep into cloth pores, sudoriferous and setaceous glands of skin. It reduces effect of sanitary processing and deactivation.

The radionuclide structure of a radioactive cloud includes some tens of various isotopes. In structure of isotopes mix of a Chernobyl radioactive cloud there were, isotopes J131, Cs137, (melting temperature of 640 ˚С), ⁹⁰Sr, ¹⁴⁰La, ¹⁴⁰Ва, ¹³³Хе, ¹³²Те etc. - more than 20 radionuclides in a whole. The doze power of g-radiation on the polluted district by 1990 was caused by presence in the polluted territories mainly of radioactive isotopes ¹³⁷Cs and ¹³⁴Cs. It has appeared and in long-term prospect, non-uniformly polluted territory («cesium stains»). A rather mixed picture was marked in different regions.

For example, the average level of radiation in area of Kiev of April 30, 1986 was 1,4 mR/hour, in Minsk - on April 30, 1986 0,06 mR/hourthe same was in Brest and Kishinev, in Chernobyl- 24 mR/hour (1.05.86). At pollution of district with a level of radiation 5 mR/hour on May 10, 1986 the population would receive 10 R per the first year. It is equal to two annual norms of a professional irradiation for the experts.

The doze of natural (background or natural) radiation received by the man per year, makes approximately 0,14-0,7 бэр, and in separate places of our country and globe it is even more. Threshold effect of occurrence of various diseases (beam illness, burns, cataracts, malignant tumors and so on) - are possible only at radiation during all life in dozes exceeding 10 бэр per years. The occurrence of beam tumors in man is proved at dozes for all life above 35 бэр or 0,5 бэра on the average per one year The man during his life receives from all sources of radiation approximately 14 rad (бэр).

The characteristic feature for a cloud at failures on NPP is a spot-like contamination of various reasons, that will require realization of careful radiating investigation and will result in a different degree of people radiation even within the limits of one settlement. Cesium background quite often is deposited on a ⁹⁰Sr background.

At ¹³⁷Cs the population’s living is permitted on the contamination territory up to 15 Ki/km2. At 15 Ki/km2 or more is a zone of strict control (children, the pregnant and feeding women are settled out), and at 40 Ki/km2 - evacuation of all population.

The degree of pollution of district at failure on NPP changes depending on distance from a place of failure and width of a trace. For increase of presentation and efficiency of use of results of revealing and estimation of radiating conditions at the decision of typical tasks it is accepted in most cases to provide display on maps (schemes) actual or forecasted of standard zones of radioactive pollution of district as an ellipse.

The size of forecasted zones of pollution (length and width) depends on amount of an outflow of a radio-activity from nuclear reactor at radiating failure, such as nuclear reactor (РБМК or ВВЭР), category of stability and speed of a wind. The main amount of radiating losses are probable in zones “C” and “C”.

The characteristic of the factors of radiating danger in radioactive pollution zones.

In the zones of radioactive pollution of an area at failures on NPP the two basic factors of radiating danger are taking place:

External gamma-radiation from radionuclide, being in the air at the moment of passage of radioactive cloud basically from the radioactive deposits which have dropped out on ground; in this case a general radiation of all human body is taking place, decreasing with of time;

Internal radiation is a result of breathing in radionuclide from a cloud of emission, radionuclide, lifted from deposits into the air, and also that which have entered the human organism with polluted water and food. It basically results in radiation of separate body organs and tissues and has smaller meaning, than general gamma-irradiation.

The main danger for a man is external irradiation (60 % of a life radiation). A ratio of a gamma-background and surface components on a skin (-radiation) 1:10, 1:20. The capacity of a doze of radiation from the struck people in a zone of failure can reach 1-2 р/hours. They are dot sources of radiation for medical and other personnel. It is not a serious danger for them, since the contact is usually short-termed (at survey, performance of procedures and so on). Besides at the expense of radionuclide disintegration the level of radiation from the patients gradually falls down.

At radionuclide incorporation through the respiratory organs (air inhalation), through gastrointestinal tract (with food, food staff) and through wounded (burnt) surfaces they quickly get into the blood (light soluble RS) and sit on tropic organs and tissues (¹³¹I in thyroid glands, ⁹⁰Sr in bones and so on). At their disintegration -particles influence directly on molecules of organs and tissues, causing to some extent pathological process. Especially is dangerous the ¹³¹I incorporation, which from blood acts in small volume and weight on the thyroid gland of the adult man (25-30 grams), quickly filling it. Taking into account a short period of its half-disintegration (8 days), the intensive influence of ¹³¹I on a thyroid gland tissue in a short period of time is possible.

Others radionuclides (¹³⁴Cs, ¹³⁷Cs, ⁹⁰Sr), having the large depot in volume and weight in organs and tissues of the man and long period of half-disintegration (30 years) cannot cause serious changes in them. However at their long receipt in significant quantities they can represent the certain danger to the human organism.

Wounded and burnt surfaces are not only the gates for radionuclides, light soluble in organism’ liquids, but also are the objects for their direct affect in places of contact. So, the local changes in a wound and on a burnt surface are possible already at pollution of 0,5-1 mKi or 1,85-3,7.104 Bk/kg.

At the combined influence of the radiating factor (the external radiation and at internal receipt of RS) the leading factor is a general external radiation.

According to «Sanitary rules of designing and operation of NPP» on and outside the border of a sanitary-protective zone the expected individual doze of influence on thyroid gland in children at the expense of iodine isotopes should not exceed 30 бэр, and expected doze from external radiation on all body and any other organs (except for thyroid gland) - 10 бэр. So, at 97 % of children in Prypiat dozes have reached 30 сGr (30 rad). Threshold effects arise only at an radiation during all life in dozes less than 10 бэр per one year. At annual dozes of less than 10 бэр and radiation during all life no one doctor has any basis to make the diagnosis of a radiation origin of this or that diseases.

The medical consequences at the irradiated man can have various character. The influence of various kinds of radiation causes changes as at irradiated person, and also at its posterity. There are allocated somatic (unstochastic) effects- early or late ones, which are observed at an irradiation of organism (beam illness- sharp and chronic, burns of a skin) and stochastic (probable) - premature aging of organism (decreased duration of life), blood diseases, malignant tumors and genetic effects developing as a result of radiating influence on embryonic cells of an organism and shown at posterity. Late (tumors) and the genetic effects also carry probable (stochastic) character.

A strict dependence of a radiation doze with the presence of minimum doze marked as a threshold is the characteristic of early somatic (unstochastic) effects.

It is counted that the external gamma-radiation in a range of 0,5-1 Gr (50-100 rad) causes light changes in blood parameters (reduction of platelet and leukocyte number) and the system of vegetative disregulation. As a threshold doze for revealing sharp beam illness it is accepted to consider 1 Gr (100 rad).

The doze of prolonged radiation which is not causing clinical symptoms, considerably exceeds a one-moment radiation doze. The chronic beam illness develops at fractional radiation in a doze of 1,5 Gr (150 rad) and above during some years.

The action of external radiation or RS application can result in various affects of skin, from subclinical up to expressed. At the influence of uranium division products the affect on skin is possible in the case if density of pollution of covers exceeds 74 KBk/cm2 (2 mKKi/СМ2 or at pollution of skin 700 mR/hour as of 24 hours after pollution (and at 2 hours after pollution 4,9-5,0 rad / hour). The average degree of an affect of skin is possible at pollution of 1,1 rad / hour on 24-12 of hours and 7,4 rad / hour at 2 hours after pollution. At capacity of a radiation doze on a surface of a human body from 50 up to 200 mrad/hour on 24-12 hours - it is considered safe. If the absorbed doze on a skin as a result of action of gamma-radiation of division products will be less than 10 Gr (1000 rad), the medical help, as a rule, practically is not required.

At failure on Chernobyl NPP in the moment of impact there were heavy and heaviest radiating and thermal burns on a platform of the fourth block. Among the population nobody had affects of RS on skin from failure on Chernobyl NPP.

At RS incorporation inside the organism the adverse consequences are also possible. However man has the certain safety factor. The affect is absent at unitary receipt in organism of the adult man the RS in a doze of 1 mKi or on 0,2 milli-Ki within 10 days, on 0,1 mKi during month and on 0,05 mKi within one year. But the unitary receipt of 15-60 mKi or till 3-10 mKI within 10 days and of 1,2-3,0 mKi within one year will result in an easy degree of beam illness at age of atomic fragments from 12 about 30 day. For children these dozes are in 4-6 times less.

Leucosis are one of most typical radiating somatic-stochastic effects. A doze equal to 1 Gr (100 rad) is the minimum doze for a man. The biggest death frequency from leucosis in Hiroshima and Nagasaki was observed in groups of the persons, which age at the moment of bomb explosion was 0-10 and more than 50 years.

If we take into account the average life length (70 years), 14000 people out of 1 mln dies annually. It is possible to consider, that the natural radiating background is guilty in destruction of one of them. The smoking is much more dangerous.

At the women of Hiroshima and Nagasaki after radiating influence in a doze exceeding 0,1 Gr (10 rad), number of death cases, from breast cancer from 1950 till 1972 has made 37 instead of 19, expected on the basis of Japanese national statistics.

Decreasing of life duration of the irradiated basically is connected to development of tumors in earlier periods of life. The excessive mortality from an irradiation, is marked in a range of dozes exceeding a natural radiating background in 100-200 times. The irradiation of 1 бэр to the man on the average can result in loss of 5 days of life (П.В.Рамзаев, Medical newspaper, March 30 1990).

The most vulnerable period for a fetus is an early period of an irradiation (9-40 days after conception). The radiation in a fetal period depending on a doze can result in defects of growth and increased mortality. At mothers, which were irradiated during pregnancy, borned children differed from control on parameters of growth and weight of a body a little. So, at radiation of the woman in first trimester of pregnancy, at newborn, the reduction of the sizes of a head on 2-3 cm, sometimes combined with delay of intellectual development was marked.

In England, for example, at radiation of a fetus of 1 up to 20 rad the woman is warned about possible heavy anomalies at a child and interruption of pregnancy is offered to her. If the fetus has received a doze more than 10 rad, the doctor should insist on interruption of pregnancy. X-ray researches can be carried out only during the first 10 days after menstruation (J. Mayer).

The genetic effects of irradiation are connected to the vulnerable to radiation spermatogones in men and ovocytes in women.

Damaging dozes at a general irradiation of embryo and fetus depending on term (day, the weeks, trimesters of pregnancy roughly make 0,05-0,20 Gr (5-20 rad). In early terms of postnatal development (first months and the years of life), there are dozes of 0,3-1 Gr (30-100 rad), that are almost in 10 times less, than dozes causing compared changes in the adults.

According to data, for 70 years in territory of RSFSR of a non-radiative carcinoma will die about 12 mln people + 11 thousands (in opinion of Robert Gale, USA-60 thousands of cases) because of the accident. Besides for the same term, (70 years), 10 % of newborns will get ordinary deviations (natural background) from norm +0,1 % due to the accident on Chernobyl NPP.

The international commission on radiating protection has developed maximum allowable dozes of irradiation for one year for the persons working with radioactive loads and for all population (МКРЗ, 1966). It permits an irradiation of the adult personnel (all body, sexual glands and bone marrow), working with irradiative loads - up to 5 бэр, and population - 0,5 бэр per one year, the thyroid gland accordingly 30 and 3 бэра, as much as on skin and bones, and on limbs even 75 and 7,5 бэр accordingly.

All over the world it is considered, that the professionals dealing with irradiation, for one year can receive 5 бэр., during labor activity up to 150 бэр. It does not influence on their health. For spacemen the doze of 400 rad for all professional activity is permitted. For the population living in the NPP area, the annual norm should not exceed 0,5 бэр (35 бэр for all life). The man without damage to health can sustain unitary or within month a radiation of less than 100 бэр. And if he receives 100-150 бэр, there can be a disease.

The radiating losses among the population in zones of radioactive pollution are defined taking into account the basic doze of an external radiation and duration of its accumulation:

а) At a doze of unitary or within 4 days radiation of 100-200 rad the light degree of radiation illness develop. At radiation of 7-60 days by such doze the loss of work capacity is absent;

b) At unitary incorporation of a doze of 15-60 mKi and more - the light degree of radiation illness is possible;

в) At RS application on skin in dozes more than 700 mR/hour as of 24 hours after pollution - light degree of an affect.

Hence, in a zone of radiating danger («М») and on external border of a zone of moderate pollution («A») at failure on NPP a doze of radiation for the first year after failure excludes the probability of development of a beam pathology among the population and occurrence of radiating losses. Their occurrence is possible, at external border of a zone «B» and further in the direction of NPP failure place or nuclear reactor.

The structure of radiating losses on their severity will be extremely variable depending on many factors (degree population protection, the power of emission, meteorological conditions etc.). The probability of RS pollution with radiation injury of man’s skin is present at external border of a zone «B» (strong contamination) and further in zones «C» and «D». The timely carried out sanitary processing (at the first hours after pollution) can exclude or considerably weaken skin covers injury, in particular of parts which have been not closed by clothes. However in these zones the population can receive significant dozes of an external radiation representing large radiating danger in comparison with injury of open body parts at RS application.