Give the definition of design basis accident. Design basis accident. Creative project activities

Lecture number 17

Topic 35. RADIATION HAZARDOUS OBJECTS

A radiation hazardous facility (ROO) means any facility, including a nuclear reactor, a plant that uses nuclear fuel or reprocessing nuclear material, as well as a storage site for nuclear material and a vehicle transporting nuclear material or a source of ionizing radiation, in the event of an accident at which or its destruction can result in irradiation or radioactive contamination of people, farm animals and plants, as well as the environment.

These facilities include nuclear power plants for various purposes, for example:

NPP - a nuclear power plant intended for the production of electrical energy;

NPP - nuclear combined heat and power plant - a nuclear power plant intended for the production of heat and electricity;

ACT is a nuclear power plant intended for the production of heat energy for domestic purposes, etc.

The ROO also includes various research reactors, installations using sources of ionizing radiation, storage facilities for waste from nuclear reactors for peaceful and military purposes, etc.

The greatest danger to the personnel of the ROO and the population of the nearby, and as the Chernobyl tragedy showed, and not only to the nearby settlement, is a radiation accident associated with the release of radioactive products and the release of ionizing radiation beyond the boundaries envisaged by the project for normal operation of the ROO in quantities exceeding the established operational safety limits object. This hazard depends on a very large number of factors, such as the amount of radioactive material released, the duration of its release, the times of replacement of fuel elements (fuel elements) at nuclear power plants, weather conditions, etc.

Depending on the possibility to foresee the occurrence of an accident in advance and to carry out the necessary preparatory measures, accidents can be divided into design and beyond design basis.

Design basis accident - an accident for which the project defines initiating events and final post-accident controlled states of elements and systems, and also provides for measures and technical systems safety, ensuring the limitation of the consequences of accidents within the established limits.

Beyond design basis accident- an accident caused by not accounted for design basis accidents initiating events and accompanied by additional failures of safety systems in excess of a single failure and erroneous actions of personnel, as compared with design basis accidents, which ultimately leads to serious consequences, including melting of the reactor core.

According to the international scale of events, 7 levels of events (accidents) are distinguished at NPPs.

7th level - global accident. There was a discharge in environment most of the radioactive products accumulated in the core, as a result of which the dose limits for beyond design basis accidents will be exceeded (the dose limit for beyond design basis accidents is understood as not exceeding the external dose, exposure of people 10 rem in the first hour after the accident and the dose of internal exposure to the thyroid gland of children 30 rem due to inhalation at a distance of 25 km from the station; which is ensured if the emergency release into the atmosphere does not exceed 30 thousand Ku for iodine and 3 thousand Ku for Cesium-137).

6th level - severe accident. Release into the environment of a significant amount of products accumulated in the core, as a result of which the dose limits of design basis accidents (in design basis accidents, the dose at the border
the sanitary protection zone and beyond should not exceed 10 rem per
the whole body in the first year after the accident and 30 rem for the child's thyroid gland for
inhalation count) will be exceeded, for beyond design-basis - no. For decreasing
serious impact on public health, it is necessary to introduce action plans to protect personnel and the public in case of accidents in an area with a radius of 25
km, including the evacuation of the population.

5th level - an accident with a risk to the environment. The release into the environment of such a quantity of fission products that leads to a slight excess of the dose limits for design basis accidents and is traditionally equivalent to the release of hundreds of terabecquerels (10 12) for iodine. Destruction of most of the reactor core caused by mechanical impact or melting in excess of the maximum design damage to fuel rods.

In some cases, partial introduction of plans of measures for the protection of personnel and the public in case of accidents (i.e. local iodine prophylaxis and / or evacuation) is required to reduce the impact of radiation on public health.

4th level - accidents within the NPP. Release of radioactive products into the environment in an amount exceeding the value for level 3, but as a result of which the dose limits for the population will not be exceeded during design basis accidents. Such damage to the core, in which the limit of safe operation of damage to fuel elements is violated, the maximum design limit is not.

Irradiation of workers with a dose (1 Sv) causing acute radiation effects.

3rd level - a serious incident. The release into the environment of radioactive products is higher than the permissible daily, but not exceeding 5 times the permissible daily release of gaseous volatile radioactive products and aerosols and (or) 1/10 of the annual permissible discharge with waste water. High levels of radiation and / or large contamination of surfaces at nuclear power plants due to equipment failure or operating errors. Events resulting in minor overexposure of workers (dose 50 mlSv).

With the considered release, it is not required to take protective measures outside the nuclear power plant. This includes incidents in which further failures in the safety systems will lead to accidents or situations where the safety systems will not be able to prevent an accident.

2nd level - accidents are not of average severity. Equipment failures or
deviations from normal operation, which, although not having a direct impact on the safety of the situation, can lead to a significant overestimation of safety measures.

1st level - minor incident. Functional deviations and deviations in management, which do not pose any risk, but indicate deficiencies in safety. These deviations may arise due to equipment failure, plant personnel errors, or deficiencies in the operation manual. Such events should be distinguished from deviations without exceeding the safe operating limits at which control is carried out in accordance with the established requirements. These deviations are generally considered “out of scale”.

0th level - below the scale level. An incident not relevant to safety.

So, a radiation accident is a loss of control of the source of ionizing radiation caused by equipment malfunction, improper actions of workers (personnel), natural disasters or other reasons that could lead or have led to the exposure of people above the established standards or to radioactive contamination of the environment.

Over the past four decades, nuclear power and the use of fission materials have become firmly established in the life of mankind. More than 450 nuclear reactors are currently in operation in the world. Nuclear power has made it possible to significantly reduce “energy hunger” and improve the environment in a number of countries. Thus, in France, more than 75% of electricity is obtained from nuclear power plants, and at the same time, the amount of carbon dioxide entering the atmosphere was reduced by 12 times. In the conditions of trouble-free operation of nuclear power plants, nuclear power is still the most economical and environmentally friendly energy production and no alternative to it is foreseen in the near future. At the same time, the rapid development nuclear industry and nuclear energy, the expansion of the scope of application of radioactivity sources led to the emergence of radiation hazard and the risk of radiation accidents with the release of radioactive substances and environmental pollution. Radiation hazard can arise during accidents at radiation hazardous facilities (ROO). ROO - an object where radioactive substances are stored, processed, used or transported, and in case of an accident, at which or its destruction may occur irradiation with ionizing radiation or radioactive contamination of people, farm animals and plants, objects of the national economy, as well as the environment.

Currently in Russia there are more than 700 large radiation hazardous facilities, which to one degree or another pose a radiation hazard, but increased danger are nuclear power plants. Almost all operating nuclear power plants are located in a densely populated part of the country, and about 4 million people live in their 30-kilometer zones. The total area of \u200b\u200bthe radiation-destabilized territory of Russia exceeds 1 million km2; more than 10 million people live on it.

Accidents at the ROO can lead to radiation emergency (RFS). Radiation is understood as an unexpected hazardous radiation situation that has led or may lead to unplanned exposure of people or radioactive contamination of the environment in excess of established hygienic standards and requires urgent action to protect people and the environment.

Classification of radiation accidents

Accidents related to disruption of normal operation of the ROO are subdivided into design and beyond design basis.

Design basis accident - an accident for which the initial events and final states are defined by the project, in connection with which safety systems are provided.

Beyond design basis accident - is caused by initiating events not taken into account for design basis accidents and leads to serious consequences. This may result in the release of radioactive products in quantities leading to radioactive contamination of the adjacent territory, possible exposure of the population above the established standards. In severe cases, thermal and nuclear explosions can occur.

Potential accidents at NPPs are divided into six types depending on the boundaries of the zones of distribution of radioactive substances and radiation consequences: local, local, territorial, regional, federal, and transboundary.

If, in a regional accident, the number of people who received a dose of radiation above the levels established for normal operation may exceed 500 people, or the number of people whose living conditions may be impaired exceeds 1,000 people, or material damage exceeds 5 million. minimum sizes wages, then such an accident will be federal.

In transboundary accidents radiation consequences accidents go beyond the territory Russian Federation, or this accident occurred abroad and affects the territory of the Russian Federation.

During the total operating life of all nuclear power plants in the world, equal to 6,000 years, only 3 major accidents occurred: in England (Windekale, 1957), in the USA (Three Mile Island, 1979) and in the USSR (Chernobyl , 1986). The accident at the Chernobyl nuclear power plant was the most severe. These accidents were accompanied by human casualties, radioactive contamination of large areas and enormous material damage. As a result of the accident in Windakale, 13 people died and an area of \u200b\u200b500 km2 was contaminated with radioactive substances. The direct damage to the Three Mile Island accident amounted to over $ 1 billion. The Chernobyl accident killed 30 people, over 500 were hospitalized and 115,000 people were evacuated.

The International Atomic Energy Agency (IAEA) has developed an international scale of events at nuclear power plants, which includes 7 levels. According to it, the accident in the USA belongs to the 5th level (with a risk to the environment), in the UK - to the 6th level (severe), the Chernobyl accident - to the 7th level (global).

General characteristics of the consequences of radiation accidents

The long-term consequences of accidents and disasters at facilities with nuclear technology, which are of an ecological nature, are assessed mainly by the amount of radiation damage caused to human health. In addition, an important quantitative measure of these consequences is the degree of deterioration in the living conditions and life of people. Of course, the level of mortality and deterioration in human health has a direct relationship with the living conditions and life activity, therefore, they are considered in conjunction with them.

The consequences of radiation accidents are caused by their damaging factors, which include ionizing radiation at the accident facility, both directly during the release and during radioactive contamination of the facility territory; shock wave (in the presence of an explosion in an accident); thermal effect and the effect of combustion products (in the presence of fires in an accident). Outside the accident object, the damaging factor is ionizing radiation due to radioactive contamination of the environment.

Medical consequences of radiation accidents

• radiological consequences resulting from direct exposure to ionizing radiation;
• various health disorders (general, or somatic disorders) caused by social, psychological or stress factors, that is, other damaging factors of the accident of a non-radiation nature.

Radiological consequences (effects) differ in the time of their manifestation: early (no more than a month after irradiation) and distant, arising after a long period (years) after radiation exposure.

The consequences of irradiation of the human body are the breaking of molecular bonds; changes in the chemical structure of compounds that make up the body; the formation of chemically active radicals with high toxicity; violation of the structure of the genetic apparatus of the cell. As a result, the hereditary code changes and mutagenic changes occur, leading to the emergence and development of malignant neoplasms, hereditary diseases, congenital malformations of children and the appearance of mutations in subsequent generations. They can be somatic (from the Greek soma - body), when the effect of radiation occurs in an irradiated person, and hereditary, if it manifests itself in offspring.

The most sensitive to radiation exposure are the hematopoietic organs (bone marrow, spleen, lymph nodes), the epithelium of the mucous membranes (in particular, the intestines), and the thyroid gland. As a result of the action of ionizing radiation, the most serious diseases arise: radiation sickness, malignant neoplasms and leukemia.

Environmental consequences of radiation accidents

Radioactive is the most important environmental consequence of radiation accidents with the release of radionuclides, the main factor affecting the health and living conditions of people in the territories exposed to radioactive contamination. The main specific phenomena and factors causing environmental consequences in radiation accidents and disasters are radioactive radiation from the accident zone, as well as from the cloud (clouds) of air contaminated with radionuclides formed during the accident and spreading in the surface layer; radioactive contamination of environmental components.

The air masses that moved westward on April 26, 1986, north and northwest on April 27, turned east, southeast from the north on April 28-29, and then south (to Kiev) on April 30.

The subsequent long-term entry of radionuclides into the atmosphere occurred due to the combustion of graphite in the reactor core. The main release of radioactive products lasted for 10 days. However, the outflow of radioactive substances from the destroyed reactor and the formation of contamination zones continued for a month. The long-term nature of exposure to radionuclides was determined by a significant half-life. The deposition of the radioactive cloud and the formation of the trail took a long time. During this time, the meteorological conditions changed and the trail of the radioactive cloud acquired a complex configuration. In fact, two radioactive traces were formed: the western and the northern. The heaviest radionuclides spread to the west, and the bulk of the lighter ones (iodine and cesium), having risen above 500-600 m (up to 1.5 km), was transferred to the northwest.

As a result of the accident, about 5% of the radioactive products accumulated over 3 years of operation in the reactor left the industrial site of the station. The volatile isotopes of cesium (134 and 137) have spread over great distances (significant amounts throughout Europe) and have been found in most countries and oceans of the Northern Hemisphere. The Chernobyl accident led to radioactive contamination of the territories of 17 European countries with a total area of \u200b\u200b207.5 thousand km2, with an area of \u200b\u200bcesium contamination above 1 Cu / km2.

If the fallout across Europe is taken as 100%, then 30% of them fell on the territory of Russia, 23% in Belarus, 19% in Ukraine, 5% in Finland, 4.5% in Sweden, and 3.1% in Norway. On the territories of Russia, Belarus and Ukraine, the level of contamination of 1 Cu / km2 was taken as the lower boundary of the radioactive contamination zones.

Immediately after the accident, the greatest danger to the population was posed by radioactive isotopes of iodine. The maximum content of iodine-131 in milk and vegetation was observed from April 28 to May 9, 1986. However, during this period of “iodine danger”, almost no protective measures were taken.

Subsequently, the radiation situation was determined by long-lived radionuclides. Since June 1986, the radiation impact was formed mainly due to the radioactive isotopes of cesium, and in some regions of Ukraine and Belarus, also strontium. The most intense fallout of cesium is characteristic of the central 30-kilometer zone around the Chernobyl nuclear power plant. Another heavily contaminated area is some areas of the Gomel and Mogilev regions of Belarus and the Bryansk region of Russia, which are located about 200 km from the nuclear power plant. Another, northeastern zone is located 500 km from the nuclear power plant, it includes some areas of the Kaluga, Tula and Oryol regions. Because of the rains, the fallout of cesium became “spots”, therefore, even in neighboring territories, the density of pollution could differ tens of times. Precipitation played a significant role in the formation of precipitation - in the zones of rainfall, pollution was 10 or more times higher than in “dry” places. At the same time, in Russia the fallout was “smeared” over a rather large area, therefore the total area of \u200b\u200bterritories contaminated above 1 Cu / km2 is the largest in Russia. And in Belarus, where the fallout turned out to be more concentrated, the largest area of \u200b\u200bterritories contaminated by more than 40 Cu / km2 was formed in comparison with other countries. Plutonium-239, as a refractory element, did not spread in significant quantities (exceeding the permissible values \u200b\u200bof 0.1 Cu / km2) over long distances. Its fallout was practically limited to a 30-kilometer zone. However, this zone with an area of \u200b\u200babout 1,100 km2 (where strontium-90 in most cases dropped out more than 10 Cu / km2) became for a long time unsuitable for human habitation and management, since the half-life of plutonium-239 is 24.4 thousand years.

In Russia, the total area of \u200b\u200bradioactively contaminated territories with a pollution density above 1 Cu / km2 for cesium-137 reached 100 thousand km2, and over 5 Cu / km2 - 30 thousand km2. In the contaminated areas, there were 7,608 settlements in which about 3 million people lived. In general, the territories of 16 regions and 3 republics of Russia (Belgorod, Bryansk, Voronezh, Kaluga, Kursk, Lipetsk, Leningrad, Nizhny Novgorod, Orel, Penza, Ryazan, Saratov, Smolensk, Tambov, Tula, Ulyanovsk, Mordovia, Tatarstan, ).

Radioactive contamination affected more than 2 million hectares of farmland and about 1 million hectares of forest land. The territory with a contamination density of 15 Cu / km2 for cesium-137, as well as radioactive reservoirs are located only in the Bryansk region, where the disappearance of contamination is predicted in about 100 years after the accident. When radionuclides propagate, the transport medium is air or water, and the role of the concentrating and depositing medium is played by the soil and bottom sediments. Areas of radioactive contamination are mainly agricultural areas. This means that radionuclides can enter the human body with food. Radioactive contamination of water bodies, as a rule, is dangerous only in the first months after the accident. The most accessible for assimilation by plants are “fresh” radionuclides when they enter the air route and in the initial period of stay in the soil (for example, for cesium-137, a decrease in the intake of plants into plants over time is noticeable, that is, when the radionuclide “ages”).

Agricultural products (primarily milk), in the absence of appropriate bans on their use, became the main source of exposure of the population to radioactive iodine in the first month after the accident. Local foodstuffs made a significant contribution to radiation doses in all subsequent years. At present, 20 years later, the consumption of products subsidiary plots and forest gifts makes the main contribution to the radiation dose to the population. It is generally accepted that 85% of the total predicted internal dose for the next 50 years after the accident is the internal dose due to the consumption of food products grown in the contaminated area, and only 15% falls on the external dose. As a result of radioactive contamination of environmental components, radionuclides are included in the biomass, their biological accumulation, followed by a negative impact on the physiology of organisms, reproductive functions, etc.

At any stage of obtaining products and preparing food, it is possible to reduce the intake of radionuclides into the human body. If you thoroughly wash herbs, vegetables, berries, mushrooms and other products, radionuclides will not enter the body with soil particles. Effective ways reducing the flow of cesium from the soil into plants - deep plowing (makes cesium inaccessible to plant roots); application of mineral fertilizers (reduces the transition of cesium from soil to plant); selection of cultivated crops (replacement for species that accumulate cesium to a lesser extent). It is possible to reduce the supply of cesium to livestock products by selecting forage crops and using special food additives. Various processing and preparation methods can be used to reduce the cesium content of food. Cesium is soluble in water, therefore, due to soaking and cooking, its content decreases. If vegetables, meat, fish are cooked for 5-10 minutes, then 30-60% of cesium will go into the broth, which should then be drained. Pickling, pickling, salting reduces the cesium content by 20%. The same applies to mushrooms. Cleaning them from soil and moss residues, soaking in a saline solution and subsequent boiling for 30-45 minutes with the addition of vinegar or citric acid (change the water 2-3 times) can reduce the cesium content up to 20 times. In carrots and beets, cesium accumulates in the upper part of the fruit, if it is cut by 10-15 mm, its content will decrease 15-20 times. In cabbage, cesium is concentrated in the upper leaves, the removal of which will reduce its content up to 40 times. When processing milk for cream, cottage cheese, sour cream, the cesium content decreases by 4-6 times, for cheese, butter - 8-10 times, for ghee - 90-100 times.

The radiation situation depends not only on the half-life (for iodine-131 - 8 days, cesium-137 - 30 years). Over time, radioactive cesium goes into the lower layers of the soil and becomes less available to plants. At the same time, the dose rate above the earth's surface also decreases. The rate of these processes is estimated by the effective half-life. For cesium-137, it is about 25 years in forest ecosystems, 10-15 years in meadows and arable lands, 5-8 years in settlements. Therefore, the radiation situation is improving faster than the natural consumption of radioactive elements occurs. Over time, the density of pollution in all territories decreases, and their total area decreases.

The radiation situation has also improved as a result of protective measures. To prevent dust spreading, roads were paved and wells covered; roofs of residential buildings and public buildings were overlapped, where radionuclides accumulated as a result of fallout; soil cover was removed in places; in agriculture were held special events to reduce pollution of agricultural products.

Features of radiation protection of the population

Radiation protectionis a set of measures aimed at weakening or eliminating the impact of ionizing radiation on the population, personnel of radiation hazardous facilities, biological objects of the natural environment, as well as protecting natural and man-made objects from radioactive contamination and removing these contaminants (decontamination).

Radiation protection measures, as a rule, are carried out in advance, and in the event of radiation accidents, upon detection of local radioactive contamination - promptly.

• radiation safety regimes are developed and implemented;
• systems for radiation monitoring of the radiation situation on the territories of nuclear power plants, in observation zones and sanitary protection zones of these stations are being created and operated;
• action plans are developed for the prevention and elimination of radiation accidents;
• personal protective equipment, iodine prophylaxis and decontamination are accumulated and kept in readiness;
• are maintained in readiness for use of protective structures on the territory of nuclear power plants, anti-radiation shelters in settlements near nuclear power plants;
• preparation of the population for actions in the conditions of radiation accidents, professional training of personnel of radiation hazardous facilities, personnel of emergency rescue forces, etc.

• detection of the fact of a radiation accident and notification of it;
• identification of the radiation situation in the accident area;
• organization of radiation monitoring;
• establishment and maintenance of the radiation safety regime;
• carrying out, if necessary, at an early stage of the accident, iodine prophylaxis of the population, personnel of the emergency facility and participants in the liquidation of the consequences of the accident;
• providing the population, personnel, participants in the liquidation of the consequences of the accident with the necessary personal protective equipment and the use of these means;
• sheltering the population in shelters and anti-radiation shelters;
• sanitization;
• decontamination of the emergency facility, other facilities, technical means and etc;

• evacuation or resettlement of the population from areas in which the level of contamination or radiation doses exceed the permissible for the population.

The identification of the radiation situation is carried out to determine the scale of the accident, to establish the size of the zones of radioactive contamination, the dose rate and the level of radioactive contamination in the zones of optimal routes for the movement of people, transport, as well as to determine possible routes for the evacuation of the population and farm animals.

Radiation monitoring under conditions of a radiation accident is carried out in order to comply with the permissible time spent by people in the accident zone, to control exposure doses and levels of radioactive contamination.

The radiation safety regime is ensured by the establishment of a special procedure for access to the accident zone, zoning of the accident area; carrying out emergency rescue operations, carrying out radiation monitoring in the zones and at the exit to the “clean” zone, etc.

The use of personal protective equipment consists in the use of insulating skin protection (protective kits), as well as respiratory and eye protection (cotton-gauze dressings, various types of respirators, filtering and insulating gas masks, goggles, etc.). They protect a person mainly from internal radiation.

To protect the thyroid gland adults and children from exposure to radioactive isotopes of iodine at an early stage of the accident, iodine prophylaxis is carried out. It consists in taking stable iodine, mainly potassium iodide, which is taken in tablets in the following doses: for children from two years of age and older, as well as for adults at 0.125 g, up to two years at 0.04 g, taken orally after meals with jelly, tea, water once a day for 7 days. A solution of iodine water-alcohol (5% iodine tincture) is indicated for children from two years of age and older, as well as for adults, 3-5 drops per glass of milk or water for 7 days. Children under two years of age are given 1-2 drops per 100 ml of milk or nutritional formula for 7 days.

Maximum protective effect (reduction of the radiation dose by about 100 times) is achieved with the preliminary and simultaneous intake of radioactive iodine with its stable analogue. The protective effect of the drug is significantly reduced when it is taken more than two hours after the start of exposure. However, even in this case, effective protection against radiation occurs in the event of repeated inflows of radioactive iodine.

Protection from external radiation can only be provided by protective structures, which must be equipped with filters-absorbers of iodine radionuclides. Temporary shelters for the population prior to evacuation can be provided by almost any pressurized room.

Under design basis accident an accident is understood for which the initial events of emergency processes characteristic of a particular object are defined in the project.

Maximum design basis accidents are characterized by the most severe initiating events that cause the occurrence of an emergency process at this facility.

Under beyond design basis (hypothetical) accident an accident is understood that is caused by initiating events that are not considered for design basis accidents and is accompanied by additional failures of safety systems in comparison with design basis accidents.

66. Features and advantages of RUBREST:

natural radiation safety

long-term provision of fuel resources due to the efficient use of natural uranium;

elimination of weapons-grade plutonium production

environmental friendliness of energy production and waste disposal

economic competitiveness due to the natural safety of nuclear power plants and fuel cycle technologies, rejection of complex engineering safety systems

67. Environmental Consequences of NPP Operation

The main environmental problems of NPP operation. Compared to fresh fuel in its composition less content uranium-235 (since it burns out), but isotopes of plutonium, other transuranic elements, as well as fragments, or fission products - nuclei of medium masses, accumulate. The physical characteristics of the structural materials of the fuel assemblies also change over time.

Dismantling of a nuclear power plant at the end of its normal operation.

68. The main radionuclides formed during the operation of nuclear power plants and their effect on the body

Tritium -can enter the human body by inhalation, as well as through the skin. In the presence of tritium, the entire human body is exposed to β-radiation with a maximum energy of 18 keV.

Carbon-14- The effect of ionizing radiation on humans is mainly due to the consumption of food (milk, vegetables, meat).

Krypton - The radiological effect of 85 Kr on humans occurs mainly due to irradiation of the skin.

Strontium - 90 Sr enters the human body with food (milk, vegetables, fish, meat, drinking water). Like calcium, 90 Sr is deposited mainly in bone tissues containing vital hematopoietic organs.

Cesium- The radiological effect of cesium, like 90 Sr, on humans is associated with its penetration into the human body along with food. In living organisms, cesium can largely replace potassium and, like the latter, spread throughout the body in the form of highly soluble compounds.

69. Spent nuclear fuel - irradiated nuclear fuel, spent fuel elements (fuel rods) of nuclear reactors of nuclear power plants removed from the core.

RAW - substances not intended for further use in any state of aggregation, in which the content of radionuclides exceeds the levels.

70. Peculiarities of handling oyat:

Nuclear hazard (criticality);

Radiation safety;

Residual heat generation.

Ensuring subcriticality during the entire operation period;

Prevention of physical damage to the fuel assembly and / or TVEL;

Providing a reliable heat conduction;

Maintaining the level of radiation exposure and the release of radioactive substances when handling irradiated fuel at a reasonably achievable low level.

72. The list of technological operations for SNF management may include:

Intermediate storage of spent fuel assemblies in the spent fuel pool;

Transportation of spent fuel to a reprocessing plant, temporary storage or repository;

Intermediate storage before processing or disposal;

Reprocessing or preparation of spent fuel assemblies for temporary storage or disposal;

Temporary storage or burial.

73. Management of radioactive waste

A typical waste management sequence is collection, separation, characterization, treatment, conditioning, transport, storage and disposal.

74. RW characteristics used for their classification + 75. RW classification

There are a number of criteria by which radioactive waste is classified.

By activity levels and heat release, with the definition of quantitative characteristics:

High activity waste; long rao

Medium activity waste;

Low activity waste; shortly rao

Very low activity waste.

Half-life of radionuclides, which determines the time of their potential danger:

Very short lived;

Short-lived;

Medium-living;

Long-lived.

By the nature of the predominant radiation:

α-emitters;

β-emitters;

1.3 Classification of radiation accidents by technical consequences

IN depending on the nature and extent of damage and destruction

accidents at radiation hazardous facilities are subdivided into design accidents,

design with the greatest impact (maximum design) and beyond design.

1.3.1 Design basis accidents

Under design basis accidentunderstand an accident for which the design defines the initial events of emergency processes that are characteristic of a particular radiation hazardous facility (type of reactor plant), final states (controlled states of elements and systems after an accident), and

safety systems are also envisaged, which, taking into account the principle of a single failure of the safety system (system channel) or one additional personnel error, limiting the consequences of an accident to established limits. Maximum design basis accidentsare characterized by the most severe initiating events that cause the occurrence of an emergency process at this facility. These events lead to the maximum possible radiation consequences within the established design limits.

Already at the design stage of a nuclear power plant, a wide range of design basis accidents is considered, which are characterized by a sufficiently low frequency of occurrence and are overcome taking into account a conservative approach in terms of the operation of systems designed to overcome accidents.

The main modes of normal operation (NE), violations of normal operation (NOE) and accidents that determine the radiation impact on the environment are the modes of operation of the reactor compartment systems.

The NPP design considers various modes carried out during normal operation, namely:

- work at power;

- work at the minimum power level;

- hot stop;

- semi-hot stop;

- cold stop;

- shutdown for repair;

- stop for overload;

- refueling.

Normal operation of the power unit is carried out in accordance with the design operating limits and conditions... Under operational limitsunderstand the values \u200b\u200bof the parameters and characteristics of the state of systems and the NPP as a whole, set by the project for normal operation.

The project considers modes of disruption of normal operation, that is, all states of equipment and systems of the power unit with deviations from

the energy production technology adopted in the project when operating at power, during the start-up, shutdown and refueling periods, which do not lead to an excess

a VVER-1000 reactor plant (RP) shall not exceed the following established limits for safe operation:

1. The operational limit (i.e., the boundary values \u200b\u200bfor normal operation) damage to fuel elements due to the formation of microcracks with defects such as gas leaks in cladding should not exceed 0.2% of fuel elements and 0.02% of fuel elements in direct contact of nuclear fuel with the coolant.

2. The safe operation limit in terms of the quality and size of fuel rod defects is 1% of fuel rods with defects such as gas leakage and 0.1% of fuel rods for which there is direct contact between the coolant and nuclear fuel;

3. The maximum design limit of damage to fuel elements corresponds to non-exceeding the following limit parameters:

- fuel element cladding temperature - 1200o С,

- local depth of fuel element cladding oxidation - 18% of the initial wall thickness,

The proportion of reacted zirconium is 1% of its mass in the fuel element cladding.

4. To maintain the integrity of the pressure boundaries of the primary circuit P

the absolute pressure in the equipment and pipelines of the primary circuit should not exceed the operating pressure by more than 15%, taking into account the dynamics of transient processes and the response time of the safety valves.

5. To maintain the integrity of the pressure boundaries of the secondary circuit P

5 kgf / cm 2 (0.49 MPa).

7. The temperature of the medium in the rooms of the containment should not exceed

150 ° C;

8. At the border of the SPZ and beyond, the dose received by children in the first 2 weeks after the accident should not exceed 10 mSv for the whole body, 100 mGy for the thyroid gland and 300 mGy for the skin (in accordance with NRBU-97 - the level of unconditional justification for the introduction of the countermeasure "Restriction of the stay of children in the open air").

IN the project analyzes the NPP safety in case of accidents, that is, in the event of NPP operation failures, in which there was a release of radioactive products and / or ionizing radiation beyond the boundaries provided for by the project for normal operation, in quantities exceeding the established safe operation limits.

For design basis accidents, initiating events, final states and

safety systems are provided that ensure, taking into account the principle of a single failure of safety systems or one, independent of the initiating event, personnel errors, limiting their consequences to the limits established for such accidents.

The list of NOE modes and design basis accidents of the reactor compartment systems, for which safety analysis is performed, is specified in the safety analysis report (SAR) of the power unit.

All design modes of the reactor plant are combined according to the groups of characteristic effects of changing parameters.

Initiating events during operation of the power unit at capacity:

- increased heat removal through the second circuit;

- decrease in heat removal through the second circuit;

- reducing the flow rate of the coolant through the reactor;

- increase in the mass of the primary coolant;

- violations of normal operation with failure of emergency protection of the reactor;

- change in reactivity and distribution of energy release.

Initiating events during cooling down of the reactor plant and at a shutdown power unit:

- reduction of the criticality margin of the reactor core;

- reducing the mass of the primary coolant;

- decrease in heat removal from the reactor core due to deterioration of the circulation of the primary coolant;

in supporting systems;

- reduction of heat removal from the reactor core due to failures

in equipment;

- increase in pressure ("overpressure") of the primary circuit.

Initiating events in the management of fresh and spent fuel and initiating events in the management of radioactive waste.

To prevent emergency situations, that is, the states of the NPP,

characterized by		breaking		limits
operation that did not turn into an accident,					their escalation into accidents,
envisageda set of technical and organizational measures,
	carried out						vital
(design, construction, manufacturing						equipment, installation,
exploitation).
The main		activities implemented					design,
are:

- application of technical solutions that have been mastered in similar conditions and taking into account the accumulated operating experience;

- the use of the principle of conservatism in assessing the adopted technical decisions affecting safety;

- widespread use of the principle of redundancy of elements, equipment, fittings, etc.... e to be able to ensure reliable and safe operation in the event of failure of individual elements of the systems;

- application for major technological systems equipment,

devices, fittings, materials made				conformity
special	technical	conditions
characterized by high level reliability and workmanship;
The use of a special regulatory and technical base in the process
design and manufacture of equipment, systems and their elements, which
makes the highest demands on			the proposed		technical
solutions;
Application of systems of periodic and continuous condition monitoring
equipment and technological systems and special diagnostic systems
the most critical equipment;

- widespread introduction of systems automatic control all

and control;

- taking into account extreme external influences (including: an earthquake up to MCE, inclusive, and an external shock wave) in order to ensure safety under these influences;

- application of the necessary technical solutions to ensure

low level of radioactive impact on the environment; reliability of the containment system;

- use of a radiation monitoring system for technological environments, NPP premises and the surrounding area for reliable monitoring technological process in terms of potential impact on the environment;

- creation of reliable power supply systems and drainage of residual

heat with the necessary redundancy and increased reliability of reserve

- use of quality materials in accordance with the requirements Technical conditions, GOSTs, special requirements in nuclear technology;

- careful incoming control with the necessary documentation;

- compliance with all necessary instructions for construction and installation,

and also work quality control;

- performing the necessary tests and special program commissioning with verification of the characteristics of equipment and systems important to safety, strict adherence to the program commissioning and a special program for commissioning the unit;

- organization effective system documenting the results of work and control.

The main activities at the stage of equipment manufacturing

are:

- manufacturing of equipment for basic safety systems in accordance with special manufacturing conditions for nuclear technology;

- performing the necessary checks and equipment control for manufacturing plants.

The main activities at the operational stage are:

- development of the necessary operational documentation for sound operational regulations and instructions;

- maintaining in good working order systems important to safety by carrying out preventive measures and replacing equipment that has left the station;

- selection of qualified personnel and further improvement of their qualifications (periodic checks of knowledge, emergency training, refresher courses, etc.), the formation of a safety culture.

The main measures to ensure the safety of nuclear power plants under design basis accidents, and not to develop these accidents into beyond design basis

are:

- special security systems designed for

preventing		restrictions			damage			nuclear,
equipment and pipelines containing radioactive substances;
Special control and providing security systems,
designed for the management and control of technological systems
security, ensuring			energy			working. environment
envisaged	emergency		sources		power supply - autonomous
diesel generator	installations			connection			most	responsible

consumers to direct current sources;

- application of the conservative principle of constructing the above systems, taking into account a single failure and the independence of various channels;

- the use of alarm systems, warning and emergency

protection (These systems inform the operator about the deviation of the parameters from

normal values, provide an emergency shutdown of the reactor in case of unacceptable deviations of the parameters);

- the presence of two independent systems for influencing reactivity (mechanical system absorber rods, CPS and boron, a system designed to introduce a liquid absorber);

- introduction of various systems of automatic interlocks preventing

undesirable development of emergency modes, and the introduction of an automatic prohibition on the operator's action in the initial period of the occurrence of accidents to avoid his erroneous actions. In this case, the process of overcoming accidents is carried out automatically;

- application special system monitoring the readiness of safety systems (SS) with the issuance of a generalized signal of readiness of each SS channel to the control room.














Design basis accident

• Design basis accident - an accident for which initiating events and final states are defined by the project and safety systems are provided that, taking into account the principle of a single failure of safety systems or one personnel error independent of the initial event, limiting its consequences to the limits established for such accidents.

• Beyond design basis accident - an accident caused by initiating events not taken into account for design basis accidents or accompanied by additional failures of safety systems in excess of a single failure in comparison with design basis accidents, the implementation of erroneous decisions of personnel.

• Severe beyond design basis accident - beyond design basis accident with damage to fuel elements above the maximum design limit, at which the maximum permissible accidental release of radioactive substances into the environment can be achieved.


















• Figure: 1. Schematic diagram of SPOT SG and SPO ZO

• 1 - tanks for emergency heat removal; 2 - steam lines; 3 - condensate pipelines; 4 - PHRS valves; 5 - heat exchangers-condensers SPOT-ZO; 6 - steam generators; 7 - shut-off valves








• 1 - reactor; 2 - melt localization device; 3 - fuel pool; 4 - shaft for revision of internals; 5 - pit tanks; 6 - pipeline for water supply to the melt surface; 7 - pipeline for water supply to heat exchanger ULR