Reasons for design basis accidents. Accidents at radiation hazardous facilities. Environmental consequences of radiation accidents
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 the ULR heat exchanger
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 of the 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 - called uncounted for design basis accidents initiating events 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, the radiation consequences of the accident go beyond the territory Russian Federationor given 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 Agency for nuclear power (IAEA) 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
Any major radiation accident is accompanied by two fundamentally different types of possible medical consequences:- 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 them 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. 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.
The following radiation protection measures are carried out in a preventive manner:- 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 action 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, and also 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 radiation 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 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 bandages different types 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, 0.125 g each, up to two years, 0.04 g each, taken orally after meals with jelly, tea, water once a day for 7 days. A solution of iodine water-alcohol (5% tincture of iodine) 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 old 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, there is an effective protection against radiation in case of repeated inflows of radioactive iodine.
Protection from external exposure can only be provided by protective structures, which must be equipped with filters that absorb iodine radionuclides. Temporary shelters for the population prior to evacuation can be provided by almost any pressurized room.
TESTS FOR PREPARATION FOR GIA ON THE DISCIPLINE "RADIATION HYGIENE"
Choose one correct answer:
1. The main measures to ensure radiation safety include:
1) legal, epidemiological, sanitary and hygienic
2) legal, organizational, sanitary and hygienic
3) economic, organizational, epidemiological
4) operational, organizational, sanitary and hygienic
5) legal, organizational, epidemiological
2. Reduction of radiation exposure of patients during radiography is provided by:
1) the health of the device
2) compliance of the device with technical standards
3) the correct choice of the picture mode
4) filtration of the primary beam
5) all of the above is true
3. Weighting factors for certain types of ionizing radiation are used when calculating:
1) exposure dose
2) absorbed dose
3) equivalent dose
4) effective dose
5) radiation output
A copy of the worker's radiation dose card should be kept in medical organization after his dismissal for ______ years
5. The following sources make the main contribution to population exposure:
1) global radioactive fallout
2) accidents at nuclear power plants
3) natural background radiation, technologically modified
natural background radiation, X-ray and radiological
diagnostics in medicine
4) nuclear power plants in normal operation
5) everything is true
6. Irradiation of patients during X-ray diagnostics is regulated by:
1) Radiation safety standards (NRB-99/2009)
2) Basic sanitary rules for ensuring radiation safety (OSPORB-2010)
3) SanPiN 2.6.1. 1192-03 "Hygienic requirements for the design and operation of X-ray rooms, apparatus and X-ray studies"
4) the federal law "On radiation safety of the population"
5) everything is correct
Planned radiation monitoring at enterprises,
using sources of ionizing radiation, includes:
1) determination of the levels of natural radiation background
2) assessment of the duration of technological processes
3) assessment of the dose rate at workplaces, determination of the content of radionuclides in the air of the working area, medical monitoring of personnel
4) determination of the levels of technologically modified natural radiation background
6) everything is correct
8. Radiation monitoring devices are subdivided into:
1) customized
2) wearable
3) portable
4) stationary
5) everything is correct
Sanitary and dosimetric control in medical institutions
includes:
1) measuring the dose rate of external radiation
2) individual dosimetric control
3) determination of the concentrations of radioactive gases and aerosols in
4) control over the collection, storage and disposal of radioactive waste
5) everything is true
10. The level of radioactive contamination of surfaces is expressed in:
3) Frequency / cm 2 / min
4) MKR / hour
11. Weighting coefficients for tissues and organs are used when calculating:
1) exposure dose
2) absorbed dose
3) equivalent dose
4) effective dose
5) ambient dose equivalent
12. The principle of optimization of radiation safety when carrying out X-ray examinations involves:
1) organization of a single X-ray department for a hospital and a polyclinic
2) carrying out X-ray examinations in the direction of the attending physician
3) establishing reference levels of exposure for different types procedures and refusal of unjustified research
4) maintaining at the lowest possible level of radiation doses to patients while maintaining the quality of their examination and treatment
5) compliance with radiation safety standards
Solid radioactive waste is processed before disposal
methods:
1) burning
2) glass transition, bituminization, glass transition cementation,
cementing
3) grinding
4) pressing
5) everything is true
14. The activity of a radioactive substance is:
1) absorbed energy, calculated per unit mass
2) the amount of radiation emitted by radioactive atoms
3) the number of radioactive decays of atomic nuclei per unit time
4) the time of elimination of radionuclides from the body
5) dose created per unit of time
15. Radiation monitoring at the workplaces of personnel, adjacent rooms and areas adjacent to the X-ray room should be carried out at least once in:
16. The highest concentration of radon is noted:
1) in the surface air in winter
2) in the surface layer of air in summer
3) in the air over the ocean
4) in the soil air
5) in the upper atmosphere
17. Monitoring and control of the radiation situation outside the sanitary protection dose is carried out by:
1) groups of radiation monitoring of the enterprise itself
2) organizations licensed to carry out such work
3) territorial offices of Rospotrebnadzor
4) regional bodies of Rostechnadzor
An accident for which the project has defined initial and final events is called:
2) design
3) actual
4) technical
5) hypothetical
19. The biological effect of radiation depends on:
1) received dose
2) body reactivity
3) exposure time, intervals between exposures
4) the size and localization of the irradiated surface
5) all of the above is true
20. Radioactive waste in health care facilities includes:
1) radioactive aerosols removed from fume hoods and
2) liquid radioactive waste arising from
decontamination of equipment
3) radioactive waste released with the feces of patients
4) used tools, overalls, PPE from open source departments
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 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 NPP design stage, a wide range of design basis accidents is considered, which are characterized by a fairly 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 (NNE) and accidents that determine the radiation impact on environment, are the operating modes 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 start-up, shutdown and refueling, 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 leakage of 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 for damage to fuel elements corresponds to the non-exceeding of the following limit parameters:
- fuel element cladding temperature - 1200o С,
- local oxidation depth of fuel element cladding - 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 "Restricting the stay of children in the open air").
IN the project analyzes the NPP safety in case of accidents, that is, in case 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;
- reduction of heat removal from the reactor core due to deterioration of the circulation of the primary coolant;
in supporting systems;
- decrease in 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, |
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envisageda set of technical and organizational measures, | ||||||||
carried out | vital | |||||||
(design, construction, manufacturing | equipment, installation, |
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exploitation). | ||||||||
The main | activities implemented | design, |
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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 |
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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 control of equipment 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 condition systems important to safety by taking 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, |
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equipment and pipelines containing radioactive substances; | ||||||||
Special control and safety systems, |
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designed for the management and control of technological systems |
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security, ensuring | energy | working. environment |
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envisaged | emergency | sources | power supply - autonomous |
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diesel generator | installations | connection | most | responsible |
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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);
- implementation of various systems of automatic interlocks that prevent
undesirable development of emergency modes, and the introduction of an automatic prohibition on the operator's actions 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.