10. STORAGE AND REPROCESSING OF THE NONREACTOR RADIOACTIVE WASTES AND SPENT IONIZING RADIATION SOURCES

10.1. General

The development of a national economy of the country is inevitably connected to formation of wastes, including those containing radioactive substances. Among the radioactive wastes are materials not to be used later on, solutions, products, equipment, biological objects, soils containing radionuclides in quantities exceeding the safety level for the person and biota established by working norms and rules.

Nonreactor radioactive wastes of low and intermediate specific activity are formed as a result of radionuclides use in medicine, industry, agriculture, and scientific researches. The basic suppliers of such wastes are numerous research organizations, industrial enterprises, medical establishments, and educational institutions, which, as a rule, are located in the regions with high density of population. These enterprises send their radioactive wastes and spent ionizing radiation sources (IRS) to 16 regional points of burial of radioactive wastes (PBRW) forming a system of special enterprises "Radon", each of which is located near to a large industrial center. For each special enterprise a region of service is determined. The zones of service and arrangement of special enterprises are shown on Fig. 10.1.

Moscow SIA "Radon" is the head enterprise on the problem of handling radioactive wastes of intermediate and low specific activity in system "Radon". Scientific, practical, methodical and other help is affected by it for special enterprises (SE) of Russian Federation, and if necessary for the countries of Commonwealth.

In the framework of scientific-methodological activity of SIA "Radon" the data collection and systematization on all possible kinds of SE activity, including radioecological monitoring of environment objects are carried out.

The list of registered parameters comprises:

• title and location of object;
• geographical and geomorphological characteristic of region of object location;
• regions of servicing:
• type and project of storehouses, and also date of commissioning;
• volume of storehouses, percent of filling up on a given moment of time;
• volume of annual receipt and total activity of the wastes since burial.

Technological processes effected at the radoactive wastes handling, include:

• cementing, which is carried out in industrial scale on stationary and mobile plants;
• bituminization, at which radioactive wastes (RW) with concentration more than 60 g/l are vaporized 5-6 times and are included into melted bitumen at a facility created on the basis of rotor vaporizer;
• burning and pressing, carried out on installations of an industrial type. Development of high-temperature methods of RW burning in pit ovens with fuel-plasma sources of heating is conducted now in SIA "Radon";
• vitrification is a new highly reliable method of RW localization; the working installation gives out the end product, designed for practically eternal storage;
• water cleaning is carried out by both stationary and mobile facilities using purified water in a system of reverse water supply of technological processes;
• solidification: spent IRS relating to a category of high level radioactive wastes are dumped in special depository at a depth of 6 m and are covered by melted metal layer to layer by "Moskit" facility.

Except for Moscow SIA "Radon" having an advanced infrastructure, hardware - technological equipment of the majority of PBRWs does not correspond to the modern requirements. Capacities of storehouses are exhausted or extremely limited. For a number of PBRWs new sites for RW disposal are required.

The general characteristic of "Radon" of Russia is submitted in the Table 10.1.

Fig 10.1. Location and zones of servicing the SE "Radon"

Table 10.1

General characteristic of SE "Radon"

10.2. Characteristics of accumulated RW

The following types of radioactive wastes enter the burial point for long-term localization and reliable utilization:

• solid radioactive wastes (SRW)
• liquid radioactive wastes (LRW)
• spent ionizing radiation sources.

The RW radionuclide content, which enter "Radon" points, are characterized by almost all known radionuclides with different half-lives, but it is possible to highlight the main: Cs-137, Sr-90, Co-60, H-3, I-131, U, Pu, Th.

The technological process of reprocessing and disposal of radioactive wastes and ionizing radiation sources, admits presence of four zones of possible radioactive substances release into environment:

1. Zone of SRW burial

2. Zone of purified waters dumping

3. Zone of purified gases releases

4. Zone of storing the spent sources

Studies carried out in Moscow SIA "Radon" have shown that concentrations of radioactive materials in soil, vegetation and water in the strict regime zone, sanitary-protective zone and supervision zone are identical for all examined SE. On criteria of the importance for 95 % confidence coefficient their distinctions are insignificant. Influence of functioning SE on an environment is not revealed, and its radiation state is caused by influence of the external factors, not connected to combines.

The RW characteristics on special enterprises of Russia are brought in the Table 10.2.

In accordance with the kind of RW, their activity and method of RW technological reprocessing, they are located in special burial grounds, which represent underground rectangular tanks with walls and bottom, assembled from reinforced concrete structures, and overlapping from composite reinforced concrete plates. The vessels for liquid wastes are made of reinforced beton monolith and clad with stainless steel from within. The RW burial technique in near surface layer is the commonly accepted. Near surface storehouses can be made as holes, trenches, superficial mines, sumps. Storehouses of barrow type are also related to the nearsurface storehouses.

General characteristics of RW storehouses are shown in the Table 10.3.

Sources of the information on a technical and radioecological condition of special enterprises are as follows:

• annual accounting materials of SE to region administrations;
• logs of receiving the radioactive wastes;
• technical projects on SE;
• logs of the radiation control of environmental objects of SE;
• logs of the individual control of irradiation of SE personnel;

accounting materials on geographical and geomorphological inspection of SE location region.

Table 10.2

Characteristics of radioactive wastes

Table 10.3

The general characteristic of RW storages

10.3. Geoinformation system of RW burial on the special enterprises of Russia

The analysis of the basic directions of nature protection activity in the sphere of the RW handling allows to make a conclusion, that it is necessary to carry out work within the framework of regional system of radioecological monitoring on the basis of using the advanced means of collecting and processing the significant data arrays.

The information system consists of a database and multilevel cartographical application. The basic system modules can be used both in local computer networks and in the remote access mode.

In development of geoinformation system a principle of its use as a regional system of tracking for the RW handling on territory of serving the SE is incorporated.

The basic tools are as follows:

• Windows environment
• DBMS Microsoft Access application
• DDE (Dynamic Data Exchange)
• OLE (Object Linking and Embedding).

The analysis of subject area in sphere of activity of regional specialized enterprise on radioactive wastes burial allows the conceptual model of information system to be developed. The data scheme and bindings between them is submitted on Fig. 10.2. The group of data, incorporated under the name "General", includes such fields as "Address", "Scheme" "Region". Using these attributes makes possible binding of objects to electronic cartography of the region, that enables the performance of the complex monitoring of radiation situation as of zones RW burial and environment of SE, and radiation-hazardous objects of region of service within the framework of one database. The submitted data scheme includes not only information blocks, connected directly to technology of RW burial, but also new modules, relating to the radiation and radioecological monitoring. To such modules can be assigned module "Doze", ensuring the individual control of the personnel, and module "Ecology", containing information about radionuclide content in a zone of a strict mode, sanitary-protective zone and zone of supervising the RW burial place.

Fig.10.2. Data scheme of RW handling system

The interface to the information is realized on the basis of multiple queries to the developed forms, which allow the interested information as in textual, and in a graphic form to be displayed conveniently for the user. The type of the form "General information" is indicated on Fig. 10.3. The analysis of parameters of the radiation monitoring is effected by the complex composit forms developed. They are presented in detail on Fig.10.4.

Fig.10.3. View of form "General information"

A

B

Fig.10.4 View of forms (A - "ecology", B - "dose").

Input and the analysis of data, connected with cartography is effected by way of geoinformation system (GIS). GIS is based on using the sets of graphic files with images of cards or plans of region. The set is incorporated by general coordinate system. The engine of benchmark nodes grids is applied to account for possible distortions of the region image. The system provides setting of a point on a card or plan, data input with binding to a place, display of information layers (on the screen and printer), constructing the isolines of studied value, etc.

The information layer "PBRW of Russia " includes the scheme of serving zones of 16 enterprises, plans of enterprise industrial zones and layouts of vicinities. The complete information about PBRW with the data, concerning radioecological monitoring of industrial zone and vicinities is stored in a database. The examples of visualizing the information with GIS application are presented on Fig. 10.5. The main blocks of the developed geoinformation complex have been part of information maintenance of the international project Radleg, containing the data on the whole spectrum of questions, involving the use of radioactive materials on the territories of RF.

(A - location scheme of SE of RF);

B - monitoring network of the Saratov SE

C - scheme of test-operating the RW storages

Fig.10.5. Examples of GIS data visualization of "PBRW of Russia":

The geoinformation complex developed also includes such important information-analytical block, as mathematical model of radionuclide migration from PBRW storages.

The study of subject area of technological process of processing and RW burial has been brought to the basis of developing the mathematical model is necessary.

The developed information system of tracking for the ionizing radiation sources handling allows the new approaches. Based on computing means application, with the purpose of performing the long-term forecast of environmental conditions by mathematical modeling of processes of radionuclide migration from a burial zone. Then estimating these processes from the standpoint of detecting the unsuccessful tendencies and probable emergencies to be considered.

The mathematical forecasting block of radionuclide migration was included for solving the above described problem in a geoinformation complex of tracking system in sphere of the RW handling.

Use of the given model gives an opportunity to predict the radioactive substances migration from the places of RW burial. On the basis of forecast the measures on selecting the storages siting, as well as the change of increasing or reducing the activities levels sent to burial and the application the most effective technologies of RW processing from the standpoint of environmental protection are being carried out.

Thus, the geoinformation system developed allows not only the carrying out of the radiation monitoring control on the SE serving regional territory on RW burial, but also the prediction of radiation situation.

Information flows on all kinds of SE activity, as well as the radioecological monitoring data of environmental objects as on combines (enterprises), and on Moscow and Moscow region, are concentrated in the Centre of Information Processes and Technologies, where databases are formed, mathematical processing and analysis of the information is conducted, and forecast of developing the radiation situation is made. From here the information processed enters the interested organizations for applicable decision making: the Government of Moscow, the prefectures of administrative districts, the State Sanitary and Atomic Supervision units, the divisions on nature protection and staff of civil defence.

REFERENCES

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10.2. Sites on harmless utilization and disposal (burial) of toxic industrial wastes. The fundamentals of designing. SNiP 2.01728-85, Moscow: Goskomstroy of the USSR, 1985, 14p.

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10.4 The life and radiation (translation from English), Moscow: Energoatomizdat, 1993, 96p. (National Council on radiation protection of Great Britain, 1990).

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10.14. Sobolev A.I., Tikhomirov V.A., Zubov V.Yu., "Regional information computing complex radioecological monitoring system", 2d International scientific and practical conference "The problems of quality control of environment of cities", M., 1-4 October, 1996, p.12-13.