RU2331732C2 - Cleaning method for beds of minor rivers in permafrost zone to remove bottom sediments contaminated with radionuclides - Google Patents

Abstract

FIELD: construction, hydrotechnics.

SUBSTANCE: invention is attributed to cleaning methods for beds of minor rivers in permafrost zone with seasonal flow from sediments contaminated with radionuclides from radioactive solid waste handling. Removal of contaminated sediments is executed in winter by segments in downstream direction after discharge cancellation and their dewatering. Bottom ground is loosened and mechanically shaved by layers as it is freezed by natural cold with stocking it in temporary piles and subsequent transportation outside river floodplain for burying or laying in surface burial hills. To speed-up layer-by-layer freezing the net of trenches with vertical walls is cut in parallel in bottom ground depth as it freezes. Trench width is defined by parameters of equipment being used, their depth is not less than half a meter and distance between trenches corresponds to double trench depth. The invention allows to isolate from biota (for a period of not less than 100 years) the most migration suspectable solid radioactive wastes and hence to lower the risk of people irradiation.

EFFECT: lowering the risk of people irradiation.

1 dwg

Description

The invention relates to the field of solid radioactive waste management (solid waste) and the cleaning of small river beds of the permafrost zone with seasonal (summer) runoff from bottom sediments contaminated with:

- natural radionuclides that hit the earth's surface during the exploration and development of mineral deposits;

- artificial radionuclides ejected from combat wells during accidents in underground nuclear explosions (APNS) carried out for peaceful purposes in the sparsely populated northern regions where there are no specialized enterprises for the processing of solid radioactive waste and burial grounds.

A known method of cleaning the channels of small rivers from toxic silty bottom sediments [1] is a prototype. According to the proposed technology, it is recommended to start cleaning work from the source of the river with preliminary opening of the channel into sections and formation of dams using mechanisms located on floating platforms. In a certain sequence, work is carried out on the development and raising of bottom sediments, washing large fractions (boulders, gravel) from sludge, settling the pulp, and neutralizing toxic sludge on special apparatuses.

The main disadvantages and factors hindering the implementation of the above method in the conditions of sparsely populated cryolithozone areas are: high energy intensity of work; the need to purchase and import special expensive equipment; a large amount of installation work; the complexity and complexity of the maintenance of installations; the need for education and training of staff; the complexity of the device dams and anti-filter screens, given the high strength of the soil in the frozen state and low speed of thawing; processing (washing) of radiation-contaminated bottom sediments related to solid waste will lead to the formation of liquid radioactive waste (LRW), which in turn must be processed and disposed of; unresolved issues of the disposal of toxic sludge; seasonality of work - only in the summer period, the duration of which in the North is not more than 3 months; the need for clean water through a special conduit; high probability of external exposure to personnel during rehabilitation works.

A new method is proposed for cleaning the beds of small cryolithozone rivers from bottom sediments contaminated with radionuclides, which consists in the fact that they are excavated only in winter time (from the top downstream) after the flow stops, the boundaries of the areas to be rehabilitated, and their drainage are determined. Contaminated bottom soil is loosened and cut in layers mechanically as it is frozen with natural cold, stored in temporary dumps and then transported beyond the floodplain and buried (laid) in surface burial mounds (PCM) [2]; at the same time, to accelerate the process of layer-by-layer freezing in the thickness of the bottom soil as it freezes, a network of trenches with vertical walls is cut parallel to each other, the width of which is determined by the parameters of the technique used, the depth is at least half a meter, and the distance between them corresponds to twice the depth, thereby ensuring a significant an increase in the contact surface of the soil with cold air and, as a consequence of this, intense freezing.

The invention is aimed at solving the problems of cleaning the channels of small rivers of the permafrost zone from bottom sediments contaminated with radionuclides that have fallen into rivers and polluting bottom sediments, the processing and burial of which in the North is currently impossible. The high-quality implementation of the proposed rehabilitation works in accordance with the technological regulations will allow reliable isolation of biologically active waste that are most susceptible to migration from biota (for a period of at least 100 years), thereby reducing the risk of radiation exposure to the population.

The required technical result in the implementation of the invention is expected to be obtained by taking into account the hydrological regime of small rivers in the region, where areas with a fast current (rifts) alternate with intervals with a low flow rate (pits, reaches, meanders), which are natural traps where natural deposition of contaminated soil occurs carried away from radiation-contaminated areas, which composes bottom sediments. In addition, it is necessary to take into account the fact that the flow of small rivers in the permafrost zone occurs only in the summer, and the floodplain soils are frozen most of the year (9 months), and it is also necessary to make maximum use of the climatic features of the region and the natural (natural) resources of the permafrost zone :

- the presence of continuous permafrost;

- cessation of runoff of small rivers in the winter (9 months a year);

- the presence of low-temperature atmospheric cold caused by a sharply continental climate with severe and long winters (7 months);

- low defrosting capacity of bottom sediments in the summer (1.5-2.0 m);

- high speed of freezing thawed soils in winter;

- low vertical migration of radionuclides, only within the power of the thawed layer.

The drawing shows the inventive method for cleaning small rivers cryolithozone from bottom sediments contaminated with radionuclides.

1 - drained, subject to rehabilitation section of the channel of the watercourse;

2 - seasonally thawed, radionuclide-contaminated bottom sediments (TPOA);

3 - the raft of the channel of the watercourse;

4 - bulldozer;

5 - temporary dumps of cut contaminated bottom sediments;

6 - ripper;

7 - mortise trench.

The implementation of the proposed method in practice is carried out in the following sequence. Preliminarily, in the winter period, by means of core exploration drilling and study of drill cores, the boundaries of contaminated sites with the setting of lighthouses are determined and the volumes of contaminated soils to be excavated are calculated, structural features of the bottom sediments of watercourses, composition of radionuclides, thaw layer thickness, etc.

Then, if necessary, the contaminated sites are drained and ice is removed in some way, and the mortise trench is drilled. Naked bottom sediments are frozen with natural (atmospheric) cold and cut off layer by layer as they freeze (if necessary, with preliminary loosening) using earthmoving and mining technologies [3]. Cutting soils are laid out in temporary dumps (see drawing).

To speed up the process of layer-by-layer freezing of soils and, as a consequence of this reduction in the time for conducting rehabilitation works, it is recommended to cut a network of trenches with vertical walls, the width of which is determined by the size of the equipment used, with depth not less than half a meter, and the distance between them is equal to twice the depth. This ensures a significant increase in the contact surface of the pillar in the soil between the trenches with cold air and, as a result, their intensive freezing to low temperatures and in a shorter period of time. Frozen pillars loosen and freeze, and then trenches deepen again, etc. until complete removal of contaminated soils at full capacity.

Then, the soil from dumps is loaded into vehicles and transported outside the floodplain to an elevated site of the relief, where it is buried without processing in the PCM using the technology developed by the IGDS SB RAS [4], thereby ensuring their reliable isolation from biota.

Rehabilitation work can be carried out in stages over a number of years, including in several areas at once, starting from the headwaters of the stream downstream; must be completed before the onset of spring (t avg. day. ≤ -10 ° C), including PCM erection time.

The main advantages of the proposed method (technology) in comparison with the analogue:

- low energy, material and labor costs;

- high mechanization of work;

- the use of conventional commercially available mechanisms and proven mining technologies;

- lack of agitation of water;

- use of a natural resource - atmospheric cold for freezing bottom sediments;

- complete removal of solid waste from floodplains and the cessation of radionuclide migration;

- low probability of external exposure to workers employed in rehabilitation work;

- simplicity of decontamination of the equipment used upon completion of work.

Literature

1. Patent for invention No. 2219305 Russia. The method of cleaning small rivers // Vershinin N.P. and Vershinin I.N. MKI 7 Е02В 3/02, 15/00. Claim 04.24.2002. Publ. 12/20/2003. Bull. No. 35 (114).

2. Patent for invention No. 2134459 Russia. The method of disposal of solid radioactive waste in the permafrost zone. // V.V. Kiselev, Yu.A. Khokholov. MKI G21F 9/24 Decl. 08/12/97. Publ. 08/10/99. Bull. No. 2.

3. Peshkov V.G. Development of alluvial deposits. - M .: Nedra, 1985 .-- 568 p.

4. Kiselev V.V., Burtsev I.S. Elimination of the consequences of emergency underground nuclear explosions in the permafrost zone. - Yakutsk, Publishing House of the NSC SB RAS, 1999. - 148 p.

Claims (1)

The method of cleaning the channels of small rivers of cryolithozone from radionuclides, including clearing the channel from sediment, characterized in that the contaminated bottom sediments are excavated in winter sections downstream after the flow ceases and is drained, the bottom soil is loosened and cut in layers mechanically as it is frozen its natural cold with storage in temporary dumps, followed by transportation outside the floodplain and burial or laying in surface burial mounds, while to accelerate I layer-by-layer freezing in the thickness of the bottom soil, as it freezes, a network of trenches with vertical walls is cut parallel to each other, the width of which is determined by the parameters of the technique used, the depth is at least half a meter, and the distance between them corresponds to twice the depth of the trench.