RU2408003C1 - Method of determining surface contamination and apparatus for collecting samples from contaminated surface - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: method of determining surface contamination is based on creating an air blowing-suction channel. Air is blown into a closed volume at an angle to the analysed surface. Contaminants are blown from the analysed surface and deposited by passing the air stream through a filter. Further, the amount and activity of radionuclides deposited on the filter is analysed and their amount per unit area of the analysed surface is calculated. A device is disclosed for taking samples from the contaminated surface in order to determine surface contamination using the disclosed method. The device consists of a housing inside of which there is a filter element having inlet and sucking connecting pipes, and a pump. The bottom part of the housing is open. Also inlet connecting pipes are connected to holes in the bottom part of the housing and lie at an angle to the analysed surface.

EFFECT: possibility of determining surface contamination with high accuracy and high rapidness of the method.

2 cl, 1 dwg, 1 ex

Description

The invention relates to the field of environmental control, namely to control the contamination of various solid surfaces with radioactive and other hazardous substances.

A known method for determining surface contamination with radioactive substances - the activity of radionuclides per unit surface area, decay / (min · cm ² ), so-called smear method ( http://www.nnc.kz/rbn/riETPB/pbtrv_pril.htm ).

The method is as follows. By contacting the sorbent material with the test surface, the operator removes contamination from it. As sorbent material, cotton swabs, gauze, filter paper are used. Smears are taken dry or wet (moistened with acid, alcohol, etc.).

Samples of smears after gamma-ray spectrometric analysis are mainly bristled with a “wet” method by heating in concentrated nitric acid for 1 h with periodic addition of 30% hydrogen peroxide. In some cases, "wet" ashing is carried out three times and the leaching are combined. For some strokes, the weight of the dust collected may be determined. In these cases, smears are subjected to thermal ashing (500-600 ° C) until the organics burn out completely and the dry residue after weighing on an analytical balance is leached with concentrated nitric acid when heated with the addition of hydrogen peroxide. Successive leaches from each sample are then combined. Then determine the alpha and beta activity of ashed smears on the corresponding devices. Knowing the area from which the pollution was removed, calculate the amount of surface pollution.

This method has a number of disadvantages. It depends on the subjective characteristics of the sampling (the degree of moisture of the sorbing material, the pressing force when taking a smear, etc.), taking smears from uneven surfaces is inefficient (dust cannot be removed from natural micro-depressions) and the results obtained with “removable” surface contamination can to be understated.

There are various methods and devices for determining the presence and amount of various kinds of contaminants, see, for example, a method for determining the MASS CONCENTRATION of DUST AND DEVICE FOR ITS IMPLEMENTATION (patent of the Russian Federation No. 2282175), according to which dust is sampled by a sampling mechanism that includes a pump and coaxially suction and suction nozzles located above and below the filter element, whose axis is perpendicular to the plane of the filter element, dust is deposited on the filter element, the intensity of the total flow is measured β radiation and flow through the filter element before deposition and then after deposition, the surface density is calculated in accordance with the actual absorption characteristic of β radiation. The absorption characteristics are calibrated once before measurements using a measure of known density, measuring, as before, the intensity of the total β-radiation flux and the flux through the measure.

The desired dust concentration is calculated based on the density of the spraying spot, its geometrical dimensions and the volume of air passed through.

A METHOD AND SYSTEM FOR SAMPLING AND DETERMINING THE AVAILABILITY OF CHEMICAL COMPOUNDS IN TANKS (RF patent No. 2126160) is also known.

In the method of sampling and determining the presence of residues of substances in the tank, a fluid medium — air — is continuously supplied to the opening of the tank. At the injection stage, at least a portion of the volatiles is expelled from the vessel to form a cloud of sample outside the vessel adjacent to its opening. The sample cloud is recovered and the recovered sample cloud is analyzed to determine the presence or absence of substance residues in it. Cloud extraction of the sample is carried out continuously by suction using a pumping pump, and the injection of fluid flow and / or the absorption of the cloud sample is performed pulsed. An apparatus for sampling and determining the presence or absence of residues in containers contains means for pumping fluid into the openings in said containers in order to displace at least a portion of their contents to form a cloud of sample in areas outside the containers. The device comprises means for extracting a sample of a specified part of the contents of each container, thus displaced by applying suction to the cloud of sample, means for maintaining said means for extracting outside the containers at some distance from their openings, and means for analyzing the sample to determine the presence or absence of it residues. The sample extractor is in the form of a pump out pump.

These methods and devices are not intended to determine surface contamination, which must be known with a high degree of reliability, especially in conditions of radioactive contamination.

The technical result to which the invention is directed is the possibility of determining surface contamination with a high degree of reliability, as well as increasing the expressness of the method.

To this end, a method is proposed for determining surface contamination by creating an air injection-suction path, in which case air is pumped into a closed volume at an angle to the surface to be studied, contaminants are blown off from the surface to be studied and sediments are precipitated by passing an air flow through the filter, and then the amount and activity of radionuclides are analyzed deposited on the filter, and count them per unit area of the investigated surface.

To take samples to determine surface contamination in this way, a device for sampling from a contaminated surface is proposed, consisting of a housing, inside which a filter element is installed, with supply and suction nozzles, a pump, while the lower part of the housing is made open, and the supply nozzles are connected to the holes made in the lower part of the body and located at an angle to the surface under study.

The drawing shows an embodiment of the device, where 1 is the test surface, 2 is the air suction pipe, 3 is the housing, 4 is the filter, 5 is the air supply pipe, 6 is the hole.

To take a sample from the test surface, the device is installed on the test surface 1 and tightly pressed against it. A pump (not shown) is turned on and a discharge-suction path, which includes air supply nozzles 5, openings 6, the interior of the housing 3 and the air exhaust nozzle 2, is pumped for some time. The air supply to the holes 6 can be carried out through the collector or individually, depending on the number, location and size of the holes. Air directed at an angle to the test surface 1 blows off contaminants from it, which, passing through the removable filter 4, settle on it. A sample is taken for about 5-30 s, after which the pump is turned off, filter 4 is removed, which is subjected to special processing (for example, ashing).

An example of measurements at the Shelter facility (Chernobyl NPP)

The sampler was pressed firmly to the test surface. In this case, it is desirable to have a dust collection area of 100 cm ² , since many sensors of beta and alpha radiometers have the same effective area and then no recalculations are required - the readings of the radiometers give the result immediately in particles / (min × cm ² ). If the area differs from the specified, then you need to recalculate the area of 1 cm ² . The time of one exposure when sampling at the Shelter object was 10-20 s. (Depended on the degree of surface contamination).

After measurements, the filter from the LFS-2-50 tape was removed, folded with a contaminated surface inside and placed in a special envelope made of polyethylene.

Directly at the facility, a preliminary determination of its gamma activity was performed on a universal dosimeter radiometer.

After the filter was delivered to the laboratory (Chernobyl), a gamma spectrometric analysis was performed using a semiconductor spectrometer using an ORTEC ultrapure germanium detector. Then the filter was subjected to thermal ashing (500-600 ° C) until the organics completely burned up and the dry residue after weighing on an analytical balance was leached three times with concentrated nitric acid under heating with the addition of hydrogen peroxide. Successive leaches from each sample were then combined. On average for dust samples, the percentage of leaching described by the method is about 70%. Beta radiometric measurements of ⁹⁰ Sr activity were performed using a RUB-01P beta radiometer. For alpha spectrometric measurements of the content of plutonium and americium isotopes, a CANBERRA facility was used.

The uranium content was measured using a luminescent spectrometer with excitation from a pulsed nitrogen laser.

As a result of the measurements, data were obtained on the surface density of radioactive dust located on the walls of the premises located at the upper marks of the Shelter, which could be released into the environment during collapse. Typical values of beta activity are (1-10) × 10 ⁴ particles / (min × cm ² ) ( ¹³⁷ Cs and ⁹⁰ Sr), alpha activity is (1-10) × 10 ² particles / (min × cm ² ) ( ^{238 + 139 + 240} Pu and ²⁴¹ Am), pollution by uranium - 2 × 10 ^-6 g / cm ² .

Thus, this invention will allow with a greater degree of reliability to determine the contamination of hard surfaces of various reliefs, including radioactive.

Claims (2)

1. A method for determining surface contamination by creating an air injection-suction path, in which case air is pumped into a closed volume at an angle to the test surface, the pollutants are blown off from the test surface and sediments are deposited by passing the air flow through the filter, and then the amount and activity of radionuclides are analyzed, deposited on the filter, and recount them per unit area of the investigated surface. 2. A device for sampling from a contaminated surface, consisting of a housing, inside which a filter element is installed, with suction and suction nozzles, a pump, characterized in that the lower part of the housing is made open, and the inlet pipes are connected to holes made in the lower part of the housing and located at an angle to the test surface.