RU2454744C1 - Method of producing sources based on radionuclide selected from alkali-earth elements - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: method involves making the active part of a source from porous ceramic material via saturation thereof with acetate of a radioactive alkali-earth element and conversion thereof to a carbonate by heating. On all steps of said process, the radioactive substance does not react with material of the matrix.

EFFECT: method enables to produce highly reliable sources based on Ca⁴⁵, Sr⁹⁰, Ba¹³³, Ra²²⁶ radionuclides using a simple method with low radiation load on personnel.

3 cl

Description

The invention relates to the field of manufacturing technology of sealed radionuclide sources of photon and beta radiation.

Sources of ionizing radiation, consisting of a ceramic active part, with the properties of thermal, radiation and hydrolytic stability, are the safest from the point of view of the potential for environmental pollution. In particular, this applies to sources of increased power operating in extreme conditions, increasing the risk of emergency depressurization of the encapsulating shell.

The need to ensure safe working conditions at the manufacturers of such products led to the gradual replacement of the traditional powder technology for the manufacture of active parts of the sources with the technology of impregnating a pre-made porous matrix with a radioactive solution, followed by fixing the radionuclide in an insoluble form.

In practice, this process is approached in two ways.

The first way is to use the matrix material as one of the starting components in the process of converting a radioactive substance into an insoluble thermally and radiation-resistant form. So, in the method according to the patent [GB 14425627, INTCL G21G 4/00, G21H 5/02, publication date 1976-02-18] it is proposed to produce the active part of the sources in the form of porous tablets from apatite-like ceramic, which when it is impregnated with halide salts of alkaline earth metals chemically fixes them by reaction:

where M is a divalent radionuclide, for example Ca, Sr, Ba;

M 'is a divalent non-radioactive metal;

X is halogen.

At the final stage of the process, the tablets are dried and fired.

Similarly, the matrix material of the active part is used in the method of the patent [US 3093593, INTCL G21F 9/12, G21F 9/30, publication date 1963-11-06]. For solid fixation of radionuclides, with the aim of their burial or the manufacture of sources, a method and composition of ceramics with the properties of surface thermal vitrification (glazing) have been developed. Salts of radionuclides deposited by impregnation and drying in the pores of such ceramics at a temperature of 1200-1400 ° C due to interaction with the components of the matrix are transformed into an insoluble silicate form. Bringing the mortgage activity to the required value is achieved by the cyclic process of "impregnation-calcination". But experience shows that already after the first cycle some zones of the matrix become inaccessible for additional introduction of a radioactive substance into them.

The consequence of this is the unevenness of the output photon and, in particular, beta radiation from sources made in this way. It is also known that the fixation of a radioactive substance on the surface of the matrix is much lower than inside, due to the limited capacity of the outer surface.

The second way is the use of a matrix as an inert carrier frame, in the pores of which the impregnating radioactive substance is fixed by chemically converting it into an insoluble form. An example is the method of the patent [US 3664148, INTCL G21G 4/04, G21G 4/00, publication date 1968-01-16]. The matrix of porous silica is sequentially impregnated with two solutions - first a solution containing radioactive material, and then - transforming it into an insoluble form. An example is the conversion of strontium chloride to insoluble sulfate using sodium sulfate or sulfuric acid. For additional sealing of the active part, its surface fusion or metallization is used.

The obvious disadvantage of this method follows from the mechanism of its implementation. The curing process of the radioactive material in the pores of the matrix develops from the periphery to the center as the impregnating fixative solution moves forward and continues until the formed insoluble salt overlaps the entrances of the capillary channels. For alkaline earth radionuclides with a low specific activity, the probability of such an event is extremely high, and therefore, the probability of leaving a radioactive substance in the depth of the matrix in a soluble form is also high.

This method can be considered as a prototype of the invention.

The objective of the invention is to create a method for reliable fixation of alkaline earth radionuclides in a porous ceramic matrix used in the manufacture of sources.

The problem will be solved in that as the radioactive material impregnating the ceramic matrix, radionuclide acetate from the group of alkaline earth elements is used.

It is known [Karjakin Yu.V., Angelov I.I. Pure chemicals. ed. 4th per. and add. M., “Chemistry”, 1974. 408 s, 66 Fig.] That as a result of thermal decomposition of acetates of alkaline-earth elements, their insoluble thermally and radiation-resistant carbonates are obtained, that is, all basic requirements for the chemical form of the active part of the source are fulfilled. The reaction proceeds with the formation of acetone, which is easily removed from the porous matrix:

M (CH ₃ COO) ₂ = MCO ₃ + (CH ₃ ) ₂ CO ↑,

where M is a divalent radionuclide, for example Ca, Sr, Ba, Ra.

The decomposition of acetates of alkaline earth elements begins already at 150 ° C, and at 550 ° C it passes quickly, simultaneously over the entire mass of the substance to the end. In the indicated temperature range, practically not one of the commonly used matrix materials (steatite, aluminosilicate, cordierite ceramics) does not interact with refractory carbonates. At the same time, carbonates easily dissolve in acetic acid, which, if necessary, allows the redistribution of the active part without loss of radioactive substance, as well as its removal from sources that have developed a specified resource. In this case, the radioactive substance is not contaminated with the structural material of the matrix and the source capsule.

The impregnation of the porous matrix with a saturated solution of the radionuclide salt is an almost one-step process, since clogging of the channels, in the future, prevents a significant correction of the embedded activity of the source. In the case of alkaline earth elements, their acetate salts, having a maximum solubility value, allow to achieve better results in the manufacture of small-sized sources of high power.

The technical result of the invention is to create a method that allows the production of highly reliable sources based on radionuclides Ca ⁴⁵ , Sr ⁹⁰ , Ba ¹³³ , Ra ^{226 in a} simple way with low radiation loads on working personnel.

Example 1

The active part is a tablet with a diameter of 4 mm and a height of 1.2 mm, made of porous aluminosilicate ceramics with a density of 1.6 g / cm, open porosity - 55%, water capacity of the tablet - 6 μl, the required mortar activity - 20 mCi. With a specific activity of Ba ¹³³ 9 mCi / g, 5.2 μl of a saturated solution of its acetate is required. This amount is selected by the dispenser and collected on a porous aluminosilicate ceramic tablet, which is dried and calcined at 550 ° C for 1 hour until the barium acetate is completely decomposed and converted to carbonate. The finished active part of the source is subjected to encapsulation.

Example 2

The active part is a tablet with a diameter of 3 mm and a height of 1.5 mm, made of porous steatite ceramics with a density of 1.7 g / cm, open porosity - 50%, tablet water capacity - 4.2 μl, required mortgage activity - 10 mCi . With a specific activity of Sr ^{90 of} 64 mCi / mg, 3.2 μl of a saturated solution of its acetate is required. This amount is selected by the dispenser and accumulated on a porous tablet made of steatite ceramics, which is dried and calcined at a temperature of 550 ° C for 1 hour until the strontium acetate is completely decomposed and converted to carbonate. The finished active part of the source is subjected to encapsulation.

Claims (3)

1. A method of manufacturing sources based on a radionuclide selected from the group of alkaline earth elements, comprising manufacturing an active part by fixing the radionuclide in a ceramic matrix, converting the radionuclide into a radiation-stable insoluble form and subsequent encapsulation, characterized in that the porous ceramic matrix is impregnated with acetate of a radioactive alkaline earth element and transfer it to carbonate by heating. 2. The method according to claim 1, characterized in that the heating of the matrix is carried out to a temperature exceeding the decomposition temperature of the acetate, but below the temperature of the interaction of the formed carbonate with the matrix material. 3. The method according to claim 1 or 2, characterized in that the matrix material using a ceramic substance that does not interact with acetates of alkaline earth metals and their thermal decomposition products.