RU2035076C1 - Source of gamma radiation provided with active core and method for manufacturing same - Google Patents

Abstract

FIELD: power engineering. SUBSTANCE: this source of gamma radiation has gamma radiation core made of cobalt constituting 10 percent by mass and europium oxide Eu₂O₃ making up 90 percent by mass, which may be uniformly distributed within core body, or core may be shaped as cobalt-made bushing inside which is disposed cylinder made of either europium or composition including cobalt plus europium oxide. In this case diameter of cylinder and external diameter of bushing relate to one another in ratio specified in patent specification. Core is disposed in hermetically sealed ampule, irradiated together with absorbing members of control units of nuclear reactions of any type and core contained in ampule is then enclosed in hermetically sealed envelope of finished product. EFFECT: more sophisticated design. 4 cl, 3 dwg, 1 tbl

Description

 The invention relates to the production of radioactive sources intended for use in specialized or multi-purpose γ-installations for irradiating various materials or goods in order to give them certain specific properties.

Known γ-source with an active core of cobalt in the form of a spiral coated with a protective layer of corrosion-resistant material [1]
Such sources provide radiation processing of products and materials both inside and outside the spiral and allow them to be placed in inaccessible places due to their plasticity and ability to change their shape.

The disadvantage of such sources is their low activity due to the small mass of material containing Co ⁶⁰ radionuclides, which limits the scope of their use, in particular, they cannot be used in large industrial plants with an activity of more than 10 ¹⁵ Bq.

The disadvantage is that γ-sources with active cores from Co have a relatively short life due to a rapid decrease in activity over time (T _1/2 = 5.27 years). In addition, the cost of such sources is high, due to the high costs of their production.

 Known methods for the manufacture of γ-sources, in which targets from the source material are placed in the active zone of a nuclear reactor, after irradiation, targets are used as the active core of the γ-source.

A known method of obtaining a γ-source by irradiating capsules with samples of a target from Co inside the regulatory body of a nuclear reactor. Capsules are placed between the absorbent elements. After working out the resource, the regulatory body is removed from the reactor, cut in protective chambers, capsules are removed from it, the target is extracted from them (cobalt with accumulated radionuclide Co-60). The target is placed in protective shells, check their tightness and carry out certification of finished products [2]
The disadvantage of this method is that due to the relatively small microscopic absorption cross section of cobalt-59 (σ _α ≈36 barn), a gap is formed when the capsule is placed between columns of absorbent material (boron carbide, In-Cd-Ag alloy, etc.) leading to the failure of the physical efficiency of the regulatory body in terms of the height of the regulatory body, which causes large uneven energy releases in the surrounding fuel assemblies, and this extremely negatively affects their performance. Therefore, the height of the targets in each capsule is very limited, because of which a small amount of cobalt is used in the regulatory body, which is used in low-power γ-sources, the scope of which is limited, and γ-sources obtained in this way are expensive.

 It is required to take additional measures to ensure security, which leads to additional costs and increases the cost of sources obtained in this way.

 In addition, the method is environmentally hazardous. All work on cutting capsule regulation bodies is carried out in protective chambers, in the technological process there is direct contact of irradiated Co with the surrounding equipment, which leads to additional pollution of rooms and equipment and requires additional costs for their decontamination.

As a prototype, well-known domestic gamma-sources of the GIK type with a working lateral surface were taken: GIK-7-1, 2,3,4, GIK-7a-1, 2,3,4; GIK-11-1,2; GIK-12a-1,2,3,4 [3]
In these sources, a column of cobalt disks of small thickness (2 mm) is used as the active core. Their irradiation to produce cobalt-60 is carried out in special irradiation devices of industrial nuclear reactors to eliminate the effect of self-shielding in order to increase the specific γ-activity.

 The active source is placed inside two sealed enclosures: an inner ampoule and an outer case.

The disadvantage of such sources is the relatively short life, since they have only one type of radionuclide-cobalt-60 with a relatively short half-life (T _1/2 = 5.27 years).

 The source consists of a large number of cobalt disks with a branched surface, which increases the pollution of the protective ("hot") chambers when they are removed from the irradiation device and then placed into the internal ampoule of the product.

 Significant costs in the manufacture of sources determine their high cost, 65-80% of which is the cost of producing radionuclides in nuclear reactors, i.e. this requires special irradiation devices.

As a prototype, a method of manufacturing well-known domestic γ-sources of the GIC type with a working side surface is taken: NN 7 1,2,3,4; 7a 1,2,3,4; 11 1.2; 12a 1,2,3,4 [3]
The main operations of the method of manufacturing these products are as follows:
manufacturing disks of cobalt-59 metal of small height (2 ≈ mm) of the required diameter for a specific number of a future source;
the manufacture of a special irradiation device and its equipment with cobalt disks;
irradiation of this device in a special (industrial) nuclear reactor to a certain neutron fluence with the provision of “opening” the surface of the cobalt disks to eliminate the effect of self-screening and increase the specific γ-activity of cobalt;
unloading the irradiation device from the reactor, cutting it in a hot chamber and removing cobalt disks from it with the cobalt-60 isotope accumulated in them;
manufacture of the case and cover of the inner ampoule of the future gamma source;
the formation in a hot chamber of irradiated cobalt disks with the accumulated radionuclide cobalt-60 active core;
placement of the active core in the ampoule body, setting the lid and welding it, tightness control;
the manufacture of the body and cover of the outer cover of the future gamma source;
loading in a hot chamber of sealed ampoules with cores from cobalt disks with cobalt-60 radionuclide into the case of the outer cover, welding of the cover and tightness control;
certification of finished products (measurement of activity and exposure dose rate of γ-radiation DER).

The main disadvantages of the method of manufacturing γ-sources of type GIK include the following:
the manufacture of targets from metal cobalt determines in the future one of the most significant drawbacks of these products due to the relatively low half-life of cobalt-60 (T _1/2 = 5.27 years), the service life of GIK-type sources is short (3-6 years);
a special one-time irradiation device is required in which targets are irradiated to produce cobalt-60 radionuclides;
an irradiating device with cobalt disks is placed to fill cobalt-60 isotopes in specialized (industrial) reactors; at the same time, absorbed neutrons make up one of the most important parts of the total cost of manufacturing GIK-type sources (50-70%), since expensive nuclear "fuel" is specially consumed to produce them;
cutting the irradiation device, removing disks from metal cobalt from it with cobalt-60 radionuclides stored in them, equipping these disks of the internal ampoule and sealing them in special hot chambers; these operations are very time-consuming and environmentally hazardous, since the inevitable smallest contamination of the hot chambers with microparticles requires special safety measures, decontamination of equipment and rooms, which further increases the cost of manufacturing sources of GIK type.

 The invention allows to obtain γ-sources with a high specific activity, to increase the period of their operation with a significant reduction in the cost of their production and reduce the environmental hazard of production.

≅ 0,8
Выполнение активного сердечника γ -источника одновременно из Со и Eu₂O₃ позволяет получить γ -источники с высокой удельной активностью (более 60 Ки/г) и длительным сроком эксплуатации (до 16 лет).According to the invention, the γ-radiation source contains an active core located in the protective shells. The active core is made of cobalt (Co) and europium oxide (Eu ₂ O ₃ ) with a content of the latter from 10 to 90 wt. Co and Eu ₂ O ₃ can be evenly distributed in the core volume or the core is made in the form of a sleeve of Co, inside which a cylinder of Eu ₂ O ₃ or the composition "Co + Eu ₂ O ₃ " is placed. In this case, the cylinder diameter d _c and the outer diameter of the sleeve d _in are related by the ratio:
0.4 ≅

≅ 0.8
The implementation of the active core of the γ-source simultaneously from Co and Eu ₂ O ₃ allows to obtain γ-sources with high specific activity (more than 60 Ci / g) and a long service life (up to 16 years).

The use of this starting material allows one to achieve a significant reduction in costs in the production of gamma sources, since the Eu ₂ O ₃ + Co composition has a high neutron absorption efficiency and can be used as an absorbing core of the regulatory body of a nuclear reactor, which reduces the cost of producing radionuclides.

Eu ₂ O _{3 is the} most stable europium compound in air and is characterized by high radiation resistance, which reduces the costs of core formation, since the work is carried out outside the protective chambers.

 The spectral properties of the material, ensuring the achievement of a technical result, are not the sum of the properties inherent in Co and Eu, which is explained by their mutual influence on each other during irradiation and their change in time and space.

The content of Eu ₂ O ₃ less than 10 wt. it does not allow the use of the Eu ₂ O ₃ + Co composition as an absorbing core of regulatory bodies due to the insufficient efficiency of neutron absorption (creation of the required reactivity margin) and ensuring reliable and efficient operation of a nuclear reactor.

The content of Eu ₂ O ₃ more than 90 wt. it does not allow to obtain a dispersion composition due to the low matrix (Co) content and strong screening from the side of europium isotopes, which leads to a sharp decrease in the production of cobalt radionuclides.

With a uniform distribution of Co and Eu ₂ O ₃ in the core volume, the process of accumulation of europium radionuclides most quickly proceeds and they are isolated from the external environment by matrix material (Co).

< 0,4 не обеспечивается необходимое соотношение между накоплением радионуклидов европия и кобальта. При этом преобладают (более, чем на порядок) радионуклиды кобальта и таким образом не достигается заявляемый технический результат.When the core is made in the form of a sleeve of Co, inside which a cylinder of Eu ₂ O ₃ or the composition "Co + Eu ₂ O ₃ " is placed, a more efficient accumulation of cobalt-60 radionuclides is ensured. If

<0.4, the necessary ratio between the accumulation of europium and cobalt radionuclides is not ensured. In this case, cobalt radionuclides prevail (more than an order of magnitude) and thus the claimed technical result is not achieved.

> 0,8 также не обеспечивается необходимое соотношение между накоплением радионуклидов кобальта и европия (с преобладанием радионуклидов европия).If

> 0.8, the required ratio between the accumulation of cobalt and europium radionuclides (with a predominance of europium radionuclides) is also not ensured.

 These dependences were obtained experimentally when conducting studies of various designs.

New significant features of the proposed solutions are the implementation of the active core of Co and Eu ₂ O ₃ with a content of the latter from 10 to 90 wt. and the distribution of these components in the core volume.

According to the invention, a method of manufacturing a γ source includes irradiating the starting material, forming a core, and placing it in protective shells. The core is formed from cobalt (Co) and europium oxide (Eu ₂ O ₃ ) with a content of the latter of 10-90 wt. place the core in a sealed ampoule. An ampoule with a core is irradiated as part of the absorbing elements of the regulatory organs of a nuclear reactor of any type. After irradiation, the ampoule with the core without cutting is placed in a sealed case of the finished product, and the γ-source is certified.

 The formation of the core from the proposed source material allows you to get γ-sources with high specific activity and increase their life.

In addition, it provides the ability to form a core outside the protective chambers, while reducing costs. At the same time, it is the use of the proposed starting material that allows irradiation as part of the absorbing elements of the regulatory organs of a nuclear reactor, since it will be absorbing material for the regulatory authorities of almost any type of nuclear reactor, because when the density of europium oxide in them is within 1.0-5, 5 g / cm ^{3 the} relative physical efficiency in the range of 80-105% of the physical efficiency of a powerful neutron absorber of boron carbide with a density of 1.8-2.2 g / cm ^{3 is} achieved. This is due to the high values of the microscopic cross section for the absorption of thermal neutrons by natural isotopes of europium: 7700 bar (Eu-151) and 450 bar (Eu-153).

Cores from Co and Eu ₂ O ₃ are placed in sealed ampoules of PEL, which are part of the regulatory body of a nuclear reactor. Such a regulatory body is loaded into the reactor and operates in it for its intended purpose.

At the same time, in the cores of ampoules (PELs), an accumulation of radionuclides occurs with high values of the γ-constant:
Eu-152 (K _γ ≈ 6.55 r / h);
Eu-154 (K _γ ≈ 6.7 r / h);
Co-60 (K _γ ≈13 r / h).

 In this case, the production of cobalt and europium radionuclides in the reactor is "free", and the sealed ampoules with them are essentially solid waste from the spent regulatory authority.

 After the necessary fluence has been set, the CPS core with dual-purpose PELs is removed from the reactor, disassembled in a hot chamber, and the ampoules with cores removed from it are placed into an external sealed case of unirradiated metal (stainless steel, titanium, etc.) without any cutting . The latter is extremely important, since the contact of the equipment and the premises of the hot chambers with the open surface of the active core, which includes cobalt and europium radionuclides, is eliminated.

 Further, the source is subjected, as well as products like GIK, certification (tightness control, activity measurement and DER).

 More clearly proposed as an invention, a method of manufacturing a γ-source is presented in the table. 1.

New significant features are the use of Co and Eu ₂ O ₃ core with a content of the latter from 10 to 90 wt. core formation before irradiation, irradiation as a part of absorbing elements of regulatory bodies of a nuclear reactor of any type, direct placement of an ampoule with a core after irradiation without cutting in a sealed case of the finished product.

 These features, together with the known ones, allow achieving a new technical result to obtain cheap γ-sources with improved characteristics.

In FIG. 1 shows the design of a γ-source with an active core of Co and Eu ₂ O ₃ uniformly distributed throughout the volume; in FIG. Figure 2 shows the construction of a γ source, the core of which consists of a cobalt sleeve with a cylinder of Eu ₂ O ₃ or the composition "Co + Eu ₂ O ₃ " placed inside it.

The table shows the manufacturing scheme of the γ-source using the proposed method, where 1 outer sealed case; 2 internal sealed ampoule; 3 active core, consisting of one or more inserts from the composition "Co + Eu ₂ O ₃ " with a content of europium oxide in the range of 10-90 wt. 4 an active core consisting of a cobalt bushing with a europium oxide cylinder or the composition "Co + Eu ₂ O ₃ " inside it.

By hot pressing, cylindrical inserts with a diameter of 7.0 were made from the composition "Co + Eu ₂ O ₃ " with a mass content of ≈20% (nuclear density 3.5x10 ²¹ cm ^-3 ) and placed in sealed ampoules with a shell with a diameter of 8.0x10, 3 from steel 06X18H101 with end parts welded to it. Ampoules, in turn, were placed inside the shells of absorbing elements (PEL) with a diameter of 9x0.4 and sealed by welding of the end parts.

 A regulatory body for a nuclear reactor was assembled from these PELs and put into operation for its intended purpose. During operation in the reactor, the radionuclides Co-60, Eu-152, Eu-154 and Eu-155 accumulated in the liners.

 After working out the resource, the regulatory body was removed from the reactor; in hot chambers, it was cut up to extract ampoules with cobalt and europium radionuclides accumulated in their cores.

 Ampoules were placed in airtight containers made of stainless steel or titanium with a shell with a diameter of 11.0x1.2 and after certification (checking for tightness and measuring the activity of the exposure dose rate), we obtained ready-made γ-sources based on cobalt and europium radionuclides.

 The specific activity of the obtained γ sources is 50-80 Ci / h.

The invention allows to reduce the cost of specific activity; increase the operating time by 1.5-2.5 times; reduce the costs of storage, transportation and burial of spent nuclear regulatory authorities, since the ampoules with Co and Eu ₂ O ₃ cores extracted from them become the basis of γ sources, rather than solid highly radioactive waste.

 The table shows the main indicators of the prototype and the proposed solution.

Claims (4)

1. The source of gamma radiation with an active core, characterized in that the active core is made of cobalt Co and europium oxide Eu ₂ O ₃ with a content of the latter 10 90 wt. 2. The source according to claim 1, characterized in that Co and Eu ₂ O _{3 are} evenly distributed in the core volume. 3. The source according to claim 1, characterized in that the active core is made in the form of a sleeve of Co, inside which a cylinder of Eu ₂ O ₃ or a composition of Co + Eu ₂ O ₃ is placed, with the cylinder diameter d _c and the outer diameter of the sleeve d _in are related by
0.4 ≅ d _c / d _at ≅ 0.8. 4. A method of manufacturing a gamma source, including irradiation of the source material, the formation of the core, placing it in protective shells, characterized in that the core is formed from the source material, which is used as Co and europium oxide Eu ₂ O ₃ with the content of the latter 10 90 wt. . place the core in a sealed ampoule, irradiate as a part of the absorbing elements of the regulatory organs of a nuclear reactor of any type, after which the ampoule with the core is placed in a sealed case.

Images