RU29382U1 - Ionization fission chamber - Google Patents

Abstract

An ionization fission chamber, including a tubular casing with an internal electrode coaxially located in it, a coating of fissile material and spacer insulators, a ceramic-metal assembly and a plug, characterized in that the tubular casing is made in the form of an integral multi-section assembly, with each section on the inside of the tubular end samples are formed in the housing, in which spacers are installed with overlapping sample volumes of adjacent sections, moreover, the ceramic-metal uze and tubulation insulators fixed end terminal sections and samples covering junctions, and a coating of fissile material applied to the inner surface of the housing between the insulators.

Description

A scam model — an ionization fission chamber (hereinafter referred to as “ICD”) refers to the technique of measuring ionizing radiation, in particular, to equipping a nuclear reactor’s immunity and protection system and is used as an in-line neutron note detector.

The main requirements for ICD include high sensitivity and reliability at the minimum non-ragged overall dimensions. Among the fission ionization chambers, the so-called small-sized ICDs are the only in-reactor detector capable of controlling the neutron flux density inside the active zone in various reactor operating modes: in the source relax, in the transition mode, and when the reactor is brought to its rated power. Thus, for intraband measurements, limiting the diameter of the ICD is one of the critical parameters.

Known ionization fission chamber, including a tubular body with axially concentric internal electrodes coated with fissile material and containing insulators (F. Neshke. Fission chamber for measuring neutrons. AS USSR No. 161085. MIC G 01 T 3 / 00, H 01 J 47/12. Declared May 28, 1962. Publ. March 9, 1964, Bull. No. 6).

This design allows you to expand the range of measurement of neutrons through the use of several switched cathodes and anodes coated with various radioactive materials having different fission ability, or materials with the same fission ability, but different thickness or area. The main disadvantage of the known multi-electrode ICD are its

overall dimensions that do not allow the use of this design for intrazone measurements.

Known ionization fission chamber, including a tubular casing, in which the inner electrode is coaxially located, separated by a spacer insulator, cermet unit and plug (V.I. Alekseev, I.Ya. Emelyanov, V.M. Ivanov and others. Ionization chamber. USSR AS No. 482704. IPC G 01 T 3/00. Declaration of 08/03/1973. Published 05.08.1976, bull. No. 29). In addition, an external collecting and intermediate-guarding coaxial electrodes are installed in the housing along the length of the chamber. The intermediate guard electrode is separated by external distance insulators from the corne and internal insulators from the internal electrode, to which an external collecting electrode is connected, insulated by conductive jumpers, divided in length into sections located with a gap between the external distance isolators, which are separated by insulators from the intermediate guard electrode, and from the tubular the chamber body — with a gas-filled gap between them, and a coating of fissile material is applied to an external surface The surface of the collecting electrode.

The considered design of the ionization chamber has found wide application in controlling the neutron flux inside the nuclear reactor vessel outside its core. The ionization chamber is structurally combined with the communication line and the external casing into a single device called the suspension of the ionization chamber.

The disadvantage of this design is the need to use numerous additional elements: an external collecting and intermediate guard coaxial electrodes, external distance insulators, internal insulators, insulated conductive jumpers, the execution of sections of the external collecting electrode, the gaps between the sections. Indicated

additional elements provide requirements for the resistance of insulating materials during the operation of ICDs under prolonged exposure to intense radiation fields and high temperatures. However, the presence in the camera design of such a large number of additional elements leads in practice to the low reliability of the considered ICD.

Thus, this multi-electrode design of the ICD does not allow minimizing the diameter of the chamber, which is usually 7 mm, which fundamentally limits the use of such a design as an intraband neutron flux detector, since the internal diameter of the channels of the reactor into which the ICD is installed does not exceed, as a rule 5-6 mm. This, in turn, excludes the use of such a chamber when operating a nuclear reactor in the source mode, during transient mode, and up to bringing the reactor to a minimally controlled level of fraud, in which the sensitivity of the cameras located outside the reactor core becomes sufficient to control the neutron flux.

The closest technical solution to the claimed utility model is an ionization fission chamber, including; a tubular housing with an internal electrode coaxially located in it, on which a coating is made of fissile material, and spacing; with insulators, a ceramic-metal assembly and a plug (Malyshev E.K. , Stabrovsky SA Small-sized ionization chambers and their use in nuclear reactors. - Nuclear technology abroad, 1983, No. 12, p.).

The indicated design of the ICD is characterized by a small diameter, is small-sized and can be used to control the neutron flux inside the reactor core. However, a significant drawback of the known ICD is its low sensitivity due to low floop1; adi coatings from fissile material.

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The authors of the utility model were faced with the task of increasing the sensitivity of the ICD to the neutron flux without increasing its transverse overall dimensions while maintaining its reliability characteristics in order to use the ICD as an intraband neutron flux detector.

The task is achieved in that in the ionization chamber of fission, which includes a tubular body with an internal electrode coaxially located in it, a coating of fissile material and spacer insulators, a cermet unit and a plug, a tubular body is made in the form of an integral multi-section assembly, while in each section with end samples are formed on the inside of the tubular body, in which spacers are installed with overlapping sample volumes of neighboring sections, and llokeramichesky node and shtepgel insulators fixed end terminal sections and samples covering junctions, and a coating of fissile material applied to the inner surface of the housing between the insulators.

The implementation of the tubular body in the form of an integral multi-section assembly allows, while maintaining the reliability characteristics inherent in the ICD adopted as a prototype, to increase the length of the sensitive element by a set of sections and thereby increase the area of the coating from fissile material.

Sectionalization of the housing allows you to form a homogeneous coating of the same thickness of fissile material on the inner surface of each individual section of the housing.

The integral multi-sectional assembly allows reliable structural integration of the ionization chamber with the communication line into a single device — the suspension of the ionization chamber, which allows it to be placed inside the reactor core channel with the minimum transverse dimensions achieved. One-piece stability

,./ 4

multi-section assembly to mechanical stresses during mounting of the suspension in the reactor and its operation is ensured by the installation of distance insulators in the volume of end samples of adjacent sections formed on the inside of the tubular body. Remote insulators provide a constant gap between the camera body and the internal electrode and electrical insulation of the body and electrode. At the same time, the overlapping by the distance insulators of the sample volume of neighboring sections increases the structural rigidity of the integral multi-section assembly after it is connected by welding on the outside of the housing.

The presence of end samples in each section on the inner side of the tubular body allows you to preserve the continuity and adhesion of the coating of fissile material when assembling the ICD into an integral structure. At the same time, burrs of the coating and the formation of filamentary delaminations are excluded, which in operating conditions can lead to a decrease in the insulation resistance between the housing and the inner electrode.

The implementation of the tubular body in the form of an integral multi-section assembly retains the possibility of placing a small-sized ICD inside the reactor core, solves the problem of increasing the ICD sensitivity by choosing the total assembly length (number of sections) and allows controlling low density neutron fluxes.

The remote insulators installed in the end samples of the end sections of the housing allow reliable fixation of the relative position of the ceramic-metal assembly, the elements of the integral assembly and the ram during the formation of the integrated ICD junctions with the help of the bundles, which eliminates the case during subsequent transportation, installation into the active zone and operation of the circuit and an electrode, while maintaining the reliability characteristics inherent in a small-sized ICD.

The specified set of distinctive features indicates compliance of the claimed ICD with the criterion of "novelty.

The claimed device solves all the basic technological problems of creating ionization fission chambers for intrazonal use: minimal non-uniform dimensions, high sensitivity, manufacturability and relative ease of manufacture while maintaining the high reliability inherent in a small single-electrode ICD. The claimed device allows you to solve the problem of controlling the density of the neutron flux inside the active zone at various modes of operation of the reactor, including monitoring the neutron fluxes of the minimum density and their distribution inside the core.

The dryness of the claimed utility model is illustrated by the drawing, which schematically shows the design of the ionization fission chamber.

The ionization fission chamber consists of a tubular body 1, in which the inner electrode 2 and the spacer insulators 3, the cermet unit 4 and the plug 5 are coaxially located. The tubular body 1 is made in the form of an integral multi-section assembly. In each section, end samples 6 are formed on the inner side of the tubular body, in which distance insulators 3 are installed. Insulators 3 overlap the sample volumes 6 of adjacent sections. On the inner surface of the housing 1 between the insulators 3 is coated 7 of fissile material. The ceramic-metal assembly 4 and the plug 5 are fixed with insulators of the end samples of the end sections of the housing 3 and covering the junctions 8.

The tubular body 1 is a multi-section assembly. The number of sections is determined by the type of reactor and the required ICD sensitivity and its total length associated with it.

the sensitivity of the ICD should be at least a cm / neutron impulse. The standard KNT-5 ICD type did not allow controlling the neutron flux of the RBMK-1000 reactor in the nusky mode, since its sensitivity is 40 times less than the required value and the normal cm / neutron impulse matters. At the same time, there are restrictions on the total length of the ICD: for example, for the RBMK-1000 reactor, the length of the ICD should not be shagging 500 mm so that the determination of the neutron note density can be considered point-wise from the point of view of mathematical processing of the measurement results.

The tubular corne 1 ICD is made of tubes with a diameter of 3 mm with a wall thickness of 0.5 mm and a length of 70 mm. Thus, the number of ICD sections for a given reactor type is 7. The main materials for the ICD design are stainless steel 12X18H10T and high-alumina ceramics. The inner electrode 2 is made of wire with a diameter of 0.8 mm. In each section, end samples 6 were formed with a diameter of 2.5 mm to a depth of 3 mm for distance insulators 3 made in the form of a cylinder with a diameter of 2.5 mm, a length of 6 mm, and an opening with a diameter of 0.9 mm. The content of ABO3 in the distance insulators is 99%.

Uranium oxides with enrichment but U isotope up to 95% were used as fissile coating material. The surface density of the coating is 1 mg / cm, selected experimentally and is consistent with the recommended values presented in the literature. The coating 7 is carried out by thermal decomposition of organometallic uranium complexes based on alpha - branched carboxylic acids of the St-Cd series.

The assembly of the ionization fission chamber into an integral multi-section design consists in joining the sections of the housing in a special fixture and laser welding (welding in the drawing is indicated by the welding symbol in accordance with ESKD). Iri this

distance insulators 3 overlap the sample size of adjacent sections. During the assembly of the ICD, an intermediate operational monitoring of the electrical breakdown of the electrode gap and insulation resistance is performed. To fix the inner electrode 2 of the tubular body 1, restriction sleeves (not shown) are welded onto the ends of the electrode by laser welding in the form of 0.1 mm thick stainless steel foil strips up to 2 mm high.

In the end sections of the tubular body 1, the cermet unit 4 and the plug 5 are fixed by insulators 3, and then welded to the body with the formation of female junctions 8.

Reliable operation of the ICD is ensured by the constant composition and pressure of the gas mixture in the small-gap gap. The interelectrode gap is 0.6 mm and is formed technologically during the assembly of the ICD. The degree of tightness of the ICD in accordance with the technological process is determined by the mass spectrometric method at all stages of manufacture.

After assembly, monitoring the tightness and electrical characteristics of the ICD, it is placed in a vacuum stand for degassing and filling the gas mixture through the plug 5. Degassing is carried out to remove residual gases in structural materials.

With the specified geometric dimensions of the sections of the integral multi-sectional assembly of the ICD, there is no short circuit between the housing 1 and the internal electrode 2 during vibration and heating of the chamber due to the bending of the internal wire electrode. The electrical output of the inner electrode 2 is carried out through a ceramic-metal assembly 4, and degassing of the ionization chamber and filling it with a gas mixture is carried out via a plug 5.

The ICD communication line with secondary measuring equipment consists of a special cable with mineral () or fiberglass (SiO2)

insulation and a connecting cable with organic insulation, directly connected to the secondary measuring equipment.

ICD works as follows. When the chamber is irradiated with a note of neutrons, fission nuclei of fission occur from fissile material. Fission fragments ionize the working gas mixture in the interelectrode gap, and the resulting volumetric electric charge creates a current pulse recorded by secondary electronic equipment. The number of current pulses is proportional to the neutron flux density. Depending on the number of pulses, the ICD operates in pulsed, fluctuation, and current modes.

The reliable operation of the measuring neutron channel, which consists of an ICD and secondary recording electronic equipment, is ensured by the technical characteristics of the ICD: the sensitivity of the 7-section ICD for RBMK-1000 is at least cm / neutron, the electron charge in the pulse is at least 1, the pulse duration is no more than sec, insulation resistance - not less than Ohm, breakdown voltage of the interelectrode gap (not less than twice the potential difference between the electrodes) - not less than 600 V.

The above characteristics convincingly indicate that the claimed device allows to solve the problem of controlling the density of the neutron flux outside the core in various reactor operating modes, including monitoring the neutron fluxes of the minimum density and their distribution inside the core.

Claims (1)

An ionization fission chamber, including a tubular casing with an internal electrode coaxially located in it, a coating of fissile material and spacer insulators, a ceramic-metal assembly and a plug, characterized in that the tubular casing is made in the form of an integral multi-section assembly, with each section on the inside of the tubular end samples are formed in the housing, in which spacers are installed with overlapping sample volumes of adjacent sections, moreover, the ceramic-metal uze and tubulation insulators fixed end terminal sections and samples covering junctions, and a coating of fissile material applied to the inner surface of the housing between the insulators.