UA32491U - Detector of direct charging - Google Patents

Abstract

Detector of direct charging for measurement of density of neutron flux in active zones of nuclear reactors consists of rhodium emitter, collector ad tube made of non-magnetic stainless alloy, electric insulator between those, connecting line shell and two current wires of which are made of same non-magnetic stainless alloy. Bottom of the collector is made of capillary thick-wall tube outer diameter of which is equal to inner diameter of collector, at that the tube is made of material same to that of collector and electric insulator is made of high-purity molten quartz.

Description

The useful model refers to the technical means of nuclear instrumentation and refers in particular to direct charge detectors (hereinafter referred to as direct charge detectors) designed to measure the neutron flux density in the active zones of nuclear reactors.

The DZ consists of a collector, an emitter, an insulator that separates the emitter from the collector, and a connecting conductive line. The emitter is made of neutron-sensitive material, from which charged particles fly out when neutrons are absorbed, capable of reaching the collector. The value of the detector signal is proportional to the value of the neutron flux density at the location of the DZ.

From the patent |RF Me2138833 (MPKb: 201 3/00; NOT) 47/12, published on 09/27/1999)| known direct charge detector, in which the insulator is made of radiation-resistant quartz, and the inner cavity is filled with helium instead of air. The collector of this detector does not have a bottom, and the sealing of the internal cavity is carried out by hermetically welding the narrowed end of the collector opposite the current line.

The closest in terms of technical essence is the direct charge detector known from (patent of Ukraine 36690 (МПК с01Т 3/00, published on 16.04.2001), consisting of a rhodium emitter, a collector in the form of a tube, an electrical insulator between them and a current lead in which the collector and the current collector is made of stainless chromium-nickel-molybdenum steel, while the thickness of the collector wall is 0.30 - 0.65 of the diameter of the emitter, and the ratio ac/agz - 0.5 - 1.0 is also maintained, where ac is the thickness of the collector wall, and aiz is the thickness of the insulating layer. The insulating layer is made of A25Oz powder, the internal cavity of the DZP is sealed with the help of an epoxy compound.

The DPZ of these structures works as follows. When the emitter is irradiated with neutrons, a radioactive isotope is formed, which decays with the formation of charged particles. Leaving the emitter, charged particles create a positive charge on it and a potential difference between the emitter and the grounded collector.

The current determined by this potential difference is proportional to the flow of neutrons at the location of the dp.

A disadvantage of known direct charge detectors is the impossibility of reliably fixing the direct charge detector in the reactor, since it is impossible to weld it to the appropriate structure by means of which it is installed in the reactor, without destroying the collector during the welding process.

In addition, the insulator made of radiation-resistant quartz was not subject to purity requirements (restrictions on impurities). This led to a gradual decrease in the electrical resistance of the insulator insulation under the influence of the operating temperature and thus to the instability of the detector current and a decrease in its sensitivity to thermal neutrons.

Pumping out the air followed by filling the inner cavity of the collector with helium and welding the narrowed end of the collector made of a thin-walled tube is a technologically complex and unreliable process that cannot guarantee the tightness of the inner cavity and the non-leakage of helium.

The task of the useful model is the development of a direct charge detector, in which, by changing the design of the collector bottom and choosing the insulating material, the improvement of the electrical parameters and the manufacturability of the detector are achieved.

This problem is solved by the fact that in the direct charge detector for measuring the neutron flux density in the active zones of nuclear reactors, which consists of a rhodium emitter, a collector in the form of a tube made of a non-magnetic stainless alloy, an electrical insulator between them, a connecting line, a shell and two current the cores of which are made of the same non-magnetic stainless alloy, according to a useful model, the bottom of the collector is made of a capillary thick-walled tube, the outer diameter of which is equal to the inner diameter of the collector, and the tube is made of the same material as the collector, and the electrical insulator is made of fused quartz high purity

In addition, the capillary tube protrudes from the collector by at least ZOmm.

Below, the useful model is explained on the example of execution using the figure, which shows the emitter 1, to which the current conductor 4 is welded. The emitter 1 is isolated from the collector 2 by an insulator C made of high-purity fused quartz. The current conductor 4 is hermetically welded to the collector 2. From the opposite end of the collector to the current conductor, a bottom 5, made of a thick-walled capillary tube, is inserted into it. The bottom 5 is hermetically welded to the collector 2, and the opening of the bottom 5 is hermetically sealed after checking the tightness and filling the inner cavity with helium.

To ensure the sealing of the internal cavity of the DPZ, the shell of the current conductor, the outer diameter of which is almost equal to the inner diameter of the collector, is hermetically welded to it; at the same time, the preservation of the electrical resistance of the insulation between the sheath and the current core of the current conductor welded to the emitter is ensured.

To ensure a stable and high value of the insulation resistance and to prevent accidental contact between the emitter and the collector, the emitter is covered with an electrical insulator made of high-purity fused quartz.

In addition, according to the implementation of the useful model, the bottom of the collector is made of a capillary thick-walled tube, the outer diameter of which is equal to the inner diameter of the collector; the bottom of the tube is welded to the collector, which ensures a reliable hermetic connection. Air is pumped out of the inner cavity through the bottom tube

DZP and fill it with helium, which additionally ensures a high and stable insulation resistance between the insulator and the emitter. After that, the hole in the tube is hermetically sealed. The tube protrudes from the collector not less than ZOmm.

This ensures the possibility of connecting the tube to the device, with the help of which the air is pumped out of the internal cavity of the DPZ and filled with helium. In addition, the thick-walled bottom tube protruding from the collector can be welded to the appropriate reactor structure without destroying the tube wall and depressurizing the reactor.

Compared to the existing one, the proposed DZ design has the following advantages: - it ensures reliable and stable operation of the DZ by maintaining the electrical resistance of the insulation at the level of 10 gΩ; - ensures stable maintenance of the value of the sensitivity of the DPS to thermal neutrons at the level of the initial sensitivity, - ensures the minimum spread of the initial sensitivity between the DPS of the same design; - ensures reliable fastening of the reactor in the reactor without risk of destruction of the collector.

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Claims (2)

1. A direct charge detector for measuring the neutron flux density in the active zones of nuclear reactors, consisting of a rhodium emitter, a collector in the form of a tube made of a non-magnetic stainless alloy, an electrical insulator between them, a connecting line, a sheath and two current cores made of of the same non-magnetic stainless alloy, which differs in that the bottom of the collector is made of a capillary thick-walled tube, the outer diameter of which is equal to the inner diameter of the collector, and the tube is made of the same material as the collector, and the electrical insulator is made of fused quartz of high purity. 2. The direct charge detector according to claim 1, which is characterized by the fact that the capillary tube protrudes from the collector by no less than 30 mm.