RU2793964C1 - Device for detecting solid fragments of spherical shape in cold neutron moderator - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: invention relates to a device for detecting spherical solid fragments of a ball-shaped cold neutron moderator and can be used to control the amount of the agent charged to the neutron moderator when visual detection is not available. A detection unit is connected to a pipeline with solid balls of a neutron moderating substance located inside a vacuum casing. The detection unit is a vacuum insulating volume. Inside the detection unit there are two tubes attached to the pipeline, inside which there are measuring devices – fibre optic cables of the emitted and reflected light, respectively. At the outlet of the vacuum insulating volume, fibre optic cables are connected to the computing device through an amplifier and a controller.

EFFECT: increasing the accuracy of measurements in the monitoring the movement and counting the number of fragments of a spherical shape passing through the cross section of the pipeline per unit of time.

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Description

The invention relates to the field of cryogenic technology and can be used to control the amount of the working substance loaded into the neutron moderator in conditions where visual detection is not available.

State of the art

The spherical moderator is used in beams of research reactors or neutron-producing targets in accelerators and is designed to produce low-energy neutrons (cold neutrons) in external beams. The ball moderator consists of a sealed chamber, which is installed near the reactor core, pipelines through which the cooled coolant (helium) circulates and through which the working substance is loaded into the sealed chamber, as well as a heat exchanger for cooling the coolant. A mixture of mesitylene and m-xylene in the form of frozen balls is used as a working substance in the ball moderator. The retarder chamber is designed to load a certain volume of the working substance. In this case, loading a smaller amount of the working substance than provided for by the chamber design leads to a change in the spectrum in external neutron beams, which is undesirable for research and experiments carried out on such beams. On the other hand, loading a larger amount of the working substance than provided may lead to a disruption in the flow of the coolant (cooled helium) through the chamber, which will lead to an increase in temperature inside the chamber, melting of the working substance and, under certain circumstances, destruction of the chamber. Therefore, when operating a ball moderator, it is important to know and control the amount of the loaded working substance.

Known analogue - gas-dynamic method of registration, described in patent RU 2487430 "Gas-dynamic method of registration of balls moving in a cylindrical pipe". This method allows you to register balls moving inside the pipeline in the gas flow when visual control is not available, by sampling gas from two points of the pipeline located at a certain distance from each other, and measuring the pressure difference. The disadvantages of the method include the fact that the differential pressure gauge used as a measuring device captures pressure drops associated not only with the movement of the ball, but also other pressure drops that are present in the pipeline due to the presence of various turbulent flows (wall gas flows, temperature drops, etc.). etc.). Thus, this registration method does not ensure the reliability of the results, does not allow counting the number of balls, in fact, the method captures only indirect signs of the movement of the ball, and not the ball itself.

The prototype of the invention is a control device for balls moving inside a pipeline in a gas flow, described in A. Belyakov, M. Bulavin, A. Chernikov, A. Churakov, S. Kulikov, E. Litvinenko, K. Mukhin, A. Petrenko, T. Petukhova, A. Sirotin, E. Shabalin, V. Shirokov, and A. Verhoglyadov, Control System of Pelletized Cold Neutron Moderator at the IBR-2 Reactor, Physics of particles and nuclei letters, vol. 12, no. 6, 2015, p. 774-775. The device is a pipeline section with an external vacuum casing. Differential pressure gauges are connected to the pipeline through a certain distance, which record the difference (differential) pressures in the form of a signal measured in millivolts. The signal is transmitted to a personal computer, where it is displayed as a continuous graph. Thus, when the ball passes inside the pipeline between the gas sampling points, the measuring instruments (differential pressure gauges) record the pressure drop, and a short-term jump (peak) is observed on the screen of the computing device on the graph.

Significant disadvantages of the prototype include the fact that the device does not allow to count the number of balls passing through the cross section of the pipeline per unit time. The device captures a large number of false signals that are not related to the movement of the balls, as a result of which visual control of such movement is difficult.

The essence of the invention

The technical problem is to increase the accuracy of measurements, namely, to control the movement and count the number of spherical fragments passing through the cross section of the pipeline per unit time, in the conditions of inaccessibility of visual control by a person.

The technical problem is solved due to the fact that the detection unit is attached to the vacuum casing. The detection unit is a vacuum insulating volume. Inside the detection unit there are two tubes attached to the pipeline, inside which are measuring instruments - fiber optic cables of the emitted and reflected light, respectively. At the outlet of the vacuum insulating volume, fiber optic cables are connected to the computing device through an amplifier and a controller. The operating principle of the detection device is based on the property of reflection from the surface of a solid body of an incident beam of light. The detection device is connected to the pipeline, in which it is necessary to control the movement and count the number of spherical fragments.

List of figures

Fig. 1 Typical layout of a cryogenic neutron moderator

1 - reactor core;

2 - retarder chamber;

3 - boot device;

4 - gas circulator;

5 - heat exchanger;

6 - cryogenic helium installation;

7 - gas tank;

8 - node for detecting fragments of a spherical shape;

9 - optical fiber cable for light emission;

10 - fiber optic cable for receiving reflected light;

11 - fiber optic digital signal amplifier;

12 - microcontroller;

13 - personal computer.

14 - solid fragments of a spherical shape

16 - pipeline

18 - biological protection

Fig. 2 General view of the device for detecting and counting the number of solid fragments of a spherical shape

9 - optical fiber cable for light emission;

10 - fiber optic cable for receiving reflected light;

11 - digital fiber amplifier;

12 - microcontroller;

13 - personal computer;

14 - solid fragments of a spherical shape;

15 - vacuum insulating volume;

16 - pipeline;

17 - tubes.

Fig. 3 Appearance of the working window of the software

Axis X - time, min

Axis Y - number of fragments, pcs.

a - Graph of the dependence of the number of fixed fragments on time

b - Graph of the dependence of the intensity of fixing fragments per second on time

c is the filling level of the cryogenic moderator chamber, %, where 100% is the level corresponding to the complete filling of the chamber.

d - The total number of recorded fragments, pcs.

Implementation of the invention

The detection device is used in cryogenic neutron moderators (hereinafter - CZ). The SC is part of the equipment of the research reactor and is a metal chamber made of aluminum alloy, which is remotely filled through pipelines with crystallized fragments of a spherical shape, consisting of a mixture of aromatic hydrocarbons of mesitylene and metaxylene. The temperature of pipelines and the chamber during filling is 80-100K, the lowest possible temperature is 17-20K.

A typical short circuit diagram is shown in figure 1. Solid crystallized fragments of a spherical shape (14) from a mixture of mesitylene and metaxylene through a loading device (3) enter the short circuit pipeline (16). The loading device has a special dispenser, which carries out the piece-by-piece supply of spherical fragments into the short circuit pipeline. The short circuit pipeline has a vacuum volume that isolates from the external environment (“jacket”), designed according to the “pipe in pipe” principle. A helium flow is created inside the pipeline using a gas circulator (4), which, passing through the heat exchanger (5), is cooled to cryogenic temperatures. Helium enters the system continuously from the gas tank (7). Spherical fragments are transferred in a cold helium flow to the moderator chamber (2) located in the immediate vicinity of the reactor core (1). On the path of fragments movement between the loading device (3) and the chamber (2), a detection assembly (8) is mounted in the pipeline. A continuous emission of light in the visible red spectrum occurs through the fiber optic cable (9), and the reflected beam is transmitted through the fiber optic cable (10) to the fiber optic digital signal amplifier (11). Next, the converted signal is transmitted to the microcontroller (12) and then to the computing device - a personal computer (13), where the total number of fixed spherical solid fragments is continuously counted.

Thus, the degree of filling of the chamber (2) is controlled, since the total number of fragments of a spherical shape required to completely fill the chamber is known. The absence of fixed reflected light rays for a certain period of time means the absence of solid spherical fragments in the gas flow, which, in turn, indicates the presence of a blockage from spherical fragments in the pipeline line to the installation site of the detection unit, blockage in the loading device (3) or failure of the boot device itself. That is, the method is also used to record the occurrence of emergency or emergency situations in the process of filling the moderator chamber with a moderating agent.

A general view of the device for detecting and counting the number of solid fragments of a spherical shape is shown in figure 2.

Solid crystallized fragments of a spherical shape (14) move inside the pipeline (16) in a gas stream cooled to cryogenic temperatures. The pipeline has an external vacuum insulating volume (15). Tubes (17) are installed in the pipeline, inside of which there are fiber optic cables: light emitter cable (9) and reflected light receiver cable (10), respectively. The length of the electromagnetic wave of light in the emitter corresponds to the visible red color (625-740 nm), the radiation is continuous in time. When a solid crystallized fragment of a spherical shape passes through the light beam of the emitter, the beam is reflected from the outer surface of the spherical fragment. The reflected beam through the fiber optic cable of the receiver (10) enters the digital fiber optic signal amplifier (11), where it is converted into an analog signal. The analog signal is processed in the microcontroller (12) and further transmitted to the personal computer (13). On a personal computer, special software continuously counts the total number of recorded reflected light rays, which corresponds to the number of solid spherical fragments that crossed the light beam of the emitter. The appearance of the working window of the software is shown in figure 3.

The detection device makes it possible to determine the degree of filling of the moderator chamber with a moderating agent in the absence of a technical possibility of visualizing the control of the filling of the chamber. In this case, the camera is located in close proximity to the reactor core, so the use of any electrical equipment (sensors, video cameras) or viewing windows is impossible.

Test tests of the device were carried out under the conditions of the operating cryogenic neutron moderator of the IBR-2 research reactor, JINR, Dubna.

Claims (1)

A device for detecting solid fragments of a spherical ball cold neutron moderator, including a pipeline with solid balls of a neutron moderating substance located inside a vacuum casing, and measuring instruments connected to a computing device, characterized in that a detection unit is attached to the vacuum casing, which is a vacuum insulating a volume with two tubes attached to the pipeline, inside which measuring devices are located - fiber optic cables of emitted and reflected light, respectively; at the outlet of the vacuum insulating volume, the fiber optic cables are connected to the computing device through an amplifier and a controller.

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