RU2785303C2 - Stand modeling thermal processes in targets in development of radioisotopes, using intensive protonic bundles - Google Patents

Abstract

FIELD: irradiation devices.

SUBSTANCE: invention relates to equipment used for the production of radioisotopes, namely to device modeling thermal processes flowing in targets in the development of radioisotopes. A stand is claimed, modeling thermal processes in targets in the development of radioisotopes, using intensive protonic bundles, containing a node with a window for supply of a bundle, in which a target is rigidly fixed, to which a temperature sensor is connected. Moreover, between the window and the target, there is a flow contour of a cooling hydraulic system, in channels of input and output of a node of which temperature sensors are installed, and the colling hydraulic system itself is closed with the input and the output in a liquid cooling installation with thermostat made with the possibility of maintenance of a given temperature mode of cooling water at an input of a target assembly. All temperature sensors are connected to a recorder, which is made with the possibility of fixation of a temperature of each sensor in a real time mode and with the possibility of connection to a computer. At the same time, a channel of an electron bundle outlet is directed to the window of the node, and the node is mounted on an output flange of an electronic accelerator. Steel membrane is installed between the window of the node and the flow contour.

EFFECT: possibility of safe correction of structural features of targets and parameters of heat removal with water cooling from targets developing isotopes.

3 cl, 11 dwg

Description

SUBSTANCE: invention relates to technique used for production of radioisotopes, namely to devices simulating thermal processes occurring in targets during production of radioisotopes.

Radioisotopes for medicine are produced by irradiating a target with a high-intensity proton beam, which is accompanied by a large heat release in the target and a high level of induced activity on the equipment.

A known method for producing isotopes of strontium Sr-82 and germanium Ge-68 by irradiation of rubidium-chlorine salt and metallic gallium [TARGETRY AT THE LANL 100 MeV ISOTOPE PRODUCTION FACILITY: LESSONS LEARNED FROM FACILITY COMMISSIONING * F.M. Nortier1, M. E. Fassbender+1, M. DeJohn3, V. T. Hamilton1, R. C. Heaton1, D. J., Jamriska1, J. J. Kitten1, J.W. Lenz2, C. E. Lowe1, C.F. Moddrell3, L. M. McCurdy1, E. J., Peterson1, L. R. Pitt1, D. R. Phillips1, L. L. Salazar1, P.A. Smith3 and F. O. Valdez1, Los Alamos National Laboratory, MS J514, Los Alamos, New Mexico 87545, USA., John W. Lenz & Associates, 412 Muskingum Road, Wax-ahachie, TX 75165, P.A. Smith Concepts & Designs, 1475 Central Ave. Suite 250, Los Alamos, New Mexico 87544].

Also known is a method for producing the strontium isotope Sr-82 by irradiating a target of metallic rubidium placed inside a sealed stainless steel capsule [Zhuykov B.L., Kokhanyuk V.M., Glushchenko V.N. Obtaining strontium-82 from a target of metallic rubidium on a proton beam with an energy of 100 MeV. - Radiochemistry, 1994, volume 36, pp. 494-498]. The method is chosen for the prototype. Heat removal from the target surface is carried out by means of forced water cooling. These targets are irradiated with a proton beam with an energy of the order of 100 MeV, a beam current of 100–250 μA, and a heat release of 3–7 kW in each target. Figure 1 shows a circuit design and a photo of an assembly with characteristic dimensions of the order of D = 40–50 mm. The target is a sealed metal capsule with the working substance placed in it. Typical dimensions of the target: diameter 25-50 mm, thickness 10-20 mm.

An increase in the beam current makes it possible to increase the production of isotopes, but in this case, the thermal load on the cooling system increases, which can ultimately lead to a heat removal crisis and, as a result, to the destruction of the target body. Therefore, to increase the current, it is first necessary to study the process of cooling the target body during irradiation with a high current of the proton beam. It is not enough and not safe to be limited only to calculations. there is no reliable calculation model of high-intensity heat removal. It is necessary to experimentally study the thermal processes in the target. Simulating thermal processes on a proton beam, firstly, is not safe and leads to high activation of structural materials, and secondly, to conduct such studies at a target station during the operation of a cyclotron in the conditions of an existing production is a violation of the technological regulations. The technical problem of the known solutions is that it is necessary to carry out bench tests with a target model having the same body dimensions and made of the same material as the real target body. On the stand, it is necessary to create in a safe way the levels of heat release and cooling conditions of the targets similar to the real ones. Experience shows that it is practically impossible to supply a power of 9 kW to a target (with characteristic dimensions D = 50 mm, thickness h = 10-20 mm) in a simple way - with an electrically heated coil.

The objective of the invention is to eliminate this technical problem.

The technical result of the invention: the ability to safely specify the design features of the targets and the parameters of heat removal by water cooling from targets producing isotopes.

The specified technical result is achieved due to the fact that a stand is claimed that simulates thermal processes in targets during the production of radioisotopes using intense proton beams, containing a node with a window for beam supply, in which a target is rigidly fixed, to which a temperature sensor is connected, and between the window and the target is a flow circuit of the hydraulic cooling system, in the channels of the inlet and outlet of the node of which temperature sensors are installed, and the hydraulic system of cooling by the inlet and outlet is closed in the liquid cooling unit with a thermostat configured to maintain the specified temperature regime of the cooling water at the inlet of the target assembly; all temperature sensors are connected to the recorder, which is designed to record the temperature of each sensor in real time and with the ability to connect to a computer, characterized in that the electron beam outlet channel is directed into the node window, and the node is mounted on the output flange of the electron accelerator, between the window node and the flow circuit is equipped with a steel membrane.

Preferably, a flow meter is installed at the outlet of the assembly behind the temperature sensor and before entering the liquid cooling unit.

The membrane can be made with a thickness of 0.5 mm and a diameter of 50 mm. Brief description of the drawings

On FIG. 1 shows a target assembly irradiated with an electron beam and cooled with water.

On FIG. 2 shows a schematic representation of a setup for studying high-intensity heat transfer at the solid-water interface.

On FIG. Figure 3 shows the image and beam profile with the quadrupole lenses turned off.

On FIG. 4 shows the image and beam profile in the case of maximum focusing.

On FIG. 5 shows the image and beam profile in the case of maximum defocusing.

On FIG. 6 shows a photograph of the working model of the electron accelerator used for the bench.

On FIG. 7 shows a working example of the assembly of the target assembly before mounting on the accelerator.

On FIG. 8 shows an example of a target assembly mounted on the output flange of the accelerator.

On FIG. 9 shows an example of a target assembly overlaid with protective lead blocks.

On FIG. 10 shows a copper target after irradiation.

On FIG. 11 shows the water-vacuum separation membrane after irradiation. On the drawings: 1 - target, 2 - temperature sensors, 3 - output flange of the electron accelerator, 4 - electron beam (10 MeV, P = 5-10 kW), 5 - water cooling circuit, 6 - inlet flow of the water cooling system, 7 - outlet flow of the water cooling system, 8 - node window, 9 - thin steel membrane, 10 - recorder, 11 - computer, 12 - video camera, 13 - liquid cooling unit with thermostat (chiller), 14 - flow meter.

Implementation of the invention.

The stand, which simulates thermal processes in targets during the production of radioisotopes using intense proton beams, contains a node with a beam supply window, in which target 1 is rigidly fixed (see Fig. 1, Fig. 2).

A temperature sensor 2 is connected to the target 1, and between the window and the target there is a flow circuit 5 of the hydraulic cooling system, in the channels of the inlet 6 and outlet 7 of the node of which temperature sensors 2 are also installed. All temperature sensors 2 are connected to the recorder 10, which is made with the possibility of fixing temperature of each sensor in real time and with the ability to connect to a computer 11. Computer 11 collects and analyzes data, if necessary, use a video camera 12 behind the stand, which is connected to a computer. The hydraulic cooling system itself is closed in the liquid cooling unit 13 with a thermostat (chiller) configured to maintain a predetermined temperature regime of the cooling water at the target assembly inlet.

What is new is that the electron beam outlet channel 4 is directed through the node window 8, and the node is mounted on the output flange 3 of the electron accelerator.

Preferably, a flow meter 14 is installed at the outlet 7 of the assembly behind the temperature sensor 2 and before entering the liquid cooling unit 13.

The task of creating heat release fields is solved by creating a cooled target assembly, to which power is supplied by an electron beam 4 with an energy of up to 10 MeV (power up to 10 kW), as shown in Fig. 1. The use of an electron beam makes it possible to simulate heat release in a target similar to that in a proton beam, but the levels of induced activity will be much lower. The study of the device performance was carried out at the stand No. 4 of the SINP MSU. The accelerated beam has the parameters presented in Table 1. The average power is controlled by the pulse repetition rate and, at a maximum frequency of 100 Hz, is 3.2 kW.

Electron accelerator beam parameters.

A pair of quadrupole lenses is installed at the output of the accelerator to form the irradiation field. The transverse size of the beam is determined from the image of the transition radiation on the titanium foil of the beam extraction by means of a metal mirror and a Videoscan-415 camera. On FIG. 3, Fig. 4, FIG. Figure 5 shows images of the beam and its profiles in the horizontal and vertical planes in the cases of turned off quadrupole lenses, maximum beam focusing, and maximum beam defocusing, respectively. As can be seen from FIG. 3 - Fig. 5 σ can be varied in the range from 0.8 mm to 5 mm. In the experiment, a configuration with a maximum defocused beam was used, the root-mean-square radius in the horizontal plane was 5.08±0.29 mm, and in the vertical plane, 3.94±0.28 mm.

The target assembly under study was cooled by chiller 13, which maintained the temperature of the cooling water at 28°C, the flow rate was 50 l/min, and the pressure was 3.5 bar. The beam power was controlled by the pulse repetition rate, starting from 10 Hz to 80 Hz with a step of 10 Hz, which corresponds to a power range of 320–2560 W with a step of 320 W.

Target node.

The scheme of the target assembly, which simulates thermal processes in targets using intense electron beams, is shown in Fig. 2. A thin steel membrane 9 (see Fig. 1) cuts off the vacuum of the accelerator from the flow of water (highlighted in blue) cooling this membrane and target 1. Membrane 9 can be made, for example, 0.5 mm thick and 50 mm in diameter.

Two types of targets were used in the experiment. Copper target with a beam thickness of 10 mm and a diameter of 25 mm. The target is cooled on one side by a stream of water. The target temperature is controlled from the other side of the target using a thermocouple. In this case, for a copper target, the temperature was controlled only in the central region of the target.

The gallium target is a gallium-filled steel capsule with beam dimensions of 10 mm and a diameter of 25 mm. The 0.3 mm thick steel inlet membrane is cooled by water flow. The gallium target temperature was controlled using two thermocouples: in the central region and in the lower part of the target.

The partial energy releases in the elements of the target assembly during the passage of electrons with an energy of 10 MeV are given below.

Calculations and experimental measurements show that in a gallium target (including the steel wall of the target capsule 0.3 mm thick):

a) 67% of the beam energy is released, which corresponds to an average heat flux density on the water-cooled target surface of approximately 350 W/ ^cm2 at a pulse repetition rate of 80 Hz and 400 W/ ^cm2 at a frequency of 90 Hz;

b) at a pulse frequency above 70–80 Hz, the temperature of gallium in the target exceeds the boiling point of water at a pressure of 3.5 bar (137°C); the target is cooled by a turbulent flow of water subcooled to the saturation (boiling) temperature, and heat transfer to a part of the cooled surface is due to water boiling;

c) for the production of the target nuclide ⁶⁸ Ge in the reaction ^nat Ga(p,x) ⁶⁸ Ge, the most effective protons with an energy of 30 MeV, whose ranges in gallium are 2.5 mm, while the average heat flux density on the cooled surfaces is 350-400 W/ cm ² will be achieved at proton beam currents of 110-130 μA (with the same parameters of water cooling, target diameter, beam size and target cooling from both sides);

d) thus, using the described device, it is possible to simulate thermal processes in targets for the production of radioisotopes using intense electron beams.

Results of target temperature measurements.

The measurements were carried out according to the following scheme:

1) measurements on each target started at a frequency of 10 Hz for a gallium target and at a frequency of 20 Hz for a copper target;

2) at a given beam power, the time of establishment of a quasi-stationary temperature (when the thermocouple readings practically did not change over time) equilibrium was fixed;

3) then the beam power was increased by a fixed value of 320 W, i.e. the electron bunch repetition rate increased by 10 Hz;

4) the beam power was increased up to a repetition rate of 90 Hz, the results were entered in the tables below;

5) note: a) during measurements on a gallium target at a frequency of 30 Hz, one of the fuses on the electron accelerator failed, while repeated measurements at this frequency after replacing the fuse were carried out starting from the target temperature equal to the temperature of the cooling water; b) the countdown for each measurement started at the zero mark, in fact, the measurement process for each target was carried out continuously in time, i.e. after the establishment of a quasi-stationary temperature at a fixed frequency, the increase in frequency occurred within a short time (with the exception of the situation described in paragraph a)).

Measurement results

copper target

When switching to a power of 30 Hz, the accelerator stopped for a technical reason (a fuse burned out). After the restoration of work, the experiment continued.

Calculation of energy release of 10 MeV electrons in copper and gallium targets.

The electron beam profile is a Gaussian with σ _x = σ _y = 5 mm. The electron beam operates in a pulsed mode with an intensity of 2⋅10 ¹³ e/pulse. The distribution of the released energy in cylindrical targets was carried out with a step of 1 mm along the target thickness, along the radius with a step of 2.5 mm. Target diameter 25 mm. The results are normalized to 1 pulse.

Copper target.

Design geometry along the beam:

Window (steel) - 0.5 mm;

water - 3 mm;

target (copper) - 10 mm;

steel - 3 mm.

gallium target.

Design geometry along the beam:

steel - 0.5 mm;

water - 3 mm;

steel - 0.3 mm;

gallium - 8 mm;

steel - 3 mm;

copper - 10 mm.

On FIG. 10 shows a copper target after irradiation and FIG. 11 shows the water-vacuum separation membrane after irradiation.

The operation of the stand and the results of measurements show that it is possible to safely refine the design features of the targets and the parameters of heat removal by water cooling from targets producing isotopes.

Claims (3)

1. A stand that simulates thermal processes in targets during the production of radioisotopes using intense proton beams, containing an assembly with a window for beam supply, in which a target is rigidly fixed, to which a temperature sensor is connected, and between the window and the target there is a flow circuit of the cooling hydraulic system, in the inlet and outlet channels of the node of which temperature sensors are installed, and the hydraulic system for cooling the inlet and outlet is closed in the liquid cooling unit with a thermostat configured to maintain the specified temperature regime of the cooling water at the inlet of the target assembly; all temperature sensors are connected to a recorder, which is designed to record the temperature of each sensor in real time and with the ability to connect to a computer, characterized in that the electron beam outlet channel is directed into the node window, and the node is mounted on the output flange of the electron accelerator, between the window node and the flow circuit is equipped with a steel membrane. 2. Stand according to claim 1, characterized in that a flow meter is installed at the outlet of the assembly behind the temperature sensor and before entering the liquid cooling unit. 3. Stand according to claim 1 or 2, characterized in that the membrane is made with a thickness of 0.5 mm and a diameter of 50 mm.

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