RU153594U1 - DEVICE FOR NEUTRON RADIOGRAPHY ON REACTOR - Google Patents

Abstract

Installation for carrying out neutron radiography in a reactor containing a source of cold neutrons, a collimator for removing neutrons from the reactor, bismuth and beryllium filters located inside the collimator along the neutron beam, a neutron velocity selector, a platform for arranging samples, a neutron detection unit that passed through the sample, characterized in that the source of cold neutrons is hermetically fixed at the input end of the collimator, and the collimator is fixed on the site above the reactor and the vertical but in an open reactor pool, which serves as the main radiation protection unit.

Description

The utility model relates to the field of experimental physics. The facility can be used in outdoor pool reactors for neutron radiography.

The relevance lies in the demand and the need to increase the number of facilities for neutron radiography in research nuclear reactors to perform non-destructive testing of various materials in the face of the limited possibility of mounting these facilities in research reactors due to the lack of suitable reactor channels.

Known installation DINGO for neutron radiography at the OPAL reactor in Australia [1]. The facility uses a beam of thermal neutrons emerging from the horizontal channel of the reactor into the reactor hall. The neutron beam collimator consists of two parts. One part is located inside the horizontal channel of the reactor and has two channels of different diameters for the passage of neutrons. The second part of the revolver type collimator is located outside the reactor, has one hole and blocks one of the neutron beams coming from the first part of the collimator, leaving the second open and allowing you to take pictures either with high resolution or with a short exposure. Behind the collimators along the neutron beam is a gate, which, if necessary, blocks the neutron beam. Behind the gate there is a neutron velocity selector and a neutron pipeline. The speed selector and the neutron pipeline are located in a chamber whose walls are made of radiation absorbing material in order to ensure radiation safety. The neutron pipeline enters the second chamber also with radiation protection, where at the end of the pipeline there is a sample platform and a neutron detecting unit.

The disadvantage of the installation is the use of thermal neutrons, which limits the possibilities of the neutron radiography method since they undergo less attenuation in materials, and the image has less contrast and selectivity than in the case of using cold neutrons. The use of thermal neutrons at the facility is associated with the lack of free space on horizontal neutron beams emanating from the cold neutron source, which is available at the OPAL reactor. Another disadvantage is the presence of a long neutron pipeline extending far beyond the radiation protection of the reactor, which leads to the need to install large radiation protection around the neutron radiography facility. Another drawback is the need to remove the intra-channel collimator when dismantling the installation from the reactor, which is associated with complex radiation hazardous work in the reactor hall.

[one]. U. Garbe, T. Randall, C. Hughes. The new neutron radiography / tomography / imaging station DINGO at OPAL. Nuclear Instruments and Methods in Physics Research A 651 (2011) 42-46.

As a prototype, the ANTARES device for neutron radiography using cold neutrons at the FRM-II reactor in Germany [2] is considered. As a source of cold neutrons, a chamber with liquid deuterium is used, installed in a heavy-water reflector of the reactor, to which a horizontal channel is suitable for outputting cold neutrons. Cold neutrons arrive at a revolver-type collimator with holes of various diameters, behind which there is a gate for shutting off the neutron beam and a neutron conduit, in which there are two places for a block recording neutrons located at different distances from the inlet of the collimator. The entire non-reactor design of the ANTARES device is housed in three silos designed for radiation protection.

The disadvantage of the prototype is that:

1 - there is a water gap between the chamber of a cold neutron source with liquid hydrogen (deuterium) and the reactor channel through which the cold neutrons are removed, which leads to a decrease in the cold neutron flux to the neutron radiography device;

2 - the presence of a long neutron pipeline that goes far beyond the biological protection of the reactor, leads to the need to install expensive large-sized radiation protection in the form of bins around a device for neutron radiography;

3 - the installation for neutron radiography ANTARES, due to large-sized radiation protection, occupies a large area of the experimental hall of the reactor, limiting the possibility of placing other experimental facilities on adjacent neutron beams;

4 - dismantling of the in-channel collimator from the reactor is associated with complex radiation hazardous work in the reactor hall for extraction, cutting and loading into special containers for the transport of radiation-hazardous cargo to a specialized enterprise for further disposal. [2]. B. Schillinger, E. Calzada, F. Grunauer, E. Steichele. The design of the neutron radiography and tomography facility at the new research reactor FRM-II at Technical University Munich. Applied Radiation and Isotopes 61 (2004) 653-657.

The objective of the claimed installation is to simplify the operation of the device, mounting it on the reactor and dismantling after completion of operation.

The technical effect consists in creating a compact, efficient facility for carrying out cold neutron neutron radiography in outdoor pool reactors, without limiting the possibility of placing other experimental facilities in adjacent neutron beams, which expands the experimental capabilities of the reactor.

The technical effect is achieved by the fact that in a known installation for conducting neutron radiography in a reactor containing a cold neutron source, a collimator for removing neutrons from the reactor, bismuth and beryllium filters located inside the collimator and located along the neutron beam, a neutron velocity selector, a platform for the location of the samples, the registration unit for neutrons passing through the sample, it is new that the source of cold neutrons is hermetically fixed at the input end of the collimator, and the collie ATOP is attached to the platform above the reactor and placed vertically in the outdoor pool of the reactor, which acts as the main radiation protection unit.

In FIG. 1 presents a General view of the inventive device, where: 1 - a collimator, 2 - a chamber of a source of cold neutrons, 3 - a beryllium block; 4 - open pool of the reactor, 5 - the area above the reactor on which the collimator is mounted, 6 - the vacuum casing, 7 - the side screen of the collimator, 8 - bismuth filter, 9 - beryllium filter, 10 - reactor core, 11 - beryllium core reflector reactor, 12 - a vacuum membrane, 13 - a neutron velocity selector, 14 - a platform for samples, 15 - a neutron detecting unit.

At the lower inlet end of the collimator (1), a vacuum casing (6) is tightly fixed, in which there is a chamber of a cold neutron source (2). A beryllium block (3) is fixed to the vacuum casing (6) from the outside. A bismuth filter (8) and a beryllium filter (9) are located inside the collimator (1). On the inner surface of the collimator (1) is a side screen of the collimator (7). The upper end of the collimator (1) is closed by a sealed vacuum membrane (12). The entire structure described is located vertically in the open pool of the reactor (4) and is fixed to the site (5) located above the pool of the reactor (4). A neutron velocity selector (13) is located above the collimator (1), above which there is a sample platform (14). The neutron registration unit (15) is located above the sample platform (4). The neutron velocity selector (13), the sample platform (14) and the neutron registration unit (15) are installed on the site (5).

Installation work.

A collimator (1) with a cold neutron source chamber (2) and a beryllium block (3) hermetically fixed at its lower end is lowered by a crane into the open pool of the reactor (4) vertically and fixed in the upper surface part to the platform (5). In the chamber of the cold neutron source (2) is a neutron moderator (liquid hydrogen). The neutron moderator has a cryogenic temperature, which is maintained by a cryogenic installation located outside the reactor. The source of CN is described in the literature: (L. Rosta, T. Grosz, T. Hargitai. Liquid hydrogen cold neutron source in operation at the Budapest Research Reactor. Appl. Phys. A 74 [Suppl.], S240-S242 (2002)) [3]. A vacuum casing (6) surrounds the chamber of the cold neutron source (2) to create thermal insulation. The vacuum in the casing (6) is maintained by a vacuum pump located outside the reactor. The collimator (1) is hermetically connected to the vacuum casing (6), to which the beryllium block (3) is fixed. The collimator (1) made of iron has a side screen (7) of cadmium, which prevents neutrons from entering the collimator through the side surface. The vacuum in the collimator (1) is maintained by a vacuum pump located outside the reactor. A bismuth filter (8) and a beryllium filter (9) are placed inside the collimator (1) in its underwater part and have a cryogenic temperature, which is maintained by a cryogenic installation located outside the reactor.

During operation, reactor neutrons from the core (10) through the beryllium reflector of the reactor (11) and the beryllium block of the device (3) enter the chamber of the cold neutron source (2), where they are cooled to the energy of cold neutrons using a neutron moderator, and then some of the neutrons enters the input of the collimator (1), hermetically connected to it. A collimated neutron beam passes through a cooled bismuth filter (8), which reduces gamma radiation, through a cooled beryllium filter (9), which cuts off thermal and fast neutrons, and through a vacuum membrane at the upper end of the collimator (12) it enters sequentially into the neutron velocity selector ( 13), on which neutrons of a certain energy are selected from the entire incoming spectrum of cold neutrons, which then shine through a sample placed on site (14). The neutrons passing through the sample enter the recording unit (15), in which an image of the sample is created.

If it is necessary to dismantle the device, which is mounted vertically in the open pool of the reactor, all communications are disconnected from it at the stopped reactor, then the collimator (1) with the cold neutron source chamber (2) and the beryllium block (3) hermetically fixed at its lower end, is disconnected from platforms (5) and transferred by a crane to the holding pool. Here, the design can withstand the necessary time to reduce the induced radioactivity of the material to an acceptable level for subsequent disposal.

The inventive design allows to circumvent the disadvantages of analogues and prototype:

a) the use in the installation of its own compact source of small cold neutrons, containing a small amount of cryogenic moderator, allows you to use the spectrum of cold neutrons in radiography without occupying the channels with cold neutrons in the reactors where they are available;

b) the vertical arrangement of the collimator with the cold neutron source of the neutron radiography unit in the outdoor pool of the reactor greatly simplifies its installation in the reactor, while the existing channels of the reactor are not occupied, which expands the experimental capabilities of the reactor;

c) placement of a collimator with a cold neutron source in the reactor pool water makes it easy to dismantle the installation at the reactor by transferring the collimator with a cold neutron source fixed to the bottom of the reactor pool from the reactor pool, which subsequently, after reducing the induced radioactivity of the material, simplifies the process recycling;

d) the placement of a collimator with a cold neutron source in the reactor pool allows the use of reactor water with an outdoor pool as a biological protection of the neutron beam used for radiography, which eliminates the need for heavy, bulk and expensive biological protection around the neutron beam in a collimator mounted outside the reactor as in the prototype. In the inventive device, the collimator is located inside the reactor pool.

e) hermetically securing the cold neutron source to the bottom of the collimator allows to reduce the loss of cold neutrons, since there is no water gap between the cold neutron source and the collimator;

e) the compactness of the cold neutron source, which is hermetically fixed to the vertical collimator, allows you to place the design in an accessible place of the reactor pool with the highest thermal neutron flux, which helps to increase the resolution of the neutron radiography method and reduces the exposure time of the sample.

The unit is intended for research on non-destructive testing of various materials at the reactor.

Literature

1. U. Garbe, T. Randall, C. Hughes. The new neutron radiography / tomography / imaging station DINGO at OPAL. Nuclear Instruments and Methods in Physics Research A 651 (2011) 42-46.

2. B. Schillinger, E. Calzada, F. Grunauer, E. Steichele. The design of the neutron radiography and tomography facility at the new research reactor FRM-II at Technical University Munich. Applied Radiation and Isotopes 61 (2004), 653-657 - prototype.

3. L. Rosta, T. Grosz, T. Hargitai. Liquid hydrogen cold neutron source in operation at the Budapest Research Reactor, Appl. Phys. A 74 [Suppl.], S240-S242 (2002)

Claims (1)

A facility for conducting neutron radiography in a reactor containing a source of cold neutrons, a collimator for removing neutrons from the reactor, bismuth and beryllium filters located inside the collimator along the neutron beam, a neutron velocity selector, a platform for arranging samples, a neutron detection unit that passed through the sample, characterized in that the source of cold neutrons is hermetically fixed at the input end of the collimator, and the collimator is fixed on the site above the reactor and the vertical but in an open reactor pool, which serves as the main radiation protection unit.

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