CN114220562A

CN114220562A - Secondary neutron source rod

Info

Publication number: CN114220562A
Application number: CN202111329984.4A
Authority: CN
Inventors: 曹进; 蔡智毅; 张利斌; 林少芳; 李长征; 李颖虹; 宋子凡; 邓勇军; 聂立红; 陈建新
Original assignee: Cgnpc Uranium Resources Co ltd; China General Nuclear Power Corp; China Nuclear Power Technology Research Institute Co Ltd; CGN Power Co Ltd; Lingao Nuclear Power Co Ltd
Current assignee: Cgnpc Uranium Resources Co ltd; China General Nuclear Power Corp; China Nuclear Power Technology Research Institute Co Ltd; CGN Power Co Ltd; Lingao Nuclear Power Co Ltd
Priority date: 2021-11-10
Filing date: 2021-11-10
Publication date: 2022-03-22

Abstract

The invention provides a secondary neutron source rod, which comprises an outer casing and an inner pipe section arranged in the outer casing, wherein the inner pipe section comprises an inner cladding, a neutron source core block for providing neutrons and an inner lining pipe for absorbing tritium, the neutron source core block and the inner lining pipe are arranged in the inner cladding, a hole is formed in the center of the neutron source core block, and the inner lining pipe axially penetrates through the hole to absorb the tritium generated by the neutron source core block. The secondary neutron source rod can reduce tritium emission, protect the health of workers in the nuclear power station, and reduce the risk of melting neutron source materials.

Description

Secondary neutron source rod

Technical Field

The invention relates to the technical field of nuclear power, in particular to a secondary neutron source rod.

Background

Most Pressurized Water reactors (Pressurized Water reactors; nuclear reactors that use high pressure Water to cool nuclear fuel) generally include fuel assemblies, moderators, control rod assemblies, burnable poison assemblies, neutron source rods, core baskets, and pressure shells, and are Reactor types that are used in nuclear power plants in large numbers and have large capacities.

The neutron source rods provide an initial neutron level for reactor loading and startup to meet regulatory requirements. The Neutron Source rods include Primary Neutron Source rods (Primary Neutron Source assemblies) and Secondary Neutron Source rods (Secondary Neutron Source assemblies).

The secondary neutron source assembly is provided with a plurality of secondary neutron source rods, and the rest are resistance stopper rods. The secondary neutron source material usually arranged in the secondary neutron source rod is antimony-beryllium (Sb-Be) pellets.

When the reactor is charged for the first time, the secondary neutron source is in an unactivated state, after irradiation in the reactor for a certain time, excited antimony (Sb) undergoes gamma decay, and gamma rays with high enough energy bombard beryllium (Be) atomic nuclei to release neutrons. The secondary source rod is continuously used in a plurality of subsequent cycles until the service life is close to the replacement. Antimony-beryllium (Sb-Be) materials generate tritium after irradiation activation in a stack.

Tritium, also known as deuterium, is one of the isotopes of hydrogen, has an atomic weight of 3.016, and has a nucleus composed of one proton and two neutrons, with radioactivity, which undergoes beta decay to give off helium-3 with a half-life of 12.43 years. Naturally occurring tritium is very small and negligible, and environmental tritium is mainly derived from various nuclear tests and nuclear power activities.

Hazard of tritium:

(one) harm to the environment

Tritium water can enter into a primary producer body to be combined with organic matters to form stable organic tritium. Because organic tritium has a low metabolic rate in organisms and gradually enriches along with the migration of food chain nutrition, the organic tritium can cause continuous internal irradiation harm to organisms.

(II) harm to human body

Beta radiation, released by tritium in radioactive decay, does not have enough energy to pass through the outer layer of dead skin cells of the skin, and thus tritium constitutes only a limited radioactive hazard outside the human body. However, when tritium is ingested by the body by inhalation, skin absorption, ingestion, and injection, a more serious hazard of internal irradiation occurs. Inhalation of tritium gas can be very close to where tritium is released, or in a closed or air-tight location, where it can interfere with health.

The absorption by the human body through inhalation and the skin results in almost 100% absorption of tritium from tritium water, which is a greater health hazard than exposure to tritium in its gaseous elemental form. For example, when handling equipment, without washing hands and drinking, applying cosmetics, or touching the mouth or lips after touching the equipment surface contaminated with tritium, a human body may eat tritium. For example, in handling damaged equipment containing tritium, it is possible that tritium may be injected into a human body after the components within the equipment unfortunately pierce the skin. Tritium water can be uniformly distributed in a human body, and beta radiation emitted by tritium can continuously irradiate surrounding tissues until tritium atoms decay or disappear through natural excretion of the human body. The greater the amount of tritium ingested, the greater the potential health hazard.

Tritium is easy to permeate in a cladding tube of a secondary neutron source rod used at present, so that radioactive tritium is easy to penetrate through the cladding tube and enter a coolant, pollution is caused, and the health of workers of a nuclear power station is greatly influenced.

Disclosure of Invention

The technical problem to be solved by the present invention is to provide a secondary neutron source rod capable of reducing tritium emission, aiming at the above defects in the related art.

The technical scheme adopted by the invention for solving the technical problem comprises the following steps: the utility model provides a secondary neutron source stick, includes outer covering and establishes interior tube segment in the outer covering, interior tube segment includes interior cladding, is used for providing the neutron source pellet of neutron and is used for adsorbing the interior bushing pipe of tritium, the neutron source pellet with interior bushing pipe is established in the interior cladding, the hole is seted up at neutron source pellet center, and interior bushing pipe axially wears to establish in the hole to adsorb the tritium that the neutron source pellet produced.

Preferably, the inner cladding is made of zirconium alloy with the surface subjected to pre-oxidation treatment, and an oxide film is formed on the surface.

Preferably, the outer diameter of the inner cladding is 6-9 mm.

Preferably, the wall thickness of the inner cladding is 0.2-2 mm.

Preferably, the thickness of the oxide film of the inner cladding is 5-30 μm.

Preferably, the neutron source core block comprises a plurality of said neutron source core blocks stacked axially.

Preferably, the hole of the neutron source core block is axially opened, and the inner lining pipe axially penetrates through the hole of each neutron source core block.

Preferably, the hole diameter of the neutron source core block is 0.5-2 mm.

Preferably, the surface of the lining pipe is plated with nickel.

Preferably, the thickness of the nickel plating layer of the lining pipe is 3-25 μm.

The technical scheme of the invention at least has the following beneficial effects: the secondary neutron source rod adopts a double-layer cladding-outer cladding and inner cladding design, and can reduce outward permeation of tritium; meanwhile, the neutron source core block adopts a central hole opening design, on one hand, the neutron source core block can radiate heat outwards, the heat transfer performance can be improved, and the risk of melting the neutron source core block is reduced, on the other hand, an inner lining pipe used for absorbing tritium is arranged in the hole, the tritium generated by the neutron source core block can be absorbed, and the risk that the tritium penetrates into the coolant outwards is reduced. The secondary neutron source rod can reduce tritium emission, protect the health of workers in the nuclear power station, and reduce the risk of melting neutron source materials.

Drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings needed to be used in the embodiments or the prior art descriptions will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on these drawings without inventive exercise.

Fig. 1 is a cross-sectional view of a secondary neutron source rod according to an embodiment of the present invention.

Fig. 2 is a sectional view in axial section of the inner pipe section of fig. 1.

Fig. 3 is a partially enlarged view of a portion a in fig. 2.

FIG. 4 is a cross-sectional view of one of the neutron source core blocks of FIG. 2 taken axially.

The reference numerals in the figures denote: an outer casing 11, a first outer end plug 12, a second outer end plug 13, an inner tube section 2, an inner cladding 21, a first inner end plug 22, a second inner end plug 23, a neutron source core block 24, a hole 241 and an inner lining tube 25.

Detailed Description

For a more clear understanding of the technical features, objects and effects of the present invention, embodiments of the present invention will now be described in detail with reference to the accompanying drawings. It is to be understood that, unless otherwise expressly stated or limited, the terms "connected," "secured," "disposed" and the like are intended to be open-ended, i.e., to mean either a fixed connection, a removable connection, or an integral part; either directly or indirectly through intervening media, either internally or in any other relationship. When an element is referred to as being "on" or "under" another element, it can be "directly" or "indirectly" on the other element or intervening elements may also be present. If the terms "first", "second", "third", etc. are used herein only for convenience in describing the present technical solution, they are not to be taken as indicating or implying relative importance or implicitly indicating the number of technical features indicated, whereby the features defined as "first", "second", "third", etc. may explicitly or implicitly include one or more of such features. The specific meanings of the above terms in the present invention can be understood by those skilled in the art according to specific situations.

In the following description, for purposes of explanation and not limitation, specific details are set forth, such as particular system structures, techniques, etc. in order to provide a thorough understanding of the embodiments of the invention. It will be apparent, however, to one skilled in the art that the present invention may be practiced in other embodiments that depart from these specific details. In other instances, detailed descriptions of well-known systems, devices, circuits, and methods are omitted so as not to obscure the description of the present invention with unnecessary detail.

Referring to fig. 1 to 4, a secondary neutron source rod in an embodiment of the present invention includes an outer cladding 11 and an inner tube segment 2 disposed in the outer cladding 11, the inner tube segment 2 includes an inner cladding 21, a neutron source pellet 24 for providing neutrons, and an inner lining tube 25 for absorbing tritium, the neutron source pellet 24 and the inner lining tube 25 are disposed in the inner cladding 21, the neutron source pellet 24 is provided with an axial hole 241, and the inner lining tube 25 is axially inserted into the hole 241 to absorb tritium generated by the neutron source pellet 24. Of these, the neutron source core blocks 24 are preferably antimony-beryllium core blocks.

The secondary neutron source rod adopts a double-layer cladding design, namely an outer cladding 11 and an inner cladding 21, and can reduce outward permeation of tritium; meanwhile, the neutron source core block 24 is designed by adopting the central opening 241, on one hand, the neutron source core block 24 can radiate heat outwards, the heat transfer performance can be improved, and the risk of melting the neutron source core block 24 is reduced, on the other hand, the inner lining pipe 25 for absorbing tritium is arranged in the hole 241, the tritium generated by the neutron source core block 24 can be absorbed, and the risk of the tritium permeating into the coolant outwards is reduced. Therefore, the secondary neutron source rod can reduce tritium emission, protect the health of workers in the nuclear power station, reduce the melting risk of neutron source materials, and is particularly suitable for serving as the secondary neutron source rod.

The secondary neutron source rod mainly has the function of providing an initial neutron level for the out-of-reactor measuring instrument in the processes of fuel loading, reactor shutdown and lower neutron flux of the critical reactor core of the subsequent cycle through the secondary neutron source loaded in the rod. When the reactor core is firstly charged, the primary neutron source assembly and the secondary neutron source assembly are simultaneously loaded, and the refueling reactor core is only loaded into the secondary neutron source assembly.

The secondary neutron source rod can be independently inserted into the fuel assembly for use, and can also be arranged into the secondary neutron source assembly for use. The secondary neutron source assembly is generally composed of a secondary neutron source rod and a resistance plug rod or other related assembly rods suspended below a hold-down component. When the reactor is operated, the secondary neutron source rod is inserted into the fuel assembly and fixed, and the secondary source rod is usually inserted into the guide tube of the fuel assembly.

Preferably, the secondary neutron source rod further comprises a first outer end plug 12 and a second outer end plug 13, the outer casing 11 is tubular with two open ends, the outer casing 11 and the end plugs are made of stainless steel materials, and the first outer end plug 12 and the second outer end plug 13 plug the two open ends of the outer casing 11 respectively.

Preferably, the inner tube section 2 further comprises a first inner end plug 22 and a second inner end plug 23, the inner cladding 21 is tubular with two ends open, and the first inner end plug 22 and the second inner end plug 23 plug the two ends open of the inner cladding 21 respectively.

Preferably, the inner cladding 21 is made of zirconium alloy with pre-oxidized inner and outer surfaces, a dense oxide film is formed on the inner and outer surfaces, the oxide film is not easy to fall off, so that the permeability of tritium is reduced, and even a trace amount of tritium penetrates through the oxide film and can be adsorbed by the zirconium alloy matrix of the inner cladding 21. Thus greatly improving the tritium resistance of the secondary neutron source rod and ensuring the tritium resistance in the reactor during long-term use.

Preferably, the outer diameter of the inner cladding 21 is 6-9 mm, the wall thickness (including the surface oxide film thickness) of the inner cladding 21 is 0.2-2 mm, and the oxide film thickness of the inner cladding 21 is 5-30 μm.

Preferably, the neutron source core block 24 comprises a plurality of axially stacked neutron source core blocks 24, holes 241 of the neutron source core blocks 24 are axially opened, the holes 241 of each neutron source core block 24 are aligned, the inner lining pipe 25 axially penetrates through the holes 241 of each neutron source core block 24, and the hole diameter of the hole 241 of the neutron source core block 24 is 0.5-2 mm.

Preferably, the inner surface and the outer surface of the lining pipe 25 are plated with nickel, the thickness of the nickel plating layer of the lining pipe 25 is 3-25 μm, the matrix zirconium alloy of the lining pipe 25 is used for adsorbing tritium generated by the neutron source core block 24, and the nickel plating on the surface is used for preventing the zirconium alloy surface from being oxidized and reducing the adsorption capacity.

The lining tube 25 may be only one, or may comprise at least two lining tubes 25 distributed axially, or it may be understood that the lining tubes 25 are segmented. As for the matching of the inner lining pipe 25 and the neutron source core blocks 24, one inner lining pipe 25 can penetrate through a plurality of neutron source core blocks 24; at least two inner lining pipes 25 which can also be axially arranged are sequentially penetrated into the holes 241 of at least two neutron source core blocks 24, wherein the inner lining pipes 25 preferably correspond to the neutron source core blocks 24 one by one, and one inner lining pipe 25 is penetrated into one neutron source core block 24, but the invention is not limited to this, and the inner lining pipes 25 can also be axially dislocated from the neutron source core blocks 24.

In conclusion, the secondary neutron source rod adopts a double-layer cladding-outer cladding 11 and inner cladding 21 design, so that outward penetration of tritium can be reduced;

meanwhile, the neutron source core block 24 is designed by adopting a central opening 241, so that on one hand, the neutron source core block 24 can radiate heat outwards, the heat transfer performance can be improved, and the risk of melting the neutron source core block 24 is reduced, on the other hand, an inner lining pipe 25 for absorbing tritium is arranged in the hole 241, the tritium generated by the neutron source core block 24 can be absorbed, and the risk of the tritium permeating into a coolant outwards is reduced, so that the secondary neutron source rod can reduce the discharge of the tritium, protect the health of workers in a nuclear power station, and reduce the risk of melting a neutron source material, and is particularly suitable for being used as a secondary neutron source rod;

the inner cladding 21 is made of zirconium alloy with pre-oxidized inner and outer surfaces, compact oxide films are formed on the inner and outer surfaces, the oxide films are not easy to fall off so as to reduce the permeability of tritium, even if trace tritium penetrates through the oxide films, the tritium can be adsorbed by the zirconium alloy matrix of the inner cladding 21, so that the tritium resistance of the secondary neutron source rod is greatly improved, and the tritium resistance in the long-term use in a reactor can be ensured;

the inner surface and the outer surface of the lining pipe 25 are plated with nickel, the thickness of the nickel plating layer of the lining pipe 25 is 3-25 mu m, the matrix zirconium alloy of the lining pipe 25 is used for adsorbing tritium generated by the neutron source core block 24, and the nickel plating on the surface is used for preventing the zirconium alloy surface from being oxidized to reduce the adsorption capacity.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the present invention, as it will be apparent to those skilled in the art that various modifications, combinations and variations can be made in the present invention. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the claims of the present invention.

Claims

1. The secondary neutron source rod is characterized by comprising an outer wrapping shell (11) and an inner pipe section (2) arranged in the outer wrapping shell (11), wherein the inner pipe section (2) comprises an inner wrapping shell (21), a neutron source core block (24) used for providing neutrons and an inner lining pipe (25) used for adsorbing tritium, the neutron source core block (24) and the inner lining pipe (25) are arranged in the inner wrapping shell (21), a hole (241) is formed in the center of the neutron source core block (24), and the inner lining pipe (25) axially penetrates through the hole (241) to adsorb the tritium generated by the neutron source core block (24).

2. The secondary neutron source rod according to claim 1, wherein the inner cladding (21) is made of a zirconium alloy material with a pre-oxidation treatment on the surface, and an oxide film is formed on the surface.

3. The secondary neutron source rod of claim 2, wherein the outer diameter of the inner cladding (21) is 6-9 mm.

4. The secondary neutron source rod according to claim 2, wherein the wall thickness (including the surface oxide film thickness) of the inner cladding (21) is 0.2-2 mm.

5. The secondary neutron source rod of claim 2, wherein the oxide film thickness of the inner cladding (21) is 5-30 μm.

6. The secondary neutron source rod of claim 1, wherein the neutron source core block (24) comprises a plurality of the neutron source core blocks (24) stacked axially.

7. The secondary neutron source rod according to claim 6, characterized in that the holes (241) of the neutron source core blocks (24) are axially opened, and the inner lining pipe (25) axially penetrates through the holes (241) of each neutron source core block (24).

8. The secondary neutron source rod according to claim 1, characterized in that the aperture of the hole (241) of the neutron source core block (24) is 0.5-2 mm.

9. The secondary neutron source rod of claim 1, wherein the surface of the liner tube (25) is nickel-plated.

10. The secondary neutron source rod according to claim 9, wherein the thickness of the nickel plating layer of the lining tube (25) is 3 to 25 μm.