CN110277177B - Method for closing gap between fuel pellet and cladding in target - Google Patents
Method for closing gap between fuel pellet and cladding in target Download PDFInfo
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- CN110277177B CN110277177B CN201910495310.8A CN201910495310A CN110277177B CN 110277177 B CN110277177 B CN 110277177B CN 201910495310 A CN201910495310 A CN 201910495310A CN 110277177 B CN110277177 B CN 110277177B
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- target
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- cladding tube
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- G—PHYSICS
- G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
- G21C—NUCLEAR REACTORS
- G21C17/00—Monitoring; Testing ; Maintaining
- G21C17/06—Devices or arrangements for monitoring or testing fuel or fuel elements outside the reactor core, e.g. for burn-up, for contamination
- G21C17/07—Leak testing
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- G—PHYSICS
- G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
- G21C—NUCLEAR REACTORS
- G21C3/00—Reactor fuel elements and their assemblies; Selection of substances for use as reactor fuel elements
- G21C3/02—Fuel elements
- G21C3/04—Constructional details
- G21C3/16—Details of the construction within the casing
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E30/00—Energy generation of nuclear origin
- Y02E30/30—Nuclear fission reactors
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- Physics & Mathematics (AREA)
- Engineering & Computer Science (AREA)
- Plasma & Fusion (AREA)
- General Engineering & Computer Science (AREA)
- High Energy & Nuclear Physics (AREA)
- Pressure Welding/Diffusion-Bonding (AREA)
Abstract
The invention belongs to the technical field of nuclear fuel preparation, and relates to a method for closing a gap between a fuel pellet and a cladding in a target. The method comprises the following steps: (1) loading the fuel pellet into a cladding tube, sealing the upper end and the lower end with the cladding tube by vacuum electron beam welding without filling high-purity helium gas to prepare a target; (2) and putting the target piece into a hot isostatic pressing furnace for hot isostatic pressing treatment, so that the clearance between the fuel pellets in the target piece and the cladding is closed. By using the method for closing the fuel pellet and the cladding gap in the target, the fuel pellet and the cladding gap in the target can be better closed without damaging the integrity of the cladding tube and the inner pellets.
Description
Technical Field
The invention belongs to the technical field of nuclear fuel preparation, and relates to a method for closing a gap between a fuel pellet and a cladding in a target.
Background
The target is formed by loading fuel pellets into a cladding tube and welding and sealing the cladding tube with upper and lower end heads respectively. When fuel elements or targets are manufactured using conventional fuel pellet tubulation processes, there is always a certain gap between the pellets and the inner wall of the cladding. In order to improve the thermal conductivity, it is often necessary to fill the component or target with high purity helium gas under pressure. However, under the condition that the excircle of the sintered pellet is not ground, the outer diameter of the pellet is difficult to accurately control, the outer diameter of the pellet is widely distributed, and the manufacturing quality of elements or targets is greatly influenced. If the outer diameter of the core block is smaller, the clearance is too large, and the heat-conducting performance and the irradiation safety are influenced; on the contrary, if the external diameter of the pellet is bigger, the pellet is difficult to be put into the cladding tube and is temporarily scrapped; if the gap is not uniform, the heat conduction and temperature distribution will also be non-uniform.
To date, the most popular way to eliminate the clearance between the pellets and the inner cladding wall has been to use a co-thermal extrusion process to form a metallurgical bond between the pellets and the cladding, forming an integral plate-type fuel element or target, such as the plate-type U used in research stacks3Si2-Al dispersed fuel and Al-NpO2The neptunium target was dispersed (earlier by co-thermal extrusion).
However, when minor actinide materials such as Pu, Np, Am, Cm and the like with high toxicity and strong radioactivity are manufactured by adopting a co-hot extrusion process, equipment and materials are required to be placed in a sealed and shielded glove box, and the difficulty in operation and maintenance is very large; and the process is complex, the efficiency is low, and the rejection rate is high. If a neptunium target is made by a co-thermal extrusion process, the pellets and cladding are dissolved together by the solvent during post-treatment after irradiation, resulting in too much radioactive waste.
Therefore, in view of the principles of high irradiation safety, high irradiation conversion yield, less post-treatment waste, simple manufacturing equipment and process, low comprehensive cost and the like of the neptunium target, a new efficient and economical technology for closing the clearance between the pellet and the cladding needs to be developed.
Disclosure of Invention
It is an object of the present invention to provide a method of closing the fuel pellet to cladding gap in a target that better closes the fuel pellet to cladding gap in the target without compromising the integrity of the cladding and the inner pellets.
To achieve this object, in a basic embodiment, the present invention provides a method of closing a gap between a fuel pellet and a cladding within a target, the method comprising the steps of:
(1) loading the fuel pellet into a cladding tube, sealing the upper end and the lower end with the cladding tube by vacuum electron beam welding without filling high-purity helium gas to prepare a target;
(2) and putting the target piece into a hot isostatic pressing furnace for hot isostatic pressing treatment, so that the clearance between the fuel pellets in the target piece and the cladding is closed.
The principle of the invention is illustrated as follows.
Taking pellet tube-loading neptunium target as an example, Al-NpO meeting the design technical conditions is firstly adopted2The fuel pellets are loaded into a 6061 aluminum alloy cladding tube with a gap between the pellets and the inner wall of the cladding, and the gap is not uniform throughout. Then, the upper and lower end heads of the target are welded by vacuum electron beam instead of TIG welding without filling high-purity helium gasAnd respectively welding and sealing with the aluminum alloy cladding tubes, checking the welding line to be qualified by a helium leak detector, and determining the surface pollution degree of the target piece to be qualified after decontamination. And then, putting the target piece into a hot isostatic pressing furnace for heating and pressurizing, preserving heat and maintaining pressure for a certain time, and carrying out uniform extrusion plastic deformation on the cladding tube under the action of temperature and uniform isostatic pressure so as to close the gap between the pellet in the cladding and the inner wall of the cladding.
Hot Isostatic Pressing (HIP) is a common sintering process in the field of powder metallurgy (cf. textbook "principles of powder metallurgy" of the university of south china (edited by huangpeyun, published by the metallurgical industry, 1997, page 226)). The powder is put into a glass or iron sheath which is not melted at high temperature, is easy to deform and does not react with the powder, and the sheath is welded and sealed after being vacuumized; and then putting the mixture into a HIP furnace for heating, introducing high-purity argon for pressurizing, and enabling the pressure to uniformly act on the outer surface of the sheath so as to cause the powder in the sheath to uniformly shrink and densify. Or after pressureless sintering, the sintered body with the relative density of more than 94 percent and no open pore is directly placed into a HIP furnace without a sheath for high-temperature high-pressure treatment to shrink and close the closed pore, thereby further improving the densification and mechanical properties of the material. The highest temperature of the HIP furnace treatment is 2000 ℃ and the highest pressure is 200 MPa.
According to Al-20 wt% of NpO2The neptunium target piece is designed under the technical conditions that the clearance between the outer diameter of the pellet and the inner wall of the outer casing and the clearance between the inner diameter of the pellet and the outer wall of the inner casing are both 0.1mm, and the deviation between the inner diameter and the outer diameter of the pellet is required to be 0.05 mm. In fact, for the pellet whose excircle is not ground after sintering, it is difficult to accurately control the inner diameter and outer diameter, and the inner diameter and outer diameter are changed due to the fluctuation of the powder performance, the forming die, the sintering temperature, the vacuum degree, the sintering time and other factors. It is necessary to study the critical process parameters of optimization of hot isostatic pressing, temperature, pressure, time, etc., to ensure that the gap is just closed but no severe elemental diffusion reactions have taken place (e.g., changes in the gap are observed using radiographic techniques), so that the pellets and cladding tube can be separated more easily after irradiation, and to ensure that the target and pellets are intact, i.e., the target does not undergo significant distortion, nor the pellets do not deform or crack. Heat preservationAnd after the pressing is finished, cooling along with the furnace, taking out the target, and then carrying out subsequent target assembly.
In a preferred embodiment, the invention provides a method of closing the gap between fuel pellets and cladding within a target wherein in step (1) the weld is also tested for helium leak detection after vacuum electron beam welding and for contamination after decontamination of the target surface.
In a preferred embodiment, the invention provides a method for closing the gap between the fuel pellet and the cladding in the target, wherein in the step (1) and the step (2), the fuel pellet is Al-NpO2Fuel pellets or U3Si2-Al fuel pellets.
In a preferred embodiment, the present invention provides a method for closing the gap between the fuel pellets and the cladding in the target, wherein in step (1) and step (2), the cladding tube is an aluminum alloy cladding tube.
In a preferred embodiment, the present invention provides a method for closing the gap between fuel pellets and cladding in a target, wherein in step (1) and step (2), the cladding tube is a 6061 aluminum alloy cladding tube.
In a preferred embodiment, the invention provides a method for closing the gap between the fuel pellet and the cladding in the target, wherein in the step (2), the hot isostatic pressing treatment is carried out at the temperature of 400-500 ℃, the pressure of 50-200MPa and the time of 30-60 min.
The method has the advantages that the method for closing the gap between the fuel pellet and the cladding in the target can better close the gap between the fuel pellet and the cladding in the target without damaging the integrity of the cladding tube and the inner pellet.
The invention still assembles the component or the target by the traditional pellet tubulation process, and carries out Hot Isostatic Pressing (HIP) treatment on the vacuum welding sealed component or the target, so that the clearance between the pellet and the inner wall of the cladding is closed, and simultaneously, the integral appearance structure and the size of the component or the target are ensured to be unchanged, thereby being beneficial to fast heat conduction of the component or the target during irradiation in a reactor and improving the irradiation safety. Compared with the traditional co-heating extrusion process, the innovative process is simple and convenient, the product qualification rate is high, the radioactive material is completely sealed when the HIP treatment is carried out, and the production operation safety is higher. In addition, the invention can optimize the design parameters of elements or target pieces on the premise of ensuring the irradiation safety, thereby improving the irradiation yield and the economy.
Detailed Description
An exemplary method of closing the fuel pellet-to-cladding gap within a target of the present invention comprises the steps of:
(1) mixing fuel pellets (Al-NpO)2Fuel pellets or U3Si2Al fuel pellets) were packed in a cladding tube (6061 aluminum alloy cladding tube) without filling high purity helium gas, and the upper and lower end heads were sealed with the cladding tube by vacuum electron beam welding, respectively, to produce a target. And after the vacuum electron beam welding, performing helium leak detector detection on the welding seam, and performing pollution degree detection after the surface of the target piece is decontaminated.
(2) And putting the target piece into a hot isostatic pressing furnace for hot isostatic pressing treatment, so that the clearance between the fuel pellets in the target piece and the cladding is closed. The hot isostatic pressing treatment temperature is 400-500 ℃, the pressure is 50-200MPa, and the time is 30-60 min.
Table 1 shows Al-20 wt% NpO2The conditions of the hot isostatic pressing of the target and the experimental results (it can be seen that temperature is the most significant factor).
TABLE 1 Al-20 wt% NpO2Conditions and experimental results of hot isostatic pressing of target
It can be seen that:
(1) HIP treatment is carried out for 60min at the temperature of 400 ℃ and the pressure of 50-200MPa, and the gap is closed.
(2) When the temperature is 450 ℃ and the pressure is 50-200MPa, the gap can be closed by HIP treatment for 60min, and the integrity of the cladding tube and the inner core block is not damaged.
(3) When the temperature is 500 ℃ and the pressure is 50-200MPa, the HIP treatment is carried out for 40min, and the effect is good.
Therefore, the optimum HIP treatment process parameters are: the temperature is 400 ℃ and 500 ℃, the pressure is 50-200MPa, and the time is 30-60 min.
It will be apparent to those skilled in the art that various changes and modifications may be made in the present invention without departing from the spirit and scope of the invention. Thus, if such modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is intended to include such modifications and variations. The foregoing examples or embodiments are merely illustrative of the present invention, which may be embodied in other specific forms or in other specific forms without departing from the spirit or essential characteristics thereof. The described embodiments are, therefore, to be considered in all respects as illustrative and not restrictive. The scope of the invention should be indicated by the appended claims, and any changes that are equivalent to the intent and scope of the claims should be construed to be included therein.
Claims (6)
1. A method of closing a gap between a fuel pellet and a cladding within a target, the method comprising the steps of:
(1) loading the fuel pellet into a cladding tube, sealing the upper end and the lower end with the cladding tube by vacuum electron beam welding without filling high-purity helium gas to prepare a target;
(2) and putting the target piece into a hot isostatic pressing furnace for hot isostatic pressing treatment, so that the clearance between the fuel pellets in the target piece and the cladding is closed.
2. The method of claim 1, wherein: and (2) in the step (1), after the vacuum electron beam welding, performing helium leak detector detection on the welding seam, and performing pollution degree detection after the surface of the target piece is decontaminated.
3. The method of claim 1, wherein: in the step (1) and the step (2), the fuel pellet is Al-NpO2Fuel pellets or U3Si2-Al fuel pellets.
4. The method of claim 1, wherein: in the step (1) and the step (2), the cladding tube is an aluminum alloy cladding tube.
5. The method of claim 1, wherein: in the step (1) and the step (2), the cladding tube is a 6061 aluminum alloy cladding tube.
6. The method of claim 1, wherein: in the step (2), the hot isostatic pressing treatment temperature is 400-.
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| Application Number | Priority Date | Filing Date | Title |
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| CN201910495310.8A CN110277177B (en) | 2019-06-06 | 2019-06-06 | Method for closing gap between fuel pellet and cladding in target |
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| CN201910495310.8A CN110277177B (en) | 2019-06-06 | 2019-06-06 | Method for closing gap between fuel pellet and cladding in target |
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| CN110277177B true CN110277177B (en) | 2020-11-24 |
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Family Cites Families (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE2842402C2 (en) * | 1978-09-29 | 1982-06-09 | Nukem Gmbh, 6450 Hanau | Process for the production of ceramic fuel pellets for nuclear reactors |
| US5383228A (en) * | 1993-07-14 | 1995-01-17 | General Electric Company | Method for making fuel cladding having zirconium barrier layers and inner liners |
| CN103295652B (en) * | 2012-02-24 | 2017-02-08 | 上海核工程研究设计院 | Nuclear fuel rod with ceramic cladding and metallic pellet |
| CN103345951B (en) * | 2013-06-21 | 2016-05-04 | 中国原子能科学研究院 | (U,Np)O2The preparation technology of transmuting fuel pellet and target part |
| CN103691956B (en) * | 2014-01-03 | 2016-06-22 | 中国原子能科学研究院 | Annular thin wall Al-NpO2The preparation technology of disperse pellet |
| JP2021501335A (en) * | 2017-10-31 | 2021-01-14 | ウエスチングハウス・エレクトリック・カンパニー・エルエルシー | High temperature atomic fuel system for thermal neutron reactors |
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