An apparatus and method for hot cell spent fuel oxidative volatilization

Abstract

The present application belongs to the technical field of spent fuel reprocessing, and particularly relates to a device and method for hot cell spent fuel oxidation and volatilization, which are used for the oxidation and volatilization treatment of spent fuel. The device comprises a sealed heating furnace body (2) arranged in a hot cell and a reaction tank (3) arranged in the heating furnace body (2). The heating furnace body (2) can be remotely controlled outside the hot cell. The device has simple structure and small floor area, and is convenient for operation by a manipulator in the hot cell. By using the device and method, the oxidation of spent fuel and the separation of cladding and powder can be effectively realized, which greatly facilitates the subsequent analysis of the cladding and powder and has important significance for promoting the related research on oxidation and volatilization.

Description

Technical Field

[0001] This invention belongs to the field of spent fuel reprocessing technology, specifically relating to an apparatus and method for the oxidation and volatilization of spent fuel in hot chambers. Background Technology

[0002] In the traditional spent nuclear fuel reprocessing process, during the dissolution of spent fuel, tritium in the fuel undergoes isotopic exchange and is transferred into the dissolution liquid. A reprocessing plant with an annual processing capacity of 800 tons processes approximately 70g of tritium from the spent fuel annually. Assuming all tritium exists in the form of HTO (hydrogenated tritium oxide), the mass of HTO is approximately 500g, with a volume of about 0.5L. However, in the traditional spent fuel reprocessing process, after subsequent treatments, the tritium is ultimately diluted into tens of thousands of cubic meters of low, intermediate, and high-level radioactive wastewater. Currently, for coastal reprocessing plants, tritium-containing nitric acid is recycled, while tritium-containing water is discharged and diluted using ocean currents. For inland reprocessing plants, nitric acid and water in high-tritium areas are reused, while tritium-containing wastewater in low-tritium areas is ultimately discharged into the environment via elevated channels. With increasingly stringent environmental regulations on emissions from nuclear-related plants, taking effective measures to reduce emissions from reprocessing plants into the environment is imperative to ensure the healthy and sustainable development of my country's reprocessing industry.

[0003] Currently, the most economical way to reduce tritium emissions into the environment is to use oxidation volatilization technology at the front end to remove tritium. This involves heating spent fuel to a certain temperature in an oxidizing atmosphere before dissolution, thereby oxidizing the UO2 pellets in the spent fuel into U3O8 powder. At this time, the tritium trapped in the spent fuel will be released and oxidized, and finally volatilized in the form of HTO. By capturing the HTO, tritium can be centrally managed.

[0004] Currently, research on oxidation volatilization is still in the laboratory stage, mainly covering two aspects: thermal experimental research, primarily aimed at obtaining real data on the oxidation volatilization process of spent fuel; and research on oxidation volatilization devices, primarily aimed at providing support for the design of engineering equipment. For thermal experimental research, the equipment used is mostly converters or muffle furnaces. The main disadvantages of converters are the presence of rotating parts and their large size, which are not conducive to installation, maintenance, and transportation within the hot chamber. The main disadvantages of muffle furnaces are poor sealing and the fact that the oxidation reaction must be carried out in a crucible, making it impossible to separate the cladding from the powder during the reaction process. Considering that the tritium content in the cladding and powder needs to be analyzed separately after spent fuel oxidation volatilization, it is necessary to develop new devices and methods to achieve the separation of the cladding and powder during the oxidation volatilization process to simplify subsequent operations. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide an apparatus and method for the oxidation and volatilization of spent fuel in a hot chamber. The apparatus meets the requirements of simple structure and small footprint, and is easy to operate using a robotic arm in the hot chamber. Using this apparatus and method, the oxidation of spent fuel and the separation of the coating and powder can be effectively realized, which greatly facilitates the subsequent analysis of the coating and powder and is of great significance for advancing research related to oxidation and volatilization.

[0006] To achieve the above objectives, the present invention provides a device for the oxidation and volatilization of spent fuel in a hot chamber. The device is used for the oxidation and volatilization treatment of spent fuel, and includes a sealed heating furnace body disposed in the hot chamber and a reaction vessel disposed in the heating furnace body. The heating furnace body can be remotely controlled from outside the hot chamber.

[0007] Furthermore, the heating furnace body is a hollow cylinder with an overall size of less than φ240×270mm. It includes a furnace shell, insulation material disposed on the inner surface of the furnace shell, and a heating element disposed inside the insulation material. The heating element is a resistance wire, and the insulation material is made of refractory brick or glass fiber. An isothermal body is disposed inside the insulation material to ensure uniform temperature distribution in the reaction vessel.

[0008] Furthermore, the reaction vessel includes a vessel body, the bottom of which is sealed, and the upper opening of which extends beyond the heating furnace body. A removable cover is also provided on the upper opening. The dimensions of the vessel body are less than φ50×180mm. The reaction vessel can be removed from the heating furnace body. The entire reaction vessel is made of 316 stainless steel.

[0009] Furthermore, the cover is also provided with an air inlet, a thermocouple interface, and an air outlet. The thermocouple interface is used to connect a thermocouple into the reaction vessel, and the air inlet and the air outlet are used to introduce and discharge reaction gases into the reaction vessel.

[0010] Furthermore, the lid is connected to the tank body by threads, and there are no threads at a position 2-10mm away from the upper opening of the tank body, so as to facilitate the tightening of the lid and ensure the sealing of the reaction tank. The air inlet and the air outlet are φ6mm quick-connect male connectors and are equipped with ball valves. The lid is a regular hexagon and can be gripped by a robotic arm.

[0011] Furthermore, the system includes a removable basket located within the reaction vessel for separating the spent fuel coating from the powder during the oxidation and volatilization process. The basket includes a sieve plate, a supporting ring surrounding the edge of the sieve plate, and a lifting rod mounted on the sieve plate. The bottom end of the lifting rod is fixedly connected to the sieve plate, and its top end is located at the upper opening of the vessel body. The lifting rod is used for transferring the basket, the sieve plate for separating the coating from the powder, and the supporting ring for fixing the coating to the basket. The basket is made entirely of 316 stainless steel. The supporting ring is machined as a single piece. The equivalent diameter of the sieve holes on the sieve plate is 1-3 mm.

[0012] Furthermore, it also includes a controller, which is placed outside the hot chamber and connected to the heating furnace body inside the hot chamber via an electrical connector, and uses a PID method to control the heating furnace body's heating and cooling process.

[0013] Furthermore, a junction box is provided on the outer shell of the heating furnace body, and the controller is connected to the junction box through the electrical connector to realize the heating furnace body's temperature control; a furnace body handle is also provided on the top edge of the heating furnace body.

[0014] To achieve the above objectives, the present invention also discloses a method for the oxidation and volatilization of spent fuel in a hot chamber, which is used in the apparatus described above for the oxidation and volatilization of spent fuel in a hot chamber, comprising the following steps:

[0015] Step S1: Use a robotic arm to select several sections of the spent fuel and place them into the basket inside the reaction vessel. Use the robotic arm to tighten the cover and insert the thermocouple into the thermocouple interface.

[0016] Step S2: Using a robotic arm, connect the air inlet to the air inlet pipe and the air outlet to the air outlet pipe, introduce the reaction gas into the reaction vessel, and start the heating element of the heating furnace body through the controller, so that the temperature inside the reaction vessel rises to the target temperature of 400-600℃.

[0017] Step S3: After maintaining the temperature for 4-8 hours, stop heating;

[0018] Step S4: Once the temperature inside the reaction vessel drops to 100°C, stop introducing the reaction gas.

[0019] Step S5: Use the robotic arm to pull out the thermocouple, the inlet pipe, and the outlet pipe; use the robotic arm to unscrew the cover; use the robotic arm to remove the basket and transfer the whole assembly to the cladding leaching device for subsequent analysis;

[0020] Step S6: After the lid is closed using a robotic arm, the entire reaction vessel is transferred to another hot chamber, and the powder therein is reserved for subsequent analysis.

[0021] further,

[0022] In step S1, the length of the spent fuel is 20-30 mm;

[0023] In step S2, the reaction gas is a mixture of oxygen and nitrogen, with an oxygen volume fraction of 20%-100%.

[0024] In step S5, the basket needs to be slightly shaken before being taken out.

[0025] The beneficial effects of this invention are as follows:

[0026] 1. The main components of the hot chamber spent fuel oxidation and volatilization device provided by the present invention, such as the heating furnace body 2, the reaction vessel 3, and the hanging basket 4, can all be quickly replaced using a robotic arm or special tooling.

[0027] 2. The main components of the hot-chamber spent fuel oxidation and volatilization device provided by the present invention, such as the reaction vessel 3 and the basket 4, are made of stainless steel that is resistant to high temperature and nitric acid, and also has strong radiation resistance.

[0028] 3. The apparatus and method of the present invention can separate the spent fuel coating from the powder without the need for rotating parts, which facilitates subsequent sampling and analysis of the coating and powder.

[0029] 4. Compared with traditional muffle furnaces and converters, the apparatus and method of the present invention have advantages such as small footprint, simple equipment structure, and ease of operation by robotic arms.

[0030] 5. Currently, domestic research on the oxidation and volatilization of spent fuel is in its initial stage. In order to effectively promote the engineering application of the oxidation and volatilization of spent fuel, a large amount of thermal experimental verification work needs to be carried out. This device can provide a good reference for the design of subsequent thermal experimental devices. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of an apparatus for the oxidation and volatilization of spent fuel in a hot chamber, as described in a specific embodiment of the present invention.

[0032] In the diagram: 1-Controller, 2-Heating furnace body, 21-Insulation material, 22-Heating element, 23-Furnace shell, 24-Furnace handle, 25-Gateway box, 3-Reaction vessel, 31-Vat body, 32-Air inlet, 33-Lid, 34-Coefficient interface, 35-Air outlet, 4-Hanging basket, 41-Screen plate, 42-Supporting ring, 43-Lifting rod, 5-Hot chamber wall. Detailed Implementation

[0033] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0034] This invention provides an apparatus for the oxidation and volatilization of spent fuel in a hot chamber (see...). Figure 1 The furnace is used for the oxidation and volatilization treatment of spent fuel, and includes a sealed heating furnace body 2 installed in the hot chamber and a reaction vessel 3 installed in the heating furnace body 2. The heating furnace body 2 can be remotely controlled from outside the hot chamber.

[0035] The heating furnace body 2 is used to provide a suitable temperature for the oxidation and volatilization reaction of spent fuel. To facilitate the transfer and operation inside the heating chamber, it is processed into a hollow cylinder with an overall size of less than φ240×270mm. It includes the furnace shell 23, the insulation material 21 set on the inner surface of the furnace shell 23, and the heating element 22 set inside the insulation material 21. The heating element 22 is a resistance wire, and the insulation material 21 is made of refractory brick or glass fiber. An isothermal body is set inside the insulation material 21 to ensure uniform temperature distribution in the reaction vessel 3.

[0036] The reaction vessel 3 is used to provide an oxidation and volatilization reaction space, including a vessel body 31. The bottom of the vessel body 31 is sealed, and the upper opening of the vessel body 31 extends outside the heating furnace body 2. A removable cover 33 is also provided on the upper opening. The dimensions of the vessel body 31 are less than φ50×180mm. The reaction vessel 3 can be removed from the heating furnace body 2. The entire material of the reaction vessel 3 is 316 stainless steel, which can withstand nitric acid and high temperature.

[0037] The cover 33 is also provided with an air inlet 32, a thermocouple interface 34 and an air outlet 35. The thermocouple interface 34 is used to connect a thermocouple into the reaction vessel 3, and the air inlet 32 ​​and the air outlet 35 are used to introduce and discharge reaction gases into the reaction vessel 3.

[0038] The lid 33 is connected to the tank body 31 by threads. There are no threads at a position about 2-10mm away from the upper opening of the tank body 31 to facilitate the tightening of the lid 33 and ensure the sealing of the reaction tank 3 (the reaction tank 3 has a slight negative pressure: ~400Pa). The air inlet 32 ​​and the air outlet 35 are φ6mm quick-connect male connectors and are equipped with ball valves. The lid 33 is a regular hexagon and can be gripped by a robotic arm.

[0039] It also includes a removable basket 4 installed inside the reaction vessel 3, used to separate the spent fuel coating from the powder during the oxidation and volatilization process; the basket 4 includes a sieve plate 41, a supporting ring 42 arranged around the edge of the sieve plate 41, and a lifting rod 43 arranged on the sieve plate 41; the bottom end of the lifting rod 43 is fixedly connected to the sieve plate 41, and the top end is located at the upper opening of the vessel body 31; the lifting rod 43 is used for transferring the basket 4, the sieve plate 41 is used for separating the coating from the powder, and the supporting ring 42 is used to fix the coating on the basket 4; the basket 4 is made of 316 stainless steel, which can withstand nitric acid and high temperature; the supporting ring 42 is machined as a whole to avoid excessive deformation at high temperature; the equivalent diameter of the sieve holes on the sieve plate 41 is 1-3mm.

[0040] It also includes a controller 1, which is placed outside the hot chamber and connected to the heating furnace 2 inside the hot chamber via an electrical connector. The controller 1 uses PID control to control the heating furnace 2’s heating and cooling process, thereby realizing remote control of the heating furnace 2.

[0041] A junction box 25 is provided on the outer shell of the heating furnace body 2. The controller 1 is connected to the junction box 25 through an electrical connector to realize the heating and cooling control of the heating furnace body 2. A furnace body handle 24 is also provided on the top edge of the heating furnace body 2.

[0042] The present invention also discloses a method for the oxidative volatilization of spent fuel in a hot chamber, which is used in an apparatus for the oxidative volatilization of spent fuel in a hot chamber as described above, comprising the following steps:

[0043] Step S1: Use a robotic arm to select several segments of spent fuel (short segments) and place them into the basket 4 inside the reaction vessel 3. Use the robotic arm to tighten the cover 33 and insert the thermocouple into the thermocouple interface 34.

[0044] Step S2: Using a robotic arm, connect the air inlet 32 ​​to the air inlet pipe and the air outlet 35 to the air outlet pipe (the air inlet pipe and the air outlet pipe are connected to an external air source for the circulation supply of reaction gas), introduce reaction gas into the reaction tank 3, and start the heating element 22 of the heating furnace body 2 through the controller 1, so that the temperature inside the reaction tank 3 rises to the target temperature of 400-600℃.

[0045] Step S3: After maintaining the temperature for 4-8 hours, stop heating;

[0046] Step S4: Once the temperature inside the reaction vessel 3 drops to 100°C, stop introducing the reaction gas.

[0047] Step S5: Use a robotic arm to pull out the thermocouple, inlet pipe and outlet pipe; use a robotic arm to unscrew the cover 33; use a robotic arm to remove the basket 4 and transfer the whole thing to the cladding leaching device for subsequent analysis;

[0048] In step S6, after the cover 33 is closed using a robotic arm, the entire reaction vessel 3 is transferred to another hot chamber, and the powder inside is reserved for subsequent analysis.

[0049] In step S1, the length of the spent fuel is 20-30 mm;

[0050] In step S2, the reaction gas is a mixture of oxygen and nitrogen, with an oxygen volume fraction of 20%-100%.

[0051] In step S5, the basket 4 needs to be slightly shaken before being taken out.

[0052] The device described in this invention is not limited to the embodiments described in the specific implementation. Other implementation methods derived by those skilled in the art based on the technical solution of this invention also fall within the scope of technical innovation of this invention.

Claims

1. An apparatus for the oxidative volatilization of spent fuel in a hot chamber, characterized in that: The system includes a sealed heating furnace body (2) housed in a hot chamber and a reaction vessel (3) housed within the heating furnace body (2). The heating furnace body (2) can be remotely controlled from outside the hot chamber. It also includes a removable basket (4) housed within the reaction vessel (3) for separating the spent fuel coating from the powder during the oxidation and volatilization process. The heating furnace body (2), the reaction vessel (3), and the basket (4) can all be quickly replaced using a robotic arm. The reaction vessel (3) includes a tank body (31) with a sealed bottom and an upper opening extending beyond the heating furnace body (2). A removable cover (33) is provided on the upper opening. The basket (4)... The device includes a sieve plate (41), a supporting ring (42) arranged around the edge of the sieve plate (41), and a lifting rod (43) arranged on the sieve plate (41). The bottom end of the lifting rod (43) is fixedly connected to the sieve plate (41), and the top end is located at the upper opening of the tank body (31). The lifting rod (43) is used for transferring the basket (4), the sieve plate (41) is used for separating the shell from the powder, and the supporting ring (42) is used to fix the shell on the basket (4). The basket (4) is made of 316 stainless steel. The supporting ring (42) is processed as a whole. The equivalent diameter of the sieve holes on the sieve plate (41) is 1-3 mm.

2. The apparatus for the oxidation and volatilization of spent fuel in a hot chamber as described in claim 1, characterized in that: The heating furnace body (2) is a hollow cylinder with an overall size of less than φ240×270mm. It includes a furnace shell (23), a heat insulation material (21) on the inner surface of the furnace shell (23), and a heating element (22) inside the heat insulation material (21). The heating element (22) is a resistance wire. The heat insulation material (21) is made of refractory brick or glass fiber. An isothermal body is provided inside the heat insulation material (21) to ensure that the temperature distribution of the reaction vessel (3) is uniform.

3. The apparatus for the oxidation and volatilization of spent fuel in a hot chamber as described in claim 2, characterized in that: The tank (31) is smaller than φ50×180mm; the reaction tank (3) can be removed from the heating furnace (2); the reaction tank (3) is made of 316 stainless steel.

4. The apparatus for the oxidation and volatilization of spent fuel in a hot chamber as described in claim 3, characterized in that: in The cover (33) is also provided with an air inlet (32), a thermocouple interface (34) and an air outlet (35). The thermocouple interface (34) is used to connect a thermocouple into the reaction vessel (3). The air inlet (32) and the air outlet (35) are used to introduce and discharge reaction gases into the reaction vessel (3).

5. The apparatus for the oxidation and volatilization of spent fuel in a hot chamber as described in claim 4, characterized in that: The lid (33) is connected to the tank body (31) by a thread. There is no thread at a position 2-10mm away from the upper opening of the tank body (31) to facilitate the tightening of the lid (33) and ensure the sealing of the reaction vessel (3). The air inlet (32) and the air outlet (35) are φ6mm quick-connect male connectors and are equipped with ball valves. The lid (33) is a regular hexagon and can be gripped by a robotic arm.

6. The apparatus for the oxidation and volatilization of spent fuel in a hot chamber as described in claim 5, characterized in that: It also includes a controller (1), which is placed outside the hot chamber and connected to the heating furnace body (2) inside the hot chamber via an electrical connector. The controller (1) controls the heating furnace body (2)’s heating and cooling process using a PID method.

7. The apparatus for the oxidation and volatilization of spent fuel in a hot chamber as described in claim 6, characterized in that: A junction box (25) is provided on the outer shell of the heating furnace body (2). The controller (1) is connected to the junction box (25) through the electrical connector to realize the heating furnace body (2) temperature control. A furnace body handle (24) is also provided on the top edge of the heating furnace body (2).

8. A method for the oxidative volatilization of spent fuel in a hot chamber, used in an apparatus for the oxidative volatilization of spent fuel in a hot chamber as described in claim 7, comprising the following steps: Step S1: Use a robotic arm to select several sections of the spent fuel and place them into the basket (4) inside the reaction vessel (3). Use the robotic arm to tighten the cover (33) and insert the thermocouple into the thermocouple interface (34). Step S2: Using a robotic arm, connect the air inlet (32) to the air inlet pipe and the air outlet (35) to the air outlet pipe, introduce the reaction gas into the reaction tank (3), and start the heating element (22) of the heating furnace body (2) through the controller (1) so that the temperature in the reaction tank (3) rises to the target temperature of 400-600℃; Step S3: After maintaining the temperature for 4-8 hours, stop heating; Step S4: When the temperature inside the reaction vessel (3) drops to 100°C, stop the flow of the reaction gas; Step S5: Use the robotic arm to pull out the thermocouple, the inlet pipe and the outlet pipe; use the robotic arm to unscrew the cover (33); use the robotic arm to remove the basket (4) and transfer the whole to the cladding leaching device for subsequent analysis; In step S6, after the cover (33) is closed using a robotic arm, the reaction vessel (3) is transferred as a whole to another hot chamber, and the powder therein is reserved for subsequent analysis.

9. A method for the oxidative volatilization of spent fuel in a hot chamber as described in claim 8, characterized in that: exist In step S1, the length of the spent fuel is 20-30 mm; In step S2, the reactant gas is a mixture of oxygen and nitrogen, with an oxygen volume fraction of 20%-100%. In step S5, the basket (4) needs to be shaken slightly before it is taken out.

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