Modular high-temperature gas cooled reactor and method for producing high-purity 238Pu

Abstract

The invention provides a modular high-temperature gas cooled reactor and method for producing high-purity 238Pu. The modular high-temperature gas cooled reactor comprises a pebble bed formed by randomly stacking spherical fuel elements, and a graphite reactor internal component, a carbon reactor internal component, a metal reactor internal component and a pressure container are sequentially arranged outside the pebble bed; the graphite stack internal component comprises a top reflecting layer positioned at the top, a bottom reflecting layer positioned at the bottom and a side reflecting layer on the peripheral side; wherein the side reflecting layer is provided with a plurality of control rod hole channels, absorption ball hole channels, cold helium hole channels and 238Pu irradiation hole channels. The 238Pu irradiation hole channels are formed in the side reflection layer made of graphite, the characteristics that the thermal neutron fluence rate of the side reflection layer made of graphite is high, and the proportion of fast neutrons with the energy higher than 6.8 MeV is limited are utilized, production of 238Pu is achieved, and the purity of 238Pu is not lower than 95%.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of radioisotope reactor irradiation production, and particularly relates to a modular high-temperature gas-cooled reactor for producing high-purity 238 Pu and a method thereof. BACKGROUND

[0002] 238 Pu is an isotope of plutonium, but in the current production process, by neutron irradiation 237 Np can produce 238 Pu, but the reactor irradiation 237 Np will generate 236 Pu side reactions when the neutron energy is higher than 6.8 MeV, 236 Pu decay produces strong gamma radiation of the daughter 212 Bi and 208 Ti, because the penetration of strong gamma radiation is extremely strong, which will cause 238 Pu products are difficult to apply. SUMMARY

[0003] The present application aims to at least solve one of the technical problems in the related art. The present application provides a modular high-temperature gas-cooled reactor for producing high-purity 238 Pu and a method thereof. The present application sets up 238 Pu irradiation channels in the graphite composition side reflection layer, uses the characteristics that the graphite composition side reflection layer has a high thermal neutron flux and a limited proportion of fast neutrons with energy higher than 6.8 MeV, realizes the production of 238 Pu, and 238 The purity of the Pu is not less than 95%.

[0004] According to the embodiment of the first aspect of the present application, a modular high-temperature gas-cooled reactor for producing high-purity 238 Pu is provided, which comprises a spherical bed composed of randomly stacked spherical fuel elements, and a graphite in-pile component, a carbon in-pile component, a metal in-pile component and a pressure vessel are sequentially arranged outside the spherical bed.

[0005] The graphite in-pile component comprises a top reflection layer located at the top, a bottom reflection layer located at the bottom and a side reflection layer located at the periphery; and a plurality of control rod channels, absorption sphere channels, cold helium channels and 238 Pu irradiation channels are arranged on the side reflection layer.

[0006] In some embodiments, the plurality of cold helium channels, the plurality of control rod channels and the plurality of absorption sphere channels are uniformly dispersed on the periphery of the spherical bed with the axis of the spherical bed as the center.

[0007] At the same time, the control rod channel is located between the cold helium channel and the ball bed; a plurality of the absorption ball channels are evenly dispersed between the plurality of the control rod channels and are at the same distance from the center of the axis of the ball bed.

[0008] In some embodiments, the 238 The size and position of the Pu irradiation channel are determined according to the irradiation target and the required neutron energy spectrum.

[0009] In some embodiments, the 238 The method for determining the size and position of the Pu irradiation channel is as follows:

[0010] Step 1: First, set the side reflective layer 238 Pu irradiated channel;

[0011] Step 2: According to the setting of the side reflection layer 238 The Pu irradiation channel is combined with the structure and material parameters of the irradiation target and the design parameters of the modular high-temperature gas-cooled reactor, and the Monte Carlo program is used to model and calculate the 238 The neutron energy spectrum in the Pu irradiation channel is compared with the calculated neutron energy spectrum. If it is "unsuitable", return to step 1; if it is "suitable", proceed to step 3;

[0012] Step 3: According to the 238 The size and position of the Pu irradiation channel are calculated using the theoretical formula 238 Pu and 236 The output of Pu; 238 Pu and 236 The output of Pu is compared with the target output. If it is not suitable, return to step 1; until the suitable output is output in step 3. 238 Pu and 236 Calculated yield of Pu.

[0013] In some embodiments, the comparison standard between the neutron spectrum calculated in step 2 and the standard neutron spectrum is a thermal neutron fluence rate of 3×10 13 n.cm -2 .s -1 , and the proportion of fast neutron fluence above 6.8MeV is less than 1 / 10000.

[0014] In some embodiments, the calculated value in step 3 238 Pu and 236 The comparison standard between Pu production and target production is 238 The content of Pu in each gram of target is 0.02g at equilibrium. 236 The content of Pu in each gram of target is less than 0.0002g;

[0015] In some embodiments, the irradiation target comprises a solid 237 NpO2.

[0016] According to a second aspect of the present application, there is provided a method for producing high purity 238 Pu using the modular high temperature gas cooled reactor as described in any of the above embodiments, wherein the purity of the 238 Pu is not less than 95%.

[0017] In some embodiments, the method for producing high purity 238 Pu comprises the following steps:

[0018] Step 1: first set the 238 Pu irradiation channel in the side reflector layer;

[0019] Step 2: according to the 238 Pu irradiation channel set in the side reflector layer, combined with the structure and material parameters of the irradiation target and the design parameters of the modular high temperature gas cooled reactor, the neutron spectrum in the 238 Pu irradiation channel is calculated using the Monte Carlo program modeling, and the calculated neutron spectrum is compared with the standard neutron spectrum. If it is not suitable, it returns to step 1; if it is suitable, it proceeds to step 3;

[0020] Step 3: according to the size and position of the 238 Pu irradiation channel, the yield of 238 Pu and 236 Pu is calculated using theoretical formula; the yield of 238 Pu and 236 Pu is compared with the target yield. If it is not suitable, it returns to step 1; until step 3 outputs the calculated yield of 238 Pu and 236 Pu that is suitable.

[0021] Step 4: put the irradiation target into the 238 Pu irradiation channel for production.

[0022] In some embodiments, the irradiation target comprises a solid 237 NpO2.

[0023] Additional aspects and advantages of the present application will be in part apparent and in part pointed out hereinafter. BRIEF DESCRIPTION OF DRAWINGS

[0024] The above and / or additional aspects and advantages of the present application will become apparent and be readily appreciated from the following description, including the appended drawings, wherein:

[0025] Figure 1It is a structural schematic diagram of a pebble bed modular high temperature gas-cooled reactor in the related art;

[0026] Figure 2 yes Figure 1 Another perspective structure diagram;

[0027] Figure 3 According to one embodiment of the present application, a high-purity 238 Flowchart of Pu's method. DETAILED DESCRIPTION

[0028] The following describes embodiments of the present application in detail. Examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended only to explain the present application and are not to be construed as limiting the present application. On the contrary, this application includes all variations, modifications, and equivalents that fall within the spirit and scope of the appended claims.

[0029] This application is based on the following technical improvements: 238 Pu is an isotope of plutonium with a specific half-life (about 87 years) and radioactive properties. 238 Pu can generate significant heat through radioactive decay, so it can be used as a heat source for nuclear batteries and generate energy for spacecraft such as satellites and spacecraft; 238 Pu is not only a heat source for nuclear batteries, but also an important power source for space nuclear power and spacecraft, such as the Viking probe, the Voyager probe and the Curiosity Mars rover, all of which use 238 Pu nuclear battery as energy source. High purity 238 Pu is also used in the medical field, especially in the production of pacemakers. As human beings expand their exploration of the solar system and deep space, the demand for Pu is increasing. 238 The demand for Pu is also increasing.

[0030] However, in the current production process, a modular high-temperature gas-cooled reactor is used to irradiate the 237 Np can produce 238 Pu, among which the modular high temperature gas-cooled reactor is a new type of reactor with the characteristics of the fourth generation of nuclear power. Its core structure can be simply described as a pebble bed in the middle of the core composed of randomly stacked spherical fuel elements. This modular high temperature gas-cooled reactor can be called a pebble bed modular high temperature gas-cooled reactor. Outside the pebble bed are graphite internal components, carbon internal components, metal internal components, pressure vessels, etc. Figure 1The Pebble Bed Modular High Temperature Gas-cooled Reactor (PBR) uses graphite as the moderator, structural material and reflector. Graphite not only has good thermal stability and mechanical strength, but more importantly, it has a high neutron moderation ratio and a low neutron absorption cross-section, which means that neutrons can be efficiently slowed down to the thermal neutron energy region in graphite, increasing the collision probability of nuclear fuels with a larger neutron capture cross-section, thereby improving the chain reaction efficiency of the reactor. Especially in the side reflector composed of graphite internal components, such as Figure 2 Since the side reflector is at a certain distance from the pebble bed core, the neutrons can be further moderated, so the energy of the neutrons is lower, and there are very few neutrons with energy above 6.8 MeV. Therefore, there is a good irradiation environment in the side reflector.

[0031] In addition, the neutron irradiation 237 Np can produce 238 Pu This process involves a series of nuclear reactions and decay steps, 238 Pu production reaction chain is as follows:

[0032] Among them 237 Np absorbs a neutron and is converted into 238 Np, 238 Np undergoes beta decay and releases an electron to become 238 Pu.

[0033] Although the principle of producing 238 Pu by reactor irradiation is relatively simple, but in actual operation, it faces many challenges. When 237 Np is irradiated by a reactor, when the neutron energy is higher than 6.8 MeV, the side reaction 236 Pu will be generated, such as the side reaction of 237 Np to produce 236 Pu when irradiated by a reactor, the side reaction chain is as follows:

[0034] But when 237 Np is irradiated by a reactor, when the neutron energy is higher than 6.8 MeV, the side reaction 236 Pu will be generated, 236 Pu decay produces strong γ radiation of daughter 212 Bi and 208 Ti, because the penetration of strong γ radiation is extremely strong, which will cause 238 Pu products are difficult to apply.

[0035] Based on this, the technical scheme of the embodiment of the application provides a kind of production high purity 238The module type high temperature gas cooled reactor and method of Pu, by setting the isotope irradiation hole in the reflector of the module type high temperature gas cooled reactor, using the characteristics of high thermal neutron flux and limited proportion of fast neutrons with energy higher than 6.8 MeV, realizing the production of high purity 237 Np can produce high purity 238 Pu and almost no by-product Pu-236 is generated.

[0036] The ranges disclosed herein are defined by the lower and upper limits of the range, and the ranges are defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of the particular range. The ranges defined in this manner can include or exclude the end values, and can be arbitrarily combined, i.e., any lower limit can be combined with any upper limit to form a range. For example, if the ranges 60-120 and 80-110 are listed for a particular parameter, it is understood that the ranges 60-110 and 80-120 are also contemplated. In addition, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4 and 5 are listed, the following ranges are all contemplated: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In this application, unless otherwise stated, the numerical range "a-b" indicates a shorthand way of describing all the real combinations between a and b, where a and b are both real numbers. For example, the numerical range "0-5" indicates that all the real numbers between "0-5" have been listed herein, and "0-5" is just a shorthand representation of these numerical combinations. In addition, when a parameter is stated to be ≥2 integers, it is equivalent to disclose that the parameter is, for example, integer 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0037] In the description of the embodiments of the present application, the term "and / or" is only a description of the association relationship of the associated objects, which means that there can be three relationships, for example, A and / or B, which means that there are three cases of A alone, A and B together, and B alone. In addition, the character " / " in this paper generally represents that the front and rear associated objects are in an "or" relationship.

[0038] According to the embodiments of the first aspect of the present application, a method for producing high purity 238 The module type high temperature gas cooled reactor of Pu includes a spherical bed randomly stacked by spherical fuel elements, and a graphite internal structure, a carbon internal structure, a metal internal structure and a pressure vessel are sequentially arranged outside the spherical bed;

[0039] The graphite internal structure includes a top reflector at the top, a bottom reflector at the bottom, and a side reflector at the side; wherein the side reflector is provided with a plurality of control rod holes, absorbing ball holes, cold helium holes and 238 Pu irradiation holes.

[0040] Among them, the production of high purity in this application 238 Pu's modular high-temperature gas-cooled reactor includes a pebble bed, outside which graphite internals, carbon internals, metal internals and a pressure vessel are arranged in sequence; wherein the pebble bed is formed by randomly stacking spherical fuel elements, such as Figure 1 As shown, the pebble bed is a cylindrical structure extending vertically. Furthermore, the graphite stack internals are constructed of graphite, serving as a moderator, structural material, and reflector. According to the structure of a modular high-temperature gas-cooled reactor, when the graphite stack internals serve as reflectors, they include a top reflector layer, a bottom reflector layer, and side reflectors. The side reflectors are provided with multiple control rod channels, absorber ball channels, and cold helium gas channels. This is similar to the structure of a modular high-temperature gas-cooled reactor in related art and will not be further described.

[0041] In particular, in the side reflector composed of the graphite pile components, since the side reflector is at a certain distance from the pebble bed, the neutrons can be further slowed down, so the neutron energy is lower, and rarely has an energy above 6.8MeV. Therefore, there is a better irradiation environment in the side reflector, and isotope irradiation channels can be set to produce high-purity 238 Pu, almost no by-products 236 Therefore, in this application, multiple side reflection layers composed of graphite stack components are provided. 238 Pu irradiated channels to generate high purity 238 Pu.

[0042] In some embodiments, 238 The size and position of the Pu irradiation channel are determined according to the irradiation target and the required neutron energy spectrum.

[0043] Right now 238 The size and position of the Pu irradiation channel need to be determined according to the irradiation target, where the irradiation target can be solid 237 NpO2 and 238 The size and position of the Pu irradiation channel are also related to the required neutron energy spectrum and 238 Confirmation of the impact of Pu irradiation production on modular high-temperature gas-cooled reactors.

[0044] In some embodiments, multiple cold helium gas channels, multiple control rod channels, and multiple absorption ball channels are all centered on the axis of the ball bed and are evenly dispersed around the ball bed; at the same time, the control rod channels are located between the cold helium gas channels and the ball bed; and the multiple absorption ball channels are evenly dispersed between the multiple control rod channels and are at the same distance from the center of the axis of the ball bed.

[0045] That is, multiple cold helium gas channels are evenly distributed around the pebble bed, centered on the pebble bed axis. In other words, the pebble bed axis extends in the vertical direction, and the multiple cold helium gas channels also extend in the vertical direction. Within a plane, with any point on the pebble bed axis as the center point, the multiple cold helium gas channels are evenly distributed around this center point, and all cold helium gas channels are at the same distance from this center point.

[0046] At the same time, multiple control rod holes are evenly distributed around the pebble bed, centered on the pebble bed axis. In other words, the pebble bed axis extends in the vertical direction, and so do the multiple control rod holes. Within a plane, with any point on the pebble bed axis as the center point, the multiple control rod holes are evenly distributed around that center point, with all control rod holes being the same distance from that center point.

[0047] Furthermore, the multiple absorption ball channels are evenly distributed around the ball bed, centered around the ball bed axis. In other words, the ball bed axis extends vertically, and so do the multiple absorption ball channels. Within a plane, with any point on the ball bed axis as the center point, the multiple absorption ball channels are evenly distributed around that center point, with all absorption ball channels being the same distance from that center point.

[0048] In some embodiments, 238 The method for determining the size and position of the Pu irradiation channel is as follows:

[0049] Step 1: Set up in the side reflection layer first 238 Pu irradiated channel;

[0050] Step 2: According to the settings in the side reflection layer 238 The Pu irradiation channel is combined with the structure and material parameters of the irradiation target and the design parameters of the modular high-temperature gas-cooled reactor, and the Monte Carlo program is used to model and calculate 238 The neutron energy spectrum in the Pu irradiation channel is compared with the calculated neutron energy spectrum. If it is "unsuitable", return to step 1; if it is "suitable", proceed to step 3;

[0051] Step 3: According to 238 The size and position of the Pu irradiation channel are calculated using the theoretical formula 238 Pu and 236 The output of Pu; 238 Pu and 236 The output of Pu is compared with the target output. If it is not suitable, return to step 1; until the suitable output is output in step 3. 238 Pu and 236 Calculated yield of Pu.

[0052] In step 1, by irradiating the target, the required neutron energy spectrum and 238Pu irradiation production impact on modular high temperature gas cooled reactor setup 238 Pu irradiation hole size and location.

[0053] To achieve the best production efficiency, the neutron spectrum in the modular high temperature gas cooled reactor needs to be precisely regulated and the neutron spectrum in the Pu irradiation hole needs to be precisely calculated according to the setup in step one. 238 Pu irradiation hole size and location, irradiation target and material parameters and modular high temperature gas cooled reactor pebble bed design parameters, using Monte Carlo program (such as MCNP), modeling calculation 238 Pu irradiation hole neutron spectrum.

[0054] The calculated neutron spectrum is compared with the standard neutron spectrum, wherein the comparison standard is that the thermal neutron fluence rate is 3x10 13 n.cm -2 .s -1 , and the share of fast neutron fluence rate above 6.8 MeV is less than 1 / 10000. When the comparison result of the neutron spectrum calculated in step two with the standard neutron spectrum is "not suitable", return to step one, and adjust 238 Pu irradiation hole size and location, until iteration to the "suitable" calculated neutron spectrum output in step two; when the "suitable" calculated neutron spectrum output in step two, proceed to step three.

[0055] Step three, according to the irradiation hole size and location output in step one and the "suitable" calculated neutron spectrum output in step two, using theoretical formula to calculate the calculated 238 Pu and 236 Pu production; compare the 238 Pu and 236 Pu production with the target production, the comparison standard of the 238 Pu and 236 Pu production calculated in step three with the target production is that 238 Pu production and the share of by-product 236 Pu, wherein the comparison standard of the 238 Pu and 236 Pu production calculated in step three with the target production is that 238 Pu balance content in each gram of target is 0.02g, 236 Pu content in each gram of target is less than 0.0002g; when the comparison is "not suitable", return to step one to adjust the size and location of the irradiation hole; until the step three output the suitable 238 Pu and 236 Pu calculated production.

[0056] According to the second aspect of the present application, a method for producing high purity 238 Pu is proposed, such as Figure 3, the production is performed by using the modular high temperature gas cooled reactor in any of the above embodiments, 238 The purity of Pu is not less than 95%.

[0057] In some embodiments, the high purity 238 The method for producing Pu comprises the following steps:

[0058] Step one: first set up 238 Pu irradiation channels in the side reflection layer

[0059] Step two: according to the setting of 238 Pu irradiation channels in the side reflection layer, combined with the structure and material parameters of the irradiation target and the design parameters of the modular high temperature gas cooled reactor, physical modeling is performed by using the general Monte Carlo program in the field of reactor design (such as MCNP, RMC, etc.), the neutron energy spectrum in the 238 Pu irradiation channel is calculated, the neutron flux in the target is obtained, and the calculated neutron energy spectrum is compared with the standard neutron energy spectrum, and the comparison standard of the calculated neutron energy spectrum and the standard neutron energy spectrum is that the thermal neutron flux is 3×10 13 n·cm -2 .s -1 Left and right, and the share of fast neutron flux above 6.8 MeV is less than 1 / 10000; if not suitable, return to step one; if suitable, proceed to step three.

[0060] Step three: according to the size and position of 238 Pu irradiation channel, the production of 238 Pu and 236 Pu is calculated by using the production yield theoretical calculation formula of reactor irradiated isotopes; the production of 238 Pu and 236 Pu is compared with the target yield, and if not suitable, return to step one; until the calculated yield of 238 Pu and 236 Pu in step three is suitable.

[0061] Step four: put the irradiation target into 238 Pu irradiation channel for production.

[0062] In some embodiments, the irradiation target comprises solid 237 NpO2,

[0063] The present application provides a modular high temperature gas cooled reactor and a method for producing high purity 238 Pu, the present application sets up 238 Pu irradiation channels in the side reflection layer composed of graphite, and by using the characteristics of the side reflection layer composed of graphite, i.e. high thermal neutron flux and limited proportion of fast neutrons with energy higher than 6.8 MeV, the production of 238 Pu is realized, and238 The purity of Pu is not less than 95%.

[0064] To facilitate further understanding of the present application, the present invention is further described below in conjunction with the embodiments. Those skilled in the art will understand that the descriptions in the present application are only partial examples, and any other suitable specific examples are within the scope of the present application.

[0065] As an example of this method, the neutron source channel in the side reflector of the high temperature gas-cooled reactor nuclear power plant demonstration project (HTR-PM) is used as 238 Pu irradiation channel, the irradiated target is solid 237 In the middle of the reactor active area, the neutron flux rate of more than 6.8 MeV in this channel is only 4.0×10 7 n / (cm 2 ·s), and the thermal neutron flux rate is less than 5.0×10 13 n / (cm 2 ·s). Calculated 238 The content of Pu in each gram of target is about 0.0175g at equilibrium. 236 The content of Pu in each gram of target is only 0.000184g, so 238 The theoretical purity of Pu can reach about 95%. Compared with the purity of less than 80% in other reactors, the production method of this patent has achieved high purity, which will be beneficial to 238 The application of Pu is especially in the biomedical field.

[0066] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification and features of different embodiments or examples without contradiction.

[0067] Although the embodiments of the present application have been shown and described above, it can be understood that the above embodiments are exemplary and cannot be understood as limitations on the present application. Ordinary technicians in this field can change, modify, replace and modify the above embodiments within the scope of the present application.

Claims

1. A modular high-temperature gas-cooled reactor for producing high-purity 238Pu, characterized in that: The fuel cell comprises a pebble bed formed by randomly stacking spherical fuel elements, and graphite internal components, carbon internal components, metal internal components and a pressure vessel are sequentially arranged outside the pebble bed. The graphite stack internal components include a top reflection layer at the top, a bottom reflection layer at the bottom, and side reflection layers on the surrounding sides; wherein the side reflection layers are provided with a plurality of control rod channels, absorption ball channels, cold helium channels, and 238Pu irradiation channels.

2. The modular high-temperature gas-cooled reactor according to claim 1, characterized in that: The plurality of cold helium gas channels, the plurality of control rod channels and the plurality of absorption ball channels are all centered on the axis of the ball bed and are evenly distributed around the circumference of the ball bed; At the same time, the control rod channel is located between the cold helium channel and the ball bed; a plurality of the absorption ball channels are evenly dispersed between the plurality of the control rod channels and are at the same distance from the center of the axis of the ball bed.

3. The modular high-temperature gas-cooled reactor according to claim 1, characterized in that: The size and position of the 238Pu irradiation channel are determined according to the irradiation target and the required neutron energy spectrum.

4. The modular high-temperature gas-cooled reactor according to any one of claims 1 to 3, characterized in that: The method for determining the size and position of the 238Pu irradiation channel is as follows: Step 1: firstly set the 238Pu irradiation channel in the side reflection layer; Step 2: Based on the 238Pu irradiation channel set in the side reflector, the structural and material parameters of the irradiation target, and the design parameters of the modular high-temperature gas-cooled reactor, a Monte Carlo model is used to calculate the neutron energy spectrum in the 238Pu irradiation channel, and the calculated neutron energy spectrum is compared with the standard neutron energy spectrum. If it is "unsuitable", return to step 1; if it is "suitable", proceed to step 3; Step three; according to the size and position of the 238Pu irradiation channel, the yield of 238Pu and 236Pu is calculated using a theoretical formula; the yield of 238Pu and 236Pu is compared with the target yield, and if "unsuitable", the process returns to step one; until the calculated yield of 238Pu and 236Pu is outputted appropriately in step three.

5. The modular high-temperature gas-cooled reactor according to claim 4, characterized in that: The comparison criteria between the neutron energy spectrum calculated in step 2 and the standard neutron energy spectrum are that the thermal neutron fluence rate is 3×10 13 n.cm -2 .s -1 , and the proportion of the fast neutron fluence rate greater than 6.8 MeV is less than 1 / 10000.

6. The modular high-temperature gas-cooled reactor according to claim 4, characterized in that: The yields of 238Pu and 236Pu calculated in step 3 are compared with the target yields based on the following criteria: the content of 238Pu in each gram of target is 0.02g at equilibrium, and the content of 236Pu in each gram of target is less than 0.0002g.

7. The modular high-temperature gas-cooled reactor according to claim 4, characterized in that: The irradiation target includes solid 237NpO2.

8. A method for producing high-purity 238Pu, characterized in that: The modular high-temperature gas-cooled reactor according to any one of claims 1 to 7 is used for production, and the purity of the 238Pu is not less than 95%.

9. The method according to claim 8, characterized in that The steps include: Step 1: firstly set the 238Pu irradiation channel in the side reflection layer; Step 2: Based on the 238Pu irradiation channel set in the side reflector, the structural and material parameters of the irradiation target, and the design parameters of the modular high-temperature gas-cooled reactor, a Monte Carlo model is used to calculate the neutron energy spectrum in the 238Pu irradiation channel, and the calculated neutron energy spectrum is compared with the standard neutron energy spectrum. If it is "unsuitable", return to step 1; if it is "suitable", proceed to step 3; Step 3: Calculate the yields of 238Pu and 236Pu using a theoretical formula based on the size and position of the 238Pu irradiation channel; compare the yields of 238Pu and 236Pu with the target yields; if the yields are "not suitable", return to step 1 until the appropriate calculated yields of 238Pu and 236Pu are output in step 3; Step 4: Put the irradiated target into the 238Pu irradiation channel for production.

10. The method according to claim 8, characterized in that The irradiation target includes solid 237NpO2.

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