Neutron hospital reactor

Abstract

The present invention relates to a neutron hospital reactor, which comprises a core placed in a water tank. The water tank is arranged in a pool, and both inside and outside the water tank are light water coolants. The core includes fuel assemblies and control rods, and the core is surrounded by a graphite reflector. Among them, an operation bridge is provided at the top of the water tank, and a target / fuel assembly handling mechanism is provided on the operation bridge. The target / fuel assembly handling mechanism is connected to the core through a target handling conduit. Target irradiation grids are respectively arranged at the four corners of the core, and isotope production targets are arranged in the target irradiation grids. A neutron beam pipe is further arranged outside the core along the tangential direction of the core side surface. The present invention has the function of co-producing isotopes and neutron beams. A lower power level can effectively reduce the complexity of the reactor safety system and the construction cost, so that it can be permitted to be arranged near densely populated areas.

Description

Technical Field

[0001] The present invention relates to the technical field of reactors, and in particular to a small medical fission reactor, which can be used for the production of medical isotopes (such as Mo-99, I-131) and provide neutron beams for neutron therapy at the same time to achieve Boron Neutron Capture Therapy (BNCT). Background Art

[0002] Nuclear medical technology is a technology for diagnosing or treating lesions in a patient's body through artificial radioactivity. Artificial radioactivity is mainly introduced into the patient's body through two ways. One way is to inject a radioactive isotope preparation (nuclear medicine) into the patient's body, and image the lesion through the decay of the radioactive isotope in the lesion area, and then achieve diagnosis or directly perform treatment. For example, Mo-99 / Tc-99m can be used for imaging of human organs such as the heart, brain, kidney, and lung. Another example is that Lu-177 can be used for targeted treatment of neuroendocrine tumors and prostate cancer. The other way is to directly irradiate the human body from the outside with a radiation source, and by reasonably modulating the energy deposition of the ray in the body, the purpose of killing the lesion cells and retaining healthy cells as much as possible is achieved, such as gamma knife (γ-ray), proton therapy (proton), boron neutron capture therapy (neutron), etc. The principle of nuclear medicine technology is relatively mature. While continuous progress has been made in diagnostic and treatment drugs and means, how to stably and timely provide medical isotopes or radiation sources for treatment to patients has always been an unsolved problem, which also greatly limits the development and application of nuclear medicine to a large extent.

[0003] The production of medical isotopes mainly comes from reactors and accelerators. At present, the isotopes produced by reactors are mainly provided by a few research reactors in the world, and their powers range from several megawatts to dozens of megawatts. The existing power levels and volumes determine that the current reactor types are not suitable for being arranged near patients and medical centers, which in turn leads to decay losses during the transportation of isotopes. Moreover, this single-reactor centralized production mode is prone to unstable supply due to planned / unplanned reactor shutdowns or conflicts in scientific research tasks, resulting in patients being unable to receive timely diagnosis and treatment. The isotopes produced by accelerators are several orders of magnitude lower in yield than those produced by reactors, and due to physical properties, it is difficult to mass-produce neutron-rich isotopes, which cannot meet the needs of the rapidly growing medical isotope market. Similarly, the radiation source can also come from a reactor or an accelerator. As a radiation source, in addition to the problem of being difficult to be arranged near the population mentioned above, there are relatively large time and operation costs for starting up and shutting down the reactor before and after each beam output. Moreover, due to the physical limitation of the "iodine pit", the time interval between two start-ups and shut-downs may be as long as 20 to 30 hours. Although the accelerator can be turned on as needed as a radiation source, it can only extract proton or heavy ion beams, and each accelerator device can only extract one beam, resulting in low equipment utilization efficiency.

[0004] In summary, the reactor generates a high neutron flux (10 12 ~10 14 n / cm 2 s), which is very suitable for the production of neutron-rich isotopes (such as Mo-99) and neutron therapy (BNCT). However, existing reactors have never been designed specifically for medical applications. The power level and structural volume determine that they cannot be deployed near the population, are not optimized for possible medical uses, or have too low power to provide only limited neutron beam channels, cannot take into account isotope production, and need to be frequently started and stopped according to treatment needs. These shortcomings limit the application of reactor technology in medical diagnosis and treatment. Summary of the invention

[0005] The purpose of the present invention is to address the deficiencies of the prior art and provide a small medical reactor system with the function of co-production of isotopes and neutron beams. The lower power level can effectively reduce the complexity of the reactor's safety system and the construction cost, thereby allowing it to be deployed near densely populated areas.

[0006] The technical solution of the present invention is as follows: a neutron hospital reactor, comprising a core placed in a water tank, wherein the water tank is arranged in a water pool, and light water coolant is present inside and outside the water tank. The core comprises a fuel assembly and a control rod, and the core is surrounded by a graphite reflective layer, wherein an operating bridge is provided on the top of the water tank, and a target / fuel assembly picking and delivering mechanism is provided on the operating bridge, and the target / fuel assembly picking and delivering mechanism is connected to the core through a target picking and delivering guide tube, and target irradiation grids are respectively provided at the four corners of the core, and isotope production targets are provided in the target irradiation grids.

[0007] Furthermore, in the neutron hospital reactor as described above, the outer side of the core also includes a neutron beam duct arranged along the tangent direction of the core side surface; the neutron beam duct is arranged outside the water tank in the water pool, and the terminal outlet of the neutron beam duct directly leads to the BNCT treatment room.

[0008] Furthermore, the neutron beam conduit includes a thermal neutron beam conduit and an epithermal neutron beam conduit, and on the side of the core where the epithermal neutron beam conduit is arranged, the outermost graphite blocks of the graphite reflective layer are replaced with aluminum blocks.

[0009] Furthermore, a thermal neutron filter and energy spectrum modulation structure is provided at the end of the thermal neutron beam pipeline, and an epithermal neutron filter and energy spectrum modulation structure is provided at the end of the epithermal neutron beam pipeline.

[0010] Furthermore, for the neutron hospital reactor described above, the size of the target irradiation grid is the same as that of the core fuel assembly. Each target irradiation grid is evenly divided into four parts, with a cross-section in the shape of a Chinese character 'tian' (field), and four isotope production targets are arranged inside the grid.

[0011] Furthermore, for the neutron hospital reactor described above, the fuel assembly is a square-column fuel assembly, and plate-shaped fuel elements are inserted into the fuel assembly.

[0012] Furthermore, the fuel element is a low-enriched uranium fuel with a U-235 enrichment not higher than 20 w%.

[0013] The manufacturing material of the low-enriched uranium fuel can be U3Si2 or metallic uranium. Among them, the fuel made of metallic uranium can further meet the requirement that the U-235 enrichment is not higher than 5 w%.

[0014] Furthermore, for the neutron hospital reactor described above, the material of the isotope production target can be selected from U3Si2 or metallic uranium, and the U-235 loading in the target is less than the U-235 loading in the fuel element.

[0015] Furthermore, for the neutron hospital reactor described above, a hot water layer is constructed above the core coolant in the water tank, so as to reduce the contact between the core coolant and the upper air.

[0016] Furthermore, for the neutron hospital reactor described above, the core includes an emergency shutdown rod. The emergency shutdown rod is controlled by an emergency rod-drop device to hover above the core during normal operation of the reactor. In the case of power failure, the emergency rod-drop device releases, and the emergency shutdown rod automatically inserts into the core by gravity to ensure that the core is in a deep subcritical state.

[0017] Furthermore, for the neutron hospital reactor described above, the core also includes a fine adjustment rod. The reactivity worth per unit length of the fine adjustment rod is smaller than that of an ordinary control rod, and it is used to compensate for the reactivity perturbations caused by target replacement and the opening and closing of the neutron beam channel.

[0018] Furthermore, for the neutron hospital reactor described above, the control rod and the fine adjustment rod are controlled by a control rod drive mechanism installed on the operation bridge.

[0019] Furthermore, for the neutron hospital reactor described above, the outside of the water pool is a concrete shielding structure, and a lining that can prevent corrosion and rust and achieve the neutron reflection effect is arranged on the inner side of the concrete shielding structure.

[0020] Furthermore, for the neutron hospital reactor described above, the stable operating power of the reactor is 30 kW to 2.5 MW, and the preferred stable operating power is 1 MW; the neutron flux level is 6×1011 ~5×10 13 n / cm 2 s, preferably the neutron flux level is 2×10 13 n / cm 2 s.

[0021] The beneficial effects of the present invention are as follows:

[0022] 1) According to the relevant regulations of "Classification of Research Reactor Safety (Trial)", for low-power reactors, "it is not necessary to consider or simplify the fifth layer of defense and even the fourth layer of defense as much as possible". Through the preliminary calculation of the source term, safety characteristics and radioactive release consequences, and considering the pool-type design, the "neutron hospital reactor" with a power level of 1 megawatt provided meets the classification criteria of Class III research reactors by the national nuclear safety regulatory department, has high inherent safety characteristics, and does not require a dedicated core cooling system. Thus, it will bring a large number of safety and economic benefits such as the simplification of the safety system and the reduction of the overall cost of the reactor system.

[0023] 2) The device has both an isotope production target grid and a neutron beam channel, and can carry out isotope production and BNCT treatment simultaneously. The reactor power of 1 megawatt can provide a neutron flux of not less than 2×10 13 n / cm 2 s, which can fully support these two design functions. Further, due to the surplus of neutrons, the traditional radial neutron extraction channel can be changed to tangential, which can reduce the contamination of γ-rays (mainly propagating along the radial direction) in the beam, simplify the γ-shielding design, reduce the harmful dose received by the patient, and still ensure that the neutron flux at the beam outlet reaches 1×10 9 n / cm 2 s required for BNCT treatment.

[0024] 3) The isotope production grid in the device is located at the four corners of the core. The neutron flux here is relatively low, and the introduction of the target has little impact on the neutron physics characteristics of the core. Moreover, since the volume of the target is only 1 / 4 of that of the fuel element, the impact of a single target on the whole reactor is even smaller. By reasonably arranging the introduction order and time interval of each target, the replacement time nodes of each target can be staggered. In this way, on the premise of only replacing one target at a time, the disturbances of the core reactivity and flux distribution can be effectively compensated by control rods or fine adjustment rods, and the continuous production of isotopes can be maintained without shutting down the reactor. Furthermore, it also enables a continuous neutron beam output from the neutron beam channel, making the treatment arrangement of BNCT more flexible. Brief Description of the Drawings

[0025] Figure 1 It is a schematic structural diagram of the reactor vessel according to a specific embodiment of the present invention;

[0026] Figure 2 Schematic top view structure of the core of a specific embodiment of the present invention.

[0027] In the figure: 1. Target / fuel assembly handling mechanism; 2. Reactor operation bridge; 3. Core (main) coolant; 4. Pool; 5. Core water tank cladding; 6. Target handling conduit; 7. Pool lining; 8. Concrete shielding structure; 9. Core; 10 and 11. Thermal neutron beam pipes; 12 and 13. Epithermal neutron beam pipes; 14 and 15. Thermal neutron beam filtering and energy spectrum modulation materials; 16 and 17. Epithermal neutron beam filtering and energy spectrum modulation materials; 18. Aluminum block; 19. Graphite block; 20. Fuel assembly; 21. Emergency shutdown rod; 22. Isotope production target; 23. Control rod; 24. Fine adjustment rod. Specific embodiments

[0028] In order to make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0029] The core component of the present invention is a small pool-type reactor with a thermal power of 1 MW, adopting an in-pool water tank layout. The reactor core is placed in a water tank, and the water tank is set in a pool. The reactor is cooled by light water without a circulation loop, and the heat of the reactor core is exported through natural circulation. A hot water layer is arranged above the core (main) coolant in the water tank to prevent the coolant from directly contacting the air above. The fuel elements of the reactor core are low-enriched uranium fuels with a U-235 enrichment not higher than 20 w%. The manufacturing materials of the low-enriched uranium fuels can be U3Si2 or metallic uranium. Among them, the fuel made of metallic uranium can further meet the requirement that the U-235 enrichment is not higher than 5 w%. The fuel assembly is square-columnar and internally equipped with plate-shaped fuel elements. Medical isotope production target grids are reserved at the four corners of the reactor core, and each grid is divided into four parts, that is, each target is only 1 / 4 the size of the fuel assembly. There are two configurations for the periphery of the reactor core according to the actual use of the reactor. I) Isotope production configuration: The reactor core is surrounded by a graphite reflector layer on all sides. II) Isotope and neutron beam co-production configuration: The reflector layer of the reactor core is composed of graphite and aluminum blocks. Outside the water tank cladding on the outer side of the reactor core, four neutron beam pipes are arranged along the tangential directions of the four sides of the reactor core respectively. The inlets of the neutron beam pipes are near the reactor core, and the outlets are outside the concrete shielding structure of the pool. Two of them are thermal neutron beam pipes, and the other two are epithermal neutron beam pipes, which are respectively used for superficial treatment and deep treatment of BNCT. The device does not shut down during the nuclear fuel refueling cycle, and makes the most of the neutron flux in the reactor to continuously produce medical isotopes. When performing neutron therapy on patients, the reserved irradiation channels can be opened at any time to lead out neutron beams. Isotope production and neutron therapy do not interfere with each other. At the same time, the device can be dispersed and deployed in multiple places as needed, forming mutual backups in the realization of the nearby supply of isotopes and radiation sources, and establishing a complete and reliable nuclear medical resource guarantee system.

[0030] Embodiment

[0031] Such as Figure 1As shown, a neutron hospital reactor adopts a water tank layout in a pool, that is, the core 9 and the target delivery pipeline 6 are placed in an aluminum inner cladding water tank 5, and the inner cladding water tank 5 is placed in a water pool 4. The coolant 3 inside and outside the water tank 5 is light water, and the water depth is 10 meters, which can effectively shield the core radioactivity, especially for neutron radiation. The outside of the water pool 4 is a concrete shielding structure 8, and a lining 7 is arranged inside the concrete shielding structure 8. The lining material is aluminum, stainless steel, beryllium, etc. that can prevent corrosion and rust and realize the neutron reflection effect of the outer periphery of the water tank. Under normal working conditions, the operating bridge 2 forms a closure on the inner cladding water tank 5, which can effectively reduce the radioactive carryover caused by the evaporation of the core coolant. At the same time, a hot water layer about 1.5 meters thick will be constructed above the core coolant in the water tank 5 (the water temperature is about 5 degrees Celsius higher than the coolant temperature), so as to further reduce the chance of the core coolant contacting the air above and reduce radiation carryover. The replacement of core fuel assemblies and targets is achieved through the pick-up and delivery drive mechanism 1 and the target pick-up and delivery guide tube 6 on the operating bridge. The coolant circulation inside and outside the water tank 5 is driven by natural convection, not by power input, avoiding the extra cost and safety hazards caused by the water pump drive circulation, so that the reactor meets the passive safety requirements.

[0032] The core of the reactor is composed of 16 square cylindrical fuel assemblies 20, each of which is 8 cm long and 100 cm high. Plate-shaped fuel elements are inserted into the fuel assemblies. Compared with rod-shaped fuel elements, plate-shaped fuel elements can effectively increase the heat exchange area with the coolant. In order to reduce the enrichment of U-235 in the fuel as much as possible, the low-enriched uranium fuel of the present invention can be made of two materials, namely U3Si2 and metallic uranium. The uranium loading of U3Si2 material can reach 4.8 g / cm 3 , can produce low-enriched uranium fuel with an enrichment of ≤20w%; the uranium loading of metallic uranium materials can reach 19g / cm 3 , it is possible to produce low-enriched uranium fuel with an enrichment of ≤5w%, further reducing the fuel enrichment (equivalent to the enrichment of the fuel used in nuclear power plants). The core is surrounded by a graphite reflector 19, and on the side where epithermal neutrons need to be drawn out, aluminum blocks are used to replace the outermost graphite blocks. The core side length is 75 cm. The core design of this reactor has a large negative reactivity feedback coefficient and under-moderated neutron moderation characteristics, which ensures that the reactor can automatically suppress power until shutdown in major accidents such as power increase and moderator loss. In order to ensure a sufficiently large backup shutdown margin, this embodiment also specially designs two emergency shutdown rods 21 for the core. The emergency shutdown rods 21 are controlled by an emergency rod drop device (which can be an electromagnetic mechanism) to hover above the core when the reactor is operating normally. In the event of a power outage, the emergency rod drop device is released, and the emergency shutdown rods 21 will automatically insert into the core under the action of gravity to ensure that the core is in a deep subcritical state.

[0033] The reactivity control under normal reactor operating conditions mainly relies on 4 control rods 23 and 1 fine adjustment rod 24, which are realized by the action of the control rod drive mechanism installed on the operation bridge. The reactivity worth per unit length of the fine adjustment rod 24 is smaller than that of the control rod 23, and it is used to compensate for the reactivity perturbations caused by the replacement of the target and the opening and closing of the neutron beam channel. In addition to the common scenarios such as reactor startup, shutdown, and power regulation, the insertion and removal of the isotope production target 22 will also affect the neutronics characteristics of the core, so it is necessary to adjust the control rods for compensation. One of the major design features of this reactor is that the target can be replaced without shutting down the reactor, thereby achieving the goal of continuously producing isotopes and being able to withdraw the neutron beam for BNCT treatment at any time. The target replacement is carried out through the conduit 6, that is, the target is put into the core or taken out of the core along the pipeline 6 by the lifting mechanism. In order to minimize the impact of target replacement on the core reactivity and neutron flux distribution as much as possible, the target irradiation grid is designed at the four corners of the core. The neutron flux here is relatively low, and the impact on the overall performance of the core is also relatively small. For the convenience of design and construction as well as subsequent core adjustment, the size of the irradiation grid is designed to be the same as that of the fuel assembly 20. The internal space of the irradiation grid is divided into four equal parts in a "field" shape, and each isotope production target 22 actually only has a volume equivalent to 1 / 4 of the fuel assembly, and thus only equivalent to 1 / 80 of the entire core. The in-core irradiation production of isotopes mainly relies on the separation from the fission products generated during the fission of U-235. Therefore, the effective material in the target is the same as that in the fuel, which is U-235. The material of the target can be selected in the form of U3Si2 or in the form of metallic U. Due to the temperature limitation when the target is irradiated, the loading amount of U-235 in the target is less than that of the fuel element. Considering all the above factors, when each target is replaced, the perturbation of the core neutronics characteristics is very limited, and these perturbations can be completely compensated by the movement of the control rods or the fine adjustment rod, thus making it possible to replace the target online during the reactor operation. The specific target replacement strategy needs to be determined according to the actual application scenario of this reactor.

[0034] Scenario I: When the reactor is only used for isotope production, the irradiated targets can be introduced or replaced at equal time intervals. Taking the production of Mo-99 as an example, considering the accumulation rate of impurities approaching saturation in Mo-99, the optimal irradiation time of a single target in the core is about 9 days. There are 16 targets in the core according to the design. Therefore, each target can be introduced and replaced at an equal time interval of 12 hours. This can ensure that only one target needs to be replaced each time, minimizing the impact on the core.

[0035] Scenario II: When the reactor is used for isotope production and neutron therapy (BNCT) simultaneously, the target replacement still follows the above principles. However, during the neutron therapy beam output process, in order to minimize the beam intensity fluctuations, the operation of replacing the target needs to be suspended. After the treatment is completed, the target operation can be resumed. Although this cannot guarantee the optimal irradiation time of the target and achieve the highest isotope production efficiency, it is crucial for ensuring the stable and controllable dose of neutron therapy.

[0036] The way of extracting the neutron beam of this reactor is different from that of the existing dedicated BNCT reactor. The main difference lies in that the existing technical solution extracts neutrons in the radial direction, that is, the neutron beam channel is directly aligned with the reactor core. This technical solution can utilize the neutrons in the reactor to the greatest extent, but it results in a large amount of γ-rays being doped in the beam, causing difficulties and increasing costs for the shielding of harmful rays in the subsequent section. The stable operating power of this reactor is 30 kW to 2.5 MW, and the preferred value is 1 MW; the neutron flux level is 6×10 11 ~5×10 13 n / cm 2 s, and the preferred value is 2×10 13 n / cm 2 s. Both the reactor power and the neutron flux level are greater than the design indicators of the existing dedicated BNCT reactor types, and the amount of neutrons generated in the reactor core is about 30 times that of the existing technical solution. Therefore, this reactor selects to extract neutrons in the tangential direction of the reactor core, thereby significantly reducing the harmful γ-rays from the reactor core. This reactor is equipped with neutron extraction channels in four tangential directions on the outer side of the reactor core. Figure 2 On the left and right sides in the middle are thermal neutron beam pipes 10 and 11, and on the front and back sides are epithermal neutron beam pipes 12 and 13. The neutron extraction channels are arranged outside the water tank in the main pool, surrounding the periphery of the reactor core, and the terminal outlets of the channels lead directly to the BNCT treatment room. At the ends of the channels, there are respectively thermal neutron filtration and energy spectrum modulation structures 14 and 15, and epithermal neutron filtration and energy spectrum modulation structures 16 and 17. For the extraction of thermal neutrons, the light water in the pool can effectively slow down the neutrons leaking from the reactor core, and through scattering, a considerable part of the neutrons can be led out of the reactor along the channel direction. For the extraction of epithermal neutrons, this reactor replaces the outermost graphite blocks of the graphite reflector layer with aluminum blocks in the reactor core reflector layer, and uses an aluminum block 18 as a water squeezer outside the reactor core (that is, an aluminum block 18 is arranged outside the epithermal neutron beam pipe) to minimize the probability of neutrons being slowed down and keep them at a higher energy. The utilization rate of neutrons extracted tangentially is lower than that extracted radially, especially for epithermal neutrons. However, through calculation, even for epithermal neutrons, the neutron flux at the beam outlet end can still meet the requirements of BNCT treatment.

[0037] The small medical reactor system provided by the present invention has a relatively low power level, which can effectively reduce the complexity of the safety system and construction costs, allowing it to be deployed near densely populated areas. At the same time, the reactor has the characteristics of co-producing isotopes and neutron beams, thus maximizing the utilization of neutrons in the reactor to provide medical services for the population in the nearby areas.

[0038] Those skilled in the art will readily conceive of other embodiments of the present invention after considering the specification and practicing the invention disclosed herein. This application is intended to cover any variations, uses, or adaptations of the present invention, which follow the general principles of the present invention and include known common general knowledge or conventional technical means in the technical field not disclosed in the present invention. Thus, if these variations, uses, and adaptations of the present invention fall within the scope of the claims of the present invention and their equivalent technologies, the present invention is also intended to include these modified and adapted variations.

[0039] The above-described embodiments are merely illustrative examples of the present invention. The present invention can also be implemented in other specific ways or other specific forms without departing from the gist or essential features of the present invention. Therefore, the described embodiments should be considered illustrative rather than restrictive in any aspect. The scope of the present invention should be defined by the appended claims, and any changes equivalent to the intention and scope of the claims should also be included within the scope of the present invention.

Claims

1. A neutron hospital reactor, comprising a core (9) placed in a water tank (5), the water tank (5) being arranged in a pool (4), with light water coolant both inside and outside the water tank, the core (9) comprising fuel assemblies (20) and control rods (23), and the core (9) being surrounded by a graphite reflector layer (19), characterized in that, An operation bridge (2) is provided at the top of the water tank (5), and a target / fuel assembly handling mechanism (1) is provided on the operation bridge (2). The target / fuel assembly handling mechanism (1) is connected to the reactor core (9) through a target handling conduit (6). Target irradiation grids are respectively arranged at the four corners of the reactor core (9), and isotope production targets (22) are arranged in the target irradiation grids. On the outer side of the reactor core (9), there is also a neutron beam pipe arranged along the tangential direction of the reactor core side. The neutron beam pipe is arranged outside the water tank (5) in the water pool (4), and the terminal outlet of the neutron beam pipe leads directly to the BNCT treatment room.

2. The neutron hospital reactor according to claim 1, characterized in that, The neutron beam pipe includes a thermal neutron beam pipe (10, 11) and an epithermal neutron beam pipe (12, 13). On the side of the reactor core where the epithermal neutron beam pipe (12, 13) is arranged, the outermost graphite blocks of the graphite reflector are replaced with aluminum blocks (18).

3. The neutron hospital reactor according to claim 2, characterized in that, Thermal neutron filtering and energy spectrum modulation structures (14, 15) are provided at the ends of the thermal neutron beam pipes (10, 11), and epithermal neutron filtering and energy spectrum modulation structures (16, 17) are provided at the ends of the epithermal neutron beam pipes (12, 13).

4. The neutron hospital reactor according to claim 1, characterized in that, The size of the target irradiation grid is the same as that of the reactor core fuel assembly. Each target irradiation grid is evenly divided into four parts, with a cross-section in the shape of a field character, and four isotope production targets are arranged in the grid.

5. The neutron hospital reactor according to claim 1, characterized in that, The fuel assembly (20) is a square-column fuel assembly, and plate-shaped fuel elements are inserted in the fuel assembly.

6. The neutron hospital reactor according to claim 5, characterized in that, The fuel element is a low-enriched uranium fuel with a U-235 enrichment not higher than 20 w%.

7. The neutron hospital reactor according to claim 6, characterized in that, The manufacturing material of the low-enriched uranium fuel is U3Si2 or metallic uranium.

8. The neutron hospital reactor according to claim 7, characterized in that, The material of the isotope production target (22) is selected from U3Si2 or metallic uranium, and the loading amount of U-235 in the target is less than the loading amount of U-235 in the fuel element.

9. The neutron hospital reactor according to claim 1, characterized in that, A hot water layer is constructed above the reactor core coolant (3) in the water tank to reduce the contact between the reactor core coolant and the upper air.

10. The neutron hospital reactor according to claim 1, characterized in that, The reactor core includes an emergency shutdown rod (21). During normal operation of the reactor, the emergency shutdown rod (21) is controlled by an emergency rod-drop device to hover above the reactor core. In the case of power failure, the emergency rod-drop device is released, and the emergency shutdown rod (21) automatically inserts into the reactor core by gravity to ensure that the reactor core is in a deep subcritical state.

11. The neutron hospital reactor according to claim 1, characterized in that, The reactor core also includes a fine adjustment rod (24) for micro-reactivity compensation during target replacement or neutron beam extraction.

12. The neutron hospital reactor according to claim 11, wherein, The control rod (23) and the fine adjustment rod (24) are controlled by a control rod drive mechanism installed on the operation bridge.

13. The neutron hospital reactor according to claim 1, characterized in that, The outside of the water pool (4) is a concrete shielding structure (8), and a lining (7) that can prevent corrosion and rust and achieve neutron reflection is provided on the inner side of the concrete shielding structure (8).

14. The neutron hospital reactor according to any one of claims 1-13, characterized in that, The stable operating power of the reactor is 30 kW to 2.5 MW; the neutron flux level is 6×10 11 ~5×10 13 n / cm 2 s.

15. The neutron hospital reactor according to claim 14, characterized in that, The stable operating power of the reactor is 1 MW; the neutron flux level is 2×10 13 n / cm 2 s.

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