CA3212782A1 - Reactor core system and gas-cooled micro reactor - Google Patents

Abstract

A reactor core system (6), comprising a reactor core, a reflective layer and a rotary drum control rod (2), wherein the reactor core, which is transversely arranged, comprises a plurality of fuel assemblies (1), and the plurality of fuel assemblies (1) are arranged according to a radial partition and in an axial layered manner; the reflective layer wraps outside the reactor core; the rotary drum control rod (2) is arranged in the reflective layer; a central graphite belt (5) is arranged in the reactor core, and the central graphite belt (5) is arranged in a vertical direction; an absorption body ball channel (4) is arranged in the central graphite belt (5), and the absorption body ball channel (4) is vertically arranged and penetrates the reflective layer; and an absorption body ball is arranged in the absorption body ball channel (4). The reactor core system (6) is small in size and convenient to transport.

Description

REACTOR CORE SYSTEM AND GAS-COOLED MICRO-REACTOR
[0001] The disclosure claims priority of Chinese patent application No.
202110333122.2, entitled "A REACTOR CORE SYSTEM OF A MODULAR LATERAL PRISMATIC
GAS-COOLED MICRO-REACTOR" filed on March 29, 2021 in the China National Intellectual Property Administration.
TECHNICAL FIELD

[0002] The disclosure relates to the field of nuclear reactor engineering technologies, and in particular, to a reactor core system and a gas-cooled micro-reactor adopting the reactor core system.
BACKGROUND

[0003] The rapid development of economy improves demands on the energy, but the traditional fossil fuels such as coal bring serious environmental problems.
This prompts various countries to continuously explore and develop clean energies, continuously optimize the existing energy structure and reduce the proportion of the fossil fuels in the energies. Among various types of new energies, nuclear energy has advantages of cleanliness, high energy density, little emission of greenhouse gases, and low fuel transportation pressure, for example. In recent years of the 21st century, the nuclear energy has been continuously developed to be an important option for improving energy structure, and further enhanced in the strategy of energy development. By the end of September 2018, China's 44 reactors had reached a net installed capacity of 40.7 GWe, accounting for 10% of the world's installed nuclear power capacity, while China also has the most nuclear power plants under construction.

[0004] At present, the existing high-temperature gas-cooled reactor design all around the world is based on a fixed immovable reactor core. The reactor core is large in size, which generally has a diameter of more than 5m and a height of more than 10m and which is suitable for a nuclear power station. Meanwhile, more auxiliary systems and dedicated safety facilities need to be equipped, which occupy a large space.
Components I

of the reactor core need to be manufactured and processed in the factories at an early stage and are transported separately to the application site. A large number of components such as fuel assemblies, reflectors, and control rods can reach a normal operation state only after long-time installation and debugging on site. It is difficult to meet requirements of container transportation, simple and convenient assembly and rapid deployment under special application situations.
SUMMARY

[0005] In order to solve the above problems existing in the related arts, the present disclosure provides a reactor core system, which is small in size and convenient for transportation, and also provides a gas-cooled micro-reactor employing the above reactor core system, which is movable and high in flexibility and adaptability.

[0006] In a first aspect, the present disclosure provides a reactor core system, which includes fuel assemblies, neutron absorber balls, reflectors, and rotary drum control rods, wherein the fuel assemblies are transversely arranged, the number of the fuel assemblies is multiple, the fuel assemblies are sequentially arranged to form a reactor core, the reflectors wrap outside the reactor core, the rotary drum control rods are arranged in the reflector, a central graphite belt is arranged in the reactor core, the central graphite belt is arranged in a vertical direction and extends along a length direction of the reactor core, neutron absorber ball channels are arranged in the central graphite belt, the neutron absorber ball channels are vertically arranged and penetrates through the reflector, and the neutron absorber balls are arranged in the neutron absorber ball channels.

[0007] In a second aspect, the present disclosure further provides a gas-cooled micro-reactor, which includes a reactor core system and auxiliary equipment, wherein the reactor core system employs the reactor core system as set forth above.

[0008] The disclosure has beneficial effects compared to the related arts:

[0009] The reactor core system according to the disclosure has a whole shape highly matched with the shape of the container, and can reduce the occupied space of an assorted auxiliary system and reduce the size of the reactor core system by arranging the rotary drum control rods and vertically arranging the neutron absorber ball channels. The reactor core system with this structure can well-disposed in the common container for the transportation and can meet the requirements of container transportation, simple and convenient assembly and rapid deployment under the special application scenes.
Further, since the fuel assemblies adopt the modularized structure, the assembling can be completed in a factory and the long-time field installation and debugging can be avoided.

[0010] The gas-cooled micro-reactor according to the disclosure has the advantages of small size, convenience in movement, high flexibility and adaptability and capability of realizing rapid deployment due to the adoption of the reactor core system.
BRIEF DESCRIPTION OF DRAWINGS

[0011] FIG. 1 is diagram illustrating a radial arrangement of a fuel assembly containing burnable poison rods in a reactor core system according to an embodiment of the disclosure;

[0012] FIG. la is diagram illustrating a radial arrangement of the fuel assembly without the burnable poison rod in a reactor core system according to an embodiment of the disclosure;

[0013] FIG. 2 is a diagram illustrating a radial arrangement of a reactor core where an neutron absorber ball channel is located according to an embodiment of the disclosure;

[0014] FIG. 3 is a diagram illustrating a radial arrangement of a reactor core where a central graphite belt is located according to an embodiment of the disclosure;

[0015] FIG. 4 is a schematic cross-sectional view taken along an axial direction of the central graphite belt according to an embodiment of the disclosure;

[0016] FIG. 5 is a graph illustrating a gas-cooled micro-reactor burnup characteristic according to an embodiment of the disclosure;

[0017] FIG. 6 is a power distribution diagram of a zero burnup reactor core assembly normalized based on an average power of assemblies, when rotary drum control rod absorbers face outward, according to an embodiment of the disclosure; and

[0018] FIG. 7 is a gas-cooled micro-reactor according to an embodiment of the disclosure.

[0019] In the figures: 1 represents a fuel assembly; 2 represents a rotary drum control rod; 3 represents a side reflector; 4 represents a neutron absorber ball channel; 5 represents a central graphite belt; 6 represents a reactor core system, 7 represents a compartment; 8 represents a graphite block; 9 represents a helium gas storage tank; 10 represents a helium fan 10; 11 represents an instrument box; 12 represents a rotary drum control rod drive mechanism; 101 represents a fuel rod; 102 represents a coolant passage;

103 represents a burnable poison rod; 104 represents a beryllium oxide rod; 11 represents a first fuel assembly; and 12 represents a second fuel assembly.
DETAIL DESCRIPTION OF EMBODIMENTS

[0020] In order for those skilled in the art to better understand the technical solutions, the disclosure will be further described in detail hereinafter with reference to the accompanying figures and embodiments.

[0021] First Embodiment

[0022] As shown in FIGS. 2 to 4, the present embodiment discloses a modular transverse prismatic gas-cooled micro-reactor core system, which includes a plurality of modular structures such as fuel assemblies 1, a rotary drum control rod 2, a neutron absorber ball, a reflector; the reflector includes a front reflector, a rear reflector and a side reflector 3, and the front reflector, the rear reflector and the side reflector 3 jointly encompass a reactor core formed by the fuel assembly 1; the rotary drum control rod 2 is arranged on the side reflector 3; the reactor core is provided with a central graphite belt 5;
the central graphite belt 5 is provided with a neutron absorber ball channel 4 in which the neutron absorber ball is arranged.

[0023] In this embodiment, the fuel assemblies 1 are arranged in 9 layers in an axial direction within a radial zone. For convenience of description, taking the center of the reactor core as an origin, x represents an axial direction, and y and z represent radial directions. There are 28 complete fuel assemblies being arranged in the radial direction of the reactor core, wherein 4 burnable poison rods 103 having a diameter of lcm and an absorber material of gadolinium are arranged in the fuel assemblies at four positions of (1, 1), (1, -1), (-1, 1) and (-1, -1), respectively; on a radial diameter where y=0, there are arranged 7 groups of incomplete fuel assemblies, including 14 fuel rods 101, 8 beryllium oxide rods 104 and 6 coolant channels 102. The whole reactor core has an axial length of 3.4m and a radial diameter of 2.1 m.

[0024] A central graphite belt having a width of 8.4cm is arranged at the center of the reactor core where y is equal to 0 (y=0), and 5 neutron absorber ball channels having a radius of 3.9cm are arranged on the central graphite belt along the axial direction x. 8 groups of control drums are arranged in the side reflector of the reactor core, and the neutron absorber is a one-third circular ring having an inner diameter of 12.5cm and an outer diameter of 14.5 cm. The rotary drum control rod is used for compensating reactivity variation, hot shutdown and the like caused by temperature change, xenon-samarium poison, fuel consumption, for example; the neutron absorber ball is used for further cold shutdown of the reactor core after the rotary drum control rod realizes the hot shutdown. The cold shutdown of the reactor core can also be realized independently.

[0025] The number of fuel rods 101 in fuel assemblies 1 close to the central graphite belt 5 is less than that of fuel rods 101 in fuel assemblies 1 remote from the central graphite belt 5.

[0026] As shown in FIG. la, the fuel assembly 1 is provided with fuel rods 101, coolant channels 102 and beryllium oxide rods 104 arranged regularly at intervals to enhance moderation. Specifically, the fuel assembly 1 is provided with fuel rod channels in which the fuel rods 10 are arranged, and the coolant channels 102 are used for flowing coolant.
In some embodiments, as shown in FIG. 1, a burnable poison rod 103 may also be disposed in the fuel assembly 1 close to the central graphite belt 5. The burnable poison rod 103 may adopt a split type arrangement; the coolant flowing in the coolant channels 102 may be helium which is single phase inert gas; the fuel assembly 1 may be a square graphite fuel assembly. Each fuel assembly 1, which may have a side length of 21cm and a height of 31cm, includes 24 fuel rods 101, 9 coolant channels; if the burnable poison rods 103 are provided, as shown in FIG. 1, 12 beryllium oxide rods 104 having a diameter of lcm are arranged in the fuel assembly; if there are no burnable poison rods 103, 16 beryllium oxide rods 104 are arranged in the fuel assembly, as shown in FIG. la.

[0027] The fuel rods 101 are in cylindrical shape, each of the fuel rods containing a plurality of fuel pellets, preferably 8 fuel pellets stacked in the axial direction. The fuel pellets are formed from a plurality of coated fuel particles dispersed in a graphite or ceramic matrix. The structure of the fuel particles includes a fuel kernel and a plurality of coating layers, preferably UO2 fuel kernel with an enrichment degree of 8.5% and four coating layers of coating fuel particles. A diameter of the fuel particles is about hundreds of micrometers. The material of the fuel kernel includes one or more of UO2, UCO or UN; the material of the coating layers includes one or more of graphite, SiC
or ZrC.
Therefore, the fuel pellet adopts micro-encapsulation, particularly ceramic micro-encapsulation, so that the release of fission products can be effectively prevented.

[0028] A neutron absorber material (including the neutron absorber ball and the neutron absorber on rotary drum control rods) includes B4C; in addition to the neutron absorber material, the neutron absorber ball includes a cladding which is coated outside the material of neutron absorber, wherein a cladding material includes stainless steel. The neutron absorber on the rotary drum control rod is in a partial annular shape.

[0029] In this embodiment, the reflector material includes graphite or Be0.

[0030] The reactor core in the technical scheme of the embodiment consists of square fuel assemblies, and the adopted fuel type is ceramic micro-packaging fuel, so that fission products can be effectively prevented from being released and the fuel is prevented from being corroded. The adopted coolant is helium which is single-phase inert gas. Neutron moderator including graphite and Be0, also serving as a reactor core structure material and a reflector material, has advantages of large heat capacity, high temperature resistance, high thermal conductivity, high moderation ratio and small thermal neutron absorption section, for example, The reactor core has an inherent safety of automatically realizing hot shutdown only by means of temperature negative feedback under the accidental conditions. The rotary drum control rod and the neutron absorber ball not only can effectively control the reactivity and ensure the security of the reactor core, but also can save the space so that the reactor core system and the reactor can be arranged in a common container for transportation.

[0031] The graphite reactor core adopted in the embodiment has large heat capacity, slow temperature transient state, and capability of bearing a high temperature and a large margin of emergency operation time. The reactor core has a small power density and a strong temperature negative feedback, and can realize automatic hot shutdown only by means of the temperature negative feedback under the accidental conditions even if no emergency measures exist, thereby physically avoiding possibilities of melting of the reactor core and release of radioactive substances. Due to the modular design, the system of a nuclear power plant can be simplified, thereby reducing the production cost, improving the manufacturing quality of parts, reducing the operation of personnel, and lowering the accidental risk. The miniaturization design can further reduce the power and the power density of the reactor core and improve the security of the reactor core.

[0032] Hereinafter, the effects of this embodiment will be described in detail by taking graphite as the material of the reactor core and the reflector, B4C as the neutron absorber material, and gadolinium as the burnable poison material.

[0033] The modular transverse prismatic gas-cooled micro-reactor core system according to the embodiment has a design life of 1 year and a design power of 5MW. In the service life, when the control rod is drawn out, a radial power peak factor is about 1.25, an axial power distribution is in a cosine function form, and an axial power peak factor is about 1.29. The reactor core is provided with two independent shutdown rod groups, so that cold shutdown and hot shutdown can be realized. The reactor core has the strong temperature negative feedback, and a temperature negative reactivity coefficient at least reaches -5 pcm/K or more. A huge margin of temperature rise guarantees that the automatic shutdown can be realized only by means of the temperature negative feedback under accidental conditions without any emergency measures even if the rotary drum control rod and the neutron absorber ball channel are completely unavailable.
The modularized transverse prismatic gas-cooled micro-reactor core system has good physical properties of the reactor core and excellent inherent safety. The reactor core system has a smaller radial size, with a smaller space occupied by the auxiliary system of the rotary drum control rod and the neutron absorber ball, can be accommodated in a container for transportation, having larger market potential.

[0034] The modularized transverse prismatic gas-cooled micro-reactor core system according to the embodiment can realize the design of different power with different service life for the reactor through reasonable reactor core fuel design and adjustment of parameters such as reactor core size and fuel enrichment degree; by increasing the fuel enrichment, the size of the reactor core can be further reduced; the power distribution of the reactor core can be optimized through the partition arrangement of the enrichment degrees of the fuel assemblies at different positions; the reactivity can be effectively controlled by adjusting the arrangements of burnable poison and control rods;
the modularized transverse prismatic gas-cooled micro-reactor core system has excellent design flexibility and environmental applicability.

[0035] In order to analyze the physical characteristics of the modular transverse prismatic gas-cooled micro-reactor core system according to this embodiment, a general Monte Carlo program is used to perform modeling and analysis on the gas-cooled micro-reactor with an assumed core temperature of 1200K, which can include the following steps:

[0036] The result of the calculation of the burnup characteristics of the gas-cooled micro-reactor is shown in FIG. 5. The core of the gas-cooled micro-reactor has a lifetime of about 435EFPD (Effective Full Power Days) at 5MW thermal power, which satisfies a design target of 1-year lifetime. During the life cycle, the reactor core has a maximum keff of 1.01494 and a minimum keff is 1.00410, and the residual reactivity change amplitude is 1074 pcm.

[0037] The core power distribution of the gas-cooled micro-reactor is shown in FIG. 6, which is a power distribution of the assemblies of a quarter of reactor core normalized based on an average power of the assemblies when the zero-bumup drum control rods 2 are completely face outward. In the radial direction, the power distribution is relatively uniform, with a radial power peak factor of about 1.25; in the axial direction, the power distribution is distributed in a cosine function, with an axial power peak factor of 1.29; a power factor of the assemblies of the reactor as a whole is 1.61 at maximum and 0.53at minimum.

[0038] The inherent security of the gas-cooled micro-reactor is mainly embodied in the core operation and shutdown in the physical aspect, and the specific discussion thereof will be as follows:

[0039] (1) The hot shutdown of the reactor core relies on the rotary drum control rods.
Assuming a temperature of the reactor core is 700K at the time of the hot shutdown, the rotary drum control rod can provide at least a shutdown depth of the hot shutdown of -2117 pcm, which completely meets a requirement of the shutdown depth of -1000 pcm, when the stuck rod criterion, a 10% uncertainty of a rod value (namely, a multiplier factor of 0.9) and a 10% uncertainty of a positive reactivity caused by temperature reduction (namely, a multiplier factor of 1.1) are considered.

[0040] (2) The emergency shutdown and the cold shutdown of the reactor core rely on the neutron absorber ball. Assuming a temperature of the reactor core is 300K
at the time of the cold shutdown, the neutron absorber ball on the basis of the hot shutdown of the rotary drum control rod can provide at least a shutdown depth of the cold shutdown of -10281 pcm, which completely meets a requirement of the shutdown depth of -1000 pcm, when a situation that one neutron absorber ball channel with the highest value is unavailable, a 10% uncertainty of an neutron absorber ball value (namely, a multiplier factor of 0.9) and a 10% uncertainty of a positive reactivity caused by a temperature reduction (namely, a multiplier factor of 1.1) are considered.

[0041] (3) The inherent security of the gas-cooled micro-reactor is the most importantly realized under the accidental conditions without any emergency measures, and the reactor core can realize shutdown only dependently on temperature negative feedback.
Assuming that all the rotary drum control rods and the neutron absorber ball channels are not available, the maximum keff of the reactor core is 1.01494 during the lifetime, and the residual reactivity is +1483 pcm; a total temperature reactivity coefficient of the reactor core is between -5pcm/K and -10pcm/K, and the reactor core can realize the automatic shutdown when the temperature is increased from an assumed 1200K to 1500K (about 1227 C) which is well below the limit temperature of the core fuel (around 1600 C). Therefore, the modularized transverse prismatic gas-cooled micro-reactor can realize automatic shutdown by only depending on temperature negative feedback without any emergency measures even under accidental conditions, and can physically eliminate the possibilities of core melting and radioactive substance release.

[0042] Through the arrangement, the radial diameter of the reactor core can be reduced to 2.1m, the auxiliary system required by the rotary drum control rod 2 and the neutron absorber ball occupies small space and can be placed in a common container with a side length of 2.5m, which is convenient for transportation of the reactor core, is flexible to use and has large market potential.

[0043] Second Embodiment

[0044] As shown in FIGS. 2 to 4, this embodiment discloses a reactor core system including a reactor core, a reflector, and a rotary drum control rod 2, wherein:

[0045] the reactor core is transversely arranged and includes fuel assemblies 1, the fuel assemblies 1 being arranged in a radial partition (or called grouping) and axial hierarchy mode, the reflector encompassing an outside of the reactor core, the rotary drum control rod 2 being arranged within the reflector to compensate reactivity changes, hot shutdown and the like caused by temperature change, xenon-samarium toxicity, burnup, for example; and

[0046] the reactor core is provided with a central graphite belt 5 therein, the central graphite belt 5 arranged in a vertical direction being provided with an neutron absorber ball channel 4 therein, the neutron absorber ball channel 4 arranged in the vertical direction penetrating through the reflector and being provided with an neutron absorber ball therein, and the neutron absorber ball being used for realizing a cold shutdown of the reactor core after the hot shutdown of the rotary drum control rod 2 or realizing the cold shutdown of the reactor core alone.

[0047] Through the above arrangement, the overall shape of the reactor core system is in a transverse cylindrical shape. Compared with the traditional reactor core system in the shape of "short and high", the cylindrical reactor core system is in the shape of "low-height and long", which can provide a high matching degree with the shape of the container. The size of the reactor core system can be reduced, so as to be conveniently transported by the container. This allows the cylindrical reactor core system to be assembled in a processing plant to avoid long-time installation and debugging on the site.
The requirements of container transportation, simple and convenient assembly and rapid deployment under the special application situation are met.

[0048] Next, the reactor core system of this embodiment will be further described in detail.

[0049] In this embodiment, the reflector is in a cylindrical shape, and the fuel assemblies 1 positioned at the outermost layer in the radial direction in the reactor core is in contact with an inner wall of the reflector. A shape of the reactor core is matched with a shape of the inner wall of the reflector. The number of the neutron absorber ball channel 4 may be one or plural. Plural neutron absorber ball channels 4 are distributed along a longitudinal direction of the reactor core.

[0050] The central graphite belt 5 is disposed in the middle of the reactor core, such that the fuel assemblies 1 in the reactor core can be divided into two regions which are symmetrically disposed, i.e., into two groups. As shown in FIGS. 2 and 3, the two groups of fuel assemblies 1 are arranged on either side of the central graphite belt 5, and each group of fuel assemblies 1 includes a first fuel assembly 11 (i.e., an incomplete fuel assembly) and a second fuel assembly 12 (i.e., a complete fuel assembly), wherein the first fuel assembly 11 is arranged at a position close to the central graphite belt 5, and the second fuel assembly 12 is arranged on the other side of the first fuel assembly 11 and on either side of the first fuel assembly 11 with respect to the central graphite belt 5.

[0051] The fuel assembly 1 may be square graphite fuel assembly. More in particular, as shown in FIGS. 2 and 3, the first fuel assembly 11 can be rectangular in cross-section, the second fuel assembly 12 can be square in cross-section, and a length of the rectangular first fuel assembly 11 can be equal to a side length of the square second fuel assembly 12. A width of the two rectangular first fuel assemblies 12 plus a thickness of the central graphite belt 5 can be equal to the side length of the square second fuel assembly 12, which facilitates arrangement. In fact, the first fuel assembly 11 can also be considered as being formed by the central graphite belt 5 penetrating the second fuel assembly 12. For convenience of description, the center of the reactor core is taken as an origin 0, the axial direction (i.e., the length direction) of the cylindrical reactor core is taken as an x axis, and the radial direction of the cylindrical reactor core is taken as a y axis and a Z axis, wherein the radial direction in the horizontal direction is taken as the y axis, and the radial direction in the vertical direction is taken as the Z
axis. The first fuel assemblies 11 in each group of fuel assemblies 1 are arranged in a row along the Z axis direction, and the second fuel assemblies 12 in each group of fuel assemblies 1 are arranged in sequence along the y axis and the z axis. In particular, the second fuel assemblies 12 in each group of fuel assemblies 1 are further divided into a plurality of groups, each group of second fuel assemblies 12 abuts against one first fuel assembly 11, respectively, and is arranged in sequence along the y axis direction into a plurality of layers, and the outermost second fuel assemblies 12 in the groups are substantially on one circumscribed circle.

[0052] Also, as shown in FIGS. 2 and 3, the reactor core can further include a graphite block 8. The graphite block 8 is shaped and sized in conformity with the second fuel assembly, and is provided in one or more groups of the second fuel assemblies and arranged in line with the respective fuel assembly in the group of the second fuel assemblies, to enhance the moderating effect.

[0053] In some embodiments, as shown in FIGS. 2 and 3, the radial diameter of the reactor core can be 2.1m, the side length of the square second fuel assemblies 12 and the length of the rectangular first fuel assemblies 11 can be 21cm, and there can be disposed 14 first fuel assemblies and 28 second fuel assemblies in the reactor core.
The width (or referred to as the thickness, i.e., the thickness in the y-axis direction) of the central graphite belt 5 in the reactor core can be 8.4cm, 5 cylindrical neutron absorber ball channels can be provided in the central graphite belt 5, and the 5 neutron absorber ball channels 4 are arranged in parallel along the x-axis (i.e., the axial direction or the length direction of the reactor core). The neutron absorber ball channel 4 can have a radius of 3.9 cm. Intervals between the neutron absorber ball channels 4 may or may not be equal.

[0054] The first fuel assemblies 11 and the second fuel assemblies 12 are divided into a plurality of layers in a longitudinal direction of the reactor core, respectively.

[0055] In some embodiments, the axial length of the entire reactor core can be 3.4m, and the first and second fuel assemblies 11 and 12 can be divided into 9 layers in the axial length direction of the reactor core.

[0056] By dividing the reactor core into a plurality of fuel assemblies 1 arranged along the y-axis and the z-axis (i.e., the radial partition) and dividing each fuel assembly 1 into a plurality of layers in the core axial direction (i.e., the axial hierarchy), structural stability and shock resistance can be improved. Moreover, the fuel assemblies can be modularized by independently arranging the first fuel assembly and the second fuel assembly, and each first fuel assembly and each second fuel assembly are equivalent to an independent module. In this way, the production and the replacement are convenient, and the design of a nuclear system and emergency design can be simplified.

[0057] Fuel rod channels, coolant channels 102 and beryllium oxide rods 104 are arranged on each of the first fuel assembly 11 and the second fuel assembly 12, and the fuel rod channels, the coolant channels 102 and the beryllium oxide rods 104 are distributed in an alternating manner, wherein the fuel rod channels are used for arranging the fuel rods 101, the coolant channels 102 are used for circulating coolant which can be single-phase inert gas such as helium, and the beryllium oxide rods 104 are used for enhancing the moderation. In particular, as shown in FIG. 1 a, taking the square second fuel assembly 12 as an example, the square second fuel assembly 12 is divided into a plurality of 7 x 7 lattices, the central grid is provided with a coolant channel 102, and the lattices is divided into three regions, i.e., a first layer, a second layer and a third layer, in a manner of surrounding the central grid according to a distance from the central grid from the near to the far side, wherein: the fuel rod channels and the beryllium oxide rods 104 are alternately arranged in the first layer, and the lattices in the first layer where the fuel rod channels are arranged are the four lattices close to the periphery of the central grid; the coolant channels 102 and the fuel rod channels are alternately arranged in the second layer, and the fuel rod channels in the second layer are next to the lattices in the first layer where the beryllium oxide rods 104 are arranged; the fuel rod channels and beryllium oxide rods 104 are alternately arranged in the third layer, and the lattices in the third layer where the fuel rod channels are arranged are next to the lattices in the second layer where the coolant channels 102 are arranged. That is, there are 24 fuel rods 101, 9 coolant channels, and 16 beryllium oxide rods arranged on the second fuel assembly 12.
Taking the first rectangular fuel assembly 11 as an example, the first rectangular fuel assembly 11 can be divided into 2 X 7 lattices, wherein the number of fuel rod channels is 7, the number of beryllium oxide rods 104 is 4, the number of coolant channels is 6.
The fuel rod channels are arranged at an interval in the 2 x 7 lattices, and at least one coolant channel 102 and one beryllium oxide rod 104 are arranged around each fuel rod channel.

[0058] The fuel rods 101 are in a cylindrical shape. Each of the fuel rods includes a plurality of fuel pellets, for example, 8 fuel pellets, and the 8 fuel pellets are sequentially stacked in an axial direction of the fuel rods.

[0059] Each of the fuel pellets include fuel particles and a matrix in which the fuel particles are dispersed. The matrix can be formed of graphite or ceramic and the fuel particles can have a particle size of about several hundred microns.

[0060] Each of the fuel particles includes a fuel kernel and a coating layer.
The fuel kernel is arranged inside the coating layer, and the coating layer is of a multilayer structure, such that the fuel pellet can realize micro-encapsulation and can effectively prevent fission products from being released.

[0061] The material of the fuel kernels can be one or more of UO2, UCO or UN, and an enrichment degree (i.e., a mass fraction of U235) of the fuel kernel can be about 8.5%.
The coating layers can be a four-layer structure, and the material of the coating layer can be one or more of graphite, SiC and ZrC.

[0062] The burnable poison rods 103 can also be disposed on second fuel assembly 12.
In particular, a square second fuel assembly 102 having 7 x 7 lattices is taken as an example. As shown in FIG. 1, compared to the case of FIG. la without the burnable poison rod, the lattices in the first layer where the beryllium oxide rods 104 were disposed in that case are disposed with the burnable poison rods 103 instead of beryllium oxide rods 104. That is, 24 fuel rods 101, 9 coolant channels, 4 burnable poison rods, and 12 beryllium oxide rods are disposed on second fuel assembly 12.

[0063] The burnable poison rods 103 are burnable poison rods which can be gadolinium as an absorber material.

[0064] The neutron absorber ball and the rotary drum control rod 2 each include a neutron absorber and a cladding, wherein the neutron absorber is made of B4C
material;
the cladding is made of stainless steel material and is wrapped outside the neutron absorber.

[0065] The cross section of the neutron absorber in the rotary drum control rod 2 can be in a partial ring shape, for example, one third of a circular ring, which may have an inner diameter of 12.5cm and an outer diameter of 14.5 cm.

[0066] The reflector can be made of graphite or Be0 material, and can specifically include an upper reflector, a lower reflector and a side reflector 3, wherein the upper reflector and the lower reflector are disposed at both ends of the reactor core composed of the arranged fuel assemblies 1, respectively, and the side reflector 3 is disposed at the outer periphery of the fuel assembly 1 arranged at the outermost layer. The rotary drum control rods 2 are arranged in the side reflector 3. The number of the rotary drum control rods 2 is plural, and in particular 8. The 8 rotary drum control rods 2 are uniformly distributed.

[0067] The reactor core system according to this embodiment has a whole shape highly matched with the shape of the container, and can reduce the occupied space of an assorted auxiliary system and reduce the size of the reactor core system by arranging the rotary drum control rod and vertically arranging the neutron absorber ball channel. As such, the radial diameter of the reactor core system can be reduced to 2.1m, so as to be arranged in a common container with the side length (width) of 2.5m for the transportation. In this way, the assembling can be completed in a factory, the long-time field installation and debugging can be avoided, and the requirements of container transportation, simple and convenient assembly and rapid deployment under the special application scenes can be met.

[0068] In addition, adopting the square fuel assembly can facilitate the arrangement of the device, thereby improving the stability and the shock resistance; the adopted fuel type is ceramic micro-packaging fuel, so that the fission product can be effectively prevented from being released, and the fuel is prevented from being corroded;
by arranging the rotary drum control rods and the absorption balls, the reactor core is provided with two independent shutdown rod groups to realize the cold shutdown and the hot shutdown; as the core structure material and the reflector material are graphite or Be0, which can serve as neutron moderator and has the advantages of large heat capacity, high temperature resistance, high heat conductivity, high moderation ratio, small thermal neutron absorption section and the like, the reactor core system can have a slow temperature transient state, bear a very high temperature, and provide a large margin of emergency operation time, a small reactor core power density, a strong temperature negative feedback (taking graphite as the reactor core and the reflector material, B4C as the absorption material and gadolinium as the burnable poison material as examples, the coefficient of temperature negative reactivity at least reaches minus 5 pcm/K
or above), and a huge temperature rise margin; under the accidental conditions, even if the rotary drum control rod and the neutron absorber ball channel are completely unavailable without any emergency measures, the automatic hot shutdown can be realized only by temperature negative feedback, such that the possibility of reactor core melting and radioactive substance release is physically avoided and the inherent security is improved;
the reactor core system has a small size, realizes miniaturization design, reduces the power and the power density of the reactor core, and improves the safety of the reactor core; the reactor core system can be conveniently designed in a modularized manner, so that the system of a nuclear power plant is simplified, the production cost is reduced, the manufacturing quality of components is improved, the personnel operation can be reduced, and the risk of accidents is reduced.

[0069] The present embodiment also discloses a gas-cooled micro-reactor, as shown in FIG. 7, which includes the reactor core system 6 and auxiliary equipment.

[0070] Specifically, the auxiliary tools include a helium gas storage tank 9, a helium gas fan 10, an instrument box 11 and a rotary drum control rod drive mechanism 12.
In this embodiment, the gas-cooled micro-reactor is disposed in a compartment 7 of a transportation facility for transportation, wherein the compartment 7 may be a container.

[0071] The gas-cooled micro-reactor according to the embodiment has the advantages of small size, convenience in movement, high flexibility and adaptability and capability of realizing rapid deployment due to the adoption of the reactor core system.

[0072] In addition, the reactor core system according to the embodiment has good physical characteristics of the reactor core and excellent inherent security.
For this reason, in this embodiment a general Monte Carlo program is used to perform modeling and analysis on the gas-cooled micro-reactor with an assumed core temperature of 1200K, and the physical characteristics of the reactor core are as follows:

[0073] The result of the calculation of the burnup characteristics of the gas-cooled micro-reactor is shown in FIG. 5. The core of the gas-cooled micro-reactor has a lifetime of about 435EFPD (Effective Full Power Days) at 5MW thermal power, which satisfies a design target of 1-year lifetime. During the life cycle, the reactor core has a maximum keff of 1.01494 and a minimum keff is 1.00410, and the residual reactivity change amplitude is 1074 pcm.

[0074] The core power distribution of the gas-cooled micro-reactor is shown in FIG. 6, which is a power distribution of the assemblies of a quarter of reactor core normalized based on an average power of the assemblies when the zero-bumup drum control rods 2 are completely face outward. In the radial direction, the power distribution is relatively uniform, with a radial power peak factor of about 1.25; in the axial direction, the power distribution is distributed in a cosine function, with an axial power peak factor of 1.29; a power factor of the assemblies of the reactor as a whole is 1.61 at maximum and 0.53at minimum.

[0075] The inherent security of the gas-cooled micro-reactor is mainly embodied in the core operation and shutdown in the physical aspect, and the specific discussion thereof will be as follows:

[0076] (1) The hot shutdown of the reactor core relies on the rotary drum control rods.
Assuming a temperature of the reactor core is 700K at the time of the hot shutdown, the rotary drum control rod can provide at least a shutdown depth of the hot shutdown of -2117 pcm, which completely meets a requirement of the shutdown depth of -1000 pcm, when the stuck rod criterion, a 10% uncertainty of a rod value (namely, a multiplier factor of 0.9) and a 10% uncertainty of a positive reactivity caused by temperature reduction (namely, a multiplier factor of 1.1) are considered.

[0077] (2) The emergency shutdown and the cold shutdown of the reactor core rely on the neutron absorber ball. Assuming a temperature of the reactor core is 300K
at the time of the cold shutdown, the neutron absorber ball on the basis of the hot shutdown of the rotary drum control rod can provide at least a shutdown depth of the cold shutdown of -10281 pcm, which completely meets a requirement of the shutdown depth of -1000 pcm, when a situation where one neutron absorber ball channel with the highest value is unavailable, a 10% uncertainty of an neutron absorber ball value (namely, a multiplier factor of 0.9) and a 10% uncertainty of a positive reactivity caused by a temperature reduction (namely, a multiplier factor of 1.1) are considered.

[0078] (3) The inherent security of the gas-cooled micro-reactor is the most importantly realized under the accidental conditions without any emergency measures, and the reactor core can realize shutdown only dependently on temperature negative feedback.
Assuming that all the rotary drum control rods and the neutron absorber ball channels are not available, the maximum keff of the reactor core is 1.01494 during the lifetime, and the residual reactivity is +1483 pcm; a total temperature reactivity coefficient of the reactor core is between -5pcm/K and -10pcm/K, and the reactor core can realize the automatic shutdown when the temperature is increased from an assumed 1200K to 1500K (about 1227 C) which is well below the limit temperature of the core fuel (around 1600 C). Therefore, the modularized transverse prismatic gas-cooled micro-reactor can realize automatic shutdown by only depending on temperature negative feedback without any emergency measures even under accidental conditions, and can physically eliminate the possibilities of core melting and radioactive substance release.

[0079] It will be understood that the above embodiments are merely exemplary embodiments provided to illustrate the principles of the present disclosure, and the present disclosure is not limited thereto. It will be apparent to those skilled in the art that various changes and modifications can be made therein without departing from the spirit and essence of the disclosure, and these changes and modifications are to be considered within the scope of the disclosure.

Claims (14)

What is claimed is:

1. A reactor core system, characterized in that, it comprises a reactor core, a reflector and a rotary drum control rod, wherein the reactor core, which is transversely arranged, includes a plurality of fuel assemblies, and the plurality of fuel assemblies are arranged according to a radial partition and in an axial layered manner;
the reflector wraps outside the reactor core; the rotary drum control rod is arranged in the reflector; a central graphite belt is arranged in the reactor core, and the central graphite belt is arranged in a vertical direction; a neutron absorber ball channel is arranged in the central graphite belt, and the neutron absorber ball channel is vertically arranged and penetrates the reflector; and a neutron absorber ball is arranged in the neutron absorber ball channel.

2. The reactor core system of claim 1, wherein the reflector is in a cylindrical shape, wherein one of the fuel assemblies positioned at the outermost layer in a radial direction in the reactor core are in contact with an inner wall of the reflector, and wherein the fuel assemblies are in a square shape.

3. The reactor core system of claim 2, wherein the central graphite strip is disposed in the middle of the reactor core such that the fuel assemblies in the core are divided into two groups which are symmetrically disposed, the two groups of fuel assemblies being arranged on either side of the central graphite strip, and each group of fuel assemblies including a first fuel assembly arranged at a position close to the central graphite belt and a second fuel assembly arranged on the other side of the first fuel assembly and on either side of the first fuel assembly with respect to the central graphite belt.

4. The reactor core system of claim 3, wherein the first and second fuel assemblies are divided into layers along a longitudinal direction of the reactor core.

5. The reactor core system of claim 3, wherein each of the first and second fuel assemblies has fuel rod channels, coolant channels, and beryllium oxide rods arranged at intervals, wherein the fuel rod channels are used to accommodate fuel rods, the coolant channels are used to flow coolant, and the beryllium oxide rods are used to enhance moderation.

6. The reactor core system of claim 5, wherein the second fuel assembly further comprises burnable poison rods disposed thereon.

7. The reactor core system of claim 5, wherein the fuel rods are in a cylindrical shape, and each of the fuel rods includes fuel pellets, and the fuel pellets are sequentially arranged and stacked along a axial direction of the fuel rods;
the coolant is helium which is a single-phase inert gas.

8. The reactor core system of claim 7, wherein each of the fuel pellets includes fuel particles and a matrix, the fuel particles being dispersed in the matrix.

9. The reactor core system of claim 8, wherein the matrix is formed of graphite or ceramic; each of the fuel particles includes a fuel kernel and a coating layer, wherein the fuel kernel is arranged inside the coating layer, and the coating layer is of a multilayer structure.

10. The reactor core system of claim 9, wherein the material of the fuel kernels includes one or more of UO2, UCO or UN; and the coating layers are made of one or more of graphite, SiC or ZrC.

11. The reactor core system of any one of claims 1 to 10, wherein the neutron absorber ball and the rotary drum control rod each include a neutron absorber and a cladding, the neutron absorber being made of B4C material, and the cladding being made of stainless steel material and being wrapped outside the neutron absorber.

12. The reactor core system of any one of claims 1 to 10, wherein the reflector is made of graphite or Be0 material.

13. The reactor core system of any one of claims 1 to 10, wherein the reflector includes a front reflector, a rear reflector, and a side reflector, the rotary drum control rod being disposed in the side reflector, and the neutron absorber in the rotary drum control rod being in a partial ring shape.

14. A gas-cooled micro-reactor characterized in that, it comprises a reactor core system and auxiliary equipment, wherein the reactor core system employs the reactor core system of any one of claims 1 to 13.