JP6615605B2 - Fast reactor core and fast reactor - Google Patents

Description

  Embodiments described herein relate generally to a fast reactor core and a fast reactor.

  In general, when a control rod insertion failure event occurs in a large fast reactor, it is necessary to introduce a negative reactivity into the core by some method. As a method of introducing a negative reactivity, there is a method of introducing a neutron absorbing material into the core using the temperature rise of the reactor coolant. Furthermore, there is a method of using a fuel assembly provided with a fuel discharge duct and discharging molten nuclear fuel from the duct to the outside of the core.

JP 2013-120119 A JP 2009-85650 A JP 2002-55187 A JP 08-297185 A

M. Schikorr, E. Bubelis, B. Carluec, J. Champigny, “Assessment of SFR reactor safety issues. Part I: Analysis of the unprotected ULOF, ULOHS and UTOP transients for the SFR (v2b-ST) reactor design and assessment of the efficiency of a passive safety system for prevention of severe accidents ”Nuclear Engineering and Design, 285, 249-262 (2015) H. Endo, M. Kawashima and A. Shimizu, “Safety Features of Liquid metal Fueled Core”, Potential of Small Nuclear Reactors for Future Clean and Safe Energy Sources (Editor; H. Sekimoto), p273-p282, 1992, ELSEVIER, ISBN-0444894322 M. Kawashima, H. Endo and A. Shimizu, “A Conceptual Study on a Liquid Metallic Fueled Core”, p283-p289, 1992, ELSEVIER, ISBN-0444894322 T. Sawada, H. Ninokata, H. Taneichi and H. Endo, “CHARACTERISTICS OF FUEL MELTING AND RELOCATION IN METALLIC = FUELED FAST REACTOR CORE AND ITS FEASIBILITY FOR ELIMINATING RECRITICALITY”, Progress in Nuclear Energy, Vol. 37, No. 1 -4, p157-162, 2000, Pergamon

  In the example of the core damage prevention element of the fast reactor described above, the fuel has already been damaged at the time when a negative reactivity is applied, such as a time delay until the neutron absorber is introduced or a malfunction due to a temperature rise. There were problems such as becoming.

  An embodiment of the present invention is made to solve the above-described problem, and in the event of a fast rod control rod insertion failure event, negative reactivity is introduced into the core to prevent core damage. Objective.

In order to achieve the above object, a fast reactor core according to the present embodiment is a fast reactor core of a fast reactor having a fuel containing a fissile material and using liquid metal as a reactor coolant, and is parallel to each other. And a plurality of core fuel assemblies that extend in the vertical direction and have solid fuel, and a plurality of core fuel assemblies that are arranged in parallel with the plurality of core fuel assemblies and have liquid liquid fuel during normal operation and extend in the vertical direction And a plurality of control rod assemblies that include a substance that absorbs neutrons and that are arranged in parallel with the plurality of core fuel assemblies and the plurality of core damage prevention structures and are movable up and down. Each of the plurality of core damage prevention structures includes a first liquid fuel element that extends in a cylindrical shape in the vertical direction and is closed at the top and bottom to store the fissile material, and is solid in normal operation. Communicating with the first liquid fuel element A melt plug that prevents the liquid fuel from flowing out from the first liquid fuel element through the flow path, and that melts due to an increase in ambient temperature at the time of an accident and allows the liquid fuel to flow out; It is characterized by having.

Further, the fast reactor according to the present embodiment has a fuel containing a fissile material, a fast reactor core using a liquid metal as a reactor coolant, the fast reactor core, and the reactor coolant. A reactor vessel to be held, and a shielding plug that covers a top portion of the reactor vessel and supports a control rod drive mechanism that drives a control rod that controls the reactivity of the fast reactor core, the fast reactor core comprising: A plurality of core fuel assemblies arranged in parallel with each other and extending in the vertical direction and having the solid fuel, and a plurality of core fuel assemblies arranged in parallel with the plurality of core fuel assemblies and extending in the vertical direction A plurality of core damage prevention structures, and a plurality of control rod assemblies containing a neutron absorbing material and arranged in parallel with the plurality of core fuel assemblies and the plurality of core damage prevention structures, Each of the core damage prevention structures of First liquid fuel element housing the fissile material is closed vertically extending in a cylindrical shape in the perpendicular direction, said first liquid member fuel through the flow path communicating with the first liquid fuel element And a molten plug that melts when the ambient temperature rises at the time of an accident and allows the liquid fuel to flow out.

  According to the embodiment of the present invention, when a control rod insertion failure event of the fast reactor occurs, a negative reactivity can be input to the core to prevent core damage.

It is an elevation sectional view showing composition of a fast reactor concerning a 1st embodiment. It is an II-II arrow top view of Drawing 1 showing the composition of the fast reactor core concerning a 1st embodiment. It is a sectional elevation showing the composition of the core fuel assembly of the fast reactor core concerning a 1st embodiment. It is a notional elevation sectional view showing composition of a fast reactor core concerning a 1st embodiment. It is a plane sectional view showing composition of a core damage prevention structure of a fast reactor core concerning a 1st embodiment. It is an elevation sectional view showing the composition of the core damage prevention structure of the fast reactor core concerning a 1st embodiment. FIG. 3 is an elevational sectional view showing a configuration of a combination of a first liquid fuel element and a second liquid fuel element of the core damage prevention structure of the fast reactor core according to the first embodiment. It is a top view of the connection part of the 1st liquid fuel element of the core damage prevention structure of a fast reactor core concerning a 1st embodiment, and the 2nd liquid fuel element. It is an elevation sectional view of the connection part of the 1st liquid fuel element of the core damage prevention structure of a fast reactor core concerning a 1st embodiment, and the 2nd liquid fuel element. FIG. 3 is an elevational sectional view showing a state when a molten plug is opened in a combined body of the first liquid fuel element and the second liquid fuel element of the core damage prevention structure of the fast reactor core according to the first embodiment. It is a graph which shows the example of the substitutional reactivity to the core damage prevention structure of the core fuel assembly for explaining the effect of the fast reactor core concerning a 1st embodiment. It is a graph which shows the example of the reactivity effect by thermal expansion for demonstrating the effect of the fast reactor core which concerns on 1st Embodiment. FIG. 6 is an elevational sectional view showing a configuration of a combined body of a first liquid fuel element and a second liquid fuel element of a core damage prevention structure for a fast reactor core according to a second embodiment. It is a top view of the connection part of the 1st liquid fuel element of the core damage prevention structure of a fast reactor core concerning a 2nd embodiment, and the 2nd liquid fuel element. It is an elevation sectional view of the connection part of the 1st liquid fuel element and the 2nd liquid fuel element of the core damage prevention structure of a fast reactor core concerning a 2nd embodiment. It is an elevation sectional view showing the composition of the combination of the 1st liquid fuel element and the 2nd liquid fuel element of the core damage prevention structure of a fast reactor core concerning a 3rd embodiment. FIG. 10 is an elevational sectional view showing a state when a molten plug is opened in a combined body of a first liquid fuel element and a second liquid fuel element of a core damage prevention structure of a fast reactor core according to a third embodiment. FIG. 10 is an elevational sectional view showing a configuration of a modified example of a combined body of a first liquid fuel element and a second liquid fuel element of a core damage prevention structure for a fast reactor core according to a third embodiment. It is a plane sectional view showing the composition of the core damage prevention structure of a fast reactor core concerning a 4th embodiment. It is an elevation sectional view showing the composition of the 1st liquid fuel element of the core damage prevention structure of a fast reactor core concerning a 4th embodiment. It is an elevation sectional view showing a state when a fusion plug opens in the 1st liquid fuel element of the core damage prevention structure of a fast reactor core concerning a 4th embodiment. It is a sectional elevation showing the composition of the combination of the 1st liquid fuel element of the core damage prevention structure of the fast reactor core concerning a 5th embodiment. FIG. 10 is an elevational sectional view showing a state when a molten plug is opened in a combined body of first liquid fuel elements of a core damage prevention structure of a fast reactor core according to a fifth embodiment. It is a sectional elevation showing the composition of the core damage prevention structure of the fast reactor core concerning a 6th embodiment. It is a sectional elevation showing the composition of the combination of the 1st liquid fuel element of the modification of the core damage prevention structure of the fast reactor core concerning a 6th embodiment. It is a plane sectional view showing the composition of the core damage prevention structure of a fast reactor core concerning a 7th embodiment. It is an elevation sectional view showing the composition of the 1st liquid fuel element of the core damage prevention structure of a fast reactor core concerning a 7th embodiment. It is an elevation sectional view showing the composition of the 1st liquid fuel element of the core damage prevention structure of a fast reactor core concerning an 8th embodiment. It is an elevation sectional view showing a fusion plug set of a core damage prevention structure of a fast reactor core according to an eighth embodiment.

  Hereinafter, a fast reactor core and a fast reactor according to an embodiment of the present invention will be described with reference to the drawings. Here, the same or similar parts are denoted by common reference numerals, and redundant description is omitted.

[First Embodiment]
FIG. 1 is an elevational sectional view showing the configuration of the fast reactor according to the first embodiment. The fast reactor 1 includes a fast reactor core 10, a core support plate 4 that supports the fast reactor core 10, a reactor vessel 2 that houses them and holds a reactor coolant 150 inside, and covers the upper portion of the reactor vessel 2. It has a shielding plug 11. Here, the reactor coolant 150 is a liquid metal, for example, sodium (Na).

  Above the fast reactor core 10 composed of the core fuel assembly 30 and the like, a core upper mechanism 7 penetrating the shielding plug 11 and supported by the shielding plug 11 is suspended toward the reactor vessel 2. It has been. The core upper mechanism 7 includes a control rod drive mechanism 7a for driving the control rod assembly 15 (FIG. 2), a fast reactor core instrumentation (not shown), and the like.

  Connected to the reactor vessel 2 are a coolant inlet pipe 8 for sending the reactor coolant 150 into the reactor vessel 2 and a coolant outlet pipe 9 for sending the reactor coolant 150 from the reactor vessel 2.

  The reactor coolant 150 that has flowed into the reactor vessel 2 from the coolant inlet pipe 8 flows into the lower plenum 2a. The reactor coolant 150 that has flowed into the lower plenum 2a is turned upward, then flows into the fast reactor core 10 from the core support plate 4, receives heat from the fast reactor core 10, passes through the fast reactor core 10, and then passes through the upper reactor core 10. It flows into the plenum 2b. The reactor coolant 150 flowing into the upper plenum 2b flows out of the reactor vessel 2 through the coolant outlet pipe 9 for heat exchange with the outside.

  FIG. 2 is a plan view taken along the arrow II-II in FIG. 1 showing the configuration of the fast reactor core according to the first embodiment. The fast core 10 is provided with a core fuel assembly 30, a core damage prevention structure 100, a control rod assembly 15, a radial blanket fuel assembly 12, a reflector 13, and a neutron shield 14. There are a plurality of these elements.

  The core fuel assemblies 30 shown in white are arranged in a substantially circular shape in plan view. The core fuel assemblies 30 are two types having different fuel enrichments, and a plurality of inner core fuel assemblies and a plurality of outer core fuel assemblies arranged radially outside thereof in two layers in the radial direction, or They may be arranged in the above layers.

  The core damage prevention structures 100 extend in the vertical direction in parallel with the core fuel assemblies 30 and are distributed in a region where the core fuel assemblies 30 are arranged.

  The control rod assemblies 15 displayed in black are arranged to be interspersed with each other in the region where the core fuel assemblies 30 are arranged. The control rod assembly 15 controls the output of the fast reactor core 10 according to the degree of insertion and extraction into the fast reactor core 10, and is inserted into the fast reactor core 10 in the event of an abnormality to reduce the reactivity of the core.

  The radial blanket fuel assembly 12 stores a fuel parent material that becomes a fissile material by absorbing neutrons, and is disposed so as to surround the radially outer side of the core fuel assembly 30.

  The reflector 13 for suppressing leakage of neutrons radially outward from the core fuel assembly 30 is arranged so as to surround the radially outer side of the radial blanket fuel assembly 12.

  A neutron shielding body 14 provided to suppress leakage of neutrons from the center side of the fast reactor core 10 to the outside is arranged so as to further surround the radially outer side of the reflector 13.

  FIG. 3 is an elevational sectional view showing the configuration of the core fuel assembly of the fast reactor core according to the first embodiment. The core fuel assembly 30 includes a plurality of core fuel elements 32 and a trumpet pipe 31 that houses the core fuel elements 32 and surrounds them in the radial direction. The core fuel assembly 30 has an entrance nozzle 33 at the bottom and a handling head 34 at the top.

  The entrance nozzle 33 and the handling head 34 are connected to the trumpet pipe 31, and together with the trumpet pipe 31 form a passage for the reactor coolant 150 flowing into the core fuel assembly 30. The reactor coolant 150 flowing in from the entrance nozzle 33 is formed in the handling head 34 after rising radially outward of each of the plurality of core fuel elements 32, cooling the core fuel elements 32, and increasing the temperature of itself. It flows out from the outlet opening 34a.

  Each core fuel element 32 contains a core fuel mainly composed of a material enriched with fissionable plutonium such as Pu239 in deteriorated uranium at an intermediate portion in the axial direction. Each core fuel element 32 stores a lower blanket fuel containing, for example, depleted uranium as a main component, in the axial direction below the intermediate portion having the core fuel. Further, each core fuel element 32 stores, for example, an upper blanket fuel mainly composed of depleted uranium or the like, in the axial direction above the intermediate portion having the core fuel.

  Here, each of the core fuel and the lower and upper blanket fuels is formed of a plurality of sintered pellets. Each fuel is in the form of an oxide, but may be carbide or nitride. Moreover, it is not limited to a sintered pellet. For example, these may be metal fuels. In the case of a metal fuel, zirconium is usually added.

  As a result, the interior of the core fuel assembly 30 that stores the plurality of core fuel elements 32 corresponds to the storage in the core fuel elements 32 in the axial direction, from the lower side, to the lower blanket portion 30b, the core fuel portion. 30a and the upper blanket part 30c.

  FIG. 4 is a conceptual vertical sectional view showing the configuration of the fast reactor core according to the first embodiment. FIG. 4 shows a state where a cylindrical core is cut along a plane including an axial center extending in the vertical direction.

  A radial blanket region 23 is formed on the radially outer side of the central region, a reflector region 24 is formed on the radially outer side, and a neutron shield region 25 is formed on the radially outer side. . The radial blanket region 23 is a region where the radial blanket fuel assembly 12 is provided, and the reflector region 24 is a region where the reflector 13 is provided. The neutron shield body region 25 is a region where the neutron shield body 14 is provided.

  The central region is divided into a lower axial blanket region 22a, a fuel region 21, and an upper axial blanket region 22b from the lower side in the axial direction. These regions correspond to the axial regions in the core fuel assembly 30 shown in FIG. That is, the lower axial blanket region 22a corresponds to the lower blanket portion 30b, the fuel region 21 corresponds to the core fuel portion 30a, and the upper axial blanket region 22b corresponds to the upper blanket portion 30c.

  That is, the fuel region 21 in FIG. 4 is a region including the core fuel stored in each core fuel assembly 30. Similarly, the lower axial blanket region 22a and the upper axial blanket region 22b are regions that include the lower blanket fuel and the upper blanket fuel, respectively, and that do not include the core fuel in a normal state that is not during an accident.

  The fuel portion accommodated in the core damage prevention structure 100 exists in the fuel region 21 in the axial direction as will be described later.

  FIG. 5 is a plan sectional view showing the configuration of the core damage prevention structure of the fast reactor core according to the first embodiment. The core damage prevention structure 100 includes a plurality of combined bodies 105a and a trumpet tube 101 that houses the combined bodies 105a. Each combined body 105a includes a first liquid fuel element 110a, a second liquid fuel element 120a, and a connecting portion 106 that connects them. The reactor coolant 150 flows on the radially outer side of the coupling body 105a in the trumpet tube 101.

  FIG. 6 is an elevational sectional view showing the structure of the core damage prevention structure of the fast reactor core according to the first embodiment. In FIG. 6, only one of the combined bodies 105a is shown for convenience, but actually, as shown in FIG. 5, a plurality of combined bodies 105a are accommodated in the core damage prevention structure 100.

  The core damage prevention structure 100 includes an entrance nozzle 103 provided below the trumpet tube 101 and a handling head 104 provided above the trumpet tube 101. Further, in the core damage prevention structure 100, a support plate 102 that supports the plurality of combined bodies 105a from below and allows the reactor coolant 150 from below to pass therethrough is provided.

  The reactor coolant 150 flows from the entrance nozzle 103 into the core damage prevention structure 100, rises while cooling the combined body 105a, and flows upward from an outlet opening 104a formed in the handling head 104.

  Liquid fuel 108 is stored in the first liquid fuel element 110a of the combined body 105a, and liquid fuel 108 is stored in the second liquid fuel element 120a.

  In the core damage prevention structure 100, a liquid fuel portion that is an axial region in which the liquid fuel 108 in each first liquid fuel element 110a and the liquid fuel 108 in each second liquid fuel element 120a are accommodated. The axial range of 100a is substantially the same as the axial range of the core fuel portion 30a in the core fuel assembly 30. Therefore, the liquid fuel part 100a in the core damage prevention structure 100 exists in the range of the fuel region 21 in the conceptual sectional elevation view of FIG.

  As will be described later, a gas plenum is formed above the liquid fuel 108 in the first liquid fuel element 110a and above the liquid fuel 108 in each second liquid fuel element 120a. Accordingly, an upper space portion 100c is formed above the liquid fuel portion 100a in the core damage prevention structure 100. Further, an inlet space 100b is formed below the liquid fuel portion 100a in the core damage prevention structure 100, as shown in FIG.

  FIG. 7 is an elevational sectional view showing a configuration of a combined body of the first liquid fuel element and the second liquid fuel element of the core damage prevention structure of the fast reactor core according to the first embodiment.

  The first liquid fuel element 110a and the second liquid fuel element 120a of the combined body 105a are connected to each other by a connecting portion 106 at their lower portions. The connecting portion 106 is formed with a communication hole 106f serving as a flow path for communicating the first liquid fuel element 110a and the second liquid fuel element 120a.

  The first liquid fuel element 110a includes a first element liquid fuel pipe 111 extending vertically upward, and a first element gas pipe 112 connected to the upper end thereof and extending vertically upward. The space in the first element liquid fuel pipe 111 and the space in the first element gas pipe 112 communicate with each other through a communication hole 113. The upper end of the first element gas pipe 112 is closed. The first element liquid fuel pipe 111 communicates with a communication hole 106f which is a flow path of the connecting portion 106 at the lower end thereof.

  The inside of the first element liquid fuel pipe 111 is filled with the liquid fuel 108. Here, the liquid fuel 108 is an alloy of elements having fissionable nuclides, and has an melting point lower than the ambient temperature during normal operation and a boiling point higher than the ambient temperature at the time of the accident. There is. Examples of such alloys include an alloy of plutonium having a melting point of about 410 ° C. and 9.5% iron (Pu-9.5Fe), an alloy of plutonium having a melting point of about 405 ° C. and 12% cobalt ( Pu-12Co), an alloy of plutonium having a melting point of about 552 ° C. and 1.5% magnesium (Pu-1.5Mg).

  The second liquid fuel element 120a includes a second element liquid fuel pipe 121 extending vertically upward, and a second element gas pipe 122 connected to the upper end thereof and extending vertically upward. The outer diameter and inner diameter of the second element liquid fuel pipe 121 are equal to the outer diameter and inner diameter of the first element liquid fuel pipe 111. The upper end of the second element gas pipe 122 is closed. As shown in FIG. 7, the second element gas pipe 122 has a larger inner diameter than the second element liquid fuel pipe 121.

  Further, in the second element gas pipe 122, an inner pipe 124 extending vertically upward from the lower end thereof is provided. The space in the second element liquid fuel pipe 121 and the space in the second element gas pipe 122 are communicated by an inner pipe 124. The second element liquid fuel pipe 121 communicates with the communication hole 106f of the connecting portion 106 at the lower end thereof. The second element liquid fuel pipe 121 is filled with the liquid fuel 108. The inner pipe 124, the second element liquid fuel pipe 121, and the communication hole 106 f are configured so that the liquid fuel 108 of the first element liquid fuel pipe 111 is placed in the space inside the second element liquid fuel pipe 121 in the state of an accident described later. Alternatively, it becomes a flow path when the liquid fuel 108 in the second element liquid fuel pipe 121 moves to the space in the second element gas pipe 122.

  A melt plug 123 is provided in the second element gas pipe 122 so as to partition the second element gas pipe 122 vertically. The space in the second element gas pipe 122 is divided by the molten plug 123 into two spaces, a lower second fuel element first space 125 and an upper second fuel element second space 126.

  Here, in the normal state of the fast reactor core 10, the melting plug 123 prevents the movement of the liquid fuel 108 in the first element liquid fuel pipe 111 and the second element liquid fuel pipe 121 and melts in the event of an accident. Therefore, it is necessary to work to allow the movement of the liquid fuel 108. Therefore, the melting plug 123 needs to have a melting point sufficiently higher than the ambient temperature in the normal state of the fast reactor core and sufficiently lower than the ambient temperature at the time of the accident. Examples of such a material include metals such as magnesium, strontium, and aluminum, alloys of these with other elements, chloride salts, and fluoride salts.

  The respective gas pressures are adjusted so that the pressure in the first element gas pipe 112 is equal to the pressure in the second fuel element first space 125. The pressure at the time of gas filling is adjusted so that the pressure in the second fuel element second space 126 is lower than the pressure in the first element gas pipe 112 and the second fuel element first space 125.

  FIG. 8 is a plan view of a connecting portion between the first liquid fuel element and the second liquid fuel element. FIG. 9 is an elevational sectional view. The connecting portion 106 includes a first element liquid fuel pipe lower end plug 106b and a second element liquid fuel pipe lower end plug 106c. The upper part of the first element liquid fuel pipe lower end plug 106b and the upper part of the second element liquid fuel pipe lower end plug 106c are coupled to each other by a coupling member 106d.

  The first element liquid fuel pipe lower end plug 106 b is connected to the lower end of the first element liquid fuel pipe 111 and functions as a lower end plug of the first element liquid fuel pipe 111. The lower portion of the first element liquid fuel pipe lower end plug 106b has a columnar shape with a reduced diameter, and is formed so as to be insertable into an insertion hole formed in the support plate 102 (FIG. 6).

  Similarly, the lower end plug 106c for the second element liquid fuel pipe is connected to the lower end of the second element liquid fuel pipe 121 and has a function as a lower end plug of the second element liquid fuel pipe 121. The lower part of the second element liquid fuel pipe lower end plug 106c has a cylindrical shape with a reduced diameter, and is formed so as to be inserted into an insertion hole formed in the support plate 102 (FIG. 6).

  A communication hole 106f is formed through the first element liquid fuel pipe lower end plug 106b, the coupling member 106d, and the second element liquid fuel pipe lower end plug 106c.

  The operation of the fast reactor core according to this embodiment configured as described above will be described below.

  In the fast reactor core 10, the events to be assumed include a reactivity insertion type event and a flow loss type event.

  The reactivity insertion type event assumes a case where an excessive degree of reactivity is added to the fast reactor core 10 for some reason, such as control rod insertion failure in addition to erroneous pulling out of the control rod. In this case, the amount of heat generated from the fast reactor core 10 is rapidly increased. That is, the amount of heat generated in the liquid fuel 108 in the core fuel assembly 30a of the core fuel assembly 30 and in each first liquid fuel element 110a and each second liquid fuel element 120a of the core damage prevention structure 100 increases rapidly. .

  For this reason, the temperature of each part in the core fuel assembly 30 and the core damage prevention structure 100 rapidly increases due to heat conduction from the heat generating portion. In addition, the temperature of the reactor coolant 150 passing through the fast reactor core 10 rapidly increases due to the rapid increase in the heat generation amount.

  The loss-of-flow-type event assumes a case where the external driving force for circulation of the reactor coolant 150 passing through the fast reactor core 10 is lost for some reason and only natural circulation force is present. In this case, there is no phenomenon such as an abrupt increase in heat generation from the fast reactor core 10, but sufficient reactor coolant 150 is not secured against the decay heat, so that the reactor cooling that passes through the fast reactor core 10 is not possible. As the temperature of the material 150 moves from the entrance to the exit of the fast reactor core 10, the temperature increase width is greatly increased compared to the normal case. As a result, the temperature of the reactor coolant 150 at the outlet of the fast reactor core 10 increases. When the reactor coolant 150 whose temperature has risen enters the fast reactor core 10 again, the temperature on the inlet side of the fast reactor core 10 also rises.

  As shown in FIG. 7, in each coupling body 105 a provided in the core damage prevention structure 100, the molten plug 123 is a first element liquid fuel pipe that is a heat generating part in the flow direction of the reactor coolant 150. 111 and a second element gas pipe 122 on the downstream side of the second element liquid fuel pipe 121. That is, it exists in the area | region (henceforth a high temperature area | region) of the downstream (upper side of the fuel area | region 21 in FIG. 4) of the fuel area | region 21 which is a heat_generation | fever area | region in the conceptual elevation sectional drawing of the fast reactor core 10 of FIG. .

  In both cases of the reactivity insertion type event and the loss of flow type event, the temperature of the reactor coolant 150 passing through the heat generation region of the fast reactor core 10 increases. The reactor coolant 150 flows directly on the radially outer side of the second element gas pipe 122 provided with the molten plug 123. Therefore, the melting plug 123 melts as the temperature of the reactor coolant 150 increases.

  FIG. 10 is an elevational sectional view showing a state when the molten plug is opened.

  When the melting plug 123 (FIG. 7) provided in the high temperature region melts, the second fuel element first space 125 and the second fuel element second space 126 in the second element gas pipe 122 communicate with each other. Before the communication, the pressure in the second fuel element first space 125 was higher than the pressure in the second fuel element second space 126. Therefore, the pressure in the second fuel element first space 125 is reduced by the communication. To do.

  As a result, the pressure in the second fuel element first space 125 becomes lower than the pressure in the first element gas pipe 112. Therefore, the liquid fuel in the first element liquid fuel pipe 111 and the second element liquid fuel pipe 121 until the pressure in the second fuel element first space 125 and the pressure in the first element gas pipe 112 are balanced. 108 moves to the 2nd fuel element 1st space 125 side the flow path including the communicating hole 106f of the connection part 106. FIG.

  The moved liquid fuel 108 passes through the inner pipe 124 and flows into the second fuel element first space 125, and the inner wall and the inner pipe 124 of the second element gas pipe 122 in the second fuel element first space 125. Is held in the annular space between the outer walls of the.

  In this state, in the conceptual sectional elevational view of the fast reactor core in FIG. 4, a part of the liquid fuel 108 in the liquid fuel part 100 a in the fuel region 21 moves from the fuel region 21 to the upper axial blanket region 22 b. It is in the state.

  This means that a part of the liquid fuel 108 has moved to a region where the neutron importance for the fission reaction is relatively low. Comparing the fuel region 21 and the upper axial blanket region 22b, the neutron flux level in the fuel region 21 is higher than the neutron flux level in the upper axial blanket region 22b. Therefore, in other words, a part of the liquid fuel 108 has moved to a region having a relatively low neutron flux level. This result leads to a decrease in the reactivity of the fast reactor core 10.

  FIG. 11 is a graph showing an example of the degree of substitution reactivity of the core fuel assembly to the core damage prevention structure for explaining the effect of the fast core according to the first embodiment. That is, an example in which the core damage prevention structure 100 is activated and enters the state shown in FIG. The horizontal axis represents the ratio (%) of the number of bodies replaced from the core fuel assemblies 30 to the core damage prevention structures 100 in the fast core 10 to the total number of core fuel assemblies 30 and core damage prevention structures 100. It is. The vertical axis represents the reactivity ($) added to the fast reactor core due to the replacement. Note that 1 $ is the magnitude of the reactivity when the reactivity ρ is equal to the delayed neutron ratio β.

  In the core shown in FIG. 2, the number of core fuel assemblies 30 when the core damage prevention structure 100 is not present is 286. Here, in the dispersion case as shown in FIG. 2 in the core fuel assembly 30, when 16 bodies are replaced with the core damage prevention structure 100, as shown by the point D1 in FIG. Negative reactivity is about minus $ 5.5. Similarly, when the number of core damage prevention structures 100 to be replaced with the core damage prevention structure 100 is 10 in the dispersion case, as shown by a point D2 in FIG. The reactivity is about minus 3.4 dollars ($).

  On the other hand, when 16 bodies are replaced with the core damage prevention structure 100 in the central concentration case concentrated in the center, the negative reactivity added by the replacement is about minus 3 as shown by the point C1 in FIG. One dollar ($).

  In the case of a fast reactor, the control rod insertion depth is adjusted in order to shift from a low temperature reactor shutdown state to an output operation state, and temperature compensation / output compensation reactivity is given. Although the magnitude of this compensation reactivity varies somewhat due to differences in core fuel specifications, etc., it is usually about 3 $ in the case of a large-sized fast reactor of a conventional oxide fuel core.

  When it is assumed that a part of the core fuel is discharged from the core region so that the core is in a healthy state, for example, equivalent to about minus 3 $ instead of inserting a control rod, the entire core is in a cold shutdown state. The soundness of many core fuels will be maintained.

  Even when the criticality is maintained even if the reactor core is damaged during the safety analysis assuming the occurrence of a reactor shutdown failure event, the output is generated in a state where the solid fuel becomes hot and enters a molten pool state, minus 3 Non-Patent Documents 2 and 3 show examples in which, when $ fuel is discharged, the fuel temperature state decreases, and even if a positive reactivity is applied, reactor shutdown is achieved. Therefore, it is considered that the furnace can be stopped if about minus 3 $ is secured.

  As described above, it is more effective to reduce the reactivity when the core damage prevention structure 100 is dispersed. Further, for example, it can be seen that in order to ensure a reactivity reduction effect of 3 dollars or more in absolute value, it is sufficient to replace 10 bodies, that is, in a ratio of about 5% to 6%.

  The above is a case where a part of the liquid fuel 108 moves from the fuel region 21 to the upper axial blanket region 22b due to the opening of the melting plug 123, but also in the case where the opening of the melting plug 123 is not accompanied. The same can be said as follows.

That is, when the temperature of the fast reactor core 10 rises, the core fuel part 30a that is the heat generating part of the core fuel assembly 30 is thermally expanded. Similarly, the liquid fuel part 100a of the core damage prevention structure 100 is also thermally expanded. By the way, the thermal expansion coefficient (linear expansion coefficient) of the liquid fuel 108, for example, liquid metal uranium is about 2.24 × 10 ⁻⁵ [1 / K], and the thermal expansion coefficient (linear expansion coefficient) of the solid metal uranium. ) Is about 2.00 ⁵ [1 / K] or so.

On the other hand, the pellet of MOX (mixed oxide fuel) has a thermal expansion coefficient (linear expansion coefficient) of about 1.50 × 10 ⁻⁵ [1 / K] at 1500 ° C., and a cladding tube such as austenitic stainless steel. Then, it is about 1.80 × 10 ⁻⁵ [1 / K], which is smaller than the thermal expansion coefficient (linear expansion coefficient) of liquid metal uranium.

  Therefore, the ratio of the liquid fuel 108 protruding beyond the fuel region 21 (FIG. 4) is increased due to thermal expansion. When a material having a small coefficient of thermal expansion is used as the material of the cladding tube, for example, if the coefficient of thermal expansion is zero as an extreme assumption, the thermal expansion in the radial direction of the liquid fuel 108 is completely achieved by the cladding tube. Therefore, the liquid fuel 108 expands in the axial direction (vertical direction) at an expansion rate that is three times the linear expansion rate.

  For this reason, due to the larger thermal expansion of the liquid fuel 108 in the liquid fuel portion 100a, a part of the liquid fuel 108 is shown in FIG. Move outside of. Therefore, even when the temperature of the fast reactor core 10 rises, the liquid fuel 108 moves from the fuel region 21 to the upper axial blanket region 22b, and has the effect of reducing the reactivity of the fast reactor core 10.

  In addition, with the thermal expansion of the liquid fuel 108 in the liquid fuel part 100a, the component which absorbs neutrons also thermally expands. This has the effect of increasing the reactivity. Therefore, whether the overall effect of these effects is to decrease or increase the reactivity depends on the ratio of fissile material in the liquid fuel 108 to the component that absorbs neutrons.

FIG. 12 is a graph showing an example of the reactivity effect by thermal expansion for explaining the effect of the fast reactor core according to the first embodiment. The horizontal axis represents the ratio of fissile material, and is indicated by the fissionable material ratio m. When the total mass of the fuel parent material in the fast reactor core 10 is M _ft and the total mass of the fissile material is M _fs , the fissile material ratio m is given by m = M _fs / (M _fs + M _ft ). That is, the fissionable material ratio m is a value corresponding to the enrichment degree. The vertical axis represents the expansion reactivity, which is the reactivity added when the temperature of the fast reactor core 10 rises by 1K.

  As shown in FIG. 12, in the region where the fissionable material ratio m is small, the effect of increasing the reactivity is large, and the expansion reactivity is positive. When the fissionable material ratio m becomes sufficiently large, the effect of decreasing the reactivity is large, and the expansion reactivity is negative. The ratio m of the fissile material whose expansion reactivity changes from positive to negative is, for example, about 10% in a normal core. Thus, when the enrichment is about 10%, the expansion reactivity can be negative.

  As described above, in the fast core 10 according to the present embodiment, when a reactivity insertion type event such as a control rod insertion failure event occurs or when a flow loss type event occurs, a negative load is applied to the core. Can be input.

[Second Embodiment]
FIG. 13 is an elevational sectional view showing a configuration of a combined body of the first liquid fuel element and the second liquid fuel element of the core damage prevention structure of the fast reactor core according to the second embodiment. This embodiment is a modification of the first embodiment.

  A lower part of the second element gas pipe 122 of the second liquid fuel element 120b and the connecting portion 106a are connected to the combined body 105d of the core damage prevention structure 100 in the second embodiment, and the liquid fuel 108 is A discharge pipe 127 serving as a flow path when discharged is provided. In addition, a melt plug 128 is provided at the outlet of the second element gas pipe 122 to the discharge pipe 127.

  FIG. 14 is a plan view of a connecting portion between the first liquid fuel element and the second liquid fuel element, and FIG. 15 is an elevational sectional view. In the connecting portion 106a, a portion different from the connecting portion 106 in the first embodiment is a portion of the second end liquid fuel pipe lower end plug 106g.

  The lower end plug 106g for the second element liquid fuel pipe is formed with a discharge hole 106h that becomes a flow path when the liquid fuel 108 is discharged, and extends from the upper end to the lower end of the lower end plug 106g for the second element liquid fuel pipe. It penetrates. The upper end of the discharge hole 106 h is connected to the discharge pipe 127, and the lower end is connected to the external pipe 109.

  The external pipe 109 is connected to the storage container 109a. The storage container 109a is installed in the lower plenum 2a (FIG. 1), for example. The installation location of the storage container 109a may be other than the lower plenum 2a, but it needs to be a position that can be transferred from the core damage prevention structure 100 by natural fall including the routing of the external piping 109. The shape of the storage container 109a is a shape considering recriticality, such as a flat shape. The storage container 109a has, for example, a sealed structure so that the liquid fuel 108 stored in the storage container 109a does not diffuse into the reactor coolant 150 in the reactor container 2 (FIG. 1).

  The storage container 109a is installed for the purpose of limiting the range of nuclear fuel spread at the time of an accident as much as possible. Therefore, when the discharge destination by the external pipe 109 is a place where the spread of nuclear fuel is restricted, the storage container 109a may not be installed.

  In the present embodiment configured as described above, the inside of the discharge pipe 127 is normally partitioned by the molten plug 128 from the inside of the second element gas pipe 122 of the second liquid fuel element 120b. When the molten plug 128 melts at the time of the accident, the liquid fuel 108 in the second element liquid fuel pipe 121 of the second liquid fuel element 120b flows into the second element gas pipe 122 via the inner pipe 124, Transition to the bottom of the second element gas pipe 122. Therefore, the molten plug 128 melts in contact with the high-temperature liquid fuel 108, and the liquid fuel 108 flows out from the discharge pipe 127 to the external pipe 109 via the discharge hole 106h in the second end liquid fuel pipe lower end plug 106g. To do.

  Thus, in the present embodiment, the discharged liquid fuel can be guided to a predetermined discharge destination. The liquid fuel that has flowed out to a predetermined discharge destination is held in the core damage prevention structure 100, is not diffused into the plant, is solidified with a decrease in the reactivity of the core, and achieves recriticality prevention.

[Third Embodiment]
FIG. 16 is an elevational sectional view showing a structure of a combined body of the first liquid fuel element and the second liquid fuel element structure of the core damage prevention structure of the fast reactor core according to the third embodiment. This embodiment is a modification of the first embodiment. Hereinafter, a description will be given centering on differences from the first embodiment. The combined body 105b has a first liquid fuel element 110b and a second liquid fuel element 120a.

  A melt plug 114 is provided in the first element gas pipe 112 of the first liquid fuel element 110b so as to partition the space in the first element gas pipe 112 vertically. As a result, the space in the first element gas pipe 112 is divided into a lower first fuel element first space 115 and an upper first fuel element second space 116. Gases are sealed so that the pressure in the first fuel element second space 116 is higher than the pressure in the first fuel element first space 115.

  On the other hand, no melting plug is provided in the second element gas pipe 122 of the second liquid fuel element 120a, and only the second fuel element first space 125 is formed in the second element gas pipe 122. Has been. The gas is sealed so that the pressure of the gas inside the second element gas pipe 122 becomes equal to the pressure in the first fuel element first space 115.

  FIG. 17 is an elevational sectional view showing a state when the molten plug is opened in the combined body. The melt plug 114 (FIG. 16) provided in the high temperature region melts, and the first fuel element first space 115 on the low pressure side communicates with the first fuel element second space 116 on the high pressure side. As a result, the gas pressure in the first fuel element first space 115 on the low pressure side increases and becomes higher than the gas pressure in the second fuel element first space 125.

  Therefore, the liquid fuel in the first element liquid fuel pipe 111 and the second element liquid fuel pipe 121 until the pressure in the second fuel element first space 125 and the pressure in the first element gas pipe 112 are balanced. 108 moves to the 2nd fuel element 1st space 125 side the flow path including the communicating hole 106f of the connection part 106. FIG. This result is the same as the case of FIG. 10 in the description of the first embodiment.

  FIG. 18 is an elevational sectional view showing a configuration of a modified example of a combined body of the first liquid fuel element and the second liquid fuel element of the core damage prevention structure of the fast reactor core according to the third embodiment. In the coupling body 105c according to this modification, a molten plug 114 is provided in the first element gas pipe 112 of the first liquid fuel element 110b, and the second element gas pipe of the second liquid fuel element 120a is provided. A melt plug 123 is provided in 122.

  The pressure in the space below the melting plug 114 in the first element gas pipe 112 and the pressure in the space below the melting plug 123 in the second element gas pipe 122 are equal. The pressure in the space above the molten plug 114 in the first element gas pipe 112 is set to be higher than the pressure of this equal pressure. The pressure in the space above the molten plug 123 in the second element gas pipe 122 is set to be lower than the pressure of this equal pressure.

  In such a modified example, when either the molten plug 114 or the molten plug 123 is melted, the liquid fuel is moved. For this reason, a more certain effect is acquired.

  As described above, also in the third embodiment and its modified examples, similar to the first embodiment, the occurrence of a reactivity insertion type event such as a control rod insertion failure event or the flow loss type When this event occurs, negative reactivity can be introduced into the core.

[Fourth Embodiment]
FIG. 19 is a cross-sectional plan view showing the configuration of the core damage prevention structure of the fast reactor core according to the fourth embodiment. This embodiment is a modification of the first embodiment.

  The core damage prevention structure 210 includes a plurality of first liquid fuel elements 110c that are arranged in parallel to each other in the vertical direction, and a trumpet tube 101 that houses them. That is, the liquid fuel element housed in the trumpet tube 101 of the core damage prevention structure 210 in this embodiment is one type of the first liquid fuel element 110c.

  FIG. 20 is an elevational sectional view showing the configuration of the first liquid fuel element of the core damage prevention structure of the fast reactor core according to the fourth embodiment. The first liquid fuel element 110 c has a first element liquid fuel pipe 111 and a first element gas pipe 112 coupled to the upper part of the first element liquid fuel pipe 111. The space in the first element liquid fuel pipe 111 and the space in the first element gas pipe 112 are communicated by the communication hole 113.

  A lower end plug 107 is coupled to the lower portion of the first element liquid fuel pipe 111. The lower end plug 107 is formed with a discharge hole 107a that serves as a flow path when the liquid fuel 108 is discharged in the event of an accident from the upper surface toward the lower portion. An external pipe 109 is connected to the lower end of the lower end plug 107. The discharge hole 107 a is connected to a flow path in the external pipe 109.

  Inside the first element liquid fuel pipe 111, an inner pipe 117 having both ends opened is provided. One end of the inner tube 117 is connected to the upper surface of the lower end plug 107 so that the inside thereof communicates with the discharge hole 107a. The other end of the inner pipe 117 is open near the lowermost part in the space inside the first element liquid fuel pipe 111.

  Further, the inner pipe 117 is formed so that the path from one end to the other end passes through the upper part in the space inside the first element liquid fuel pipe 111. That is, the inner pipe 117 extends upward from the connection portion with the lower end plug 107 inside the first element liquid fuel pipe 111, reaches the top, and then turns downward to face downward. It extends.

  In the vicinity of the uppermost portion of the inner tube 117, a melt plug 114a is provided in the inner tube 117 so as to block the flow path. Here, the position in the height direction where the molten plug 114 a is provided is the uppermost part of the inner pipe 117, which is also near the uppermost part inside the first element liquid fuel pipe 111. The range in the height direction occupied by the first element liquid fuel pipe 111 is the same range as the range in the height direction of the fuel region 21 in the conceptual elevation sectional view of the fast reactor core 10 in FIG. 4. Therefore, the height position in the vicinity of the uppermost portion inside the first element liquid fuel pipe 111 is in the vicinity of the uppermost portion of the fuel region 21 that is a heat generating portion.

  As described above, the region above the fuel region 21 is a region where the temperature of the reactor coolant 150 that has passed through the heat generating portion is high, and is called a high temperature region. On the other hand, the temperature of the reactor coolant 150 in the vicinity of the uppermost portion of the fuel region 21 that is the heat generating portion is slightly lower than the temperature of the reactor coolant 150 that has passed through the heat generating portion, but the temperature of the fuel region 21 that is the heat generating portion. This is sufficiently higher than the temperature of the reactor coolant 150 before the temperature rises at the inlet. If the molten plug 114a melts due to the temperature rise of the reactor coolant 150 in this region at the time of an accident, it will be referred to as a high temperature region including this region. That is, the height range of the high temperature region is determined in accordance with the melting point of the molten plug 114a.

  FIG. 21 is an elevational sectional view showing a state in which the molten plug is opened in the first liquid fuel element of the core damage prevention structure of the fast reactor core according to the fourth embodiment. When the temperature in the high temperature region rises at the time of the accident, the temperature inside the first element liquid fuel pipe 111 rises and the melting plug 114a melts. The molten fuel 108 stored in the first element liquid fuel pipe 111 is pushed out by the pressure of the gas in the first element gas pipe 112 and flows out from the inner pipe 117 to the external pipe 109.

  In the present embodiment, since the melting plug 114a is provided in the high temperature region, the molten plug 114a is melted in the event of an accident, whereby the liquid fuel is discharged from the fuel region 21 (FIG. 4), and the negative reactivity is increased. Can be thrown in. Further, the ambient temperature of the inner pipe 117 surrounded by the liquid fuel 108 rises, the molten plug 114a is melted, and negative reactivity is input.

[Fifth Embodiment]
FIG. 22 is a plan view showing the configuration of the first liquid fuel element assembly of the core damage prevention structure of the fast reactor core according to the fifth embodiment. This embodiment is a modification of the fourth embodiment. The core damage prevention structure 220 includes a plurality of first liquid fuel elements 110c that are arranged in parallel to each other in the vertical direction, and a trumpet tube 101 that houses them. Two first liquid fuel elements 110c adjacent to each other are connected to each other by a connecting portion 221.

  FIG. 23 is an elevational sectional view showing a state in which a molten plug is opened in the first liquid fuel element assembly of the core damage prevention structure of the fast reactor core according to the fifth embodiment. The configuration of the liquid fuel element 110c is the same as that of the third embodiment.

  In the combined body 105f of the fifth embodiment, a connecting portion 221 is provided instead of the individual lower end plugs, and two adjacent liquid fuel elements 110c are connected to each other. The number of liquid fuel elements 110c to be connected is not limited to two and may be three or more. A discharge hole 107a is formed inside the connecting portion 221, and the liquid fuel elements 110c coupled to each other communicate with each other and extend from the lower portion of one liquid fuel element 110c to the external pipe 109 to be melted plugs. When 114 a is melted, the liquid fuel 108 can be discharged to the storage container 109 a via the external pipe 109.

[Sixth Embodiment]
FIG. 24 is an elevational sectional view showing the configuration of the core damage prevention structure of the fast reactor core according to the sixth embodiment. This embodiment is a modification of the fifth embodiment.

  That is, in the sixth embodiment, the core damage prevention structure 240 includes the storage portion 109b and the connecting pipe 109c. The storage portion 109b is a cylindrical container and is provided in the inlet space portion 100b of the core damage prevention structure 240. The central portion of the storage portion 109b in the radial direction serves as a flow path for the reactor coolant 150, and the reactor coolant 150 flowing from below flows into the upper support plate 102. The connection pipe 109c connects the discharge hole formed in the connection part 106 and the storage part 109b.

  In the sixth embodiment configured as described above, when the liquid fuel 108 is discharged, the liquid fuel 108 is stored in the storage portion 109b via the connection pipe 109c. Thus, at the time of an accident, the liquid fuel 108 that has flowed out of the fuel region 21 remains in the core damage prevention structure 100.

  As a result, the liquid fuel 108 can be handled integrally with the core damage prevention structure 100 in each core damage prevention structure 100 even when the fuel is taken out from the fast core after the accident has converged.

  FIG. 25 is an elevational sectional view showing a configuration of a first liquid fuel element assembly of a modified example of the core damage prevention structure of the fast reactor core according to the sixth embodiment. In the coupled body 105e of the present modification, a storage portion 109d is formed above the portion that forms the lower end plug portion of the first liquid fuel element 110e. In this modification, the liquid fuel 108 discharged from the fuel portion 21 (FIG. 4) does not flow out of the first fuel element 110e but stays inside the first fuel element 110e, and the liquid after the accident Higher reliability is ensured for the containment of the fuel 108.

[Seventh Embodiment]
FIG. 26 is a plan sectional view showing the structure of the core damage prevention structure of the fast reactor core according to the seventh embodiment. This embodiment is a modification of the fourth embodiment. The core damage prevention structure 230 includes a plurality of first liquid fuel elements 110d that are arranged in parallel to each other in the vertical direction, and a trumpet tube 101 that houses them. That is, the liquid fuel element housed in the trumpet tube 101 of the core damage prevention structure 230 in the present embodiment is one type of the first liquid fuel element 110d.

  FIG. 27 is an elevational sectional view showing the configuration of the first liquid fuel element of the core damage prevention structure of the fast reactor core according to the seventh embodiment.

  The first liquid fuel element 110 d has a first element liquid fuel pipe 111 and a first element gas pipe 112 coupled to the upper part of the first element liquid fuel pipe 111. The space in the first element liquid fuel pipe 111 and the space in the first element gas pipe 112 are communicated by the communication hole 113.

  A lower end plug 107 is coupled to the lower portion of the first element liquid fuel pipe 111. The lower end plug 107 is formed with a discharge hole 107a from the upper surface to the lower portion. An external pipe 109 is connected to the lower end of the lower end plug 107. The discharge hole 107 a is connected to a flow path in the external pipe 109.

  A molten plug 114b is provided at the upper inlet of the discharge hole 107a of the lowermost end plug 107 in the first element liquid fuel pipe 111 so as to block the flow path. Here, the position in the height direction where the melting plug 114 b is provided is the lowest part inside the first element liquid fuel pipe 111. That is, the melt plug 114b is provided at the lowermost portion of the fuel region 21 (FIG. 4) that is a heat generating portion.

  When a reactivity insertion type event occurs, the amount of heat generated from the fuel region 21 that is the heat generating portion of the fast reactor core 10 increases rapidly. For this reason, the temperature of the fuel region 21 increases rapidly. As a result of the temperature of the fuel region 21 becoming abruptly high, if the soundness at the bottom of the fuel region 21 exceeds the melting point of the melting plug 114b, the melting plug 114b is melted.

  When the molten plug 114b is melted, the gas pressure in the first element gas pipe 112 is high, so that the gas is pushed out and the liquid fuel 108 inside the first element liquid fuel pipe 111 is discharged into the discharge hole 107a of the lower end plug 107. It flows out to the external piping 109 via.

[Eighth Embodiment]
FIG. 28 is an elevational sectional view showing the configuration of the first liquid fuel element of the core damage prevention structure of the fast reactor core according to the eighth embodiment. This embodiment is a modification of the seventh embodiment. In the present embodiment, a molten plug set 130 is provided at the upper inlet of the discharge hole 107a of the lowermost end plug 107 in the first element liquid fuel pipe 111 so as to block the flow path.

  FIG. 29 is an elevational sectional view showing a molten plug set of the core damage prevention structure of the fast reactor core according to the eighth embodiment. The molten plug set 130 includes a molten plug 131 and a heating element 132 provided on the radially outer side of the molten plug 131. The heating element 132 is not limited to the radially outer side of the melting plug 131, and may be at the center of the melting plug, for example, as long as the melting plug 131 can be heated.

  The molten plug 131 is a material having a melting point equal to or higher than the inlet temperature of the fuel region 21 (FIG. 4) during normal operation and a low melting point. Examples of the material of the molten plug 131 include metals such as magnesium, strontium, and aluminum, or alloys thereof, chloride salts, and fluoride salts.

  The heating element 132 uses a material that generates heat by absorbing neutrons. Examples of such a material include a boron compound containing boron 10, a hafnium alloy / compound, a gadolinium alloy / compound, and a material containing a fissile substance.

  When a reactivity insertion type event occurs, the reactivity of the fast reactor core increases, resulting in an increase in the neutron flux level in the fuel region 21 (FIG. 4). As a result, the reaction amount of the heating element 132 with neutrons increases, and the heating value of the heating element 132 increases. As a result, the molten plug 131 is melted, and the upper and lower sides of the molten plug 131 communicate with each other.

For example, assuming a case where B ₄ C, which is a material for a control rod of a general fast reactor, is used, heat generation during normal operation is about 100 W / g. Consider a case where the power of the fast reactor core 10 is increased by 1.5 times due to the reactivity insertion event. Assuming that the flow rate of the reactor coolant 150 remains constant, the amount of heat accumulated in the fast reactor core 10 is 50 (= 100 * 1.5-100) W / g. Since the specific heat of B ₄ C is 0.95 J / m ³ , the temperature rise rate is 52.6 [° C./s]. Thus, the temperature of the molten plug 131 rises rapidly.

  As described above, by using the molten plug set 130 having the molten plug 131 and the heating element 132, the liquid fuel 108 can be more reliably discharged from the fuel region 21 and the negative reactivity can be inserted.

[Other Embodiments]
As mentioned above, although some embodiment of this invention was described, these embodiment is shown as an example and is not intending limiting the range of invention.

  For example, in the embodiment, the case of having a radial blanket and an axial upper and lower blanket has been described as an example, but in the case of a core that does not perform proliferation, such as a core intended for combustion of an actinide element, These blanket portions may not be provided.

  In the embodiment, the core damage prevention structure has been described by way of example only having the liquid fuel element, but the structure is not limited thereto. For example, there may be a case where liquid fuel elements and normal fuel elements are mixed in the trumpet pipe. Here, the normal fuel element is a fuel element used in the core fuel assembly.

  Moreover, you may combine the characteristic of each embodiment.

  For example, the installation of the storage unit for the discharged liquid fuel according to the sixth embodiment or its modification may be combined with the second, fourth, fifth, seventh, or eighth embodiment.

  Further, in each of the first to seventh embodiments, each core damage prevention structure is provided with a plurality of melting plugs. However, if a sufficient number of core damage prevention structures are provided, some of them are provided. Even if the molten plug is not melted, a predetermined amount of negative reactivity can be inserted. Further, a certain proportion of the plurality of fusion plugs installed may be replaced with the fusion plug set in the eighth embodiment. By providing the two types of means of the melting plug and the melting plug set, it is possible to avoid the malfunction due to the common cause and further improve the reliability of the negative reactivity insertion.

  Furthermore, these embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are also included in the invention described in the claims and the equivalents thereof.

  DESCRIPTION OF SYMBOLS 1 ... Fast reactor, 2 ... Reactor vessel, 2a ... Lower plenum, 2b ... Upper plenum, 4 ... Core support plate, 7 ... Core upper mechanism, 7a ... Control rod drive mechanism, 8 ... Coolant inlet piping, 9 ... Cooling Material outlet pipe, 10 ... Fast reactor core, 11 ... Shield plug, 12 ... Radial blanket fuel assembly, 13 ... Reflector, 14 ... Neutron shield, 15 ... Control rod assembly, 21 ... Fuel region, 22a ... Lower part Axial blanket region, 22b ... Upper axial blanket region, 23 ... Radial blanket region, 24 ... Reflector region, 25 ... Neutron shield region, 30 ... Core fuel assembly, 30a ... Core fuel part, 30b ... Lower blanket , 30c ... upper blanket part, 31 ... trumpet tube, 32 ... core fuel element, 33 ... entrance nozzle, 34 ... handling head, 34a ... outlet opening, 100 Core damage prevention structure, 100a ... liquid fuel part, 100b ... inlet space part, 100c ... upper space part, 101 ... trumpet tube, 102 ... support plate, 103 ... entrance nozzle, 104 ... handling head, 104a ... outlet opening, 105a 105b, 105c, 105d, 105e, 105f ... combined body, 106, 106a ... connecting portion, 106b ... lower end plug for the first element liquid fuel pipe, 106c ... lower end plug for the second element liquid fuel pipe, 106d ... coupling member, 106f ... Communication hole, 106g ... Second end liquid fuel pipe lower end plug, 106h ... Discharge hole, 107 ... Lower end plug, 107a ... Discharge hole, 108 ... Liquid fuel, 109 ... External piping, 109a ... Storage container (discharge destination ), 109b... Storage part (discharge destination), 109c... Connecting pipe, 109d... Storage part (discharge destination), 110a, 110b, 1 0c, 110d, 110e ... 1st liquid fuel element, 111 ... 1st element liquid fuel pipe, 112 ... 1st element gas pipe, 113 ... Communication hole, 114, 114a, 114b ... Molten plug, 115 ... 1st fuel element 1st space, 116 ... 1st fuel element 2nd space, 117 ... Inner pipe, 120a, 120b ... 2nd liquid fuel element, 121 ... 2nd element liquid fuel pipe, 122 ... 2nd element gas pipe, 123 ... Melting Plug, 124 ... Inner pipe, 125 ... Second fuel element first space, 126 ... Second fuel element second space, 127 ... Discharge pipe, 128 ... Molten plug, 130 ... Molten plug set, 131 ... Molten plug, 132 ... Heating element, 150 ... reactor coolant, 210, 220, 230, 240 ... core damage prevention structure, 221 ... connecting part

Claims (8)

A fast reactor core of a fast reactor having a fuel containing a fissile material and using a liquid metal as a reactor coolant,
A plurality of core fuel assemblies arranged in parallel with each other and extending in the vertical direction and having solid fuel;
A plurality of core damage prevention structures arranged in parallel with the plurality of core fuel assemblies and having a liquid fuel in a liquid state during normal operation and extending in a vertical direction;
A plurality of control rod assemblies that include a substance that absorbs neutrons and that are arranged in parallel with the plurality of core fuel assemblies and the plurality of core damage prevention structures, and are movable up and down;
With
Each of the plurality of core damage prevention structures includes:
A first liquid fuel element that extends vertically in a cylindrical shape and is closed at the top and bottom to contain fissile material;
During normal operation, the liquid fuel is prevented from flowing out of the first liquid fuel element through a flow path communicating with the first liquid fuel element, and the ambient temperature rises during an accident. A molten plug that melts and allows the liquid fuel to flow out,
A fast reactor core characterized by comprising: The fast reactor core according to claim 1, wherein the molten plug further includes a heating element that generates heat by reaction with the neutrons and applies heat to the molten plug . A second liquid fuel element adjacent to the first liquid fuel element and communicating with the first liquid fuel element and extending vertically;
The second liquid fuel element has a space for storing the liquid fuel when moved with the outflow of the liquid fuel from the first liquid fuel element, and the melting plug includes the space and the liquid The fast reactor core according to claim 1, wherein the fast reactor core is arranged so as to separate fuel . The second liquid fuel element is connected to a discharge destination for discharging the moved liquid fuel, and the melting plug is arranged to separate the discharge destination and the second liquid fuel element. The fast reactor core according to claim 3, wherein: The first liquid fuel element is connected to a discharge destination for discharging the flowing out liquid fuel, and the melting plug is arranged to separate the discharge destination from the first liquid fuel element. The fast reactor core according to claim 1 , wherein the fast reactor core is provided. The fast reactor core is installed in the reactor vessel,
6. The fast reactor core according to claim 4, wherein the discharge destination is a closed vessel provided in the reactor vessel and below the plurality of core damage prevention structures . 7. Before SL output tray, fast reactor core according to claim 4 or claim 5, characterized in that a storage section provided in the respective inlet space portion before Symbol plurality of core damage prevention structure. A fast reactor core with fuel containing fissile material and liquid metal as reactor coolant;
  A reactor vessel that houses the fast reactor core and holds the reactor coolant;
  A shielding plug that covers an upper portion of the reactor vessel and supports a control rod drive mechanism that drives a control rod that controls the reactivity of the fast reactor core;
  With
  The fast reactor core is:
  A plurality of core fuel assemblies arranged in parallel with each other and extending in the vertical direction and having the solid fuel,
  A plurality of core damage prevention structures arranged in parallel with the plurality of core fuel assemblies and having the liquid fuel and extending in a vertical direction;
  A plurality of control rod assemblies including a neutron absorbing material and arranged in parallel with the plurality of core fuel assemblies and the plurality of core damage prevention structures;
  With
  Each of the plurality of core damage prevention structures includes:
  A first liquid fuel element that extends vertically in a cylindrical shape and is closed at the top and bottom to contain fissile material;
  The liquid fuel is prevented from flowing out from the first liquid fuel element through the flow path communicating with the first liquid fuel element, and melted due to an increase in the ambient temperature at the time of an accident. A melt plug that allows spillage;
  A fast reactor characterized by comprising:

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