JPH0715503B2 - Liquid metal cooling fast reactor - Google Patents

Description

Detailed Description of the Invention [Industrial applications]

The present invention relates to a technology for simplifying a liquid metal cooling fast reactor structure for realizing a microminiature intrinsic safety reactor that can be used in both heat supply plants and power generation plants.

[Prior art]

Liquid metal-cooled fast reactors used in conventional large-scale power plants, etc. are equipped with a control rod drive mechanism and a fuel exchange device toward the inside of the reactor vessel, and a heat exchanger and a reactor outside the reactor vessel. The structure is such that a primary cooling circulation pump that circulates the coolant in the container is connected by piping. Microminiature reactors, which have an output scale several orders of magnitude smaller than the current liquid metal cooled fast reactors, are being studied in various countries, but they have not been put to practical use because they have the disadvantage that the unit price of power generation becomes higher as they become smaller.

[Problems to be Solved by the Invention]

If the conventional liquid metal cooling fast breeder reactor system is downsized as it is, the system becomes complicated and the economy is remarkably inferior. Therefore, an object of the present invention is to simplify the structure of a liquid metal cooled fast reactor, the operation control technique, and the operation control system necessary for realizing a micro reactor while maintaining the inherent safety.

[Means for Solving the Problems]

A liquid metal-cooled fast reactor of the present invention for achieving the above object, a reactor vessel filled with a liquid metal coolant,
An annular radial reflector arranged and fixed in the reactor vessel, an output unit extending vertically in the reactor vessel and penetrating through the ring of the radial reflector, and the atom. And a driving device which is arranged above the outside of the reactor vessel and drives the output unit up and down. The output unit includes a core and an upper part which is attached above and below the core and has a coolant passage in the axial direction. An integrated structure comprising a lower axial reflector and an output unit pipe connected to the upper end of the upper axial reflector and extending vertically upward in the reactor vessel and having a plurality of coolant outlet holes at predetermined positions The length of the output unit tube is such that even if the lower end of the upper axial reflector falls to the same level as the lower end of the radial reflector in the ring of the radial reflector, the upper end of the output unit tube Has a length protruding above the outside of the reactor vessel And wherein the door.

[Action]

In the liquid metal cooling fast reactor of the present invention having the above configuration,
Depending on the position of the core inserted in the ring of the radial reflector,
The enclosure is surrounded by two upper and lower axial reflectors and an annular radial reflector which are sandwiched between the cores, and the surrounding condition changes, and the amount of heat energy output from the core changes depending on the surrounding condition. Output changes in the order of criticality → rated output → maximum output → rated output → partial output → scrum. The coolant flows upwards from the bottom in the reactor vessel, usually through natural convection or an attached circulation pump, through the axial coolant passages formed in the axial reflector and the core gap. A primary cooling system loop formed by a nuclear power container, a circulation pump, and a pipe connecting the nuclear power container in the case where the circulation pump is provided inside the nuclear power container or outside the nuclear power container through the coolant circulation hole of the output unit pipe Circulate. The reactivity of the core varies depending on the arrangement position of the core corresponding to the power output of the core with respect to the radial reflector and the core temperature, and is suppressed as the core temperature increases, and has the property of reducing the power output of the core. Therefore, when the temperature of the coolant flowing through the core gap increases or the core flow rate decreases, the core temperature rises temporarily, but this suppresses the reactivity of the core and reduces the core temperature. Once again, the endothermic capacity of the coolant, ie the power of the furnace, is reduced. The opposite is true when the coolant temperature is low or the core flow is reduced. In addition, when the temperature of the coolant rises, the output unit pipe, etc. expands thermally, and the upper end of the output unit pipe is fixed during reactor operation, so the core moves toward the bottom of the reactor vessel. To do. On the other hand, since the radial reflector is fixed to the reactor vessel, it moves upward due to thermal expansion, and the core is relatively deeply inserted into the ring of the radial reflector. Therefore, the relative reactivity of the two causes a slight decrease in the reactivity of the core.

【Example】

Hereinafter, the present invention will be described more specifically with reference to examples. FIG. 1 shows an example of the liquid metal cooling fast reactor of the present invention. This liquid metal cooled fast reactor is configured to include a reactor vessel 1 and an output unit 2. In the reactor vessel 1 in this, molten metal such as Na or Na
A coolant 3 made of K is contained. In addition, an annular radial reflector 4 is provided at the bottom of the reactor vessel 1 at the support 5
Is fixed through. This support 5 is composed of an annular support plate 5a having the same inner diameter as the ring of the radial reflector 4 and an open pipe 5b. The annular support plate 5a is joined inside the reactor vessel 1 and the open pipe 5b is connected to the annular support plate 5a. Are joined downward, and the radial reflectors 4 are joined upward with their inner edges aligned with each other, and the annular support plate 5a
A plurality of holes 5c for allowing the coolant 3 to flow therethrough are formed in the. Furthermore, the reactor vessel 1 has a bottom end with the reactor vessel 1
Rolling is prevented by a steady rest 7 which is fixed to a pit 6 surrounding the pit 6 and projects from the pit 6 at the upper position. On the other hand, in the output unit 2, the two cores 8 having a plurality of flow passages 9c of the coolant 3 formed in the axial direction of the core 8 having a diameter penetrable through the ring of the radial reflector 4 and the cores 8 sandwiching the core 8 to be joined. The core 8 and the axial reflector 9 are provided on one edge of the directional reflectors 9a, 9b.
The lower end of an output unit pipe 10 having the same diameter as a and 9b is connected. This output unit tube 10 is such that even if the lower end of the upper axial reflector 9a reaches the same level as the lower end of the radial reflector 4 in the ring of the radial reflector 4, the upper end of the output unit tube is atomized. It has a length that protrudes above the outside of the furnace vessel 1,
Further, at this time, on the peripheral surface at a predetermined position located near the liquid surface in the coolant 3, the coolant 3 is allowed to flow from the inner side to the outer side of the output unit pipe 10 and on the coolant 3. A vent hole 10d is formed in the peripheral surface at a predetermined position to smoothly flow the coolant 3. Also,
In the output unit pipe 10, a secondary heat pipe 11 having a flow path 11c for the coolant 3 formed from the upper end to the lower end is circulated between the axial reflector 9a and the secondary heat pipe 11. A pump 12 is provided, and the upper end of the output unit pipe 10 is covered with a shield 13.
Is airtightly covered by. Further, the thermocouple converter 14 is joined to the lower section and the heat radiating section 16 through which the working fluid flows is joined to the upper section at the upper end outer peripheral portion of the output unit pipe 10 with the upper end surface as a boundary, and also penetrates both sections. A heat radiation system heat pipe 17 is provided. The output unit 2 of the integral structure composed of the above components is connected to a drive system (not shown) at the upper end of the heat dissipation unit 16, and the upper end of the reactor vessel 1 has a through hole through which the output unit 2 can move up and down. It is sealed by a shielding plug 18 that it has. Further, in the above-mentioned constituent members, for example, the fuel used in the core 8 may be a mixed oxide of U and Pu or UN,
As the material of the reflectors 4 and 9, for example, Be or BeO is used. As the material of the heat pipes 11 and 17, especially the heat radiation system heat pipe 17, Ti or Nb-Zr is suitable when the working fluid is Ce, and in this case, it is usually applied in the temperature range of 450 to 900 ° C. . When the working fluid is K, Ni is suitable,
In this case, it is usually applied in the temperature range of 50 to 1000 ° C. Also, the inner wall of the reactor vessel 1, the support 5, the output unit pipe
For example, stainless steel is used as the material of the materials that are in contact with the coolant 3 such as 10 and other than the above-mentioned constituent members, and the material of the shield 13 is a neutron shield such as LiH, B ₄ C or the like. Materials and gamma ray shielding materials such as W are used. In the liquid metal cooling fast reactor configured as described above, the molten metal such as Na and NaK used for the coolant 3 may be wound around the reactor vessel 1 with an electric heater or between the reactor vessel 1 and the pit 6. It is injected while being heated to a temperature equal to or higher than the melting point by, for example, flowing a high temperature gas into the gap. Next, the output unit 2 is installed in the reactor vessel 1, and the coolant 3 in the reactor vessel 1 is circulated by natural convection or a circulation pump 12. The circulation of the coolant 3 is performed according to the arrow in FIG.
That is, the coolant 3 flows into the open pipe 5b of the support 5 and sequentially passes through the flow passage 9c of the axial reflector 9a, the gap of the core 8 and the flow passage 9c of the other axial reflector 9b. It flows upward in the output unit pipe 10, then flows out of the flow hole 10c to the outside of the pipe, flows downward between the output unit pipe 10 and the reactor vessel 1, and is opened in the annular support plate 5a of the support body 5. It again flows into the open pipe 5b through the open hole 5c. To start the reactor, the output unit 2 is gradually inserted into the radial reflector 4 from the axial reflector 9b located at its lower end. Then, the arrangement of the radial reflector 4 and the core 8 is gradually changed so that the core 8 is surrounded by the two axial reflectors 9a and 9b and the radial reflector 4 (Fig. 2a). The output of the cooled fast reactor reaches a critical level. Furthermore, the axial reflector 9a located at the lower end of the output unit 2 is the radial reflector 4a.
As it is deeply inserted inside, the power of the furnace gradually increases,
The core 8 is located in the center of the radial reflector 4 (Fig. 2c).
In this case, the output of the furnace is maximum. In this case, the rated output at the midway position (Fig. 2b) until the output of the furnace changes from the critical level to the maximum exceeds the rated output by several tens of percent, but it can be dealt with by the heat absorption and release process of the heat transfer system described later. . When the core 8 is inserted further deeper than the central position of the radial reflector 4 (Fig. 2c), the power of the reactor gradually decreases and reaches the rated power again at the position shown in Fig. 2d. Then, at the position shown in FIG. 2e, a partial power corresponding to the critical power is reached and the core 8 is scrammed when it has completely passed the radial reflector 4 (FIG. 2f). The heat generated in the core 8 according to the reactivity of the core 8 is absorbed by the coolant 3 around the core 8 to raise the temperature of the coolant 3 around the core 8. Then, the coolant 3 having a high temperature heats the secondary heat pipe 11 in the output unit pipe 10 along the flow, and after being absorbed by the secondary heat pipe 11, it is outside from the flow hole 10c of the output pipe 10. Is leaked to. On the other hand, the heat absorbed by the secondary heat pipe 11 is
It is transmitted to the upper end of the secondary heat pipe 11 and part of it is converted into electric energy by the thermocouple converter 14 (conversion efficiency of about 7%), and the rest is transferred to the heat radiation system heat pipe 17 for heat dissipation. Cooled in section 16. Then, the thermocouple converter 14 generated in the process of absorbing and releasing heat in the heat transfer system
This electric energy will be output from the furnace and used. The self-controllability of the power output of this reactor is
When Pu mixed oxide or UN is used, the feedback effect by each Doppler effect can be expected. Further, even if the temperature of the coolant 3 in the core 8 becomes too high, the reactor vessel 1 and the output unit 2 are thermally expanded as described above, and the core 8 moves downward from the center with respect to the radial reflector 4. Since it moves toward the center, the reactivity of the core 8, and hence the power of the furnace, is suppressed and controlled not only by the temperature of the coolant 3 but also by the arrangement position of the core 8 with respect to the radial reflector 4. As described above, the liquid metal cooled fast reactor shown in FIG. 1 has inherent safety. For example, even if the circulation pump 12 is stopped, the coolant 3 circulates without trouble due to natural circulation, and scram cannot be performed due to a failure of the drive system. Even if the temperature of the core 8 rises to some extent, the coolant 3 becomes high in temperature. The reactivity of the core 8 is reduced, and the temperature of the core 8 can be suppressed below the allowable value. In this way, after the core 8 is scrammed after, for example, 7 to 8 years, the power unit 2 is pulled out from the reactor vessel 1 and is replaced with a new power unit 2 to refuel the core 8. Even when maintenance and repair of the components in the output unit 2 are performed, the entire output unit 2 is pulled out and placed in a shielding container in an inert gas atmosphere to shield the radiation from the adhering coolant 3. It is transported and the maintenance and repair of the components in the output unit 2 are performed. An example of the liquid metal cooled fast reactor of the present invention has been described above. However, this reactor has a circulation pump 12 depending on, for example, the scale of the core.
Alternatively, the thermocouple converter 14 and the heat radiation system heat pipe 17 may be omitted when only the thermal energy is used as the output of the furnace, and the secondary unit may be provided at the outer peripheral portion of the upper end of the output unit pipe 10. The structure may be such that the upper end of the system heat pipe 11 is located. Also, the secondary heat pipe 11 and the circulation pump 12 built in the output tube unit 2 are deleted,
A circulation pump 12 is provided outside the reactor vessel 1 as shown in FIG. 3a.
Piping to form the primary cooling system loop through the heat exchanger 20
They may be connected by 19a, 19b, 19c, or as shown in FIG. 3b, the circulation pump 12 and the heat exchanger 20 may be arranged outside the output unit pipe in the reactor vessel 1, respectively. Furthermore, it goes without saying that the circulation pump 12 may be removed from the furnace shown in FIGS. 3A and 3B depending on the scale of the core. Also, when the core is enlarged to some extent, it is shown in FIG.
As shown in FIG. 5, the required number of control rods 21 may be vertically fixed to the bottom of the reactor vessel 1 at positions where they can be taken in and out in the core 8 and the axial reflectors 9a and 9b along the axial direction. In the furnace of FIG. 3c, the control rod 21 is attached to the control rod mounting base 22, and the control rod mounting base 22 is detachably mounted to the control rod mounting base 23 provided on the bottom of the reactor vessel 1. A control rod guide tube 24 is attached inside the core 8 and the axial reflectors 9a, 9b so as to penetrate in the axial direction.
Control rod 21 is fully inserted at least during rated operation,
As a result, the control rod 21 can be exchanged after the output unit 2 is pulled out, and there is no problem in the control rod insertability during an earthquake. As described above, the liquid metal cooled fast reactor of the present invention can be variously modified within the scope described in the claims depending on the usage of the core-scale reactor.

【The invention's effect】

As is apparent from the above description, according to the present invention, the control rod drive mechanism and the fuel exchange device, which were required in the conventional liquid metal cooled fast reactor, can be omitted, and further, the circulation pump or the like can be provided depending on the scale of the reactor core. Since it can be omitted, the simplification required for downsizing of the liquid metal cooled fast reactor can be performed, and it has excellent inherent safety, and it has an appropriate structure for realizing the future ultra-small intrinsic safety reactor. A liquid metal cooled fast reactor is provided.

[Brief description of drawings]

FIG. 1 is an explanatory view showing an example of a liquid metal cooled fast reactor of the present invention, and FIGS. 2 a to f sequentially show the arrangement of the core according to the present invention from when the power of the reactor reaches the critical to the scrum. Explanatory drawing and FIG. 3 a-c are explanatory drawings which show another example of the liquid metal cooling fast reactor of this invention, respectively. 1 ... Reactor vessel, 2 ... Output unit, 3 ... Coolant, 4 ... Radial reflector, 8 ... Reactor core, 9 ... Axial reflector, 10 ... Output unit tube, 11 ... Secondary heat pipe, 12 ... Circulation pump, 14 ... Thermocouple converter, 17 ... Radiating heat pipe, 20 ... Heat exchanger, 21 ... Control rod, 9
c, 11c ... Coolant flow path, 10c ... Coolant flow hole.

Claims (9)

[Claims] 1. A nuclear reactor vessel filled with a liquid metal coolant, an annular radial reflector arranged and fixed in the nuclear reactor vessel, and extending vertically in the nuclear reactor vessel. ,
The output unit is capable of penetrating the inside of the ring of the radial reflector, and a drive device arranged above the outside of the reactor vessel to drive the output unit up and down.
A core, upper and lower axial reflectors mounted above and below the core and having a coolant flow path in the axial direction, and connected vertically to the upper ends of the upper axial reflectors to move vertically upward in the reactor vessel. It has an integral structure consisting of an output unit tube extending and having a plurality of coolant outlet holes at predetermined positions, the output unit tube having a length such that the lower end of the upper axial reflector is the same as the lower end of the radial reflector. A liquid metal-cooled fast reactor characterized in that the upper end of the output unit tube has a length protruding above the outside of the reactor vessel even when the radial reflector is lowered to the level. 2. A liquid metal cooled fast reactor according to claim 1, wherein a secondary heat pipe having a coolant passage formed from the upper end to the lower end is arranged in the output unit pipe. 3. The liquid metal cooling fast reactor according to claim 2, wherein a heat radiation system heat pipe and a thermocouple converter are arranged at the outer peripheral portion of the upper end of the output unit pipe. 4. The liquid metal cooled fast reactor according to claim 2, wherein a circulation pump is provided between the secondary heat pipe and the upper axial reflector. 5. The liquid metal cooled fast reactor according to claim 1, wherein the heat exchangers are connected by a pipe forming a primary cooling system loop of the reactor vessel. 6. The liquid metal cooled fast reactor according to claim 5, wherein a circulation pump is provided between the heat exchanger and the reactor vessel. 7. The liquid metal cooled fast reactor according to claim 1, wherein a heat exchanger is arranged around the output unit pipe arrangement position in the reactor vessel. 8. A liquid metal cooling fast reactor according to claim 7, further comprising a circulation pump arranged around the output unit pipe arrangement position in the reactor vessel. 9. A plurality of control rods are erected and fixed from the bottom of the reactor vessel toward the inside of the ring of the radial reflector, and the output unit descends to a predetermined position within the ring of the radial reflector. 9. The liquid metal cooled fast reactor according to claim 1, wherein the control rods are axially inserted inside the core and the axial reflector when the liquid is cooled.