JP5829465B2 - Nuclear fuel cooling system - Google Patents

Description

  The present invention relates to an apparatus for cooling nuclear fuel that generates decay heat after a nuclear reactor is shut down.

  An example of an apparatus that removes decay heat generated from nuclear fuel after the reactor is shut down is described in Patent Document 1 and Patent Document 2. Patent Document 1 describes a device in which one end of a heat pipe is inserted into the reactor vessel and the other end is inserted into a heat radiating duct provided outside the reactor vessel. . Thermal insulation valves are provided at the entrance and exit of the heat radiating duct, respectively. Each heat insulation valve is closed during normal operation of the reactor to close the heat radiating duct to the outside air. On the other hand, when the main cooling device that cools the reactor is stopped and the nuclear fuel of the reactor is replaced, or when the main cooling device fails or accidents, or the power supply for operating the main cooling device is lost. In the event of an emergency, each heat insulation valve is opened to open the heat radiating duct to the outside air. Therefore, in the event of an emergency such as that described above, the heat insulation valve is opened to start heat transport by the heat pipe, and the heat of the reactor is forcibly released from the heat radiating duct into the atmosphere. ing.

  Patent Document 2 discloses a decay heat removal apparatus that combines a heat exchanger that transfers heat generated in a nuclear reactor directly from a so-called primary system that directly contacts nuclear fuel to a so-called secondary system that does not directly touch the nuclear fuel, and a heat pipe. Have been described. Specifically, in the heat exchanger, the secondary cooling water is vaporized by exchanging heat between the secondary cooling water and the steam generated in the core. The steam of the secondary cooling water is supplied to the turbine via the secondary piping to rotate the turbine. A generator connected to the turbine so as to be able to transmit power is driven to generate power. Above the heat exchanger, one end of a pipe communicates, and the other end of the pipe is immersed in water stored in a pool outside the core. And, when the nuclear reactor is urgently stopped (that is, when the nuclear reactor is scram), the secondary cooling water vapor generated by the heat exchanger described above is supplied to the other end of the pipe, The other end is configured to function as a condensing unit. That is, by making the above-mentioned pipe function as a heat pipe, the heat of the core is effectively radiated to the outside of the core.

JP 58-1118988 JP-A-1-172800

  Each device described in Patent Document 1 and Patent Document 2 is configured to cool the nuclear reactor using heat pipes, and these heat pipes do not function during normal operation of the nuclear reactor, It is configured to function only in an emergency. However, in order to remove the decay heat immediately after the reactor shuts down, there is a possibility that the above decay heat cannot be removed sufficiently and sufficiently unless a large number of heat pipes are installed around the nuclear fuel or the reactor. is there.

  On the other hand, so-called spent nuclear fuel taken out from a nuclear reactor is generally immersed in cooling water and cooled and stored in a pool outside the nuclear reactor. Since the cooling water is heated by decay heat generated by the spent nuclear fuel, it is cooled by the cooling device so as to be in a predetermined temperature range. Therefore, the cooling water in the pool is generally circulated between the pool and the cooling device by a pump. However, if the power supply is lost, the pump breaks down and the circulation of the cooling water stops or the cooling device does not operate in the emergency as described above, the cooling water becomes insufficiently cooled. As a result, the spent nuclear fuel stored in the pool may not be sufficiently cooled.

  This invention has been made paying attention to the above technical problem, even if the cooling device for cooling the cooling water in the pool or the power source for operating this malfunctions or is lost, It is an object of the present invention to provide a so-called passive nuclear fuel cooling device capable of sufficiently cooling spent nuclear fuel stored in a pool.

In order to achieve the above-mentioned object , the present invention takes a heat from outside in a nuclear fuel cooling device that cools a nuclear fuel that generates decay heat by immersing it in the cooling water and taking heat from the cooling water. The evaporating part and the condensing part that radiates heat to the outside are connected by a steam pipe and a liquid return pipe so as to form a ring as a whole, and a working fluid that circulates and flows by changing the state to the gas phase and the liquid phase is enclosed The evaporation section is configured by communicating a plurality of evaporation pipes with upper and lower header pipes and immersed in the cooling water, and each of the condensing sections includes a plurality of heat radiation fins. a plurality of condensing tube with upper and lower header tubes plurality of sets of units constructed in communicated to the said header pipe at the top of each unit is in communication with the upper collecting pipe, the lower the lower the header pipe With communicates with the engagement tube, the condensing tube is shorter than said evaporation pipe, and the condensing unit is placed in the ambient air at a position higher than the previous SL evaporation portion, the upper of definitive to the evaporating portion and the upper collecting pipe wherein f and Dda pipe are communicated by the steam pipe, one or the a lower collecting pipe and the f Dda tube before Symbol lower the definitive to the evaporation portion are communicated by the liquid return pipe, the evaporator section and number of the evaporator tubes and that make up the condensable portion and the condensing tube, while being set to the number of the smaller becomes the surface area than the required heat resistance between the outside air and the coolant, the condenser portion number of the condensing tube constituting are those wherein the more than this number of the evaporator tubes constituting the evaporator unit.

According to this invention, the evaporation part and the condensation part of the loop heat pipe are configured by communicating a plurality of evaporation pipes and condensation pipes with the upper and lower header pipes, and the evaporation part and the condensation part are communicated by the steam pipe, and The evaporation part and the condensation part are communicated with each other by a liquid return pipe. The evaporation unit is immersed in immersed allowed to save them and cooling water of nuclear fuel For example, is configured to vaporized working fluid is supplied to the condenser portion through a steam pipe at the evaporator section . The condensing unit is provided above the evaporating unit and exposed to the atmosphere so that the working fluid condensed by releasing heat from the condensing unit is returned to the lower evaporating unit through the liquid return pipe by gravity. It is configured. A large number of heat dissipating fins are provided in each condensing tube constituting the condensing part, and the heat dissipating area in the condensing part is enlarged. That is, the heat dissipation efficiency is increased. In addition, in the present invention, the surface area where the number of the evaporation pipes and the condensation pipes constituting the evaporation section and the condensation section of the loop heat pipe is smaller than the required thermal resistance between the cooling water and the outside air, The number is set to be. As a result, the cooling water is cooled as necessary and sufficiently by heat transported by the loop heat pipe and dissipated into the atmosphere. As a result, the nuclear fuel can be sufficiently and sufficiently cooled. In this way, the loop heat pipe transports heat in the form of latent heat of the working fluid whose state changes, and thus does not require, for example, a cooling device or a pump for circulating cooling water. In addition, heat transport due to changes in the state of the working fluid occurs without a break if there is a temperature difference between the cooling water and the outside air temperature. If or deleted mourning (ie, emergency) even, it is possible to require sufficiently cool the cooling water. Furthermore, the loop heat pipe according to the present invention does not cause a counter flow between the liquid-phase working fluid and the gas-phase working fluid. Therefore, the heat transport amount of the loop heat pipe according to the present invention is increased as compared with a normal single pipe heat pipe. And since the condensed working fluid is recirculated to the lower evaporation part by gravity, the member for recirculation | recirculation of working fluids, such as a wick, is not required, and material cost can be suppressed by that much. From the above, the cooling device according to the present invention cools the cooling water in the pool as necessary and sufficiently even when the so-called nuclear reactor is scrammed, thereby cooling the nuclear fuel stored in the pool as necessary and sufficiently. can do. Since the cooling device according to the present invention is a so-called completely passive cooling device, the “cooling” among “stopping”, “cooling”, and “confining” that are the basics of safety of nuclear power generation is stably and continuously maintained. It is possible to contribute to the development of nuclear power generation.

Further, according to the present invention comprises a plurality of units communicated a plurality of condensing tubes to the header pipe above under the top of the header pipe of each unit is in communication with the upper collecting pipe, a lower header tube bottom It communicates with the collecting pipe. The upper collecting pipe communicates with the steam pipe, and the lower collecting pipe communicates with the liquid return pipe. Therefore, the heat radiation area in the condensing part can be further expanded. As a result, the heat dissipation efficiency of the loop heat pipe can be further improved.

It is a figure showing typically an example of composition at the time of applying a loop type heat pipe concerning this invention to a spent nuclear fuel storage pool. It is a figure which shows the simulation result of the change of the water temperature at the time of applying the loop type heat pipe which concerns on this invention to a spent nuclear fuel storage pool. It is a figure which shows typically an example of a structure of the boiling water reactor which can be made into object by this invention. It is an upper view which shows typically an example of a spent nuclear fuel storage pool. It is a side view of an example of the spent nuclear fuel storage pool shown in FIG. It is a figure which shows typically an example of a structure of a nuclear fuel assembly. It is sectional drawing which follows the VII-VII line shown in FIG. 4 is a chart showing the burnup of a nuclear fuel assembly used in the boiling water reactor shown in FIG. 3 as a reference example. It is a figure showing typically an example of composition of a loop type heat pipe concerning this invention. FIG. 10 is a top view of an example of the radiating fin shown in FIG. 9.

  Next, the present invention will be specifically described. FIG. 3 schematically shows an example of the configuration of a boiling water reactor that can be the subject of the present invention. A reactor containment vessel 2 is stored in the reactor building 1. The reactor containment vessel 2 includes a dry well 3 and a wet well 4, and a reactor pressure vessel 5 is stored in the dry well 3. A nuclear fuel assembly is immersed in water and stored in the reactor pressure vessel 5.

  The wet well 4 is connected to the dry well 3 through a vent pipe 6, and a pressure suppression pool 7 is provided inside the wet well 4. When water is stored inside the pressure suppression pool 7, the internal pressure of the reactor pressure vessel 5 rises, and the steam in the reactor pressure vessel 5 is released to the pressure suppression pool 7 through the vent pipe 6. In addition, the pressure is adjusted by cooling and condensing the steam with water stored therein. In addition to this, the pressure suppression pool 7 is also configured to function as a water source when an emergency cooling device for a nuclear reactor is operated, for example.

  In the example shown in FIG. 3, the fuel storage pool 8 is provided in the upper part of the reactor building 1 and at substantially the same height as the top of the dry well 3. FIG. 4 schematically shows a top view of an example of the fuel storage pool, and FIG. 5 shows a side view of the fuel storage pool shown in FIG. The fuel storage pool 8 is used to cool the spent nuclear fuel by immersing it in water (that is, cooling water) until the decay heat generated from the aggregate of spent nuclear fuel is reduced to some extent. As an example, the fuel storage pool 8 is made of concrete, and a stainless steel plate is affixed to the inside and the outside of the fuel storage pool 8 so as to shield radiation emitted from spent nuclear fuel. In the example shown here, the fuel storage pool 8 is formed as a water tank having a length of about 12 m, a width of about 10 m, and a water depth of about 12 m, and the thickness of one side wall formed of the above-mentioned concrete is about 1.5 m. Here, for example, about 1400 Ton of water is filled. The above-described nuclear fuel assemblies are arranged and accommodated in a rack 9, and the racks 9 are arranged at intervals of, for example, 0.2 m at the bottom of the water tank.

  The nuclear fuel assembly described above will be described. FIG. 6 schematically shows an example of the configuration of the nuclear fuel assembly. The nuclear fuel assembly 10 includes a fuel rod 11, a water rod 12, and a channel box 13 in which a plurality of fuel rods 11 and the water rod 12 are accommodated. The fuel rod 11 is configured by filling a fuel cladding tube 14 made of a zirconium alloy with fuel pellets 15. The fuel pellet 15 is pushed toward one end of the fuel cladding tube 14 by an internal spring 16. The fuel cladding tube 14 is formed to have a length of, for example, 4.0 to 4.5 m, and hundreds of fuel pellets 15 formed in a cylindrical shape having a diameter of 10 mm and a height of 10 mm are filled therein. . As the fuel pellet 15, for example, uranium dioxide baked and hardened can be used. For example, water flows through the water rod 12, and heat generated by the fuel rod 11 is taken out through the water. The channel box 13 is formed in, for example, a prismatic shape with one side of 140 mm. Since the channel box 13 is for accommodating the fuel rod 11 and the water rod 12 therein, the height thereof is formed substantially the same as that of the fuel rod 11 and the water rod 12, for example. Therefore, the distance from the upper end of the rack 9 containing the nuclear fuel assemblies 10 arranged at the bottom of the fuel storage pool 8 to the water surface is about 8 m.

  The fuel rod 11 and the water rod 12 are arranged vertically or substantially vertically inside the channel box 13. One end of the fuel rod 11 is fixed to the lower portion of the channel box 13 by a lower tie plate 17. The other end of the fuel rod 11 is supported on the upper portion of the channel box 13 by an upper tie plate 18 and an external spring 19. An intermediate portion of the fuel rod 11 is supported by a support grid 20. The support grid 20 is fixed to the water rod 12. Therefore, even if the fuel rod 11 expands and contracts due to heat, the expansion and contraction can be absorbed by the elastic deformation of the external spring 19.

  FIG. 7 schematically shows a cross-sectional view taken along the line VII-VII shown in FIG. The nuclear fuel assembly 10 shown here is a so-called 8-row 8-column nuclear fuel assembly 10 in which fuel rods 11 are arranged in 8 rows and 8 columns. In the 8-row, 8-column nuclear fuel assembly 10, water rods 12 are arranged near the center of the fuel rods 11 arranged as described above. Therefore, the number of the fuel rods 11 of the nuclear fuel assembly 10 shown in FIG.

  When the channel boxes 13 configured as described above are provided in the reactor pressure vessel 5, the channel boxes 13 are arranged at predetermined intervals. A control rod 21 for controlling the chain fission reaction by adjusting the number of neutrons in the reactor pressure vessel 5 is inserted between the channel boxes 13 by the control rod drive mechanism 22. Yes. In the example shown in FIG. 7, the cross section of the control rod 21 perpendicular to the length direction is “+”. Since the control rod 21 is for controlling the reaction in the reactor pressure vessel 5, the length thereof is the same as or substantially the same as the nuclear fuel rod 11 described above. For example, as shown in FIG. 3, the control rod drive mechanism 22 is provided in the lower part of the reactor pressure vessel 5.

FIG. 8 shows the burnup of the nuclear fuel assembly 10 used in the boiling water reactor shown in FIG. 3 as a reference example. The burnup is the amount of heat generated cumulatively per unit weight of nuclear fuel, and is approximately proportional to the cumulative number of fission per unit weight of nuclear fuel. As shown in FIG. 8, the removal average burnup of the high burnup 8-row, 8-column fuel assembly using uranium dioxide as fuel is 39.5 GWd / t, and the 9-row, 9-column A type and 9 rows The 9-column B-type fuel assemblies have a take-out average burnup of 45 GWd / t, respectively, and the 8-row 8-column fuel assemblies using MOX as a fuel have a take-out average burnup of 33 GWd / t. On the other hand, when converting the average discharge burnup in the fuel rods 11 one per nuclear fuel assemblies, average discharge burnup per one fuel rod is in the range of 0.55~0.65GWd / t I understand that.

  In the present invention, the heat of the water in the fuel storage pool 8 heated by the decay heat generated by the used nuclear fuel assembly 10 is transported by the loop heat pipe and radiated to the atmosphere. In addition to this, the present invention is configured such that the temperature of the water in the fuel storage pool 8 falls within a predetermined temperature range as a result of heat transport by the loop heat pipe. The number of loop heat pipes installed depends on the target heat transport amount, that is, the required heat resistance between the temperature of the cooling water immersed in the evaporation part of the loop heat pipe and the outside air temperature to which the condensation part is exposed. Will be decided accordingly. FIG. 9 schematically shows an example of the configuration of a loop heat pipe according to the present invention. The loop heat pipe 23 basically uses, as a working fluid, a fluid that evaporates and condenses in a target temperature range such as water or alcohol, and the working fluid is evaporated by receiving heat from the outside. After flowing toward a location where the pressure is low, heat is dissipated and condensed to transport heat.

  Specifically, in the loop heat pipe 23, the portion where the working fluid enclosed in the pipe evaporates is the evaporation portion 24, and the portion where the working fluid vapor dissipates heat and condenses is the condensation portion 25. Then, the evaporating unit 24 and the condensing unit 25, the vapor pipe 26 that causes the working fluid vaporized in the evaporating unit 24 to flow toward the condensing unit 25, and the working fluid that has dissipated heat and condensed in the condensing unit 25 are evaporated. A liquid heat return pipe 27 that is refluxed toward the section 24 is connected in a loop to form a loop heat pipe 23. For example, water is used as the working fluid.

  When the phase of the working fluid changes from liquid to vapor, the volume of the working fluid increases as compared to the liquid state. Therefore, the vapor pipe 26 is formed larger in diameter than the liquid return pipe 27. In other words, since the volume of the working fluid condensed in the condensing unit 25 is smaller than that in the gas state, the liquid return pipe 27 has a smaller diameter than the steam pipe 26.

  In the example shown in FIG. 9, the evaporation unit 24 of the loop heat pipe 23 is configured as an evaporation tube group including a plurality of evaporation tubes 28. The upper end portion of each evaporation pipe 28 is in communication with the first header pipe 29, and the lower end portion is in communication with the second header pipe 30. In addition to this, the respective evaporation tubes 28 are arranged vertically or substantially vertically. The first header pipe 29 is in communication with the steam pipe 26, and the second header pipe 30 is in communication with the liquid return pipe 27. The first header pipe 29 collects the working fluid vaporized in each evaporation pipe 28 and supplies it to the vapor pipe 26. Therefore, the inner diameter of the first header pipe 29 is formed larger than that of the second header pipe 30. In addition, the inner diameter of the first header pipe 29 is formed to be the same as or substantially the same as the inner diameter of the steam pipe 26. On the other hand, the second header pipe 30 is for supplying a liquid-phase working fluid that has been refluxed through the liquid return pipe 27 to each evaporation pipe 28. Therefore, the inner diameter of the second header pipe 30 is smaller than the inner diameter of the first header pipe 29 and is formed to be the same as or substantially the same as the inner diameter of the liquid return pipe 27. The evaporation unit 24 configured as described above is immersed in the cooling water in the fuel storage pool 8 and disposed between the racks 9.

  The condenser 25 of the loop heat pipe 23 is provided above the evaporator 24 and outside the reactor building 1. That is, the condensing part 25 is provided exposed to the atmosphere. The condensing unit 25 is configured as a condensing tube group including a plurality of condensing tubes 31. In the example shown here, the upper end portion of each condensing tube 31 communicates with the third header tube 32 and the lower end portion communicates with the fourth header tube 33. Each condenser tube 31 is arranged vertically or substantially vertically. Each condensing tube 31 is provided with a plurality of radiating fins 34. FIG. 10 shows a top view of the radiation fin shown in FIG. As shown in FIG. 10, the radiating fins 34 are formed in a flat ring shape, and the inner circle of the radiating fins 34 and the outer surface of the condenser tube 31 are in contact with each other so as to be able to transfer heat. Since the heat transmitted to the condensing pipe 31 is transmitted to the plurality of heat radiating fins 34, the heat radiating area in the condensing part 25 is expanded and the heat radiating efficiency is improved.

  The condensing part 25 of the loop heat pipe 23 according to the present invention includes a plurality of units in which a plurality of condensing pipes 31 are communicated with the third header pipe 32 and the fourth header pipe 33 described above. As shown in FIG. 1 to be described later, each unit is arranged in parallel, and both ends of each third header pipe 32 in each unit communicate with the upper collecting pipe 35. One of them communicates with the steam pipe 26. In addition, both ends of each fourth header pipe 33 in each unit are communicated with the lower collecting pipe 36, and one of the lower collecting pipes 36 is communicated with the liquid return pipe 27.

  The length of each condensation pipe 31 described above is shorter than the length of the evaporation pipe 28. This improves the heat radiation efficiency by expanding the contact area between the working fluid vapor and the condensing tube 31 immediately after being supplied to the condensing tube 31, in other words, the heat transfer area of the heat transported in the form of latent heat of the working fluid. Because. As described above, the upper collecting pipe 35 branches the working fluid vapor flowing through the steam pipe 26 and supplies it to each third header pipe 32, and each third header pipe 32 supplies the working fluid vapor to each condensing pipe 31. To supply. Therefore, the third header pipe 32 and the upper collecting pipe 35 are formed with a larger diameter than the fourth header pipe 33 and the lower collecting pipe 36. In addition, the diameters of the third header pipe 32 and the upper collecting pipe 35 are the same as or substantially the same as the inner diameter of the steam pipe 26. On the other hand, the fourth header pipe 33 collects the working fluid condensed in each condensing pipe 31 and supplies it to the lower collecting pipe 36, and the lower collecting pipe 36 further collects the working fluid collected in each fourth header pipe 33 to obtain a liquid. Supply to the return pipe 27. Therefore, the inner diameters of the fourth header pipe 33 and the lower collecting pipe 36 are formed to be the same as or substantially the same as the inner diameter of the liquid return pipe 27.

  For each pipe constituting the loop heat pipe 23 described above, for example, a stainless pipe whose surface is coated with titanium nitride, titanium carbide or the like is preferably used. If the surface is coated with titanium, the corrosion resistance and durability of the stainless steel tube can be improved.

Next, the loop heat pipe 23 according to the present invention configured as described above will be described more specifically. First, for example, the decay heat Pt (W) generated by the fuel rod 11 stored in the fuel storage pool 8 is calculated using the No. 4 unit of the Fukushima Daiichi Nuclear Power Station as a model. Unit 4 of the Fukushima Daiichi NPS uses about 548 nuclear fuel assemblies 10 in which 72 fuel rods 11 are assembled into one during normal operation, and its rated heat output Po (W) is about 2381 MW. The following formula was used for calculation of decay heat Pt (W).
^{Pt / Po = 0.066 [t -0.2} - (ts-t) -0.2] ··· (1) formula

  Assuming that the nuclear fuel assembly 10 in which new fuel rods 11 are assembled is used as fuel for a reactor for about one and a half years, the operating time Ts (s) of the fuel rods 11 is about 47,304,000 (s ) Assuming that the nuclear fuel assembly 10 is cooled in the reactor pressure vessel 5 for about 30 days after the operation of the reactor is stopped, and then the nuclear fuel assembly 10 is moved to the fuel storage pool 8, The elapsed time t (s) after the furnace is stopped is about 2,592,000 (s). Then, by substituting these values into the above equation (1) and solving the equation (1), the decay heat Pt (W) generated by the fuel rod 11 immediately after being moved to the fuel storage pool 8 is 3 , 659, 338 MW. That is, the water in the fuel storage pool 8 is heated by the decay heat of about 4 MW per hour. Since about 40,000 spent fuel rods 11 are stored in the fuel storage pool 8 as described above, the decay heat Pt (W) obtained as described above is used as one of the fuel rods 11. In terms of decay heat per book, the decay heat per fuel rod 11 is about 100 W / book. Next, the loop heat pipe 23 according to the present invention is designed that can dissipate the amount of heat Pt (W) obtained as described above into the atmosphere.

In addition to the above various conditions, it is assumed that the water temperature in the fuel storage pool 8 is 40 ° C., that is, a so-called cold stop state in which the temperature is maintained, and the outside air temperature is 30 ° C. In other words, the water temperature can be said to be the target water temperature of the fuel storage pool 8. The required heat resistance of the loop heat pipe 23 is calculated based on the total heat quantity in the fuel storage pool 8 described above, that is, the decay heat Pt (W), the target water temperature, and the outside air temperature. As a result, the total required thermal resistance Rt (K / W) of the loop heat pipe 23 was 2.5 × 10 ⁻⁶ K / W. If the total required heat resistance Rt (K / W) is configured to be supplemented by, for example, a plurality of loop heat pipes, the required heat resistance Rd (K / W) per loop heat pipe can be reduced. it can. Therefore, for example, when the total required heat resistance Rt (K / W) is supplemented by 35 loop heat pipes, the required heat resistance Rd (K / W) per loop heat pipe is set. Is 8.75 × 10 ⁻⁵ K / W.

  The loop heat pipe is designed so as to satisfy the above required thermal resistance Rd (K / W). As the evaporation pipe 28, for example, a stainless steel pipe having an outer diameter of 0.0508 m, an inner diameter of 0.0488 m, a thickness of 0.002 m, and a length of 8.0 m is used. The surface of the stainless steel tube is preferably covered with titanium nitride or titanium carbide. For example, 95 evaporation tubes 28 are arranged between the first header tube 29 and the second header tube 30 at intervals of 0.1 m to form the evaporation section 24. Therefore, the length of each first header pipe 29 and second header pipe 30 is at least 9.5 m or more.

  The first header tube 29 and the second header tube 30 are made of titanium-coated stainless steel tube as with the evaporation tube 28. Further, since the evaporation pipe 28 functions as the substantial evaporation section 24, the thermal resistance of the evaporation section, which will be described later, was calculated by ignoring the thermal resistance of the first header pipe 29 and the second header pipe 30.

Based on the specifications of the evaporator 24, the external heat transfer coefficient and the external heat transfer area of the evaporator 24 are calculated, and the external heat resistance Rv1 (K / W) of the evaporator 24 is calculated based on the calculation result. calculate. In addition, the in-tube evaporation heat transfer coefficient and the in-tube heat transfer area of the evaporation unit 24 are calculated, and the in-tube evaporation heat resistance Rv2 (K / W) of the evaporation unit 24 is calculated based on the calculation result. As a result, the heat transfer coefficient outside the tube of the evaporation section 24 was 1,000 W / m ² · K, and the heat transfer area outside the tube was 121 m ² . Moreover, the heat resistance Rv1 outside the tube of the evaporation section 24 was 8.26 × 10 ⁻⁶ K / W. The evaporation heat transfer coefficient in the tube of the evaporator 24 was 5,000 W / m ² · K, and the heat transfer area in the tube was 112 m ² . Moreover, the pipe | tube evaporation thermal resistance Rv2 of the evaporation part 24 became 1.79 * 10 < ^-6 > K / W.

  On the other hand, in the condensing unit 25, as the condensing pipe 31, for example, a stainless pipe having an outer diameter of 0.0508 m, an inner diameter of 0.0488 m, a thickness of 0.002 m, and a length of about 4.0 m is used. As described above, the surface of the stainless steel tube is preferably covered with titanium nitride, titanium carbide, or the like. In addition, for example, 180 to 200 radiating fins 34 having an outer diameter of 0.15 m and a thickness of 0.002 m are attached to each condensing tube 31 at intervals of 0.02 m, for example. For example, 42 condenser tubes 31 are arranged between the third header tube 32 and the fourth header tube 33 at intervals of 0.18 m. Each of the third header pipe 32 and the fourth header pipe 33 has a length of at least 7.56 m. Then, for example, as shown in FIG. 1 to be described later, the units configured in this way are arranged in parallel to connect each third header pipe 32 to the upper collecting pipe 35, and each fourth header pipe 33. Is connected to the lower collecting pipe 36. One of the upper collecting pipes 35 is connected to the steam pipe 26 as described above, and one of the lower collecting pipes 36 is connected to the liquid return pipe 27.

  The third header pipe 32 and the fourth header pipe 33 as well as the upper collecting pipe 35 and the lower collecting pipe 36 are preferably made of titanium-coated stainless steel pipes similarly to the condensation pipe 31. Further, since the condensing pipe 31 functions as a substantial condensing part 25, the heat resistance of the third header pipe 32, the fourth header pipe 33, the upper collecting pipe 35 and the lower collecting pipe 36 is ignored, and the condensation described later. The thermal resistance of the part 25 was calculated.

The tube condensation heat transfer coefficient and the tube heat transfer area of the condensation unit 25 are calculated based on the specifications of the condensation unit 25, and the tube heat resistance Rc1 (K / W) of the condensation unit 25 is calculated based on the calculation result. To do. In addition, the outside air heat transfer coefficient is 20 W / m ² · K, the heat dissipating efficiency by the heat dissipating fins 34 is 90%, and the outside heat transfer area and the external heat resistance Rc 2 (K / W) is calculated. As a result, the heat transfer area of the condenser 25 is 868 m ² , the heat resistance Rc1 is 2.7 × 10 ⁻⁶ K / W, and the heat resistance Rc2 is 6.4 × 10 ⁻⁵ K / W. became.

Based on the above-described heat resistance Rv1 outside the tube, the heat resistance Rv2 inside the tube, the heat resistance Rc 1 (K / W) inside the condenser 25, and the heat resistance Rc2 outside the tube, the required heat resistance Rd · Calculate simu (K / W). As a result, the required thermal resistance Rd · simu was 7.675 × 10 ⁻⁵ K / W. Therefore, the total required thermal resistance Rt · simu when using 35 loop heat pipes having such a configuration was 2.19 × 10 ⁻⁶ K / W. This is a value smaller than the total required thermal resistance Rt (K / W) described above, and therefore, the thermal resistance of the loop heat pipe configured as described above satisfies the required specification. In addition, the required thermal resistance Rt · simu (K / W) of the loop heat pipe 23 according to the present invention has a margin of about 14% compared to the total required thermal resistance Rt (K / W).

  FIG. 1 schematically shows an example of a configuration when the loop heat pipe according to the present invention configured as described above is applied to a fuel storage pool. As shown in FIG. 1, the evaporator 24 of the loop heat pipe 23 is disposed between the racks 9 in the fuel storage pool 8, and the condenser 25 of the loop heat pipe 23 is exposed to the atmosphere. In FIG. 1, the radiating fins 34 are not shown for the sake of clarity. As described above, the water in the fuel storage pool 8 is warmed by, for example, about 4 MW of decay heat, and when the heat of the water warmed by the decay heat is transferred to the evaporation unit 24, each of the evaporation pipes 28. The working fluid is vaporized at. The working fluid vapor is collected by the first header pipe 29 and supplied to the vapor pipe 26. The working fluid vapor that has flowed through the steam pipe 26 is branched by the upper collecting pipe 35 and supplied to the third header pipes 32, and then supplied to the plurality of condensing pipes 31 through the third header pipes 32. The heat transported in the form of latent heat of the working fluid is radiated to the atmosphere through the surface of each condenser tube 31 and the heat radiation fins 34. The working fluid condensed by radiating heat drops by gravity under each condensing tube 31, is collected by each fourth header tube 33, and is collected by the lower collecting tube 36 via each fourth header tube 33. The working fluid collected in the lower collecting pipe 36 is refluxed to the evaporation section 24 through the liquid return pipe 27.

  FIG. 2 shows a simulation result of a change in water temperature when the loop heat pipe according to the present invention configured as described above is applied to a fuel storage pool. The heat dissipated from the water surface of the fuel storage pool 8 is ignored. According to the simulation result, when the cooling of the water in the fuel storage pool 8 is stopped, it is recognized that the water temperature increases with the passage of time. On the other hand, when the heat of the water in the fuel storage pool 8 is thermally transported by the loop heat pipe 23 according to the present invention and radiated to the atmosphere, the water temperature of the fuel storage pool 8 is maintained near the target water temperature. It is recognized that That is, by configuring as described above, it is possible to cool the nuclear fuel assembly 10 stored in the fuel storage pool 8 continuously and stably and sufficiently and sufficiently. In addition, since the operation of the loop heat pipe 23 does not require mechanical devices, even if various cooling devices in the nuclear reactor and the power source for operating them are lost, the fuel storage pool 8 Water can be effectively cooled, and a so-called completely passive nuclear fuel cooling device can be obtained.

  8 ... Fuel storage pool, 23 ... Loop heat pipe, 24 ... Evaporating section, 25 ... Condensing section, 26 ... Steam pipe, 27 ... Liquid return pipe, 28 ... Evaporating pipe, 29 ... First header pipe, 30 ... Second Header pipe 31 ... Condensation pipe 32 ... Third header pipe 33 ... Fourth header pipe 34 ... Heat radiation fin.

Claims (1)

In a nuclear fuel cooling device that stores nuclear fuel that generates decay heat immersed in cooling water and takes heat from the cooling water and cools it,
The evaporating part that takes heat from the outside and the condensing part that radiates heat to the outside are connected by a steam pipe and a liquid return pipe so as to form a ring as a whole, and the state changes into a gas phase and a liquid phase and circulates and flows A loop heat pipe filled with working fluid
The evaporator is configured by communicating a plurality of evaporator tubes with upper and lower header tubes and immersed in the cooling water,
The condensing unit has a plurality of units each configured by communicating a plurality of condensing pipes each having a plurality of heat radiation fins with upper and lower header pipes, and the upper header pipe in each unit is an upper collecting pipe the communicated, together with the header tubes of the lower is communicated to the lower collecting pipe, the condenser tube is shorter than said evaporation pipe, and the condensing unit is placed in the ambient air at a position higher than the previous SL evaporator unit,
Wherein the upper collecting pipe of the upper side definitive in the evaporation section F and a Dda tube communicated by the steam pipe, or One, the lower the f Dda tube and said liquid of definitive to the lower collecting pipe and the front Symbol evaporator section Communicated by return pipe and
Number of the evaporation section and that make up the condensable part and the evaporator tube and the condensation tube is set to the number of the smaller becomes the surface area than the required heat resistance between the outside air and the cooling water In addition, the number of the condensation tubes constituting the condensation unit is larger than the number of the evaporation tubes constituting the evaporation unit.
Cooling system of the nuclear fuel characterized by a crotch.

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