JP2012047531A - Power generation system by molten salt reactor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power generation system that utilizes nuclear reaction energy from thorium by a molten salt reactor with higher efficiency.SOLUTION: A power generation system includes a reactor 10 in which a moderator is arranged inside and fuel molten salt in which a nuclear reactive substance is melted flows to carry out nuclear reaction, a pump 16 for moving the fuel molten salt between a molten salt exit 42 and a molten salt entrance 40 provided to the reactor respectively, a heat exchanger 14 which removes heat from the fuel molten salt flowing out of the molten salt exit 42, a steam turbine 22 which is driven by heat-removed heat energy to generate electric power, and a controller 26 which controls flow rate of the molten salt circulated by the pump 16 so that a reactor exit temperature of the fuel molten salt at the molten salt exit 42 is a contant temperature of 730-800°C.

Description

  The present invention relates to a highly efficient power generation system using a molten salt furnace using nuclear reaction energy.

  In recent years, there has been a worldwide demand for power reactors that are safe and have an output of about 1 to 20,000 kW for the spread of electric vehicles and computer servers. However, existing power reactors have their respective problems. In other words, solid nuclear fuel was used for exhaust gas treatment at thermal power plants, for stable power supply with solar power generation and wind power generation, and for local constraints such as areas where water generation is low or water levels cannot be secured. In nuclear power generation, there are difficulties in safety, proliferation resistance, nuclear waste disposal, and low power generation efficiency.

  Nuclear power generation has not yet been put into practical use, but there are attractive power reactors that are capable of industrial power generation after sufficient basic research. It is a molten salt furnace that uses nuclear reaction energy from thorium that uses a nuclear reaction that is completely different from the conventional uranium solid nuclear fuel, and its principle is as follows.

Although natural thorium 232 is not fissile, it can be converted to fissile uranium 233 by absorbing one neutron. Moreover, by dissolving these in the form of fluoride and dissolving them in the molten salt of ⁷ LiF-BeF _{2, there is} no fear of being diverted to nuclear weapons, and there is no risk of core melting as seen in solid nuclear fuels. Energy can be obtained (Non-patent Document 1). In addition, spent nuclear fuel uranium 235 and plutonium that are in need of processing can be used as nuclear fuel instead of uranium 233, and these spent nuclear fuel can be safely incinerated and extinguished. Moreover, the output when this furnace is used as a power generation furnace is high in power generation efficiency and can be selected from a wide range. For example, a small furnace of about 5 to 250,000 kW and a microminiature furnace of about 0.2 to 20,000 kW can be obtained. (Patent Documents 1 and 2). Among these, the small reactor shown in Patent Document 1 is named “FUJI”, and the micro reactor shown in Patent Document 2 is named “miniFUJI”.

Japanese Examined Patent Publication No. 5-62714 Japanese Patent Publication No. 8-27363

Furukawa Kazuo, “Nuclear Power Revolution”, Bungei Shunju, August 20, 2001 (Internet <URL: http://www.ithems.jp/e_books.html>)

  The furnaces shown in these Patent Documents 1 and 2 have the performance of obtaining a power generation efficiency of about 43% at a steam temperature of 593 ° C., respectively, at a furnace inlet temperature and a furnace outlet temperature of the fuel molten salt of 560 ° C. and 700 ° C., respectively. there were.

  However, since it is a power generation furnace, it is preferable to make the furnace outlet temperature as high as possible. This is because power generation efficiency can be improved and it is useful as an industrial high-temperature heat source.

Furthermore, when PuF ₃ is used as the nuclear fuel, the solubility of PuF ₃ is low in the molten salt. Therefore, if the temperature of the molten salt is low, there is a problem that the selection range of the operating conditions is limited.

  In view of such a background, an object of the present invention is to provide a highly efficient power generation system using a molten salt furnace using nuclear reaction energy.

  The present invention relates to a power generation system capable of controlling the flow rate of molten salt so that the furnace outlet temperature of the molten salt furnace is 730 to 800 ° C. and improving the power generation efficiency as compared with a conventional molten salt furnace. To do.

  Specifically, a moderator is disposed inside, a furnace in which a fuel molten salt in which a nuclear reactive substance is dissolved flows and a nuclear reaction is performed, and a molten salt outlet and a molten salt inlet respectively provided in the furnace And a pump for moving the fuel molten salt between, a heat exchanger for removing heat from the fuel molten salt flowing out from the molten salt outlet, and driving the turbine with the removed heat energy to generate electricity The furnace temperature of the fuel molten salt at the steam turbine and the molten salt outlet is a constant temperature of 730 to 800 ° C., or the steam temperature from the boiler is a constant temperature of 600 to 700 ° C. And a controller for controlling the flow rate of the molten salt circulated by the pump.

  Further, the controller controls the pump so that a furnace temperature of the fuel molten salt at the molten salt inlet becomes 600 ° C. or more.

  Further, at least a portion of the steam turbine that is in contact with water vapor is made of a heat-resistant material having a base of nickel and a temperature of 600 ° C. or higher.

  The fuel molten salt is a fluoride that dissolves a fluoride of a nuclear reactive substance.

In addition, PuF ₃ is used as a fluoride of the nuclear reactive substance.

  The heat exchanger performs heat exchange between the fuel molten salt and the molten salt coolant, and the boiler generates steam by heat exchange with the molten salt coolant.

  According to the present invention, the furnace outlet temperature of the molten salt becomes a constant temperature of 730 to 800 ° C. compared to the conventional 700 ° C., or the steam temperature is 600 to 700 ° C. compared to the conventional 593 ° C. By raising the temperature so as to be a constant temperature, it is possible to increase the thermal efficiency, and it is possible to provide a power generation system that can increase the output. As a result, the heat generation and exhaust heat burden of the furnace are reduced. As this effect, the life of the moderator can be extended from the decrease in the amount of neutrons, and the life of the furnace can be extended. Moreover, along with a decrease in the amount of fuel consumed per unit of power generation, which is a direct effect of an increase in thermal efficiency, power generation costs can also be reduced due to an indirect effect of an increase in thermal efficiency, which extends the life of the furnace.

  Such adjustment of the constant temperature can be easily performed by adjusting the flow rate of the fuel molten salt, and can have high load followability.

  In addition, by using a steam turbine made of a material having higher heat resistance, it is possible to increase the thermal efficiency and to increase the output.

Further, by increasing the furnace inlet temperature of the fuel molten salt, when PuF ₃ is used as the fluoride of the nuclear reactive substance, the solubility in the molten salt can be greatly increased. As a result, it is possible to increase the capacity of trivalent cations in protoactinium and fission products that increase with the operation of the reactor, thereby reducing the need for fuel salt replacement. In addition, the composition selection (impurity) range of the fuel molten salt to be adopted and used can be further expanded, and furnace operation management becomes easier.

1 is a schematic block diagram of a power generation system according to an embodiment of the present invention. It is a longitudinal cross-sectional view of the furnace which concerns on embodiment of FIG. It is the schematic diagram which looked at the high temperature storage room from the upper part. FIG. 3 is a partially enlarged view of FIG. 2 showing an enlarged furnace. It is a cross-sectional view (however, the container is not displayed) which follows the AA line of FIG. (a) is an enlarged view of the core graphite shown in FIG. 5, and (b) is an enlarged view of the blanket graphite shown in FIG.

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

  As shown in FIG. 1, a power generation system according to the present invention generally includes a furnace 10, a molten salt pipe 12, a heat exchanger 14, a fuel molten salt pump 16, a cooling system pipe 18, and a cooling system pump 19. , A boiler 20, a steam turbine 22, a condenser 23, a feed water pump 24, and a controller 26.

  As shown in FIGS. 2 and 3, a furnace 10, a molten salt pipe 12, a heat exchanger 14, a fuel molten salt pump 16, and a part of the cooling system pipe 18 are high-temperature storage chambers defined by thick walls. 29. The high temperature storage chamber 29 has a radiation shielding function by keeping the internal temperature above the melting point of the molten salt.

  Specifically, as shown in FIG. 2, for example, miniFUJI or a similar form thereof can be used for the furnace 10. That is, the furnace 10 has a cylindrical container 30 as shown in FIGS. As a material constituting the container 30, a Ni alloy added with Mo and Cr called Hastelloy (registered trademark) N is suitable. Of these, Hastelloy N added with Nb is effective.

  A reflection layer 32 made of graphite is provided inside the container 30 in order to reduce the influence from neutrons. FIG. 5 is a cross-sectional view taken along the line AA in FIG. 4, but the container 30 is not shown. As shown in FIG. 5, a moderator 34 made of graphite is laid in the furnace 10 so as to surround the core with almost no gap (only a part thereof is shown in FIGS. 2 and 4).

  The moderator 34 is an elongated member made of graphite, and has a different cross-sectional shape and a different porosity in the core region and the blanket region surrounding the core region. For example, the moderator 34 has, for example, a substantially hexagonal column shape, the core region has a low porosity shown in FIG. 6A, and the surrounding blanket region has a high porosity shown in FIG. 6B. can do. The dimensions in the figure show an example and do not mean that the present invention is limited to this size.

  A control rod 36 is disposed in the core. A drive mechanism 38 is provided above the container 30 so that the control rod 36 can be inserted by moving up and down. As shown in FIG. 2, a fuel molten salt inlet 40 is provided at the lower portion of the container 30, and a fuel molten salt outlet 42 is provided at the upper portion. Furthermore, a drain port 44 is provided at the bottom of the container 30. The control rod 36 and the drain port 44 are provided for safety.

  The furnace 10 is filled with a reflective layer 32 and a moderator 34 made of graphite and then sealed. Therefore, the movable part is only the drive mechanism 38 of the central control rod 36.

  Fuel molten salt flows in from the lower inlet 40 of the container 30, flows upward through a flow path provided along the moderator 34, etc., and is accompanied by a nuclear reaction and heat generation. It flows out from 42 to the said piping 12 for molten salts.

The molten salt consists of a fluoride that dissolves the fluoride of the nuclear reactive material. Nuclear reactive substances, such as thorium and uranium 238, which do not have fissile properties but have fissile properties by absorbing neutrons, so-called fertile, uranium 235, uranium 233 or plutonium 239 is required. Plutonium 239 can be obtained from spent nuclear fuel, which is difficult to process worldwide. Uranium 233 has a very high neutron regeneration rate, that is, the number of neutrons regenerated by fission per neutron absorbed by a certain nuclide is 2.29, which is much higher than uranium 235 and plutonium 239 over a wide range of neutron energy It does not change much until around 1 eV. Therefore, those using thorium as the parent nuclide and uranium 233 as the neutron source are preferably used. Fluorides that dissolve the fluorides of these nuclear reactive substances are stable against high heat and have low thermal neutron absorption, and have a function as a heat medium generated by nuclear reactions. For example, ⁷ LiF—BeF ₂ , LiF—NaF—KF, and the like are suitable. Among them, ⁷ LiF—BeF ₂ is particularly preferably used. As the gas in contact with the molten salt, an inert gas such as helium is used as the cover gas.

  The fuel molten salt flowing out from the outlet 42 at the upper part of the vessel 30 to the molten salt pipe 12 is circulated between the heat exchanger 14 and the furnace 10 by the fuel molten salt pump 16. Since the fuel salt is a liquid at normal pressure and high temperature, the equipment for fast breeder reactors that handles sodium of liquid at normal pressure and high temperature can be used as the fuel molten salt pump 16. The upper space of the fuel molten salt pump 16 is also an expansion tank having a capacity for absorbing the thermal expansion of the molten salt that may occur during abnormal operation.

  Although not shown, a pump and piping for sending the molten salt from the molten salt storage tank or drain tank outside the high temperature storage chamber 29 to the furnace 10 are also provided as appropriate.

The heat exchanger 14 performs heat exchange between the fuel molten salt and the cooling medium. The cooling medium for performing heat exchange may be water serving as water vapor for driving the steam turbine 22, but it is more advantageous in terms of safety to perform heat exchange with another coolant interposed. As another coolant in that case, a molten salt such as ⁷ LiF—BeF ₂ , LiF—NaF—KF, NaBF ₄ —NaF, or the like is preferably used, and among these, NaBF ₄ —NaF is particularly preferably used.

  The cooling medium is circulated through the cooling system pipe 18 by the cooling system pump 19 to exchange heat with water in the boiler 20 to generate water vapor.

  The portions of the boiler 20 and the steam turbine 22 that are in contact with the water vapor are made of a heat resistant material of 600 ° C. or higher, more preferably 650 ° C. or higher. Examples are based on nickel, C: 0.01 to 0.15 mass%, Cr: 10 to 28 mass%, Co: 10 to 25 mass%, Mo + W: 5 to 12 mass%, Al: 0.8 3.6% by mass, Ti: 0.1 to 0.6% by mass, B: 0.001 to 0.006% by mass, Re; 0.1 to 2.5% by mass of alloy and austenitic heat resistant Material is used.

  The controller 26 includes a temperature sensor 50 that detects a furnace inlet temperature Tinlet of the fuel molten salt near the inlet 40, a temperature sensor 52 that detects a furnace outlet temperature Toutlet of the fuel molten salt near the outlet 42, and a cooling medium for the heat exchanger 14. The temperature sensor 54 for detecting the inlet temperature of the coolant, the temperature sensor 56 for detecting the outlet temperature of the cooling medium, and the temperature sensor 58 for detecting the outlet temperature of the boiler 20 are fetched to control the fuel molten salt pump 16. To control the flow rate.

  In the power generation system configured as described above, the molten fuel salt flows into the furnace 10 from the inlet 40, flows into the gap of the moderator in the core region and the blanket region, generates thermal energy by the nuclear reaction, and exits 42 Spill from. In this nuclear reaction, various nuclear reaction products are generated. Of these, Kr, Xe, etc. are not always soluble in the molten salt, so they are always transferred to the cover gas. When these are present in the reaction field, they easily absorb thermal neutrons, but since there is no such fear, neutron loss can be greatly reduced, and these radioactive disasters during an accident can be reduced. In addition, tritium, which is one of the nuclear reaction products, passes through the heat exchanger wall and moves to the molten salt, which is a cooling medium, and is always separated by being combined with moisture in the cover gas. Further, Cs, Sr, Zr, Br, I, actinoids and the like of the nuclear reaction products are stably dissolved in the molten salt and are generally in a very small amount. In addition, nuclear reaction products such as Mo, Nb, Ru, Sb, Ag, and Te adhere to and deposit on the solid surface, float on the liquid surface, and move into the gas together with the liquid droplets. There is no problem other than the increase in performance. The Te problem can be dealt with by using Hastelloy N added with Nb and electrochemical adjustment.

The controller 26 monitors the temperature of the fuel molten salt inlet 40 and outlet 42 via the temperature sensors 50 and 52, and adjusts the furnace outlet temperature T outlet to a constant temperature of 730 to 800 ° C. To control. In particular, when PuF ₃ is used as the fluoride of the nuclear reactive substance, the furnace inlet temperature Tinlet is controlled to be 600 ° C. or higher.

  The cooling medium that has exchanged heat with the fuel molten salt in the heat exchanger 14 circulates in the cooling system pipe 18 by the cooling system pump 19, performs heat exchange with water in the boiler 20, and generates water vapor. The steam generated in the boiler 20 drives the steam turbine 22 to generate power. Condensate condensed from the steam turbine 22 by the condenser 23 is sent to the boiler 20 by the feed water pump 24.

  In response to load fluctuations in the steam turbine 22, the furnace 10 originally has load followability due to the negative reactivity temperature coefficient of the fuel molten salt. In addition to this, the present invention controls the temperature of the furnace outlet to be a constant temperature of 730 to 800 ° C. by adjusting the flow rate of the fuel molten salt in response to the load fluctuation. High efficiency of the turbine can be achieved. That is, when the load by the steam turbine 22 is reduced, the flow rate of the fuel molten salt is further decreased, and when the load by the steam turbine 22 is increased, the flow rate of the fuel molten salt is further increased.

  Instead of controlling the furnace outlet temperature to be a constant temperature of 730 to 800 ° C, the flow rate of the fuel molten salt is adjusted so that the steam temperature Tturbine from the boiler becomes a constant temperature of 600 to 700 ° C. Is also possible.

  A specific design example is shown below.

  As the vessel 30 of the furnace 10, a simple thin cylinder having a diameter of 1.8 m, a height of 2.1 m, and a thickness of 1.4 cm is made of Hastelloy N, and a reflective layer made of graphite is formed on the inside thereof with a thickness of 35 cm. Provide.

  The diameter of the core region is 30 cm, the thickness of the blanket region is 20 cm, and the height of the core region is 90 cm. The pipe diameter of the molten salt pipe 12 is 8 cm.

The moderator 34 has graphite of the size and shape shown in FIG. 6 (a) in the core region, and graphite of the size and shape shown in FIG. 6 (b) in the blanket region as shown in FIG. Is used. Graphite occupies 90, 70, and 99% by volume in the core, blanket, and reflective layer, respectively, and the total volume occupied by the heat generating portion in the core and blanket is about 1 m ³ .

The fuel molten salt ^{_{7 LiF-BeF 2 -ThF 4 -}} 233 a UF _4, mol% each is 71.53,16,12,0.47. The amount of molten salt is 45 liters, of which Th is 650 kg, the amount held by the ²³³ U furnace is 27 kg, and the annual replenishment amount is 2.1 kg. The coolant that exchanges heat with the molten salt uses NaBF ₄ -NaF molten salt, and the parts that come into contact with the steam of the boiler 20 and the steam turbine 22 are 2.1 mass% Al, 12.0 mass% Co, and 16.0 mass% Cr. , Mo 8.0 mass%, W 1.5 mass%, C 0.006 mass%, B 0.004 mass%, and an alloy consisting of Ni remaining amount.

  The other conditions were as follows: the furnace temperature of the molten fuel salt was 670 ° C., the furnace outlet temperature was 780 ° C., the heat exchanger inlet temperature of the coolant molten salt was 580 ° C., the heat exchanger outlet temperature was 680 ° C. The fuel molten salt pump 16 is controlled by the controller 26 so that the outlet temperature of the fuel becomes 680 ° C., and the flow rate of the fuel molten salt is adjusted.

  As a result, since the steam temperature can be increased as compared with the conventional case, a heat exchange rate of 47% can be obtained.

  As a result, waste heat that is wasted can be greatly reduced. For example, when the quantity is shown in the case of the conventional molten salt power reactor shown in Patent Document 1, the exhaust heat is (1.5 million kW / 0.429 (= 3.5 million kW) −1.5 million kW) = 2 million kW. However, [(1.5 million kW / 0.47) -1.5 million kW] = 169.1 million kW, that is, about 15% reduction in exhaust heat, which contributes greatly to environmental conservation.

  Regarding the heat of reaction of the furnace, 42.9% / 47% = 0.913, that is, about 9% reduces the heat generation burden of the furnace, which can increase the life of the graphite from the decrease in the amount of neutrons and extend the life of the furnace To. Of course, the amount of fuel consumed per unit of power generation is reduced accordingly, and the power generation cost is reduced by about 9%. In addition to this, the power generation cost can be reduced by extending the furnace life.

Further, when PuF ₃ is used as the fuel molten salt, the solubility in the molten salt can be greatly increased. As a result, it is possible to increase the capacity of trivalent cations in protoactinium and fission products that increase with the operation of the reactor, thereby reducing the need for fuel salt replacement. In addition, the composition selection (impurity) range of the fuel molten salt to be adopted and used can be further expanded, and furnace operation management becomes easier.

  Also, when this furnace is used as an industrial furnace other than a power generation furnace, for example, it can be made higher temperature so as to be suitable for hydrogen production, so that the usefulness can be further increased.

10 Furnace 14 Heat exchanger 16 Fuel molten salt pump 20 Boiler 22 Steam turbine 26 Controller 40 Molten salt inlet 42 Molten salt outlet

Claims (6)

A moderator is disposed inside, and a furnace in which a nuclear molten material flows and a molten salt flows to cause a nuclear reaction,
A pump for moving fuel molten salt between a molten salt outlet and a molten salt inlet provided in each furnace;
A heat exchanger for removing heat from the fuel molten salt flowing out from the molten salt outlet;
A steam turbine for generating electricity by driving a turbine with the heat energy removed, and
Circulation by the pump so that the furnace outlet temperature of the fuel molten salt at the molten salt outlet becomes a constant temperature of 730 to 800 ° C., or the steam temperature from the boiler becomes a constant temperature of 600 to 700 ° C. A controller for controlling the flow rate of the molten salt;
A power generation system comprising:   The power generation system according to claim 1, wherein the controller controls the pump so that a furnace inlet temperature of the fuel molten salt at the molten salt inlet becomes 600 ° C. or higher.   3. The power generation system according to claim 1, wherein at least a portion of the steam turbine that is in contact with water vapor is made of a heat-resistant material having a temperature of 600 ° C. or more based on nickel.   The power generation system according to any one of claims 1 to 3, wherein the fuel molten salt is a fluoride that dissolves a fluoride of a nuclear reactive substance. The power generation system according to claim 4, wherein PuF ₃ is used as a fluoride of the nuclear reactive material. The heat exchanger performs heat exchange between the fuel molten salt and the molten salt coolant,
The power generation system according to claim 1, wherein the boiler generates water vapor by heat exchange with the molten salt coolant.

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