JP6145752B2 - Nuclear power generation system without sodium leakage - Google Patents

Description

  The present invention relates to an incidental structure of a nuclear power reactor, and particularly proposes an improvement in the structure of a fast breeder nuclear power plant using liquid sodium as a coolant.

The reason why the fast breeder reactor has not been put to practical use is due to sodium leakage as a coolant.
The structure of the fast breeder reactor nuclear power generation is detailed in the following patent document. In the schematic diagram shown in FIG. 3, A is a nuclear reactor, B is a heat exchanger, C is a primary cooling system sodium liquid circulation pump, D Is a high temperature sodium liquid discharge pipe, E is a steam generator, F and H are sodium liquid reflux pipes, G is a pump, I is a steam pipe, and J is a containment vessel.

The sodium leak of “Monju” in Japan occurred in part X of the secondary cooling system in FIG.
In addition to the fracture mechanics factors of the structure, the corrosion of piping materials of sodium is also examined, and it is reported that the corrosion of piping materials decreases when the oxygen concentration in sodium is 20 ppm or less.

  In addition, since sodium is an active element, there is also a proposal of a lead-bismuth system that is relatively inactive and generates little corrosion.

  Japanese Patent Application No. 2002-257967

(1) Issued by the Power Reactor and Nuclear Fuel Development Corp. Technical Prospects of Fast Breeder Reactor (FBR)-Sodium Technology-(Document No. 6-3) (2) Mamoru Konomura and 7 other authors September 2001 Japan Cycle Technical Report No. issued by JAEA 12 separate pages, pages 19-54 "Plant design evaluation for fast breeder reactors with various coolants (1) (2)"

Problems to be solved by the invention

  The sodium cooling system has been extensively studied, but it is still difficult to say that the leakage accident can be solved reliably. An object of the present invention is to provide a technique for eliminating sodium liquid leakage and further improving the safety of a nuclear power generation system.

Means for solving the problem

In the fast breeder reactor secondary cooling system sodium liquid leak accident, the present inventors have reacted with oxygen and the high-temperature dissociation reaction shown below between the generated sodium oxide (Na ₂ O) and other oxides, and high-temperature sodium. We focused on the thermoelectromotive force based on the thermocouple formation in the liquid piping and the cooled low temperature sodium liquid piping. It was concluded that the discharge phenomenon at the leaking part was a major cause. Here, the sodium liquid is an electric conductor, and the piping between the heat exchanger outlet and the steam generator inlet and the piping system returning from the steam generator outlet to the heat exchanger form a thermocouple. For this reason, it is assumed that the short-circuit current is concentrated in the portion X in FIG. Therefore, the occurrence of discharge corrosion can be inferred in the vicinity. As a solution, it is desirable to electrically neutralize the high potential of the high temperature side pipe and the low potential of the low temperature pipe side. The thermocouple's hot junction is considered to be the outlet of the pipe in the heat exchanger, that is, the pipe from the discharge pipe mounting part to the inlet to the steam generator. This is because it is a place that should be kept warm. It is reasonable to view the cold junction side from the outlet of the pipe from the steam generator, that is, from the attachment part of the reflux pipe to the entrance to the heat exchanger. During this time, the temperature of sodium is low and the potential is stable and low. Therefore, the portion to which the ground or reverse phase voltage is applied is between the above on both the high potential side and the low potential side.

  FIG. 1 schematically shows a mechanism to which the present invention is applied. 1 is a heat exchanger for secondary cooling, 2 is a pump for circulating the primary cooling system Na, 3 is Na for the secondary cooling system Piping to circulate, 4 is a steam generator and condenser, 5 is an electromagnetic pump for circulation, 6 is ground wiring at two locations on the high temperature discharge pipe side, 7 is an earth ammeter and ground wiring on the Na reflux pipe side, 8 Is a DC power supply and control device for applying a reverse phase voltage, 9 is an insulating ceramic insulator tube to be attached if necessary, and 10 is a containment vessel.

Here, as a solution to the problem, first, the vicinity of the heat exchanger outlet which becomes the high potential point on the hot junction side is grounded. It is 6 parts of FIG. The figure shows the case where it is also attached to the steam generator side. This is because it is considered more effective if the vicinity of the steam generator inlet is grounded. The wiring shown by the broken line between 6 and 7 may also be used to increase the grounding effect. 7 is for grounding the vicinity of the cold junction of the low-temperature side pipe, whereby the potential difference between the two can be eliminated.

However, this alone may not be sufficient due to the degree of earth current and earth resistance. In addition, there is a concern about the influence on the piping in the heat exchanger, the internal structure and other equipment due to the continuous flow of the ground current. Therefore, there is a method of neutralizing by adding an antiphase voltage between the high temperature side pipe and the low temperature side pipe. This is a method using the power supply 8 in FIG. That is, this is a case where the switch of FIG. 1 is switched to the connection side. Connect the positive electrode of the DC power source indicated by the battery symbol to the low temperature side pipe. The negative electrode is grounded through a control device indicated by a variable resistor and a monitoring ammeter. As a result, the current flowing from the high temperature side pipe is neutralized. If the control and management is performed so that the current flowing through the control device to the low-temperature pipe is reduced within an allowable range, the adverse effect due to the potential difference can be eliminated. The advantage of this method is that the current flowing through the piping system can be reduced. Therefore, it is better to select and use these. This is because grounding alone is sufficient when the operating temperature is low and the temperature of the secondary piping system is low, but the thermoelectromotive force and dissociation voltage also increase during high-temperature operation. The added current waveform may be a pulsating flow.
Although this phenomenon can occur even in the primary cooling system, it cannot be said that it is not necessary to apply the present invention. However, since the temperature of the reflux sodium is high in the primary cooling system, the potential difference is considered small. However, sufficient care is required for operating temperature control management.

の解離反応が起こりうると考えねばならない。すなわち高温側ではナトリウムは正の電荷を持ちうるし、高温であるほど大きいのである。Above is the claim 1, in terms of occurrence of dissociation voltage by Na 2 _O generated believed to provide good results. That is, when the oxygen concentration in sodium is high and exceeds 20 ppm, it is considered that the following reaction is likely to occur. Here, the piping material is SUS304 stainless steel, and an oxide film represented by Cr ₂ O ₃ is provided on the inner surface of the steel pipe. Therefore,

It must be considered that a dissociation reaction can occur. That is, on the high temperature side, sodium can have a positive charge, and the higher the temperature, the larger.

  This is naturally added to the thermoelectromotive force. Therefore, in the current structure that is electrically shorted at the outlet of the containment vessel, a discharge phenomenon may occur. (9 parts in Fig. 1)

  Also, consideration such as controlling the short-circuit current via insulators as shown in FIG.

Furthermore, the structural improvement of the heat exchanger is also effective.
In the example of FIG. 2, in order to isolate the primary cooling system sodium liquid circulating from the reactor core, it is led to the lower vessel 11 and then the molten material bath 14 other than the primary cooling system liquid in the intermediate vessel above it. Heat exchange, and then heat exchange from this material bath to the water in the upper container to generate water vapor, which is an intermediate heat exchange steam that isolates the sodium-based primary coolant and the circulating water system This is a nuclear power generation system that constitutes a generator.

  In the embodiment of FIG. 2, the primary coolant is sodium, 11 is a primary cooling system sodium liquid bath coming from the reactor, 12 is a primary cooling pipe coming from the reactor core, and 13 is a pump for circulating sodium liquid. The sodium liquid discharged into the center of the bathroom rotates along the spiral fins 14 such as the molten metal bath or the molten salt bath for the secondary cooling as shown by the arrow on the circumferential side. 13 pumps from the outlet. During this time, heat exchange is performed on a 14-part molten metal bath or a molten salt bath. Then, on the steam tank side of the steam generator 15, the water jetted to the central part goes around the upper spiral fin part and reaches the outer peripheral part.

  Reference numeral 16 denotes a turbine pipe, and reference numeral 17 denotes a steam turbine, a condenser, and a return water pump. 18 is a condensate piping, and 19 is a valve for degassing and pressure adjusting the molten material bath. Further, 20 is an additional electrode for cathodic protection described later, and 21 is a circulating pump for a molten metal or molten salt bath. By this system, heat can be exchanged from the primary sodium solution to water vapor at once.

  In addition, the sodium bath and the water vapor chamber are not adjacent to each other, and the sodium combustion reaction due to the leakage of the sodium solution and the generation of hydrogen gas by the water are the sodium silicate-based double-shell container that is a sodium silicate-based sealing barrier provided outside the bath 11. This can be prevented in combination with the 22 and 3 layer pipes 12 and 13.

  Also, if the fin part is fixed to the outer shell container, the earthquake resistance is good, and a partition wall between the primary cooling system is not required as in the pool type, and it is safe because it can be semi-underground.

Also immediately stop the recovery flowing water even should happen primary sodium leakage at high temperature operation, the steam generating chamber 15 can also be switched to the inert gas cooling ventilation, such as N _2.

  That is, structurally, the discharge corrosion is prevented by not using a sodium liquid coolant in the secondary cooling system and by making the secondary cooling vessel chamber compact.

  The second aspect relates to the composition of the molten metal bath, electrical treatment, and the like. In the superimposed heat exchanger structure and other intermediate heat exchanger structures in FIG. 2, when the material bath that receives heat from the primary cooling system is a molten metal other than an alkali metal, the basic components of the material bath are Bi, Pb. , Sn, Cd, a eutectic component system containing two or more, and in addition, a readily soluble alloy containing at least one of In, Ga, Al, Mg, Zn, Sb, Se, Te, Ge, Tl, Ag, Cu It is what.

In addition, when the structure of the cooling device is made of steel or Ni-base alloy, the inner surface of the structure is subjected to an oxide conversion treatment if necessary to prevent corrosion of the structure by molten metal, such as Cr, Al, etc. Either a thermally stable and dense oxide film is formed, or a heat-resistant and corrosion-resistant film such as carbide or nitride is formed, or Mo, W, Nb, Ta, V, Ti, Zr, Cr, Hf, etc. A film made of a single metal or a high melting point metal of these alloys is formed by a method such as a plating method or a surface diffusion penetration method. And further Naked used, in either case the anticorrosive film formation, a cooling vessel for heat exchange with the negative electrode at the time in service, by performing energization corrosion of a positive electrode for a molten metal bath, the corrosion of the cooling vessel by easily soluble molten metal It is characterized by preventing .

  The energization corrosion prevention here is a method of Japanese Patent Application No. 2015-98600, which is a prior application of the inventor. The prior application can also be used to form the various anticorrosion films.

  In the application example of FIG. 2, the positive electrode is attached to the position 20 and the negative electrode is attached to the outer wall of the container.

  It is possible to prevent leakage of cooling system sodium in a nuclear power generation structure having a sodium cooling system, which contributes to practical use. Also, a safe nuclear power generation system can be put into practical use.

  Mechanism diagram showing an example of applying the anticorrosion of the present invention   The integrated structure figure of the heat exchange steam generator of the structure which integrated the heat exchange mechanism and the steam generation mechanism. A spiral arrow indicates the flow of the liquid.   Schematic diagram showing the structure of a loop type fast breeder reactor nuclear power generation

DESCRIPTION OF SYMBOLS 1 Heat exchanger for secondary cooling 2 Pump which circulates primary cooling system Na 3 Piping which circulates secondary cooling system Na Steam generator, condenser 5, G Electromagnetic pump for circulation 6 Ground wiring of high temperature discharge pipe In case of two places 7 Earth wiring of reflux tube and ammeter 8 DC power source and control device for applying reverse phase voltage 9 Insulating ceramic insulator tube 10, J containment vessel 11 Primary cooling system sodium liquid bath from reactor core 12 Sodium piping from the reactor core, sodium silicate filled double pipe 13 Sodium recirculation pump to the reactor core, sodium silicate filled double pipe 14 Molten metal or molten salt bath or mixed bath 15, E Steam generator 16 Steam piping 17 Turbine, condenser and recirculation pump 18 Condensation piping 19 Deaeration, pressure regulating valve 20 Electrolytic protection electrode attachment part of intermediate heat exchanger molten material bath, + electrode attached in bath Carbon electrode, negative electrode can be attached to the bath wall, and multiple electrodes can be installed 21 Secondary cooling bath circulation pump 22 Double shell container for sodium silicate filling 23 Heat-resistant load-resistant foundation A Reactor B Heat exchanger C Primary cooling Sodium circulation pump D Secondary cooling system High temperature sodium discharge pipe F, H Low temperature sodium reflux pipe I Steam pipe

Claims (2)

  As a reactor coolant, a secondary cooling system heat exchanger and a steam generator of a loop-type nuclear power plant with liquid sodium as the main coolant are connected, and a vessel in which sodium liquid circulates inside these In the piping system, in order to eliminate the negative effects of dissociation voltage and thermoelectromotive force of sodium compounds generated due to the temperature difference of the sodium solution, high temperature sodium discharge to the hot junction side of the thermocouple made by the secondary cooling system, that is, to the heat exchanger The pipe between the pipe attachment part and the steam generator container inlet and the cold junction side, that is, between the attachment part of the reflux pipe to the steam generator serving as the outlet for the cooled sodium and the heat exchanger inlet part. In order to carry out a discharge treatment or neutralize the thermoelectromotive force etc. by providing an electrical ground at least at one place on both sides of the piping, each grounding portion of the secondary cooling piping system By adding a reverse phase voltage and controlling the current flowing to the ground to be below the allowable value, the discharge phenomenon during power generation operation in the secondary cooling piping system is suppressed, and the discharge corrosion caused by the coolant is prevented. A nuclear power generation system characterized by   Regardless of the structural system of the nuclear power generation structure, a molten metal is used as a heat medium in at least a part of the cooling system, and the basic chemical component of the molten metal bath includes two or more of Bi, Pb, Sn, and Cd. Is a readily soluble alloy containing at least one of In, Ga, Al, Mg, Zn, Sb, Se, Te, Ge, Tl, Ag, and Cu, and the inner surface of the cooling system vessel is made of steel. Or make it bare use made of Ni-based alloy, or form a corrosion-resistant and heat-resistant ceramic film such as oxide or nitride on the inner surface of the container, or form a refractory metal material film that is not easily eroded by a readily soluble alloy In any case, in addition, the cathode and the internal structure are easily soluble by conducting cathodic protection and anti-corrosion using a cooling vessel for heat exchange as a negative electrode and a molten metal bath as a positive electrode in each case. Corrosion by metal bath Nuclear power generation system, characterized in that to prevent.

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