JPH02196998A - Nuclear power generation facility - Google Patents

Abstract

PURPOSE:To prevent corrosion products from being formed owing to a decrease in the dissolved oxygen concentration of a condensation system, to prevent the system from being contaminated, and to reduce the exposure of an operator by providing a hydrogen peroxide injecting mechanism in the system water in the hot well of the condenser of a nuclear reactor primary system and a hydrogen injecting mechanism on the downstream side of a condensate purification system. CONSTITUTION:In the nuclear reactor primary system, hydrogen is injected at an injection point 11 which is on the downstream side of the condensate purification system 5 and on the upstream side of a high-pressure condensate pump 6. Further, oxygen is injected from a feeding condensate system oxygen injection point 19 by a feeding condensate system oxygen injecting mechanism 20 for the corrosion prevention of the feeding condensate system. Further, the hydrogen peroxide injecting mechanism 21 which is linked with the hot well of the condenser 3 of the nuclear reactor primary system is provided to inject hydrogen peroxide into the system water in the hot well of the condenser 3 from this injecting mechanism 21. Thus, the hydrogen peroxide is injected to suppress the generation of corrosion products from the condenser 3 to the feeding condensate system oxygen injection point 19 even during the oxygen injection.

Description

[Detailed description of the invention] [Object of the invention] (Industrial application field) The present invention is a boiling water reactor (BWR) - a mechanism for injecting hydrogen into the primary system of a nuclear reactor as a measure to inhibit corrosion of secondary system constituent materials. Regarding nuclear power generation equipment equipped with

(Prior Art) The reactor coolant in a nuclear power plant is in the form of high-temperature, high-pressure water, and the plant structural materials are under extremely harsh environmental conditions. Under the above conditions, the corrosion behavior of the material becomes an important issue, especially in BWR plants, stress corrosion cracking of austenitic stainless steel piping
SS Corrosion Cracking (hereinafter referred to as SCC) has become a subject of great interest at home and abroad.

It is generally believed that this SCC phenomenon occurs when three factors, namely material, stress, and environment, are superimposed. In a newly constructed BWR nuclear power plant, sufficient consideration must be given to the three factors mentioned above to prepare for stress corrosion cracking.

However, since it is difficult to take measures from the viewpoint of materials and stress in existing atomic couplants, attempts have been made to take measures from an environmental viewpoint. Environmental SCC
Dissolved oxygen concentration in the reactor water is the most important factor.

Since oxygen is generated in the reactor core by radiolysis of water, it is inevitable that about 200 to 300 ppb of oxygen will be dissolved in the reactor water. At the reactor temperature (285° C.), dissolved oxygen of around 200 ppb is at a sufficiently significant level for SCC, and management of dissolved oxygen concentration is important for plant operation.

For this reason, hydrogen injection technology into nuclear reactors has been developed as a countermeasure against SCC, and is being put into practical use in some plants. This technology injects a small amount of hydrogen into the water supply and dissolves it.
This is intended to suppress the generation of oxidizing chemical species such as oxygen and hydrogen peroxide. When reactor water is made into a moderately reducing atmosphere by hydrogen injection, in the presence of radiation, the recombination reaction of oxygen, hydrogen peroxide, and hydrogen into water is promoted radiochemically.

An example of hydrogen injection technology in an existing plant (Doresten No. 2 reactor in the United States) will be explained with reference to FIG.

This figure is a system diagram of the primary reactor system that performs hydrogen injection6
That is, the steam generated in the core 1 performs work in the turbine 2, and then is led to the condenser 3, where it is cooled and condensed and condensed. This condensate is pumped 4. High pressure condensate pump 6° feed water heater 7. via condensate purification system 5. The water is heated and pressurized by the feed water pump 8 and then injected into the reactor pressure vessel 9. Note that the reference numeral 10 in the figure is a reactor recirculation pump, which forcibly recirculates the reactor water in the reactor pressure vessel 9 to increase the reactor core flow rate. In the primary system configured as described above, hydrogen is injected from an injection point 11 located downstream of the condensate purification system 5 and upstream of the high-pressure condensate pump.

Even in plants other than the exemplified existing plants, there are many examples in which water is injected from the injection point 11 described above.

FIG. 3 also shows the gaseous waste treatment system. The off-gas discharged from the condenser 3 is sent to the air extractor 13. The gas passes through an off-gas preheater 14, is treated in an off-gas recombiner 15, and passes through an off-gas condenser 16 to reach the gaseous waste treatment system. In hydrogen injection technology, oxygen and hydrogen generated by radiolysis in the reactor core return to water through a recombination reaction, but hydrogen equivalent to the amount injected from the outside is discharged to the gaseous waste treatment system as surplus hydrogen. For safety reasons, this excess hydrogen must be recombined in the gaseous waste treatment system.

Oxygen is injected into the gas waste treatment system, and the off-gas recombiner 15 causes the excess hydrogen to react with the oxygen injected into the gas waste treatment system. Oxygen injection point 17 is typically located intermediate between air extractor 13 and off-gas preheater 14 and is injected with oxygen from oxygen injection mechanism 18 .

Figure 4 shows Dolestin No. 2 and Beech Bottom No. 3.

FIG. 2 is a diagram showing test results of the effect of hydrogen injection on reducing dissolved oxygen concentration at existing Pilgrim, Fitzpatrick, and Duane Arnold plants in the United States. The vertical axis is the dissolved oxygen concentration (pp
b), the horizontal axis shows the feed water dissolved hydrogen concentration (39m). In the diagram, line 1 (0 mark) is Peach Bottom 3, line 2 (Δ mark) is Dresden 2, line 3 (☆ mark) is Pilgrim, and line 4
(◇) indicates Fitzpatrick, and line 5 (mark) indicates Duane Arnold.

From FIG. 4, it can be seen that although the oxygen concentration reduction effect varies depending on the plant, as the hydrogen concentration in the feed water increases, the dissolved oxygen concentration in the reactor water decreases.

As is clear from the above, it has been proven in actual reactors that hydrogen injection can reduce the dissolved oxygen concentration in reactor water, and is an effective measure against SCC from an environmental perspective.

Note that FIG. 4 and FIG. 5, which will be described later, are taken from the following literature.

R.L., Covan at al., “Experie.
nce with HydrogenWater Ch
Emistey in Boiling Water
Reactors"watsr Chemistry
of Nuclear Reactor System
s 4゜BNES, London, 1986゜On the other hand, in Japan's BWR nuclear power generation facilities, oxygen is injected into the water supply and condensate systems for a completely different purpose. In other words, when corrosion products such as rust that occur mainly on the inner surface of carbon steel piping in the condensate and water supply systems flow into the reactor pressure vessel, these corrosion products become radioactive and circulate within the system. The entire system will be contaminated and the exposure dose of operators etc. will increase. Conventionally, in order to prevent this, oxygen is dissolved in the system water at a predetermined concentration to form a stable oxygen film on the inner surface of the piping, thereby preventing the generation of corrosion products such as rust.

This feed condensate oxygen injection is conventionally performed downstream of the condensate demineralizer or, in some plants, upstream of the condensate demineralizer. FIG. 3 shows the oxygen injection point 19 of the water supply and condensate system (downstream of the demineralizer). The purpose of this is to form a stable oxide film on the inner surface of the water supply and condensate system piping to prevent the generation of corrosion products, and regardless of whether or not hydrogen injection is carried out as a countermeasure against SCC, it is completely independent. It has been done.

(Problems to be Solved by the Invention) As already shown in FIG. 4, when hydrogen injection is performed in conventional BWR nuclear power generation equipment, the dissolved oxygen concentration in reactor water is reduced. It has already been found that at this time, the oxygen concentration in the main steam is also reduced at the same time. This situation is shown in FIG. 5. Most of the oxygen and hydrogen generated by radiolysis of water in the reactor core are transferred to the main steam and finally treated in the off-gas system.

If the amount of oxygen and hydrogen generated by this radiolysis during hydrogen injection is suppressed, not only the dissolved oxygen concentration in the reactor water will decrease, but also the oxygen concentration itself in the main steam will decrease.

Therefore, the dissolved oxygen concentration in the condensed water condensed in the condenser 3 also decreases significantly. - For example, 1 during normal operation.
It is reported in the following literature that the dissolved oxygen concentration in condensate, which was 0 to 20 Pppb, became less than IPPb when hydrogen was injected.

T. Kitabata et al., “Experi
ence with Hydrogen Addition
n Water Che++1try in the
Fugen Nuclear Power 5tati
on”, Proc of 1988 JAIF Iv
t Covf onstar Chemistry
in Nuclear Power Plants, J
A.I.F.

Tokyo, 19813゜ When conditions of such low oxygen concentration occur, the condenser.

A problem arises in that corrosion elution from carbon steel, which is the main constituent material of hot wells, condensate piping, etc., increases. This is because the oxygen necessary to maintain a stable oxide film is no longer supplied. For example, during actual hydrogen injection in the new converter reactor "Fugen", ionic (soluble) and cladding (insoluble) corrosion products (the main element is F
e) It is reported in the above literature that the amount of generation increases together. FIG. 6 shows how the Fe ion level in the condensate increases before and after hydrogen injection. According to this, 19
Since the start of hydrogen injection in 1984, the Fe ion concentration has gradually increased, from 3PPb or below to 5PPb.
It has increased to about ~1 Oppb.

An increase in the generation of corrosion products is undesirable because it leads to an increase in the radiation dose to operators and the like, as described above.

In addition, the load on the condensate purification system increases, and the frequency of backwashing of the pre-filter (powdered resin) or mixed bed condensate demineralizer increases. This leads to an increase in the workload of the operator and an increase in the amount of waste generated such as waste resin and waste liquid. Therefore, it is necessary to take measures to maintain the condensate-based carbon steel oxide film stably even during hydrogen injection.

On the other hand, in the current oxygen injection system for water supply and condensation, oxygen is supplied to the system water downstream of the condensate demineralizer. That is,
A stable oxide film is formed only on the inner surface of the pipe on the downstream side of this condensate demineralizer, and corrosion products generated on the inner surface of the pipe on the upstream side of this condensate demineralizer are removed by this condensate demineralizer. It was configured to remove. However, in reality, this condensate demineralizer accounts for 50 to 70% of the corrosion products contained in the system water.
The problem is that only about 30% can be removed, and the remaining 30% to 50% flows into the reactor pressure vessel and circulates within the system, increasing the contamination level of the entire system and increasing the radiation exposure of operators. There were challenges that arose.

The present invention has been made based on the above circumstances,
The purpose of this is to reliably prevent the generation of corrosion products associated with a decrease in dissolved oxygen concentration in the condensate system in BWR nuclear power generation facilities that perform hydrogen injection, prevent system contamination, and reduce radiation exposure for operators. Our goal is to provide the following.

[Structure of the invention]

(Means for Solving the Problems) The present invention provides a nuclear power generation facility equipped with a hydrogen injection mechanism for injecting hydrogen into system water of a reactor water supply system or a reactor primary system, in which corrosion products of the reactor water supply and condensate system are removed. A hydrogen peroxide injection mechanism is provided for injecting hydrogen peroxide into the system water in the hot well of the condenser of the reactor primary system for the purpose of reducing generation, and a hydrogen injection mechanism is provided downstream of the condensate purification system. It is characterized by becoming.

(Function) During hydrogen injection, the concentration of dissolved oxygen between the condenser and the oxygen injection point downstream of the condensate purification system is extremely low, which accelerates corrosion and elution of the carbon steel that is the constituent material. By injecting hydrogen peroxide from the tank, a stable oxide film is maintained and the generation of corrosion products is reduced.

Hydrogen peroxide has a higher standard electrode potential than oxygen, and acts on the cathode of corrosion as well as or better than oxygen. The standard electrode potential values at 25°C are as follows.

Therefore, it is possible to achieve corrosion protection of the condensate system by injection of hydrogen peroxide.

Hydrogen peroxide has extremely high solubility in water.

When injected into the system water from the condenser hotwell, it effectively protects equipment and piping from corrosion. On the other hand, when oxygen is injected, its solubility is low, so there is concern that it will not be effectively dissolved in the system water and will migrate to the off-gas system. In addition, excess hydrogen peroxide in the water supply and condensate system is thermally decomposed into water and oxygen through the feed water heater, so it does not have a direct adverse effect on reactor system equipment and piping.

This makes it possible to achieve corrosion protection upstream of the condensate system, and to prevent an increase in the radiation exposure of operators due to the introduction of corrosion products into the reactor core. Furthermore, the frequency of backwashing of the condensate purification device can be reduced6.Furthermore, the conventionally installed water supply oxygen injection becomes unnecessary.

(Example) Hereinafter, the present invention will be explained based on an example shown in the drawings.

FIG. 1 is a first embodiment of the present invention, which is a system diagram showing a primary reactor system for hydrogen injection and part of a gaseous waste treatment system. That is, in the primary reactor system, steam generated in the reactor core 1 performs work in the turbine 2, and then is led to the condenser 3, where it is cooled and condensed to condense. This condensate is pumped 4. High pressure condensate pump 6 via condensate purification system 5;
Feed water heater7. The water is heated and pressurized by the feed water pump 8 and then injected into the reactor pressure vessel 9. Note that lO in the figure is a reactor recirculation pump, which forcibly recirculates the reactor water in the reactor pressure vessel 9 to increase the reactor core flow rate. In the primary reactor system with the above configuration.

Hydrogen injection takes place from an injection point 11 located downstream of the condensate purification system 5 and upstream of the high pressure condensate pump. Even in plants other than the exemplified existing plants, there are many examples in which water is injected from the above-mentioned injection points.

Now, in this hydrogen injection technology, as mentioned above, it is necessary to recombine excess hydrogen in the gaseous waste treatment system (off-gas system), and normally oxygen is injected into the gaseous waste treatment system, and then the off-gas recombiner The excess hydrogen is processed by reacting it with the oxygen injected into the off-gas system.

The configuration of the gaseous waste treatment system is also shown in FIG.
It passes through an off-gas preheater 14, is processed in an off-gas recombiner 15, and passes through an off-gas condenser 16 for gaseous waste treatment. The oxygen injection point 17 is located between the air extractor 13 and the off-gas preheater 14 and injects oxygen from the oxygen injection mechanism 18 .

Furthermore, oxygen is injected from the water supply and condensate system oxygen injection point 19 by a water supply and condensate system oxygen injection mechanism 20 to prevent corrosion of the water supply and condensate system.

In such a WR nuclear power generation facility, the present invention provides a hydrogen peroxide mechanism 21 that communicates with the hot well of the condenser 3 of the reactor primary system as shown in FIG. Hydrogen peroxide is injected into the system water in the hot well of condenser 3. By injecting hydrogen peroxide, it is possible to suppress the generation of corrosion products between the condenser 3 and the oxygen injection point 19 in the water supply and condensate system even during hydrogen injection.

Normally, the amount of oxygen required for corrosion protection in water supply and condensate systems is less than <50 ppb in terms of feed water concentration. Therefore, the amount of hydrogen peroxide corresponding to this amount is )120. → From the formula 1/202 + H, O, the feed water concentration is converted to approximately 100 ppb or less, which is twice as much.

FIG. 2 is a system diagram showing a second embodiment of the present invention.
Components that are the same as those in the figures are indicated by the same reference numerals, and explanations of overlapping components will be omitted. FIG. 2 shows an embodiment in which the water supply and condensate system oxygen injection mechanism 2o in FIG. 1 is removed. That is, if the water supply and condensate system is sufficiently protected against corrosion and a stable oxide film is maintained, the hydrogen peroxide injected from the condenser 3 will not be significantly consumed in the water supply and condensate system. Therefore, upstream of the condensate purification system 5, the hydrogen peroxide injection mechanism 21 contains 100 pp.
By injecting hydrogen peroxide in an amount of about b, the conventional oxygen injection into the water supply and condensate system becomes unnecessary.

〔Effect of the invention〕

According to the present invention, by injecting hydrogen peroxide into the condenser hot well of the BWRIJK child power generation facility where hydrogen injection is carried out, even if the condensate system is in a low dissolved oxygen state at the time of hydrogen injection, recovery is possible. Corrosion protection of water-based equipment and piping has been achieved,
It is possible to reduce radiation exposure. Furthermore, the frequency of backwashing of the condensate purification device can be reduced. Furthermore, there is an advantage that the conventional oxygen injection into the water supply and condensate system is not necessary.

[Brief explanation of the drawing]

FIG. 1 is a system diagram showing a first embodiment of the present invention. Fig. 2 is a system diagram showing the second embodiment of the present invention, Fig. 3 is a system diagram showing a conventional example, and Figs. 4 and 5 respectively show the effect of reducing dissolved oxygen concentration in reactor water by conventional hydrogen injection. A characteristic diagram showing the effect of reducing oxygen concentration in main steam, and FIG. 6 is a characteristic diagram showing an increase in condensate system metal impurity concentration due to conventional hydrogen injection. 1... Core 2... Turbine 3... Condenser 5... Condensate purification system 9... Reactor pressure vessel 11... Hydrogen injection point 12... Hydrogen injection mechanism
14...Off gas preheater 17...Oxygen injection point
18... Oxygen injection mechanism 19... Water supply condensate system oxygen injection point 20... Water supply condensate system oxygen injection mechanism 21... Hydrogen peroxide injection mechanism Agent Patent attorney Yoshiaki Inomata (and one other person) Kiken 41 Ashikyo rho
4 temporary z4 busy station (fl-chibun rod (branch) 10 ice medium yK4:yg (PPtn) Kayan

Claims (1)

[Claims] In nuclear power generation equipment equipped with a hydrogen injection mechanism that injects hydrogen into the reactor water supply system or reactor primary system water,
A hydrogen peroxide injection mechanism is provided for injecting hydrogen peroxide into the system water in the hot well of the condenser of the reactor primary system in order to reduce the generation of corrosion products in the reactor feed water condensate system, and a condensate purification system is provided. Nuclear power generation equipment characterized by being provided with a hydrogen injection mechanism on the downstream side of.