JPH0631817B2 - Boiling water nuclear plant - Google Patents

Description

TECHNICAL FIELD The present invention relates to a boiling water nuclear power plant (hereinafter referred to as a BWR plant) equipped with a heater drain recovery line.

[Conventional technology]

In a BWR plant, radioactive nuclides adhere to the inner surfaces of equipment and pipes due to the operation of the plant, so that these equipment and pipes have a dose rate. When this dose rate is large, it causes a problem from the viewpoint of worker exposure at the time of periodic inspection of the plant (hereinafter referred to as regular inspection), and therefore it is desired to suppress the increase of this dose rate as low as possible.

In the BWR plant, the increase in dose rate is caused by the following mechanism.

First, the feed water supplied to the nuclear reactor contains corrosion products (clads) such as iron (Fe), nickel (Ni), and cobalt (Co) produced by the corrosion of plant structural materials. These claddings are brought into the reactor and the cladding adheres to the boiling surface of the fuel cladding. During this adhesion, radiation was emitted from the fuel rods to generate ⁵⁴ Mn and ⁵⁸ C, respectively.
o, ⁶⁰ Co. The desorption of these radioactive cladding from the fuel adheres to the inner surfaces of the reactor primary system equipment and piping, causing a rise in the dose rate.

Therefore, in order to keep the dose rate of the plant low, it is effective to use the low range of the cladding brought in from the water supply. However, when the iron cladding among the above-mentioned claddings has been extremely lowered recently, Ni, which is adsorbed on the fuel rods along with the iron cladding,
It was found that Co did not adhere, resulting in an increase in the radioactivity concentration of the reactor water.

From the above facts, the "method for controlling the impurity concentration in the boiling water reactor feed water system" described in JP-A-62-85897 is based on the above facts.
It is said that the radioactivity of reactor water is reduced by adjusting the / Ni ratio. That is, the following formula shows a means for setting the Fe / Ni ratio to 2 or more.

^{_{Ni 2+ + Fe 2 O 3 +}} H 2 O → NiFe 2 O 4 + 2H 2 ... (1) 60 Co 2+ + Fe 2 O 3 + H 2 O → 60 CoFe 2 O 4 + 2H + ... (2) from the above equation ⁶⁰ Co is Combined with the iron cladding (Fe ₂ O ₄ ) of the fuel rod, ⁶⁰ Co of the reactor water decreases. This also applies to ⁵⁸ Co.

In order to increase the Fe / Ni ratio to 2 or more in the feed water, the cladding generated in the condenser is increased by increasing the iron concentration in the feed water by bypassing the condensate purification system (condensate filter or condensate demineralizer). Facilities to inject iron cladding into the system will be installed.

[Problems to be Solved by the Invention]

The above-mentioned conventional technique has the ability to arbitrarily change the Fe / Ni ratio in order to suppress the increase in radioactivity, but has the following problems.

(1) When the condensate filter of the condensate purification system is bypassed in order to increase the Fe / Ni ratio to 2 or more, a claddle leak of the condensate demineralizer is expected in order to secure a sufficient iron supply amount. It must be done, and the iron removal performance of the demineralizer is not constant at 60 to 95% depending on the plant, and a certain amount cannot be obtained at the required time.

(2) In order to eliminate the above factors, in addition to the condensate filter bypass, a condensate demineralizer bypass may be considered.In this case, in the case of a seawater cooling pipe breakage accident in the condenser, seawater is directly fed into the reactor. It could flow into the interior and cause irreparable damage to the reactor.

(3) In addition to the iron concentration increase by the above-mentioned bypass of the condensate purification system, there is a method of directly injecting iron clad into the water supply system.

In this case, you can infuse without other obstacles,
Not only is an iron injection facility system required to complicate the plant system configuration, but it is also an idle facility because it is not required for a plant operating life of 40 years as described later.

An object of the present invention is to provide a BWR plant capable of controlling the iron concentration in the feed water without increasing the equipment and reducing the radiation exposure.

[Means for Solving the Problems]

In order to achieve the above object, the present invention, in a boiling water electronic power plant comprising a nuclear reactor, a turbine, a condenser, a condensate purification device, a low-pressure feed water heater, and a high-pressure feed water heater,
The condensate purifier comprises a condensate filter and a condensate demineralizer located downstream of the condensate filter, and drains the low-pressure feed water between the condensate filter and the condensate demineralizer. And a second line for returning the drain water to the downstream side of the condensate demineralizer, and a flow rate adjusting valve for each of the first and second lines. Is.

[Action]

According to the present invention, the flow rate of drain water directly returned to the water supply system via the second line and the flow rate of drain water returned to the water supply system via the first line and the condensate demineralizer. By adjusting the flow control valve provided in each line, the iron concentration in the feed water can be controlled within the range where the dose rate of the plant can be suppressed to a low level, so that the radiation exposure of the worker can be reduced.

At this time, the condensate demineralizer removes the clad in the drain water, but since the original ion removal performance is not significantly deteriorated by removing the clad, it is not necessary to add a condensate demineralizer. Further, since the clad adhering to the condensate demineralizer can be removed by the backwash treatment, the ion removal performance of the condensate demineralizer can be maintained also by this.

Further, as will be described later, since magnetite, which is easily removed by the condensate demineralizer, is generated in the drain water, the condensate demineralizer has sufficient clad removal performance, and the feed water concentration It becomes possible to control.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG. The steam generated in the reactor 1 works in the high-pressure turbine 2, is heated and dehumidified again in the moisture separator / heater 3, and then enters the low-pressure turbine 4 to drive the generator, and then in the condenser 5. After the water is condensed, the pressure is increased by the condensate pump 6, purified by the condensate filter 7, the condensate demineralizer 8, and then passed through the low-pressure heater 9, the water supply pump 10 and the high-pressure heater to about 200 ° C. And is returned to the reactor 1. A is a heater drain recovery line. Part of the steam is sent from the high-pressure turbine 2 to the feed water heater as a heat source for heating the feed water, and the condensed water
The high-pressure heater drain (hereinafter referred to as “high-pressure heater drain”) is collected at the inlet of the water supply pump 10 via the drain tank 16 and the high-pressure drain line 12. The steam used to heat the main steam in the moisture separator / heater 3 enters the high-pressure feed water heater 11 and the high-pressure heater drain tank 16 as a drain, is mixed with the high-pressure heater drain, and is collected in the feed water. Further, the low-pressure turbine 4 enters the low-pressure feed water heater 9, the steam used for heating the feed water enters the low-pressure heater drain tank 13, passes through the low-pressure heater drain pump 14, and then passes through the low-pressure heater drain line 15 and then returns to the recovery state. A line entering the inlet line of the water demineralizer 8 through the low pressure heater drain line 17 and the flow rate adjusting valve 18, the low pressure heater drain line 19 and the flow rate adjusting valve 20.
A line connected to the outlet side of the condensate demineralizer 8 is provided.

The flow rate adjusting valves 18 and 20 are supposed to adjust the respective openings according to the measurement result of the iron concentration in the water supply system of the sampling line 21 on the way to the reactor 1 via the high pressure water supply heater 11.

Another embodiment according to the present invention will be described with reference to FIG. This is the flow control valve 1 before and after the condensate demineralization tower of the low pressure heater drain.
8 and 20 are automatically controlled. That is, the flow rate adjusting valves 18 and 20 are operated by the control device 22 by a signal from the iron concentration measuring device 23 installed in the high-pressure water supply heater 11 and the water supply pipe to the reactor 1.

According to the present invention, the iron concentration in the feed water can be arbitrarily controlled, so that the iron content rate can be significantly reduced.

FIG. 3 is a diagram showing reduction of reactor water radioactivity by controlling feed iron concentration. By setting the feed water iron concentration to an Fe / Ni ratio of 2 or more, for example, in the A plant, reduction of reactor water radioactivity,
That is, it succeeded in significantly suppressing the generation of ⁶⁰ Co and ⁵⁸ Co.

Fig. 4 shows the results of gamma-scan measurement of the radioactivity adhering to the primary piping of the reactor, which would result in a reduction in radioactivity in reactor water. According to this, the 2nd constant dose rate after the end of the 2nd cycle of the B plant where Fe / Ni control was started is conversely lower than that in FIG.
The effect is more clear when compared with the D plant that carries in excessive iron without performing the e / Ni ratio control. In other words, not only was there an increase of ⁵⁸ Co on the 2nd regular inspection day of D plant, but F
The species such as ⁵⁴ Mn and ⁵⁹ Fe in which e is the parent element have been observed.

According to this heater drain recovery method, the plant thermal efficiency is 4.5 MWe at 1300 MWe class compared to the conventional cascade method, that is, the method in which the heater drain is recovered to the condenser.
The gain of is obtained.

Also, the clad removal performance in the condensate demineralization tower is improved. That is, it is a well-known fact that the biggest reason why the removal performance of the condensate demineralization tower differs between plants is due to the chemical form of the cladding present in the condensate. The chemical form of the cladding is iron hydroxide (Fe
(OH) ₂ etc., magnetite (Fe ₃ O ₄ ) or hematite (Fe ₂ O ₃ ) is determined. The iron removal performance of the condensate demineralization tower is extremely good for magnetite and hematite,
In the case of iron hydroxide, it drops significantly. However, according to the present invention, since magnetite that is easily removed by the demineralizer is generated in the heater drain recovery line, this magnetite is removed in the form of encapsulating hematite in the condensate demineralizer tower. The clad removal efficiency is improved.

FIG. 5 shows the results of measuring the chemical forms of the cladding in the heater drain water and the condensate water in the E plant and the F plant by an X-ray diffractometer. In both plants, amorphous iron hydroxide in the condensate occupies 60 to 70%, but only 20 to 30% in the heater drain water. This is also a controlling factor for improving the removal performance of the condensate demineralizer, and is an important merit for recovering the heater drain water directly to the demineralizer. According to the heater drain recovery system of the present invention, the temperature of the condensate demineralization tower inlet is about 80 ° C.
Since the drainage will be collected, the condensate temperature will be about 40 ° C during the summer seawater temperature rise, so the temperature after the confluence will be increased by 10 ° C. That is, the temperature at the inlet of the condensate demineralization tower will be temporarily raised from the conventional 40 ° C to 50 ° C. The effect on the anion exchange resin in this case is shown in FIG. This is a measurement of the residual ion exchange capacity of the anion exchange resin for 5 years or more. According to this, the ion exchange capacity is lost to about 70% in 3 years and 60% in 5 years. Therefore, it is necessary to consider the amount of resin in the condensate demineralization tower or the ratio of cation / anion exchange resin. This means that the above-mentioned prior art example "Japanese Patent Application No. 58-98452 Condensation / Water Supply Device in a Plant" is exposed to a water temperature of 80 ° C, which is a sufficiently improved point.

In this heater drain recovery system, since the dissolved oxygen concentration contained in the heater drain water is about 200 ppb, the dissolved oxygen concentration at the inlet of the condensate demineralization tower is increased to 80 to 90 ppb. In the conventional plant, an oxygen injection system is installed at the inlet of the condensate demineralization tower to raise the dissolved oxygen concentration of the condensate to about 20 to 50 ppb. This is to reduce the corrosion of carbon steel as shown in FIG.

The present invention eliminates the need for these oxygen injection facilities as well as the 40 years of oxygen gall and maintenance required during operation.

〔The invention's effect〕

According to the present invention, without increasing the equipment, it is possible to control the feedwater iron concentration within a range that keeps the dose rate of the plant low by utilizing the clad removal performance of the condensate demineralizer. Can be reduced.

[Brief description of drawings]

1 and 2 are system diagrams of a BWR plant showing an embodiment of the present invention, FIG. 3 is a graph showing the relationship between reactor water radioactivity and feedwater iron concentration, and the operating years of the plant, and FIG. 4 is an atomic diagram. Fig. 5 is a graph showing the measurement results of the dose rate by gamma scan in the furnace recirculation system. Fig. 5 shows the condensate of the actual equipment and the chemical chemical composition (composition ratio) in the heater drain water. Fig. 6 shows the anion exchange resin. FIG. 7 is a characteristic diagram showing the residual exchange capacity, and FIG. 7 is a characteristic diagram showing the correlation between the dissolved oxygen concentration and the carbon steel corrosion rate. 1 ... Reactor, 2 ... High-pressure turbine, 3 ... Moisture separation heater, 9 ... Low-pressure feed water heater, 11 ... High-pressure feed water heater, 15 ... Low-pressure heater drain line, A ... Heater drain recovery line.

Claims (2)

[Claims] 1. A boiling water electronic power plant comprising a nuclear reactor, a turbine, a condenser, a condensate purification device, a low-pressure feed water heater, and a high-pressure feed water heater, wherein the condensate purification device is a condensate filter device. A first line for returning the drain water of the low-pressure feed water heater between the condensate filtering device and the condensate demineralizer, and the condensate demineralizer located downstream of the condensate demineralizer. A boiling water nuclear power plant comprising: a second line for returning to the downstream side of the condensate demineralizer; and a flow rate adjusting valve for each of the first and second lines. 2. The measuring device for measuring the iron concentration in the feed water to the nuclear reactor according to claim 1, and the flow control valve for the first line and the second device based on the measurement result. And a control device for controlling the opening degree of the flow rate adjusting valve of the line of boiling water nuclear power plant.