JPH0468525B2 - - Google Patents

Description

[Detailed description of the invention]

[Field of Application of the Invention] The present invention is applicable to thermal power plants, boiling water nuclear power plants, and pressurized water nuclear power plants. Further, the present invention is suitable for nuclear power plants where it is required to strictly suppress the inflow of iron into the boiler, since the concentration of crud in the feed water can be kept low. In particular, the present invention is suitable for a heater drain recovery type turbine plant, which aims to improve the thermal efficiency and economic efficiency of the plant by recovering heater drain into feed water. [Background of the Invention] Conventionally, heater drain recovery systems have been adopted in thermal power plants, etc. for the purpose of improving the thermal efficiency of plants by recovering water supplied from heater drains and condensate. It is expected that it will also be adopted in power plants. However, for example, in a boiling water nuclear power plant described in the Turbine Power Generation Course of Thermal Power Generation Technology Association, heater drain is temporarily collected in a condenser in order to reduce the amount of impurities flowing into the reactor as much as possible. It is generally designed to supply water after being purified using a condensate purification system. In addition, in conventional boiling water nuclear power plants,
In order to reduce the amount of iron crud that adheres to the surface of the fuel rods due to the inflow of iron crud into the reactor, as well as to reduce the radioactive corrosion products in the reactor water, the iron concentration in the water supply system is managed at a low concentration, with the goal of approx. Since it is desired to reduce the iron concentration to 1 ppb or less, it has been considered a problem in terms of water quality control to directly collect heater drain, which may have a high iron concentration, into the water supply and condensate system. Therefore, conventionally in plants where heater drain is collected into a water supply and condensate system, it has been necessary to provide a purification device in the heater drain system and once purify it, to collect it into the water supply system. Conventionally, powder-type over-demineralizers, electromagnetic filters, and the like have been considered practical as purification devices. However, the use of a purification device in the heater drain system has the disadvantage of increasing plant costs and equipment maintenance costs. FIG. 2 shows such a conventional example. As shown in this example, the steam generated from the reactor 1 is transferred to the main steam system 2.
through the low pressure turbine 4, and the high pressure turbine 5
sent to. This steam is transferred to the heater drain line 2
1 through the first feed water heater 13, second feed water heater 14, third feed water heater 15, fourth feed water heater 1
6, fifth feed water heater 17, sixth feed water heater 18,
After being purified by a purifying device 21 via a drain tank 12, the drain is collected into a water supply system 20. On the other hand, the condensate collected in the turbine condenser 6 in the main steam system 2 is purified by the low-pressure condensate pump 7, the condensate prefilter 8, and the condensate demineralizer 9, and then sent to the heater drain described above. is collected and guided to the water supply system 20. Figure 5 also shows the balance of iron concentration in the water supply and condensate system. An evaluation based on conventional water quality results shows that the iron concentration in the heater drain system is approximately 10 ppb.
Furthermore, assuming that the removal performance of the heater drain type purifier 22 is 80%, the iron concentration in the water supply system is approximately 1.2 ppb.
The concentration is higher than the target value of 1ppb. In addition, as the purification device 22, a powder-type over-desalination device, an electromagnetic filter, etc. are conceivable, but not only does the operation and management cost of the device increase, but the former powder-type over-desalination device in particular generates a large amount of waste due to waste resin. This has become a factor in the increase in the cost of the entire plant. On the other hand, if a purification device is not used for the heater drain, the iron concentration in the water supply system will be even higher, resulting in several
There was a problem in that it was not possible to achieve the target value of 1 ppb for reducing the radioactivity level in the plant because it was expected to be 1 ppb. Therefore, recently, a system that can rationally meet water quality management requirements, including plant thermal effects, equipment costs, and waste generation volume, is most desired. Therefore, the present invention was devised focusing on this point. [Purpose of the Invention] The present invention is to significantly reduce the overall cost of the plant by reducing the iron concentration in the water supply system in a turbine system that employs a heater drain up method and by creating a plant with low equipment costs. The purpose is to Therefore, the present invention improves the water quality of the heater drain by using materials with excellent corrosion resistance for the equipment and piping of the turbine system of a boiling water nuclear power plant, thereby reducing the iron concentration in the water supply system. The aim is to reduce the amount of carbon dioxide to the target value of 1ppb or less. [Summary of the Invention] According to the present invention, in a boiling water nuclear power plant characterized in that the heater drain is not returned to the condenser but is pumped up to the water supply system using a drain pump, the equipment piping of the turbine system, that is, We have adopted corrosion-resistant materials such as 1-1/4Cr-0.5Mo steel for the bleed air/heater drain piping, moisture separator, etc., and have reduced the iron concentration in the heater drain system.
Furthermore, by connecting the heater drain directly to the output side of the condensate demineralizer, equipment costs are reduced compared to conventional equipment. Furthermore, according to the present invention, by setting the iron concentration in the water supply system to about 1 ppb or less, a plant with a low radioactivity level can be achieved. Moreover, since it is a heater drain recovery method, it is characterized by reducing the heat loss of the plant and greatly improving the thermal efficiency of the plant, making it a highly efficient plant. [Embodiments of the Invention] An embodiment of the present invention will be described below with reference to FIG. FIG. 1 shows a low-pressure heater drain-up type turbine system, and the system outline is as follows. Steam generated from the nuclear reactor 1 is sent to a low pressure turbine 4 and a high pressure turbine 5 through a main steam system 2. Steam passes through the heater drain line 21 to the first feed water heater 13 , the second feed water heater 14 , the third feed water heater 15 , the fourth feed water heater 16 , the fifth feed water heater 17 , and the sixth feed water heater 18
It is characterized in that after the drain is collected in a drain tank 12 via a drain tank 12, the drain is directly pumped up to the water supply system by a drain pump 11. Furthermore, the present invention is characterized in that the amount of iron corrosion is reduced compared to the conventional method by applying corrosion-resistant materials to the equipment and piping of the turbine system. As shown in Figure 5, where corrosion-resistant materials are used and the materials to be applied, low-alloy steel or corrosion-resistant steel is used in turbine systems where gas-liquid two-phase flow occurs, and where conditions are particularly severe in terms of material thinning. It is characterized by Figure 4 shows the corrosion test results for these corrosion-resistant materials by Masakiyo Izumitani et al.
Symposium Water Chemistry and Corrosion Problems of New Clear Reactor Systems and Components, IAEA, Vienna, IAEA-SM-26 (International
Symposium Water Chemistry and Corrosion Problems of
Nuclear Reactor Systems and Components;
IAEA, Vienna, IAEA-SM-26) 4/4
(1982). As shown in Figure 4, the corrosion loss varies greatly depending on the material.
Cu, Cr, Nr-SB46 containing Cr etc. compared to SS41
It was found that steel and 11/4Cr-0.5Mo steel had little corrosion loss and had excellent corrosion resistance. A similar trend was also observed for weathering steel SMIA. Based on the results of this test, the amount of iron produced in the entire turbine system was calculated using data on the wetted area and the corrosion rate of the materials used. The results are explained in Table 1. As shown in this figure, by using low-alloy steel or weathering steel for turbine system equipment piping, it has been shown that the amount of iron corrosion can be reduced to approximately 1/5 compared to cases using conventional carbon steel. Ta. In particular, for the heater drain system, it was found that the amount of iron corrosion could be reduced to about 1/10 by using corrosion-resistant materials.

【table】

[Table] (Note) Calculated evaluation value assuming the amount of corrosion in the main steam pipe as 1. Figure 1 shows the above evaluation data reflected in the iron balance of the plant water supply and condensate system. In other words, by using corrosion-resistant steel for the equipment piping of the turbine system as shown in this figure, the iron concentration in the heater drain system can be reduced to approximately 1 ppb, and the target value of 1 ppb can also be easily achieved in the water supply system. As described above, the present invention is characterized by adopting both material measures for the turbine system and a direct water recovery system without a purification system for the heater drain, and by both of these, the iron concentration in the water supply system can be reduced to 1 ppb or less. Furthermore, since no purification equipment is used, equipment costs are significantly reduced, and thermal efficiency is improved by recovering heater drain from the water supply system, resulting in a highly efficient power generation system. Another embodiment of the invention is shown in FIG. According to this example, the condensate sent from the main steam system 2 to the turbine and condensed and recovered in the turbine condenser 6 whose wetted material is weather-resistant steel is sent to the low-pressure condensate pump 7 and the condensate demineralizer. 9
After being purified, the heater drain is directly collected into the water supply system, similar to the embodiment shown in FIG. In other words, according to this example, in the condensate system, the condensate iron concentration is low due to the use of weather-resistant steel for the turbine condenser, so the condensate is purified only by the condensate demineralizer, and a condensate prefilter is not particularly required. It won't happen. In addition, similar to the above-mentioned example, the equipment piping of the turbine system is made of 1/1/4Cr-0.5Mo steel, Cu,
Adopting corrosion-resistant steel such as Cr, Ni-SB46 steel, heater drain is directly collected into the water supply. The crud concentration of the feed and condensate water obtained by implementing the present invention is shown in the diagram of FIG. That is, according to the present invention,
By setting the iron concentration in the heater drain to 1 ppb and the iron concentration at the condensate demineralizer outlet to 1 ppb, the iron concentration in the feed water can be brought to the target value of about 1 ppb. Therefore, since a condensate prefilter and a heater drain purification device are not required, the system can be simplified, and this is highly effective in reducing plant costs and waste. Table 2 shows comparative evaluations of the examples of the present invention and the conventional method. This figure shows the application of three measures to reduce the iron concentration in the feed water: () corrosion-resistant materials, () heater drain system purification equipment, and () condensate purification system prefilter when applied to a turbine system with heater drain recovery method. The effect of reducing iron concentration in water supply by combining items, the economic efficiency including equipment cost, and the results of a comprehensive evaluation of these are shown.

【table】

〔Effect of the invention〕

According to the present invention, by using corrosion-resistant materials for turbine equipment and piping materials, the heater drain can be drained into the water supply system without installing a purification device in the heater drain system, thereby reducing plant equipment costs and improving plant efficiency. It is possible to improve thermal efficiency. On the other hand, regarding water quality in the plant water supply system, the iron concentration in the heater drain system can be reduced to approximately 1 ppb by using corrosion-resistant materials, which can be recovered to reduce the iron concentration in the water supply system to 1 ppb or less. This makes it possible to achieve the feedwater iron concentration required to reduce radioactivity levels in BWR plants. Furthermore, since no purification equipment is required, operational management can be facilitated, and the amount of radioactive waste generated is expected to be significantly reduced. Figure 7 shows the relationship between the pipe surface dose rate and feedwater iron concentration in the reactor recirculation system in a BWR plant. As shown in this figure, reducing the iron concentration in the water supply has the effect of reducing the dose rate. Therefore, according to the present invention, the iron concentration in the water supply is reduced to about 1 ppb or less,
The dose rate can be kept low.

[Brief explanation of the drawing]

Figures 1 and 3 are schematic diagrams of a plant showing an example of the present invention, Figure 4 is a graph showing the relationship between corrosion loss and materials, and Figure 5 is a graph showing the relationship between piping dose rate and water supply iron concentration. The graph shown in FIG. 2 is a thin line diagram showing a conventional plant. 1... Nuclear reactor, 2... Main steam system, 3... Reheater, 4... High pressure turbine, 5... Low pressure turbine,
6... Condenser, 7... Low pressure condensate pump, 8... Condensate prefilter, 9... Condensate demineralizer, 10...
High pressure condensate pump, 11... Heater drain/drain up pump, 12... Feed water heater drain tank, 13... First feed water heater, 14... Second feed water heater, 15... Third feed water heater , 16...4th
Feed water heater, 17... Fifth feed water heater, 18...
6th feed water heater, 19... Water pump, 20...
Water supply line, 21...Heater drain line.

Claims (1)

[Scope of Claims] 1. A condenser for condensing main steam generated in a nuclear reactor and sent to a turbine, and a condensate desalination device for purifying condensate from the condenser; After recovering some of the condensed water through a water heater installed in the water supply piping system,
In a boiling water nuclear power plant where drain water is recovered to the water supply piping system by a pump, corrosion-resistant steel is used for the condensate system's turbine extraction system piping, moisture separator, heater drain system piping, and equipment piping of the feedwater heater body, and , a boiling water nuclear power plant comprising: a drain tank for recovering drain water through the feed water heater; and a drain pump that drains the drain water as it is to the output side of the condensate demineralizer. . 2. The boiling water nuclear power plant according to claim 1, wherein the corrosion-resistant steel is 1-1/4Cr-0.5Mo steel.