JPH0666000B2 - Condensate purification system control method for boiling water nuclear power plant - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for controlling a condensate purification system for reducing the surface dose of primary system piping of a boiling water nuclear power plant and the radioactivity concentration in reactor water. .

[Background of the Invention] The increase in the radioactivity concentration in the reactor water of a boiling water nuclear power plant and the increase in the surface dose of pipes means that corrosion products generated from plant components, pipes, etc. are brought into the reactor from the water supply system It is said that after being activated by neutron irradiation on the surface, it adheres to the primary equipment and piping again. Corrosion products include Fe (mainly clad), Co, Ni (mainly ions), etc.
Ni becomes a Co-58 nuclide. At this time, Fe is hardly activated and exists as an insoluble matter (clad), and is repeatedly attached and separated on the surface of the fuel rod, but Ni and Co are activated while adsorbing and desorbing on the Fe cladding. Therefore, by suppressing the Fe clad brought in from the water supply system to a concentration of about 1 ppb or less, it is possible to suppress the activation of Co and Ni and the adhesion of radionuclides to the primary system piping of the reactor, which in turn results in the radioactivity level of the plant. Hitachi's review VOL.62
It was clarified in No. 9 (1980).

In recent boiling water nuclear power plants, as a measure to reduce the clad, the condensate purification system should be doubled as a condensate demineralizer and a pre-condensate over-desalinizer to improve the clad removal efficiency. In addition, a material with good corrosion resistance is used for the extraction system and the condenser to reduce the amount of clad generation, and oxygen is injected into the water supply system to form a stable oxide coating on the material surface of the water supply system piping and equipment. , It is becoming common to prevent corrosion. This makes it possible to easily reduce the Fe clad concentration in the water supply system to 1 ppb or less.

However, the present inventors have found that simply suppressing the Fe clad concentration to 1 ppb or less cannot sufficiently reduce the radioactivity concentration in the reactor water. Also, when purifying condensate, there is a risk that seawater will leak from the condenser, and it is necessary to take safety into consideration. Therefore, it is possible to further reduce the radioactivity concentration in the reactor water,
It is desirable to develop a safe control method for the condensate purification system.

[Object of the Invention]

In view of the background of the invention described above, an object of the present invention is to provide a control method of a condensate purification system capable of coping with seawater leak of a condenser in a boiling water reactor and reducing the radioactivity concentration in the reactor water. To provide.

[Outline of Invention]

The present inventors examined the relationship between the Fe clad concentration in the feed water and the radioactivity concentration in the reactor water, and regarding the management of the feed water quality in the initial operation of the plant, it was found that the Fe clad concentration in the reactor water was appropriately large. We obtained the result that the radioactivity concentration of can be kept low. This is shown in FIG. In Plant A, where the Fe clad concentration at the initial stage of operation was appropriately increased as shown in Fig. 5 (a), the radioactivity concentration in the reactor water can be kept low as shown in Fig. 5 (b), and the Fe clad concentration is maintained. It can be seen that the plant B, which has been lowered from the initial stage, has a higher radioactivity concentration than the plant A.

This is because if the Fe clad concentration in the feed water is extremely low, the Ni and Co ion concentrations in the reactor water will be higher than the Fe clad concentration, and Ni and Co will not be able to adhere stably to the fuel rod surface. This is because Co is eluted and dispersed in the reactor water after being activated, and the concentrations of the radionuclides Co-58 and Co-60 in the reactor water increase, and conversely, the Fe clad concentration is moderately increased. Then, increases adhesion Fe clad amount on the fuel rod surface, Ni, Co is Fe-Ni complex compound _{(NiO · Fe 2 O 3)} , Fe
It is considered that this is because a —Co composite compound (CoO · Fe ₂ O ₃ ) is formed and taken into the Fe clad, and is not eluted and dispersed in the reactor water.

By the way, since the Co ion concentration is extremely lower than the Ni ion concentration, the Fe ion is substantially
A sufficient effect can be obtained by controlling the clad concentration. Therefore, the method of the present invention is applicable to Fe in the feedwater of a nuclear power plant.
The condensate purification system is controlled so that the clad concentration is controlled to a concentration that allows Ni ions to sufficiently bond and stabilize with the Fe clad according to the time-dependent curve of the concentration of Ni ions in the feed water. As described above, by optimally controlling the Fe clad concentration according to the Ni ion concentration, Ni can be stably fixed to the fuel rod surface in the form of the Fe-Ni composite compound. Therefore, even if Ni is activated on the surface of the fuel rod, Fe-
Since the Ni composite compound is difficult to elute, the radioactivity concentration in the reactor water is not increased, and as a result, the radioactivity concentration can be reduced.

FIG. 6 is an illustrative diagram for the explanation, and Fe of the water supply system
FIG. 3 is a diagram showing changes over time in clad concentration and Ni ion concentration. A curve II shows the case where the Fe clad concentration is kept low from the initial stage of operation without changing the Fe clad concentration control over time, and the Ni ion concentration becomes like the concentration time varying curve I. This is presumed to be because the Ni ion concentration generated in the feed water heater tube and the like is higher than the Fe clad concentration, and the radioactivity concentration in the reactor water is increased by the mechanism as described above. On the other hand, in the present invention, the Fe clad concentration is controlled to be high in the initial stage of operation and then decreased in correspondence with the curve I, and if the Fe clad concentration is controlled as shown by the curve III, for example. An Fe clad concentration that can sufficiently bond and stabilize Ni ions is secured, and the radioactivity concentration in reactor water can be sufficiently reduced. Since Co ions also show the same temporal change in concentration as Ni ions, it is possible to stably bond the Co ions and the Fe cladding by controlling the Fe cladding concentration.

The means shown in Table 1 can be considered as the means for controlling the Fe clad concentration. This is shown in Table 1 together with the comparative evaluation.
In other words, as the control means, seven means such as bypass operation and performance control of the condensate purification system, control of the concentration of dissolved oxygen in the water supply, and iron injection can be mainly considered, but the water quality controllability of the water supply system, driving operability, and economic efficiency. In terms of performance, bypass operation of the condensate purification system and then performance control are considered to be the most appropriate.

Usually, the system configuration of the condensate purification system consists of a condensate demineralizer alone, a condensate super-desalinator alone, or an ascites demineralizer, an electromagnetic filter or an ultra-precision over-filter on the upstream side of the condensate demineralizer. In some cases, there is a condensate dual purification system with a pre-filter, but the control by bypass operation is
It is applicable in any case. Regarding the removal performance control of each purifier, the condensate demineralizer changes the removal performance by increasing / decreasing the water flow rate, and the condensate super-desalinator changes the precoat adjustment conditions of the powder resin. , The electromagnetic filter can be achieved by changing the magnetic field strength.

Next, to describe the method for controlling the condensate purification system according to the present invention, as described above, as the means for controlling the Fe clad concentration, the bypass operation of the condensate purification system is most preferable. In order to control the concentration, a configuration is adopted in which a condensate purification system is provided with a bypass line having a valve device capable of controlling the flow rate. And
The bypass line with the valve device that can control the flow rate,
Bypassing the pre-condensate filter such as the condensate super-desalinizer described in the above case in a general double-condensate purification system consisting of a condensate super-desalinizer and a condensate desalinator. It is composed.

As the above-described flow rate controllable valve device, a flow rate control valve having a continuously variable valve opening degree may be provided in the bypass line and the opening degree of the flow rate control valve may be adjusted. A plurality of on / off switching valves may be provided in parallel, and the bypass flow rate may be controlled by selectively opening / closing these switching valves. Further, in the present invention,
Condensate purified by the pre-condensate filter as described above is supplied to the condensate demineralizer provided downstream thereof,
Even if the condenser tube is damaged and seawater leaks, the condensate demineralizer can remove chlorine ions and the like caused by the seawater leak to prevent the inflow into the reactor.

Example of Invention

Before starting the description of the embodiments of the present invention, the system configuration of a boiling water nuclear power plant including a condensate purification system will be described with reference to FIG.

The steam generated in the reactor 1 is recovered as condensate by the turbine condenser 10, and then treated by a condensate purification system consisting of a condensate super-desalinizer 12 and a condensate demineralizer 13 to heat the feed water. After being heated in the reactor 14, water is supplied to the reactor 1. The water held by the reactor 1 is
It is purified by the super-desalination unit 6 of the nuclear reactor purification system 4. 20 to 200 ppb of oxygen is injected into the water supply system by the oxygen injection system consisting of the oxygen cylinder 22 and the oxygen injection line 21, and an oxide film is formed on the surface of the water supply system piping equipment to prevent corrosion and Of Fe clad is suppressed. In addition,
The concentration of Fe clad and Ni ion, etc.
Primary cooling water is sampled from 15,16,17,18, and the concentration is analyzed, measured and monitored. Condensate purification system
In addition to the case where the 12 is placed in front, there are cases where an electromagnetic filter and a super-sedimentary overfilter are installed, and there is also a case where the condensate demineralizer 12 is not installed and the condensate demineralizer 13 is installed alone is there.

Next, examples of the present invention will be described.

Example 1 FIG. 1 is a diagram showing an example in which the condensate superdesalting unit 12 as a prefilter is bypassed.

In the figure, the condensate collected by the turbine condenser is
In order to remove the iron clad generated by the corrosion of the wetted material, it is purified by the condensate super-desalination unit 12 provided in parallel with 12 units. In the condensate super-desalinizer 12, in order to uniformly control the flow rate of each tower, the flow meter 30 detects the flow rate, and the flow rate control valve 32 of each tower regulates and controls the flow rate. Condensate over-desalination unit 12
The condensate demineralizer 13 provided downstream of the condensate demineralizer 13 is provided for the treatment of seawater leak when the condenser tube is broken, that is, for preventing chlorine ion inflow into the reactor. ,Ten
Although it will be installed side by side, it has little impact on driving performance,
No equal flow control is performed. Further, a bypass line 44 is provided for performing a bypass operation for protection system purification during supply / condensate circulation operation during abnormal rise of differential pressure or plant stop, and the bypass valve 43, which is a fully open / closed on-off valve. By opening and closing, it is possible to pass the water supply / condensate recirculation flow rate when the plant is stopped (about one-third of the rated flow rate during plant operation).

The condensate flows into the condensate super-desalinizer 12 from the condensate mother pipe 38, and part of the condensate is passed to the bypass system 420. The bypass system 420 is provided with a flow meter 50 and a flow rate control valve 51, the opening degree is adjusted by a flow rate control device 52 such as a condensate super desalting device, and the bypass flow rate is controlled to an arbitrary level. At this time, some of the tower inlet valves 31 and some of the tower flow control valves 32 of the condensate super-desalination unit 12 are closed according to the bypass flow rate (in the figure, the closed valve is shown as a black valve). ) Part of the condensate that has passed through the bypass system 420 and has been treated by the condensate super-desalination unit 12 is then entirely treated by the condensate desalination unit 13 and sent to the reactor.

FIG. 9 is a diagram showing the relationship between the Fe clad concentration in the feed water and the bypass flow rate. In Example 1, the Fe clad concentration at the inlet of the condensate demineralizer 13 changes when the bypass flow rate is changed, but since the Fe clad is further removed by the condensate demineralizer 13, the feed water quality is condensate demineralized. It also depends on the removal performance of the vessel 13. Since the Fe clad removal performance of the condensate demineralizer 13 varies from 50 to 80%, the relationship between the Fe clad concentration and the bypass flow rate in Example 1 is shown in Case B in FIG. 9 and has a certain range. . That is, assuming that the Fe clad concentration in the condensate system is 5 ppb, 1 ppb to 2.5 pp due to 100% bypass operation of the condensate superdesalting unit 12.
Fe clad concentration of ppb, 0.3ppb-0.7 by 25% bypass
Water quality can be maintained at the Fe clad concentration of ppb.
Further, as described above, the condensate demineralizer 13 for removing the Fe clad 13
Even if a seawater leak occurs due to an accident such as a condenser tube leak, chlorine ions and other metal ions generated by this accident can be removed.

Example 2 An example in which the condensate demineralizer 13 is bypassed is shown in FIG. The entire amount of the condensate is first treated in the condensate super-desalination unit 12, and the treated water further flows into the condensate desalination unit 13 on the downstream side, and part of the condensate is passed to the bypass system 440. The bypass system 440 has a flow meter
53 and a flow rate control valve 54 are provided, the opening degree is adjusted by the condensate demineralizer bypass system flow rate control device 55, and the bypass flow rate is controlled to an arbitrary level. At this time, some of the tower inlet valves 34 and some of the tower outlet valves 35 of the condensate demineralizer 13 are closed according to the bypass flow rate (in the figure, the closed valves are shown as black valves). The condensate treated by the condensate demineralizer 13 through a part of the bypass system 440 is then sent to the reactor.

The relationship between the Fe clad concentration in the feed water and the bypass flow rate in Example 2 is shown in Case C in FIG. Condensed Fe
When the clad concentration is 5 ppb, the Fe clad concentration is 0.25 ppb by setting the bypass flow rate of the condensate demineralizer 13 to 100%.
Can be maintained at ~ 0.5ppb and also has a bypass flow rate of 50%
Can be maintained at 0.15ppb-0.3ppb.

The condensate demineralizer 13 is originally provided for the purpose of removing chlorine ions and other metal ions when seawater leaks due to leakage of the condenser tube or the like. When such a leak occurs, the flow control valve 54 can be closed promptly as necessary, and the entire amount of condensate can be treated to deal with the trouble.

Example 3 FIG. 3 shows an example in which both the condensate super-desalination unit and the condensate deionization unit, that is, the entire condensate purification system is bypassed. The bypass system 58 branches from the upstream condensate piping of the condensate super-desalination unit 12,
It merges with the outlet side pipe of the condensate demineralizer 13 via the flow meter 56 and the flow control valve 57. Part of the condensate is passed through the bypass system 58, and the rest is treated by the condensate super-desalination unit 12 and the condensate desalination unit 13. The bypass flow rate is controlled to an arbitrary level by adjusting the opening degree of the flow rate control valve 57 by the condensate purification system bypass system flow rate control device 59. At this time, some of the tower inlet valves 31, the tower flow rate control valves 32 of the condensate demineralizer 12 and the tower inlet valves 34 of the condensate demineralizer 13 and some of the tower outlet valves 35 correspond to the bypass flow rate. Then closed (the closed valve in FIG. 3 is shown as a black valve). Partly bypass system 58
The condensate, which has passed through the condensate super-desalination unit 12 and the condensate de-salination unit 13, is sent to the reactor.

The relationship between the Fe clad concentration in the feed water and the bypass flow rate in Example 3 is shown in Case A of FIG. In Example 3, by setting the bypass flow rate to 100%, the Fe clad concentration can be maintained at 5 ppb and the Fe clad concentration of about 0.5 ppb at the bypass flow rate of 10%.

Curve III in FIG. 6 shows the time-dependent change in the Fe clad concentration in Example 3 due to the bypass of the condensate purification system. In this embodiment, the water quality is controlled in accordance with the change over time of the Ni ion concentration (curve I) as shown by curve III.
It is possible to secure a Fe clad concentration that can sufficiently bond with Ni ions, and suppress an increase in reactor water radioactivity.

Embodiment 4 FIG. 4 shows an embodiment using a bypass line provided with a plurality of on-off valves in parallel. In FIG. 4, a bypass line is provided in the condensate super-desalination unit 12. In this embodiment, the bypass flow rate can be controlled to an arbitrary level by selectively opening and closing a plurality of parallel open / close valves 410. FIG. 4 shows a state in which three of the four on-off valves are opened and water is passed through the bypass. At this time, each tower inlet valve of the condensate super-desalination unit 12
31, some of the tower flow rate control valves 32 are closed according to the bypass flow rate (the closed valve is shown as a black valve in FIG. 4). In this embodiment, the bypass flow rate can be controlled only by selectively opening and closing the valve.

INDUSTRIAL APPLICABILITY The present invention is not limited to the above-described condensate duplexing system in which the condensate super-desalination device is used as a pre-filter, and also to a condensate purifying system in which a condensate super-desalination device or a condensate de-salting device is installed independently. Applicable. Further, the present invention can be applied to a plant that employs an electromagnetic filter or an ultra-precision overfilter in addition to the condensate demineralizer as a prefilter.

〔The invention's effect〕

As described above, in the present invention, the Co concentration is extremely low as compared with the Ni ion concentration in the feed water, and therefore, by substantially controlling the Fe clad concentration according to the Ni ion concentration, sufficient feed water can be obtained. Purifying effect can be obtained. Then, by optimally controlling the Fe clad concentration in the condensate prefilter according to the Ni ion concentration, Ni can be stably adhered to the fuel rod surface in the form of the Fe-Ni composite compound. The Fe-Ni composite compound is difficult to elute even if is activated on the surface of the fuel rod, so that the radioactivity concentration in the reactor water can be reduced. Further, the condensate demineralizer provided downstream of the pre-condensate filter can remove chlorine ions and other metal ions when seawater leaks due to damage to the condenser tube or the like, and can deal with the trouble.

[Brief description of drawings]

FIGS. 1, 2, 3, and 4 are schematic views of different embodiments of the present invention. FIGS. 5 (a) and 5 (b) are graphs showing the relationship between the Fe clad concentration, the ratio of radioactivity in reactor water, and the operating time of the plant. Fig. 6 shows Ni ion concentration and Fe
It is a figure showing the change over time of the clad concentration. FIG. 7 is a diagram showing a system configuration of a boiling water nuclear power plant. FIG. 8 is a diagram showing the relationship between the Fe clad concentration and the bypass flow rate in each example of the present invention. 1 ... Reactor pressure vessel, 2 ... Reactor recirculation system, 3 ... Reactor recirculation pump, 4 ... Reactor coolant purification system, 5 ... Reactor coolant purification system, Heat exchanger, 6 ... Atom Reactor coolant purification system Demineralizer 7 …… Main steam system, 8 …… Water supply system 9 …… Supply / condensate recirculation system, 10 …… Turbine condenser 11 …… Low pressure condensate pump, 12 …… Recovery Water demineralizer 13 …… Condensate demineralizer, 14 …… Feed water heater 15 …… Condensate pump outlet water sampling system 16 …… Condensate demineralizer outlet water sampling system 17 …… Condensate Demineralizer outlet water sampling system 18 …… Water supply system sampling point 19 …… Millipore sampling holder for metal impurities collection 20 …… Sample collection system rack 30 …… Condensate over-desalination tower Flow meter 31 …… Inlet valves for each tower of the water demineralizer 32 …… Flow control valves for each tower of the condensate demineralizer 33 …… Water supply system 34 …… Inlet valves for each tower of the condensate demineralizer 35 …… Each tower of the condensate demineralizer Outlet valve 36 …… Condensate demineralizer towers Volume meter 37 …… Condensate flow meter, 38 …… Condensate system 41 …… Condensate excess desalinator bypass valve 42 …… Condensate excess desalinator bypass system 43 …… Condensate desalter bypass valve 44 …… Condensate demineralizer bypass system 45 …… Orifice 50 …… Condensate over-desalinator bypass system flow meter 51 …… Condensate over-demineralizer bypass system flow control valve 52 …… Condensate over-demineralizer flow controller 53 …… Condensate demineralizer bypass system flowmeter 54 …… Condensate demineralizer bypass system flow control valve 55 …… Condensate demineralizer bypass system flow control device 56 …… Condensate purification system bypass system flowmeter 57 …… Condensate purification system bypass system flow control valve 58 …… Condensate purification system bypass system 59 …… Condensate purification system bypass system flow control device

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Katsumi Ohsumi 3-1-1, Saiwaicho, Hitachi-shi, Ibaraki Hitachi Ltd. Hitachi factory (56) References JP-A-61-79194 (JP, A) JP-A-60-78390 (JP, A) JP-A-55-63798 (JP, A) JP-A-58-83105 (JP, A) JP-A-59-70999 (JP, A) JP-A-59-120893 (JP, A)

Claims (1)

[Claims] 1. A valve device capable of controlling the flow rate of a condensate pre-filter in response to the change with time of the concentration of Ni ions so that Ni ions in the reactor feed water are sufficiently bonded and stabilized with the Fe clad. By adjusting the bypass flow rate,
A method for controlling a condensate purification system of a boiling water nuclear power plant, characterized in that the concentration of Fe clad is controlled, and the controlled feed water is passed through a condensate demineralizer provided downstream of the prefilter. .