JPH0797153B2 - Direct cycle atomic plant - Google Patents

Description

TECHNICAL FIELD The present invention relates to a direct cycle nuclear power plant.

[Conventional technology]

Boiling water nuclear power plant (hereinafter referred to as BWR plant)
Alternatively, in a direct cycle nuclear power plant such as a new converter, the turbine is directly driven by the steam generated in the reactor by the heat of the nuclear fission reaction, but the water molecules of the reactor water (hereinafter referred to as reactor water) The carryover of radioactive nitrogen atoms ¹⁶ N produced by the activation of oxygen atoms in neutrons is the main cause of the increase in the dose rate of turbine systems. The dose rate of the turbine system with ¹⁶ N is several R / h in terms of the surface dose rate of the main steam pipe, but it must be reduced in the following two points.

(1) Reduction of radiation exposure during inspection work during reactor operation.

(2) Dose rate regulation at the boundary of the nuclear power plant site (Skyshine regulation).

For the above purpose, conventionally, as shown in FIG. 2, the upper part of the main steam pipe 9 and the turbine 10 has been shielded by the iron plate 14, but the countermeasure from the aspect of suppressing generation and release of ¹⁶ N in the reactor is It was not done because the understanding of the phenomenon itself was not advanced.

In plants where no measures have been taken to prevent stress corrosion cracking of sensitized stainless steel in terms of stress or materials, measures to reduce the oxygen concentration in reactor water by hydrogen injection are being widely applied. As shown in the figure, the problem that the concentration of ¹⁶ N in main steam increases as the amount of hydrogen injection increases has been confirmed in all seven plants that have undergone the injection test. There is also. The mechanism of ¹⁶ N increase by hydrogen injection has not been clarified. For this purpose, for example, JP-A-57
A nuclear power plant described in JP-A-194399 or JP-A-62-151797 has been proposed.

[Problems to be Solved by the Invention]

Among the above-mentioned conventional techniques, the one disclosed in JP-A-57-194399 is provided with a device for removing N ₂ . However, substantially ¹⁶ N does not exist in the chemical form of N ₂ , but is entrained in water vapor in the form of NO _x . Therefore, it is extremely impossible to effectively remove the ¹⁶ N by the N ₂ removing device.
Further, in the case of the N ₂ gas injection apparatus described in JP-A-62-151797, there is a drawback that the isotope exchange reaction efficiency between the non-radioactive ¹⁴ NH ₃ and the radioactive ¹⁶ NH ₃ produced by injection is poor. is there.

Meanwhile, ¹⁶ N of the turbine system is in Atsuta shielding by the iron plate is the only measure conventionally this has problems as follows.

(1) The energy of gamma rays emitted from ¹⁶ N is 6 to 7
Since it is as high as MeV, the thickness of the iron plate required for shielding is about 150 mm. Therefore, the total weight of the iron plate covering the main steam piping and the turbine body is several hundred tons, and the turbine building itself must have a structure capable of supporting such heavy objects. You will be subject to the above restrictions.

(2) During regular inspection, the main steam system piping and turbine are dismantled and repaired, but at this time, the heavier the shield iron plate, the worse the workability.

(3) When hydrogen is injected, the dose rate increases to about 5 times the normal rate as shown in FIG. When the dose rate is to be reduced by strengthening the shielding, it is necessary to include a major remodeling of the turbine building itself in some cases due to the above-mentioned restrictions such as weight.

As explained above, the ¹⁶ N dose rate reduction measures by strengthening shielding cannot be essential measures in various aspects.

An object of the present invention is to provide a direct cycle nuclear power plant capable of reducing the absolute amount of ¹⁶ N generated in reactor water transferred to the main steam system and minimizing the influence on material corrosion. It is in.

[Means for Solving the Problems]

In the direct cycle nuclear power plant equipped with a reactor, a turbine, a condensate purification device, a feed water heater and a reactor water purification device, the above-mentioned object is (a) to convert radioactive nitrogen oxides in the reactor water into negative ions. A device for injecting a hydrogen radical scavenger having a function of reducing the hydrogen atom concentration by reacting with the hydrogen atoms, and (b) a hydrogen radical generator for reducing and removing the excess hydrogen radical scavenger in the reactor water. A device for injecting, (c) a corrosion potential monitoring device for detecting the corrosion potential of the reactor internal structural material in the reactor water and comparing it with an allowable corrosion potential, (d) a hydrogen radical scavenger based on the result of the monitoring. An injection amount control device for controlling the injection amount, and (e) an injection amount control device for controlling the injection amount of the hydrogen radical generator based on the result of the monitoring are provided. It is achieved by the.

[Action]

The present invention firstly uses the property that ¹⁶ N converts to a non-radioactive oxygen atom with a half-life of 7.2 seconds. That is, if ¹⁶ N can be maintained in the liquid phase or solid phase in the reactor pressure vessel for a time corresponding to the half-life or longer,
By itself, ¹⁶ N in main steam can be reduced to a concentration of less than half. The specific means for holding the liquid phase or the solid phase is based on the following findings.

(1) The present inventors conducted an experiment using an experimental apparatus as shown in FIG. 4 in order to clarify the mechanism of ¹⁶ N into the main steam system. First, the solution in which hydrogen and nitrogen are dissolved in the solution storage tank 20 is pumped by the pump 19 to the gamma irradiation chamber.
It is supplied into the autoclave 17 in 21 and heated to a predetermined temperature by the heater 16, and then gamma rays are irradiated from the gamma ray source 15 to generate decomposition products such as OH radicals, which react with hydrogen and nitrogen. The concentration of the ammonia thus produced was measured by the water quality measuring device 18. The results are 15, 60, 10
For each temperature of 0, 150, and 200 ° C., it is as shown by the circles in FIGS.

(2) On the basis of the experimental results obtained here, the present inventors found a large number of reaction schemes composed of the main components shown in FIG. Using, the behavior of radiolysis reaction of nitrogen-water system was simulated by a computer.
The results are shown by the solid lines in FIGS. The results of the simulation and the measured values agree with each other at factor 2 over the entire temperature range. Further, the tendency that the increase of the concentration of ammonia at a low temperature shows a saturation tendency, while the tendency of a linear increase at 200 ° C. is in good agreement.

(3) Fig. 11 shows the results of simulating the concentration increase rate of the turbine system ¹⁶ N during the hydrogen injection experiment of the BWR plant using the same reaction scheme. The calculated values are in good agreement with the measured values for the rate of rise and the hydrogen concentration at the core inlet at which the rise begins, compared to the measured values for ordinary plants, and the reaction scheme given here is sufficient as a ¹⁶ N dose rate evaluation model. It can be said to be realistic.

(4) The findings newly obtained from the results shown in FIG.
The chemical form of ¹⁶ N transferred to the turbine system is that most of it is nitric oxide and not ammonia as conventionally thought.

This will be explained with reference to FIG. 10 showing the mutual relation of the components. ¹⁶ N formed from oxygen atoms in water molecules in the core reacts with hydrogen atoms in water radiolysis products to form NH,
Furthermore, although it is reduced to eventually ammonia, since the rate constant of this pathway is relatively slow, NO formed by the reaction of N and OH is the main component initially formed from ¹⁶ N. NO
Is relatively stable and is also a gas, so it is released into water vapor.

On the other hand, when the atmosphere is oxidative, NO is oxidized by OH radicals or the like and converted into nonvolatile nitrous acid, nitric acid or the like. During normal operation without hydrogen injection, about 80% of ¹⁶ N is retained in water as nitric acid. When hydrogen is injected, nitric acid is converted to nitrous acid from the injected hydrogen by the hydrogen atom formed by H ₂ + OH → H + H ₂ O (1), and the NO concentration in equilibrium with this is increased. , ¹⁶ N in main steam also increases. Summarizing the above, (i) ¹⁶ N is released in the main steam in the chemical form of ¹⁶ NO.

(Ii) As the concentration of hydrogen atoms increases, the amount of ¹⁶ NO released increases.

Therefore, the reduction of ¹⁶ N is to reduce the hydrogen atom concentration or
This is achieved by increasing the H radical concentration and reducing the equilibrium concentration of ¹⁶ NO in water. To this end, in order to convert radioactive nitrogen oxides into negative ions in the reactor water, a hydrogen radical scavenger having a function of reacting with hydrogen atoms and reducing the hydrogen atom concentration may be injected into the reactor water. The injection into the reactor water does not necessarily have to be directly into the water in the reactor, but may be from the feed water or the condensate system.

The above measures may be effective only in the region between the core portion and the separator outlet. That is, the two-phase flow section is up to the separator outlet, and ¹⁶ N held in the liquid phase at the separator outlet becomes stable ¹⁶ O by radioactive decay while circulating in the primary system regardless of its chemical form. Therefore, the influence on the main steam system dose rate is eliminated. In other words, do it the transition to the gas phase from ¹⁶ N in the liquid phase in the flow path to the separator average delayed by means for reducing the aforementioned ¹⁶ N, ¹⁶ N reduction in main steam system can be achieved.

The effectiveness of the hydrogen atom concentration reduction measures by injecting NO, NO ₂ , and NO ₂ ⁻ will be described below. Figures 12 to 14 show the calculated ¹⁶ NO concentration in water vapor and oxygen concentration, nitric acid concentration, and nitrite concentration in the reactor water when the injection amount of the selected component was changed. . In all cases, the core inlet concentration was 10
By maintaining the concentration of ^-6 to 10 ^-5 mol / l, the concentration of ¹⁶ NO can be reduced by about one digit. On the other hand, if it is injected up to about 10 ^-4 mol / l, the concentration of nitric acid and nitrous acid becomes high, and the concentration of oxygen also increases.

The above results can be interpreted as follows. That is, in the process in which the concentration of NO increases as a result of the injected components reacting with the radiolysis product of water, for example, NO ₂ ⁻ + H → NO + OH ⁻ (2) NO ₂ + H → NO ₂ ⁻ + H ⁺ … ( The equilibrium concentration of hydrogen atoms decreases due to reactions such as 3), and the reactions such as H + OH → H ₂ O (4) become difficult to proceed, and the concentration of OH radicals increases relatively. Also a go-between to ¹⁶ N is ¹⁶ NO that has been generated by the go-between the reactor core ^{and, 16 NO + OH → H +} 16 NO 2 - ... (5) likely to take the form of'm an alien nitric acid, and once become nitrite, ¹⁶ NO ₂ ^- The reaction of + H → ¹⁶ NO + OH ⁻ (6) is difficult to proceed because the hydrogen atom concentration is low.

As described above, the equilibrium concentration of ¹⁶ NO is lowered, so the ¹⁶ NO concentration in the main steam is also reduced.

Next, Fig. 15 shows the solution when N ₂ is injected. In the case of N ₂ , it is not as significant as the above three compounds. This is probably because N ₂ partially changes to NO, NO _2, etc., but is not efficient, and a high proportion of N ₂ escapes to steam.

From the above results, the most effective method for reducing hydrogen atoms is the method of injecting NO ₂ or NO ₂ ⁻ .

In the present invention, in addition to the effect of reducing ¹⁶ N, the effect of reducing ¹⁶ NH ₃ can be obtained.

Next, reducing the excess hydrogen radical scavenger in the reactor water,
The injection operation of the hydrogen radical generator for removing will be described. As described above, with the injection of the hydrogen radical scavenger such as the nitrogen compound, as shown in FIGS. 12 to 14,
The nitric acid concentration in the reactor water increases. Therefore, the inside of the furnace becomes oxidative atmosphere, that is, corrosive, which is an unfavorable environment for the materials inside the furnace. Therefore, in the present invention, in addition to the operation of reducing the hydrogen atom concentration, the operation of injecting the hydrogen radical scavenger (reduction of the hydrogen atom concentration) is stopped as necessary, for example, when the inspection work of the equipment is not performed. Injecting a hydrogen radical generator to reduce and remove excess hydrogen radical scavenger to increase the hydrogen atom concentration, thereby reducing nitrate ion and nitrite ion to NO, and reducing the nitric acid concentration early. It was done like this. By controlling the hydrogen atom concentration in this way, it is possible to effectively reduce ¹⁶ N while controlling the impact on the corrosive environment in the furnace.

〔Example〕

Example 1 An example of applying the present invention for steady reduction of ¹⁶ N dose rate will be described below with reference to the drawings.

FIG. 1 shows a schematic configuration diagram of a plant when applied to a BWR plant. 1 is a nitrous acid injection device, 2 is a pressure vessel, 3 is a NOx processing device, 4 is a core, 5 is a recirculation pipe, 6
Is a reactor cleaning system, 7 is a water supply pipe, 8 is an emergency core cooling system, 9 is a main steam pipe, 10 is a turbine, 11 is an in-core instrumentation pipe, 12 is a control rod cooling device, 13 is a water quality monitoring device, and 37 is Hydrogen cylinder, 42
Is a condensate purification device. The nitrous acid injection device 1 as a hydrogen radical scavenger is installed on the downstream side of the condensate purification device 42. In addition to this, it is possible to connect to any place of the water supply pipe 7, the condensate purification device 42, the reactor purification system 6, the control rod cooling device 12, the in-core instrumentation pipe 11, the core emergency cooling system 8, etc. Is. In principle, these injection points have the same effect regardless of which one is selected.
If the shape is likely to change due to some factors before reaching the core 4 inside, the injection point is the control rod cooling device 12,
A point close to the core 4 like the in-core instrumentation pipe 11 is desirable. Since injection components can be expected to accumulate in the primary cooling system, it is not necessary to inject a large amount from the beginning, and the concentrations of nitric acid, nitrous acid, etc. are measured by the monitor device 13, and the main steam pipe 9 or turbine is measured.
The optimum injection rate and injection amount may be set based on changes in the surface dose rate at 10 or the like. When nitrogen oxides such as NO and N ₂ O are injected, NOx is released to the off-gas system, so it may be better to provide the NOx treatment device 3.

FIG. 17 shows a schematic view of a liquid injection device, which uses nitric acid,
Water containing nitrous acid or the like is stored in a storage tank 26, and is injected into the reactor primary system piping 22 by a water injection pump 25 through a flow rate control valve 24 and a heat exchanger 23. Here, nitrogen oxide gas is used, and water in the solution storage tank 26 is put therein, and nitrogen oxide gas is injected from the cylinder 27 into this to generate nitric acid or nitrous acid. It is designed to be injected into 22. In this case, 0.3-1 Nm ³ / h NO per hour
Is released. Therefore, the injection amount should be commensurate with this loss, and the maximum daily dose is 20 to ³⁰ Nm ³ . The injection rate can be controlled by changing the opening of the valve 24.

FIG. 18 shows a monitor system for measuring the concentrations of nitric acid and nitrous acid. Water sampled from the reactor primary system piping 22 is cooled by a heat exchanger 29 through a bypass valve 28, and then a high pressure constant flow pump. 30, separation column 31, conductivity system 32
To the ion chromatograph 33, which separates and quantifies nitric acid and nitrous acid. The water that has passed through the ion chromatograph device 33 may be heated in the heat exchanger 34 and then returned to the reactor primary system piping 22 by the high pressure pump 35.

The above-mentioned operation can reduce the dose rate to about 1/10, and thus has the following advantages.

(1) It is possible to reduce radiation exposure during inspection work while the reactor of the Turbi building is operating.

(2) It is possible to improve the work efficiency and reduce the design strength of the turbine building by reducing the weight or eliminating the shielding iron plate around the turbine.

(3) The efficiency of inspection work is improved by making the turbine building a non-controlled area.

(4) Due to the low dose rate region at the boundary of the nuclear power plant site, it is possible to construct 4 to 5 plants on the site of the existing plant.

Next, Fig. 19, nitrite ions to the reactor water (NO ₂ ^-)
Injection and hydrogen gas (H ₂₎ turbine system dose rate of infusion time was repeated alternately in and the reactor water of NO ₂ ^- shows the time course of the concentration. In FIG. 19, A indicates normal operation, B indicates NO ₂ ⁻ injection operation, and C indicates H ₂ injection operation. During normal operation, the turbine system dose rate ^{results 16} N generated by the reactor water is Kiyari over over the turbine system in a chemical form of a ¹⁶ NO, indicating the value of the constant level (X) due to ¹⁶ N. At this time, in the reactor water NO ₂ ^- concentration as low as ppb level (x). NO ₂ ⁻ Generated in reactor water during injection operation ¹⁶
N is ¹⁶ NO ₂ ^- or ¹⁶ NO ₃ ^- and changes in chemical form, the amount is reduced to Kiyari over over to the turbine system to dissolved in reactor water as an anion. As a result, the dose rate level drops from X to Y. At this time, in the reactor water NO ₂ ^- concentration
Increase to ppm level (y). Then, at the time of H ₂ injection operation, present in the reactor water NO ₂ ^- is chemical form changes to NO, molecular (volatile), and a result of Kiyari over over the turbine system, in the reactor water NO ₂ ^- The concentration gradually decreases from level y to z. At this time, ¹⁶ NO ₂ ^- or ¹⁶ NO ₃ ^- chemical forms in ¹⁶ N which has been dissolved at the same time Kiyari chromatography over to a result, the level of dose rate on the contrary, increases from Y to Z. By repeating the above operation, the turbine system dose rate can be variably controlled.

FIG. 20, NO ₂ into reactor water ^- the time course of concentration ^- NO ₂ injection and the concentration of hydrogen atoms changes in the reactor water and the turbine system dose rates and reactor water when was repeated injection of H ₂ alternating It is shown. When NO ₂ ⁻ is injected, the equilibrium concentration of hydrogen atoms decreases due to the following reaction.

NO ₂ ⁻ + H → NO + OH ⁻ (7) When the hydrogen atom concentration decreases, the radiolysis reaction of the N-water system shown in FIG. 21 shifts to the oxidation side, so ¹⁶ NO is a water-soluble ¹⁶ NO ₂ ⁻ and ¹⁶ NO _2. NO ₃ ^- in the dissolved in water by changing the chemical form, Kiyari chromatography over amount to the steam system is greatly reduced. Such a mechanism makes it possible to significantly suppress the radioactivity caused by ¹⁶ NO.

On the other hand, when H ₂ is injected, the equilibrium concentration of hydrogen atoms increases due to the following reaction.

H ₂ + OH → H + H ₂ O (8) When the concentration of hydrogen atoms increases, the radiolysis reaction of the N-water system shown in Fig. 21 shifts to the reduction side, so NO in the reactor water
₂ ^- chemical form changes to NO, to Kiyari over over in the vapor. As a result, in the reactor water NO ₂ ^- concentration is decreased. On this occasion,
¹⁶ NO ₂ ⁻ and ¹⁶ NO ₃ ⁻ also carry over to the vapor system in the form of ¹⁶ NO, which increases the dose rate. But H ₂
Injection period, NO ₂ ^- sufficiently shorter than the injection period, ¹⁶ transient increase in N dose rate Taken averaged throughout the plant operating time, small enough to be negligible in comparison with the reduction effect.

NO ₂ after injection stops, if not performed the injection of hydrogen radical generating agent such as H _2, the nitrite and nitrate ions remaining in high concentrations in the reactor water. Flow rate of the furnace the purification system is a feed water flow Since it is as small as about 1%, it takes several days to reduce the concentration to the level before injection of NO ₂ . Further, there is a problem that the frequency of exchanging the ion exchange resin in the purification system is increased accordingly, and the plant operation and maintenance work and the amount of radioactive waste are increased. On the other hand, in the present invention, as shown in FIGS. 19 and 20, when the hydrogen radical generator is injected after the NO ₂ injection is stopped, the nitrous acid is generated within an extremely short time of about 2 to 3 hours. It was also confirmed that the concentration of nitrate ions can be reduced, the corrosive environment can be quickly mitigated, and the effect on the ion exchange resin of the purification system can be reduced to a negligible level.

In the above examples, NO ₂ ⁻ was taken as the nitrogen compound to be injected, but even if a nitrogen compound such as nitric oxide, nitrogen dioxide, or dinitrogen monoxide is injected, ¹⁶ NO in the radiolysis reaction process.
It suppresses the generation of and exhibits the same effect.

Further, in the above embodiment, H _{2 is} used as the hydrogen compound to be injected.
Although gas was used, even if a hydrogen compound such as NH ₃ is injected,
It promotes the production of NO in the radiolysis reaction process and exerts the same effect.

Further, although the concentration of the injected substance is kept constant over time, the same effect can be exhibited even if the concentration is changed with time. For example,
By making the initial injection amount higher than the steady value,
It is possible to accelerate the injection effect.

Furthermore, at the same time as the injection was stopped, the operation to remove the nitrogen compounds remaining in the reactor water was started, but the removal operation was performed after a certain period of time after the injection was stopped (injection operation of the hydrogen radical generator).
It is also possible to start. Furthermore, it is possible to temporally overlap the injection timing and the removal time.

In the above embodiment, NO ₂ in the reactor water ^- such as but having conducted by chemical forms varying concentrations reduction, are conventionally generally performed,
It is also possible to remove using an ion exchange resin, an adsorbent or the like.

Second Embodiment Next, another embodiment will be described with reference to FIG. This system is a radiation monitor for measuring the dose rate in the main steam system.
36, tank 1 for nitrogen compound, hydrogen cylinder 37, valves 24 and 38 for controlling nitrogen compound and hydrogen injection amount, corrosion monitor 39 for measuring corrosion potential at high temperature, control device for controlling nitrogen compound and hydrogen injection amount 40 and injection line 41 for injection. The corrosion monitor 39 may be installed inside the primary cooling system boundary where the temperature and pressure are high,
Since the influence of radiation on the measurement is small and the maintainability is good, it is installed, for example, on the upstream side of the heat exchanger for purifying the reactor, and measures the high temperature corrosion potential during normal operation and during injection of nitrogen compounds and the like. The radiation monitor 36 may be installed anywhere in the turbine building near the surface of the main steam pipe. The controller 40 controls the opening amounts of the valves 24 and 38 whose flow rates can be adjusted based on the corrosion potential and the dose rate of the main steam system, and controls the injection amount of nitrogen oxide or hydrogen. With the above system, it is possible to carry out an operation in which the injection of nitrogen oxides into the reactor water and the operation of reducing the nitrogen compounds after the injection is stopped are repeated. In the above embodiment, the corrosion potential was used as the control index for the optimum control of the NO ₂ ⁻ injection amount and the optimum control of the H ₂ injection amount and the injection period, but other indexes can also be used. For example, it is possible to measure the NO ₂ ⁻ or NO ₃ ⁻ concentration in the reactor water or the hydrogen atom concentration and use the measured value as the control index.

A concrete example of applying the present invention to the plant shown in FIG. 22 will be described with reference to FIG. FIG. 23 shows the process of monitoring the injection effect of nitrogen compounds and controlling the injection in the form of a flow chart. The process for reducing the dose rate in the main steam system starts the injection with the default nitrogen compound injection rate. In order to confirm that the integrity of structural materials of the primary system of the reactor is not impaired by the injected nitrogen compound or the nitrogen compound having a different chemical form generated by the chemical reaction in these reactors. First, measure the corrosion potential at high temperature. It is known that the service life of a material generally increases as the corrosion potential decreases. When injected into the reactor water, NO ₂ in the reactor water ^{- -} NO ₂ with increasing concentration, NO ₂ ^- it is further oxidized the NO ₃ ^- concentration increases.
NO ₃ ⁻ acts as an oxidant on metal materials, resulting in an increase in corrosion potential. Accordance connexion, NO ₂ ^- by the time of the injection operation is controlled so as not to increase the permissible value or more necessary to ensure the design life of the corrosion potential materials, NO ₂ ^- injection has on the health of the reactor internal member It is possible to manage the impact sufficiently small. When the corrosion potential obtained by measurement exceeds the upper limit set value, the injection rate of the nitrogen compound is reduced and the corrosion potential is measured again. If the corrosion potential is below the established upper limit, the next step is to measure the dose rate of the main steam system. When the measured dose rate exceeds the target value, the injection rate of the nitrogen compound is increased and the process returns to the corrosion potential measurement process again. If the dose rate in the main steam system is below the target value,
Since the process for reducing the dose rate in the main steam system is completed, it is indicated that entry into the main steam system is possible. After that, return to the measurement of the corrosion potential at high temperature, confirm that the corrosion potential does not increase due to the accumulation of nitrogen compounds in the reactor water, and if it increases, control to reduce the injection amount of nitrogen compounds at any time. To do. By injecting nitrogen compounds in such a process, it is possible to significantly reduce the dose rate of the main steam system, especially the turbine system, while ensuring the integrity of the pressure boundary and equipment of the reactor primary system, which is important for safety. Therefore, it is possible to reduce the exposure of workers approaching around the main steam system during the reactor operation.

After the work around the main steam system is finished, it is necessary to finish the injection of the nitrogen compound in order to make the corrosion potential at high temperature as low as possible. The process begins with the end of the nitrogen compound injection, but begins with the hydrogen injection in order to remove the nitrogen compound remaining in the reactor water as soon as possible. During the hydrogen injection period, the corrosion potential at high temperature is measured, and when the measured value falls below the set value, the injection is terminated and the entire process ends. The reason for injecting hydrogen in this way is that the injected hydrogen reacts with a highly soluble nitrogen compound in the reactor water, and the chemical form of the nitrogen compound can be changed to volatile ammonia or the like. Therefore, the nitrogen compound remaining in the reactor water rapidly moves to the gas phase and the nitrogen compound in the reactor water disappears, so that the corrosion potential can be restored to the state before the nitrogen injection.

When the nitrogen compound is injected from the water supply, the condensate purification device 42 is used in order to prevent the injected nitrogen compound from being attenuated by the purification device and shortening the life of the purification device.
It is desirable to inject from downstream.

Similarly, the anion exchange resin (usually OH type strongly basic anion exchange resin) of the reactor water purification device adsorbs nitrogen compound ions,
If there is a concern that the exchange capacity of the ion-exchange resin will be reduced and the life will be shortened by the exchange, an anion obtained by converting the ion-exchange group into a NO ₂ -type instead of the above-mentioned OH-type strongly basic anion-exchange resin is used. By using the exchange resin, it is possible to prevent the problem of shortening the life of the anion exchange resin of the reactor water purification device and the loss of the injected nitrogen compound in the reactor water purification device at the same time. Is desirable. At this time, the anion exchange resin of the reactor water purification device was replaced with NO ₂
Even if the anion-exchange resin converted into the mold is used, the original function of the anion-exchange resin in the reactor water purification device is sufficient to remove chlorine ions and the like from the ion selectivity of the ion-exchange group.

〔The invention's effect〕

According to the present invention, during the operation of a direct cycle nuclear power plant, oxygen atoms in the water molecules of the reactor water are activated by neutron irradiation to generate radioactive nitrogen atoms ¹⁶ N, the main steam system from the reactor. It is possible to remarkably suppress the carryover to the turbine system and further to the turbine system, and to significantly reduce the dose rate. Further, the air dose rate in the turbine building is reduced, and the turbine building as a whole can be downsized.

Furthermore, by combining the injection operation of the hydrogen radical generator, the dose rate can be reduced and the corrosive environment for the material in the furnace can be mitigated.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a boiling water nuclear power plant showing an embodiment in which the present invention is applied to intermittently reduce the ¹⁶ N dose rate, and FIG.
Figure shows the arrangement of shielding iron plates around the turbine, Figure 3 and Figure showing changes in the dose rate of the turbine system during hydrogen injection in a boiling water reactor, and Figure 4 evaluates the radiolysis of nitrogen-dissolved water. The block diagrams of the experimental apparatus manufactured for this purpose, and Figs. 5 to 9 show the concentration of ammonia produced in water when nitrogen and hydrogen are added to the water, together with the measured value and the result of numerical simulation by a computer. Fig. 5 shows the results at water temperatures of 15, 60, 100, 150, and 200 ℃ in order from Fig. 5, Fig. 10 shows the relationship between nitrogen compounds, and Fig. 11 shows hydrogen injection in a boiling water reactor. Figures showing the calculated values of the increase rate of ¹⁶ NO in the turbine system during the experiment in comparison with the measured values and the calculated values of the concentration of hydrogen atoms in the reactor water.Figures 12 to 16 show various nitrogen oxides and nitrogen. ¹⁶ NO concentration in water vapor when molecules are injected,
FIG. 12 is a diagram showing changes in oxygen concentration, hydrogen peroxide concentration, nitric acid concentration and nitrite concentration in the reactor water.
^{_{NO, NO 2, NO 2 -}} , shows the case of N _2, N ₂ O, Figure 17 Figure showing the injection device of the hydrogen radical scavenger solution, FIG. 18 nitrite, a monitoring device for nitric acid concentration Figure, Figure 19 is a diagram showing an example when the method of the present invention is applied only at the time of inspection of the plant, Figure 20 is a hydrogen atom concentration when NO ₂ ^- and H ₂ are alternately injected into the reactor water, turbine dose rate of the system and NO ₂ ^- shows the change in concentration, FIG. 21 NO ₂ ^- shows oxidation, the reduction reaction of the 22
The figure is a block diagram of a boiling water nuclear power plant to which the present invention is applied, and FIG. 23 is a flow chart showing a control method at the time of injecting NO ₂ ⁻ and H ₂ . 1 ... Injection device, 2 ... Pressure vessel, 3 ... NOx treatment device, 4 ... Reactor core, 5 ... Recirculation piping, 6 ... Reactor purification system,
7 ... Water supply pipe, 8 ... Emergency core cooling system, 9 ... Main steam pipe, 10 ... Turbine, 11 ... In-core instrumentation pipe, 12 ... Control rod cooling device, 13 ... Water quality monitoring device, 14 …… Shielding iron plate,
15 …… Gamma ray source, 16 …… Heater, 17 …… Autoclave, 18 …… Water quality measuring device, 19 …… Liquid transfer pump, 20 ……
Solution storage tank, 21 ... Gamma irradiation chamber, 22 ... Reactor primary system piping, 23 ... Heat exchanger, 24 ... Flow control valve, 25 ... Liquid transfer pump, 26 ... Solution storage tank, 27 ... … Nitrogen oxide gas cylinder, 28 …… Valve, 29 …… Heat exchanger, 30 …… High pressure pump,
31 …… Separation column, 32 …… Conductivity meter, 33 …… Ion chromatograph, 34 …… Heat exchanger, 35 …… Liquid transfer pump, 36…
… Radiation monitor, 37 …… Hydrogen cylinder, 38 …… Valve, 39…
… Corrosion monitor, 40 …… Control device, 41 …… Injection line,
42 …… Condensate purification device,

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Makoto Nagase 1168 Moriyama-cho, Hitachi, Hitachi, Ibaraki Energy Research Institute Co., Ltd.Hitate Manufacturing Co., Ltd. (72) Hidetoshi Karasawa 1168, Moriyama-cho, Hitachi, Ibaraki Japan Energy Research Institute (72) Inventor Shoji Sakagami 1168 Moriyama-cho, Hitachi City, Ibaraki Prefecture Hitate Manufacturing Co., Ltd. (72) Inventor Motoaki Utamura 1168 Moriyama-cho, Hitachi City Ibaraki Hitachi, Ltd. Energy Research Institute (72) Inventor Fumio Kawamura 1168 Moriyama-cho, Hitachi City, Ibaraki Prefecture Hiritsu Manufacturing Co., Ltd.Energy Research Institute (72) Inventor Shunsuke Uchida 1168 Moriyama-cho, Hitachi City, Ibaraki Hitachi Research Institute Energy Research Institute ( 72) Inventor Minoru Miki 3-1, 1-1 Sachimachi, Hitachi City, Ibaraki Prefecture Hitachi, Ltd., Hitachi Plant (72) Inventor, Katsumi Okazumi, 3-1, 1-1, Saiwaicho, Hitachi, Ibaraki Stock Company, Hitachi, Ltd., Hitachi Plant, (72) Inventor, Yoshiki Chiba, 3-chome, Hitachi City, Ibaraki Prefecture No. 1 within Hitachi Engineering Co., Ltd. (56) Reference JP-A-1-127999 (JP, A) JP-A 1-102396 (JP, A) JP-A-63-151900 (JP, A)

Claims (4)

[Claims] 1. A direct cycle nuclear power plant comprising a reactor, a turbine, a condensate purification device, a feed water heater and a reactor water purification device, wherein: (a) a reactor for converting radioactive nitrogen oxides in the reactor water into anions. A device for injecting a hydrogen radical scavenger having an action of reacting with hydrogen atoms in water to reduce the hydrogen atom concentration, (b) reducing excess hydrogen radical scavenger in reactor water,
A device for injecting a hydrogen radical generator for removal, (c) A corrosion potential monitoring device for detecting the corrosion potential of the reactor internal structural material in the reactor water and comparing it with the allowable corrosion potential, (d) Results of the monitoring An injection amount control device for controlling the injection amount of the hydrogen radical scavenger based on the above, and (e) an injection amount control device for controlling the injection amount of the hydrogen radical generator based on the result of the monitoring. A direct cycle nuclear power plant characterized by the above. 2. A direct cycle nuclear power plant comprising a nuclear reactor, a turbine, a condensate purification device, a feed water heater and a reactor water purification device, wherein: (a) a reactor for converting radioactive nitrogen oxides in the reactor water into anions. Means for injecting a hydrogen radical scavenger having the action of reacting with hydrogen atoms in water to reduce the concentration of hydrogen atoms, and (b) reducing excess hydrogen radical scavenger in reactor water,
A direct cycle nuclear power plant characterized in that a means for injecting a hydrogen radical generator for removal is provided, and (c) the reactor water purification device is a purification device filled with NO ₂ type anion exchange resin. 3. The direct cycle nuclear power plant according to claim 2, wherein the hydrogen radical scavenger injection means is a hydrogen or ammonia injection device. 4. The direct cycle nuclear power plant according to claim 2 or 3, wherein the hydrogen radical scavenger injection means and the hydrogen radical generator injection means are provided downstream of the condensate purification device. Direct cycle nuclear power plant characterized by being installed on the side.