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Method of stress corrosion cracking mitigation for nuclear power plant structural materials

a technology of stress corrosion cracking and nuclear power plant, which is applied in nuclear engineering, nuclear elements, greenhouse gas reduction, etc., can solve the problems of increasing the concentration of radioactive cobalt co-60 in the cooling water of the reactor, and achieve the effect of suppressing the rise in the dose rate of the main steam line and reducing the concentration of radioactive cobalt co-60

Inactive Publication Date: 2005-01-27
HITACHI-GE NUCLEAR ENERGY LTD
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Benefits of technology

[0007] It is an object of this invention to provide a method for mitigating the stress corrosion cracking of reactor structural materials by which the rise in the main steam line dose rate can be suppressed without side reactions such as the elevation of radioactive cobalt Co-60 concentration in the cooling water of the reactor.
[0008] A reductive nitrogen compound containing nitrogen having a negative oxidation number is injected into the reactor water of a boiling water nuclear power plant. By injecting a reductive nitrogen compound containing nitrogen having a negative oxidation number into the reactor water, the stress corrosion cracking of the structural material of the reactor can be mitigated without secondary effects such as the elevation of cobalt 60 (Co-60) concentration.

Problems solved by technology

If an element of the platinum group is made to adhere to the surface of a material in order to accelerate the reaction between hydrogen and oxygen and hydrogen peroxide, however, there arises a new problem that the concentration of radioactive cobalt Co-60 in the cooling water for the reactor rises.

Method used

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  • Method of stress corrosion cracking mitigation for nuclear power plant structural materials
  • Method of stress corrosion cracking mitigation for nuclear power plant structural materials
  • Method of stress corrosion cracking mitigation for nuclear power plant structural materials

Examples

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example 1

[0065] As the first example of this invention, an example in which only a reductive nitrogen compound is injected at the times of start up and shut down will be mentioned. At the times of start up and shut down, temperature is low and γ-ray exposure is small, so that the water-forming reaction between reductive nitrogen compound and oxygen and hydrogen peroxide does not take place readily. FIG. 5 illustrates hydrazine concentration dependence of ECP of 304SS, wherein hydrazine was added as a reductive nitrogen compound. If the ECP dependence of CGR shown in FIG. 2 is taken into consideration, it is necessary to add hydrazine in an amount of 50 ppb or more or further preferably in an amount of 100 ppb or more in order to reduce CGR to {fraction (1 / 10)} of that in the case of no hydrazine injection. On the other hand, addition of 300 ppb or more brings about no change in the ECP-lowering effect. From the electric conductivity dependence of CGR shown in FIG. 2, it is apparent that, eve...

example 2

[0071] Next, as the second example of this invention, an example in which only a reductive nitrogen compound is injected at the time of operation will be mentioned. Since temperature is high and γ-ray exposure is greatest at the time of operation, the water-forming reaction between reductive nitrogen compound and oxygen and hydrogen peroxide is accelerated. Accordingly it is necessary to inject the reductive nitrogen compound continuously.

[0072] In FIG. 6 are shown the changes of oxygen and by-products in a case of adding hydrazine as a reductive nitrogen compound to high-temperature water containing dissolved oxygen and carrying out a γ ray irradiation. In case that the concentration of reductive nitrogen compound does not reach the amount needed for converting oxygen to water, a residual part of oxygen remains. In case that the concentration of reductive nitrogen compound is higher than the amount necessary for converting oxygen to water, oxygen is consumed and ammonia is formed....

example 3

[0078] Next, as the third example of this invention, an example in which hydrogen and a reductive nitrogen compound are injected into the cooling water will be mentioned. In case that hydrogen is injected, the hydrogen concentration in the cooling water at the bottom of reactor pressure vessel increases. If the hydrogen concentration exceeds a definite value, dose rate of the main steam line can increase. Accordingly, it is necessary to control the amount of injected hydrogen together with the reductive nitrogen compound to obtain an optimum condition. Since hydrogen is usually cheaper in price than reductive nitrogen compound, it is preferable to increase the amount of hydrogen and decrease the amount of reductive nitrogen compound.

[0079]FIG. 13 diagrammatically illustrates the changes of concentrations of oxygen, hydrogen and ammonia in the cooling water at the bottom of reactor pressure vessel, and the dose rate of main steam line, in the case of changing the amount of injection...

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Abstract

The object of this invention is to provide a method for mitigating a stress corrosion cracking of reactor structural material which makes it possible to suppress the rise in the main steam line dose rate without secondary effects such as a rise in the concentration of radioactive cobalt-60, etc. in the reactor water. Hydrogen and a reductive nitrogen compound containing nitrogen having a negative oxidation number (for example, hydrazine) are injected into the core water of boiling water nuclear power plant. By injecting the reductive nitrogen compound containing nitrogen having a negative oxidation number into the core water, the stress corrosion cracking of structural material of reactor can be mitigated without side reactions such as a rise in the concentration of cobalt-60, etc.

Description

FIELD OF THE INVENTION [0001] This invention relates to a technique for a preventive maintenance of boiling water nuclear power plant (hereinafter, referred to as “BWR”), and particularly to a method for mitigating a stress corrosion cracking (hereinafter, referred to as “SCC”) of nuclear power plant structural materials. BACKGROUND OF THE INVENTION [0002] In BWR, it is an important problem to suppress the SCC of the materials constructing the core structures and pressure boundaries (stainless steel, nickel-base alloys) from the viewpoint of improving the plant operating rate. SCC takes place when the three factors (materials, stress, environment) fall on one another. Accordingly, SCC can be mitigated by mitigating at least one of the three factors. [0003] When a plant is operated, the core cooling water is radioactively decomposed by the intense gamma and neutron rays emitted from the core. As its result, the structural materials constructing the in-core structures and pressure bou...

Claims

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Application Information

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IPC IPC(8): G21D3/08G21C17/00G21D1/00
CPCG21C17/0225Y02E30/30
Inventor ISHIDA, KAZUSHIGEWADA, YOICHINAGASE, MAKOTOTACHIBANA, MASAHIKOENDO, MASAOFUSE, MOTOMASAUSUI, NAOSHIAIZAWA, MOTOHIRO
Owner HITACHI-GE NUCLEAR ENERGY LTD
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