JPH0222899B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a radiation water decomposition concentration detection device, and is particularly suitable for constantly monitoring the water activity of corrosive radioactive decomposition products present in the cooling water of a water-cooled nuclear reactor. Regarding a radiation water decomposition concentration detection device.

Corrosion behavior of structural materials inside the reactor of a light water reactor is caused by O ₂ ,
Because radioactive decomposition products such as O ₂ ^- and HO ₂ are always present, these effects are said to cause corrosion behavior to differ from normal corrosion.

Therefore, in order to accurately understand the corrosive environment inside the reactor, we used dissolved oxygen meters in high-temperature water and PH meters (LW).
Niedrach, J. Electrochem Soc 127 , 10, 2122
(1980)) have been developed and used, but since they are installed near the reactor core taking into account the effects of irradiation and non-irradiation, there are problems with the radiation resistance of the oxygen permeable membrane, and the decomposition of the membrane has a short lifespan. It was not suitable as a monitor for a corrosive environment that also includes products. Furthermore, measurements using corrosion potential, which are carried out in recirculation bypass systems, etc., cannot be used as a continuous corrosion environment monitor because the reliability of the reference electrode is low.

The purpose of the present invention is to eliminate the drawbacks of the prior art described above, to have pressure resistance, high temperature resistance, and radiation resistance that are suitable as a corrosive environment monitor, and to continuously monitor the concentration of radiolysis products in reactor water for a long period of time. An object of the present invention is to provide a radiation water decomposition concentration detection device that can be monitored.

In order to achieve the above object, the present invention includes a conductive sealed container filled with water in which hydrogen is dissolved, and a conductive sealed container that is electrically insulated from the conductive sealed container and provided so as to be immersed in the water in the container. a first electrode; a second electrode provided outside the container so as to be immersed in the water to be measured; and means for measuring a potential between the first electrode and the second electrode. It is characterized by

Hereinafter, the principle and embodiments of the present invention will be explained based on the drawings.

In the core of a water-cooled reactor, high dose rate gamma rays (approximately 10 ⁸ R/h) and high neutron flux density (approximately
10 ¹⁴ n/cm ³ s), radiolysis of water occurs. Specifically, from water molecules, for example, hydrated electrons (e _aq ), H radicals, O ₂ ,
Eleven types of radiolysis products such as OH radicals are constantly present in reactor water. These decomposition products react and recombine with each other and ultimately return to water molecules, but in a nuclear reactor, they are constantly present at a constant concentration depending on the irradiation dose.

Figure 1 shows the above 11 types of radiolysis products under irradiation (absorbed energy: 1w/g (neutron), 1/
This shows the numerical analysis results for steady concentration at 8w/g (gamma rays) and water temperature of 285°C. The absorbed energy is matched to the level of a boiling water reactor, indicating that under such heavy irradiation, the decomposition product concentration reaches a steady-state value within a very short time.

Furthermore, it is known that radiolysis of water can be suppressed by dissolving hydrogen in water in advance. FIG. 2 shows the analysis results regarding the effect of initially dissolved hydrogen on the radiolysis of water. According to FIG. 2, it is clear that when dissolved hydrogen is less than 0.3 cm ³ /Kg, the oxygen concentration decreases by more than two orders of magnitude.

Next, based on the above analysis results, the electrode potential when decomposition products are present in water is determined between the metal electrode 1 to be measured and the reference electrode 2 in the corrosion potential measurement system configuration shown in FIG. The potential difference can be measured by the potentiometer 3, and the electrode potential in this case can be expressed as follows using Nernst's equation.

E _M = Eo + 2.3 RT / nFloga _pxid / a _red ... (1) where, E _M ; potential of metal electrode Eo; when 1 unit activity each of oxidizing and reducing components exists in water. Reference electrode potential n; Number of electrons that move during redox reaction R; Gas constant F; Faraday constant T; Absolute temperature a _pxid ; Activity of oxidizing component a _red ; Activity of reducing component In the furnace, Due to irradiation, a _pxid and a _red change, so the electrode potential changes. A reference electrode 2 is required to measure the change as an absolute value. The corrosion potential measurement system shown in FIG. 3 includes a metal electrode 1 to be measured and a reference electrode 2 placed in a container 5 filled with immersion liquid 4, surrounded by a shield 6, and irradiated with a cobalt-60 radiation source 7. (approximately 10 ⁵ R/h). Figure 4 shows the change in corrosion potential under gamma ray irradiation at a constant temperature. According to FIG. 4, it can be seen that the electrode potential increases due to the irradiation. This is thought to be because a _pxid and a _red change due to irradiation.

FIG. 5 is an embodiment showing the basic configuration of the radiation water decomposition concentration detection device according to the present invention.

A first electrode 11 and a second electrode connected to a potentiometer 13
It has an electrode 12, the first electrode 11 is immersed through the insulating material 16 in hydrogen-filled water 17 filled in a water tank formed by a conductor wall 15 and an insulating material 16, and the second electrode 12 is Immersion liquid 1, which is the liquid to be measured
It is immersed in 4.

With this configuration, when the first electrode is immersed in a water tank at temperature T and exposed to radiation,
Since almost no radiolysis occurs in the electrode potential in hydrogen-filled water, no effect of irradiation appears on the electrode potential. On the other hand, the potential E ^* _M of the second electrode 12 directly immersed in the immersion liquid 14 of the liquid to be measured is expressed by the following equation.

E ^* _M = Eo + 2.3RT / nFloga ^* _pxid / a ^* _red ... (2) Here, the asterisk (*) means under irradiation.

Since a _pxid and a _red of the hydrogen filled liquid remain unchanged, the potential difference V between both electrodes 11 and 12 is V=E ^* _M − E _M = 2.3RT/nFlog (a ^* _pxid / a ^* _red )K becomes.

However, K=a _pxid /a _red , which is the value of the electrode in the hydrogen filled liquid, is taken as a constant because changes due to irradiation can be ignored.

In this way, the potential difference V between the first and second electrodes will correspond one-to-one to the concentration of decomposition products in the water. Therefore, by measuring the potential difference V with the potentiometer 13, the concentration of water decomposition products caused by radiation can be detected.

FIG. 6 shows another specific embodiment of the present invention.

The metal electrodes 21 and 22 are made of corrosion-resistant platinum wire and are fixed to a flange 28 mounted on the pressure boundary 29 via an alumina insulating material 26.

The metal electrode 22 on the reactor water 24 side is connected to the alumina end plug 26
The metal electrode 21 is fixed so that it does not move, and the other metal electrode 21 is also fixed in the same way.
Hydrogen-filled water 27 containing approximately 10 cm ³ /Kg of dissolved hydrogen is sealed in a SUS316 conductor tube 25 made of stainless steel and having bellows 25a for absorbing thermal expansion, and is bounded by reactor water 24 . The platinum wire metal electrodes 21 and 22, the SUS316 conductor tube 25, and the alumina insulating material 26 are fixed together by silver soldering or the like after the alumina insulating material 26 is metalized.

In such a configuration, the metal electrodes 21, 22
The potential difference between
Measurements are now being taken outside the furnace.

According to this embodiment, it can be constructed as a heat-resistant and pressure-resistant reactor water radiolysis monitor, and radiation resistance can also be improved because a radiation-sensitive material such as Teflon resin is not used.

In addition, in the conventional technology, a method is also used in which the corrosion potential of SUS etc. immersed in reactor water is directly measured using a high-temperature reference electrode (Katsuhisa Sugimoto, Anticorrosion Technology, 29, 521 (1980)) (Tetsuo Fujii, Bulletin of the Japan Institute of Metals, 17, 1, 54 (1978)), this method is also unreliable in terms of radiation resistance, etc., and has poor high temperature resistance.
For example, Ag/AgCl electrodes have had problems such as being unable to be used continuously due to high temperature oxidation of the electrode itself.

However, according to the present invention, as described above, it is possible to measure the concentration of highly active radiolysis products in reactor water without using a reference electrode, and furthermore, it is made of heat-resistant and radiation-resistant materials. Therefore, it is possible to provide a radiation water decomposition concentration detection device that can continuously monitor the concentration of radiolysis products in reactor water as a corrosive environment over a long period of time.

[Brief explanation of drawings]

Figure 1 shows the results of numerical analysis of the concentration change of water radiolysis products after the start of irradiation, Figure 2 shows the effect of initial dissolved hydrogen on the radiolysis of water, and Figure 3 shows the corrosion potential. FIG. 4 is a diagram showing the change in corrosion potential under gamma ray irradiation, FIG. 5 is a diagram showing the configuration of a radiation water decomposition concentration detection device according to an embodiment of the present invention, and FIG. 6 is a diagram showing the configuration of the measurement system. 3 is a cross-sectional view of a device according to another embodiment; FIG. 11, 21...first electrode, 12,22...second
Electrode, 13... Potentiometer, 14, 24... Water to be measured (reactor water), 15... Conductor, 16, 26... Insulating material, 17, 27... Hydrogen-filled water, 25...
SUS316 conductor tube, 25a...bellows.

Claims (1)

[Scope of Claims] 1. A conductive sealed container filled with water in which hydrogen is dissolved, and a first electrode that is electrically insulated from the conductive sealed container and provided to be immersed in the water in the container. , comprising a second electrode provided outside the container so as to be immersed in the water to be measured, and means for measuring the potential between the first electrode and the second electrode. Radiation water decomposition concentration detection device. 2. The radioactive water decomposition concentration detecting device according to claim 1, wherein at least a portion of the conductive sealed container is constituted by a bellows whose volume can be changed by pressure.