JPS618697A - Afterward provided stop system constitutional part for high-temperature gas furnace - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to backup shutdown system components used in high temperature gas reactors. More specifically, the present invention relates to parts that have been surface-treated to prevent corrosion in the helium gas environment of a high-temperature gas furnace.

[Technical background of the invention and its problems]

In a high-temperature gas reactor that uses helium as a coolant, the constituent materials of the backup shutdown system are used at a high temperature of about 400° C., and the reactor is placed in a high-temperature helium environment. Helium, which is essentially inert, also acts as a carrier for various impurities at high temperatures, creating a special corrosive environment. In other words, H2)Co and CO2)CH are produced by the reaction of graphite with moisture from the graphite itself in the reactor core and moisture that has entered the piping, so helium contains trace amounts of these impurity components, and their amounts and composition vary. It is known that the corrosion environment, which depends on the ratio, greatly affects the corrosion behavior and mechanical strength of structural members made of heat-resistant alloys. In the primary circulating helium of a high-temperature gas furnace, oxygen molecules (0□) do not coexist with graphite and are virtually non-existent, so structural materials have low oxidizing properties due to trace amounts of H20 and CO2, and carburizing properties. environment. The high-temperature gas reactor standby shutdown string is a string that is used to stop the reactor separately from the control rods, and is used to inject the control elements (neutron absorption boron balls) installed at the top of the reactor core into the reactor core when the reactor is shut down. A control element with a mechanism, a hopper that accommodates the control element, a loveture disk that ruptures when the control element is thrown into the reactor core, a holder that supports this loveture disk, and a control element that holds the control element after being thrown into the reactor core. It consists of a guide tube to guide the reactor to the core, a gas introduction tube to pressurize the inside of the hopper with helium gas, etc. These backup shutdown system components are placed in the corrosive high-temperature helium gas environment as described above, so they are required to have excellent corrosion resistance in addition to heat resistance and high-temperature strength. The corrosion resistance of parts is
It does not significantly affect the reliability of mechanical strength during use, but also affects the problem of radioactive contamination of the helium circulation system due to K, such as detachment of corrosion products from the surface and peeling of the corrosion film. . Therefore, in order to improve the durability of the components of the backup shutdown system and ensure healthy operation of the backup shutdown system during use, it is necessary to take some measures to improve corrosion resistance.

[Purpose of the invention]

In light of the above-mentioned special circumstances related to the backup shutdown system of high-temperature gas reactors, this invention has been developed to provide a backup shutdown system with excellent corrosion resistance that is extremely effective in maintaining mechanical strength and reducing radioactive contamination in the primary circulating helium system. The purpose is to provide stop system components.

[Summary of the invention]

The present invention is an austenitic stainless steel used as a component of a high-temperature gas reactor backup shutdown system.

It is characterized by improving the corrosion resistance of parts under the usage environment by forming a nickel coating layer on the surface of a member such as a nickel-based alloy.

As mentioned above, corrosion in the helium environment of a high temperature gas reactor is
It depends on the amount and component ratio of impurities in helium. For oxidation, for example, the partial pressure of HzO and H governs the oxidation characteristics of the alloying elements of the member, and for carburization, for example, C
Partial pressures of H and CO govern carburizing characteristics. Among the alloying elements of the member, AA and Ti.

Elements that are easily oxidized, such as Si, undergo selective oxidation in helium, which promotes localized erosion such as grain boundary erosion and internal oxidation, leading to deterioration of mechanical properties and poor adhesion of oxide films. do.

On the other hand, Cr, which is an element with a high affinity for carbon, forms chromium carbide (due to the intrusion of carbon).

As this reaction progresses, the oxidation resistance of the alloy substrate is lost, the brittle surface layer peels off, and the mechanical properties of the alloy substrate deteriorate. However, Ni is an element that is extremely stable against both oxygen and carbon in a low oxidizing and carburizing helium environment, so the formation of altered products due to oxidation and carburization does not occur as described above, and corrosion resistance is good. . The present invention focused on this point and found that forming a nickel coating layer on the surface of a member, regardless of the type of material of the member, has a great effect on improving corrosion resistance.

Methods for forming a nickel coating layer on the surface of a component include electroplating, which involves depositing nickel from an aqueous nickel salt solution, metal spraying, which involves spraying molten nickel particles for coating, vacuum vapor deposition (PVD), and chemical vapor deposition (CVD). ) and a gas phase plating method in which Ninocale is precipitated from the gas phase. The present invention does not limit the method of forming the nickel coating layer, but an optimal method may be adopted in consideration of the applicable member, application location, usage conditions of the member, required thickness of the nickel coating layer, etc. . The nickel coating layer formed by the electroplating method is characterized by good adhesion to the base metal and good uniformity in thickness, resulting in a highly pure nickel precipitated layer. The metal spraying method has the advantage of being able to thicken the coating layer, and the chemical evaporation method has the advantage of being able to uniformly coat members with a complex shape with a coating having excellent adhesion strength.

The present invention will be specifically explained below using Examples.

[Embodiments of the invention]

FIG. 1 shows a configuration diagram of a lubrication disk attachment part in a high-temperature gas reactor backup shutdown system. The Loveture Disk mounting part is Loveture Disc (1).

Holder (2), hopper (3) and bolt/nut (4)
), a guide tube (5), etc. Among these members, a loveture disk holder made of austenitic stainless steel was coated with nickel by electroplating. After the holder was degreased and washed with water, it was pickled for 15 minutes in a 15% aqueous hydrochloric acid solution (20°C). After washing it with water, it was dried with dry nitrogen and nickel sulfate (NiSO4, 150r/l) - ammonium chloride (
NH2Ot, 15 f/l) - using a boric acid (HBOs, 15 f/l) electrolytic bath at a current density of 0
．． Electrolytic nickel plating was performed at 8 A/dm' and a temperature of 25°C. High purity (99,
95%) Ni plate was used, and auxiliary anodes made of the same material as the anode material were used on the outer and inner surfaces of the support, which is the member to be treated, in order to obtain uniformity of current density.

Through this treatment, a coating layer with a thickness of about 15 μm was formed on the surface of the support member. The nickel-coated support member had a healthy appearance with no peeling of the coating or uneven plating observed. In addition, the nickel coating layer has high purity (
99.9%) of Ni, and it was confirmed that the thickness was approximately uniform in each part. In order to confirm the corrosion resistance of the support member of the present invention in high-temperature impure helium, the following comparative experiment was conducted. A small sample made of the same material as the support member was prepared, and a sample coated with nickel in the same manner as above and an untreated sample that had been degreased and washed with water were coated with high-temperature impure helium (temperature near 00℃).
, H2 as an impurity: about 200 μatm.

CO: approx. 100μ atm, HIO: approx. 5 p atm
m, CH,: approx. 5 μ atm, CO2: approx. 2 μ
A 1000 hour exposure test was conducted in He (including ATM).

As a result, formation of a corrosion film and partial peeling of the film were observed on the surface of the untreated material without nickel coating.
On the surface of nickel-coated materials.

It had a healthy appearance with no deterioration or peeling observed.

The cross sections of these samples were polished and analyzed for Cr in the depth direction from the surface using EPMAK. The results are shown in FIGS. 2 and 3. In the nickel-coated material, there is no change in the Cr concentration in the depth direction, but in the untreated material, there is a region that exhibits a lower Cr concentration than the base material from just below the corrosion film on the surface to a depth of about 100 μm. In other words, it is clear that a chromium-deficient layer is formed. The existence of such a Cr-depleted layer and corrosion film in the untreated material is thought to be due to the intrusion of carbon and bonding with Cr, which resulted in loss of oxidation resistance, and the surface was oxidized, forming chromium carbide near the surface. It will be done.

〔Effect of the invention〕

As shown in the above examples, Trap 5 according to the present invention exhibits excellent corrosion resistance and heat resistance even in the low-oxidizing and carburizing high-temperature helium environment of a high-temperature gas furnace.

Backup shutdown system components are realized. That is, since the nickel coating layer on the surface of the member exhibits a strong resistance to carburization and oxidation and plays a role in protecting the base material of the member, reaction products resulting from carburization and oxidation are not formed. Therefore, the mechanical strength does not decrease due to corrosion during the period of use, and it is possible to prevent the spread of radioactive contamination of the helium circulation system due to separation of reaction products and the like from the surface of the member.

As described above, the member of the present invention has sufficient durability as a component of a high-temperature gas reactor backup shutdown system, and can guarantee sound operation during the period of use. In addition, the design conditions of conventional parts (materials, shape, 2 dimensions, etc.) can produce great effects simply by applying the above-mentioned processing to conventionally used parts.
There is no need to change it to a large cloth, and its industrial value is great.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view showing the configuration of the lubture disk attachment part of the backup stop system of a member according to an embodiment of the present invention, and FIGS. 2 and 3 show the distribution of Cr concentration in the member according to the present invention. Curve diagram. l...Hopper, 2...Holder, 3...Holder, 4...Loveture disk, 5...Guide tube.

Claims (1)

[Claims] 1) A component for a high-temperature gas reactor backup shutdown system whose surface is coated with a nickel layer. 2) The component according to claim 1 is made of austenitic stainless steel. Back-up shutdown system components for high-temperature gas reactors characterized by