JPS60158392A - High-temperature filter element for light-water reactor - 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 is directed to reducing the amount of Co contained in the primary cooling water of a light water reactor.
This is a dispute regarding high-temperature filter elements for light water reactors that selectively adsorb and remove.

[Technical background of the invention and its problems]

In recent years, as the number of years of operation of light water reactors has increased, radionuclides have been deposited in various parts of the secondary cooling system piping, and the radiation dose rate during reactor shutdown has gradually increased.

Such accumulation of radioactivity leads to an increase in the radiation dose of inspection personnel during inspection work when the reactor is shut down for periodic inspections, etc., and has negative effects such as a decrease in operating efficiency.

The increase in dose rate during reactor shutdown due to radioactivity accumulation varies widely depending on the reactor type and maintenance management method, but for example, EPRI (Electric Power
According to a summary by Re5each Institute +USA, several boiling water reactors (B
The surface dose rate of the recirculation line (WR) is determined by the effective operating period (IEFRY: I EffectiveFu) of one year.
ll Povrer Year) Current page 100-15
It shows an increase of 0 mR/h.

Among the radionuclides that cause this accumulation of radioactivity, Co and Co, which have long half-lives, pose a particular problem because of their large influence on radiation dose rates. The cause of this accumulation of radioactivity is that Co, which is a constituent element of the structural material, is ionized by elution into the cooling water system due to corrosion of the structural material, and this ionized Co is adsorbed to metal oxides, or due to ion exchange reactions. and is incorporated into metal oxides. When this metal oxide is carried into the reactor core, the Co taken in is made radioactive.

Currently, in actual equipment, metal oxides containing radioactive Co are removed by once lowering the reactor water temperature to room temperature. However, in this method of removing Co, since reactor water is once cooled and removed, it is heated again and circulated, which causes a problem of large heat loss in the plant.

In order to improve this, we developed a system that uses high temperatures (such as the water reactor environment of light water reactors).
Inorganic ion exchangers with high heat resistance are attracting attention as they can efficiently and effectively remove Co under conditions of high pressure (56 to 76 atm).

Examples of this inorganic ion exchanger include magnetite,
It is used by filling the reactor water passage in the form of ceramic powder such as aluminum oxide or zorconium dioxide, or in the form of a sintered body.

However, if the flow rate of the reactor water increases beyond the specified value or if flow rate fluctuations such as pulsation occur, there is a risk that the powder will flow into the reactor water, and the powder may also leak into the reactor water due to the occurrence of cracks in the sintered body. There is a risk that it may leak out. Furthermore, since these inorganic ion exchangers are ceramic, their shapes are limited,
Moreover, the filter element must be formed separately and the receptacle must be incorporated into the flow path, making processing and assembly cumbersome.
It has not yet been put into practical use.

[Purpose of the invention]

The present invention has been developed in view of these points, and has a large adsorption capacity for Co contained in the reactor water of a light water reactor, and there is no risk of Co being leaked into the reactor water, and it can be processed into any shape as a filter. The object of the present invention is to provide a high-temperature filter element for a light water reactor that is capable of producing a filter material even in high-temperature, high-pressure reactor water.

[Summary of the invention]

As a result of comparative studies on the Co adsorption ability of various inorganic ion exchangers, the present inventors have found that a spinel type oxide containing Mn is the most excellent.

That is, in the present invention, Cr9 to 20%, Mn
9-25%, C0.5% or less, N1% or less, Sl
2% or less, the balance F'e, by oxidizing the surface of any alloy,
This method is characterized by selectively adsorbing Co to this oxide.

The present invention will be explained in detail below. First, the composition of the material alloy forming the high temperature filter element for a light water reactor according to the present invention will be explained.

Cr is effective for improving the corrosion resistance of steel, and if it is less than 9%, the effect of addition is small, and if it is added in excess of 20%, it impairs workability, so it is defined in the above range, preferably 11 to 18%. is good.

In the present invention, Mn has Co adsorption ability on the alloy surface (
Mn, Fe) is the most important element for forming 304, and if it is less than 9 thi, its effect will be small, and if it is added in excess of 25 thi, it will impair workability and corrosion resistance. ~20 inches is good.

C functions to provide the necessary strength for forming and processing the steel, and also to provide sufficient strength to maintain the filter base. Excessive addition of more than 0.5 inch will result in corrosion resistance.
Since it impairs toughness, it should be less than this, preferably 02
% or less.

N acts to improve strength and corrosion resistance,
If it is added in excess of 1 inch, micro-bores will occur, so the amount should be less than this, preferably 0.6 inch or less.

Sl is an element necessary as a deoxidizing agent and improves sludge during steel production. Excessive addition of more than 2% impairs toughness, so it should be kept below this value.

Manganese ferrite (MntFe) 304 is a typical method for forming an oxide having Co adsorption ability on the surface of an alloy having the above composition, which can be roughly divided into high-temperature water treatment, (1) atmospheric oxidation treatment, (2) wet nitrogen treatment, etc. A spinel-type oxide is formed.

In the high-temperature underwater treatment method, the above alloy is formed into a filter shape and placed in the flow path of reactor water, so that the alloy surface is oxidized during use in high-temperature, high-pressure reactor water, and manganese having Co adsorption ability is produced. A Suginel type oxide, typified by ferrite, is formed. According to this method, the filter material is not formed separately outside the furnace, but is formed by contact with reactor water during furnace operation, so it is extremely easy to process and assemble compared to conventional ceramic materials. be. In addition, as a high-temperature underwater treatment method, in an autoclave outside the furnace,
Alternatively, the surface may be oxidized by leaving it in water or steam at 500° C. and 40 to 100 atm.

In addition, the oxide formed on the alloy surface may be mixed with an oxide other than the (Mn + Fe) 504 spinel type oxide represented by manganese ferrite; for example, (M
Although corundum type oxides such as n, Fe) 203 have a low Co adsorption ability, they may be mixed depending on the oxidizing atmosphere. Moreover, Fe in (Mn, Fe) s 04 is another element,
For example, Cr, Tl + At + Zr contained in the alloy
+M.

(Mn, Fe, CrlTilAtlZrlMO)3
04 spinel type oxide may also be used.

Furthermore, the shape of the filter element of the present invention may be mesh-like or ?
- It can be molded into any shape such as a round shape or a chip shape, and unlike conventional ceramic adsorbents, the shape is not limited.

The high-temperature filter element for light water reactors of the present invention has improved Co adsorption ability by several orders of magnitude compared to conventional ceramic filters.The principle behind this is that spinel-type oxides, typified by manganese ferrite, formed on the alloy surface. It is thought that it exhibits an excellent adsorption effect due to some action.

In addition, the filter element of the present invention does not contain Ni, which may be radioactive, and Co, which is an impurity thereof, in its base alloy composition, and even when installed in a light water reactor, it is made of austenitic stainless steel. Like steel, corrosion products such as Ni and C are often released into the reactor water, and this is in line with the current trend toward lower CO2 emissions.

[Embodiments of the invention]

(Example 1) Alloy samples A, B, and C having the compositions shown in Table 1 were prepared, and after surface wet polishing with Emelina 600, each sample was immersed separately in a solution containing about 220 PPb of Co ions. ,
This was inserted into a stationary autoclave and maintained at 290°C under saturated vapor pressure for 24 hours. Thereafter, the solution was taken out from the autoclave, and the Co concentration ions remaining in the solution were measured, and the concentration and Co adsorption rate are shown in Table 2. This adsorption test was repeated three times and the average value is shown.

For comparison, a Co adsorption test was also conducted on SUS 304 steel, and the results are also listed in Table 2.

As is clear from the results shown in Table 1 and Table 2, all of the example products of the present invention had an extremely excellent Co adsorption rate of 87 cm or more, and SUS 304
The amount of Co adsorption is about 5 times that of .

In addition, when the surface condition of the samples after oxidation treatment in an autoclave was investigated by X-ray diffraction, it was found that Example product samples A and B
, C, (Mn, Fe) 504 containing Am is formed on the surface, and Cr, F is formed on the surface of SUS 304 steel.
An oxide containing e as a main component was formed.

(Example 2) Samples A, B, and C having the compositions shown in Table 1 were prepared and immersed in an autoclave in advance to generate oxides on the surfaces. Next, this sample was immersed in a solution containing 2Q OPPb with Co ions in the same manner as in Example 1 above, and left in an autoclave for 24 hours. After this, the remaining Co concentration ions were measured, and the results are shown in Table 3.

For comparison, the CO adsorption capacity was similarly measured using magnetite (PA3O4), which is an inorganic ion exchanger, and the results are also listed in Table 3.Table 3 [Effects of the Invention]

Claims (1)

[Claims] M amount? -St, chromium (Cr) 9-20%. Manganese (Mn) 9-25%, Carbon (C) 0.
5% or less, nitrogen (N) 1 t or less, silicon (81) 2-
below. A high-temperature filter element for a light water reactor, characterized in that the surface of an alloy, the remainder of which is essentially iron (Fe), is oxidized to selectively adsorb copal (Co) to the oxide.