RU2377675C2 - Method of regenerating spent metals and alloys in contact with radioactive materials - Google Patents

Abstract

FIELD: nuclear physics.

SUBSTANCE: invention relates to a method of decontaminating and treating scrap metal and alloys continuously accumulating in nuclear power engineering and industry. Scrap steel or non-ferrous metals (alloys) are held at temperature of 700°C under slag-molten mixture of chlorides of (mol %): sodium (35), magnesium (31-33), potassium (35) and refined metal (2-4) for 30-40 minutes; slag with impurities which have been oxidised to chlorides is poured off. The scrap is then melted again at temperature 1600-1700°C under the slag: molten mixture of fluorides of (mol %): calcium (50) and magnesium (50) for 20-30 minutes.

EFFECT: obtaining construction metals (alloys) of cleaner metals and alloys from contaminated scrap metal.

2 ex

Description

APPLICATION AREA

Decontamination and remelting of scrap metals and alloys, constantly accumulating in nuclear energy and industry.

BACKGROUND

For the processing of “infected” metals and alloys (for example, stainless steels, nickel-based alloys and other structural metal products), methods for their remelting under synthetic slags are patented.

Known RF Patent "Method for the processing of metal waste containing radionuclides" RU 2159473 C1, 10.28.1999. Patent holder - LLC “Environmentally Friendly Technologies in Industry Plus”. Inventors: A.F. Lositsky, N.A. Hansa, V.V. Rozhdestvensky, R.N. Kasimov, A.R. Beketov, Yu.P. Zaikov, A.I. Goncharov, K.A. Plekhanov, I.S.Soloboev.

Remelting “infected” steel wastes (for example, Х18Н10Т) under slag - a mixture of oxide with calcium fluoride, allows one to reduce the initial activity from 180-200 Bq / g to 5-12 Bq / g, i.e. about 40-20 times.

The simplicity and affordability of these processing methods is attractive with relatively low requirements for the removal of contaminants from secondary metals and alloys. However, not always achieved cleaning factors are sufficient for the safe use of reclaimed materials in existing processes and structures.

BACKGROUND OF THE INVENTION

Obtaining from contaminated scrap metals (alloys) of cleaner metals and alloys that can be freely used, due to the implementation of the proposed method of cleaning and remelting.

SUMMARY OF THE INVENTION

A study of the distribution of radioactive contaminants in even very long-serving structural materials (and not only metallic ones) showed that, with rare exceptions, they end up in surface layers in contact with aggressive media. From this we concluded that for more effective cleaning, it is necessary first, not leading to melting, to cure scrap under slag - a molten mixture of chloride (mol.%) Sodium (35), magnesium (31-33), potassium (35) with the addition of 2-4% chloride of refined metal for 20-30 minutes at a temperature of 700 ° C. The proposed slag has very strong oxidizing properties, it moistens the surface of the refined metal well, penetrates microcracks, transfers primary and secondary fission radionuclides: isotopes of strontium, yttrium, cesium, barium, lanthanides, into the slag phase - into the chloride melt. In order not to reduce the oxidative activity of the slag, a small amount of refined metal chloride is introduced into it. Counter reconstitution Me ^{n +} ions allows to maintain consistency of the oxidation process. Almost all isotopes of polluting elements pass into slag in the form of a suspension of oxides, oxyfluorides, and other compounds. Slag is drained. It is recyclable.

Then the scrap is remelted under synthetic slag - a molten mixture of fluorides (mol.%) Calcium (50) and magnesium (50) for 20-30 minutes at a temperature of 1700 ° C. The regenerated metal (alloy) is poured into the molds, giving the desired shape and dimensions of the ingots. Fluoride slag is also recyclable.

The technology of a two-stage process eliminates the risk of radioactive contamination entering the volume of the melted metal due to exchange reactions and capture of slag by convective flows of molten metal (alloy).

EXAMPLES OF IMPLEMENTATION OF THE DECISION

1. Starting material: scrap of nickel and its alloys contaminated with fluorides, oxyfluorides, uranium oxides and fission radionuclides. It was kept in a graphite crucible of the bottom-casting induction furnace under a layer of molten slag of chlorides (mol%) of sodium (35), magnesium (31-33), potassium (35) and nickel (2-4) at a temperature of 700 ° С for 40 min. The slag was poured. For remelting, slag of the second stage was induced: fluorides (mol.%) Calcium (50) and magnesium (50). At a temperature of 1700 ° C, they held for 20 minutes. Refined nickel (alloy) was poured into molds. Purification of metal from contamination is achieved by measured radioactivity 200-300 times. Fluoride slag is suitable for remelting.

2. Starting material: X18H10T steel scrap. In the first stage, it was kept under chloride slag at a temperature of 700 ° C for 20 minutes. Then remelted under fluoride slag at a temperature of 1600 ° C. Achievement of metal purification by measured radioactivity in 160-220 times.

It should be noted that the main components of refining slags are pure chlorides and fluorides - waste from magnesium and calcium thermal production of titanium (TiCl ₄ + 2Mg = Ti + 2MgCl ₂ ), uranium (UF ₄ + 2Ca = U + 2CaF ₂ ), etc. This will significantly reduce costs when implementing the proposed method on an industrial scale.

Claims (1)

The method of regeneration of metals and alloys, spent in contact with radioactive materials, which consists in the fact that to remove contaminants from scrap, structural metals (alloys) are remelted under synthetic halide slag, characterized in that the pre-refined metal is maintained at a temperature of 700 ° C under the slag - molten mixture of chlorides (mol.%): sodium (35), magnesium (31-33), potassium (35) and refined metal (2-4) for 30-40 minutes, then melted under slag - a molten mixture of fluorides (mol.%) ): calcium (50) and magnesium (50) 20-30 yn at a temperature 1600-1700 ° C.