CS215568B1 - Method of preventing the corrosion effect of acidic liquid waste - Google Patents

Description

The invention relates to a process for preventing the corrosive effect of acidic liquid wastes containing high, medium or low radioactivity cleavable nitrates.

When disposing of liquid radioactive wastes, especially high radioactivity wastes, but including medium or low activity wastes, today's technological trend follows both the removal of radiolytically unstable waste components and the solidification of the waste until its incorporation into relatively very stable materials approaching natural tops that prove to be most suitable for temporary and permanent storage.

Concentrates of radioactive fission products mostly fall off in the form of nitrates dissolved in nitric acid.

215 588 (H) (B1) (51) Int. Cl? G 21 P 9/04 concentrations. At high activity ae, the nitrate ion is highly volatile rediolytically and releases toxic nitrous gases; it is therefore necessary to remove nitrates from the storage waste, as a rule by reductive degradation by some organic reducing agents, such as formeldehyde, formic acid, molasses or some sugars below, which in addition reduce the total concentration of salts in the solutions. With the addition of glass-forming substances such as lime, soda, boric acid and silicic acid, the precipitate formed after drying and kaleinisation can then be converted into a glass or ceramic melt at a temperature of about 1200 ° C. As an alternative technique, but in the presence of glass-forming phosphoric acid, the denitrated emulsion can be converted into polyfoaphate glasses at temperatures of 800 to 1000 ° C. In such a process, a reduction with formic acid, e.g.

Both these methods, practiced in a number of other alternative variants on a continuous and discontinuous route, have undoubtedly a considerable perspective. However, the disadvantage of these processes is, in particular, that corrosion problems occur under acidic conditions at very high temperatures; toxic and corrosive exhalations also arise, which need to be disposed of costly to generate another form of waste. The presence of phosphoric acid increases the corrosivity of the environment.

part of the mentioned deficiencies, ie · the formation of toxic nitrous exhalation, are eliminated, for example, by the procedures according to MS. Certificate No. 202 109 or according to Art. No. 202,611, but these procedures leave unnoticed the corrosion of the acid environment from elevated temperatures. The lack of corrosion is eliminated by the process according to the invention in logical connection to the two mentioned articles. copyright certificates.

SUMMARY OF THE INVENTION The present invention provides a process for preventing the corrosion effect of acidic liquid wastes containing high, medium or low radioactivity fission cation nitrates by treating them with ammonia and / or urea to pH 7.5 to 10e by subsequent pyrolytic degradation and denitrification Deň: 32 ° C.

The higher effect of the invention is in particular in that the alkaline and, in addition, at significantly elevated temperatures also allows a reduction environment to work in conventional steel containers which are extremely corrosive in an acid environment; this makes it possible to replace a single compliant material - platinum - with completely unpretentious construction materials, which can also continue to be used as stacking containers for special storage.

The process according to the invention can be advantageously applied in continuous and diaconal processes for the disposal, stabilization and fixation of nuclear waste and any radioactivity. Especially preferred is the application of the invention to polyphosphate glasses having a melting point of 850 to 950 ° C, which also allows the use of conventional steel as a construction material. Higher melting points of borosilicate glasses require thermally more stable nickel and chromium-nickel structural steels.

The method is further described in the examples, which, however, can be varied or adapted to the composition of the waste, so that the summary of said examples does not limit the possibility of implementing the invention.

Example 1

Model solution of a highly radioactive concentrate after spent nuclear fuel recovery, containing ▼ 1 dm ^ 189 g of duic acid, 85 g of sodium nitrate, 93 g of ferric nitrate, 24 & bromine nitrate, 18 g of nickel phosphate, 65 g of cerium nitrate and 21,5 g of nitrate Alumina, mixed with 200 g of orthophosphoric acid (85% w / w), and the mixture was adjusted with ammonia gas stream to pH 7.5 with stirring. The resulting suspension was directly injected into a heated degradation and melting vessel where it was treated at 250 ° C. up to 840 ° C. The melt vessel was made of conventional steel material (by welding the bottom to a part of the water pipe) ·

The material resulting from cooling of the melt in the vessel showed a glassy structure with a shiny appearance with a light gray tinge.

The steel container remained without obvious material.

Example 2

The same mixture as in Example 1, the pH of which was adjusted to 10 with ammonia, was pyrolytically and thermally treated at a temperature of up to 1 050 ° C in a melting pot of chromium-nickel alloy AKCP / according to ČSN 17249 / ·

The resulting vitreous material showed a bluish color upon cooling, leaving the melt vessel simulating the storage container without visible disturbance.

Claims (1)

Process for preventing the corrosive effect of acidic liquid wastes containing high, medium or low radioactivity fission cation nitrates, with optional additives of ecloric constituents such as phosphoric acid and / or silicic acid and boric acid, characterized in that the liquid acid waste is first treated with ammonia and / or urea to a pH of 7.5 to 10, whereupon it is converted into kaleinate or glass melt at 250 to 1050 ° C in steel containers by pyrolytic degradation and denitrification.