DE2836081A1 - METHOD FOR PROCESSING HYDRAZINE-CONTAINED WASTEWATER FROM NUCLEAR POWER PLANTS - Google Patents

Description

BENCKISEB

wassertechmk

Dr. B / MF / P-KS 516 August 8, 1978

Process for processing hydrazine-containing wastewater from nuclear power plants

The invention relates to a method for processing hydrazine-containing waste water from nuclear power plants.

In nuclear power plants, large cooling circuits are operated with fully demineralized water.To avoid corrosion, you add hydrazine to the water. The hydrazine content of Water can generally be up to 200 mg / l.

As a result of the wide branching of these cooling water systems certain leakages occur, which, depending on the construction of the individual units, can amount to up to 2 cbm per day. This water is fed to other radioactive wastewater and processed together with it. The waters must due to the radioactivity are "disposed of" through a special processing. The waters are initially in a The evaporator is concentrated, then the distillate is passed through an ion exchanger, the residue in the evaporator and the mixed bed must be treated as hazardous waste and transported away.

When water containing hydrazine is worked up, the hydrazine or the hydrazine formed by the decomposition of the hydrazine is present Ammonia in the distillate, which means that the mixed bed downstream of the evaporation system is relatively fast exhausted. Since the mixed bed must not be regenerated for safety reasons, this means an increased amount of hazardous waste.

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BENCKISEB

water technology

Attempts have therefore already been made to remove the hydrazine from the water before it evaporates. This succeeds perfectly using chlorine or sodium hypochlorite. However, this results in considerable amounts of sodium chloride, which remain in the evaporator as an additional residue, so that this is drained and emptied in a quarter of the usual time and the waste is transported away as hazardous waste must become. This causes considerable additional costs.

The use of hydrogen peroxide as an oxidizing agent also gave unsatisfactory results. Hydrogen peroxide reacts with hydrazine only in the presence of a catalyst, e.g. a complex halogen compound, which also remains in the evaporator as a salt residue, which means that the evaporator must be emptied earlier.

It has now been found that these disadvantages do not occur if an ozone-containing water is passed through the water in front of the evaporator Sucks in the gas mixture, then distilled in the usual way and the distillate passes through an ion exchanger.

Ozone-air and ozone-oxygen mixtures in all concentrations are suitable as ozone gas mixtures. Ozone concentrations of at least 10 g of ozone per m ^{3 of} accompanying gas have proven particularly favorable.

It has been shown that the reaction rate towards the end of the reaction with decreasing hydrazine concentration and increasing ozone concentration becomes slower. By adding small amounts of an oxygen intermediate carrier as a catalyst this can be avoided and an accelerated and quantitative conversion can be achieved by the end of the reaction.

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BENCXISEB

water engineering

a- 4

Suitable catalysts are potassium iodide or manganese salts such as MnCl ₂ or MnSO ₄ , which are added in amounts of ^{0.5-50 g / m 3} , preferably 1-2 g / m ³ .

The end point of the reaction can be determined by determining the ozone content in the supernatant gas phase, in that the excess amount of ozone dissolved in the water has a corresponding amount of ozone in the supernatant Gas space is proportional. The determination can be carried out with an ozone analyzer, e.g. via UV absorption at 254 nM. In this way, the end point of the reaction can be identified safely and safely without having to deal with the circumstances coming into contact with radioactive wastewater by analytical methods.

The destruction of hydrazine by means of ozone is just in nuclear power plants a particularly suitable process, because of the unproblematic reaction products nitrogen and water does not lead to an accumulation of radioactive waste.

Another advantage is to be seen in the use in nuclear power plants in the fact that ozone with the use of electrical Energy, of which there is enough in nuclear power plants, is produced from air, so that no additional chemicals, Chemical transport, safety devices, etc. are required.

Besides hydrazine, the waters in nuclear power plants also contain still other impurities, for example traces of detergents, etc. It has surprisingly been found that in In these differently polluted waters the hydrazine is oxidized quickly and almost quantitatively.

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ENCKISER

The goal of all nuclear power plants, radioactive waste Keeping as small as possible is thus achieved according to the invention from the wastewater side.

The invention is illustrated by the following examples, without being restricted to these examples.

example 1

^{An ozone-air mixture containing 12 g of ozone per m 3 of} air is passed through radioactive waste water containing 50 mg / 1 chloride and 50 mg / 1 hydrazine until an ozone content in the supernatant air of 0.4 g ozone / m ^{3 is} reached.

The water treated in this way is fed to the evaporator and up to a chloride content of 10,000 mg / 1, i.e. around Thickened 200 times (10,000 mg / 1 chloride, highest permissible amount for reasons of corrosion). There could be no in the distillate Ammonia can be detected.

The distillate is passed through a mixed-bed filter with a resin quantity of 1,900 liters of catalyst, corresponding to an exchange capacity of 1,900 VaI. After a passage of 90 m ^{3 of} water per day, no exhaustion of the mixed bed could be determined after 200 days.

Example 2

As in Example 1, only 2 g / m ^{3 of} potassium iodide were added to the wastewater before the ozone treatment.

In contrast to Example 1, an ozone content of 0.4 g ozone / m ³ in the supernatant gas phase was achieved almost suddenly. No ammonia could be found in the distillate and the mixed bed was not yet exhausted after 200 days.

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ENCKISEB

water technology

KS 516
Comparative example A.

A radioactive waste water containing 50 mg / 1 chloride and 50 mg / 1 hydrazine was given to the evaporator without oxidative treatment supplied, up to a chloride content of 10,000 mg / 1, i.e. thickened to 200 times and as radioactive sludge discharged.

Thermal decomposition of the 50 mg / l hydrazine gives 38 mg / l ammonia, corresponding to 2.1 meq / l, which distill over. The distillate was passed through a mixed bed filter with a resin quantity of 1,900 liters of cation exchanger. After a throughput of 900 m ³ , the exchanger was exhausted, which means that with a daily production of 90 m ^{3 of} evaporation, the mixed-bed filter must be deposited as radioactive hazardous waste after 10 days.

Comparative example B

A radioactive waste water containing 50 mg / 1 chloride and 50 mg / 1 hydrazine was mixed with approx. 1.5 ml / 1 sodium hypochlorite (150 g / l active chlorine) added. From the 50 mg / 1 hydrazine there are 180 mg / 1 NaCl, that is 114 mg / 1 chloride, the are also present in the wastewater. The water treated in this way is fed to the evaporator and concentrated. The permissible chloride content of 10,000 mg / 1 has already been reached with an approximately 80-fold thickening, i.e. the radioactive attack in the evaporator more than doubles compared to untreated water (Comparative example A). No ammonia can be detected in the distillate.

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Claims (5)

BENCKISER water technology Claims Process for processing hydrazine-containing wastewater in nuclear power plants, characterized in that that one sucks in an ozone-containing gas mixture through the water in front of the evaporator, then on The usual way is distilled and the distillate is over ion exchangers. 2. The method according to claim 1, characterized in that an ozone-air mixture or ozone-oxygen mixture is used which contains at least 10 g ozone / m ^{3 of} accompanying gas. 3. The method according to claim 1 and 2, characterized in that the waste water, a catalyst in amounts of 0.5 50 g / m ³ , preferably 1-2 g / m ^{3 is} added. 4. The method according to claim 1-3, characterized in that the catalyst is potassium iodide or manganese salts, such as MnCl ₀ or MnSO _A. 5. The method according to claim 1-4, characterized in that the end of the reaction by determining the ozone in the supernatant gas phase is determined. _A3 _! 030008/0503