A low-waste technology for treating discharged water from Mayak pond No. 9

Abstract

66.064At present, there are several open stores for liquid radioactive wastes in the region of the Mayak organization. The stores for low-activity wastes are certain ponds in the valley of the R. Tech. However, the main hazard is represented by liquid wastes stored in Lake Karachai (pool No. 9), to which medium-activity solutions have been discharged since 1951. The water leaking from pool No. 9 causes a danger of radioactive pollution in water-supply sources and represents a hazard on passage to the open river network [1]. This hazard can be avoided by halting the motion of the polluted water towards the pools or trapping it and purifying it from radionuclides and dissolved salts until it meets discharge standards.These infiltrating waters from pool No. 9 constitute a multicomponent system having total salt contents up to 80 g/liter, 90% of which is accounted for by sodium nitrate. The radioisotopes are mainly 9~ 137Cs, and 6~ The total radioactivity is up to 1.5-105 Bq/liter. There are difficulties in using standard treatment methods [2, 3] for liquid radioactive wastes in these waters because they do not provide the necessary degree of purification, consume large amounts of reagents and energy, and are complicated to implement. It has been shown [4] that electromembrane methods in combination with others are effective for treating radioactive wastes produced at the nuclear fleet installations.We consider that electromembrane technology is best for treating these waters, which includes electrochemical precipitation of the hardness salts and polyvalent metals, electroosmotic concentration, and electrodialysis desalination. Experience exists in treating radioactive wastes by electromembrane methods, which suggests that one should include an electromembrane apparatus of EKhO type intended for the electrochemical precipitation of hydroxides and carbonates, which enables one to eliminate hardness salts and heavy-metal ions from the wastes by means of electrochemical processes. Figure 1 shows the block diagram of a laboratory apparatus handling 2 liter/la for treating liquid wastes whose composition is given in Table 1.The cathode chamber of the EKhO apparatus accumulates hydroxyl ions by the electrolysis of water: H20 + 2e ---H 2 + OH, and the bicarbonate ions become carbonate ones HCO 3 + OH --, CO 3-2 + H20, and sparingly soluble calcium carbonates (SPcacO 3 4.3" 10 -9) and magnesium hydroxide (SPMg(OH) 2 5.5-10 -12) are precipitated along with the carbonate and hydroxides of other heavy metals.