Analysis and Selective Treatment of Radioactive Waste Waters and Sludges

In the Hungarian PWR-type nuclear power plant Paks (four 500 MWe capacity VVER440/213 blocks) the radioactive waste waters are collected in common tanks. These water streams contain radioactive isotopes in ultra-low concentration and inactive compounds as major components (borate 1.7 g/dm3, sodium-nitrate 0.4 g/dm3, sodium-hydroxide 0.16 g/dm3, and oxalate 0.25 g/dm3). Up to the present the low salinity solutions were evaporated (by adding sodium-hydroxide) till 400 g/dm3 salt content (pH~13) and after solidification by cementing buried. There is about 6000 m3 concentrated evaporator bottom residue in the tanks of the PWR. In order to separate the inactive salt content before cementing a Liquid Wastewater Treatment Technology (LWT see Figure 1.) was developed to treat this wastewater before solidification and burial (Patzay et al., 2006). The long-life radionuclides are present in very low concentration (10-9-10-12 mol/dm3) as ions, suspended, colloid particles and in complex (EDTA, oxalate, citrate) form. In this technology the SELION CsTreat cesium selective ion exchanger is used for the selectice separation of radiocesium isotopes (134Cs, 137Cs). The SELION CsTreat cyanoferrate based cesium-selective ion exchanger is not stable at pH>11 (see reaction equation below), so the use of CsTreat needs partial neutralisation of the evaporator bottom residue to pH~9-11, and during neutralisation sodium-borate crystals precipitate with about 15-30% of the radioactivity. [ ] 4 2 6 6 2 ( ) 2 2 [ ( ) ] ( ) K Co Fe CN OH K Fe CN Co OH − + − + ⇒ + + (1)