Radiation Stability of Dibenzo-21-Crown-7 Used for Solvent Extraction of Cesium-137
- PDF / 393,836 Bytes
- 8 Pages / 386.64 x 620.1 pts Page_size
- 56 Downloads / 169 Views
ABSTRACT Crown ether Dibenzo-21-crown-7 (DB-7) has demonstrated a high capability for removing cesium-137 both from acidic and alkaline solution. However, there is a very important problem concerning changes in physical and chemical properties of such mixtures as a result of high irradiation. High radiation doses may cause a decrease in extraction efficiency and selectivity, formation of hazardous radiolysis products, disturbance hydrodynamics, and even decay of extractant. It is necessary to estimate such changes before extraction testing on "hot" solutions. A special procedure, earlier developed in the RRICT (Russian Ministry for Atomic Energy), was used for testing of radiation and chemical stability of extraction mixtures. This method is based upon continuous control of extraction parameters - distribution coefficients of the specified radionuclides, their hold-up in organic phase, of hydrodynamic properties - kinetics of separation of mixed phases, surface tension, etc., and formation of radiolysis products. The dose rate, determined using a ferrosulfate dosimeter was 1.7 W*h/l (1.05*10 1( eV/ml*s) taking into account the electronic density of organic solution. Maximum total dose of gamma-irradiation was 80 W*h/l (1.6* 1021 eV/ml). The specimens of irradiated organic solution - DB-7 in the mixture of fluorinated alcohol (FA) and higher alcohol - after phase separation were analyzed to determine the hydrodynamic parameters. Both organic and aqueous phases were analyzed to estimate the decay of extractant and the composition of radiolysis products. The primary emphasis for the first radiolytic experiments was given to the estimation of the FA decay by means of measuring the fluoride-ion concentration in the aqueous phase. It was shown that this value increases through the dose of 60 W*h/l and then decreases again. Such behavior may be attributed to an interaction of the fluoride ion with nitric acid and formation of volatile or organic phase extractable compounds. Our tests performed on real HLW acid solutions in P/A "Mayak" also demonstrated that solutions of DB-7 in fluorinated alcohols have a high resistance to radiolysis. INTRODUCTION Cesium-137, and also strontium-90, are major generators of heat in nuclear waste. These two long-lived isotopes are great concern to US DOE and nuclear industry in environmental and waste management. The medium-level wastes (MLW) originating from the reprocessing of irradiated fuel elements as solutions, can be vitrified or solidified by means of cement and thus be transferred into a state ready for the final disposal. The original waste volume is raised by about 100 times by the cementation process and particularly by the concrete shields additionally needed for safe further handling, transport and final disposal. Decontamination of liquid waste from Cs-137 (T1 /2 = 30 years) producing high gamma radiation, before 1291
Mat. Res. Soc. Symp. Proc. Vol. 556 © 1999 Materials Research Society
vitrification (cementation) has to diminish a volume and weight of final disposal to ab
Data Loading...
