Radionuclide decontamination iodine

The experiments have proved that membrane distillation can be applied for radioactive wastewater treatment. In one-stage installation the membrane retained all radionuclides and decontamination factors were higher than those obtained by other membrane methods. The distillate obtained in the process was pure water, which could be recycled or safely discharged into the environment. It seems the process can overcome various problems of evaporation such as corrosion, scaling, or foaming. There is no entrainment of droplets, which cause the contamination of condensate from thin-film evaporator. Operation at low evaporation temperature can decrease the volatility of some volatile nuclides present in the waste, such as tritium or some forms of iodine and ruthenium. The process is especially economic for the plants, which can utilize waste heat, e.g., plants operating in power and nuclear industry. 

With regard to long-lived radionuclides that show a low decontamination factor on the purification system (e. g. Cs in PWR primary coolant containing LiOH), the purification constant e also has to include the coolant losses via water exchange or leakages. On the other hand, fission products which form insoluble compounds or can be adsorbed onto non-dissolved corrosion product particulate matter may be removed from the coolant by plate-out onto the primary circuit surfaces. These and other parameters which are liable to affect the activity concentrations of the radionuclides in the primary coolant are the reason why a trustworthy calculation of source strengths can only be made using specific radionuclides such as fission product noble gas isotopes and iodine isotopes. 

The decontamination factors mentioned above may be affected over time by mechanisms which lead to a revolatilization of fission products from the pool water. When the bubbles break up at the pool surface, they produce new aerosol droplets by which non-volatile fission products can be carried to the containment atmosphere. Calculations using the Sparc code (Owczarski and Burk, 1991), however, showed that radionuclide entrainment caused by this mechanism is very small and, thus, can be ignored in source term analyses. Iodine, on the other hand, can be revolatilized if the pH of the aqueous phase is decreased as a consequence of water radiolysis. In the presence of alkalizing substances such as CsOH, such a decrease in pH leading to a lower I2 partition coefficient is not to be expected. The existing codes (such as Sparc, Supra, Busca) do not take chemical reactions into consideration and, thus, do not provide any information on chemical iodine revolatilization from the pool. 

Guntay, S. Experiment Poseidon Pool scrubbing effect on iodine decontamination. Paper presented at the ENC 90, ENS/ANS - Foratom Conf. Lyon, Sept. 1990 Hahn, R., Ache, H. J. Thermodynamic calculations on the behavior of gaseous iodine species following a hypothetical severe LWR accident. Nucl. Technology 67,407-410 (1984) Harman, N. F., Clough, P. N. A review of radionuclide release and transport in recent inpile experiments. Report EUR 14230 EN (1992)... 

The isotope separator has been applied to iodine isotopic analysis (Rook et al., 1975). In this method, neutron activation is used to produce radioactive iodine activities. The isotope separator serves to mass-separate the radioiodine and also to decontaminate the irradiated sample from other interfering radionuclides such as %r. 

As a commercial company that provides analytical services for the determination of radionuclides for a wide variety of clients, AMEC required a more accurate and reliable method to be developed. It needed to use relatively low hazard chemicals, have improved accuracy and precision and utilise common radiochemical analytical laboratory equipment such as liquid scintillation counters and gravity fed chromatography columns. In addition, the process must have realistic and commercially viable batch sizes, operator time and turnaround times, so that samples can be analysed in a cost-effective manner. Ideally the whole process for a batch of samples should not exceed more than one working week. As part of the validation process both internal and external quality control (QC) samples were used along with statistical tests, such as zeta (Q scores and student t-tests , to determine the accuracy of the improved method. In addition, elution profiles for iodine and chlorine and decontamination tests for potentially interfering radionuclides were also carried out in order to further validate the process. 

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