Separation methods for radiometric and mass-spectrometric (ICP-MS) determination of technetium

Declaration of specific activities of important radionuclides arisen by liquidation low-level nuclear waste represents an actual problem by decommissioning of NPP Jaslovske Bohunice. 99Tc is an anthropological, long term half life radionuclide and belongs to the significant beta emitter with the influence on the radionuclides composition of the radwastes produced in NPP A-1 Jaslovske Bohunice. 99Tc was determined in samples of soils, solid and liquid radioactive wastes from NPP Jaslovske Bohunice. 1. Several sorbents for Tc-99 separation were prepared. The prepared extraction materials were based on: Aliquat-336/ Polymer 7K1195, Aliquat-336/Teflon, Aliquat-336/hydrophobized silica gel with different concentrations of anchored quaternary amine (Aliquat-336), TOA/silica gel and TOA/Teflon. Prepared sorbents anchored on Teflon and polymer were not suitable as chromatographic bed material because of their non porously surface. Prepared sorbents based on TOA/Teflon Alq./ Teflon were viscously in the concentration range of amines (30%-60%), in concentration in the range (10%-20%) were amines sorbed with low yields - bounded Aliquat-336 on the prepared sorbent were about 4%-18%. It was found out: - By Tc desorption using prepared sorbents based on Aliquat-336/Polymer 7K1195 and Aliquat-336/Teflon were not reached satisfying recoveries - Organic phase - TOA was eluted with 99mTcO4- by Tc desorption using sorbents TOA/silica gel and TOA/Teflon. 2. The best for effective separation of Tc-99 was found out the chromatographic material based on Aliquat-336 and hydrophobized silica gel. The highest retention of pertechnate was obtained in 0.1 mol.dm-3 HNO3 media - chemical recovery of the sorption was nearly 100%. The elution of 99mTcO4- was also tested with nitric acid concentration in the range 0.1-8 mol.dm-3. The highest yields were using 20 ml of 8 mol.dm-3 HNO3 - R=96.4%. The highest KD value of 99mTcO4- 2778 ml.g-1 were obtained in 0.1 mol. dm-3 HNO3 medium. 3. Prepared sorbent based on 40% Aliquat-336/hydrophobized silica gel substituted with its properties the commercially reachable chromatographic material TEVA Spec. 4. The prepared sorbent based on Aliquat-336/silica gel was used as a filling to the chromatographic column by Tc separation from the samples of soils and radioactive wastes. Three methods have been used for the determination of 99Tc in soils and solid radioactive wastes using 99mTc as a yield monitor. The chemical recovery of 99mTc was optimised in the process of extraction chromatography and leaching. 5. The best method for Tc separation for samples of soils and solid radioactive wastes was proposed. The separation process contained sample treatment with ammonia adding - neutralisation of free acids soils and pertechnate acid inhibition, which had negative influence on chemical recovery, ashing, leaching, co-precipitation with Fe(OH)3 and column extraction chromatography. Chemical recoveries for 99mTcO4- for this method (method 3) varied between 57.1%-73.6 %, for method 2 - separation with H2SO4 were about 44.8%-60.4 % and finally the chemical recoveries for method 1 - separation with HNO3 were in the range 56.7%-68.3 %. 6. Samples of liquid radioactive wastes presented miscellaneous matrices of radionuclides with many times higher specific activity then 99Tc had. Samples of liquid radioactive wastes contained 137Cs, 60Co, transuranium elements, lanthanides and actinides. It was necessary to remove interfering radionuclides, including the main contaminant 137Cs before detection of 99Tc. By purification and removal of 137Cs in liquid radioactive wastes were found out: - A carrier method was done for the desorption of cesium from the column. The highest chemical recovery of 137Cs - R=92% and the highest decontamination factor - 1336 were reached after elution of 40 ml of carrier solution with concentration 10-4 mol. dm-3 CsCl. Low chemical yields for cesium desorption could caused colloid particles, which occurred in the frit, they obsturated the column and reduced the NIFSIL efficiency and the chemical recovery. For purification and quantitative removal of 137Cs using of extraction chromatographic column and liquid extraction system with 2.5x10-3 mol. dm-3 tetrephenylarsomium chloride in chloroform was necessary by Tc separation. 137Cs can be partially removed using column separation step, for full re-motion of cesium, it is necessary to integrate liquid extraction system with 2.5x10-3 mol. dm-3 solution tetraphenylarsonium chloride in the separation process to purificate the sample. 99Tc was re-extracted with 0.5 mol. dm-3 NaClO4 to the water phase. 7. Tc-99 separated from soils, solid and liquid radioactive waste, was measured using LSC, low-background proportional detector and ICP-MS. The lowest concentration of 99Tc was determined on mass spectrometer due high sensitivity of the equipment and effective elimination of interfering isobaric nuclides. The differences between measurement on mass spectrometer and radiometric detection of Tc-99 were markedly shown by detection of 99Tc. Cs-137 occurred in samples of radioactive wastes increased the results of Tc-99 detection by radiometric detection. The results of Tc measured on proportional and scintillation counter were higher then the results obtained from ICP-MS detection. 99Tc concentration measured on liquid scintillation counter were nearly two time less in some samples then the results obtained form the proportional measurements. ICP-MS technique was the best method choice for Tc-99 determination, namely for radioactive wastes. The results achieved by methods mentioned about could be applied on samples of radioactive waste by decommissioning NPP A-1 Jaslovske Bohunice and presented possible alternative for Tc-99 separation from these samples. (author)