B U N S E K IBoron isotope ratios were analyzed in seven domestic analytical labs for boric acid solutions with various compositions of boron isotope abundances, using an Inductively Coupled PlasmaQuadrupole Mass Spectrometer (ICP-QMS). Five sample solutions with different isotope abundances of 10 B were prepared in the range of 10 to 20% by mixing two boric acid solutions containing natural B and enriched 11 B, respectively. Then, the 10 B isotope abundances of each sample were certified by analyzing with thermal ionization mass spectrometry (TI-MS) according to ASTM-C791-04. Results obtained from each lab have indicated good coincidences with TI-MS results. Also, the relative standard deviations of results with ICP-QMS of seven analytical labs were 0.11 to 0.81%. The measurement precision for ICP-QMS would be sufficient in terms of practical use, while taking into consideration a valid requirement required for verifying a depletion of the 10 B isotope abundance in the PWR coolant, while this is greater than a nominal analytical error (relative value : 0.22%) for TI-MS shown in ASTM-C791-04.
The formation mechanism and chemical form of insoluble C-14 found in PWR need to be examined in order to predict its environmental behavior after disposal. This study investigates the alteration of ion-exchange resin by heating and irradiation, because past studies indicated the ion-exchange resin may be the origin of insoluble C-14.Resin was heated at 300 °C in solution with low oxygen content to simulate the environment of PWR coolant. The sulfo group was found to detach within 8 h, and structures similar to polystyrene were remained. This is followed by detachment of H from the alkyl group, condensation reaction, and the formation of amorphous carbon-like structure. After heating for 24 and 96 h, the resin was irradiated by 60Co γ-rays in the solution. The FT-IR and TG measurements after irradiation suggested that OH and COOH groups were formed on the surface of the resin. These functional groups may be involved in reactions that finally form the amorphous carbon.In addition, the characteristics of heated and irradiated resin were compared to real insoluble-C (CRUD) sample in PWR (in Appendix).
In the safety assessment of a radioactive waste disposal, it is extremely important to assess the migration behavior of long-half-life radionuclides in the disposal environment. The migration behavior in the disposal environment for a radionuclide varies with the chemical form of the nuclide. In particular, C-14 has various chemical forms, and its migration behavior in the disposal environment substantially varies with the chemical forms. It has been reported that hardly soluble C-14 is generated in PWRs. However, the chemical form of this hardly soluble C-14 is little known. In this study, the thermal decomposition behavior of particles containing C-14 and the mass spectra of gases released through thermal decomposition were analyzed in order to examine the chemical form of C-14 generated in PWRs. In this study, the gases released during the thermogravimetric (TG) analysis were partially oxidized to CO2, trapped in an alkaline solution and analysed for C-14. Another part of the gas was analysed directly by mass spectrometry (MS). The residues obtained after TG analysis were also analysed for C-14 by oxidizing the residue to CO2, trapping the CO2in alkaline solutions and analysing C-14 by LSC. During TG-analysis in inert gas (He) atmosphere, about 90% of C-14 was found in residue, while when air was used during TG-analysis, no C-14 could be detected in residue. From the MS-analysis of species released during TG-analysis in inert gas, fragments regarded as originating from ion-exchange resins were detected in released gases. Based on this result, it was found that while substances originating from ion-exchange resin were present in radioactive particles generated in a PWR, the main part of C-14 was contained in the residue after heating in the form of thermally stable substances, easy to be oxidized by air at high temperature. It was not possible to determine their exact chemical composition in this work but also, In addition, sorption of insoluble C-14 to cementitious materials was preliminarily examined. As a results, the concentration of insoluble C-14 decreased greatly in 7 days. That means insoluble C-14 tended not to stay in water. Elucidation of the sorption mechanism in the disposal environment of these C-14 is also a future task.
Accurate estimation of radioactive inventory is essential for nuclear power plant, since it effects on nuclide screening for clearance, disposal cost, collective dose and public exposure estimation. This paper describes contamination estimation method. Authors have developed contamination estimation method for PWR primary circuit and other systems. The method is based on the assumption that only particulates in the coolant are responsible for contamination and S. K. Beal's theory of particle deposition and erosion model. There are various contamination calculation conditions and some of them, such as failed fuel fraction, are difficult to determine with plant design data and thus measured data of radioactive waste generated from the existing plant is used for estimating fission products contamination. Contamination estimation results are in good agreement with the measured data. For the application of this method to the contamination density estimation for the PWR operational waste and for decommissioning, the improvement of estimation accuracy will be required by conducting further data accumulation regarding the plant operating data and accurate plant design parameters.
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