Chang-Jong Kim

Analytical evaluation of natural radionuclides and their radioactive equilibrium in raw materials and by-products

An investigation into the distribution of natural radionuclides and radioactive secular equilibrium in raw materials and by-products in a domestic distribution was conducted to deduce the optimum conditions for the analytical evaluation of natural radionuclides for (238)U, (226)Ra, and (232)Th using a gamma-ray spectrometer and inductively coupled plasma mass spectrometer (ICP-MS). The range of the specific activities of natural radionuclides was first evaluated by analyzing (228)Ac and (214)Bi, which are (232)Th and (226)Ra indicators, respectively, in about 100 samples of raw materials and by-products through a gamma-ray spectrometer. From further experiments using several samples selected based on the results of the distribution of natural radionuclides, the validation of their analytical evaluations for the indirect measurements using a gamma-ray spectrometer and direct measurements using ICP-MS was assured by comparing their results. Chemically processed products from the raw materials, such as Zr sand and ceramic balls, were generally shown for the type of bead and particularly analyzed showing a definite disequilibrium with above a 50% difference between (238)U and (226)Ra in the uranium series and (232)Th and (228)Ra in the thorium series.

Combustion/absorption process for the separation of 14C and 3H in radwastes released from nuclear power plants and their analysis

Radioactivities of 3H and 14C in spent radioactive ion exchange resins and spent radioactive lubricant oils released from nuclear power plants, has been determined using a combustion and sorption method (combustion method). The liquid scintillation counting (LSC) spectra showed that the interference of other radionuclides has not significantly affected the determination of radioactivities of 3H and 14C in the radwaste samples. The chemical structure of 14CO2, which originated from the combustion of radwastes, trapped 14C sorbent has been investigated using Fourier transform infrared spectroscopy (FT-IR). FT-IR study showed interesting results that peaks for uncoupled CO2 and carbonic amide appeared at FT-IR spectra of CO2 high-absorbed 14C sorbents, while the peak for carbamate was only observed at the spectra of CO2 low-absorbed sorbents. During the CO2 sorption in 14C sorbent, temperature and viscosity of the sorbent increased owing to decrease of enthalpy and increase of apparent molecular weight of the sorbent caused by the bonding formation between sorbent molecules.

Validation of the quantification of natural radionuclides in raw materials and by-products using gamma-ray spectrometry

The validation of a method for the indirect quantification for 238U, 226Ra, and 232Th activity and the direct quantification for 40K activity using gamma-ray spectrometry was performed in view of consistency, reliability, and accuracy of the results. The gas tightness of Al containers used to confine the radon gas was verified from the establishment of the secular equilibrium between 226Ra and its indicator. To evaluate validation parameters such as linearity, range, and accuracy, it was important to verify the equilibrium state of the reference materials (RM) for U and Th, because the ingrowth of progenies in the uranium decay series can affect the quantification of 226Ra activity even if based on a certified reference material (CRM), while the ingrowth of 228Ra from the thorium decay series should be secured in order to use 228Ac as an indicator of 232Th. In addition, the ruggedness of the method regarding different materials was checked using two kinds of CRM, namely bauxite as an example of a raw material and coal fly ash as a by-product.

Limitations of gamma-ray spectrometry in the quantification of 238U and 232Th in raw materials and by-products

The effect of interference and disequilibrium was evaluated in analyzing 238U and 232Th using gamma-ray spectrometry. The interference in 234Th as an indicator of 238U was considerably increased according to the activity level of 232Th compared with that of 238U. However, its correction was necessary to assume that the secular equilibrium in the thorium decay series must be secured in the material. In addition, the disequilibrium in the decay series can be easily shown in the chemical process for manufacturing materials. This makes the limitation in the indirect measurement of natural radionuclides using gamma-ray spectrometry, especially in chemically processed products.

Simultaneous Determination of the Depth of an Embedded Source and its Radioactivity in the Medium.

AbstractThe simultaneous determination of the depth of an embedded source and its radioactivity in the medium at the environmental surveys is a very useful and advisable method for an in-situ gamma-ray measurement with respect to the time and cost constraint. An algorithm for the determination of the source depth and its radioactivity in the medium was developed using the information on the uncollided photon fluences and measured net count rates, which mean not scattered fluences and background subtracted count rate, at the detector positions. Uncollided photon fluences were calculated at several source depths in the medium as well as at detector positions from the Monte Carlo N-Particle (MCNP) simulation. The results were then used to establish a database to output their values according to the source depth in the medium by inputting the photon energy and detector position from the medium. A simple program about the simultaneous determination of two variables was applied to the results on a task to find out the depth and activity of 134Cs and 137Cs at in-situ gamma-ray spectrometry. Less than 10% and 15% differences compared with the real values at the source depth and radioactivity, respectively, were achieved using the developed program.

Survey Study on Radioactivity of Domestic Fishery Product

Samples of fishery products were tested for radioactivity by using the intake frequency data from Korea Health Statistics. The radioactivity of 40 K, 137 Cs, 134 Cs, and 131 I was analyzed using gamma spectrometry with a simplified sample pre-treatment procedure. The radioactivity range for 40 K was 21.9-3050 Bq/kg, whereas the radioactivities of 137 Cs, 134 Cs, and 131I were under minimum detectable activity which were in the range of 0.140-1.97, 0.0900-1.89 and 0.124-1.94 Bq/kg, respectively, for the three species. The results suggest that the Fukushima accident did not have a significant impact on domestic fishery products, which were analyzed during the period from 2013 to 2015. Additionally, there seemed to be no significant impact of additional exposure dose by the analyzed radionuclides.Samples of fishery products were tested for radioactivity by using the intake frequency data from Korea Health Statistics. The radioactivity of K, Cs, Cs, and I was analyzed using gamma spectrometry with a simplified sample pre-treatment procedure. The radioactivity range for K was 21.9-3050 Bq/kg, whereas the radioactivities of Cs, Cs, and I were under minimum detectable activity which were in the range of 0.140-1.97, 0.0900-1.89 and 0.124-1.94 Bq/ kg, respectively, for the three species. The results suggest that the Fukushima accident did not have a significant impact on domestic fishery products, which were analyzed during the period from 2013 to 2015. Additionally, there seemed to be no significant impact of additional exposure dose by the analyzed radionuclides.

Application of a high-temperature tube furnace and liquid scintillation counter for radioactivity determination of 14C and 3H in solid waste samples

This study reports the method for measuring 3H and 14C in sludge samples from the National Physical Laboratory (NPL) proficiency program (Environmental Radioactivity Proficiency Test Exercise 2012). The samples were combusted by a high-temperature furnace and trapped beta-emitting nuclides, especially 3H and 14C, were measured by LSC. The validation of method was checked by using initial calibration verification (ICV) samples and laboratory control sample (LCS). The results were in agreement with assigned radioactivity concentration for 3H and 14C. Thus, reliable and accurate method for 3H and 14C was developed using high-temperature tube furnace and LSC.