The leach test of radionuclide in cement-solidified waste form was performed. After leach test, compressive strength of waste form was measured. Cement-solidified waste form produced at Korean nuclear power plant, Kori (PWR) was chosen for the leach test. Specimens were cored out from a full-scale waste form (2001 drum size). The leach test procedure used for this study was ANSI/ANS 16.1 procedure. The leach ability indexes for cesium and cobalt isotopes were determined. Semi-infinite model was used for analysis of the controlling mechanism in the release of isotopes. Release mechanism of cesium was dominated by diffusion but release of cobalt behaved somewhat differently from the diffusion controlled release. Averaged leachability indexes were 8.6 for cesium and 11.4 for cobalt. Compressive strength after leach/ immersion test was 7.34 MPa for the sample immersed in simulated seawater and 8.34MPa for the sample immersed in deionized water.
The bentonite-based material being evaluated in several countries as potential barriers and seals for a nuclear waste disposal system is of mostly sodium type, whereas most bentonite available in Korea is known to be of calcium type. In order to investigate whether local Korean bentonite could be useful as a buffer or sealing material in an HLW repository system, raw bentonites sampled from the south-east area of Korea were examined in terms of their physicochemical properties such as surface area, CEC, swelling rate, and distribution coefficient. The diffusion behavior of some radionuclides of interest in compacted bentonite was also investigated. Considering that HLW generates decay heat over a long time, the thermal effect on the physicochemical properties of bentonite was also included. Four local samples were identified as Ca-bentonite through XRD and chemical analysis. Of the measured values of surface area, CEC and swelling rate of the local samples, Sample-A was found to have the greatest properties as the most likely candidate barrier material. The distribution coefficients of Cs-137, Sr-85, Co-60 and Am-241 for Sample-A sample were measured by the batch method. Sorption equilibrium was reached in around 8 to 10 days, but that of Sr was found to be reached earlier. Comparing the results of this study with the reference data, domestic bentonite was found to have a relatively high sorption ability. For the effect of varying concentration on sorption, the values of Kd peaked at 10(-9)-10(-7) mol/l of radionuclide concentration. In XRD analysis, the (001) peak of Sample-A was fully collapsed above 200 degrees C. The shoulder appearing at about 150 degrees C in the DSC curve was found to be evidence that Sample-A is predominated by Ca-montmorillonite. The loss of swelling capacity and CEC of Sample-A started at about 100 degrees C. The swelling data and the (001) peak intensity of the heat-treated sample showed that they were linearly interrelated. The measured Kd values of Co-60, Cs-137 and Am-241 for the samples heat-treated at various temperature showed that the domestic bentonite still retained sorption capacity below 100 degrees C. In addition to such findings of thermal effects, it was found that the presence of calcium in bentonite may help to assure long-term stability under the expected thermo-hydro conditions. The Da values of Sr-85, Cs-137, Co-60, Am-241 and Cl-36 were measured to be 1.073 x 10(1), 6.705 x 10(-1), 1.226 x 10(-1), 1.310 x 10(-2) and 9.490 x 10(1) microns 2/sec, respectively, which could be arranged with the magnitude of their distribution coefficients, i.e. Cl > Sr > Cs > Co > Am. As the as-pressed density of bentonite increasing from 1.8 to 2.0 g/cm3, the Da-value of Cs-137 decreased by 25%. From the analyses of the diffusion mechanism of radionuclides in compacted bentonite, the surface diffusion due to the concentration gradients of radionuclide sorbed on the bentonite particles was found to be a dominating transport process of radionuclides in compacted bentonite with 1.8 g/cm3....
To assess a proper dose for radiation therapy fitting the typical physical characteristics of male Korean bodies, a mathematical phantom was prepared based on standard Korean male measurements. Upon brachytherapy of prostate cancer by implanting 192Ir into the prostate gland (the source organ), the absorbed dose of the prostate gland and surrounding organs and the expected dose of people within the vicinity were assessed. 192Ir, which has been the radionuclide of choice for prostate cancer brachytherapy, was selected for the simulation. It was assumed that 1 Ci of initial radioactivity would be administered. As a result, 1.28E-02 Gy/Ci was exhibited in the prostate gland of the source organ, and the dose to which persons within the vicinity were exposed was exhibited to be 9.19E-06 Sv at a distance of 30 cm from the front.
The authors have developed a mathematical model for calculating internal radionuclide dosimetry for the Korean Reference Adult Male, and have also derived paired-organ and other selected inter-organ photon-specific absorbed fractions for this model. Each lung, kidney and adrenal gland was set as a separate source region even though each of them shares an identical physiological function with their complementary half. The thyroid gland was also set as a source region. Specific absorbed fractions (SAFs) were then derived by selecting 10 photon energies from 0.02 to 4.0 MeV inclusive. For this purpose the Monte Carlo methodology was used, and the derived SAF was compared with the resulting value of MIRD Pamphlet No. 5 and ORNL TM-8381, both of which were derived on the basis of the ICRP-23 reference man. The comparison showed that MIRD No. 5 and ORNL TM-8381 resulted in a higher absorbed fraction, but the phantom created on the basis of the Korean reference man led to a higher SAF. The weight of the organs of the phantom, and the size and location of the trunk seem to account for the differences. The energy-dependent differences in the SAFs are considered to be related to the distance between the source and target regions, the composition of the intervening tissues, and the photon energies and mean free paths. Also, as a result of deriving SAFs after setting each separate lung, kidney and adrenal gland as a source region, it was found that, although they are of the same physiological function, each individual organ serves as a source region on its own. Differences were noted in SAFs exerted on the source and target organs in accordance with the location of the organs, that is, whether they were located to the left or right of the source organs. The SAF derived in this study can be used for a more accurate internal radionuclide dosimetry for Koreans and other Orientals whose physiology, lifestyle and dietary habits are similar to those of Koreans.
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