The objective of this study was the establishment of clearance method that can ensure radiological safety and reasonably minimize radioactive waste when demolishing contaminated buildings at KRR-1&2. By reviewing Korean and international laws related to decommissioning, the method for clearance of contaminated buildings presented in this study is to first decontaminate the building and then conduct a radiological safety assessment, such as measuring residual radioactivity, to determine whether the radiation dose criteria for clearance are satisfied. The measurement results meet the radiation dose criteria, the contaminated buildings are regarded as clearance and can be converted into the general buildings. The demolition of the cleared buildings is carried out using conventional demolition methods. The waste generated during the demolition is classified as general construction waste and is disposed of according to relevant laws. The proposed method significantly optimized the number of samples analyzed and reduced the time and cost associated with the decommissioning. The established method will be applied to the ongoing decommissioning of contaminated buildings at KRR-1&2, and its application will be verified by regulatory bodies. The study suggests that this method could be used for the decommissioning of contaminated buildings at other Korean nuclear facilities in the future.© 2017 Elsevier Inc. All rights reserved.

The removal of Sr, Cd, and Pb from nuclear and industrial waste is important as these are harmful to living organisms and the environment. Immobilization of these ions in a zeolite framework is a simple and suitable method. However, zeolitic water is easily dehydrated or rehydrated at high temperatures. Therefore, the environmental changes around these adsorbed cations and water molecules in the zeolite framework must be explored for effective immobilization and waste removal. In this study, we investigated the structural changes in fully Sr-, Cd-, and Pb-exchanged natrolites (NAT) from room temperature to 350 °C using in situ synchrotron X-ray powder diffraction and Rietveld analysis. In the thermogravimetric analysis, Sr-NAT showed a gradual weight loss up to 210 °C, whereas Cd- and Pb-NAT showed a two-step weight loss in the ranges 90–280 °C and 100–180 °C, respectively. Sr-, Pb-, and Cd-NAT exhibited approximately zero thermal expansions with the thermal expansion coefficients of -3(1)´10-6, -1.0(7)´10-6, and 1(2)´10-6 K-1, respectively, at the initial stage of increasing the temperature. During the dehydration process, the coefficients of Sr- and Cd-NAT were -2.7(7)´10-4 K-1 up to 300 °C with a 2.9% volume contraction and -5.3´10-4 K-1 up to 150 °C with 2.7% volume contraction, respectively. At high temperatures, structurally, the Sr2+ and Cd2+ cations had six- and seven-coordinated bonding with framework oxygens and extra-framework species, whereas Pb2+ cations had three- and five-coordinated bonding. In contrast, the extra-framework water molecules in Sr-NAT had three to five bonds, Cd-NAT had five, and Pb-NAT had six. The chain rotation angle of the secondary building units (T5O10) increased in all cases, indicating that the channel shape becomes more elliptical during dehydration. Sr- and Pb-NAT were amorphized at 350 °C and 150 °C, whereas Cd-NAT remained intact. We concluded that Sr- and Pb-NAT were not thermally stable owing to the order-disorder transition of Sr2+ and high-disorder distribution of Pb2+, respectively. Our findings provide a fundamental understanding of the structural changes and mechanism of thermal stability in natrolites containing hazardous elements.

The grouping analysis is a method guided by the Korea Radioactive Waste Agency for efficient analysis of radioactive waste for disposal. In this study, experiments to verify the adequacy of grouping analysis were conducted with radioactive soil, concrete, and dry active waste in similar environments. First, analysis results of the major radionuclide concentrations in individual waste samples were reviewed to evaluate whether wastes from similar environments correspond to a single waste stream. As a result, the soil and concrete waste were identified as a single waste stream because the distribution range of radionuclide concentrations was "within a factor of 10", the range that meet the criterion of the U.S. Nuclear Regulatory Commission for a single waste stream. On the other hand, the dry active waste was judged to correspond to distinct waste streams. Second, after analyzing the composite samples prepared by grouping the individual samples, the population means of the values of "composite sample analysis results/individual sample analysis results" were estimated at a 95% confidence level. The results showed that all evaluation values for soil and concrete waste were within the set reference values (0.1–10) when five-package and ten-package grouping analyses were conducted, verifying the adequacy of the grouping analysis.

Due to industrialization and population growth, water shortage has emerged as a critical global issue. Pollution of existing water supplies is a critical part of this issue, and organic contaminants are one of the main causes of water pollution. The non-thermal plasma-based advanced oxidation process (AOP) is one of the most widely studied and best developed processes owing to its simple structure and ease of operation. In this study, a plasma-based AOP was stably generated using submerged multi-hole dielectric barrier discharge (DBD) and added to an aqueous solution. Using a plasma system, the complexity of the process for generating hydroxyl radicals ((OH)-O-center dot) can be simplified by allowing ozone, hydrogen peroxide, ultraviolet light (UV), and (OH)-O-center dot to be generated simultaneously in one device. The electrical properties and concentrations of the active species were analyzed to establish optimal plasma operating conditions. Among the organic pollutants, methylene blue (MB) and methyl orange (MO) were selected as experimental targets because they are representative cationic thiazine and azo dyes, respectively. The results were analyzed by measuring the absorbance of UV-Vis, total organic carbon (TOC), chromaticity, and changes in solution properties. The effects of hydroxyl radical ((OH)-O-center dot) scavengers (D-mannitol) on the MB and MO degradation rates were also investigated. Based on these results, degradation mechanisms of MB and MO are proposed. After 3 min of plasma treatment, the concentration, chromaticity, and TOC of MB and MO rapidly decreased. Consequently, we believe that plasma-based AOP using submerged multihole DBD has advantages as an alternative technology for treating organic pollutants.

Nuclear Chemistry Research Division at the Korea Atomic Energy Research Institute (KAERI) has used the grouping method for efficient radioactive waste analysis during the sampling. However, it is currently not easy to apply the grouping method due to the difficulty of decision on optimum amount of drum for grouping and proving its validity. In this study, we applied the waste concentration averaging method proposed by US NRC [1] to

We report the pressure-induced insertion (PII) of gases in a zeolitic imidazolate framework (ZIF) at high pressure. ZIF-8 crystals were compressed in the presence of nonpolar CO2 and SF6 as well as polar CHClF2 (aka R22) up to 4.07, 0.81, and 2.06 GPa, respectively, in a diamond anvil cell, and their X-ray powder diffraction data were analyzed by Rietveld methods. ZIF-8 showed pressure-induced amorphization in SF6 but maintained its crystallinity in the presence of other gases. In general, the unit cell volume of ZIF-8 expanded via PH of CO2 or R22 up to ca. 0.5 GPa and contracted linearly after completion of the PH processes. The total volumes of the inserted guest molecules, which were estimated from the residual electron densities, indicated that the inserted guest molecules fully occupy the pores of ZIF-8. The relationship between the total occupied volumes by guests and applied pressures was best represented with an asymptotic logarithmic curve regardless of the type of molecules. These results reveal the universal gasuptake behavior of ZIF-8 at high pressure, which requires only the penetration of molecules into the pores of the framework of ZIF-8.

An effective combination of host and guest molecules in a framework type of architecture can enhance the structural stability and physical properties of clathrate compounds. We report here that an organic clathrate compound consisting of a fullerene (C-60) guest and a hydroquinone (HQ) host framework shows enhanced hydrogen-storage capacity and good structural stability under pressures and temperatures up to 10 GPa and 438 K, respectively. This combined structure is formed in the extended beta-type HQ clathrate and admits 16 hydrogen molecules per cage, leading to a volumetric hydrogen uptake of 49.5 g L-1 at 77 K and 8 MPa, a value enhanced by 130% compared to that associated with the beta-type HQ clathrate. A close examination according to density functional theory calculations and grand canonical Monte Carlo simulations confirms the synergistic combination effect of the guest host molecules tailored for enhanced hydrogen storage. Moreover, the model simulations demonstrate that the lithium-doped HQ clathrates with C-60 guests reveal exceptionally high hydrogen-storage capacities. These results provide a new playground for additional fundamental studies of the structure property relationships and migration characteristics of small molecules in nanostructured materials.

현재, 한국원자력연구원은 부산 기장에 연구용 원자로(Ki-Jang Research Reactor, KJRR)를 건설 계획하고 있다. 원자로를 운영하면 중 저준위 방사성폐기물이 발생하므로 방사성 폐기물을 안전하게 처리 하는 것이 중요하다. 현재, 다양한 형태의 방사성 폐기물을 처리 할 수 있는 시멘트 고화 방법을 일반적으로 사용하고 ...

The electronic ground state in many iridate materials is described by a complex wave-function in which spin and orbital angular momenta are entangled due to relativistic spin-orbit coupling (SOC). Such a localized electronic state carries an effective total angular momentum of $J_{eff}=1/2$. In materials with an edge-sharing octahedral crystal structure, such as the honeycomb iridates Li2IrO3 and Na2IrO3, these $J_{eff}=1/2$ moments are expected to be coupled through a special bond-dependent magnetic interaction, which is a necessary condition for the realization of a Kitaev quantum spin liquid. However, this relativistic electron picture is challenged by an alternate description, in which itinerant electrons are confined to a benzene-like hexagon, keeping the system insulating despite the delocalized nature of the electrons. In this quasi-molecular orbital (QMO) picture, the honeycomb iridates are an unlikely choice for a Kitaev spin liquid. Here we show that the honeycomb iridate Li2IrO3 is best described by a $J_{eff}=1/2$ state at ambient pressure, but crosses over into a QMO state under the application of small (~ 0.1 GPa) hydrostatic pressure. This result illustrates that the physics of iridates is extremely rich due to a delicate balance between electronic bandwidth, spin-orbit coupling, crystal field, and electron correlation.

Understanding the stability of volatile species and their compounds under various surface and subsurface conditions is of great importance in gaining insights into the formation and evolution of planetary and satellite bodies. We report the experimental results of the temperature- and pressure-dependent structural transformation of methane hydrates in salt environments using in situ synchrotron X-ray powder diffraction, solid-state nuclear magnetic resonance, and Raman spectroscopy. We find that under pressurized and concentrated brine solutions methane hydrate forms a mixture of type I clathrate hydrate, ice, and hydrated salts. Under a low-pressure condition, however, the methane hydrates are decomposed through a rapid sublimation of water molecules from the surface of hydrate crystals, while NaCl.2H(2)O undergoes a phase transition into a crystal growth of NaCl via the migration of salt ions. In ambient pressure conditions, the methane hydrate is fully decomposed in brine solutions at temperatures above 252K, the eutectic point of NaCl.2H(2)O.

Powder samples of natural lawsonite (Ca-lawsonite, ) was studied structurally up to 8 GPa at room temperature using monochromatic synchrotron X-ray powder diffraction and a diamond anvil cell (DAC) with a methanol : ethanol : water (16 : 3 : 1 by volume) mixture solution as a penetrating pressure transmitting medium (PTM). Upon pressure increase, lawsonite does not show any apparent pressure induced expansion (PIE) or phase transition. Pressure-volume data were fitted to a second-order Birch-Murnaghan equation of state using a fixed pressure derivative of 4 leading to a bulk modulus () of 146(6) GPa. This compression is further characterized to be isotropic with calculated linear compressibilities of ${\beta}^a

Pressure-dependent structural and chemical changes of the zeolitic imidazolate framework compound ZIF-8 have been investigated using different pressure transmitting media (PTM) up to 4 GPa. The unit cell of ZIF-8 expands and contracts under hydrostatic pressure depending on the solvent molecules used as PTM. When pressurized in water up to 2.2(1) GPa, the unit cell of ZIF-8 reveals a gradual contraction. In contrast, when alcohols are used as PTM, the ZIF-8 unit cell volume initially expands by 1.2% up to 0.3(1) GPa in methanol, and by 1.7% up to 0.6(1) GPa in ethanol. Further pressure increase then leads to a discontinuous second volume expansion by 1.9% at 1.4(1) GPa in methanol and by 0.3% at 2.3(1) GPa in ethanol. The continuous uptake of molecules under pressure, modeled by the residual electron density derived from Rietveld refinements of X-ray powder diffraction, reveals a saturation pressure near 2 GPa. In non-penetrating PTM (silicone oil), ZIF-8 becomes amorphous at 0.9(1) GPa. The structural changes observed in the ZIF-8-PTM system under pressure point to distinct molecular interactions within the pores.

We report on high-pressure and high-temperature chemical transformations of Pb(2+)-exchanged natrolite (Pb-NAT, Pb8Al16Si24O80·16H2O) using a combination of in situ synchrotron X-ray powder diffraction and ex situ HAADF-STEM real space imaging. Three high-pressure polymorphs of natrolites (Pb-NAT-I, II, III) are observed via step-wise pressure-induced hydrations (PIH) up to 4.5 GPa, during which the number of H2O molecules located inside the natrolite channel increases from 16 to 40 H2O per unit-cell. At 4.5 GPa after heating the high-pressure Pb-NAT-III phase at 200 °C a reconstructive phase transits into a lawsonite phase (Pb-LAW, Pb4Al8Si8O28(OH)8·4H2O) with an orthorhombic space group Pbnm and a = 5.8216(9), b = 9.114(1) and c = 13.320(1) Å is observed. The structure of the recovered Pb-LAW phase was characterized using Rietveld refinement of the in situ synchrotron X-ray powder diffraction data and HAADF-STEM real space imaging. In the recovered Pb-LAW phase the Pb(2+) content is close to 42 wt% and as bond valence approximations reveal the Pb(2+) cations are more tightly coordinated to the framework oxygen atoms than originally in the natrolite phase.

Pressure-dependent structural and chemical changes of the metal organic framework (MOF) compound MIL-47(V) have been investigated up to 3 GPa using different pore-penetrating liquids as pressure transmitting media (PTM). We find that at 0.3(1) GPa the terephthalic acid (TPA) template molecules located in the narrow channels of the as synthesized MIL-47(V) are selectively replaced by methanol molecules from a methanol ethanol water mixture and form a methanol inclusion complex. Further pressure increase leads to a gradual narrowing of the channels up to 1.9(1) GPa, where a second irreversible insertion of methanol molecules leads to more methanol molecules being inserted into the pores. After pressure release methanol molecules remain within the pores and can be removed only after heating to 400 degrees C. In contrast, when MIL-47(V) is compressed in water, a reversible replacement of the TPA by H2O molecules takes place near 1 GPa. The observed structural and chemical changes observed in MIL-47(V) demonstrate unique high pressure chemistry depending on the size and type of molecules present in the liquid PTM. This allows postsynthetic nonthermal pressure-induced removal and insertion of organic molecules in MOFs forming novel and stable phases at ambient conditions.

We report here a pressure-driven metathesis reaction where Ag-exchanged natrolite (Ag16Al16Si24O80·16H2O, Ag-NAT) is pressurized in an aqueous CsI solution, resulting in the exchange of Ag(+) by Cs(+) in the natrolite framework forming Cs16Al16Si24O80·16H2O (Cs-NAT-I) and, above 0.5 GPa, its high-pressure polymorph (Cs-NAT-II). During the initial cation exchange, the precipitation of AgI occurs. Additional pressure and heat at 2 GPa and 160 °C transforms Cs-NAT-II to a pollucite-related, highly dense, and water-free triclinic phase with nominal composition CsAlSi2O6. At ambient temperature after pressure release, the Cs remains sequestered in a now monoclinic pollucite phase at close to 40 wt % and a favorably low Cs leaching rate under back-exchange conditions. This process thus efficiently combines the pressure-driven separation of Cs and I at ambient temperature with the subsequent sequestration of Cs under moderate pressures and temperatures in its preferred waste form suitable for long-term storage at ambient conditions. The zeolite pollucite CsAlSi2O6·H2O has been identified as a potential host material for nuclear waste remediation of anthropogenic (137)Cs due to its chemical and thermal stability, low leaching rate, and the large amount of Cs it can contain. The new water-free pollucite phase we characterize during our process will not display radiolysis of water during longterm storage while maintaining the Cs content and low leaching rate.

Corrigendum to ‘‘Thermodynamic stability, spectroscopic identification and cage occupation of binary CO2 clathrate hydrates’’ [Chem. Eng. Sci. (2009) 5125–5130] Hyung Joon Shin , Yun-Je Lee , Jun-Hyuck Im , Kyu Won Han , Jong-Won Lee , Yongjae Lee , Ju Dong Lee , Won-Yil Jang , Ji-Ho Yoon a, a Department of Energy and Resources Engineering, Korea Maritime University, Busan 606-791, Republic of Korea b Department of Environmental Engineering, Kongju National University, Chungnam 330-717, Republic of Korea c Department of Earth System Sciences, Yonsei University, Seoul 120749, Republic of Korea d Busan R&D Center, Korea Institute of Industrial Technology, Busan 609-735, Republic of Korea