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• Multi-layer repository design for high-level radioactive waste disposal is proposed. • Applicability of the multi-layer concept is analyzed by numerical simulations. • Multi-layer repositories meet the temperature criterion of 100 °C. • Stress evolutions in bentonite buffer materials are not significantly different from existing repository concept. • Rock mechanical behavior is different and potential for spalling failure exists. A multi-layer repository concept is proposed as an alternative to the single-layer repository concept to improve the disposal density of high-level radioactive waste (HLW) in Korea. Numerical simulations are performed to compare the coupled thermo-hydro-mechanical (THM) behavior in the existing Korean reference HLW disposal system (KRS) based on the single-layer repository concept to that in the new multi-layer repository concept. The applicability of the multi-layer repository concept, such as double- and triple-layer repositories, for the disposal of HLW is analyzed with respect to a maximum temperature criterion of 100 °C, evolution of saturation and pore pressure, and mechanical stability. Maximum temperatures are below 100 °C in the double- and triple-layer repository concepts, as in the single-layer reference, although two peaks in simulated temperatures are observed during the evolution of the thermal pulse, resulting from superposition of decay heat at different vertical levels in the multi-layer repository concept. There is no significant difference in the evolution of pore pressure and saturation among the three concepts. The evolutions of mean effective stress at the bentonite blocks and backfill materials are also not significantly different between the single-, double-, and triple-layer repository concepts, because the hydraulic behavior is quite similar, resulting in almost the same change in swelling pressure. Stress states in the rock mass near the tunnels and deposition holes remain below the Mohr-Coulomb failure envelopes at the repositories of 500 m depth in the single-, double-, and triple-layer repository concept simulations. However, the stress states exceed the Mohr-Coulomb failure envelopes at the repositories below 500 m depth (beneath the top layer) in the double- and triple-layer repository concepts. Also, mechanical analysis shows high potential for spalling failure around the deposition holes and tunnel roof in the double- and triple-layer repository concepts. Subsidence in the double- and triple-layer concepts due to the construction of repositories is much deeper than that in the single-layer concept, and uplift induced by heating the rock mass due to the decay heat in the double- and triple-layer concepts is much higher than in the single-layer concept. These results indicate that multi-layer repositories with larger depth intervals between layers are a feasible alternative to the KRS to safely achieve higher disposal density. [ABSTRACT FROM AUTHOR]

Abstract: Polybrominated diphenyl ethers (PBDEs), commonly used flame retardants, have been reported as potential endocrine disruptor and neurodevelopmental toxicants, thus giving rise to the public health concern. The goal of this study was to investigate the relationship between umbilical cord blood, maternal blood, and breast milk concentrations of PBDEs in South Korean. We assessed PBDE levels in paired samples of umbilical cord blood, maternal blood, and breast milk. The levels of seven PBDE congeners were measured in 21 paired samples collected from the Cheil Woman’s Hospital (Seoul, Korea) in 2008. We also measured thyroid hormones levels in maternal and cord blood to assess the association between PBDEs exposure and thyroid hormone levels. However, there was no correlation between serum thyroxin (T4) and total PBDEs concentrations. The total PBDEs concentrations in the umbilical cord blood, maternal blood, and breast milk were 10.7±5.1ngg−1 lipid, 7.7±4.2ngg−1 lipid, and 3.0±1.8ngg−1 lipid, respectively. The ranges of total PBDE concentrations observed were 2.28–30.94ngg−1 lipid in umbilical cord blood, 1.8–17.66ngg−1 lipid in maternal blood, and 1.08–8.66ngg−1 lipid in breast milk. BDE-47 (45–73% of total PBDEs) was observed to be present dominantly in all samples, followed by BDE-153. A strong correlation was found for major BDE-congeners between breast milk and cord blood or maternal blood and cord blood samples. The measurement of PBDEs concentrations in maternal blood or breast milk may help to determine the concentration of PBDEs in infant. [Copyright &y& Elsevier]