Byung-Seon Choi

New mesoporous silica/carbon composites by in situ transformation of silica template in carbon/silica nanocomposite

Hard template-based fabrication of mesoporous carbon unavoidably goes through the removal process of the template to generate template-free carbon replica, including troublesome disposal of template waste often accompanied by toxic etchant, which not only increases the fabrication cost of materials but also raises serious environmental concerns. As a novel strategy to overcome such problem, a direct in situ synthesis approach using silica waste in carbon/silica nanocomposite as a silica source and cetyltrimethylammonium bromide as a porogen under basic condition is reported in this study for the generation of a new composite composed of mesoporous MCM-41 silica and hollow carbon capsule. The resultant MCM-41/carbon capsule composite offers a 3-D interconnected multimodal pore system, which discloses a wide pore range of ordered uniform mesopores (ca 2.3 nm) resulting from MCM-41 silica and disordered uniform mesopores (ca 3.8 nm) and macropores (ca 300 nm) from hollow mesoporous carbon, respectively. The composite has a high specific surface area (ca 909 m2/g) and large pore volume (ca 0.73 cm3/g). The in situ transformation approach of silica waste into valuable mesoporous silica is considered as a promising scalable route for efficient new multi-functional composites useful for a wide range of applications such as adsorption of volatile organic compounds and radioactive wastes produced in a nuclear facility.

Design of a heavy-duty manipulator for dismantling of a nuclear power plant

Some of the nuclear power plants in Korea have reached their end of life-cycle, and the importance of developing dismantling techniques has been emphasized. We designed a manipulator for decommissioning a reactor pressure vessel. We analyzed the work environment for disassembly and the workspace of the manipulator, and verified the validity of kinematic variables through a kinematic simulation. We verified through a dynamics simulation that each joint of the designed manipulator can be operated within the maximally allowed torque despite a load of 250 kg. Finally, we verified through the stress analysis that the manipulator is designed to secure at least two times higher safety factor.

A Training System Based On Virtual Environments To Prevent Incidents And Reduce Accidents During Decommissioning Of Nuclear Facilities

Decommissioning of nuclear facilities should be accomplished by assuring the safety of workers because these decommissioning activities take place under high radioactivity and difficult work condi tions. Before decommissioning, it is necessary to evaluate and assess the radiation exposure dose of workers under the principle of ALARA (as low as reasonably achievable). Furthermore, to improve the proficiency of decommissioning environments, methods and systems need to be developed. The legacy methods of exposure dose measurement and assessment have the limitations to modify and simulate the exposure dose of workers prior to practical activities because those should be accomplished without changes of working routes under predetermined scenarios. To simulate many decommissioning scenarios, decommissioning environments were designed in virtual reality. To simulate and assess exposure dose of workers, a human model was also designed in a virtual environment. These virtual decommissioning environments made it possible to simulate and assess in real time the exposure dose of workers. It can be concluded that this system is able to protect workers from accidents and enable them to improve their familiarization about their working environment. This system is expected to reduce human errors because workers can improve their proficiency of hazardous working environments due to virtual training like real decommissioning situations. In the end, safety during decommissioning of nuclear facilities will be guaranteed under the principle of ALARA.

Laser Removal of Contaminants on the Metal Surface

A Q-switched Nd:YAG laser with a 532 nm and 450 mJ/pulse was employed to study the decontamination characteristics of Type 304 stainless steel specimens and aluminum specimens artificially contaminated with CsNO3 , Co(NH4 )2 (SO4 )2 , Eu2 O3 and CeO2 , respectively. The relative atomic molar percent of the contaminants on metal surface before and after laser irradiation was determined by EPMA. The morphology of specimen surface was examined by SEM. The ablation behavior of contaminants on Type 304 stainless steel specimens was investigated for the decontamination variables such as a number of laser shots, laser fluence and an irradiation angle. Their optimum values were found to be 8, 13.3 J/cm2 and 30°, respectively. The removal of contaminants on aluminum surface, however, was found to be more difficult by laser.Copyright