The design of a wooden impact limiter equipped to a transportation cask for radioactive materials was optimized. According to International Atomic Energy Agency Safety Standards, 9 m drop tests should be performed on the transportation cask to evaluate its structural integrity in a hypothetical accident condition. For impact resistance, the size of the impact limiter should be properly determined for the impact limiter to absorb the impact energy and reduce the impact force. Therefore, the design parameters of the impact limiter were optimized to obtain a feasible optimal design. The design feasibility criteria were investigated, and several objectives were defined to obtain various design solutions. Furthermore, a probabilistic approach was introduced considering the uncertainties included in an engineering system. The uncertainty of material properties was assumed to be a random variable, and the probabilistic feasibility, based on the stochastic approach, was evaluated using reliability. Monte Carlo simulation was used to calculate the reliability to ensure a proper safety margin under the influence of uncertainties. The proposed methodology can provide a useful approach for the preliminary design of the impact limiter prior to the detailed design stage.

This study is about the production of radiation sources of simulated concrete and soil reference materials to verify the validity of the quality establishment and measurement of the detector (HPGe) of the radioactive soil and concrete waste classification system, which is being developed to quickly and accurately classify nuclear decommissioning waste. Specific activity of gamma nucleus among radioactive wastes is evaluated using gamma spectroscopy. At this time, in order to verify the validity and reliability of measuring equipment, it shall be a standardized substance of the same medium as nuclear decommissioning waste (chemical ingredients, particles, density, etc.) in order to correct the energy and efficiency of gamma nuclide analysis equipment. The CRM used for the detector’s energy correction used a 1 L Marinelli beaker standard correctional radiation source consisting of 10 radioactive isotopes. In order to correct efficiency, in accordance with the production and certification process of the Korea Standards and Research Institute, it has produced artificial simulated radioactive concrete similar to nuclear decommissioning waste (30% for cement, 60% for regulation and 10% for bentonite). The radioactive homogeneity of the simulated concrete reference materials was evaluated using dispersion analysis (ANOVA) in accordance with ISO Guide 35, while 137Cs and 60Co of concrete reference materials were able to obtain homogeneous measurements both in and between bottles. The self-absorption rate of the simulated concrete reference material was determined by the MCNP computer simulation measurement method, and the self-absorption correction coefficients of 137Cs and 60Co were assessed at 0.995 and 0.996, respectively, and the standard value for the radiation of the simulated concrete reference material was calculated on the weighted average of the measurements of 20 samples. The uncertainty about the reference value was calculated by combining measurement uncertainty (Type B evaluation), bottle to bottle standard deviation, and uncertainty within bottle by modifying the formula suggested in ISO Guide 35. The concentration of 137Cs and 60Co of reference materials was divided into high-speed measurement mode and precision measurement mode in consideration of the self-disposal standard. The reference value and uncertainty of expansion among reference materials for high-speed measurement mode were rated at 1,032.7 ± 64.0 Bq·kg−1and 1,083.7 Bq·kg−1, respectively. The standard value and expansion uncertainty for 137Cs and 60Co among reference materials for precision measurement mode were rated at 113.7 ± 10.0 Bq·kg−1 and 122.3 ± 10.3 Bq·kg−1, respectively.

Laser scabbling experiments were conducted with the aim of developing concrete decontamination technology. Laser scabbling system contains a 6 kW fiber laser (IPG YLS-6000, λ=1,070 nm) and optical head, which are connected with process fiber (core dia.: 600 μm, length: 20 m). Optical head consists of two lenses (f = 160 mm and 100 mm) to collimate and focus laser beam. The focused laser beam is passed through the small diameter of nozzle (throat dia.: 3 mm) to prevent the laser-produced debris into head. And then, the focused beam is directed toward concrete block as continuously diverging. The diverged laser beam was incident on the high-strength concrete with 300 mm (length) × 300 mm (height) × 80 mm (width) to induce explosive spalling on the concrete surface. The optical head was moved by X-Y-Z manipulate coupled with a computerized numerical control while scabbling. We have observed not only active spalling on the concrete surface but energetic scattering of laserproduced debris when scabbling on high-strength concretes. It indicates the need for a device capable of collecting the laser-produced debris. We newly designed and manufactured dust collector coupled with cylindrical tube to prevent scattering of laser-produced debris into ambient environment. The collecting system was evaluated by estimating the collecting efficiency for laser-produced debris while scabbling. The collecting efficiency was calculated on the basis of the information on the mass loss of concrete block after laser scabbling and the mass of collected debris in a container. The collecting efficiency was found to be over 85%.

Cutting reactor pressure vessels (RPV) into acceptable sizes for waste disposal is a key process in dismantling nuclear power plants. In the case of Kori-1, a remote oxyfuel cutting method has been developed by Doosan Heavy Industry & Construction to dismantle RPVs. Cutting radioactive material, such as RPV, generates a large number of fine and ultrafine particles incorporating radioactive isotopes. To minimize radiological exposure of dismantling workers and workplace surface contamination, understanding the characteristics of radioactive aerosols from the cutting process is crucial. However, there is a paucity of knowledge of the by-products of the cutting process. To overcome the limitations, a mock-up RPV cutting experiment was designed and established to investigate the characteristics of fine and ultrafine particles from the remote cutting process of the RPV at the Nuclear Decommissioning Center of Doosan Heavy Industry & Construction. The aerosol measurement system was composed of a cutting system, purification system, sampling system, and measurement device. The cutting system has a shielding tent and oxyfuel cutting torch and remote cutting robot arm. It was designed to prevent fine particle leakage. The shielding tent acts as a cutting chamber and is connected to the purification system. The purification system operates a pressure difference by generating an airflow which delivers aerosols from the cutting system to the purification system. The sampling system was installed at the center of the pipe which connects the shielding tent and purification system and was carefully designed to achieve isokinetic sampling for unbiased sampling. Sampled aerosols were delivered to the measurement device. A high-resolution electrical low-pressure impactor (HR-ELPI+, Dekati) is used to measure the size distribution of inhalable aerosols (Aerodynamic diameter: 6 nm to 10 μm) and to collect size classified aerosols. In this work, the mock-up reactor vessel was cut 3 times to measure the number distribution of fine and ultrafine particles and mass distribution of iron, chromium, nickel, and manganese. The number distribution of aerosols showed the bi-modal distribution; two peaks were positioned at 0.01−0.02 μm and 0.04–0.07 μm respectively. The mass distribution of metal elements showed bi-modal and trimodal distribution. Such results could be criteria for filter selection to be used in the filtration system for the cutting process and fundamental data for internal dose assessment for accidents. Future work includes the investigations relationships between the characteristics of the generated aerosols and physicochemical properties of metal elements.

본 연구에서는 국내산 돌미나리에서 GABA생성능이 있 는 신규 유산균을 분리, 동정한 결과, Enteroccoccus casseliflavus로 확인되었다. 최근까지 Lactobacillus속과 같 은 GABA 생성 유산균에 대한 보고는 많이 되고 있고, 일 부 Enterococcs속 유산균도 보고되고 있으나 E. casseliflavus 종에 대한 보고는 없었다. 따라서 본 연구에서는 E. casseliflavus PL05 균주에 대한 GABA 생성 최적 조건을 찾기 위하여 배지의 유형, 생육 온도, 초기 pH 조건, 배양 시간, MGS 농도 및 탄소원을 포함한 다양한 조건을 테스 트하였다. PL05 균주는 MRS 혹은 TSB 배지보다 BHI 배 지에서 생육이 잘 되었으며, 배지의 초기 pH는 7-9 조건 에서 가장 생육이 왕성하였고, GABA 생성 조건 역시 유 사한 결과로 확인되었다. GABA의 기질에 해당하는 MSG 의 농도별 GABA 생성량을 조사한 결과, 7%에서 가장 높 은 생성량을 나타내었으나 5%에서도 유사한 수준으로 확 인되어 효율적인 측면에서 5%가 적합할 것으로 판단된다. 탄소원에 따른 생육 및 GABA 생성량은 말토오스를 사용 하였을 때 가장 높은 것으로 확인되었고, 이러한 최적의 조건들로 최종 테스트를 진행한 결과, 24시간째 140.06±0.71 mM의 GABA가 생성되었고, 전환율은 78.95%로 확인되 었다. 또한 반코마이신을 포함한 10개의 항생제에 대한 감 수성을 조사한 결과 내성이 없는 것을 확인하였다.