In this study, the load fluctuation of the main engine is considered to be a disturbance for the jacket coolant temperature control system of the low-speed two-stroke main diesel engine on the ships. A nonlinear PID temperature control system with satisfactory disturbance rejection performance was designed by rapidly transmitting the load change value to the controller for following the reference set value. The feed-forwarded load fluctuation is considered the set points of the dual loop control system to be changed. Real-coded genetic algorithms were used as an optimization tool to tune the gains for the nonlinear PID controller. ITAE was used as an evaluation function for optimization. For the evaluation function, the engine jacket coolant outlet temperature was considered. As a result of simulating the proposed cascade nonlinear PID control system, it was confirmed that the disturbance caused by the load fluctuation was eliminated with satisfactory performance and that the changed set value was followed.

Cutting tools tend to wear gradually with progressing of machining process due to extremely high surface loads and temperature from the relative motions between tool and workpiece. Especially, the high cutting temperature is a dominant factor in the relation to tool life. High-pressure coolant has been reported as an effective method to prevent the severe wear from cutting temperature. This research investigates efficient supplying conditions of high-pressure coolant with the CFD results from a internal-flush drilling process. The flow rate of coolant is increased drastically up to three times under 70 bar compared to conventional way.

In this paper, a structural integrity on the test rig with assembly plug to perform intermediate examination is evaluated. Structural analysis results between the test rig with non assembly plug and assembly plug are compared, because the assembly plug has an effect on the flow of the coolant in the test rig. A equivalent stress value on the test rig with assembly plug is increased more than the stress on the test rig with non-assembly plug. A shape optimization of the assembly plug is performed to decrease the stress. Considering a connection with the transport tool, a optimized shape of the assembly plug is presented to minimize the stress on the test rig. Using the optimized assembly plug, the equivalent stress on the test rig with the optimized plug is less than the stress on the test rig with the non-optimized plug.

지온상승억제 효과는 차광망(50%) +냉각수순환 평균 18.8oC(최고 23oC)가 가장 좋았으며, 차광망(50%) +지 하수순환 23.2oC(28.5oC), 차광도포제(30%)와 차광망 (50%)이 각각 24oC(최고 30oC) 순으로 나타났다. 고온기 근권냉각수 순환 효과가 가장 큰 모데나 품종은 절화장이 95.9 cm, 생체중이 67.0 g으로 가장 좋게 나타났다. 처리별 수량증가는 차광망(50%)처리에 비해 차광망(50%) +냉 각수순환이 121%로 가장 많았고, 차광망(50%) +지하수 순환, 차광도포제(30%)는 각각 59%와 65% 증가하였다. 하우스내부 야간온도를 8oC로 관리하였을 때 근권온수 순환이 평균 18oC 유지하여 무처리에 비해 약 8oC 정도 지온상승효과가 있는 것으로 나타났다. 동절기 지하부 온수순환처리에 의한 알스트로메리아 생육은 아스펜, 모데나, 샤넬 품종에서 절화장, 생체중 등 생육이 가장 좋았으며, 보르도 품종은 절화장이 다소 작게 나타났다. 근권온수 순환처리가 생육을 증가시킨 결과로 아스펜 등 4품종 모두에서 꽃목길이, 꽃목경경, 꽃수 및 꽃무게 등절화품질 또한 증가하였다. 생산량 또한 크게 증가하여 모데나 품종에서 38% 이상으로 가장 높았고, 아스펜, 보르도, 샤넬 순이었다.

The small break loss-of-coolant accidents for the HANARO fuel test loop have been predicted by MARS code. Conservative method was used for the prediction of the loss-of-coolant accidents. The maximum peak cladding temperature was calculated as 1286K, which was lower than the design limit temperature (1477K) of nuclear fuels for the HANARO fuel test loop. The maximum peak cladding temperature occurred for the cold leg break in the HANARO pool. The hydrogen generation and oxidation of the fuel cladding were also negligible. Consequently, it is ensured that the emergency cooling water system for the HANARO fuel test loop is appropriate for the small break loss-of-coolant accidents.

본 논문은 가장 극한 조건(공정모델-2)에서 화학 제염한 경우 원자로 냉각재 펌프용 스테인리스강의 내식성 평가에 관하여 연구하였다. 사이클 경과에 따른 304 스테인리스강의 전기화학적 특성은 다른 스테인리스 강보다 우수한 특성을 나타냈다. 또한 공정모델-1과 공정모델-2의 304 스테인리스강은 가장 낮은 무게 감량을 나타냈다. 공정모델 용액에서 304 스테인리스강, 415 스테인리스강, 431 스테인리스강에 대한 실험 결과 공정모델-1에 대한 공정모델-2의 무게감량비는 각각 2.908, 2.372,그리고 2.370배를 나타냈다. 그 이유는 공정모델-2의 경우가 공정모델-1에 비하여 화학약품 농도나 온도가 높은 가혹한 조건에 기인한 것으로 사료된다.

The main objective of this paper is to search whether containment vessel's best pressure may increase until how long when loss of coolant accident (LOCA) happened in containment vessel of Ulchin nuclear power plant 1 and 2. Another goal of this research is to find the influential factors that increase containment vessel pressure. Model for this research is Ulchin nuclear power plant 1 with 10 cycles. Data were collected by simulator of Ulchin nuclear power plant 1 and design of experiment was used for data analysis. For the experiment, seven factors that are going to influence in containment vessel pressure were chosen. It was found that fatter which influences in early rise of containment vessel pressure after LOCA is only explosion size. Also, containment vessel's best pressure (3.74 bar.a) was much lower than limit (4.86 bar.a) of FSAR (Final Safety Analysis Report).

Radioactive Oxide is formed on the surface of the coolant pipe of the nuclear power plant. In order to remove the oxide film that is formed on the surfaces of the coolant pipe, chemical and physical decontamination technologies are used. The disadvantage of traditional technologies is that they produce secondary radioactive wastes. Therefore, in this study, the short-pulsed laser eco-friendly technology was used in order to reduce the production of secondary radioactive wastes. It was also used to minimize the damage that was caused to the base material and to remove the contaminated oxide film. The study was carried out using a Stainless steel 304 specimen that was coated with nickel-ferrite particles. Additionally, a transport robot was 3D modeled and manufactured in order to efficiently remove the oxide film from the coolant pipe of the nuclear power plant. The transport robot has a fixed laser head to move inside the horizontal and vertical pipes. The rotating laser head removes the contaminated oxide film on the inner surface of the coolant pipe. In the future, as a condition of the 1064nm short-pulsed laser ablation technique determined by basic analysis, we plan to analyze whether the transport robot is applicable to the radiation contamination site of the nuclear power plant.

When a loss of coolant accident which causes a partial or a full drainage in the SFP would happen, Zircaloy-4 spent fuel cladding begin to react with high temperature air, and the heat generates by exothermic reaction between Zircaloy-4 cladding and surrounding air. Due to the heat, the ignition may occur in the surface of Zircaloy-4 cladding. If the Zr-fire phenomenon occurs during the accident in a SFP, the spent fuel cladding and pellets would be severely fragmented and powdered and it may bring about a massive release of radioactive source terms. Therefore, it is crucial to prevent the zirconium fire phenomenon for the spent fuel pool safety. However, a main cause to trigger the zirconium fire was not identified. In order to identify a possible mechanism of the Zr-fire phenomenon, OECD-NEA SFP Project I, II was initiated. In this paper, we reviewed the Zr-fire phenomenon which may occur in the spent fuel pool for complete loss of coolant accident scenario. The Spent Fuel Pool Project (hereinafter SFP project) is the experimental program to investigate the phenomena of spent fuel pool complete loss of coolant accident using a 17×17 PWR fuel assembly. In this section, the zirconium fire phenomenon which was observed from the SFP project is briefly investigated. This paper presented the fuel assembly temperature (i.e. zirconium alloy cladding temperature) and oxygen concentration profile of the SFP project phase-1 ignition test. At around 12.7 hour, the temperature abruptly increased and the oxygen concentration also dramatically decreased. This abrupt temperature escalation is the zirconium fire phenomenon. In order to investigate the mechanism of this zirconium fire phenomenon, behaviors of both temperature and oxygen concentration were fully compared. This paper reviewed the results of OECD-NEA SFP project experiment and then a mechanism of Zr-fire phenomenon was dscussed. It seems that the Zr-fire phenomenon might be a consequence of thermal mismatch between heat generation and dissipation. A large amount of heat might be generated by the air oxidation of Zircaloy-4 spent cladding immediately after the kinetic transition which is a breakaway phenomenon. This paper discussed the relationship between the breakaway phenomenon and the Zr-fire phenomenon in case of air oxidation of Zircaloy-4 spent cladding. This paper presents preliminary findings on the Zr-fire phenomenon from the open experiment data of the prototypic spent fuel severe accident scenario. These findings would enhance the understanding of Zircaloy-4 spent cladding air oxidation and severe accident scenario progression in a SFP.

Activated corrosion products deposited on the reactor coolant system in a nuclear power plant should be removed to reduce the radiation exposure to workers. Chemical decontamination processes using organic acids have been widely applied to remove the activated corrosion products. However, they are highly corrosive to the base metal and generate a considerable amount of ion exchange resin waste, which is hard to be treated. In order to resolve this problem, KAERI has been developed a chemical decontamination process using chelate-free inorganic acid, HyBRID (Hydrazine Based Reductive metal Ion Decontamination) process. Especially, the Cyclic SP (Sulfuric acid/Permanganate)- HyBRID process was suggested as the decontamination process for applying to the remove the double oxide layer generated on the reactor coolant system in the pressurized water reactor (PWR). During the Cyclic SP-HyBRID process, the process is continuously applied without discharging or recharging of the decontamination process solution from the primary circuit. Thus, it is necessary to include the removal processes of the decontamination reagents middle of the Cyclic SP-HyBRID process, e.g., ‘Mn removal step’ for removing the permanganate ions and ‘hydrazine decomposition step’ for decomposition of the remaining hydrazine. During these removal processes, the metal ions can also be removed from the process solution. In this study, the behaviors of metals were investigated during the Cyclic SP-HyBRID process. The concentration changes of metal ions in the process solution were analyzed using atomic absorption (AA) spectroscopy. The metal precipitates generated during the process were characterized using X-ray diffraction (XRD) and Fourier Transform Infrared (FT-IR) spectroscopy. From the results of the analysis, it was observed that the metal ions dissolved in the process solution were converted into metal hydroxides and precipitated at the Mn removal process. It was confirmed by equilibrium calculation result that the OH− ions generated at the Mn removal can react with the metal ions and form the metal hydroxides. It is considered that this removal behaviors of the metals can contribute the decontamination performance.