Jintae Hong

Development of Coolant Flow Simulation System for Nuclear Fuel Test Rigs

핵연료를 이용한 원자력 발전에서 가장 중요한 것 중 하나는 핵분열중 발생하는 열을 효과적으로 제거하는 일이다. 핵연료의 열이 냉각수를 통해 효과적으로 제거되지 못할 경우 과도한 열에의해 핵연료봉 피복관이 녹아 폭발로 이어질 위험이 있다. 연소중인 가압 경수로 핵연료의 중심온도는 약1400℃까지 상승하며, 냉각수는 300℃, 150기압의 고온 고압 상태에서 1.6 kg/s 의 유속으로 순환된다. 새로운 핵연료를 개발하여 성능을 검증하기 위해서는 조사리그를 제작하여 연구로의 테스트 루프에서 연소시험을 수행해야 한다. 이때 핵연료 연소시험 중 발생하는 열을 제어하기 위하여 일정한 압력, 온도를 갖는 냉각수가 조사리그를 통과하여 루프내에서 순환하도록 설계되어 있으며, 특정 중성자속에서 조사 시험중인 핵연료의 발열량 측정은 순환중인 냉각수의 핵연료봉 주변 통과 전후 온도변화와 냉각수의 유속을 측정함으로써 간Key Words: Nuclear Fuel Irradiation Test(핵연료 조사시험), Coolant Flow Simulation System(냉각수 유동 모의장치), Nuclear Fuel Test Rig(핵연료조사리그) 초록: 핵연료 연소시험 도중 핵연료봉에서 발생하는 열을 효괻적으로 제거하기 위해서는 핵연료의 발열량을 정확하게 괃산하괟 충분한 유속을 갖는 냉각수를 순환시켜야 한다. 하나로는 개방형 수조 형태로서 핵연료 연소시험을 위한 별도의 냉각수 순환 루프를 갖추괟 있는데, 여기에 핵연료 조사리그를 장착하괟 냉각수를 순환시킴으로써 조사중인 핵연료봉의 온도를 일정온도 이하로 유지시킨다. 특히 순환되는 냉각수의 유속이 매우 높은 상태에서 조사리그 내에 부착된 부품이나 센서들이 유체유발 진동에 의해 파손되거나 기능을 상실하는 과우 매우 큰 기회비용을 야기한다. 본 연궫에서는 조사리그 부품의 건전성 사전 검토 및 괟속 유동에서의 센서 동작 특성에 대한 사전검토를 위해 냉각수 모의 순환장치를 개발하였다. Abstract: To remove heat generated during a burn-up test of nuclear fuels, the heat generation rate of nuclear fuels should be calculated accurately, and a coolant should be circulated in the test loop at an adequate flow rate. HANARO is an open pool–type reactor with an independent test loop for the burn-up test of nuclear fuels. A test rig is installed in the test loop, and a coolant is circulated through the test loop to maintain the temperature of the nuclear fuel rods within a desired temperature during an irradiation test. The components and sensors in the test rig can be broken or malfunction owing to the flow-induced vibration. In this study, a coolant flow simulation system was developed to verify and confirm the soundness of components and sensors assembled in the test rig with a high flow rate of the coolant.

Study on the Thermal Design of Nuclear Battery for Lunar Mission

For a stable electric power supply in the space, nuclear batteries have been used as the main power source in a spacecraft owing to their long lifetime and high reliability. In accordance with the plan for lunar mission in Korea, nuclear batteries will supply electricity to the rover that needs to be developed. According to the information about the estimated payload, Korea Atomic Energy Research Institute started with the conceptual design based on the previous studies in USA and Russia. Because a nuclear battery converts the decay heat of the radioisotope into electricity, thermal design, radiation shield, and shock protection need to be considered. In this study, two types of nuclear batteries, radial type and axial type, were designed according to the alignment of the thermoelectric module. Heat transfer analyses were performed to compare their thermoelectric efficiency, and test mockups were fabricated to evaluate their performances.For a stable electric power supply in the space, nuclear batteries have been used as the main power source in a spacecraft owing to their long lifetime and high reliability. In accordance with the plan for lunar mission in Korea, nuclear batteries will supply electricity to the rover that needs to be developed. According to the information about the estimated payload, Korea Atomic Energy Research Institute started with the conceptual design based on the previous studies in USA and Russia. Because a nuclear battery converts the decay heat of the radioisotope into electricity, thermal design, radiation shield, and shock protection need to be considered. In this study, two types of nuclear batteries, radial type and axial type, were designed according to the alignment of the thermoelectric module. Heat transfer analyses were performed to compare their thermoelectric efficiency, and test mockups were fabricated to evaluate their performances.

A study on temperature control of induction brazing coil

Induction brazing is generally used in the fields of sealing and joining. The temperature control performance is one of the important parameters in induction brazing process. In this paper, an accurate temperature control scheme of induction brazing coil is studied. The experimental results show that excellent temperature control performance is achieved by the proposed control scheme.

Development of Precision Drilling Machine for the Instrumentation of Nuclear Fuels

When a new nuclear fuel is developed, an irradiation test needs to be carried out in the research reactor to analyze the performance of the new nuclear fuel. In order to check the performance of a nuclear fuel during the irradiation test in the test loop of a research reactor, sensors need to be attached in and out of the fuel rod and connect them with instrumentation cables to the measuring device located outside of the reactor pool. In particular, to check the temporary temperature change at the center of a nuclear fuel during the irradiation test, a thermocouple should be instrumented at the center of the fuel rod. Therefore, a hole needs to be made at the center of fuel pellet to put in the thermocouple. However, because the hardness and the density of a sintered UO2 pellet are very high, it is difficult to make a small fine hole on a sintered UO2 pellet using a simple drilling machine even though we use a diamond drill bit made by electro deposition. In this study, an automated drilling machine using a CVD diamond drill has been developed to make a fine hole in a fuel pellet without changing tools or breakage of workpiece. A sintered alumina (Al2O3) block which has a higher hardness than a sintered UO2 pellet is used as a test specimen. Then, it is verified that a precise hole can be drilled off without breakage of the drill bit in a short time.

An Experimental Study on Drilling Conditions for the Instrumentation of Nuclear Fuel

To develop a new nuclear fuel, it needs to make a test fuel rod and carry out burn-up test in the test loop of a research reactor to check the irradiation characteristics of the nuclear fuel. At that time, several sensors such as thermocouples, LVDTs and SPNDs are needed to be attached in and out of the fuel rod and connect them with instrumentation cables. Then, the instrumentation cables deliver the signals measured by the sensors to the measuring device located outside of the reactor pool. In particular, to install a thermocouple in a fuel rod, it needs to drill off holes on the alumina blocks and sintered pellets. However, because the hardness of a sintered pellet is 700 Hv (or HRC 61) and that of an alumina block is 1480 Hv, a special drilling machine which adapts a diamond coated drill bit had developed. In this study, several case experiments have been carried out to find an optimal drilling condition of the drilling machine. And, using the optimal drilling condition, minimum numbers of the holes that a drill bit can drill off are verified.