[en] Twyman-green interferometer has been stabilized to measure the length, surface profile, displacement, vibration, and etc. The interferometer is actively stabilized by using He-Ne laser with the wavelength of 633 nm. The interferometer was stabilized by using fringe locking method, which the reference mirror was pushed back to the original position of the fringe by applying the amplified error voltage when a fringe moves due to the harsh environment perturbations such as vibration, air turbulence, and etc.

[en] Recently, rapid progress on the globalization of the nuclear safety issues is being made in IAEA (International Atomic Energy Agency) and its member states. With the globalization, the need for international cooperation among international bodies and member states continues to grow for resolving these universal nuclear safety issues. Furthermore, the importance of strengthening the global nuclear safety regime is emphasized through various means, such as efforts in application of IAEA safety standards to all nuclear installations in the world and in strengthening the code of conduct and the convention on nuclear safety. In this regards, it is important for us to keep up with the activities related with the global nuclear safety regime as an IAEA member state and a leading country in nuclear safety regulation

[en] Containment has a principal function of leakage barrier, after the reactor coolant pressure boundary, to control the release of radioactive materials from the fuel in the reactor core under accident conditions. Therefore the containment shall be tested periodically to ensure the leak-tight integrity under design basis conditions. Containment leakage test methods include three types; Integrated Leakage Rate Test (ILRT or Type A test), Local Leakage Rate Test (LLRT or Type B and Type C tests). ILRT is the test to measure the containment system overall integrated leakage rate under conditions representing Design Basis Accident (DBA) containment pressure and system alignments. Type C test is intended to measure the leakage rate of containment isolation valves under DBA pressure. Type B test is for the leakage limiting boundaries other than isolation valves, such as personnel doors, equipment hatch and so on. For ILRT, it usually takes several days to finish the test and there may be some moments to make difficult decisions during test, for example when to finish the atmosphere stabilization. Hence, in this paper, the results of past ILRTs in Korea are reviewed to find some insights that can help in making such decisions

[en] The methodology being used today for assuring nuclear safety is based on analytic approaches. In the 21st century, holistic approaches are increasingly used over traditional analytic method that is based on reductionism. Presently, it leads to interest in complexity theory or system dynamics. In this paper, we review global academic trends, social environments, concept of nuclear safety and regulatory frameworks for nuclear safety. We propose a new safety paradigm and also regulatory approach using holistic approach and system dynamics now in fashion

[en] Korea currently has 25 operating NPP units in 4 sites (Kori, Wolsong, Hanbit and Hanul) and every site has at least 6 units in a single site. In addition, the population density near the site is higher than that of other NPP operating countries. Therefore, the public has concerns on the safety of multiple NPPs. International agencies related with nuclear energy and several countries with multiple units in a single site are currently performing R&D projects on site risk. Currently, it is phase of establishing the concept on methodologies for assessment and regulation of site risk at both home and abroad. This paper presents an international survey of the development of site-level or multi-unit PSA methodologies and regulatory systems to address arriving concerns about the same site multi-unit being addressed following the Fukushima accident in Japan. The move is led by the international joint research center for nuclear energy, such as the International Atomic Energy Agency, and major nuclear plant operators including the United States and Canada. At this stage, there is no internationally established and recognized system of related assessment methods and regulations, and it is still at a research and development stage and needs time to be applied to reality.

[en] The DYLAM-3 code which overcomes the limitation of event tree/fault tree was applied to LOOP (Loss of Off-site Power) in the mid-loop operation employing HEPs (Human Error Probabilities) supplied by the ASEP (Accident Sequence Evaluation Program) and SEPLOT (Systematic Evaluation Procedure for Low power/shutdown Operation Tak) procedure in this study. Thus the time history of core uncovery frequency during the mid-loop operation was obtained. The sensitivity calculations in the operator's actions to prevent core uncovery under Loop in the mid-loop operation were carried out. The analysis using the time dependent HEP was performed on the primary feed and bleed which has the most significant effect on core uncovery frequency. As the result, the increment of frequency is shown after 200 minutes duration of simulation conditions. This signifies the possibility of increment in risk after 200 minutes. The primary feed and bleed showed the greatest impact on core uncovery frequency and the recovery of the SCS (Shutdown Cooling System) showed the least impact. Therefore the efforts should be taken on the primary feed and bleed to reduced the core uncovery frequency in the mid-loop operation. And the capability of DYLAM-3 in applying to the time dependent concerns could be demonstrated. (author)

[en] Concentric Annular Heat Pipes (CAHP) were fabricated and tested to investigate their thermal characteristics. The CAHPs were 25.4mm in outer diameter and 200mm in length. The inner surface of the heat pipes was covered with screen mesh wicks and they were connected by four bridge wicks to provide liquid return path. Three different heat pipes were fabricated to observe the effect of change in diameter ratios between 2.31 and 4.23 while using the same outer tube dimensions. The major concern of this study was the transient response as well as isothermal characteristics of the heat pipe outer surface, considering the application as uniform heating device. A better performance was achieved as the diameter ratio increased. For the thermal load of 180 W, the maximum temperature difference on the outer surface in the axial direction of CAHP was 2.3 .deg. C while that of the copper block of the same outer dimension was 5.9 .deg. C. The minimum thermal resistance of the CAHP was measured to be 0.04 .deg. C/W. In regard to the transient response during start-up, the heat pipe showed almost no time lag to the heat source, while the copper block of the same outer dimensions exhibited about 25 min time lag

[en] Currently, many countries have plans to increase their nuclear energy use in several areas, especially in electric power generation. Those countries include not only the developed countries such as, U.S.A., Russia, U.K., Canada but also the developing counties like China, India, Vietnam, Indonesia, Nigeria and so on. The worldwide trend to increase nuclear energy use is due to recent rapid increase in energy demand for economic growth, Kyoto Protocol and the advance in nuclear technologies resulting in enhancement of the safety level and the performance of NPPs. In this situation, the international nuclear community is continuously making effort to ensure and to improve the global nuclear safety through Conventions (Convention on Nuclear Safety and etc.), the development and application of international safety standards and the international cooperation. Among these efforts for global nuclear safety, recent activities in INRA (International Nuclear Regulators' Association) and in MDEP (Multinational Design Evaluation Program), which have caught attention from many countries, will be introduced in this paper

[en] The INRA (International Nuclear Regulators' Association) was established as an association of top regulators in 1997 to influence and enhance nuclear safety and radiological protection from the regulatory perspective. The members include the most senior officials of well-established independent national nuclear regulatory organizations. Previously, it had 9 members from 8 member countries; U.S. (NRC), France (ASN), Sweden (SKI), U.K. (NII), Canada (CNSC), Germany (BMU), Spain (CSN) and Japan (NSC and NISA). As of March 2006, the Director General for Atomic Energy Bureau in MEST of Korea became the 10^th member of the INRA. From this time, Korea has participated in the INRA regular meetings and shared its knowledge and experience in nuclear safety regulation area with members

[en] Nowadays, many countries announce their plans to increase the nuclear energy use in wide range, especially in electric power generation. The worldwide trend to increase nuclear energy use in electric power generation is due to recent rapid increase in energy demand for economic growth, the reduction of greenhouse gas emissions and the advance in nuclear technologies resulting in enhancement of the safety level and the performance of nuclear power plants. In the situation, the international nuclear community is continuously emphasizing on the fact that every country pursuing the nuclear energy use must place the nuclear safety in their top priority. With this priority, the international nuclear community has been making effort to ensure and to improve the global nuclear safety through Conventions (Convention on Nuclear Safety and etc.), the development and application of international safety standards and the international cooperation. Among the efforts for global nuclear safety improvement, this paper will show the recent activities of INRA (International Nuclear Regulators' Association), which has a significant impact on international community of nuclear safety