[en] Hydrogen control in the case of severe accidents has been required by nuclear regulations to ensure the integrity of the nuclear containment building after Three Mile Island (TMI) accidents. Up to now, many experiments have been conducted to estimate the distribution of hydrogen during accidents in nuclear power plants. In this study, local hydrogen behavior has been experimentally investigated in a cylindrical multi-subcompartment mixing chamber of the SNU (Seoul National University) hydrogen mixing facility, measuring the local concentration in various conditions and mixture injection locations. Hydrogen is simulated by helium in the experiments. Results showed remarkably different local behavior of helium in experiments of several conditions, and the local analysis for hydrogen concentration rather than the lumped compartment analysis, used widely in most plants, would be important to ensure the equipment survivability or to determine the positions of ignitors

[en] Hydrogen control in the case of severe accidents has been required by nuclear regulations to ensure the integrity of containment after Three Mile Island (TMI) accidents. Up to now, many experiments have been conducted to estimate the distribution of hydrogen during accidents in nuclear power plants. In this article, we proposed a computer code named HYCA3D developed to calculate the local hydrogen distribution with three-dimensional time-dependent governing equations, which can simulate the transport of multiple species. Also, local hydrogen behavior has been experimentally investigated in a cylindrical multi-subcompartment mixing chamber, measuring the local concentration in various conditions. Hydrogen is simulated by helium in the experiments. The proposed code was verified with these experimental results, followed by pre-tests with EPRI/HEDL standard problems. The calculation results show good agreement with the experimental data

[en] During severe accidents in nuclear power plant (NPP), the limit of local hydrogen concentration is regulated to ensure the integrity of containment. In this study hydrogen mixing experiments were conducted to investigate the hydrogen concentration distribution in a sub-compartment of NPP. The mixing compartment is a vertical rectangular type with the dimension of 1 x 1 x 1.5 m³. The helium gas was used as a simulant of hydrogen. The goals of this study are to understand local hydrogen mixing phenomena and to examine the effects of the wall condensing, of the existence of obstacle and of the containment spray operation on local hydrogen concentration in NPP. Experimental results showed that the hydrogen might be locally accumulated in the sub-compartment and the local hydrogen concentration could instantaneously rise during the spray operation. (authors)

[en] Concerns about the local hydrogen behavior in a nuclear power plant (NPP) containment during severe accidents have increased with the 10CFR50.34(f) regulation after TMI accident. Consequently, investigations on the local hydrogen behaviors under severe accident conditions were required. An analytical model named HYCA3D was developed at Seoul National University (SNU) to predict the thermodynamics and the three dimensional behavior of a hydrogen/steam mixture, within a subdivided containment volume following hydrogen generation during a severe accident in NPPs. In this study, the HYCA3D code was improved with a steam condensation and spray model, and verified with hydrogen mixing experiments executed in a SNU rectangular mixing facility. Helium was used to simulate hydrogen in both the calculations and the experiments. The calculation results show good agreement with the experimental data

[en] In Korea, KHNP has developed the vitrification technology and plans to export the technology to USA, Japan, etc. with much preliminary R&D achievements as well as to adopt it in D&D project towards Kori #1. For the expanding of acceptability of vitrification technology, this paper shows the recent patent trend and presents useful acceptability of the technologies registrated as patent towards D&D project targeting Kori #1 LLW whose decommissioning is expected to start in 2022. 50 patents are registrated by 13 entities for vitrification technology. Especially KHNP, the owner of Kori #1, whose decommissioning is expected in 2022 after the approval of termination plan by KINS, has much registrated the patents and achieved the technology development for vitrification acceptability towards D&D projects. KHNP’s technology is approved as the most useful vitrification technology towards D&D projects for LLW, so it is necessary to merge patent technologies around KHNP’s technology if necessary. And KHNP’s efforts to help the patent registration companies is also required before the start of Kori #1 decommissioning. Based on the experience and upgrade through vitrification technology application at Kori #1 in near future, the patent registration companies around KHNP are expected to enter the world D&D market easily and efficiently with the sole and unique vitrification technology toward LLW generated at D&D sites.50 patents are registrated by 13 entities for vitrification technology. Especially KHNP, the owner of Kori #1, whose decommissioning is expected in 2022 after the approval of termination plan by KINS, has much registrated the patents and achieved the technology development for vitrification acceptability towards D&D projects. And the other companies which want to participate in D&D also contribute the vitrification technology development so far. 50 patents registrated in KIPRIS can contribute to D&D project towards Kori #1 if the characteristics LLW at Kori #1 is clarified and investigated and the merits of each vitrification technology is appealed during the decommissioning of Kori #1.

[en] For the settlement of peace on the Korean peninsula, the complete dismantlement of all North Korean nuclear facilities should be prioritized. However, for the complete denuclearization of North Korea, managing dismantled waste is more important than dismantling North Korean nuclear facilities. In this study, the status of dismantling waste of North Korean nuclear facilities and the treatment method according to waste type are reviewed. Among the waste produced from dismantling of North Korean nuclear facilities, particular waste is high-level liquid waste from reprocessing facility. In order to safely manage these wastes for thousands of years, we can conclude that the best management practices for dismantling wastes of this facility must be vitrification, as can be seen in decades of experience in foreign countries. In addition Korean government should recognize that it is necessary to advance the technology of Uljin vitrification plant through further research for utilization in the dismantling of North Korea reprocessing facility

[en] As the time for the dismantling of the nuclear power plant of Kori No. 1 in Korea approaches, preparations for the disposal of various types and large amounts of radioactive waste generated during the dismantling process are urgently needed. In this study, the conceptual design of a Mobile Compaction Facility for treatment and volume reduction of incombustible radioactive waste, which occupies about 90% of the volume of nuclear power plant decommissioning waste, was conducted. Differentiated design elements for improvement were derived by analyzing the problems of existing radioactive waste compaction facilities. In order to determine the compacting force suitable for the purpose of this study, a supercompaction experiment was performed by selecting simulated dismantled waste, and the International Standardization Organization (ISO) container and the outline shape and moving parts of trailer-based mobile compaction type volume reduction facility were implemented as a 3D model. Based on this, a design concept of a variable stroke method that can be used for both 200 L and 320 L drums and utilizes limited installation space was introduced. The mobile compaction facility developed through this study has improved economic efficiency and operational convenience compared to the supercompaction facility, and is expected to reduce the risk of radiation exposure of workers. Therefore, it is expected to be a facility for reducing the volume of nuclear power dismantling waste that can be useful when dismantling nuclear power plants

[en] Considering workers and public safety, the low and intermediate-level waste (LILW), which is generated from nuclear power plants (NPPs), should be transported with the codes related with domestic and international regulations. Transport container of IP-2 Type should be also designed to meet the technical standard from the related codes. In this article, radiation shielding evaluation for the transport container, in which the wastes in the interim storage facilities of NPPs could be transported, is introduced briefly. From the analysis surface dose rate of the waste drum that could be carried through the container was evaluated

[en] A spray system in a containment of a nuclear power plant is required to be installed in order for the integrity of the containment by its heat removal functionality during an accident. It is known that the spray system can affect the behaviors of the hydrogen generated by an oxidation of a fuel cladding and released in the containment during a severe accident, which must be considered for the hydrogen safety. The spray effects can be described as follows in view of the hydrogen safety. The good point of the effects is to help the mixing of the hydrogen and finally reduce its concentration. But the bad point is that the spray can also reduce the steam concentration by condensing it, and increase the hydrogen concentration locally. Those spray effects on the hydrogen behaviors are dependent on the specifications of the spray system and accident scenarios. So, it is necessary to quantify the spray effects on the hydrogen behaviors during a severe accident for an interesting containment. The GASFLOW code has been used to study the hydrogen behaviors and the effectiveness of the hydrogen mitigation system in the APR1400 during a severe accident. As a continuous work, the effects of the spray system of the APR1400 are evaluated by the GASFLOW analysis during LOCAs in view of the hydrogen safety. For the validation of the spray model included in the GASFLOW code, the TOSQAN experiment is analyzed with the code

[en] To reduce Occupational Radiation Dose (ORD) effectively and enhance the radiological safety, the comprehensive assessment of the experiences to reduce ORD should be made by regulatory body as well as utilities. Hence, the objective of this study is to assess the experiences for reducing ORD from the regulatory viewpoint. With the research objective, the followings are performed in this research; analysis of occupational dose trends at domestic and foreign NPPs, identification of the effective technologies for reducing ORD, examination of the effects of the technologies for reducing ORD, derivation of the regulatory means for implementing he research results. From this study, the regulatory means for effective reduction of ORD are derived. Hence, the results can be utilized as a basic materials for ALARA requirements