[en] A substitute energy development have been required due to the dry up of the fossil fuel and an environmental problem. Consequently, among substitute energy to be discussed, producing hydrogen from water which does not release carbon is a very promising technology. Also, Iodine-Sulfur(IS) thermochemical water decomposition is one of the promising process which is used to produce hydrogen efficiently using the high temperature gas-cooled reactor(HTGR) as an energy source that is possible to supply heat over 1000 .deg. C. In this study, to make a safety assessment of the hydrogen production using the IS process, an initiating events analysis and an accident scenario modeling considering the relief system were carried out. A method for initiating event identification used the Master Logic Diagram(MLD) that is logical and deductive. As a result, 9 initiating events that cause a leakage of the chemical material were identified. 6 accident scenario based on the initiating event are identified and quantified to the event trees. The frequency of the chemical material leakage produced by IS process is estimated relatively high to the value of 1.22x10^-4/y. Therefore, it requires more effort on safety of the hydrogen production which can be considered as a part of the nuclear system and safety management research to increase social acceptability. Moreover, these methods will be helpful to the safety assessment of the hydrogen production system of the IS process in general

[en] SMART (System-Integrated Modular Advanced Reactor) is under developing by Korea Atomic Energy Research Institute (KAERI) for power generation and seawater desalination. It employs advanced design concepts, therefore it is essential to develop the new Probabilistic Safety Assessment (PSA) validation guidance or add and remove some items in the current PSA review guidance considering the unique characteristics of SMART. In this paper major technical considerations for SMART PSA review are suggested as well as a brief discussion of the essential results from the worldwide documentation that can be used in reviewing PSA

[en] The thermochemical water decomposition cycle is one of the methods for the hydrogen production process from water. The successful continuous operation of the IS-process was demonstrated and this process is one of the thermochemical processes, which is the closest to be industrialized. Currently, Korea has also started a research about the IS process and the construction of the IS process system is planned. In this study, for risk analysis of the IS process, initiating events of the IS process are identified by using the Master Logic Diagram (MLD) which is the method for initiating the event identification. Also, 6 events were identified among 9 initiating events above and performed quantification of events using event tree analysis

[en] Since early 1999, the U.S. Nuclear Regulatory Commission (NRC) has suggested the Reactor Oversight Process (ROP) that is a risk-informed approach to improve the operational safety of nuclear power plants (NPPs). Seven cornerstones in the ROP contain inspection program and performance indicator (PI) to assure that the performance criteria are met. The Significance Determination Process (SDP) is a tool to help that the regulatory staff determine the potential safety significance of inspection findings. Currently, various fields of SDP have been suggested. Among them, fire protection SDP (FPSDP) was developed and implemented to evaluate the safety significance of fire protection inspection findings. The KINS has also proposed a comprehensive implementation R and D plan for achieving risk-informed and performance-based regulation since 2006, which has an objective to optimize current regulatory activities by integrating risk and safety performance information with existing deterministic approaches. As a part of this R and D regulation program, SDP methodology is essential to evaluate the risk significance of inspection findings resulted from risk-informed periodic inspection. In this paper, a FPSDP methodology being used by NRC staff is presented and the feasibility of FPSDP implementation to operating NPPs in Korea is checked

[en] It is well known that on-line maintenance (OLM) has some potential for safety enhancement of operating nuclear power plants. The Korea Institute of Nuclear Safety (KINS) is developing a regulatory framework for OLM implementation under the auspices of MEST. This paper introduces drafts of regulatory technical requirements which will constitute the regulatory framework for OLM

[en] It is well known that on-line maintenance (OLM) has some potential for safety enhancement of operating nuclear power plants. In recent years, Korea Hydro and Nuclear Power Co. Ltd. (KHNP) is eager to apply OLM. Ministry of Education, Science and Technology (MEST) has established the related technology development program as an item of 'Overall Planning on Nuclear Safety(2010-2014)' through acceptance to the request of KHNP in 2009. The Korea Institute of Nuclear Safety (KINS) is developing the assessment technology of safety concerns for OLM under the auspices of MEST. This paper provides various options for accepting OLM within a regulatory framework, considering lack of domestic OLM experience

[en] Radioactive materials would be released to the atmosphere in case severe accidents at nuclear power plants occur. When such an accidental release occurs, the radioactive materials in the plume while dispersing in the atmosphere would be transported by a prevailing wind. As a result, the radioactive materials would contaminate the environment, and finally the population would be exposed to radiation. The consequences resulting from such an accidental release are related to health effects. These consequences are estimated by the method of the in Level 3 PSA. The offsite health effect assessment of an accidental release from a nuclear power plant is a function of many factors such as the source terms, weather condition, emergency response plan, and plant specific data. An assessment of the impact of such releases to the environment and the general public requires the calculation of airborne and ground concentrations of each radionuclide for various distances from the reactor. When they are released into the atmosphere, radioactive gases and aerosols follow prevailing winds and are diffused due to atmospheric turbulence. The prediction of dispersion is most commonly made from the Gaussian plume model using its simplified input requirements and reasonable agreement with experimental data over flat terrain. In this study, we've developed web-based risk assessment simulator by using MACCS2 code (RASUM) with input values of source term, meteorological data, ground data and population distribution data, etc for KSNP (Korea Standard Nuclear Power Plant) when SBLOCA breaks out

[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] Most world-wide operating commercial nuclear reactors are classified in Generation-II category. The Gen-III reactors have just started to be deployed, and Gen-III+ reactors are at the advanced stage of commercialization. Since the safety and reliability of these reactors have had a good grade, it is widely recognized that the nuclear energy has a crucial role to play in mitigating the ever-increasing world energy needs. In 2000, the U.S. Department of Energy (DOE) launched a new program, called Gen-IV Initiative, to broaden the opportunity of nuclear energy utilization by making further advances in nuclear energy systems design. Recently, Very High Temperature Reactor (VHTR) and Sodium-Cooled Fast Reactor (SFR) among the Gen-IV reactors are being considered in domestic companies. The Probabilistic Safety Assessment (PSA) is one of the key technologies for the safety evaluation and licensing of the VHTR and the SFR. In addition, PSA technology takes charge of the important role for risk-informed design and licensing of Gen-IV reactors, so it has been recognized more importantly. In this paper, technical issues of Modular High-Temperature Gas-Cooled Reactor (MHTGR) and Power Reactor Innovative Small Module (PRISM) PSA are identified, and major considerations for the VHTR and SFR PSA review are suggested

[en] The current regulations for nuclear power plants focus on light water reactors (LWRs), and as such they may not be properly applied to non-LWR reactors such as Generation IV Reactors. For instance, there is no plant state comparable to core damage in pebble bed reactors. As a result, the surrogate safety goal based on core-damage frequency (CDF), as being applied to LWRs in many countries directly or indirectly, needs to be somehow modified for such advanced plants. Therefore, there are considerable interests worldwide in developing new licensing structure for advanced nuclear power plants. In this paper, we briefly discuss the new licensing approaches developed by the NRC and suggested by PBMR, Pty. LTD focusing on the two topical areas mentioned above. Next, our insights are given with respect to these approaches along with our suggestions for future research