[en] The safety Significance Determination Process (SDP), being applied by USNRC, is one of regulatory approaches which can improve the regulatory effectiveness and efficiency by utilizing the risk information to any regulatory inspections and issue resolution. The decision-making criteria and some risk thresholds for the determination of significance can be, therefore, essential elements in actual SDP implementation. Based on USNRC's experiences, this study has the purpose to identify the rationale and background for the determination of significance and to check the feasibility of the implementation to Korean nuclear power plants. Our attentions have been basically concentrated on establishing its step-by-step processes, identifying the current issues, and assessing major issues for the application to domestic plants. Practically, two examples have been analyzed after consulting the database on our actual regulatory inspections and incidents

[en] For the purpose of keeping up the capability for independent regulatory audit of risk information, we developed an PSA model, independent on that of the licensee. The developed regulatory PSA model, as named MPAS (Multi-purpose Probabilistic Analysis of Safety), is primarily based on the result of feasibility study about ASME PSA standard and done by the cooperation work with KAERI PSA research team. Current MPAS model is limited to the work scope on Level 1 internal full power analysis, which is finally implemented for the KSNP. The development of MPAS model consists of plenty of works establishing overall items which comprehensively implements all subjects such as detailed logic and input data for each analysis fields. In addition, relevant computational framework utilizing PSA and risk monitoring codes is also developed for users' convenience

[en] The synthesis of aluminum nitride (AlN) powders was carried out by combustion of aluminum (Al) powder under low nitrogen pressure (less than or (double) equal 0.5 MPa) with carbon black (CB) as the dispersion agent to prevent the coalescence of the aluminum. The combustion was successful when the weight ratio between CB and Al, CB/Al, ranged from 0.02 to 1.5, while the combustion failed at CB/Al=0 (pure Al) or 1.75. As CB/Al varied, different combustion behaviors were observed: steady, unsteady and spin combustion. The combustion temperature and velocity reached the respective maximum at an intermediate CB/Al value (0.2). The measured combustion temperature quantitatively agrees with the adiabatic temperature calculated from a thermodynamic analysis for various CB/Al. The as-synthesized AlN product had various morphologies: aggregated fine particles, flakes, aggregated faceted particles, honeycomb-like microstructure, as well as hexagonal crystals. It was found that the hexagonal crystal structure was favored when CB/Al=0.2 and 0.5. The combustion temperature at these ratios was larger than those synthesized at different CB/Al ratios. The reaction yield monotonically increased with the increasing CB/Al up to a ratio of 1.25. The maximum reaction yield at CB/Al=1.25 did not correspond to the largest combustion temperature. An increase of nitrogen pressure greatly increased both the combustion temperature and velocity, and the reaction yield was moderately enhanced. The experimental reaction yield agreed well with the theoretical reaction yield based on a diffusion-limited core-shell model

[en] In this study, the state-of-the art for estimating LERF is considered for the regulatory risk-informed decisions. The consideration is mainly focused on (1) the relationship between Level 2 PSA and LERF evaluation methodology, (2) the standard requirements in terms of modeling preparation and the acceptance criteria based on the application capability II of ASME PRA standard, and (3) some pending issues for developing and proposing a simplified LERF model. This study is preliminarily presented and will be updated for establishing detailed evaluation scheme of extended MPAS (multi-purpose probabilistic analysis of safety) model and preparing the technical basis

[en] In order to confirm whether the regulatory consistency is maintained in the relationship between the traditional practices and the risk-informed approach, it is necessary to identify that both are not different in view of the defense-in-depth(DID) philosophy, where the former is mainly based on the conservatism such as single failure criteria and safety margin, on the other hand, the latter is focused on the realism in the actual implementation. In this study, the attributes of risk insights are firstly identified for each DID level, which can be classified in the overall accident progression from the incident prevention to the ultimate public radiological protection. Risk criteria are provided for the implementation of these risk-informed DID attributes. In addition, more detailed risk acceptance criteria are suggested, considering some DID-related areas for the actual application of risk criteria

[en] In order to give the technical basis to the safety goals which are proposed from the regulatory aspect for domestic nuclear power plants, the characteristics of technical issues like uncertainties, occurred in developing probabilistics safety criteria (PSC) and in defining the risk concept have been investigated. Based on the categorization of root causes of each uncertainty occurred during calculation of the PSC measures like core damage frequency, a simple uncertainty calcuation and some PSC comparison studies for various plant types have been performed. As a result, it was found that the analysis quality inadequacy, modeling error, and database incompleteness, which could be generally occurred during PSA, are major factors causing increase of the bias/deviation of the PSC measures at final stage

[en] Molecular sizing potency results are presented for irradiated samples of one lot of Haemophilus b conjugate vaccine, pneumococcal polysaccharide type 6B and typhoid vi polysaccharide vaccine. The samples were irradiated (25 kGy) by gamma rays, electron beams and X-rays. IgG and IgM antibody response in mice test results (ELISA) are given for the Hib conjugate vaccine irradiated at 0 deg. C or frozen in liquid nitrogen

[en] This project aims to develop the detailed regulatory technology for the severe accident prevention and mitigation, and severe accident management to implement the nuclear safety policy statement of the MOST. The confirmatory analysis technology such as the improvement of the major analysis modelling (MELCOR and SR5 codes) of KNPP and the fission product behavior evaluation and the regulatory guideline such as the performance review guideline for maintaining containment integrity (draft) are developed for the regulatory research of the severe accident prevention and mitigation. Regulatory research of the severe accident management are performed to develop the safety review guideline of the accident management program (draft) and the regulatory review guideline for the accident management strategy (draft)

[en] The conventional scope of In-service test and Motor-Operated valve test in NPP includes safety-related components and their test intervals in same components are identical regardless of their safety importance. It means that excessive effort has been given to low significant components in view of operational risk. Recently, US Utilities have tried to adjust the test frequency according to the PSA risk as well as deterministic consideration regarding components (Risk-informed). R-I method has been being implemented in numerous US plants. This study intends to prepare the regulatory guidelines on future Korean licensee's submittal for license of RI-IST and RI-MOV. It contains regulatory insights for regulatory review and inspection as well

[en] In order to provide the technical rationale for future risk-informed regulatory applications, four essential regulatory areas, i.e., PSA regulatory audit model, quality certification procedure on PSA, risk-informed performance indicator, and risk monitoring were surveyed, and the corresponding state-of- technology for each area was summarized. Actually, this study was performed by way of the analysis and in-depth survey on the previous experience done by any individual organizations like USNRC or US NEI, as well as the international organizations like IAEA or OECD/NEA. Through the survey results, we might look for the regulatory positions on national development