• Korean Journal of Metals and Materials
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• v.50 no.10
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• pp.721-728
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• 2012

This paper evaluates the reliability of creep rupture life under service conditions of Alloy 617, which is considered as one of the candidate materials for use in a very high temperature reactor (VHTR) system. A Z-parameter, which represents the deviation of creep rupture data from the master curve, was used for the reliability analysis of the creep rupture data of Alloy 617. A Service-condition Creep Rupture Interference (SCRI) model, which can consider both the scattering of the creep rupture data and the fluctuations of temperature and stress under any service conditions, was also used for evaluating the reliability of creep rupture life. The statistical analysis showed that the scattering of creep rupture data based on Z-parameter was supported by normal distribution. The values of reliability decreased rapidly with increasing amplitudes of temperature and stress fluctuations. The results established that the reliability decreased with an increasing service time.

• Korean Journal of Metals and Materials
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• v.49 no.6
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• pp.462-467
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• 2011

In order to understand why annealing at $480^{\circ}C$ for several hour prevents the initiation of PWSCC, the residual stress variation with isothermal annealing at $480^{\circ}C$ and isochronal annealing between 480 and $800^{\circ}C$ in cold rolled Alloy 600 was investigated by the XRD method. The isothermal annealing decreased residual stress slightly in the rolling direction but not in the transverse direction, whereas the isochronal annealing for two hours increased residual stress. It seemed that the decrease in residual stress by isothermal annealing was due to lattice contraction by an ordering reaction because the isothermal annealing increased hardness. The effects of the isochronal annealing could be interpreted as the influence of thermal expansion and a disordering reaction.

• Korean Journal of Metals and Materials
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• v.50 no.10
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• pp.703-710
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• 2012

The effects of the ordering reaction on high temperature mechanical behavior is investigated by tensile tests at $2{\times}10^{-2}/s-3.3{\times}10^{-5}/s$ up to $745^{\circ}C$. The tensile deformed region is examined by differential scanning calorimeter (DSC), TEM, and high resolution neutron diffraction (HRPD). The results showed that a plateau of tensile strength appeared at $150-500^{\circ}C$ whereas the elongation minimum occurred at about $600^{\circ}C$. This suggests that the occurrence of a plateau does not cause the elongation minimum. The temperature of the elongation minimum decreases with the strain rate. HRPD results show a lattice contraction in the tensile deformed specimen at the temperature of the plateau occurring region. The plateau of tensile strength, the lattice contraction, and the occurrence of serration appeared in the same temperature region.

• Korean Journal of Metals and Materials
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• v.47 no.10
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• pp.613-620
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• 2009

The Kachanov-Rabotnov (K-R) creep model was proposed to accurately model the long-term creep curves above $10^5$ hours of Alloy 617. To this end, a series of creep data was obtained from creep tests conducted under different stress levels at $950^{\circ}C$. Using these data, the creep constants used in the K-R model and the modified K-R model were determined by a nonlinear least square fitting (NLSF) method, respectively. The K-R model yielded poor correspondence with the experimental curves, but the modified K-R model provided good agreement with the curves. Log-log plots of ${\varepsilon}^{\ast}$-stress and ${\varepsilon}^{\ast}$-time to rupture showed good linear relationships. Constants in the modified K-R model were obtained as ${\lambda}$=2.78, and $k=1.24$, and they showed behavior close to stress independency. Using these constants, long-term creep curves above $10^5$ hours obtained from short-term creep data can be modeled by implementing the modified K-R model.

• Korean Journal of Metals and Materials
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• v.47 no.12
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• pp.819-827
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• 2009

This work is concerned with a statistical analysis of factors affecting the irradiation-assisted stress corrosion cracking (IASCC) of austenitic stainless steels for core internals of pressurized water reactors (PWR). The microstructural and environmental factors were reviewed and critically evaluated by the statistical analysis. The Cr depletion at grain boundary was determined to have no significant correlation with the IASCC susceptibility. The threshold irradiation fluence of IASCC in a PWR was statistically calculated to decrease from 5.799 to 1.914 DPA with increase of temperature from 320 to $340^{\circ}C$. From the analysis of the relationship between applied stress and time-to-failure of stainless steel components based on an accelerated life testing model, it was found that B2 life of a baffle former bolt exposed to neutron fluence of 20 and 75 DPA was at least 2.5 and 0.4 year, respectively, within 95% confidence interval.

• Korean Journal of Metals and Materials
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• v.47 no.5
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• pp.283-289
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• 2009

This paper dealt with a statistical analysis for evaluating the creep crack growth rate (CCGR) for Modified 9Cr-1Mo (ASTM Grade 91) steel. The CCGR data was obtained by the creep crack growth (CCG) tests conducted under various applied loads at $600^{\circ}C$. To obtain logically the B and q values used in the CCGR equation, three methods such as the least square fitting method (LSFM), the mean value method (MVM) and the probabilistic distribution method (PDM) were adopted and their CCGR lines were compared, respectively. In addition, a number of random variables were generated by using the Monte Carlo simulation (MCS), and the CCGR lines were predicted probabilistically. It was found that both the B and q coefficients followed a 2-parameter Weibull distribution well. In the case of the ranges of 10-90% for the probability variables, P(B, q), the CCGR lines were predicted. Fractographic study was conducted from the specimen after the CCG tests.

• Journal of the Korean Society of Safety
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• v.12 no.4
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• pp.241-248
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• 1997

This paper presents the development procedure and application of the generic component reliability data base considering the dependency among dependent generic compendia in NPPs (Nuclear Power Plants) PSA (Probabilistic Safety Assessment) under construction or without operating history. We use MPRDP (Multi-Purpose Reliability Data Processor) code developed in KAERI (Korea Atomic Energy Research Institute) based on a PEB (Parametric Empirical Bayesian) procedure to estimate the reliability. The employed model in this study accounts for the relative credibility as well as the dependency among generic estimates. Numerical examples and the part of summarized reliability data table are provided as the application.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.9 no.3
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• pp.181-189
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• 2011

The smooth construction and operation of nuclear facilities requires understanding and support of both the local residents and the national people. It is essential that our country, which should maintain using nuclear energy for national energy security and economic growth, shall improve the social acceptance of nuclear energy. In order to identify the level of social acceptance of nuclear energy, this study investigated the perception of the local residents in Gyeongju and the public in other areas on a nuclear power plant and a low- and intermediate-level radioactive waste disposal facility through an individual interview. The subjects of the investigation were 450 persons. This study identified that perceptions of the respondents were somewhat dependent on the residential area, and derived the implications to be reflected in establishing the customized public-relation strategies.

• Journal of Radiation Industry
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• v.7 no.2_3
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• pp.177-182
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• 2013

This study was conducted to evaluate the effect of gamma irradiation on the microbial populations of dried raw materials (9 products) and Saengsik powder. The samples were gammairradiated at doses of 2, 4, 6 and 8 kGy and the microbiological populations were evaluated. The total numbers of bacteria and Bacillus cereus in non-irradiated dried-raw materials for Saengsik powder was 1.3~3.4 and $1.7{\sim}2.4log\;CFU\;g^{-1}$. However, gamma irradiation reduced the microbiological populations in all samples, and Saengsik powder were sterilized at more than 6 kGy. Moreover, Clostridium perfringens were not observed in all samples within detection limit (<$1log\;CFU\;g^{-1}$). Therefore, the results of this study suggest that gamma irradiation at 6 kGy is sufficient to sterilize Saengsik powder, and thus, irradiated Saengsik powder at 6 kGy fulfills the microbiological requirements for sterilized food.

• Journal of Radiation Industry
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• v.9 no.3
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• pp.153-159
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• 2015

Reliability of printed circuit board (PCB), which is based on high integrated circuit technology, is having been important because of development of electric and self-driving car. In order to answer these demand, automated X-ray inspection (AXI) is best solution for PCB non-destructive test. PCB is consist of plastic, copper, and, lead, which have low to high Z-number materials. By using dual energy X-ray imaging, these materials can be inspected accurately and efficiently. Dual energy X-ray imaging, that have the advantage of separating materials, however, need some solution such as energy separation method and enhancing efficiency because PCB has materials that has wide range of Z-number. In this work, we found out several things by analysis of X-ray energy spectrum. Separating between lead and combination of plastic and copper is only possible with energy range not dose. On the other hand, separating between plastic and copper is only with dose not energy range. Moreover the copper filter of high energy part of dual X-ray imaging and 50 kVp of low energy part of dual X-ray imaging is best for efficiency.