• Nuclear Engineering and Technology
• /
• v.53 no.5
• /
• pp.1524-1533
• /
• 2021

The structural stability of a waste package is essential for containing radioactive waste for the long term in a repository. A silo-type disposal facility would require more severe verification for the structural integrity, because of radioactive waste packages staked with several tens of meters and overburdens of crushed rocks and shotcretes. In this study, structural safety was analyzed for a silo-type repository, located approximately 100 m below sea level in Gyeongju, Korea. Finite element simulation was performed to investigate the influence of the loads from the backfilling materials and waste package stacks on the mechanical stress of the disposed of wastes and containers. It was identified that the current design of the waste package and the compressive strength criterion for the solidified waste would not be enough to maintain structural stability. Therefore, an enhanced criterion for the compressive strength of the solidified waste and several reinforced structural designs for the disposal concrete container were proposed to prevent failure of the waste package based on the results of parametric studies.

• Nuclear Engineering and Technology
• /
• v.49 no.1
• /
• pp.103-112
• /
• 2017

Application of the supercritical condition in reactor core cooling needs to be properly justified based on the extreme level of parameters involved. Therefore, a numerical study is presented to compare the thermalhydraulic performance of supercritical and single-phase natural circulation loops under low-to-intermediate power levels. Carbon dioxide and water are selected as respective working fluids, operating under an identical set of conditions. Accordingly, a three-dimensional computational model was developed, and solved with an appropriate turbulence model and equations of state. Large asymmetry in velocity and temperature profiles was observed in a single cross section due to local buoyancy effect, which is more prominent for supercritical fluids. Mass flow rate in a supercritical loop increases with power until a maximum is reached, which subsequently corresponds to a rapid deterioration in heat transfer coefficient. That can be identified as the limit of operation for such loops to avoid a high temperature, and therefore, the use of a supercritical loop is suggested only until the appearance of such maxima. Flow-induced heat transfer deterioration can be delayed by increasing system pressure or lowering sink temperature. Bulk temperature level throughout the loop with water as working fluid is higher than supercritical carbon dioxide. This is until the heat transfer deterioration, and hence the use of a single-phase loop is prescribed beyond that limit.

• ETRI Journal
• /
• v.30 no.6
• /
• pp.790-798
• /
• 2008

Recently, NAND flash memory has emerged as a next generation storage device because it has several advantages, such as low power consumption, shock resistance, and so on. However, it is necessary to use a flash translation layer (FTL) to intermediate between NAND flash memory and conventional file systems because of the unique hardware characteristics of flash memory. This paper proposes a new clustered FTL (CFTL) that uses clustered hash tables and a two-level software cache technique. The CFTL can anticipate consecutive addresses from the host because the clustered hash table uses the locality of reference in a large address space. It also adaptively switches logical addresses to physical addresses in the flash memory by using block mapping, page mapping, and a two-level software cache technique. Furthermore, anticipatory I/O management using continuity counters and a prefetch scheme enables fast address translation. Experimental results show that the proposed address translation mechanism for CFTL provides better performance in address translation and memory space usage than the well-known NAND FTL (NFTL) and adaptive FTL (AFTL).

• English Language & Literature Teaching
• /
• v.12 no.4
• /
• pp.185-210
• /
• 2006

This study has two purposes. First, it aims to suggest an appropriate approach to English writing education for Korean high school students in a cooperative learning situation. It also aims to suggest what type of learner grouping, either homogeneous or heterogeneous, is appropriate by comparing the learners' writing abilities and the changes of their affective factors after being exposed to cooperative EFL writing instruction. Two homogeneous classes were selected and instructed to write in English for 11 weeks. One was composed of homogeneous small groups based on the students' writing scores, and the other was composed of heterogeneous small groups, again based on the students' writing scores. The results showed that the improvement between the two class types was quite different across different proficiency levels. For example, although there is little difference between the homogeneous and the heterogeneous classes of low and intermediate-level learners in writing ability improvement, high-level students showed a significant difference between the classes. In addition, it was found that class participation correlated significantly to writing ability improvement. Cooperative learning was proved to be an effective writing instructional approach to encourage learners' interest and increase their self-confidence; however, the results did not show any significant differences in learners' affective domain between the homogeneous and the heterogeneous classes. Similarly, the learners' grouping preference was not affected by the grouping method.

• Korean Journal of Materials Research
• /
• v.25 no.9
• /
• pp.429-434
• /
• 2015

Resistance switching memory cells were fabricated using atomically dispersed Pt-$SiO_2$ thin film prepared via RF co-sputtering. The memory cell can switch between a low-resistance-state and a high-resistance-state reversibly and reproducibly through applying alternate voltage polarities. Percolated conducting paths are the origin of the low-resistance-state, while trapping electrons in the negative U-center in the Pt-$SiO_2$ interface cause the high-resistance-state. Intermediate resistance-states are obtained through controlling the compliance current, which can be applied to multi-level operation for high memory density. It is found that the resistance value is related to the capacitance of the memory cell: a 265-fold increase in resistance induces a 2.68-fold increase in capacitance. The exponential growth model of the conducting paths can explain the quantitative relationship of resistance-capacitance. The model states that the conducting path generated in the early stage requires a larger area than that generated in the last stage, which results in a larger decrease in the capacitance.

• Journal of Nutrition and Health
• /
• v.32 no.4
• /
• pp.394-400
• /
• 1999

Since it has generally been considered that high-hat diets promote carcinogenesis, fat intake of less than 30% of total calories has been recommended to reduce the risk of cancer. Specific dietary guidelines for fat intake to reduce the risk of colon cancer have not yet been established. In order to determine the level of dietary fat needed the risk of colon cancer, rats were fed one of four experimental fat diets, very low(7% of total calories from corn oil, VLC), low(15% LC), medium (30%, MC), and high fat(45%, HC). Cell proliferation as an intermediate biomarker of color carcinogenesis was measured by the in vivo incorporation of bromodeoxyuridine into DNA. Fecal lipid excretion was measured by gravimetric method. As fat levels in the diet increased, fecal lipid concentrations also increased (VLC

• Asian Pacific Journal of Cancer Prevention
• /
• v.16 no.6
• /
• pp.2527-2530
• /
• 2015

Background: The cancer of the prostate risk assessment (CAPRA) score has been defined to predict prostate cancer recurrence based on the pre-clinical data, then pathological data have also been incorporated. Thus, CAPRA post-surgical (CAPRA-S) score has been developed based on six criteria (prostate specific antigen (PSA) at diagnosis, pathological Gleason score, and information on surgical margin, seminal vesicle invasion, extracapsular extension and lymph node involvement) for the prediction of post-surgical recurrences. In the present study, biochemical recurrence (BCR)-free probabilities after open retropubic radical prostatectomy (RP) were evaluated by the CAPRA-S scoring system and its three-risk level model. Materials and Methods: CAPRA-S scores (0-12) of our 240 radical prostatectomies performed between January 2000-May 2011 were calculated. Patients were distributed into CAPRA-S score groups and also into three-risk groups as low, intermediate and high. BCR-free probabilities were assessed and compared using Kaplan-Meier analysis and Cox proportional hazards regression. Ability of CAPRA-S in BCR detection was evaluated by concordance index (c-index). Results: BCR was present in 41 of total 240 patients (17.1%) and the mean follow-up time was $51.7{\pm}33.0$ months. Mean BCR-free survival time was 98.3 months (95% CI: 92.3-104.2). Of the patients in low, intermediate and high risk groups, 5.4%, 22.0% and 58.8% had BCR, respectively and the difference among the three groups was significant (P = 0.0001). C-indices of CAPRA-S score and three-risk groups for detecting BCR-free probabilities in 5-yr were 0.87 and 0.81, respectively. Conclusions: Both CAPRA-S score and its three-risk level model well predicted BCR after RP with high c-index levels in our center. Therefore, it is a clinically reliable post-operative risk stratifier and disease recurrence predictor for prostate cancer.

• Proceedings of the Korean Radioactive Waste Society Conference
• /
• 2005.11a
• /
• pp.126-133
• /
• 2005

Securing of radioactive waste disposal site and the related operations for disposal of low and intermediate level radioactive waste is being actively carried out in Korea. For disposal of radioactive wastes, physicochemical and radiological status and integrity of radioactive wastes must be secured first. Also, waste generators must provide this information to disposers. In addition, to secure the safety of waste disposal, waste acceptance criteria (WAC) and site specific waste acceptance criteria (SWAC) to consider characteristics of the disposal site are required. Radioactive wastes must be processed, generated, managed and transferred in accordance with these criteria. [1] For this, evaluation of properties on each of the radioactive wastes must be performed. However, in reality, atomic power plants are experiencing difficulties in relation to this due to the large quantity of radioactive waste generation. In order to solve this problem, IAEA and major overseas countries have developed, thus are using waste certification program (WCP) and quality assurance program (QAP) [2,3]. On the basis of these programs, radioactive waste certification program has been developed for safe disposal of radioactive wastes in Korea to satisfy the provisions specified in 'low and intermediate level radioactive waste transfer guidelines' of announcement No. 2005-18 from the Ministry of Science and Technology and specific site waste acceptance criteria (tentative plan). In addition, it is being planned to administer amendment on commercial atomic power plant related procedures and ensile staff training in order for early introduction and operation of radioactive waste certification system.

• Journal of Korean Tunnelling and Underground Space Association
• /
• v.24 no.1
• /
• pp.39-55
• /
• 2022

This study carried out the laboratory tests for AE signal attenuation to determine the attenuation coefficient (α) of silo concrete in Gyeongju low and intermediate-level disposal environments. The concrete samples were prepared by satisfying the concrete mixing ratio used in the Gyeongju disposal silo, and these samples were additionally exposed depending on the temperature conditions and saturation and, dry condition. As a result of attenuation tests according to the transmission distance on three concrete specimens for each disposal condition, the AE amplitude and absolute energy measured on the saturated concrete were higher than that of the dry concrete in the initial range of the signal transmission distance, but the α of the saturated concrete was higher than that of the dry concrete. Regardless of the saturation and dry conditions, the α tended to decrease as the temperature increases. The α had a more major influence on the saturation and dry condition than the temperature condition, which means that the saturation and dry condition is the main consideration in measuring the signal attenuation of a concrete disposal structure. The α of concrete in the disposal environment expect to be used to predict the integrity of silos concrete in Gyeongju low and intermediate-level disposal environments by estimating the actual AE parameter values at the location of cracks and to determine the optimum location of sensors.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
• /
• v.15 no.2
• /
• pp.161-172
• /
• 2017

To evaluate radiological impact from the operation of a low- and intermediate-level radioactive waste disposal facility, a logical presentation and explanation of expected accidental scenarios is essential to the stakeholders of the disposal facility. The logical assessment platform and procedure, including analysis of the safety function of disposal components, operational hazard analysis, operational risk analysis, and preparedness of remedial measures for operational safety, are improved in this study. In the operational risk analysis, both design measures and management measures are suggested to make it possible to connect among design, operation, and safety assessment within the same assessment platform. For the preparedness of logical assessment procedure, classification logic of an operational accident is suggested based on the probability of occurrence and consequences of assessment results. The improved assessment platform and procedure are applied to an operational accident analysis of the Korean low- and intermediate-level radioactive waste disposal facility and partly presented in this paper.