Yanggu, South Korea
Yanggu, South Korea

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Kim D.,KAIST | Kim D.,Korea Atomic Energy Research Institute | Lee H.J.,KAIST | Jang C.,KAIST | Yoon D.J.,KHNP Central Research Institute
Journal of Nuclear Materials | Year: 2013

The hot steam corrosion behavior of Alloy 617 and Haynes 230 were evaluated in corrosion tests performed at 900 °C in steam and steam + 20 vol.% H 2 environments. Corrosion rates of Alloy 617 was faster than that of Haynes 230 at 900 °C in steam and steam + 20 vol.% H2 environments. When hydrogen was added to steam, the corrosion rate was accelerated because added hydrogen increased the concentration of Cr interstitial defects in the oxide layer. Isolated nodular MnTiO3 oxides were formed on the MnCr2O4/ Cr2O 3 oxide layer and sub-layer Cr2O3 was formed in steam and steam + 20 vol.% H2 for Alloy 617. On the other hand, a MnCr2O4 layer was formed on top of the Cr 2O3 oxide layer for Haynes 230. The extensive sub-layer Cr2O3 formation resulted from the oxygen or hydroxide inward diffusion in such environments. When hydrogen was added, the initial surface oxide morphology was changed from a convex shape to platelets because of the accelerated diffusion of cations under the oxide layer. © 2013 Elsevier B.V. All rights reserved.

Yang K.-H.,Kyonggi University | Mun J.-H.,Kyonggi University | Cho M.-S.,KHNP Central Research Institute | Kang T.H.-K.,Seoul National University
ACI Structural Journal | Year: 2014

This study aims to develop a simple and rational stress-strain model that is applicable to unconfined concretes in compression, covering a wide range of compressive strengths between 10 and 180 MPa (1.5 and 26.1 ksi) and concrete densities between 1200 and 4500 kg/m3 (75 and 280 lb/ft3). In developing the stressstrain model, the modulus of elasticity, the strain at peak stress, and the strain at 50% of the peak stress on the descending branch were formulated using regression analysis of 3295, 415, and 96 data points, respectively. Numerical and statistical analyses were then performed to derive equations for the key parameter determining the shapes of the ascending and descending branches of the stress-strain curves. The reliability of the developed model was confirmed by comparisons with actual stress-strain curves obtained from 100 specimens with different compressive strengths and densities. On the other hand, other existing models were shown to have limitations for use on lightweight concrete, heavyweight concrete, and high-strength concrete. © 2014, American Concrete Institute.

Kim H.G.,KHNP Central Research Institute | Kong T.Y.,KHNP Central Research Institute
Radiation Protection Dosimetry | Year: 2012

In general, internal exposure from tritium at pressurised heavy water reactors (PHWRs) accounts for ~20-40 % of the total radiation dose. Tritium usually reaches the equilibrium concentration after a few hours inside the body and is then excreted from the body with an effective half-life in the order of 10 d. In this study, tritium metabolism was reviewed using its excretion rate in urine samples of workers at Korean PHWRs. The tritium concentration in workers' urine samples was also measured as a function of time after intake. On the basis of the monitoring results, changes in the tritium concentration inside the body were then analysed. © The Author 2012. Published by Oxford University Press. All rights reserved.

Kim H.G.,KHNP Central Research Institute | Kong T.Y.,KHNP Central Research Institute
Radiation Protection Dosimetry | Year: 2012

During a maintenance period at a Korean nuclear power plant, internal exposure of radiation workers occurred by the inhalation of. 131I that was released into the reactor building from a primary system opening due to defective fuels. The internal activity in radiation workers contaminated by. 131I was immediately measured using a whole body counter (WBC). A whole body counting was performed again a few days later, considering the factors of equilibrium in the body. The intake and the committed effective dose were estimated based on the WBC results. The intake was also calculated by hand, based on both the entrance records to the reactor building, and the counted results of the air concentration for. 131I were compared with the whole body counting results. © The Author 2012. Published by Oxford University Press. All rights reserved.

Youn B.-S.,KHNP Central Research Institute
International Congress on Advances in Nuclear Power Plants, ICAPP 2014 | Year: 2014

An integral effect test for a main stem line break (MSLB) was performed with the ATLAS (Advanced Thermal-Hydraulic Test Loop for Accident Simulation) by KAERI. A MSLB is defined as a pipe break in the main steam system. This data was used to validate the safety analysis code SPACE (Safety and Performance Analysis Code for Nuclear Power Plants). In the test, a double-ended guillotined break of the main steam line was simulated. After a steady-state was reached, the test was started by opening the break simulation valves. With the start of the test, the pressure of the secondary system was decreased rapidly, which is the set-point of the LSGP signal. With the occurrence of the LSGP signal, the secondary system was isolated. The SIP actuation signal was issued by the LPP signal. When the MSLB event was initiated by opening the break simulation valve, the SG was depressurized. The calculation results and experimental values differed due to the difference in the flow rate corresponding to the break point. In order to validate the SPACE code, a double-ended guillotine break of the main steam line at ATLAS was simulated. Most of the results were identical between the experiment data and the code values.

Lee H.C.,KHNP Central Research Institute
Applied Chemistry for Engineering | Year: 2013

ETA (ethanolamine), a pH control agent, has been used as an ammonia substitute in the secondary system of nuclear power plants since 2001. It is impossible to remove ETA from the wastewater treatment system in the nuclear power plant operating currently, because it is the non-biodegradable organics in terms of the environmental. The optimum process and chemicals for the removal of chemical oxygen demand (COD) & N with the field sample were investigated. More than 95% of Ammonium ions, contained much in wastewater, was removed with a diffused aeration system. COD could be removed over 90% through the process that includes the oxidation with mixed peroxidants (sodium persulfate/sodium percarbonate) followed by the physicochemical treatment with coagulants.

Kwak H.-G.,Korea Advanced Institute of Science and Technology | Kwon Y.,KHNP Central Research Institute
Annals of Nuclear Energy | Year: 2016

This paper proposes a modified stress-strain relation for bonded internal tendon in containment structures on the basis of the tension stiffening effect and the bond characteristics between a tendon and its surrounding concrete. Differently from general approaches for the consideration of bond-slip, which take the double nodes in defining the displacement field, the proposed model indirectly considers the bond-slip effect through the modification for the stress-strain relation of tendon. Since the proposed tendon model takes into account the bond-slip effect without taking double nodes in the numerical modeling of containment structures, it can effectively be implemented into commercialized programs which have a lot of limitation in considering the bond-slip effect at large complex containment structures. The solution algorithm for an un-bonded internal tendon whose structural response is not section-dependent but member-dependent is also introduced. The different structural responses from those in bonded tendon are evaluated by successive iterations and finally considered by the additional modification for the stress-strain relation of tendon. The validity of the proposed tendon model is verified through correlation studies between analytical and experimental results for PSC beams and 1/4 PCCV containment structures. © 2016 Elsevier B.V. All rights reserved.

Lee Y.,KHNP Central Research Institute | Won Y.,KHNP Central Research Institute | Kang K.,KHNP Central Research Institute
Radiation Protection Dosimetry | Year: 2015

Passive integrating dosemeters [thermoluminescent dosimeter (TLD) and optically stimulated luminescence (OSL)] are the only legally permitted individual dosemeters for occupational external radiation exposure monitoring in Korea. Also its maximum issuing cycle does not exceed 3 months, and the Korean regulations require personal dosemeters for official assessment of external radiation exposure to be issued by an approved or rather an accredited dosimetry service according to ISO/IEC 17025. KHNP (Korea Hydro & Nuclear Power, LTD), a unique operating company of nuclear power plants (NPPs) in Korea, currently has a plan to extend a TLD issuing cycle from 1 to 3 months under the authors' fading error criteria, ±10 %. The authors have performed a feasibility study that minimises post-irradiation fading effects within their maximum reading cycle employing preheating technique. They repeatedly performed irradiation/reading a bare TLD chip to determine optimum pre-heating conditions by analysing each glow curve. The optimum reading conditions within the maximum reading cycle of 3 months were decided: a pre-heating temperature of 165°C, a pre-heating time of 9 s, a heating rate of 25°C s-1, a reading temperature of 3008C and an acquisition time of 10 s. The fading result of TLD-600 and TLD-700 carried by newly developed time temperature profile (TTP) showed a much smaller fading effect than that of current TTP. The result showed that the fading error due to a developed TTP resulted in a ~5 % signal loss, whereas a current TTP caused a ~15 % loss. The authors also carried out a legal performance test on newly developed TTP to confirm its possibility as an official dosemeter. The legal performance tests that applied the developed TTP satisfied the criteria for all the test categories. © The Author 2014. Published by Oxford University Press. All rights reserved.

Chang C.-J.,KHNP Central Research Institute
Nuclear Engineering and Technology | Year: 2011

Siting criteria for nuclear power plants require that faults be characterized as to their potential for generating earthquakes, or that the absence of the potential for these occurrences be demonstrated. Because the definition of active faults in Korea has been applied by the deterministic method, which depends on the numerical age of fault movement, the possibility of inherent uncertainties exists in determining the maximum earthquake from the fault sources for seismic design. In an attempt to overcome these problems this study suggests new criteria and a probabilistic quantitative diagnostic procedure that could estimate whether a fault is capable of generating earthquakes in the near future.

Kim S.,KHNP Central Research Institute | Jun H.-Y.,KHNP Central Research Institute
Annals of Nuclear Energy | Year: 2014

A transient analysis of an ATLAS (Advanced Thermal-Hydraulic Test Loop for Accident Simulation) 6-in. cold-leg break was carried out with the MARS (Multi-dimensional Analysis for Reactor Safety) safety analysis code in the frame of the Domestic Standard Problem exercise in Korea. The calculated major sequence of events of the 6-in. cold-leg break simulation showed good agreement with the measured data. The calculated break mass flowrate was predicted well, whereas accumulated mass of the break outflow was underestimated due to the underestimation of the break mass flowrate in a later phase. The general trends of the collapsed water level were well predicted in the core and the downcomer region. The loop seal clearing phenomena were observed at about 400 s in the 1-A and 2-B intermediate legs in the calculation results which is identical to the experiment. To investigate the emergency core coolant (ECC) bypass phenomena, variation of the boron concentration in safety injection water was adopted. In the loop seal clearing phase of the 6-in. cold-leg break, about 40-50% of the ECC bypass fraction was calculated and after the loop seal clearance, 20-30% of ECC water bypassed, that is, not participating in core cooling directly. The boron tracking approach is considered to be a feasible methodology with which quantify the ECC bypass flow in the early phase of a small-break loss-of-coolant accident (SBLOCA). © 2013 Elsevier Ltd. All rights reserved.

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