[en] Due to the Fukushima accident of reactor No.4, the safety of the fuels stored in the wet storage pool became one of important issues. To analyze the oxidation and failure of the fuels in the storage pool, we have to know the detail information related with the oxidation kinetics of fuel claddings under the mixture of air and steam at high temperatures. There is not enough available data related with the oxidation of Zr alloys under the mixture of air and steam. The goal of the study is to obtain the fundamental data, and to develop a calculation tool for the analysis of fuel failure in the wet storage pool accident. The Zr alloy claddings used in the experiments were Zry-4 and Zirlo claddings. The temperature ranges were 700 - 1200 C, and 7 different steam-air mixtures were used steam:air=100:0, 90:10, 70:30, 50:50, 30:70, 10:90, 0:100. In-situ measurement of oxidation of the cladding specimens were done using TGA and a tube furnace. Calculation method was developed for the analysis of the thermal behavior of the fuels under the wet storage pool accident. The oxidation rate in air was turned out to be higher than that under the steam. The main reason was the development of nitride phases in the metal layer below the oxide. These nitrides destroy the protective oxide layers locally, and enhance the oxidation rate in total. In the case of the oxidation under the mixture of steam and air, the oxidation rate was measured to be in between the rates under the steam and in the air. As the fraction of air in the mixture increased, the oxidation rate became close to that in the air. The fraction of air in the mixture of steam and air can be related with the oxidation rate transition from the oxidation under steam to that in air. We can apply these results to the analysis of the spent fuel oxidation exposed to the steam-air mixture such as the dry-out accident of the wet storage pool and the core melt down accident

[en] In this study, we observed the oxidation behaviors of Zircaloy-4 and Zirlo under accident conditions. In an extreme case, the fuels could be exposed to mixtures of steam and air, which could start oxidation reactions with ambient gases. To analyze these accidents realistically, we have to know the details of the oxidation kinetics of Zr-alloy claddings with steam and air. Also, the kinetics are related to the oxidation mechanism. We also examined the oxidation of Zr-alloy claddings with oxygen to observe the oxidation mechanism. In this study, we measured the oxidation kinetics of Zry-4 and Zirlo claddings at 700 .deg. C. 1200 .deg. C. The scale surfaces developed on the Zry-4 under the different conditions are compared in Figure 3. In Figure 3, a crack can be observed under the air condition, and it may be that the nitride effect caused the crack in the protective layer. Therefore, rapid and substantial oxygen material diffusion occurred in the preformed oxide layer at 1200 .deg. C. In the steam condition, the oxide layer formed substantial protective oxide material at 700. 1200 .deg. C (Figure 3). As the EDAX results show, under the air oxide layer there was measured a small amount of carbon and oxygen. This is clear evidence of the results. Further examination of the oxidation kinetics of Zry-4 and Zirlo is needed for the safety evaluation of accidents occurring in air-steam mixtures

[en] In Fukushima Daiichi Nuclear Power Plant accident, No.4 plant was exploded by hydrogen explosion. There was a strong speculation about the possibility of the reaction between the overheated fuels and the steam-air mixture in the storage pool. Later, it turned out to be due to the hydrogen leaked from No.3 plant. However, the reaction of the hot fuels with the steam-air mixture became an important issue. There have been a lot of data accumulated about Zr-alloy interaction with steam. However, Zr-alloy interactions with air and steam-air mixtures have not been studied relatively much. In this study, we measured the oxidation kinetics of Zry-4 and Zirlo claddings in air, and steam-air mixtures, and analyzed the kinetics

[en] A loss of the coolant accident is one of the most important design-based accidents when concerning the behavior of a fuel behaviors. Also, as the fuel burn-up increases, corrosion occurs with hydrogen absorption, resulting in degradation of cladding properties. Investigating the effect of the pre-hydride cladding's surface will be of importance. In this study, we measured the oxidation rate of Zircaloy-4, Zirlo, pre-hydride Zircaloy-4 and pre-hydride Zirlo to compare the effect of hydride on the oxidation in air

[en] The Fukushima nuclear reactor accident has made the safety of the nuclear plants as a global issue. In this study, we observed the oxidation behaviors of Zircaloy 4 and Zirlo under accident conditions in pressurized water reactors. Even in the shutdown state of the reactor, the decay heat from the fission products has to be removed. As shown in the Fukushima nuclear reactor accident, the heated fuels by the decay heat react with steam transformed from the coolant by the reduced pressure inside the reactor. The reaction kinetics of Zr alloy claddings with steam is very important, and there have been a lot of data regarding the reaction kinetics. Another important phenomenon that occurred in the Fukushima reactor accident was that spent nuclear fuels in the pool were heated due to the loss of cooling. At the extreme case, the fuels are exposed to the mixtures of steam and air and start to make oxidation reactions with ambient gases. To analyze these accidents realistically, we have to know the detail oxidation kinetics of Zr alloy claddings with steam and air. Also, the kinetics are related with the oxidation mechanism. We also examined the oxidation of Zr alloy claddings with oxygen to observe the oxidation mechanism. In this study, we measured the oxidation kinetics of Zry 4 and Zirlo claddings at 700 .deg. C-1200 .deg. C

[en] This study was performed to improve the corrosion resistance and the stability of passive film on copper tube by potentiostatic polarization method in synthetic tap water. Formation of passive film was carried out by anodic potentiostatic polarization at various passivation potentials and passivation times in 0.1 M NaOH solution. Stability of passive film and corrosion resistance was evaluated by self-activation time, τ₀ from passive state to active state on open-circuit state in 0.1 M NaOH solution. Addition of polyphosphate in NaOH solution prolonged the self-activation time and improved the corrosion resistance, and the addition of 5 ppm polyphosphate was most effective. It was also observed that better corrosion resistance was obtained by potentiostatic polarization at 1.0 V (vs. SCE) than at any other passivation potentials. Passivated copper tube showed perfect corrosion resistance for the immersion test in synthetic tap water showing that the anodic potentiostatic polarization treatment in 0.1 M NaOH with 5 ppm polyphosphate solution would be effective in improving the corrosion resistance and preventing the blue water problem

[en] A deposition of corrosion products on fuel rods from the coolant circulated in a nuclear power plant (NPP) is commonly known as CRUD (Chalk River Unidentified Deposit).It has been an issue for NPP as increasing the level of radioactivity in reactor coolant system (RCS) and generating reactor imbalance of power distribution due to boron (AOA) and carrying on excess burden to the coolant purification system for a few decades. However there have been many technologies applied for the mitigation of CRUD such as high pH operation, the use of enriched boric acid, H injection, chemical purification, magnetic filtering, and injection of metal ions such as Zn. In this study, we checked the effect of Zn on the formation of CRUD, especially the composition change to see the effect of Zn (50 ppm)

[en] The characteristics of oxidation for the Zry-4 and Zirlo were measured in the temperature ranges of 700-900degC under air and steam conditions, using an apparatus for high temperature oxidation in the air and steam. Zry-4 and Zirlo follow a parabolic rate law at 700degC. However, oxidation rates of both alloys in air are higher than the rates in steam at 800-900degC. And oxidation rates of Zry-4 at high temperatures are similar or slightly more than those of Zirlo under the steam. However, Zirlo oxidized faster than Zry-4 in air at these high temperatures. (author)

[en] Microlens is known for optical component that has a great deal of applications in the field of communication, medical equipment, multi media equipment, electronic equipment and so on. Thermal reflow method using photoresist, etching method using laser pulse, dry etching method, the glass surface treatment method using CO_2 gas laser have been known as manufacture methods of microlens. In this paper, we fabricated the arrays of microlenses from droplets using dispenser system. UV curable optical adhesive is transparent in the optical region with the transmittance of over 99% in the wavelength range from 350nm to 1300nm and it has a viscosity of 1900cP and it is possible to perform a spin coating process on surface of semiconductor with is. After the exposure by UV it does not be removed in the acetone although it is dissolve in the acetone in the general state. In the dispenser system we can do a fine control of the dispensing amount of the given glue using the control of the dispensing pressure and time. In this research, we fabricated UV curable optical adhesive microlens arrays using the dispenser system. We characterized the microlens array with measurement of a radius of curvature and a focal length of the microlens with a physical and optical method. As one application of the our method, we consider the integration of microlens on a light emitting diode

[en] It is very important to analyze fuel cladding mechanical properties. Polycarbosilane(PCS) is a special ceramic whose protection films inhibit oxidation chemical resistance and strength at high temperatures. The PCS coating was carried out under various reaction conditions. The results showed that the supercritical process tries to moderate oxidation conditions such as temperature, time, and solution amount. In this study, we used specimens of the types currently used in nuclear reactors(zry-4, zirlo), as well as their corresponding coating specimens (PCS, CrN and CrN + Tungsten), to conduct an oxidation analysis four type of conditions(water, LiOH, LiOH + Boron, and steam) over the course of a month. CrN coating layers were successfully formed with good protection on metal surface and without any defect. CrN coated specimen formed protective coating layers, inhibiting oxidized layers. However, both Zry-4 and Zirlo PCS coated specimens experience suddenly high oxidation rates in all kinds of conditions. As a result, the specimens supported the acceleration of oxidation by PCS