• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.13 no.2
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• pp.75-83
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• 2017

In severe accident conditions of light water reactors, the loss of coolant may cause problems in integrity of zirconium fuel cladding. Under the condition of the loss of coolant, the zirconium fuel cladding can be exposed to high temperature steam and reacted with them by producing of hydrogen, which is caused by the failure in oxidation resistance of zirconium cladding materials during the loss of coolant accident scenarios. In order to avoid these problems, we develop a multi-metallic layered composite (MMLC) fuel cladding which compromises between the neutronic advantages of zirconium-based alloys and the accident-tolerance of non-zirconium-based metallic materials. Cold pilgering process is a common tube manufacturing process, which is complex material forming operation in highly non-steady state, where the materials undergo a long series of deformation resulting in both diameter and thickness reduction. During the cold pilgering process, MMLC claddings need to reduce the outside diameter and wall thickness. However, multi-layers of the tube are expected to occur different deformation processes because each layer has different mechanical properties. To improve the utilization of the pilgering process, 3-dimensional computational analyses have been made using a finite element modeling technique. We also analyze the dimensional change, strain and stress distribution at MMLC tube by considering the behavior of rolls such as stroke rate and feed rate.

• Korean Journal of Metals and Materials
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• v.49 no.1
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• pp.17-24
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• 2011

To investigate the relationship between heat treatment in zirconium alloy tubing process and metallurgical characteristics of Zr-1Nb-0.69Sn-0.11Fe alloy tubes, mechanical and oxidation behaviors of tubes heat treated at different temperatures after the final pilgering were investigated. The stress strain curves exhibited the saturation behaviors in all heat treatment conditions ($460{\sim}600^{\circ}C$) in this study with the onset strain of saturation increased with increase of post-pilgering annealing temperature. The strength fell off rapidly with increasing annealing temperature. The ultimate strength of the low tin Zr-1Nb-0.69Sn-0.11Fe alloy with slightly higher iron and oxygen contents in this study was found to be higher than Zr-1Nb-1Sn-0.1Fe alloy. The oxidation experiments in steam condition revealed that the corrosion resistance of low tin Zr-1Nb-0.69Sn-0.11Fe alloy was better than the Zr-1Nb-1Sn-0.1Fe alloy with a higher Sn content. The weight gain of low tin Zr-1Nb-0.69Sn-0.11Fe alloy tubes gradually increased with the increasing annealing temperature possibly due to the decreased Nb content in the matrix because of the formation of ${\beta}-Nb$ particles.

• Korean Journal of Materials Research
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• v.26 no.12
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• pp.681-687
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• 2016

Zirconium(Zr) nuclear fuel cladding tubes are made using a three-time pilgering and annealing process. In order to remove the oxidized layer and impurities on the surface of the tube, a pickling process is required. Zr is dissolved in HF and $HNO_3$ mixed acid during the process and pickling waste acid, including dissolved Zr, is totally discarded after being neutralized. In this study, the waste acid was recycled by adding $BaF_2$, which reacted with the Zr ion involved in the waste acid; $Ba_2ZrF_8$ was subsequently precipitated due to its low solubility in water. It is very difficult to extract zirconium from the as-recovered $Ba_2ZrF_8$ because its melting temperature is $1031^{\circ}C$. Hence, we tried to recover Zr using an electrowinning process with a low temperature molten salt compound that was fabricated by adding $ZrF_4$ to $Ba_2ZrF_8$ to decrease the melting point. Change of the Zr redox potential was observed using cyclic voltammetry; the voltage change of the cell was observed by polarization and chronopotentiometry. The structure of the electrodeposited Zr was analyzed and the electrodeposition characteristics were also evaluated.

• Resources Recycling
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• v.26 no.5
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• pp.97-104
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• 2017

Nuclear fuel cladding tubes are manufactured through pilgering and the annealing process. In order to remove the oxidized layer and impurities on the surface of the tube, a pickling process is required. Zirconium (Zr) is dissolved in a HF and $HNO_3$ acid mixture during the process and the pickling waste acid, including the dissolved Zr, is completely discarded after neutralization. This study observes the effects of the residual impurities (Ba) in the pickling solution regenerated from the $BaF_2$ precipitation process on the waste pickling solution. In addition, the concentration of Ba and Zr for the actual nuclear fuel cladding tube process was optimized. The regenerated pickling solution was tested through a pilot plant pickling process device that simulates the commercial pickling process of nuclear fuel cladding tubes, and the pickling efficiency was analyzed through AFM analysis of the roughness of the cladding tube surface.

• Resources Recycling
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• v.26 no.6
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• pp.29-37
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• 2017

Nuclear fuel cladding tube is fabricated by pilgering and annealing process. In order to remove impurity and oxygen layer on the surface, pickling process is carried out. When Zirconium(Zr) is dissolved and saturated in acid solution during the pickling process, all the waste acid including Zr is disposed. Therefore, $BaF_2$ is added into the waste acid to extract Zr and $Ba_2ZrF_8$ is subsequently formed. To recycle Zr by electrowinning process, $Ba_2ZrF_8$ is used as electrolyte, but it has high melting point ($1053^{\circ}C$). $ZrF_4$ should be added into $Ba_2ZrF_8$ to decrease the melting point. In this paper, it was investigated that $Ba_2ZrF_8$ was separated to $BaF_2$ and $ZrF_4$ by vacuum distillation. Firstly, $BaF_2$ with different particle size ($1{\mu}m$, $35{\mu}m$, $110{\mu}m$) was added into the waste acid and the respective precipitation property was estimated. $BaF_2$ obtained by vacuum distillation was shattered by ball-milling with different time. The precipitation efficiency was compared with $1{\mu}m$ of ${BaF_2}^{\prime}s$ one, which was not used as precipitation agent.

• Clean Technology
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• v.19 no.3
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• pp.264-271
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• 2013

In this study, we optimized the removal condition of contaminants attached on the scrap surface to recycle the scrap generated from the Zr alloy tube manufacturing process back to the nuclear grade. The main contaminant is remnant of watersoluble cooling lubricant that is used in the pilgering manufacture during the tube production, and it is assumed to be compressed and carbonized on the surface of tube. Zirlo alloy tube of ${\phi}9.50mm$, which has high occurrence frequency of scrap, was selected as the object to be cleaned, and cleaning abilities of reagents were evaluated by measuring the characteristics of contaminants remained and by analyzing the surface of the tube after cleaning process. For evaluation of each cleaning agent, we selected two types of sodium hydroxide series and three types of potassium hydroxide series. Furthermore, to confirm dependence on tempe-rature and ultrasonic intensities, cleaning at the room temperature, $40^{\circ}C$, and $60^{\circ}C$ was conducted, and results showed that higher the cleaning temperature and higher the ultrasonic intensity, better the cleaning effect. As a result of the bare-eye inspection, while the use of sodium hydroxide provided satisfactory condition on the tube surface, the use of potassium hydroxide series provided satisfactory condition on the tube surface only when the ultrasonic intensity was over 120 W. In the cleaning effect analysis using the gravimetric method, cleaning efficiency of sodium hydroxide series was as high as 97.6% ($60^{\circ}C$, 120 W), but since the tube surface condition was poor after the use of potassium hydroxide, the gravimetric method was not appropriate. In the analytical result of surface contaminants on the tube surface, C, O, Ca, and Zr were detected, and mainly C and O dominated the proportion of contaminants. It was also found that the degree of cleaning on the tube affected the componential ratio of C and O; if the degree of cleaning is high, or if cleaning is well-conducted, the proportion of C is decreased, and the proportion of O is increased. Based on these results, optimal cleaning for application in the industry can be expected by categorizing cleaning process into three steps of Alkali cleaning, Rinsing, and Drying and by adjusting cleaning parameters in each step.