In this study, we investigated the suppression of the corrosion of cast iron in a copper–cast iron double-layered canister under local corrosion of the copper layer. The cold spray coating technique was used to insert metals with lower galvanic activity than that of copper, such as silver, nickel, and titanium, between the copper and cast iron layers. Electrochemically accelerated corrosion tests were performed on the galvanic specimens in KURT groundwater at a voltage of 1.0 V for a week. The results revealed that copper corrosion was evident in all galvanic specimens of Cu–Ag, Cu–Ni, and Cu–Ti. By contrast, the copper was barely corroded in the Cu–Fe specimens. Therefore, it was concluded that if an inactive galvanic metal is applied to the areas where local corrosion is concerned, such as welding parts, the disposal canister can overcome local or non-uniform corrosion of the copper canister for long periods.

The aim of this study is to ensure the structural integrity of a canister to be used in a dry storage system currently being developed in Korea. Based on burnup and cooling periods, the canister is designed with 24 bundles of spent nuclear fuel stored inside it. It is a cylindrical structure with a height of 4,890 mm, an internal diameter of 1,708 mm, and an inner length of 4,590 mm. The canister lid is fixed with multiple seals and welds to maintain its confinement boundary to prevent the leakage of radioactive waste. The canister is evaluated under different loads that may be generated under normal, off-normal, and accident conditions, and combinations of these loads are compared against the allowable stress thresholds to assess its structural integrity in accordance with NUREG-2215. The evaluation result shows that the stress intensities applied on the canister under normal, off-normal, and accident conditions are below the allowable stress thresholds, thus confirming its structural integrity.

Due to the necessity of isolating spent nuclear fuel (SNF) from the human life zone for a minimum of 106 years, deep geological disposal (DGD) has emerged as a prominent solution for SNF management in numerous countries. Consequently, the resilience of disposal canisters to corrosion over such an extended storage period becomes paramount. While copper exhibits a relatively low corrosion rate, typically measured in millimeters per million years, in geological environment, special attention must be directed towards verifying the corrosion resistance of copper canister welds. This validation becomes inevitable during the sealing of the disposal canister once SNFs are loaded, primarily because the weld zone presents a discontinuous microstructure, which can accelerate both uniform and localized corrosion processes. In this research, we conducted an in-depth analysis of the microstructural characteristics of copper welds manufactured by TIG-based wire are additive manufacturing, which is ideal for welding relatively large structures such as a disposal canister. To simulate the welds of copper canister, a 12 mm thick oxygen-free plate was prepared and Y and V grooves were applied to perform overlay welding. Both copper welding zones were very uniform, with negligible defects (i.e., void and cracks), and contained relatively large grains with columnar structure regardless of groove types. For improving microstructures at welds with better corrosion resistance, the effect of preheat temperature also investigated up to 600°C.

In this study, a fracture evaluation of the spent nuclear fuel storage canister was conducted. Stainless steel alloys are typically used as the material for canisters, and therefore, a separate destructive evaluation is not required for safety analysis reports. However, in this research, a methodology for conducting a destructive evaluation was proposed for assessing the acceptability of cracks detected during in-service inspections for long-term storage due to reasons such as stress corrosion cracking. For the fracture evaluation, analytical equations provided in the design code such ASME were employed, and finite element method (FEM) based linear elastic fracture mechanics (LEFM) was performed to validate the effectiveness of the analytical equations. Impact analyses such as tip-over of the storage cask on a concrete pad were performed, and the fracture evaluation using stresses resulting from the impact analysis under accident conditions and residual stresses from welds were carried out. Through this research, geometric dimensions for cracks exceeding the fracture criteria were established.

One of the options for spent fuel dry storage systems is to store them in canisters using metal or concrete casks close to shore. The interaction between the austenitic stainless steel and the chloride atmosphere generated from the sea creates detrimental conditions leading to chloride induced stress corrosion cracking (CISCC) in the canister. The corrosion integrity of the canister in the concrete cask is very important because the canister is sealed and used for a long period of time. A canister made of austenitic stainless steel has several welding lines on the wall and lid, which are generated during the welding process and have high residual tensile stress. The interaction between the austenitic stainless steel and the chloride atmosphere generated from the sea creates detrimental conditions leading to chloride induced stress corrosion cracking (CISCC) in the canister. The corrosion integrity of the canister in the concrete cask is very important because the canister is sealed and used for a long period of time. In order to evaluate such soundness, an accelerated test capable of simulating the CISCC crack propagation phenomenon of the canister weld is required. In this study, a test device for performing the CISCC simulation test was constructed using the DCPD device. The direct current potential drop (DCPD) technique is a widely accepted method of monitoring crack initiation and growth in controlled laboratory tests. Total 10 types of test specimens with varying welds, base metal, salinity and stress were selected and a sealed chamber with DCPD test apparatus were designed and constructed to evaluate them. The chamber for CISCC simulation was manufactured as a sealed with a solution containing 10% MgCl2. A 1/2 CT specimen with precracked pre-cracks was loaded into the prepared container, and gauze was attached from the bottom for smooth delivery to the specimen to facilitate penetration of chloride. After the test, the measured DCPD data were correlated with Electron Back scattered Diffraction (EBSD) data.

When storing spent fuel in a dry condition, it becomes essential to ensure that any remaining moisture bound to the canister and spent fuel is effectively removed and stored within an inert gas environment. This is crucial for preserving the integrity of the spent fuel. According to the NRC- 02-07-C-006 report, it is advised to reduce pressure gradually or in incremental stages to prevent the formation of ice. In the context of vacuum drying, it is desirable to perform testing using a prototype model; however, utilizing a prototype model can be difficult due to budget constraints. To address this limitation, we designed and constructed a laboratory-scale vacuum drying apparatus. Our aim was to assess the impact of vacuum pump capacity on the drying process, as well as to evaluate the influence of canister volume on drying efficiency. The vacuum drying tests were carried out until the surface temperature of the water inside reached 0.1°C. In the tests focusing on vacuum pump capacity, vacuum pumps with capacities of 100, 200, 400, and 600 liters were employed. The outcomes of these tests indicated that smaller vacuum pump capacities resulted in increased evaporation rates but also prolonged drying times. In the case of drying tests based on canister volume, canisters with volumes of approximately 100 and 200 liters were utilized. The results revealed that larger canister volumes led to longer drying times and lower rates of evaporation. Consequently, if we were to employ an actual dry storage cask for vacuum drying the interior of the canister, it is anticipated that the process would require a substantial amount of time due to the considerably larger volume involved.

An austenitic stainless steel canister functions as a containment barrier for spent nuclear fuel and radioactive materials. The canister on the spent fuel storage system near the coastal area has several welding lines in the wall and lid, which have high residual tensile stresses after welding procedure. Interaction between austenitic stainless steel and chloride environment from a sea forms a detrimental condition causing chloride induced stress corrosion cracking (CISCC) in the canister. The South Korea is concerned with the dry storage of high-level spent nuclear fuel and radioactive wastes to be built on the site of a nuclear power plant. The importance of aging management has recently emerged for mitigating CISCC of dry storage canisters. When a corrosive pit is created by a localized corrosion in a sea water atmosphere, it initiates and grows as CISCC crack. Surface stress improvement works by inducing plastic strain which results in elastic relaxation that generates residual compressive stress. Surface stress improvement methods such as roller burnishing process can effectively mitigate the potential for CISCC of the canister external surfaces. The generation of compressive stress layer can inhibit the transition to cracking initiation. In this study, a flat roller burnishing process was applied as a prevention technology to CISCC of stainless steel canisters. Roller burnishing process parameters have been selected for 1:3 scale canister model having a diameter of 600 mm, a length of 1,000 mm and a thickness of 10 mm on the basis of the burnishing conditions available to control residual tensile stress of austenitic stainless steel plate specimens. The surface roughness of the scaled canister model was investigated using a surface roughness measurement equipment after roller burnishing treatment. The surface residual stresses of the scaled canister model were measured by a hole drilling contour method attached with strain gauge. The burnishing test results showed that the surface roughness of the scaled canister model was considerably improved with flat rollers having the tip width of 4 mm. The surface of the scaled canister model had significant residual compressive stress after burnishing treatment. The roller burnished canister with good surface roughness could reduce the number of crack initiation sites and the residual compressive stress formed on the welded surface might prevent the crack initiation by reducing tensile residual stress in the weld zone, finally leads to CISCC resistance.

In-depth disposal of spent nuclear fuel means safe disposal of spent nuclear fuel by the concept of a multi-barrier system composed of an artificial barrier, an engineering barrier, and a natural barrier system of natural rock at a depth of less than 500 m underground. Disposal canisters are needed to store high-level waste in a deep environmental for a long time, and in order to demonstrate the performance of deep disposal canisters for spent nuclear fuel at underground research facilities (URL), it is intended to design disposal canisters and manufacture internal canisters. The internal canisters of spent nuclear fuel disposal canisters manufactured as a result of the study are combined with external copper canister technology and are directly used for demonstration of engineering barrier performance in underground facilities (URL) essential for final disposal of spent nuclear fuel. Disposal canister manufacturing technology and manufacturing process are used to manufacture disposal canisters for future final disposal projects in connection with domestic unique disposal systems. The quality inspection and quality management technology applied when manufacturing disposal canisters contribute to securing the soundness of disposal canisters that primarily maintain the safety of in-depth disposal by using them in the actual disposal business. By visually showing the development status of domestic disposal technology by displaying the prototype of disposal canisters manufactured as major achivements, the public can raise awareness of the domestic technology and safety of in-depth disposal of spent nuclear fuel.

Since spent nuclear fuel (SNF) should be isolated from the human life zone for at least 106 years, deep geological disposal (DGD) is considered a strong candidate for SNF management in many countries. Therefore, a disposal canister should be nearly immune to corrosion in such a long-term storage environment. Even though copper has a low corrosion rate of a few millimeters per million years in geological environments, the corrosion resistance of the copper welds must be preferentially validated, which inevitably occurs during the sealing of the disposal canister after the SNF is loaded. This is because the weld zone is a discontinuous area of microstructure, which can accelerate uniform and localized corrosion. In this study, the microstructural characteristics of copper welds in different welding conditions such as friction stir welding, electron beam welding, cold spray, were analyzed, focusing on the formation of microstructure, which affects resistance to corrosion. In addition, the microstructure and corrosion properties of the copper weld zone manufactured by recent wire-based additive manufacturing (AM) technology were experimentally evaluated. From this preliminary test result, it was found that the corrosion characteristics of the welds produced by the AM process using wire are comparable to those of the conventional forged copper plate.

The purpose of this study was to examine whether galvanic corrosion of copper occurs by inserting a third barrier layer with a higher corrosion potential than copper between copper and cast iron when the copper layer is locally perforated by pitting or partial corrosion. A triple layer composed of copper, inserted metal, and carbon steel was manufactured by cold spray coating of inserting metal powders such as Ag, Ni, and Ti on carbon steel plate followed by Cu coating on it. First, the corrosion properties were evaluated electrochemically for each metal coating. As a result of Tafel plot anaylsis in KURT groundwater condition, the corrosion potential of Fe (-567 mV) was much lower than that of Cu (-91 mV), and the corrosion potential of Ni (-150 mV) was also lower than that of Cu. Therefore, Ni was likely to corrode before Cu. However, the corrosion current of Ni was lower than that of the Cu. In the galvanic specimen where the copper and inserting metal were exposed together, Cu-Fe was much lower corrosion potential of -446 mV, and the corrosion potential of Cu-Ti, Cu-Ni, and Cu-Ag were slightly higher than that of Cu. Therefore, it seemed that Ag, Ni, and Ti all might promote galvanic corrosion of surrounding copper when the copper layer was perforated to the inserted metal layer. If the metal insertion presented in this study operates properly, the disposal container does not need to worry about the partial corrosion or non-uniform corrosion of external copper layer.

One of the options for spent fuel dry storage systems is to store them in canisters using metal or concrete casks close to shore. The interaction between the austenitic stainless steel and the chloride atmosphere generated from the sea creates detrimental conditions leading to chloride induced stress corrosion cracking (CISCC) in the canister. The corrosion integrity of the canister in the concrete cask is very important because the canister is sealed and used for a long period of time. A canister made of austenitic stainless steel has several welding lines on the wall and lid, which are generated during the welding process and have high residual tensile stress. The interaction between the austenitic stainless steel and the chloride atmosphere generated from the sea creates detrimental conditions leading to chloride induced stress corrosion cracking (CISCC) in the canister. The corrosion integrity of the canister in the concrete cask is very important because the canister is sealed and used for a long period of time. In order to evaluate such soundness, an accelerated test capable of simulating the CISCC crack propagation phenomenon of the canister weld is required. In this study, a test device for performing the CISCC simulation test was constructed using the DCPD device. The direct current potential drop (DCPD) technique is a widely accepted method of monitoring crack initiation and growth in controlled laboratory tests. In its simplest form it involves passing a constant current through the test piece and accurately measuring the electrical potential across the crack plane, and it is a suitable device to measure crack growth in real time. The requirements for the CISCC simulation test selected based on the literature search results include test material 316 L, load range 1.75YS, positive displacement load, and 7% MgCl2 concentration. In order to smoothly evaluate these various conditions, it was determined that it is advantageous to collect crack length data in real time using a DCPD device, rather than receiving and analyzing specimens maintained for a certain time in the chamber. Therefore, in this study, 4 types of test conditions in real time was built, and data collection on crack propagation could be performed in real time by using it.