This study aims to assess the effect of postulated seismic loads on the structural integrity of a spent nuclear fuel dry storage facility. Firstly, three-dimensional modal and response spectrum analyses were carried out. With regard to the latter analysis, the effect of incident angles against two horizontal and one vertical response spectra was also considered. Results showed that even though two critical locations were predicted at the longitudinal axis central part of upper flow path as well as the end discontinuity part of upper and lower flow paths connector, their maximum principal stress values were less than the tensile strength. Moreover, since the influence of vertical angle was 87% higher than that of horizontal angle in particular, which should be carefully handled to demonstrate integrity of the facility.

The 3D printing technology is one of the fourth industrial revolution technology that drives innovation in the manufacturing process, and should be applied to nuclear industry for various purposes according to the manufacturing trend change. In nuclear industry, it can be applied to manufacture obsolete items and new designed parts in advanced reactors or small modular reactors (SMRs), replacing the traditional manufacturing technologies. A gate valve body was manufactured, which was obsolete in nuclear power plant, using DED(Directed Energy Deposition) metal 3D printing technology after restoring design characteristics including 3D design drawing by reverse engineering. The 3D printed valve body was assembled with commercial parts such as seat-ring, disk, stem, and actuator for performance test. For the valve assembly, including 3D printed valve body, several tests were performed, including pressure test, end-loading test, and seismic test according to KEPIC MGG and KEPIC MFC. In the pressure test, hydraulic pressure of 391kgf/cm² was applied to 3D printed valve body, and no leak was detected. Also the 3D printed valve assembly was performed well in end-loading and seismic tests.

The thickness of pipe can be locally reduced during operation due to wall thinning. Due to its significance on structural integrity, many non-destructive detecting techniques and assessment methods are available. In this study, the elastic bending compliance of local wall-thinned pipe is presented in terms of the wall thinning geometry: wall thinning depth, circumferential angle and longitudinal length. Elastic finite element (FE) analysis further shows that the presented equation can be used for any wall thinning shape. The proposed solution differs from FE results by less than 6% for all cases analyzed. The bending compliance increases linearly with increasing longitudinal thinning length and non-linearly with increasing thinning angle and depth.

Molten corium-concrete interaction (MCCI) is one of the most important phenomena that can lead to the potential hazard of late containment failure due to basemat penetration during a severe accident. In this study, MCCI analytical models of the CORQUENCH code were prepared through verification calculations of several experiments, which had been performed using concrete types similar to those of the calandria vault floor in CANDU-6 plants. The behaviors of thermal-hydraulic variables related to MCCI phenomena were analyzed under the conditions of dry floor and water flooding during the severe accident stemming from a hypothetic station blackout. Uncertainty analyses on the ablation depth were also carried out. It was estimated that the concrete ablation was not interrupted due to the continuous MCCI process under the dry condition but was terminated within 24 hours under the water flooding condition. It was confirmed that the water flooding as a mitigating action was effective to achieve the quenching and thermal stabilization of the melt discharged from the calandria vessel, showing that the present models are capable of reasonably simulating MCCI phenomena in CANDU-6 plants. This study is expected to provide the technical bases to the accident management strategy during the late-phase severe accidents.

To date, a number of stress intensity factor (SIF) solutions have been proposed for the cylindrical structure with circumferential through-wall cracks. However, each solution has a different format as well as applicable range. It is also known that there is a significant difference in predicted SIF values depending on the shape of the structure and the size of the crack. In this study, the applicability of various SIF solutions was analyzed by comparing the finite element analysis results for the case where a tensile load is applied to the cylindrical structure with circumferential through-wall crack. It is found that the calculated SIF gradually decreases and converges to a certain value with increasing length-to-radius ratio. Therefore, an appropriate length-to-radius ratio should be set in consideration of the dimensions of the actual cylindrical structure. For piping with sufficiently long cylinder, the ASME solution is found to be the most appropriate, and for a short cylinder, the API solution should be applied. On the other hand, the WEC solution requires careful attention to its application.

In the periodic surveillance material test for the spacer component of fuel channel assembly in CANDU, a microstructural characterization analysis is required in addition to the mechanical property evaluation test. In this study, detailed microstructure analysis and simple mechanical property evaluation of archive spacer parts were conducted to indirectly support the surveillance test and assist in the study of spacer material degradation. We investigated the microstructural characteristics of the spacer garter spring coil through comparative analysis with the plate material. The main microstructure characteristics of the garter spring coil X-750 are represented by the fine grain size distribution, the ordering phase distribution developed inside the matrix, the high dislocation density inside the grains, and the arrangement of coarse carbides. In addition, the yield strength of the garter spring coil X-750 was indirectly evaluated to be approximately 1 GPa. We also established an analytical method to elucidate the microstructural evolution of the radioactive spacer garter spring coil X-750 based on Canadian research experiences. Finally, we confirmed the measurement technique for helium bubble formation through TEM examination on the helium implanted X-750 material.

Subsea pipelines are widely used to transport hydrocarbons from ultra-deep seawater to facilities on the coast. A sandwich pipe is a pipe-in-pipe system in which the annulus between the two concentric steel pipes is filled with polymer cores and fillers for insulation and structural reinforcement. Sandwich pipeline is always exposed to complex loading such as bending moment, bulking, internal and external pressures caused by installation, operation and environmental factors. This research provides insights into the structural integrity of sandwich pipeline exposed to complex loading conditions using a linear matching method (LMM). The finite element model of the sandwich pipeline has been generated from previous research, and the model validation is performed by comparing the results of the linear analysis between the two models. The temperature dependent material properties are used to simulate the behavior of real pipeline, and the elastic-perfectly plastic (EPP) model has been taken into account for the material non-linearity. Numerical results provide comprehensive insights into the structural response of the sandwich pipeline under monotonic and cyclic loading and provide notable points about the evaluation of the plastic collapse limit and the elastic shakedown limit of the sandwich pipeline.

During operation of nuclear power plants, the fatigue assessment should be conducted repeatedly, considering changes of operating environments. For the case that cumulative usage factors (CUFs) may exceed the acceptance limit, flaw tolerance evaluation can be an alternative method to meet the regulatory requirements. In this respect, this paper analyzes the effects of the input variables for flaw tolerance evaluation based on ASME BPVC Section XI Appendix L. The reference analysis is performed for the example problem in NUREG/CR-6934. Then effects of the crack orientation, stress intensity factor solutions, thermal stress profiles, fatigue stress decomposition and fatigue crack growth curves are considered for the sensitivity analysis. The results show that the stress analysis considering the actual environment plays a crucial role in flaw tolerance evaluation.

The mode superposition time history analysis method is commonly used in a seismic analysis. The maximum response in the time history analysis can be derived by combining the responses of individual modes. The residual mode response is the response of the modes which are not considered in the time history analysis. In this paper, the residual vector method to consider the residual mode response in the time history analysis is introduced and evaluated. Seismic analyses for a sample structure model and a reactor vessel model are performed to evaluate the residual vector method. The analysis results show that residual mode response is well calculated when the residual vector method is used. It is confirmed that the residual vector method is useful and acceptable to consider the residual mode response in a seismic analysis of the nuclear power plant equipment.

Ultrasonic Nanocrystal Surface Modification (UNSM) is a peening technology that generates elastic-plastic deformation on the material surface to which a static load of a air compressor and a dynamic load of ultrasonic vibration energy are applied by striking the material surface with a strike pin. In the UNSM-treated material, the structure of the surface layer is modified into a nano-crystal structure and compressive residual stress occurs. When UNSM is applied to welds in a reactor coolant system where PWSCC can occur, it has the effect of relieving tensile residual stress in the weld and thus suppressing crack initiation and propagation. In order to quantitatively evaluate the compressive residual stress generated by UNSM, many finite element studies have been conducted. In existing studies, single-path UNSM or UNSM in a limited area has been simulated due to excessive computing time and analysis convergence problems. However, it is difficult to accurately calculate the compressive residual stress generated by the actual UNSM under these limited conditions. Therefore, in this study, a minimum finite element peening analysis area that can reliably calculate the compressive residual stress is proposed. To confirm the validity of the proposed analysis area, the compressive residual stress obtained from the experiment are compared with finite element analysis results.