Advancements in technology have led to electronics with higher power densities, which strains the sustainability of these devices. In this context, using metal foams in pool boiling can provide solutions by enhancing heat transfer. The porous structure of metal foams affects the boiling parameters such as critical heat flux (CHF) and boiling heat transfer coefficient (BHTC). To study these effects, copper foams of varying thicknesses and PPI were used, and they were attached to smooth silicon surfaces to simulate chip cooling. This research focused on thin foams with 1 mm thickness, which had been sparsely explored in the previous studies. In the ten samples, the CHF increased by up to 85.8 %, and the BHTC increased by up to 141.1 %. Vapor bubble dynamics on copper foam surfaces, which were affected by the foam thickness and PPI, were analyzed. The experimental results show that copper foams significantly enhance pool boiling heat transfer . However, thicker foams increase the frequency of bubble trapping, causing localized overheating which leads to deterioration of heat transfer performance. There was also an optimal PPI value for each foam thickness, which is 40 PPI for the 1 mm thickness and 30 PPI for the 3 mm thickness. • The effect of metal foam thickness and pore size on boiling heat transfer is investigated. • Critical heat flux is increased by metal foam up to 86 % and decreased down to 67 %. • Bubble trap in the metal foam can degrade the critical heat flux and boiling heat transfer coefficient .

Advancements in technology have led to electronics with higher power densities, which strains the sustainability of these devices. In this context, using metal foams in pool boiling can provide solutions by enhancing heat transfer. The porous structure of metal foams affects the boiling parameters such as critical heat flux (CHF) and boiling heat transfer coefficient (BHTC). To study these effects, copper foams of varying thicknesses and PPI were used, and they were attached to smooth silicon surfaces to simulate chip cooling. This research focused on thin foams with 1 mm thickness, which had been sparsely explored in the previous studies. In the ten samples, the CHF increased by up to 85.8 %, and the BHTC increased by up to 141.1 %. Vapor bubble dynamics on copper foam surfaces, which were affected by the foam thickness and PPI, were analyzed. The experimental results show that copper foams significantly enhance pool boiling heat transfer . However, thicker foams increase the frequency of bubble trapping, causing localized overheating which leads to deterioration of heat transfer performance. There was also an optimal PPI value for each foam thickness, which is 40 PPI for the 1 mm thickness and 30 PPI for the 3 mm thickness. • The effect of metal foam thickness and pore size on boiling heat transfer is investigated. • Critical heat flux is increased by metal foam up to 86 % and decreased down to 67 %. • Bubble trap in the metal foam can degrade the critical heat flux and boiling heat transfer coefficient .

원자력발전소에서 중대사고 발생 시 노심의 현저한 손상에 의해 다량의 핵분열생성물이 격납건물 내부로 방출될 수 있다. 중대사고 관리 및 대응 능력의 제고를 위해 중대사고 시 사고 진행 상황을 신속하게 파악하고 그에 따른 최적 사고대응 방안을 제시할 수 있는 운전원 지원체계가 필요하다. 현재 중대사고 분야에서는 사고 전개과정의 모의를 위해 중대사고 종합해석 코드인 MELCOR, ASTEC, MAAP 등의 코드를 사용하고 있다. 하지만, 이와 같은 코드는 많은 불확실도를 포함하고 있기에 코드 내 불확실도를 평가·개선하기 위한 많은 연구가 진행되고 있다. 본 연구에서는 노심의 열화와 핵분열생성물의 방출 거동을 살펴볼 수 있는 대표적인 실험 중 하나인 PHEBUS FPT-1 실험의 벤치마킹을 수행하였다. 해석에는 MELCOR 2.2를 사용하였으며, 노심의 열화 과정을 평가하기 위해 핵연료 및 피복재의 온도 변화와 수소발생량을 살펴보았다. 또한, 격납건물로 방출된 핵분열생성물의 최종 방출 비율을 분석하고, MELCOR에서 사용하는 노심방출모델(core release model)에 따른 방출 비율 변화에 대한 민감도 분석을 수행하였다.

A reliable prediction on the behavior of source terms is essential for devising effective accident response measures to cope with the severe accident of a nuclear power plant. However, modeling the release, transport, and deposition of radioactive materials under severe accident conditions inherently involves significant uncertainties. This study was intended to evaluate epistemic uncertainties in predicting source term behavior during the severe accident on the release of fission products into the containment in the PHEBUS FPT-1 experiment using the MELCOR 2.2 code. The release fractions of cesium, iodine, and all fission products into the containment were selected as the figure of merit (FOM) in the uncertainty quantification. This study categorized the uncertain parameters into two groups: variables used to model fuel degradation phenomena and those involved in describing radionuclides behavior from the fuel. A total of 140 simulations were performed for each set of calculations, followed by regression analysis and correlation analysis to quantify the influence of selected model parameters. The possible distributions of selected FOMs were quantified, and critical parameters were identified for analysis packages of the MELCOR code in predicting the release fraction of major radionuclides.

The in-vessel retention through external reactor vessel cooling (IVR-ERVC) strategy is a key management strategy for early termination of a nuclear severe accident that can threaten the integrity of the reactor vessel. To simulate the physical phenomena of the molten corium, the smoothed particle hydrodynamic (SPH) method is utilized in this study. The SPH method is a Lagrangian computational fluid dynamic (CFD) method that can simulate multi-fluid stratification, turbulence, natural circulation, radiative heat transfer, thermal ablation, and crust formation. To address the external vessel cooling, it is coupled with a conventional 1-D nuclear system analysis method. The 1-D system analysis code can calculate the two-phase natural circulation of cooling water and the convective heat transfer on the external reactor vessel wall. These two simulation codes exchange the temperature and heat flux of the reactor vessel outer wall. This study numerically simulated the IVR-ERVC strategy for a Korean high-power reactor and compared it with the traditional lumped parameter method (LPM). Unlike LPM, this study provides localized detailed data about the thermal hydraulic behavior of molten corium and visualization of phenomena in the IVR-ERVC strategy. This enhances our understanding of the phenomena in IVR-ERVC strategy and introduces new perspectives.