Hee Cheon No

• Korea Advanced Institute of Science and Technology

The passive safety design concept is essential to remove decay heat under the station blackout. We conducted experimental and CFD-based studies on condensation in the presence of non-condensable gas to analyze the performance of a Passive Containment Cooling System. External condensation experiments were performed in 2 ∼ 4 bar, air mass fraction in...

The gap cooling phenomenon is a key issue to explain why the 19 tons of melt retained in the RPV lower head in the TMI accident did not significantly damage the vessel. This study developed the model for gap cooling phenomenon and was validated against the several gap cooling experiments with 30 kg, 50 kg, 70 kg of Al2O3 melt (LAVA and ALPHA experi...

The existing gap cooling studies have shown the coolability of debris retained in the lower head of a vessel and effective mitigation of the rupture of a reactor vessel, but no plausible mechanism of the gap formation has been clearly identified. Several experiments of the gap formation, pretests of FARO-19, LAVA, ALPHA, and EC-FOREVER- 5 and 6, we...

An air-ingress accident in a VHTR is anticipated to cause severe changes of graphite density and mechanical strength by oxidation process resulting in many side effects. However, quantitative estimations have not been performed yet. In this study, the focus has been on the prediction of graphite density change and mechanical strength using a therma...

As molten corium is released from the reactor pressure vessel (RPV) under severe accidents, the molten corium is going to experience various complicated phenomena. If there is no steam explosion, the corium is going to be ejected through the reactor vessel, fragmented, and cooled through the interaction between the corium and water existing in the...

In this study, data classification and modeling of the flooding phenomenon were performed in a narrow channel with a gap thickness of several millimeters. To implement the conventional classification study to a narrow channel case, three key ideas for two-phase flow in a narrow channel were proposed; characteristic length, the flow path for each ph...

In this paper, two-phase drag models for a packed bed of uniform-size particles were suggested, and they were applied to the calculation of pressure drop and dryout heat flux. We provided physical basis for the two-phase flow regime model through the analysis of the interfacial friction (Fi). The suggested model provides flow patterns representing...

The consideration of the Design Extension conditions (DEC) has been introduced with great importance to enhance the plant safety capabilities. DEC have low occurrence probabilities but high consequences, and relatively complex scenario progression compared to Design Basis Accidents (DBA). This study suggests the estimation methodology of the DEC sa...

To evaluate the released radioactive materials to an environment under a nuclear severe accident, it is necessary to analyze the ex-vessel phenomena. The releasing diameter is one of the most essential parameters to estimate the ex-vessel phenomena. The diameter is enlarged because the wall of a reactor vessel melts due to the high temperature of c...

Zircaloy cladding oxidation is an important phenomenon for both design basis accident and severe accidents, because it results in cladding embrittlement and rapid fuel temperature escalation. For this reason during the last decade, many experts have been conducting experiments to identify the oxidation phenomena that occur under design basis accide...

In this paper, a simple and fast-running model for the quenching of a particulate bed is suggested assuming two-step quenching: downward quench front propagation step and upward quench front propagation step. Most of the existing models are based on the assumption that the quenching rate is only hydraulically limited. However, the model suggested i...

A passive containment cooling system (PCCS) has been developed as advanced safety feature for innovative power reactor (iPOWER). Passive systems are inherently less stable than active systems and the PCCS encountered the flashing-induced instability previously identified. The objective of this study is to develop stability maps for flashing-induced...

Droplet size and distribution are important parameters determining venturi scrubber performance. In this paper, we proposed physical models for a maximum stable droplet size prediction and upper limit log-normal (ULLN) distribution parameters. For the proposed maximum stable droplet size prediction model, a Eulerian-Lagrangian framework and a Reitz...

During an LWR severe accident, top flooding strategy is usually used in order to achieve the coolability of corium. Water ingression phenomenon, where water percolates through cracks in the crust, is identified as one of the phenomena that enhance the heat removal during cooling of the corium via top flooding. In this study, a model for the water i...

Recently advanced visualization techniques such as total reflection and IR methods have been applied to observe thermally and hydraulically the CHF mechanism at the surface as well as macroscopic bubble dynamics simultaneously. Based on observation Ha and No (1998a,b, 2000), and Choi et al. (2016) developed a Dry spot model and a Dry patch model, w...

CRUD is the corrosion product deposit found on a fuel rod surface of pressurized water reactors (PWRs). Problematic phenomena caused by CRUD – CRUD Induced Power Shift (CIPS) and CRUD Induced Localized Corrosion (CILC) – are closely related to the heat transfer mechanism of CRUD. However, heat transfer regimes of CRUD are still not well clarified....

High-temperature film boiling in forced convection is dominant heat transfer regime after corium jet breakup in fuel-coolant interaction (FCI). Considering radiation contribution to heat transfer in a high superheat condition, we modified the Epstein-Hauser model by reflecting the radiation term on the energy balance at vapor-liquid interface. This...

The concept of the APDHR (Air-cooled Passive Decay Heat Removal) system was suggested to preserve the safety of a nuclear reactor during accidents. Until 3 days after the reactor shutdown caused by non-LOCA accident, water in the Passive Condensate Cooling Tank (PCCT) was used to condense the steam in secondary side. Since then, the steam was coole...

A porous medium with separated paths for liquid and vapor flows does not fail even after part of the porous medium is dried out. Instead, a vapor film resides within the porous medium, and it grows very slowly. This heat transfer regime was named as “confined film-boiling regime” in this study, and a heat transfer model for this regime was suggeste...

The air-cooled passive decay heat removal system (APDHR) was proposed to provide the ultimate heat sink for non-LOCA accidents. The APDHR is a modified one of Passive Auxiliary Feed-water system (PAFS) installed in APR+. The PAFS has a heat exchanger in the Passive Condensate Cooling Tank (PCCT) and can remove decay heat for 8 h. After that, the he...

A model that predicts thicknesses and permeability of the crust before water ingression was suggested. This model can predict the crust formation and fracture along the time. In addition, it was found that most of solid crust was fractured as flooding begins. The model can also predict the permeability at an onset of water ingression. However, in o...

A fouling on a fuel rod, which is called CRUD, has induced many problems such as CRUD Induced Power Shift (CIPS) and CRUD Induced Localized Corrosion (CILC). Boiling has a significant role in these phenomena. It not only accelerates the deposition of CRUD, but also changes chemical environment near the fuel rod by concentrating chemical additives...

Experiments were performed to determine the film boiling heat transfer of a hot stainless steel sphere of 10 mm diameter, whose initial temperature is about 850 °C, immersed in a 43–81 °C water pool. From the experimental results, and direct visual aid, it was found that non-negligible amounts of heat transfer exist from the sphere to the support r...

CRUD is the deposit that is found on the fuel cladding surface, and it has been suspected as one of the challenges regarding higher burnup operation and power uprates. Two major phenomena caused by CRUD – CRUD Induced Power Shift (CIPS) and CRUD Induced Localized Corrosion (CILC) are highly related to the heat transfer mechanism within the CRUD sin...

Experiments have been carried out to apply PCHE as a steam generator in Small Modular Reactors. KAIST designed the straight-type PCHE for the application of the steam generator, and constructed a high-pressure test facility. We investigated the effects of system pressure, inlet water temperature and heat input on the thermal-hydraulic characteristi...

The model was developed to predict the heat transfer within the Chalk River Unidentified Deposit (CRUD), which is a kind of fouling found on the fuel rods of pressurized water reactors (PWR). The CRUD tends to develop steam chimneys that separate the liquid from the vapor phase. Therefore, the model describes the CRUD as a porous medium with steam...

A structural model for stress distributions of coated zircaloy subjected to realistic incore stresses - pressure difference, thermal expansion, irradiation-induced axial growth, and creep has been developed in this study. In normal operation, the structural integrity of coating layers is anticipated to be significantly challenged with increasing bu...

A parametric study that demonstrates a methodology for determining the optimum bilayer composition in a duplex SiC cladding is discussed. The structural performance of multi-layer SiC cladding design is significantly affected by radial thickness fraction of each layer. This study shows that there exists an optimal composite/monolith radial thicknes...

We developed a CFD (Computational Fluid Dynamics) analysis methodology for predicting an overpressure buildup due to a hydrogen explosion as well as the blast wave propagation from the near field to the far field of the hydrogen explosion site with an error range of about ±30% on the basis of test results with the small-scale obstacle at the stoich...

This study investigates the engineering compatibility between emergency core cooling system criteria and safety water injection systems, in the pursuit of safety margin increase of light water reactors. This study proposes an acceptable temperature increase to 1370 °C as long as equivalent cladding reacted calculated by the Cathcart–Pawel equation...

The concern regarding passive safety systems and corium-cooling related to severe accidents has been raised following the Fukushima accident. As a critical heat flux (CHF) is a predominant restricting factor of the heat removal capacities of both types of safety systems, a number of researches have been performed to understand and improve the CHF....

This study presents the importance of coherency in modeling thermal-hydraulics and mechanical behavior of a solid for an advanced prediction of cladding thermal shock fracture. In water quenching, a solid experiences dynamic heat transfer rate evolutions with phase changes of the fluid over a short quenching period. Yet, such a dynamic change of he...

A Single-tube COndensation exPeriment (SCOP) was performed at Korea Advanced Institute of Science and Technology (KAIST) to simulate the condensation phenomena of Passive Auxiliary Feedwater System (PAFS), which is introduced in Advanced Power Reactor Plus. SCOP tests were conducted for two pipes of different diameters [22.6 and 44.8 mm inside diam...

In this study, we performed critical heat flux (CHF) experiments using structured surfaces to validate the parameter effects and understand their physical meanings. Experimental results showed that the CHF has a peak value as the fin geometry changes. Fins with height of 0.5 mm produced the largest CHF, 1.7 MW/m2, and fins longer than 2 mm reduced...

s Heat removal capability through a steel containment is important in accident situations to preserve the integrity of a nuclear power plant which adopts a steel containment concept. A heat transfer rate will be enhanced by using fins on the external surface of the steel containment. The fins, however, cause to increase flow resistance and to deter...

To ensure safe operation of nuclear power plants even in the case of a prolonged station blackout, advanced reactors adopt passive systems that can operate without electricity supply. In Korea, a passive auxiliary feedwater system was successfully validated, and a passive containment cooling system (PCCS) has recently attracted attention. To invest...

Structural integrity of SiC clad fuels in reference Small Modular Reactors (SMRs) (NuScale, SMART, IRIS) and a commercial pressurized water reactor (PWR) are assessed with a multi-layered SiC cladding structural analysis code. Featured with low fuel pin power and temperature, SMRs demonstrate markedly reduced incore-residence fracture probabilities...

Experiments on high pressure steam condensation inside a nearly horizontal tube were performed for application into Passive Auxiliary Feedwater System (PAFS) of Advanced Power Reactor Plus (APR+). At KAIST, a Single-tube COndensation experiment facility of PAFS (SCOP) was constructed. The one-through type open loop test, where steam circulation is...

The Bunsen reaction section of I-S cycle has two parts, reaction and phase separation. Some previous work focused on phase separation using a simulated reaction mixture with four components (H2SO4, HI, H2O and I2). Based on phase separation data an operating window was suggested. This previous work had the limitation that reaction was not included....

One of the critical regulation issues for the development of a very high temperature reactor (VHTR) with a hydrogen production facility is the safety distance between a VHTR and a hydrogen production facility. The multi-energy method (MEM) was found as the effective correlation because it predicts an overpressure buildup rising from a detonation sh...

In this paper, we suggest the conceptual design of a water-cooled reactor system for a low-pressure inherent heat sink nuclear desalination plant that applies the safety-related design concepts of high temperature gas-cooled reactors to a water-cooled reactor for inherent and passive safety features. Through a scoping analysis, we found that the cu...

This study investigates heat transfer in a concrete cask such as one used at intermediate storage facilities of PWR spent fuels. Sufficient removal of decay heat is necessary not to damage fuel cladding that functions as a radioactive materials barrier. The experimental design parameters were derived in the half-scale model for the assessment of th...

Various reactor concepts and technologies have been devised and evaluated to ensure the integrity of the core and the containment under a prolonged station blackout. After the successful validation of the passive auxiliary feedwater system (PAFS) of Advanced Power Reactor Plus (APR+), Korea is considering an improved APR+ with a passive containment...

The hydrogen iodide (HI) decomposition process is a limiting step for the efficiency of the sulfur–iodine nuclear hydrogen production process, owing to its low kinetics and complicated reaction characteristics. Therefore, the Korea Advanced Institute of Science and Technology (KAIST) suggested a simple high-temperature HI decomposition process at 6...

Because of high marketability of SMR, although many countries are trying to develop SMR, the SMR market is not formed yet. For early dominance of SMR market, the SMR system should be fail-safe, simple and economical. In order to develop FAil-safe Simple Economical SMR (FASES) system we applied the design characteristics of HTGRs into water-cooled r...

A promising candidate for the intermediate heat exchanger (IHX) in high temperature gas-cooled reactors (HTGRs) and sodium-cooled fast reactors (SFRs) is a printed circuit heat exchanger (PCHE) due to its high effectiveness and compactness. We developed the thermal–hydraulic correlations for an airfoil PCHE by three-dimensional computational fluid...

We propose a hybrid HI decomposer, which combines a high-temperature catalytic decomposition reactor with a dual bed temperature-swing decomposer. For the high temperature step, we screened and identified a catalyst that is stable above 700 °C by preparing nickel catalysts supported on mesoporous alumina and evaluating their activity toward the hig...

The accident of the Fukushima nuclear power plant emphasized passive systems against prolonged station blackout. This paper aims at conceptual design of passive containment cooling system (PCCS) based on APR+, an advanced PWR developed in Korea with passive auxiliary feedwater system (PAFS). In the design, decay heat removal rate is to be maximized...

The design scheme and system codes for fusion application have been developed for the ITER Test Blanket Module (TBM) program in Korea in parallel with the breeding blanket development, which were based on the developed system codes in Gen. IV reactor development projects such as MARS (Multi-dimensional Analysis of Reactor Safety) and GAMMA (GAs Mul...

The design scheme and system codes for fusion application have been developed for the ITER Test Blanket Module (TBM) program in Korea in parallel with the breeding blanket development, which were based on the developed system codes in Gen. IV reactor development projects such as MARS (Multi-dimensional Analysis of Reactor Safety) and GAMMA (GAs Mul...

A Printed Circuit Heat Exchanger (PCHE) is considered as a promising candidate for the use of an intermediate heat exchanger (IHX) in High Temperature Gas-cooled Reactors (HTGRs), since PCHEs offer high effectiveness and a compact size. It has been reported that the use of binary mixture gas can increase the thermal efficiency and reduce the turbo-...

A visualization study was performed to identify the near-surface boiling structure and critical heat flux (CHF) triggering mechanism in a horizontal pool boiling of saturated water using a narrow transparent ITO heating surface. Total reflection and diagonal inside view techniques were applied in a synchronized manner. Contrary to the common postul...

Highlights ► The GAMMA-T code was well validated through benchmark experiments. ► Based on the KAIST coupling scheme, the GTHTR300 + MED systems were made. ► Safety analysis was performed for overcooling and undercooling accidents. ► In all accidents, maximum peak fuel temperatures were well below than 1600 °C. ► In all accidents, the HTGR + MED sy...

The supercritical CO2 Brayton cycle option for energy conversion in a sodium-cooled fast reactor (SFR) has recently received a great deal of attention due to highly reliable system design features that make it essentially free from risk of a sodium–water reaction in a traditional Rankine cycle power conversion. Although this novel approach will yie...

The efficiency of sulfuric trioxide decomposition strongly affects to the overall efficiency of the Iodine–Sulfur (IS) cycle, because the decomposition process is highly endothermic and most energy-consuming process. Therefore, we carefully selected iron (III) oxide (Fe2O3) for high temperature decomposition on the assumption of commercialization c...

The development of a small-sized nuclear heat-only plant with maximized safety features dedicated to seawater thermal desalination was proposed to address both a serious water crisis and nuclear safety issues, which continue to be perennial problems. In this study, the feasibility of a dedicated nuclear heat-only desalination system for a target co...

Boric acid precipitation in the core vessel of Pressurized Water Reactors (PWRs) must be avoided in order to assure that the core is maintained at acceptably low temperatures following any rupture in the primary system. A new evaluation method for boric acid ...

The sulfur-iodine thermo-chemical cycle (S-I cycle) is one of the promising nuclear hydrogen production methods combined with a high temperature gas-cooled reactor. However, extremely corrosive environments limit the selection of structural materials. Therefore, in this study, corrosion behaviors of several metallic materials were investigated to s...

The Korea nuclear industry has been developing the thermal-hydraulic system analysis Safety and Performance Analysis CodE (SPACE) and the GAs Multicomponent Mixture Analysis (GAMMA) code for safety analysis of pressurized water reactors (PWRs) and hightemperature gas-cooled reactors (HTGRs), respectively. SPACE will replace outdated vendor-supplied...

This summary provides an overview of the results of the U.S. DOE funded NERI (Nuclear Research Energy Initiative) program on development of the internally and externally cooled annular fuel for high power density PWRs. This new fuel was proposed by MIT to allow a substantial increase in power density (on the order of 30% or higher) while maintainin...

B.1.1 VIPRE modeling of PWR core with annular fuel: Optimization studies in the first year used an isolated channel and models for MDNBR analyses. These analyses provided sufficient knowledge of potential thermal hydraulic performance of annular fuels to select the 13x13 array as the most promising configuration. To obtain more realistic and accura...

The overall objective of this NERI project is to examine the potential for a high performance advanced fuel design for Pressurized Water Reactors (PWRs), which would accommodate a substantial increase of core power density while simultaneously providing larger thermal margins than current PWRs. This advanced fuel employs an annular geometry that al...

The nuclear desalination based on the high temperature gas-cooled reactor (HTGR) with gas turbomachinery and multi-effect distillation (MED) has been drawing attention, because it can utilize waste heat for desalination. In this paper, research objectives are as follows: (a) proposing an optimal design of HTGR + MED systems and (b) performance and...

An air ingress accident is a major safety issue pertaining to high-temperature gas-cooled reactors (HTGRs). When a helium depressurization accident occurs, air enters the core through broken pipes. The natural circulation (NC) phase of this accident leads to massive air ingress, causing extensive oxidation of the core graphite structure. The oxidat...

Various efforts have been made to improve the models and correlations of RELAP5/MOD3.3, which are activated only during the reflood phase of a large break loss-of-coolant-accident, the so-called “reflood model”. The film boiling heat transfer regime was divided into three sub-regimes and appropriate wall-to-fluid heat transfer coefficient correlati...

Seawater desalination is one of the most promising technologies to provide fresh water especially in the arid region. The most used technology in seawater desalination are thermal desalination (MSF and MED) and membrane desalination (RO). Some developments have been done in the area of coupling the desalination plant with a nuclear reactor to reduc...

A CFD (computational fluid dynamics) calculation for the SRI's hydrogen explosion test was performed to establish an analysis methodology for a hydrogen explosion phenomenon. A spark ignition model to simulate an electric spark of 40J in the SRI's hydrogen explosion test was developed based on an energy conservation law. The CFD analysis can reason...

Air-ingress events caused by large pipe breaks are important accidents considered in the safety analysis of Very High-Temperature Reactors (VHTRs). A main safety concern is the possibility of core-collapse following the failure of the graphite support column, which can be oxidized by ingressed air. The strength of the oxidized cylindrical graphite...

Capacitive deionization, CDI, is an economical desalination technology which has drawn much attention and progress recently. A tool to extend a pore model into an electrode model was developed for CDI simulation based on a single pore simulation model. By comparing two Biesheuvel's experimental data with the tool result, diffusion coefficients insi...

The off-take and the slug transition on air-water interface are experimentally investigated at the T-junction of the horizontal pipe with a vertical upward branch to simulate the loss-of-residual-heat-removal during a mid-loop operation in the Korea standard nuclear power plant. Scaling analysis is performed to scale down the experimental facility...

A printed circuit heat exchanger (PCHE) is considered for use as an intermediate heat exchanger (IHX) in high temperature gas-cooled Reactors (HTGRs), since PCHEs offer high effectiveness and a compact size. A PCHE consists of many micro-wavy channels, which increase heat transfer and pressure drop. The design parameters of PCHEs, such as angle, pi...

A steep increase in water demand and desertification has brought about much interest in desalination. Among existing desalination methods, capacitive deionization (CDI) gets attention due to its lower cost and simpleness. The most influential factor on CDI lies on the quality of electrodes. Though various investigations and developments of electrod...

This project is developing a fundamental conceptual design for a gas-cooled, modular, pebble bed reactor. Key technology areas associated with this design are being investigated which intend to address issues concerning fuel performance, safety, core neutronics and proliferation resistance, economics and waste disposal. Research has been initiated...

A Printed Circuit Heat Exchanger (PCHE) is a promising candidate with excellent performance to satisfy the heat exchanger requirements of High Temperature Gas Cooled Reactors (HTGRs). These heat exchangers are composed of many micro-wavy channels, which cause an increase in both heat transfer and pressure drop. We investigated thermal-hydraulic per...

An air-ingress accident is a major safety issue pertaining to high-temperature gas-cooled reactors. To see the effect of a stratified flow, which is a multi-dimensional phenomenon that occurs in large broken pipes, we perform 1-D and 2-D air-ingress simulations in the guillotine break of the main coaxial pipe of a 600MWth GT-MHR with the GAs multic...

To assess the boundary failure event in a supercritical CO_2 Brayton cycle power conversion system of a sodium-cooled fast reactor (SFR), sodium-CO_2 interaction tests were carried out and the major consequences were investigated. The tests were performed for normal operating temperature conditions of SFRs, and it was found the reaction kinetics de...

Capacitive deionization, CDI, is a new desalination technology which gained interest recently due to its economic advantages over existing technologies. To develop better electrode materials, this study focused on revealing CDI mechanisms and the most effective parameters. As current experimental techniques have limitations in producing well-define...

A series of experiments were carried out to investigate phenomena from bubble nucleation to lift-off for a subcooled boiling flow in a vertical annulus channel. A high-speed digital video camera was used to capture the bubble dynamics. The bubble lift-off diameter and bubble nucleation frequency were evaluated in terms of heat flux, mass flux, and...

For the supercritical C02 Brayton cycle of a sodium-cooled fast reactor, we carried out surface reaction tests for sodium temperatures ranging from 200 to 600°C. Based on the test results, we found that the reaction kinetics over the sodium temperature range of 300 to 550°C depends heavily on the temperature but is not sensitive to the velocity of...

This work involves the development of physical models for the constitutive relations of a two-fuid, three-dimensional sodium boiling code, THERMIT-6S. The code is equipped with a fluid conduction model, a fuel pin model, and a subassembly wall model suitable for simulating LMFBR transient events.

It is known that the typical six equation two-fluid model of the two-phase flow possesses complex characteristics, exhibits unbounded instabilities in the short-wavelength limit and constitutes an ill-posed initial value problem. Among the suggestions to overcome these difficulties, one model for the virtual mass force terms was studied here, becau...

A computational fluid dynamics (CFD) calculation for a hydrogen explosion test with a complicated obstacle tube geometry of pitch 21.3mm and diameter 99.1mm at a stoichiometric condition was performed to establish a CFD analysis method for a hypothetical hydrogen explosion accident between a very high temperature reactor (VHTR) and a hydrogen produ...