KAERI underground research laboratory: Overview of in-situ experiments

Social concerns regarding the safety of high-level radioactive waste have increased with growing public awareness of environmental issues and nuclear power.The performance assessment of deep geological disposal systems is crucial to reduce the uncertainties associated with high-level radioactive waste disposal and enhance the overall public confidence in nuclear safety.Accordingly,the Korea Atomic Energy Research Institute(KAERI)has undertaken various studies on the development of a deep geological disposal system for high-level waste and disposal safety evaluation.The KAERI Underground Research Tunnel(KURT),South Korea's only underground research laboratory dedicated to radioactive waste disposal,was constructed in 2006 and expanded in 2015.Since its construction,numerous in-situ experiments have been conducted and are currently underway in the KURT.The KURT plays a significant role in assessing the feasibility,safety,stability and appropriateness of a deep geological disposal system in South Korea and also provides an opportunity to revitalize industrial-academic-scientific cooperation between related institutions.This report summarizes two key in-situ experiments and international joint research conducted between 2007 and 2017 to assess the performance of the engineered and natural barriers of the KURT.The research experiences from the in-situ tests conducted at the KURT will provide crucial information on the safety and feasibility validation of the deep geological disposal system and will be an important contributor to the success of the Korean high-level radioactive waste disposal program in the future.

ICRF Heated Long-Pulse Plasma Discharges in LHD

A long-pulse plasma discharge for more than 30 min.was achieved on the LargeHelical Device(LHD).A plasma of n_e=0.8×10^(19)m^(-3)and T_(iO)=2.0 keV was sustained withP_(ICH)=0.52 MW,P_(ECH)=0.1 MW and averaged P_(NBI)=0.067 MW.Total injected heatingenergy was 1.3 GJ,which was a quarter of the prepared RF heating energy.One of the keys to thesuccess of the experiment was a dispersion of the local plasma heat load to divertors,accomplishedby shifting the magnetic axis inward and outward.

Properties of Dispersion Casting of Y2O3 Particles in Hypo,Hyper and Eutectic Binary Al-Cu Alloys

In the present work,the dispersion casting of Y-2O-3 particles in aluminum-copper alloy was investigated in terms of microstructural changes with respect to Cu contents of 20 （hypo）,33 （eutectic） and 40 （hyper） wt pct by scanning electron microscopy （SEM） and energy dispersive spectroscopy （EDS）.For the fabrication of Al-Cu alloy dispersed Y-2O-3 ceramic particles,stir casting method was employed.In case of Al-20 wt pct Cu alloy （hypoeutectic）,SEM images revealed that primary Al was grown up in the beginning.After that,eutectic phase with well dispersed ceramic particles was formed.In case of eutectic composition,Y-2O-3 particles were uniformly dispersed in the matrix.When the Cu is added into Al up to 40 wt pct （hypereutectic）,primary phase was grown up without any Y-2O-3 ceramic particles in the early stage of solidification.Thereafter, eutectic phase was formed with well dispersed ceramic particles.It can be concluded that Y-2O-3 ceramic particles is mostly dispersed in case of eutectic composition in Al-Cu alloy.

A Review of the Scaling Study of the CANDU-6 Moderator Circulation Test Facility

Following the previous relevant works [1]-[3], a scaling analysis is performed to derive a set of scaling criteria which were thought to be suitable for reproducing the major thermal-hydraulic phenomena in a scaled-down CANDU moderator tank similar to that in a prototype power plant during a full power steady state condition. The objective of building a scaled-down moderator tank is to generate the experimental data necessary to validate the computer codes which are used to analyze the accident analysis of CANDU-6 plants. The major variables of interests in this paper are moderator flow velocity and temperature of the moderator which is D2O inside the moderator tank during a steady state and transient conditions. The reason is that the local subcooling of the moderator is found to be a critical parameter determining whether the stable film boiling can sustain on the outer surface of the calandria tube if the contact of overheated pressure tube and cold calandria tube should occur due to pressure tube ballooning during LBLOCA with ECC injection failure [4]. The key phenomena involved include the inlet jet development and impingement, buoyancy force driven by the moderator temperature gradient caused by non-uniform direct heating of the moderator, and the pressure drop due to viscous friction of the flow across the calandria tube array. In this paper, the previous researches are reviewed, some concerns or potential problems associated with them implied by comparing CFD analyses results between the CANDU-6 moderator tank and 1/4 scaled-down test facility are described, and as a way to examine the assumption of the scaling analysis is true an order-of-magnitude analyses are performed. Based on the results of these analyses the assumption of neglecting ?and ?terms cannot be justified for the power of 0.5 MW and 1.566 MW for the 1/4 scaled-down facility. Further investigation is thought to be necessary to confirm this result, i.e. if the scaling of the previous work1 is justifiable by some other independent analyses.

PIV Measurement of Velocity Distribution in the Moderator Circulation Test (MCT)

Korea Atomic Energy Research Institute (KAERI) has been carrying out a scaled-down moderator test program to simulate the CANDU-6 moderator circulation phenomena during steady state operation and accident conditions. The Moderator Circulation Test (MCT) facility was designed and constructed as 1/4 scale of the prototype of CANDU-6 reactor. In the present work spatial distribution of two-dimensional velocity in the MCT facility under isothermal condition was measured using planar Particle Image Velocimetry (PIV) system which consists of double pulsed laser, synchronizer, and high speed camera. TSI’s Insight TM 4G software was used to perform PIV image capturing, PIV calculation and post processing. 10 μm sized silver-coated hollow sphere particles were used as flow tracer particles. Multiple experiments were conducted to cover large area of the MCT facility with limited field of view of a single camera. Instantaneous and averaged velocity field were analyzed for each spatial position and flow rate. This research is capable of offering validation data for self-reliant CFD tools to predict moderator subcooling margin in CANDU-6 reactor.

Comparison of numerical codes for coupled thermo-hydro-mechanical simulations of fractured media

Geo-energy and geo-engineering applications,such as improved oil recovery(IOR),geologic carbon storage,and enhanced geothermal systems(EGSs),involve coupled thermo-hydro-mechanical(THM)processes that result from fluid injection and production.In some cases,reservoirs are highly fractured and the geomechanical response is controlled by fractures.Therefore,fractures should explicitly be included into numerical models to realistically simulate the THM responses of the subsurface.In this study,we perform coupled THM numerical simulations of water injection into naturally fractured reservoirs(NFRs)using CODE_BRIGHT and TOUGH-UDEC codes.CODE_BRIGHT is a finite element method(FEM)code that performs fully coupled THM analysis in geological media and TOUGH-UDEC sequentially solves coupled THM processes by combining a finite volume method(FVM)code that solves nonisothermal multiphase flow(TOUGH2)with a distinct element method(DEM)code that solves the mechanical problem(UDEC).First,we validate the two codes against a semi-analytical solution for water injection into a single deformable fracture considering variable permeability based on the cubic law.Then,we compare simulation results of the two codes in an idealized conceptual model that includes one horizontal fracture and in a more realistic model with multiple fractures.Each code models fractures differently.UDEC calculates fracture deformation from the fracture normal and shear stiffnesses,while CODE_BRIGHT treats fractures as equivalent porous media and uses the equivalent Young’s modulus and Poisson’s ratio of the fracture.Finally,we obtain comparable results of pressure,temperature,stress and displacement distributions and evolutions for the single horizontal fracture model.Despite some similarities,the two codes provide increasingly different results as model complexity increases.These differences highlight the challenging task of accurately modeling coupled THM processes in fractured media given their high nonlinearity.

Practical Activities to Improve Transfer of Learning in the Nuclear-Related Continuing Professional Educations for Developing Countries in Korea

Much in-class education and training for developing countries have focused on how a learner absorbs knowledge and skills efficiently or effectively in the class,but are less interested in how the learners should transfer the knowledge and skills into their jobs in their workplace.In principle,in-class education and training have a difficulty with applying the learned knowledge and skills to learners’jobs in the workplace in comparison with any other practical-basis training.To overcome this difficulty,many educational stakeholders in the nuclear field have concentrated on how learners can transfer the knowledge and skills absorbed in the class into their jobs in their workplace.The action learning activity for learners can be one of the solutions to apply the knowledge and skills to their job in the workplace.The purpose of this study is to clarify how the transfer of learning has been implemented in the nuclear-related continuing professional educations and training for developing countries in Korea.To accomplish this purpose,this study is implemented as follows.The first is to define the concept of the“transfer of learning”clearly.The second is to clarify the core elements of the transfer of learning.Along with the clarification,the third is to show how the transfer of learning has been implemented in the continuing professional nuclear-related education and training for developing countries in Korea.The fourth is to present core problems in such education and training.As the fifth,this study suggests alternatives to overcome the core problems in the nuclear-related continuing professional education and training.

Critical factors to inhibit water-splitting side reaction in carbon-based electrode materials for zinc metal anodes

Zinc metal anodes(ZMA)have high theoretical capacities(820 mAh g−1 and 5855 mAh cm−3)and redox potential(−0.76 V vs.standard hydrogen electrode),similar to the electrochemical voltage window of the hydrogen evolution reaction(HER)in a mild acidic electrolyte system,facilitating aqueous zinc batteries competitive in next-generation energy storage devices.However,the HER and byproduct formation effectuated by water-splitting deteriorate the electrochemical performance of ZMA,limiting their application.In this study,a key factor in promoting the HER in carbon-based electrode materials(CEMs),which can provide a larger active surface area and guide uniform zinc metal deposition,was investigated using a series of threedimensional structured templating carbon electrodes(3D-TCEs)with different local graphitic orderings,pore structures,and surface properties.The ultramicropores of CEMs are the determining critical factors in initiating HER and clogging active surfaces by Zn(OH)2 byproduct formation,through a systematic comparative study based on the 3D-TCE series samples.When the 3D-TCEs had a proper graphitic structure with few ultramicropores,they showed highly stable cycling performances over 2000 cycles with average Coulombic efficiencies of≥99%.These results suggest that a well-designed CEM can lead to high-performance ZMA in aqueous zinc batteries.

1.45 GPa ultrastrong cryogenic strength with superior impact toughness in the in-situ nano oxide reinforced CrMnFeCoNi high-entropy alloy matrix nanocomposite manufactured by laser powder bed fusion

CrMnFeCoNi high-entropy alloys(HEAs)exhibit an excellent combination of tensile strength and ductility at cryogenic temperatures.This study led to the introduction of a new method for the development of high-performance CrMnFeCoNi HEAs at cryogenic temperatures by jointly utilizing additive manufacturing(AM)and the addition of interstitial atoms.The interstitial oxygen present in the powder feedstock was transformed into beneficial nano-sized oxides during AM processing.The HEA nanocomposite fabricated using laser powder bed fusion(L-PBF)not only contains heterogeneous grains and substructures but also a high number density of nano-sized oxides.The tensile results revealed that the L-PBF HEA nanocomposite has superior yield strengths of 0.77 GPa and 1.15 GPa,and tensile strengths of 0.92 GPa and 1.45 GPa at 298 K and 77 K,respectively.In addition,the Charpy impact energies of the samples tested at 298 K and 77 K were measured as 176.2 J and 103.7 J,respectively.These results indicate that the L-PBF HEA nanocomposite successfully overcomes the well-known strength-toughness trade-off.The tensile deformation microstructure contained a relatively large number of deformation twins(DTs)at cryogenic temperature,a possible consequence of the decrease in the stacking fault energy with decreasing temperature.On the other hand,cracks were found to propagate along the grain boundaries at room temperature,whereas a transgranular crack was observed at cryogenic temperature in the specimens fractured as a result of the Charpy impact.

Heavy Metals in Brown Rice(Oryza sativa L.) and Soil After Long-Term Irrigation of Wastewater Discharged from Domestic Sewage Treatment Plants

A pot experiment was conducted in a plastic film house to evaluate the translocation and uptake of heavy metals(Pb,Cd,Cu,and Zn) into brown rice(Oryza sativa L.) and the heavy metals residues in soils which had previously been irrigated with domestic wastewater for a long time(3 years).The range of Pb,Cd,Cu,and Zn was 5.10 ± 0.01,0.105 ± 0.017,5.76 ± 0.42,and 23.56 ± 1.40 mg kg-1,respectively in the domestic wastewater-irrigated soil,and 0.370 ± 0.006,0.011 ± 0.001,0.340 ± 0.04,and 2.05 ± 0.18 mg kg-1,respectively,in the domestic wastewater-irrigated brown rice.The results indicated that application of domestic wastewater to arable land slightly increased the levels of Pb,Cd,Cu,and Zn in soil and brown rice(P < 0.01).The concentrations of heavy metals in brown rice were lower than the recommended tolerable levels proposed by the Joint FAO/WHO Expert Committee on Food Additives.However,the continuous monitoring and pollution control of hazardous materials from domestic wastewater are needed in order to prevent excessive build-up of heavy metals in the food chain.

Superior anti-icing strategy by combined sustainable liquid repellence and electro/photo-responsive thermogenesis of oil/MWNT composite

This paper introduces an effective anti-icing strategy that uses passive anti-icing property and active de-icing functions concurrently.These dual capabilities can alleviate the icing problem more effectively than either a passive or active function alone.The developed material is a slippery liquid-repellent elastic conductor(SLEC);it is an organogel that is composed of multi-walled carbon nanotubes,oil,and polydimethylsiloxane.The SLEC maintains passive water-droplet sliding ability even on wet surfaces that frequently occur in cold conditions(e.g.,during condensation and defrosting),suppresses ice nucleation,and shows ice adhesion strength as low as^20 kPa.The SLEC releases heat when it is subject to electrical or photonic stimulation,and can therefore it can prevent ice formation and melt ice that has already formed on a surface.This material has sustainable liquid repellence by syneresis and replenishment;this ability ensures long-lasting anti-icing property,and results in exceptional durability.This durability is stable against mechanical damage.The superior dual anti-icing capabilities together with the sustainable and stable liquid repellence should generate synergistic effects,and yield a powerful anti-icing tool that can broaden the range of icing applications.