The Colloid Formation and Migration (CFM) international joint research initiative continues as a part of the GTS’s Radionuclide Retardation Programme, which has been in progress since 1984. This project focuses on examining the formation of colloids from a bentonite-engineered barrier system and exploring how these colloids impact the migration of radionuclides in fractured host rock when subjected to advective flow. Phase 1 of the project was launched in 2004 and concluded in early 2008, focusing on preliminary studies related to in-situ boundary conditions, predicting models, and supplementary lab works. Following that, Phase 2 spanned from 2008 to 2013 and aimed at fortifying the field setup by adding three new monitoring boreholes and suitable instrumentation in both the boreholes and tunnel. This phase also tested the system’s resilience while mapping the flow domain. Phase 3 kicked off in January 2014 and extended until December 2018. During this period, the Long-term In-situ Test (LIT) was introduced in May 2014, featuring a set of compacted bentonite rings laced with radionuclide tracers. These were placed in a borehole to serve as a colloid and radionuclide source. CFM Phase 4 initiative commenced in January 2019, marking the successful deployment of the i-BET (In-situ Bentonite Erosion Test). This project component involves placing approximately 50 kg of compacted bentonite in a natural water-conducting shear zone. Korea Atomic Energy Research Institute (KAERI) joined CFM in 2008 to examine the behavior of colloid generation and migration with radionuclides in the Underground Research Laboratory. The fourth phase of the CFM project was also scheduled to include a post-mortem evaluation of the LIT and additional tracer experiments in the well-mapped MI shear zone. This study aims to provide an interim update on the ongoing i-BET, a key component of Phase 4 of the CFM project. We will also discuss the current status of the post-mortem analysis for the LIT experiment. In addition, we will outline plans for the forthcoming Phase VI of the project. These plans will continue to advance our understanding of radionuclide migration and the influence of bentonite-based disposal systems.

In the high-level waste disposal systems, colloids generated through the chemical erosion of bentonite buffers can serve as critical mediators for the transport of radionuclides from the disposal environment to the biosphere. The stability of these colloids is influenced by the chemical composition of the groundwater. According to DLVO theory, the Critical Coagulation Concentration (CCC) is the ionic strength at which the total repulsive force between colloids is either less than or equal to the total attractive force. At ionic strengths lower than the CCC, electrostatic double-layer repulsion outweighs van der Waals attraction, forming a repulsive barrier between particles. Conversely, at ionic strengths higher than the CCC, attractive forces dominate, leading to particle aggregation. To investigate the CCC of bentonite colloids, this study focused on Ca-type WRK bentonite. Colloids separated from a ten g/L bentonite suspension underwent centrifugation (1,200 g for 30 minutes) and dialysis (3,500 MWCO) to produce colloid samples. After adjusting the ionic strength from 0.1 mM to 10 mM, the particle size distribution was monitored as a function of aggregation time for approximately 20 days. Rate constants, calculated based on variations in ionic strength, were used to interpret the observed results. The experimental outcomes revealed that the CCC value for WRK bentonite colloids was an order of magnitude lower with CaCl2 than with NaCl. This suggests that Ca ions have a more significant impact on colloid stability, which has implications for the longterm safety of high-level waste disposal systems.

Concerns with colloids, dispersed 1~1,000 nm particles, in the LILW repository are being raised due to their potential to enhance radionuclide release. Due to their large surface areas, radionuclides may sorb onto mobile colloids, and drift along with the colloidal transport, instead of being sorbed onto immobile surfaces. To prevent adverse implications on the safety of the repository, the colloidal impact must be evaluated. In this paper, colloid analysis done by SKB is studied, and factors to be considered for the safety assessment of colloids are analyzed. First, the colloid generation mechanism should be analyzed. In a cementitious repository, due to a highly alkaline environment, colloid formation from wastes may be promoted by the decomposition of organic materials, dissolution of inorganic materials, and corrosion of metals. Radiolysis is excluded when radionuclide inventory is moderate, as in the case of SKB. Second, colloid stability should be evaluated to determine whether colloids remain in dispersion. Stable colloids acquire electric charges, allowing particles to continuously repel one another to prevent coagulation. Thus, stability depends on the pH and ionic condition of the surroundings, and colloid composition. For instance, under a highly alkaline cementitious environment, colloids tend to be negatively charged, repelling each other, but Ca2+ ion from cement, acting as a coagulant, makes colloid unstable, promoting sedimentation. As in the case of SKB, the colloidal impact is assumed negligible in the silo, BMA, and BTF due to their extensive cement contents, but for BLA, with relatively less cement source, the colloidal impact is a potential concern. Third, colloid mobility should be assessed to appraise radionuclide release via colloid transport. The mobility depends on the density and size of colloids, and flow velocity to commence motion. As a part of the assessment, the filtration effect should also be included, which depends on pore size and structure. As in the case of SKB, due to static hydraulic conditions and engineering barriers, acting as efficient filters, colloidal transport is expected to be unlikely. In the domestic underground repository, the highly alkaline environment would lead to colloid formation, but due to high Ca2+ concentration and low flow velocity, colloids would achieve low stability and mobility, thus colloidal impact would be a minor concern. In the future, with further detailed analysis of each factor, waste composition, and disposal condition, reliable data for safety evaluation could be generated to be used as fundamental data for planning waste acceptance criteria.

Bentonite is a promising buffer material for high-level radioactive waste (HLW) disposal due to the high nuclides sorption capacity and swelling property. However, bentonite has the potential to generate colloid particles, with small particle sizes less than 1,000 nm when in contact with groundwater. The bentonite colloids easily form pseudo-colloid with the released nuclides and migrate through the water-conducting rock to the biosphere. Therefore, understanding the generation and migration of bentonite colloids is crucial in assessing the safety of the HLW repository. In this study, an artificial fracture system was prepared to investigate colloid release from compacted bentonite. A 250 mm diameter acrylic artificial fracture system was used, with 30 mm of compacted calcium bentonite installed. Artificial groundwater flow was injected into the system at a flow rate of 250 μL/h, and every 6 mL of leachate was collected by a fraction collector. A film-type pressure sensor was equipped to monitor the swelling pressure, and the swelling was observed using a digital microscope. The results indicate that the compacted bentonite formed a mineral ring originating from the swelling of the bentonite, and the end of the ring generated colloid particles due to chemical erosion. Although the release rate of colloids increased with increasing flow rate, the colloid ratio depended on the low ionic strength of the injected artificial groundwater. This work contributes to the understanding of the chemical erosion and colloid release mechanism of compacted bentonite.

Colloid Formation and Migration (CFM) project is being carried out within the Grimsel Test Site (GTS) Phase Ⅵ. Since 2008, the Korea Atomic Energy Research Institute (KAERI) has joined CFM to investigate the behavior of colloid-facilitated radionuclide transport in a generic Underground Research Laboratory (URL). The CFM project includes a long-term in-situ test (LIT) and an in-rock bentonite erosion test (i-BET) to assess the in-situ colloid-facilitated radionuclide transport through the bentonite erosion in the natural flow field. In the LIT experiment, radionuclide-containing compacted bentonite was equipped with a triple-packer system and then positioned at the borehole in the shear zone. It was observed that colloid transport was limited owing to the low swelling pressure and low hydraulic conductivity. Therefore, a postmortem analysis is being conducted to estimate the partial migration and diffusion of radionuclides. The i-BET experiment, that focuses more on bentonite erosion, was newly designed to assess colloid formation in another flow field. The i-BET experiment started with the placement of compacted bentonite rings in the double-packer system, and the hydraulic parameters and bentonite erosion have been monitored since December 2018.

According to the continued generation of spent nuclear fuel, a reliable safety assessment is highly required with the precise modeling of the migration and retardation behavior of radionuclides to enhance public acceptance and hinder excessive conservativeness during the construction of the repository. In particular, the colloids formed in the repository-relevant condition are known to accelerate the migration of radionuclides. Thus, geochemical behavior and relevant characteristics of colloids are needed to be unambiguously clarified. The objective of the present work is to investigate the fundamental characteristics of colloids contained in the natural groundwater system by using various analytical methods and the tangential flow ultra-filtration (TFUF) system. The granitic groundwater sample from the DB-3 borehole at the KURT (KAERI Underground Research Tunnel) was taken by an airtight stainless steel cylinder coated on the inside with PTFE to prevent the infiltration of ambient air into the geologic groundwater sample. And then, the groundwater sample was transferred to the inert glovebox filled with Ar gas to monitor the pH and Eh equilibrium of the aqueous sample. For further investigation, the colloid contained in the groundwater sample was concentrated by using the TFUF system equipped with a membrane filter (pore size: 3 kDa). The concentrated groundwater sample was analyzed with various methods such as ICP-MS/OES, IC, DLS/ELS, FE-TEM/SEM-EDS, ATR-FTIR, TOC, LC-OCD, etc. In this study, the size of groundwater colloids was determined to be 182.3 ± 52.7 nm with the major constituents of C, S, O, Fe, Al, Si, etc. The amount of organic carbon and the concentrations of organic substances determined by means of the molecular weight fraction with the TOC and LC-OCD provide further detailed information for the colloids in the KURT groundwater sample. The results obtained in this study are expected to be used as preliminary experimental data for modeling the colloid-facilitated migration of radionuclides to improve the reliability of the safety assessment of the geologic repository.

분리막을 이용한 생물학적 처리 공정(MBR)은 과다한 에너지 사용, 제품의 높은 단가 등이 단점으로 지목되었으나, 제품 및 시스템 개선이 이루어지고 있는 추세이다. 그럼에도 불구하고 MBR 공정의 운영시 발생되는 대부분의 막 오염은 슬러지 특성에 따른 유기물 오염이라고 할 수 있다. 일반적으로 슬러지 여과능과 TMP 증가 기울기는 연관성이 높은 것으로 알려져 있으며 MBR 공정에서 분리막의 막오염 제어를 위해 슬러지 여과능은 중요한 관리 지표가 될 수 있다. 본 연구에서는 슬러지 여과능에 대해 colloid 물질, 특히 EPS 와 SMP 유분이 미치는 영향을 확인하고자 하였다.

본 연구에서는 콜로이드와 핵종의 복합이동에 관한 수치모델을 개발하였다. 콜로이드와 핵종의 반응-이동 지배방정식을 풀기 위하여 Operator Splitting Method 중 Strang의 분리 SNI 방식을 수치해석 방법으로 채택하였고 이는 MATLAB을 이용하여코드화 되었다. 개발된 수치모델은 용질의 이동 및 분산만을 고려한 해석해를 통한 검증과정에서 피어슨 상관계수의 제곱값(r2)이 0.99 이상으로 나타나 모델의 정확성이 입증되었다.

Ag spot-coated Cu nanopowders were synthesized by a hydrothermal-attachment method (HA) using oleic acid capped Ag hydrosol. Cu nano powders were synthesized by pulsed wire exploding method using 0.4 mm in diameter of Cu wire (purity 99.9%). Synthesized Cu nano powders are seen with comparatively spherical shape having range in 50 nm to 150 nm in diameter. The oleic acid capped Ag hydrosol was synthesized by the precipitation-redispersion method. Oleic acid capped Ag nano particles showed the narrow size distribution and their particle size were less than 20 nm in diameter. In the case of nano Ag-spot coated Cu powders, nanosized Ag particles were adhered in the copper surface by HAA method. The components of C, O and Ag were distributed on the surface of copper powder.

Polyvinyl acetate (PVAc) prepared by emulsion polymerization has broad applications for additive such as paint binder, adhesive for wood and paper due to its low glass transition temperature which help to plasticize substrate resins. Since emulsion polymerization has a disadvantage that surfactant and ionic initiator degrade properties of the product polymer, poly (vinyl acetate-eo-ethyl acrylate) (VAc-EA) was synthesized using potassium persulfate as catalyst and polyvinylalcohol (PVA) as protective colloid to prevent the degradation. The copolymer latex product was internally plasticized and has enhanced adhesion, water resistance during VAc-EA emulsion polymerization. No coagulation and complete conversion occur with the reactant mixture of 10 mmol/L potassium persulfate, 10 mmol/L poly ( vinyl alcohol) (PVA 17). As the concentrations of PVA increase, the viscosity becomes increase.

본 연구에서는 KURT (KAERI 지하처분연구시설)를 포함한 지하연구시설에서 핵종 및 콜로이드 이동에 대 한 연구현황을 조사하였다. 화강암과 같은 결정질 암반층에 건설된 해외 지하연구시설들을 간략하게 소개하 고 비교하였다. 특히 Grimsel Test Site (GTS)와 ¨Asp¨o Hard Rock Laboratory에서의 핵종 및 콜로이드 이동연 구에 대한 주요 국제공동연구의 연구항목 및 내용, 진행중인 연구 프로젝트, 연구계획 등에 대해 조사하였다

The purpose of this study was to assess the removal efficiency of formaldehyde using carbon nano colloid (CNC) which was produced by comparatively easy and cheap method. In this study, carbon nano colloid based on water was produced by an electro‐chemical method. The particles which have mostly a spherical shape whose diameter was, what is called,‘nano‐size’were produced. Non‐woven fabric filter, which is currently on the market as a medium filter, was used for the removal efficiency test. Known concentration (0.5 ppm) of formaldehyde standard gas was used as a pollutant. The overall results indicate that (1) nanosize carbon colloids which have a stable dispersibility of which diameter is approximately 10 nm or less, (2) filters treated with carbon nano colloids showed higher removal efficiency, 44.47 ㎍ of HCHO removed/g of carbon and 19.28 ㎍ of HCHO removed/g of carbon, compared to the control experiment using a normal carbon filter, 1.45 ㎍ of HCHO removed/g of carbon.

본 연구에서는 국내산 경주벤토나이트를 이용하여 제조한 벤토나이트 콜로이드에 대한 산화환원 반응에 대체적으로 안정한 다가 핵종인 Eu(III)와 Th(IV)의 실험적 수착 연구를 수행하였다. 수착실험에 대한 공시험을 수행하여 반응용기 벽면에 의해, 침전에 의해, 콜로이드 형성에 의해 손실된 핵종들의 양을 평가하였다. 그리고 이러한 손실들을 반영한 Eu(III)와 Th(IV)의 벤토나이트 콜로이드에 대한 수착분배계수 값을 구하고 조사하였다. 세 종류의 손실양을 반영한 벤토나이트 콜로이드의 순수한 수착분배계수 값은 pH 변화에 따라 Eu(III)의 경우 정도의 값을 가지고, Th(IV)의 경우 정도의 값을 가지는 것으로 관측되었다. 특히 Eu(III)의 경우엔 pH 5 이상에서 침전의 영향이 크게 나타났고, Th(IV)의 경우엔 pH 3 이후에 콜로이드 형성과 침전의 영향이 크게 나타났다. 따라서 주어진 농도에서 콜로이드 형성 및 침전 영향이 커지는 pH 이후에는 Eu(III) 및 Th(IV)과 같은 다가 핵종들의 정확한 수착분배계수를 구하기 위해서는 이러한 침전 및 콜로이드 형성과 같은 영향이 반영되어야 할 것이다.

본 연구에서는 현재 국내에서 고준위 방사성폐기물 처분장의 잠재적인 완충재 물질로 고려되고 있는 경주벤토나이트에서 발생 가능한 벤토나이트 콜로이드로의 우라늄(VI) 수착특성에 대한 실험적 연구를 pH 및 이온강도의 함수로 수행하였다. 경주벤토나이트로부터 분리된 콜로이드는 주로 몬모릴로나이트로 구성되어 있다. 중력여과법을 사용하여 측정한 결과 농도 및 크기는 약 5100 ppm 및 200-450 nm 이었다 우라늄 수착실험에 대한 공시험을 수행하여 수착 반응용기 벽면에 흡착, 침전, 한외여과에 의해 손실된 우라늄 양을 평가하였다. 이러한 과정에 의해 제거된 우라늄의 양은 미량이었다. 그러나 한외여과에 의한 우라늄 손실의 경우 이온강도가 낮은 경우 즉, 0.001 M 의 경우 한외여과 필터의 표면전하 역전에 의한 양이온 수착 영향으로 인해 매우 높은 핵종 손실을 유발하였다. 벤토나이트 콜로이드에 대한 우라늄(VI)의 수착 분배계수 (또는 의사콜로이드 형성상수)는 PH 및 이온강도에 따라 값을 가지며 pH 중성영역인 6.5 근처에서 최대값을 가지는 것으로 나타났다. 벤토나이트에 대한 우라늄(VI)의 수착은 pH, 이온강도, 탄산농도 등과 같은 지화학적 변수들에 의존하는 수용액에서 우라늄화학종과 매우 밀접한 관련이 있다 따라서 벤토나이트 완충재로부터 발생된 벤토나이트 콜로이드는 높은 수착능으로 인해 우라늄(VI)을 의사콜로이드(pseudo-colloid)의 형태로 지질학적 매질을 통해 이동시킬 수 있을 것이다.

본 연구에서는 금 나노입자 콜로이드를 이용하여 safranin-O의 광촉매적 분해를 관찰하였다. 금 나노입자는 용액상에서 safranin-O의 분해 속도를 빠르게 하기 위해서 사용되었다. 금 나노입자 콜로이드는 수용액상에서 Na₂CO₃ 와 PVP 고분자(poly(vinyl pyrrolidone))를 이용하는 환원방법에 의하여 제조하였다. Safranin-O의 분해현상은 자외선(UV light)와 과산화수소(H₂O₂)의 존재 하에서 금 나노입자 콜로이드와 염화금의 농도, 반응계의 산도(pH), 반응시간과 같은 실험조건들의 조절을 통해 연구되었다. 분해반응에 사용된 금 나노입자 콜로이드의 농도가 증가함에 따라서 염료가 분해되는 속도가 증가하였다. Safranin-O의 광산화 반응은 광학적으로 측정되었고, 금 나노입자의 기본적인 물성과 촉매 특성은 UV-Vis 광학계를 이용하여 측정되었다.