During the dismantling of nuclear facilities, a large quantity of radioactive concrete is generated and chelating agents are required for the decontamination process. However, disposing of environmentally persistent chelated wastes without eliminating the chelating agents might increase the rate of radionuclide migration. This paper reports a rapid and straightforward ion chromatography method for the quantification of citric acid (CA), a commonly used chelating agent. The findings demonstrate acceptable recovery yields, linearities, and reproducibilities of the simulated samples, confirming the validity of the proposed method. The selectivity of the proposed method was confirmed by effectively separating CA from gluconic acid, a common constituent in concretes. The limits of detection and quantification of the method were 0.679 and 2.059 mg·L−1, respectively, while the recovery yield, indicative of the consistency between theoretical and experimental concentrations, was 85%. The method was also employed for the quantification of CA in a real concrete sample. These results highlight the potential of this approach for CA detection in radioactive concrete waste, as well as in other types of nuclear wastes.

Chelating agents, such as EDTA, NTA, and citric acid, possess the capacity to establish complexes with radionuclides, potentially enhancing the migration of such radionuclides from the disposal sites. Hence, quantification of these chelating agents in radioactive wastes is required to ensure secure disposal protocols. The determination of chelating agents in radioactive wastes is mainly composed of two steps, e.g. extraction and detection. However, there are little information on the extraction of the chelators in various radioactive wastes. We endeavored to optimize the extraction conditions for citric acid (CA) found within concrete, a prevalent component in the context of dismantled waste materials. Given the inherent high solubility of CA in water, we applied an aliquot of deionized water to the concrete and conducted a one-hour ultrasonic leaching procedure to facilitate chelate extraction. Subsequently, following the preparation of the concrete leachate via vacuum filtration and centrifugation to yield a clarified solution, we quantified the concentration of CA within the solution using Ion Chromatography (IC). To enhance leaching efficiency, we examined the % recovery variation with respect to the pH of the leaching solution. The optimized extraction method will be applied to diverse chelating agents and radioactive waste categories.

Chelating agents, such as ethylenediaminetetraacetic acid (EDTA), diethylenetriaminepentaacetic acid (DTPA), and nitrilotriacetic acid (NTA) are widely used in industry and agriculture as water softeners, detergents, and metal chelating agents. In wastewater treatment plants, a significant amount of chelating agents can be discharged into natural waters because they are difficult to degrade. Since those compounds affect the mobility of radionuclides or heavy metals in decontamination operations at nuclear facilities and radioactive waste disposal, quantification of the amount of ligand is very important for safe nuclear waste management. To predict the behavior of the main complexation in sample matrices of radioactive wastes, it is essential to evaluate the distribution of the metal-chelating species and their stabilities in order to develop analytical techniques for quantifying chelating agents. We have investigated to collect information on the pH speciation of metal chelation and the stability constants of metal complexes depending on three chelating agents (EDTA, DTPA, and NTA). For example, Zhang’s group recently reported that the initial coordination pH of Cu(II) and EDTA4− is delayed with the addition of Fe(III), and the pH range for the stable existence of [Cu(EDTA)]2− is narrowed compared to when it is alone in the sample matrix. The addition of Fe(III) clearly impacts the chemical states of the Cu(II)-EDTA solution. Additionally, Eivazihollagh’s group demonstrated differences in the speciation and stability of Cu(II) species between Cu(II) and three chelating ligands (EDTA, DTPA, and NTA). This study will be greatly helpful in identifying the sample matrix for binding major chelating agents and metals as well as developing chemically sample pretreatment and separation methods based on the sample matrix. Finally, these advancements will enable reliable quantitative analysis of chelating agents in decommissioning radioactive wastes.

본 연구에서는 시가독소 생성 대장균(STEC)을 검출하 기 위해 식품공전의 polymerase chain reaction (PCR)검사 법과 loop-mediated isothermal amplification (LAMP)를 비 교하였다. PCR 및 LAMP의 검출 한계(LOD) 및 정량화 한계(LOQ), 민감도, 특이성 및 효율성을 평가하기 위해 다 양한 식품에 STEC를 접종하였다. LOD는 PCR의 경우 104 CFU/mL 이하, LAMP의 경우 103 CFU/mL 이하로 측정되 었다. LOQ 값은 PCR과 LAMP 간에 차이가 없었다. 그러 나 4가지 식품군에서 민감도는 양념육이 최대 11.1%, 간 소고기가 최소 8.1% 차이가 났다. LAMP는 네 가지 음식 유형 모두에 대해 높은 민감도와 100% 특이도를 보였다. 따라서 LAMP는 식품 유형에 따라 검출률이 비슷하고 특 이도와 민감도가 식품공전 PCR보다 우수하기 때문에 STEC 에 대한 신뢰할 수 있는 분자 검출 방법이다.

Plutonium exhibits a variety of oxidation states and has a strong affinity for complexation with organic ligands. Isosaccharinic acid (ISA) is a major degradation product of cellulose materials present in the low to intermediate radioactive wastes. The interaction between trivalent plutonium and ISA can significantly impact the migration and containment of plutonium in the repository environment. In this study, formation of Pu(III) and ISA complexes was investigated at an ionic strength of 1 M of NaClO4 using UV-Vis absorption spectrophotometry. To exclude the effect of the Pu(III) oxidation, absorption spectra were measured within 10 min after adding ISA into Pu(III) solution and processed using HYPSPEC software for deconvolution after baseline correction. Several previous studies showed that the presence of ligands accelerates the oxidation of Pu(III) to Pu(IV). To investigate whether ISA complexation can also accelerate the Pu(III) oxidation, UV-Vis absorption spectra changes over 24 hours were analyzed as a function of the ratio of ISA to plutonium concentration.

Low- and intermediate-level radioactive waste for permanent disposal often contains organic complexing agents, so-called chelating agents. Organic complexing agents, which are polycarboxylic acids, can increase the mobility of radionuclides into the environment by forming water-soluble complexes with most heavy metals. Therefore, analyzing the complexing agents in radioactive waste is crucial for comprehensive management of nuclear wastes. According to regulatory guidelines, specifically Notice No. 2021-16 issued by the Nuclear Safety and Security Commission, the determination of chelating agent content in radioactive waste materials is required to ensure proper management and safe disposal. However, only a few methods are available to analyze the chelators in various matrices such as concrete, metals, soil, and mixed solid wastes like plastics, vinyl, and rubber. Recently, we found a UV-Vis method based on an enzymatic reaction is inadequate for analyzing citric acid in radioactive waste with a complex matrix like concrete. To address this, we developed a method to determine the contents of EDTA and NTA using a UV-Vis spectrophotometer and citric acid using ion chromatography. The results showed good validity and reliability to determine the chelating agents in various radioactive wastes.

Complexing agents used at various nuclear facilities exist in low- and intermediate level radioactive wastes deposited in the repository site. In addition these will be generated through the degradation of the wastes such as cellulose materials. The presence of chelating agents may possibly affect the safety of the wastes repository by promoting the migration of radionuclides into geosphere. Thus, under Nuclear Safety and Security Commission’s Notice No. 2021-16, the contents of chelating agents in radioactive wastes are required to be determined for the secured disposal. UV-Vis method based on an enzymatic reaction was proved to be in adequate to analyze citric acid in radioactive wastes with complex matrix, especially for concrete. A rapid automated method using ion chromatography (IC) for analysis of citric aicd in concrete samples is developed. This automated method enables a sample solution to measure without pretreatment and a target substance to separate from other concrete admixtures. Also, the developed method here, for radioactive concrete wastes was successfully applied to real samples with lowering a limit of quantification value.

Chelating agents, such as EDTA, NTA, and citric acid, can form radionuclide-chelate complexes that may enhance the migration of radionuclides from disposal sites. Therefore, the contents of these chelators in radioactive wastes are determined for the secured disposal. In this study, a rapid automated method using ion chromatography (IC) is described for analysis of chelating agents. The method enables direct use of a sample solution for the measurement unlike colorimetric or enzymatic methods. In these cases, lots of chemicals are consumed to convert the chelating agents to be UV-Vis-active compounds during the pretreatment process and finally, absorbance or transmittance are measured at specific wavelength using UV-Vis spectrophotometer. In particular, the enzymatic method for determination of citric acid, because of its strong dependence on experimental conditions including sample types and chemical reagents may produce inconsistent results. The automated system using IC allows a laboratory to directly measure the amount of citric acid while reducing total analysis time and increasing efficiency. In addition, this method is capable of detecting a trace amount of citric acid, thereby lowering LOD and LOQ values.

본 연구는 자원의존이론에 기반하여 해외주식시장에 직상장하는 기업들의 자원 제공자에 대한 의 존도가 IPO 저가발행에 미치는 영향을 분석한다. 기존 IPO 연구들은 다양한 외부 자원제공자들과 의 네트워크를 전략적 이점으로 제시하여왔으나, 자원에 대한 의존도가 양날의 검처럼 존재함을 간 과해왔다. 따라서 본 논문은 자원 제공자에 대한 의존도는 사업 리스크로 여겨질 수 있음을 제시하 고, 이것이 주식발행가격에 미치는 영향을 분석한다. 더 나아가 외부 자원제공자(공급망 파트너) 와의 관계만을 주로 제시해온 기존 연구들에서 벗어나 기업의 핵심자원역량은 인적자원임에 착안 하여 내부 자원제공자(주요 경영진) 의존도로부터 발생하는 사업 리스크를 제시한다. 또한 자원제 공자에 대한 의존도 및 협상력이 기업이 가지고 있는 자원 경쟁력에 따라 달라질 수 있는 점에 착 안하여 자원 경쟁력의 조절효과를 보여준다. 자원 경쟁력이 높을 수록 외부 자원제공자들에 대한 협상력이 높아져 저가발행의 정도가 낮아지지만, 자원 경쟁력이 높을수록 그러한 자원에 대한 정보 를 소유하고 있는 내부 자원제공자의 중요성이 커지기 때문에 내부 자원제공자에 대한 의존도 위험 은 높아짐을 발견하였다.

The purpose of this study is to examine the effects of task complexity on the quality of L2 learners’ argumentative writing using both global measures of complexity, accuracy, and fluency (CAF) and task-specific measures, namely, for conjunctions. A group of 110 Korean high school students in South Korea performed either a simple or complex argumentative writing task. Task complexity was manipulated by +/–reasoning demands and +/–few elements. A set of 110 argumentative essays were analyzed on 6 global measures of CAF and 2 task-specific measures. The results showed that task complexity affected the fluency of the argumentative writings, in that the complex task group produced more fluent writings than the simple group. However, task complexity did not affect accuracy or syntactic complexity of the argumentative writings. In the task-specific measures, task complexity affected neither frequency nor target-like use of conjunctions. These results have pedagogical implications for task design to help learners develop their L2 proficiency.