Polypropylene (PP) filters are used for the treatment of radioactive liquid waste containing gamma nuclides such as Co-60, and filter physical and chemical properties can be altered by means of γ-rays during the treatment process. In this study, irradiation tests were carried out to evaluate the effect of γ-ray on PP yarns under air and water condition. In the tensile test results, significant changes were observed when the absorbed dose exceeded 10 kGy. At the same time, the tensile strength and elongation at the break of irradiated yarns decreased with increasing absorbed doses, and showed great reductions under air condition compared to under water condition. Through the XPS results, it was confirmed that C–C bonds in PP yarn was radiolytically decomposed during irradiation, and this decomposition more actively progressed under air than under water.

Radiolysis of chemical agents occurs during the decontamination of nuclear power plants. The γ-ray irradiation tests of the N2H4–Cu+–HNO3 solution, a decontamination agent, were performed to investigate the effect of Cu+ ion and HNO3 on N2H4 decomposition using a Co-60 high-dose irradiator. After the irradiation, the residues of N2H4 decomposition were analyzed by Ultraviolet-visible (UV) spectroscopy. NH4+ ions generated from N2H4 radiolysis were analyzed by ion chromatography. Based on the results, the decomposition mechanism of N2H4 in the N2H4–Cu+–HNO3 solution under γ-ray irradiation condition was derived. Cu+ ions form Cu+N2H4 complexes with N2H4, and then N2H4 is decomposed into intermediates. H+ ions and H● radicals generated from the reaction between H+ ion and eaq− increased the N2H4 decomposition reaction. NO3− ions promoted the N2H4 decomposition by providing additional reaction paths: (1) the reaction between NO3− ions and N2H4●+, and (2) the reaction between NO● radical, which is the radiolysis product of NO3− ion, and N2H5+. Finally, the radiolytic decomposition mechanism of N2H4 obtained in the N2H4–Cu+–HNO3 was schematically suggested.

This study investigates the dissolution behavior of oxide layers containing radionuclides using perfluorocarbon (PFC) emulsion as a reusable medium. Chemicals such as PFC, anionic surfactant, and H2SO4 are used for preparing the PFC emulsion, and emulsified using an ultrasonication process. The FTIR results show O–H stretching that is formed by the interaction of the carboxyl group of the anionic surfactant with the hydroxyl group of water containing H2SO4, and find that the H2SO4 can be homogeneously dispersed in the PFC–anionic surfactant–H2SO4 emulsion. The dissolution test of the simulated Cr2O3 specimen is conducted using PFC emulsion containing KMnO4. Through the weight losses of specimens and Scanning Electron Microscope-Energy Dispersive X-ray Spectrometer (SEM-EDS) analysis, it is confirmed that the Cr2O3 layer on the SUS304 specimen is easily dissolved using PFC emulsion. During the dissolution of the Cr2O3, it is observed that the dispersed H2SO4–KMnO4 became unstable and separated from PFC emulsion. Based on these results, the behavior of the PFC emulsion during the dissolution of the oxide layer is explained.

The SP-HyBRID process, which has a similar performance to commercial technologies for the decontamination of a nuclear reactor coolant system, can reduce the secondary waste generation significantly. However, the process has a problem of discharging decontamination wastewater every cycle. In this study, an improved SP-HyBRID process that can conduct the process cycles continuously without discharging decontamination wastewater every cycle was designed. It was confirmed that the improved process could be effectively applied to equipment for a decontaminating test of contaminated components, and the waste reduction can be close to 15% when compared with the existing SP-HyBRID process.

In June 2018, it was decided to close the Wolsong Unit 1, of which the reactor type is a pressurized heavy water reactor (PHWR) [1]. After this, the importance of the decommissioning of the PHWR has become an issue. It is necessary to apply the decontamination process to the carbon steel heat transport system of the PHWR before the decommissioning for reducing the radiation expose to the workers [2]. During the decontamination process, the corrosion oxide (mainly Fe3O4) layers including radioactive metals can be removed from the carbon steel heat transport system [3]. The Hydrazine Base Reductive metal Ion Decontamination (HyBRID) process was developed by KAERI for the decontamination of the Fe3O4 on a primary coolant circuit in a pressurized water reactor (PWR) [4]. This process can also be applied to the Fe3O4 decontamination in the PHWR. However, the thickness of the oxide layer in the PHWR (~75 μm) is much greater than that in the PWR (~3 μm) as shown in Table I [5]. The decontamination performance of the HyBRID process solution can be decreased during decontamination of thick oxide layer in the PHWR because the high concentration of Fe ions dissolved in the process solution can prevent the progress of more dissolution reactions. Therefore, it is required to discharge the spent process solution, called the process solution remained after finishing the decontamination cycle, and charge the fresh process solution. The fresh decontamination solution is the solution of which condition is the initial composition of HyBRID process solution. This repetitive replacement of process solution is necessary to keep up the decontamination performance. However, the large amount of secondary wastes can be generated when the process solutions are discharged and charged over agiain. In this study, the effective decontamination process of the corrosion oxide layers from the heat transport system in the PHWR without any discharge of the spent process solution was suggested. The key method of this process was recycling the spent process solution by reducing the solution to the fresh process solution. This recycling method was derived by the experimental test using spent process solution surrogate. Moreover, the Fe3O4 dissolution test using the recycled process solution was also performed. Table I: Characteristics of corrosion oxide layers in the reactor [2].

A N2H4-Cu(I)-HNO3 solution was used to dissolve magnetite powders and a simulated oxide film on Inconel 600. The addition of Cu(I) ions to N2H4-HNO3 increased the dissolution rate of magnetite, and the reaction rate was found to depend on the solution pH, temperature, and [N2H4]. The dissolution of magnetite in the N2H4-Cu(I)-HNO3 solution followed the contracting core law. This suggests that the complexes of [Cu+(N2H4)] formed in the solution increased the dissolution rate. The dissolution reaction is explained by the complex formation, adsorption of the complexes onto the surface ferric ions of magnetite, and the effective electron transfer from the complexes to ferric ions. The oxide film formed on Inconel 600 is satisfactorily dissolved through the successive iteration of oxidation and reductive dissolution steps.

Decontamination wastewater generated from the HyBRID decontamination process of the primary system in a nuclear power plant contains impurities such as sulfate ions, metal ions containing radioactive nuclides, and hydrazine (carcinogenic agent). For this reason, it is necessary to develop a technology to remove these impurities from the wastewater to a safe level. In this study, it has been conducted to remove the impurities using a decontamination wastewater surrogate, and a treatment process of the HyBRID decontamination wastewater has been established. The performance and applicability of the treatment process have been verified through 1 L scale of replicates and a pilot scale (300 L/batch) test.

Before decommissioning of the nuclear power plant, the chemical decontamination process to the reactor coolant system (RCS) is required for reducing the worker exposure. An oxidation and a reductive step are carried out alternately in the chemical decontamination process. Reductive decontamination agent is used for removing oxide layer including Fe by reducing the Fe ions to the Fe. The HyBRID (Hydrazine Based Reductive metal Ion Decontamination) agent developed by KAERI can be applied in a reductive dissolution step. It is composed of N2H4-Cu(I)-H2SO4, and hydrazine (N2H4) is used as a reductant. However, the hydrazine in HyBRID agent can be decomposed during the decontamination due to an irradiation released from the radionuclide such as Co-60 in the RCS. In this regard, the objective of this study is to investigate the effects of -ray irradiation on the radiolytic decomposition of hydrazine. In addition, we compared the results of hydrazine decomposition by varying the solution pH.

NiFe2O4 thin film has been prepared by electron beam evaporation method and has been investigated as anode materials providing large reversible Li+ capacity with high cycling performance for lithium ion batteries. The NiFe2O4 thin film crystallized with annealing process after NiFe2O4 thin film deposition. In electrochemical measurements, the first discharge and charge capacity of NiFe2O4 thin film were found to be 1693 mAh g-(1) and 1108 mAh g(-1), which is above its theoretical capacity (915 mAh g(-1)). In addition, the cycle performance test of NiFe2O4 thin film also showed steady charge- discharge capacity at 0.1 C during 100 cycles compared to other NiFe2O4 materials, indicating that the empty space or porous surface of electrode was beneficial for accessibility of electrolyte and served as buffer to alleviate stress. (C) 2017 Published by Elsevier B.V.

to minimize the damage of base metals by the corrosion in this study. Type 304 stainless steel (304SS) and Inconel-600 (I-600) that are major components of the primary coolant system in pressurized water reactor were tested. To improve the integrity of base metal to the corrosion, we tested Ni2+, Fe3+, Cr6+, or Cu2+ by adding in NP solutions as a corrosion inhibitor and found that general and local corrosions were suppressed by the addition of Cu2+ ion. Decontamination performance and corrosion tests for NP(Cu) process with HYBRID (HYdrazine Base Reductive metal Ion Decontamination) process as a multi-step process were carried out and compared with existing processes such as citric-oxalic acid and oxalic acid. Our tests revealed that NP(Cu)-HYBRID process greatly inhibited local corrosions such as pits and Intergranular Attack. Moreover the proposed process was assured by the decontamination performance equivalent to other conventional processes.

Decomposition tests of hydrazine were conducted in an acidic solution using a hydrogen peroxide solution in a temperature range of 50 to 80 °C.The decomposed fraction of hydrazine was calculated from an analysis of the hydrazine ion concentration in solution by a UVvisible spectrometer.The increase of [Cu 2+ ] increased the decomposition reaction rate of hydrazine.The decomposition reaction rate of hydrazine also increased with the increase of temperature and the solution pH.It was explained that the formation of N2H5 + ion retards the reaction in the lower pH region.One step excess injection of hydrogen peroxide could not decompose the hydrazine efficiently.The decomposed portion of hydrazine could be increased by the repetitive injection of hydrogen peroxide.

For the decontamination of primary coolant system, we have developed a new chemical decontamination process named HYBRID (HYdrazine Based Reductive metal Ion Decontamination) which is not containing organic chelates and organic acids. In the first phase to develop HYBRID process, dissolution tests of magnetite using hydrazine based chemical solutions were carried out in various conditions. We found out the effects of parameters such as the concentration of hydrazine, solution pH, temperature, and the addition of transition metal ions on the dissolution behavior. We suggested the concept of HYBRID process with the dissolution mechanism by the complex formation between hydrazine and copper ions, and the reducing power of the hydrazine copper coordination compound to the ferric ions in magnetite. In the second phase to verify the performance of HYBRID process, the chemical decontamination tests using HYBRID coupled with NP were carried out with radioactive specimen taken from the fuel test loop in which operating conditions are same as those in pressurized water reactor. The contact does rate was greatly decreased after the repetitive application of NP and HYBRID. In addition, the corrosion compatibility of the structural material and the decomposition of hydrazine to reduce the secondary waste have been investigated. INTRODUCTION Decontamination is conducted for equipment and systems which have been contaminated by the activity build-up with time evolution for maintenance or decommissioning. During the periodic maintenance of nuclear power plant (NPP), the action is mainly focused to reduce the occupational exposure, and additionally to reduce the radioactive waste at the time for decommissioning. Especially, a primary coolant system of NPP after long-term operation has been deposited by radioisotopes which are responsible for the most of the radiation exposure of plant workers. The removal of radioactive isotopes from the primary coolant system takes place with the dissolution of oxide layer in which radioisotopes (e.g. Co-60) are deposited [1]. The dissolution of metal oxides up to the boundary layer of oxide and base metal is ideally required to remove all radioactivities from the target surface. However, too aggressive solution is deemed to cause the undesirable corrosion damage to the base metal as well as generate a large volume of decontamination waste so that relatively mild decontamination solutions have been developed. WM2015 Conference, March 15-19, 2015, Phoenix, Arizona, USA 2 Chemical decontamination utilized by oxidation and reduction processes is considered most effective method for system decontamination to date. It is well known that permanganate processes using nitric permanganate (NP), alkaline permanganate (AP), and permanganic acid (HP) have been developed to mainly oxidize chromite oxides. On the other hand, reductive decontamination processes such as CAN-DEREM, CITROX, LOMI, and CORD were developed to dissolve the iron oxides and now widely used in the decontamination of primary system. Acidic solutions such as oxalic acid, vanadous picolinate, citric acid, ethylenediaminetetraacetic acid (EDTA) or mixture of them are mostly used as reducing agents under the pH range of 2 to 3 [2]. Organic chelates are used in most commercial reductive decontamination processes to prevent the precipitation of dissolved metal ion by forming metal-organic acid chelation, which accordingly increases decontamination efficiency compared to the cases with the absence of chleating agents. However, organic chelates such as EDTA in CAN-DEREM or oxalic acid in CORD and CITROX processes are considered detrimental for disposal safety because not only EDTA in the mixed waste may form stable and soluble complexes with radionuclides that can enhance and promote its migration in the subsurface and groundwater but also oxalic acid has the risk of potential release of chemo-toxic substances in the case of accidents of the final repository [3, 4]. To overcome the limited use of organic acids and organic chelating agents, KAERI has developed alternative technologies without using any organic acids or organic chelating agents. Newly developed chemical decontamination processes named HYBRID applicable to primary coolant system were described in this paper. MAGNETITE DISSOLUTION IN HYDRAZINE BASED SOLUTIONS The spinel type oxides are formed on the surface of iron-based metals, especially when in contact with the coolant in nuclear power plants so that the dissolution of magnetite as a model oxide was carried out in various conditions using hydrazine which is a potent strong reductive reagent in aqueous solution. Fig. 1 shows the effect of solution temperature on the dissolution of magnetite in 70 mM N2H4 at pH 3 adjusted by the addition of HNO3. In the Fig. 1, a significant dissolution reaction was observed at the temperatures greater than 90°C and the dissolution rate increases as the reaction temperature goes higher. Under such a low concentration of N2H4, it was evaluated that the solution temperature above 120°C is required to achieve reasonable dissolution performance. WM2015 Conference, March 15-19, 2015, Phoenix, Arizona, USA 3 60 90 120 150 0.0 0.1 0.2 0.3 0.4 0.5 Di ss ol ve d fr ac tio n of F e 3 O 4

Dissolution tests of Fe3O4 powders were performed in an acidic solution using a hydrazine base solution at a temperature range of 90-150 degrees C. The dissolved fraction of Fe3O4 was calculated from the analysis of iron ion concentration in solution using an atomic absorption spectrometer. The dissolution rate of Fe3O4 increased with [N2H4], time and temperature. The addition of copper ions to the hydrazine base solution greatly increased the Fe3O4 dissolution rate. This was explained by the complex formation between N2H4 and Cu ions and the reducing power of the hydrazine-Cu complex to the ferric ions of Fe3O4. The solution was also applied to the decontamination of Type 304 stainless steel specimen which was radioactively contaminated with a spinel type oxide layer. The contact dose rate of the specimen was measured before and after application of the solution to evaluate the decontamination performance. The contact dose rate was greatly decreased by the repetitive application of nitric acid-permanganate and the hydrazine base solution.

가압경수로의 일차계통 제염을 위해 개발된 HYBRID 제염제의 재료부식 특성을 틈부식 시험방법을 사용하여 수행하였다. 기존 제염제의 부식특성과 비교하기 위하여 상용 제염제인 OA, CITROX 제염제의 부식특성도 함께 평가하였다. 시험재료는 가압경수로의 일차계통의 주 재료인 Alloy 600과 304 SS을 대상으로 시험하였다. 틈부식 시험은 가혹조건의 부식시험으로써 내식성이 강한 원전 구조재료의 건전성을 짧은 시간에 잘 확인할 수 있었다. 시험결과 OA와 CITROX 제염제에서는 crevice 시편 표면에 pitting과 IGA가 나타났으나 HYBRID 제염제에서는 국부부식이 전혀 발생되지 않았다. 무게감소 측정결과 HYBRID 제염조건에서는 $1.3{\times}10^{-3}{\mu}m/h$ 이하의 매우 낮은 부식속도를 나타내었다. 반면에, OA 제염제의 경우 Alloy 600은 $4.0{\times}10^{-2}{\mu}m/h$ 로 비교적 균일한 부식율을 나타내었으나, 304 SS의 경우 pH = 2.0 이하에서 급격한 가속부식을 나타내었다. HYBRID 제염제의 경우 일반부식에서뿐만 아니라 crevice 부식조건에서도 거의 부식이 일어나지 않아 PWR 계통제염 시 산화막 용해 후 제염제가 계통재료에 노출되어도 재료의 건전성이 입증되었다. Crevice corrosion tests were conducted to examine the corrosion properties of HYBRID (HYdrazine Base Reductive metal Ion Decontamination) which was developed to decontaminate the PWR primary coolant system. To compare the corrosion properties of HYBRID with commonly existing decontamination agents, oxalic acid (OA) and citric oxalic acid (CITROX) were also examined. Type 304 Stainless Steel (304 SS) and Alloy 600 which are major components of the primary coolant system in Pressurized Water Reactor (PWR) were evaluated. Crevice corrosion tests were conducted under very aggressive conditions to confirm quickly the corrosion properties of primary coolant system structure components which have high corrosion resistance. Pitting and IGA were occurred in crevice surface under OA and CITROX conditions. But localized corrosion was not observed under HYBRID condition. Very low corrosion rate of less than $1.3{\times}10^{-3}{\mu}m/h$ was observed under HYBRID condition for both materials. On the other hand, under OA condition, Alloy 600 indicated comparatively uniform corrosion rate of $4.0{\times}10^{-2}{\mu}m/h$ but 304 SS indicated rapid accelerated corrosion in lower case than pH 2.0. In case of HYBRID condition, general corrosion and crevice corrosion were scarcely occurred. Therefore, material integrity of HYBRID in decontamination of primary coolant system in pressurized water reactor (PWR) reactor was conformed.

The perfluorocarbon decontamination process using a dilute solution of a high molecular weight fluorinated surfactant in a perfluorocarbon liquid is very effective for the removal of micron sized hot particulate from surfaces in a hot cell. After the decontamination process, the removal of the fluorinated anionic surfactant within the perfluorocarbon solution through adsorption using a carbon adsorbent is needed for the reuse of spent perfluorocarbon. From the experimental results on the adsorption behaviour of a surfactant in a perfluorocarbon solution in terms of the structural and chemical properties of the activated carbon fiber and active carbon, it was found that the structural properties of the carbon adsorbent, particularly the surface area, have an important influence on the adsorption behaviour, rather than the chemical properties. A ACF-15 adsorbent with a large surface area has an excellent adsorption efficiency of 56 %, compared with other adsorbents such as ACF-7, AC-45X100 or AC-20X45.