Development of a Conceptual Design for the Solidification Facility of Long-Stored Radioactive Waste

Hyun Chul Lee,Dong-Seok Lim,Woo Young Jung,Ji-Hoon Kang 한국방사성폐기물학회 2023 한국방사성폐기물학회 학술논문요약집 Vol.21 No.2

The development of existing radioactive waste (RI waste) management technologies has been limited to processing techniques for volume reduction. However, this approach has limitations as it does not address issues that compromise the safety of RI waste management, such as the leakage of radioactive liquid, radiation exposure, fire hazards, and off-gas generation. RI waste comes in various forms of radioactive contamination levels, and the sources of waste generation are not fixed, making it challenging to apply conventional decommissioning and disposal techniques from nuclear power plants. This necessitates the development of new disposal facilities suitable for domestic use. Various methods have been considered for the solidification of RI waste, including cement solidification, paraffin solidification, and polymer solidification. Among these, the polymer solidification method is currently regarded as the most suitable material for RI waste immobilization, aiming to overcome the limitations of cement and paraffin solidification methods. Therefore, in this study, a conceptual design for a solidification system using polymer solidification was developed. Taking into account industrial applicability and process costs, a solidification system using epoxy resin was designed. The developed solidification system consists of a pre-treatment system (fine crush), solidification system, cladding system, and packing system. Each process is automated to enhance safety by minimizing user exposure to radioactive waste. The cladding system was designed to minimize defects in the solidified material. Based on the proposed conceptual design in this paper, we plan to proceed with the specific design phase and manufacture performance testing equipment based on the basic design.

단일 결정립 내의 국소 레이저 조사를 이용한 일방향응고 및 단결정 초내열합금의 응고균열 억제 용접기술

이성진,김경민,강희신,서성문,박원아,천은준 대한용접접합학회 2023 대한용접·접합학회지 Vol.41 No.4

In this study, possibility of solidification crack-free welding of directionally solidified CM247LC and single crystal CMSX-4 superalloys was metallurgically investigated using single-mode fiber laser scanning. The key metallurgical factors of solidification cracking have been identified as the formation of highly misoriented solidification grain boundaries (low level of epitaxial growth behavior) at the fusion zone that affects the repulsive force between two adjacent dendrites and dendrite coalescence undercooling at the terminal stage of weld solidification. In particular, under extremely low heat input and ultra-high-speed laser beam scan conditions (welding speed: 1,000 mm/s, heat input: 2 J/mm, and energy density: 65 J/mm2), an effective fusion zone could be achieved within a single directionally solidified grain of CM247LC alloy owing to the characteristics of single-mode fiber laser. The fusion zone successfully showed a 99.9% of epitaxial growth achievement ratio (that is, low fraction of highly misoriented solidification grain boundaries at the fusion zone) without solidification cracking. Based on these results on CM247LC alloy, solidification crack-free welds could be successfully achieved using quadruple-pass and square-type weld geometries.

Influence of Metallic Sodium on Repair Weldability for Type 316FR Stainless Steel

Eun-Joon Chun,Su-Jin Lee,Jeong Suh,Ju-Seung Lee,Namhyun Kang,Kazuyoshi Saida 대한용접·접합학회 2017 대한용접·접합학회지 Vol.35 No.1

The effect of residual metallic sodium on the solidification cracking susceptibility of type 316FR stainless steel was investigated via transverse-Varestraint tests. And a solidification brittle temperature range (BTR) of type 316FR stainless steel was 37 K. However, the BTR expanded from 37 to 67 K, as the amount of metallic sodium at the specimen surface increased from 0 to 7.99 mg/㎠. Microstructural observation of the weld metal suggested that metallic sodium existed in the weld metal, including in the cell boundaries, during welding solidification. Thermodynamic calculations suggested that sodium expanded the temperature range of solidliquid coexistence during welding solidification of the steel weld metal. Therefore, the increased solidification cracking susceptibility (i.e., expansion of the BTR) in the residual sodium environment was attributed to enhanced segregation of sodium during the welding solidification; this segregation, in turn, resulted in an expanded temperature range of solid-liquid coexistence.

세슘 침출 저항성 증진 시멘트 고화체의 제조 및 특성 평가

김지용,장원혁,장성찬,임준혁,홍대석,서철교,손종식 한국방사성폐기물학회 2018 방사성폐기물학회지 Vol.16 No.2

Currently, the Korea Atomic Energy Research Institute (KAERI) is planning to build the Ki-Jang Research Reactor (KJRR) in Ki-Jang, Busan. It is important to safely dispose of low-level radioactive waste from the operation of the reactor. The most efficient way to treat radioactive waste is cement solidification. For a radioactive waste disposal facility, cement solidification is performed based on specific waste acceptance criteria such as compressive strength, free-standing water, immersion and leaching tests. Above all, the leaching test is important to final disposal. The leakage of radioactive waste such as 137Cs causes not only regional problems but also serious global ones. The cement solidification method is simple, and cheaper than other solidification methods, but has a lower leaching resistance. Thus, this study was focused on the development of cement solidification for an enhancement of cesium leaching resistance. We used Zeolite and Loess to improve the cesium leaching resistance of KJRR cement solidification containing simulated KJRR liquid waste. Based on an SEM-EDS spectrum analysis, we confirmed that Zeolite and Loess successfully isolated KJRR cement solidification. A leaching test was carried out according to the ANS 16.1 test method. The ANS 16.1 test is performed to analyze cesium ion concentration in leachate of KJRR cement for 90 days. Thus, a leaching test was carried out using simulated KJRR liquid waste containing 3000 mg·L-1 of cesium for 90 days. KJRR cement solidification with Zeolite and Loess led to cesium leaching resistance values that were 27.90% and 21.08% higher than the control values. In addition, in several tests such as free-standing water, compressive strength, immersion, and leaching tests, all KJRR cement solidification met the waste acceptance or satisfied the waste acceptance criteria for final disposal. 현재, 한국원자력연구원은 부산 기장에 연구용 원자로(Ki-Jang Research Reactor, KJRR)를 건설 계획하고 있다. 원자로를 운영하면 중·저준위 방사성폐기물이 발생하므로 방사성 폐기물을 안전하게 처리 하는 것이 중요하다. 현재, 다양한 형태의방사성 폐기물을 처리 할 수 있는 시멘트 고화 방법을 일반적으로 사용하고 있으며, 방사성 폐기물 처분시설 인수 기준(압축강도, 유리수, 침수 및 침출시험 등)을 만족해야 한다. 특히, 폐기물에 함유된 방사성 세슘이 유출 될 경우 범 국제적인 문제를 야기하므로, 고화체 인수 기준 중에서 침출시험이 가장 중요한 인자이다. 시멘트 고화 방법은 다른 고화 방법 보다 공정이 간단하며 비용이 적게 들지만, 침출 저항성이 낮다. 이에 본 연구는 시멘트 고화체 세슘 침출 저항성 증진을 위하여 기장연구용 원자로(KJRR) 모사폐액과 대표적인 세슘 흡착제인 제올라이트와 황토를 혼합하여 기장로 모의폐액 시멘트를 제조하였다. 제올라이트와 황토가 시멘트 고화체와 결합되어 있는 것을 SEM-EDS를 통하여 정량적으로 확인하였다. 침출 시험은ANS 16.1 방법에 의해 90일동안 진행하였다. 기장로 모의폐액 시멘트의 세슘(3000 ppm)을 첨가하여 90일간의 침출시험 후침출수의 세슘 농도 분석 결과, 제올라이트와 황토가 포함된 모의폐액 시멘트는 제올라이트와 황토를 첨가하지 않은 대조군에 비해 최대 27.90%, 21.08%의 세슘 침출 저항성 정도를 나타내는 것을 확인하였다. 또한, 제올라이트와 황토가 포함된 기장로 모의폐액 시멘트는 인수 기준(압축강도, 유리수 유무, 침수 및 침출 지수)을 통과 하는 것을 확인하였다.

Characterization of Cement Solidification for Enhancement of Cesium Leaching Resistance

Gi Yong Kim,Won-Hyuk Jang,Sung-Chan Jang,Junhyuck Im,Dae Seok Hong,Chel Gyo Seo,Jong Sik Shon 한국방사성폐기물학회 2018 방사성폐기물학회지 Vol.16 No.2

Currently, the Korea Atomic Energy Research Institute (KAERI) is planning to build the Ki-Jang Research Reactor (KJRR) in Ki-Jang, Busan. It is important to safely dispose of low-level radioactive waste from the operation of the reactor. The most efficient way to treat radioactive waste is cement solidification. For a radioactive waste disposal facility, cement solidification is performed based on specific waste acceptance criteria such as compressive strength, free-standing water, immersion and leaching tests. Above all, the leaching test is important to final disposal. The leakage of radioactive waste such as 137Cs causes not only regional problems but also serious global ones. The cement solidification method is simple, and cheaper than other solidification methods, but has a lower leaching resistance. Thus, this study was focused on the development of cement solidification for an enhancement of cesium leaching resistance. We used Zeolite and Loess to improve the cesium leaching resistance of KJRR cement solidification containing simulated KJRR liquid waste. Based on an SEM-EDS spectrum analysis, we confirmed that Zeolite and Loess successfully isolated KJRR cement solidification. A leaching test was carried out according to the ANS 16.1 test method. The ANS 16.1 test is performed to analyze cesium ion concentration in leachate of KJRR cement for 90 days. Thus, a leaching test was carried out using simulated KJRR liquid waste containing 3000 mg·L-1 of cesium for 90 days. KJRR cement solidification with Zeolite and Loess led to cesium leaching resistance values that were 27.90% and 21.08% higher than the control values. In addition, in several tests such as free-standing water, compressive strength, immersion, and leaching tests, all KJRR cement solidification met the waste acceptance or satisfied the waste acceptance criteria for final disposal.

오스테나이트계 스테인리스강 용접부의 금속학적 현상에 관한 연구(2) - STS 304 용접부 조직특성 및 고온균열 감수성에 미치는 질소의 영향 -

이종섭,김숙환 대한용접접합학회 2000 대한용접·접합학회지 Vol.18 No.1

The purpose of the present study was to investigate weld metallurgical phenomena such as primary solidification mode, microstructural evolution and hot cracking susceptibility in nitrogen-bearing austenitic stainless steel GTA welds. Eight experimental heats varying nitrogen content from 0.007 to 0.23 wt.% were used in this study. Autogenous GTA welding was performed on weld coupons and the primary solidification mode and their microstructural characteristics were investigated from the fusion welds. Varestraint test was employed to evaluate the solidification cracking susceptibility of the heats and TCL(Total Crack Length) was used as cracking susceptibility index. The solidification mode shifted from primary ferrite to primary austenite with an increase in nitrogen content. Retained delta ferrite exhibited a variety of morphology as nitrogen content varied. The weld fusion zone exhibited duplex structure(austenite+ferrite) at nitrogen contents less than 0.10 wt.% but fully austenitic structure at nitrogen contents more than 0.20 wt.%. The weld fusion zone in alloys with about 0.15 wt.% nitrogen experienced primary austenite + primary ferrite solidification (mode AF) and contained delta ferrite less than 1% at room temperature. Regarding to solidification cracking susceptibility, the welds with fully austenitic structure exhibited high cracking susceptibility while those with duplex structure low susceptibility. The cracking susceptibility increased slowly with an increase in nitrogen content up to 0.20 wt.% but sharply as nitrogen content exceeded 0.20 wt.%, which was attributed to solidification mode shift fro primary ferrite to primary austenite single phase solidification.

A Background Study of VLLW Spent Resin Solidification

Hyun Woo Song,Sang June Park,Jun-gi Yeom,Moonoh Kim 한국방사성폐기물학회 2023 한국방사성폐기물학회 학술논문요약집 Vol.21 No.2

Domestic waste acceptance criteria (WAC) require flowable or homogeneous wastes, such as spent resin, concentrated waste, and sludge, etc., to be solidified regardless of radiation level, to provide structural integrity to prevent collapse of repository, and prevent leaching. Therefore, verylow level (VLL) spent resin (SR) would also require to be solidified. However, such disposal would be too conservative, considering IAEA standards do not require robust containment and shielding of VLL wastes. To prevent unnecessary cost and exposure to workers, current WAC advisable to be amended, thus this paper aims to provide modified regulation based on reviewed engineering background of solidification requirement. According to NRC report, SR is classified as wet-solid waste, which is defined as a solid waste produced from liquid system, thus containing free-liquid within the waste. NRC requires liquid wastes to be solidified regardless of radiation level to prevent free liquid from being disposed, which could cause rapid release of radionuclides. Furthermore, considering class A waste does not require structural integrity, unlike class B and C wastes, dewatering would be an enough measure for solidification. This is supported by the cases of Palo Verde and Diablo Canyon nuclear power plants, whose wet-solid wastes, such as concentrated wastes and sludge, are disposed by packaging into steel boxes after dewatering or incineration. Therefore, dewatering VLL spent resin and packaging them into structural secure packaging could satisfy solidification goal. Another goal of solidification is to provide structural support, which was considered to prevent collapse of soil covers in landfills or trenches. However, providing structural support via solidification agent (ex. Cement) would be unnecessary in domestic 2nd phase repository. As the domestic 2nd phase repository is cementitious structure, which is backfilled with cement upon closure, the repository itself already has enough structural integrity to prevent collapse. Goldsim simulation was run to evaluate radiation impact by VLL SR, with and without solidification, by modelling solidified wastes with simple leaching, and unsolidified wastes with instant release. Both simulations showed negligible impact on radiation exposure, meaning that solidifying VLL SR to delay leaching would be irrational. Therefore, dewatering VLL SR and packaging it into a secure drum (ex. Steel drum) could achieve solidification goals described in NRC reports and provide enough safety to be disposed into domestic repositories. In future, the studied backgrounds in this paper should be considered to modify current WAC to achieve efficient waste management.

The optimum solidification and crucible rotation in silicon czochralski crystal growth

Jeong, Hyo-Min,Lee, Yong-Hun,Ji, Myoung-Kuk,Lee, Gyeong-Hwan,Chung, Han-Shik 대한기계학회 2010 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.24 No.1

Silicon crystallization is very important in many industrial processes, and it is desirable that maker should have a low cost manufacturing and high efficiency for producing semiconductors. One semiconductor process is the Czochralski (CZ) silicon melt flow and this CZ process has an excellent manufacturing feature and is utilized for silicon solidification. But CZ silicon melt flow is very complicated and this defect can be erased by the numerical analysis of the melt flow. In this paper, the optimum solidification conditions were shown for crucible rotation. This is because the solidification conditions depend on crucible rotation under the cooling process and the solidification conditions were investigated on heat generation rate on crucible wall and rotation by using numerical analysis. For the numerical validations, we verified with experimental data and showed good agreement with current numerical results. The solidification regions are classified with crystal rotation and crucible rotation. For the heat generation rate, qw, the optimum heat generation rate was estimated for 20 W/cm2 and when crystal rotation and crucible rotation is 5 rpm, the maximum solidification length can be obtained and has a stable solidification.

A Numerical Model of the Temperature Field of the Cast and Solidified Ceramic Material

Frantisek Kavicka,Jana Dobrovska,Bohumil Sekanina,Karel Stransky,Josef Stetina 한국소성가공학회 2010 기타자료 Vol.2010 No.6

Corundo-baddeleyit material (CBM) ? EUCOR ? is a heat- and wear-resistant material even at extreme temperatures. This article introduces a numerical model of solidification and cooling of this material in a non-metallic mould. The model is capable of determining the total solidification time of the casting and also the place of the casting which solidifies last. Furthermore, it is possible to calculate the temperature gradient in any point and time, and also determine the local solidification time and the solidification interval of any point. The local solidification time is one of the input parameters for the cooperating model of chemical heterogeneity. This second model and its application on samples of EUCOR prove that the applied method of measurement of chemical heterogeneity provides detailed quantitative information on the material structure and makes it possible to analyse the solidification process. The analysis of this process entails statistical processing of the results of the measurements of the heterogeneity of the components of EUCOR and performs correlation of individual components during solidification. The crystallisation process seems to be very complicated, where the macro- and microscopic segregations differ significantly. The verification of both numerical models was conducted on a real cast 350 x 200 x 400 mm block.

다결정 실리콘 웨이퍼 직접제조에 대한 공정변수 영향

위성민 ( Sung Min Wi ),이진석 ( Jin Seok Lee ),장보윤 ( Bo Yun Jang ),김준수 ( Joon Soo Kim ),안영수 ( Young Soo Ahn ),윤우영 ( Woo Young Yoon ) 한국주조공학회 2013 한국주조공학회지 Vol.33 No.4

A ribbon-type polycrystalline silicon wafer was directly fabricated from liquid silicon via a novel technique for both a fast growth rate and lagre grain size by exploiting gas pressure. Effects of processing parameters such as moving speed of a dummy bar and the length of the solidification zone on continuous casting of the silicon wafer were investigated. Silicon melt extruded from the growth region in the case of a solidification zone with a length of lcm due to incomplete solidification. In case of a solidification zone wieh a length fo 2 cm, on the other hand, continuous casting of the wafer was impossible due to the volume expansion of sil-icon derived from the liquid-solid transformation in solidificatioon zone. Consequently, the optimal length of the solidification zone was 1.5 cm for maintaining the position of the dummy bar was 6 cm/min, but liquid silicon extruded from the growth region without solidification when the moving speed of the dummy barr was≥9 cm/min. This was due to a shift of the position of the solid-liquid interface from the solidification zone to the moving area. The present study repots experimental findings on a new direct growth sys-tem for obtaining silicon wafers with both high quality and producticity, as a candidate for an altemate route for the fabrication of ribbon-type silicon wafers.