초록 ▼

○ 사용후핵연료 지르칼로이-4 피복관의 LiCl-KCl 용융염 전해정련을 통한 제염 가능성을 평가하기 위해 방사화학분석 코드(ORIGEN-2)를 통해 원자로 내에서 방사화 지르칼로이 피복관 핵종 조성을 분석하고 1차원 전기화학 반응 분석 코드(REFIN)을 사용하여 피복관 제염에 주요한 핵종을 도출하고 제염계수를 평가한 결과, 충분히 깨끗한 용융염을 사용하고 양극 전위를 모니터링하면서 전해정련이 진행되면 1단계 전해정련으로도 Co-60 및 기타 불순물에 대한 충분한 제염이 가능함을 보임.
○ LiCl-KCl-ZrCl4에 대한

○ 사용후핵연료 지르칼로이-4 피복관의 LiCl-KCl 용융염 전해정련을 통한 제염 가능성을 평가하기 위해 방사화학분석 코드(ORIGEN-2)를 통해 원자로 내에서 방사화 지르칼로이 피복관 핵종 조성을 분석하고 1차원 전기화학 반응 분석 코드(REFIN)을 사용하여 피복관 제염에 주요한 핵종을 도출하고 제염계수를 평가한 결과, 충분히 깨끗한 용융염을 사용하고 양극 전위를 모니터링하면서 전해정련이 진행되면 1단계 전해정련으로도 Co-60 및 기타 불순물에 대한 충분한 제염이 가능함을 보임.
○ LiCl-KCl-ZrCl4에 대한 순환전위법을 수행함으로써 용융염에서의 지르코늄의 산화-환원 반응에 대한 연구를 진행하였으며 이를 통해 음극 전위가 낮은 경우 Zr(IV)가 지르코늄 금속이 아닌 ZrCl로 환원되고 음극 전위가 충분히 높을 경우 Zr(IV)이 지르코늄 금속으로 환원시키는 것이 가능함을 확인함.
○ 지르칼로이-4에 포함된 주요원소가 지르코늄보다 환원 경향성이 강해 음극에서 회수되는 지르코늄의 순도를 높이기 위해 양극 전위를 조절하며 전해정련을 진행하였으며 음극 전착물의 조성을 분석한 결과 다른 원소의 전착 없이 지르코늄만을 전착시키는 것이 가능함을 확인함.
○ 파일럿 스케일 설계 또는 설계 최적화를 위한 도구로 3차원 다원소 전착 전산 모델을 개발하였으며, 실험의 용이성 및 정확성을 위해 수용액 시스템에서 개발된 모델을 검증함. 비교반 시스템 및 교반 시스템에서 실험으로 도출된 분극곡선을 벤치마크 하였으며 Rotating Hull Cell의 음극 과전압 분포를 성공적으로 벤치마크하여 개발된 전산 모델의 효용성을 확인함.
○ 개발된 전산모델을 통해 보조음극을 사용하는 전해정련로와 회전형 드럼 전해정련로가 설계되었으며, 전산모델을 통해 파일럿 스케일 지르칼로이-4 피복관 제염 시스템으로 적합함을 확인함.
○ 최종적으로 연구된 지르칼로이-4 전해정련을 바탕으로 사용후핵연료 지르칼로이-4 피복관을 제염하기 위한 공정흐름도를 제시함.

Abstract ▼

Ⅳ. PROJECT RESULTS
Since zircaloy-4 cladding consists of various elements including Zr, Sn, Cr and Ni, a lot of activation products are generated during irradiation. Increasing the number of elements in a three-dimensional simulation requires substantially more expensive computational resources a

Ⅳ. PROJECT RESULTS
Since zircaloy-4 cladding consists of various elements including Zr, Sn, Cr and Ni, a lot of activation products are generated during irradiation. Increasing the number of elements in a three-dimensional simulation requires substantially more expensive computational resources and modelling complexity at the expense of computational accuracy. Therefore, to conduct three-diemsional simulation more efficiently, key elements for irradiated zircaloy-4 cladding electrorefining were selected by computational codes, ORIGEN-2 and REFIN.
The amount and radioactivity of activation products in irradiated zircaloy-4 cladding was investigated by ORIGEN-2. All activation products had lower radioactivity than their LILW criteria after 3 years cooling but some nuclides including Co60, Sb125 and Zr93 had higher radioactivity than their clearance level. It was also estimated that there could be about 1g of uranium and 14mg of plutonium in 1kg of Zircaloy cladding by Rudisill’s research.
To select elements which could be codeposited with zirconium during Zircaloy-4 electrorefining among major elements of zircaloy-4, activation products and actinides within irradiated zircaloy-4, one-dimensional transient
electrorefining simulation was conducted by REFIN. Co and U are utilized with major elements of Zircaloy-4 as composition elements of irradiated cladding to reflect activation products and actinides respectively. Since Sn, Cr and Co are more reductive than Zr, at the initial stage of electrorefining, Sn2+, Cr2+ and Co2+ which were contained in initial molten salt were reduced on cathode with Zr deposition. At the last stage of electrorefining, because of Zr depletion in molten salt and anode, other elements were deposited on the cathode. However, since U and Fe are much more oxidative than other elements, uranium was not deposited on cathode for all simulation cases. From the ORIGEN-2 and REFIN simulation, in the aspect of radioactivity and purity of recovered zirconium, Co could be one of key elements in irradiated Zircaloy-4 electrorefining. Using REFIN code, the effect of diffusion boundary layer thickness and initial concentration of Co2+ on decontamination factor for Co was also examined.
Three-dimensional multi-species electrodeposition computational model was developed for understanding the electrolytic zirconium recovery system, which is based on the process of competitive electrodeposition. As a part of computational model validation, Cu and Ni deposition experiments were conducted in static cell and RCH cell. Transfer coefficient, exchange current density and diffusion boundary layer thickness were estimated from cathodic polarization curve fitting and they are used for the computational model. Cathodic polarization curves on Cu and Ni deposition were benchmarked by the computational model. There were not significant discrepancies between polarization curves of experimental and computational results. For the RCH cell, overpotential distribution along the cathode for the Cu deposition was benchmarked.
To investigate dissolution and deposition behavior of zirocnium in molten salt, cyclic voltammetry was conducted in LiCl-KCl-ZrCl4 at 500℃. Each three peaks for oxidation and reduction reaction of zirconium appeared and detail oxidation and reduction reactions for each peak were defined based on electrolysis experiment and previous cyclic voltammetry results in literatures. For the zirconium reduction, Zr(IV) is reduced into ZrCl not Zr metal when cathode potential is not negative enough. Therefore, to recover zirconium metal at once, cathode potential should be maintained over –1.5V (vs. Ag/AgCl). Cyclic voltammetry for Co which is the element that should be eliminated was conducted and it was revealed that oxidation and reduction reaction of cobalt is much simpler than zirconium and cobalt was more reductve than zirconium.
In addition, lab-scale electrorefining for Zircaloy-4 specimen was conducted.
Anode potential was controlled to prevent dissolution of all elements except zirconium. Composition of deposits on cathode was evaluated by ICP-MS analysis. Only zirconium and molten salts were detected in deposits. Since molten salts in deposits could be separated by salt evaporation process, recovered element on cathode was almost 100% zirconium.
Two pilot scale electrorefiners for zircaloy cladding were designed. One is a electrorefiner including auxiliary electrode and another is a rotaing drum cell electrorefiner. Characteristics of each electrorefiner were simulated by developed three-dimensional multi-species electrodeposition model. It was confirmed that very high purity zirocnium is deposited on main cathode and most of other elments dissolved from andoe were deposited on auxiliary cathode in electrorefiner including auxiliary cathode. In addition, it was expected that zirconium metal not ZrCl could be obtained on cathode since cathode potential is more negative than –1.5V (vs. Ag/AgCl). For the rotating drum cell electrorefiner, uniform contact of cladding cuts on molten salts could be achieved and chlorine gases in anode could be removed easily.

목차 Contents

• 표지 ... 1
• 제출문 ... 2
• 보고서 요약서 ... 3
• 요약문 ... 4
• SUMMARY ... 9
• CONTENTS ... 14
• 목차 ... 15
• 표 목차 ... 16
• 그림 목차 ... 17
• 1 장 연구개발과제의 개요 ... 21
• 제2장 국내외 기술개발 현황 ... 24
• 제 1 절 국외 기술개발 현황 ... 24
• 제 2 절 국내 기술개발 현황 ... 27
• 제3장 연구개발수행 내용 및 결과 ... 28
• 제 1 절 방사화 피복관 전해정련 특성 평가 ... 28
• 1. 특성 평가 전략 및 모델링 조건 ... 28
• 2. 방사화 피복관 조성 평가 ... 31
• 3. 전해정련 주요 핵종 도출 ... 34
• 4. 전해정련 주요 운전 조건 도출 ... 37
• 제 2 절 지르칼로이 제염 실험적 평가 ... 42
• 1. 순환전위법 ... 42
• 2. 용융염 내 지르코늄 거동 ... 44
• 3. 용융염 내 코발트 거동 ... 51
• 4. 지르칼로이-4 전해정련 ... 53
• 제 3 절 3차원 전해전착 모델 개발 ... 57
• 1. 전해전착 모델 ... 57
• 2. 비교반 시스템 모델 검증 ... 71
• 3. 교반 시스템 모델 검증 ... 81
• 4. 다원소 전착 시스템 전산모델 ... 87
• 5. 대용 시스템의 모델기반 검증체계 마련 및 평가 ... 96
• 제 4 절 방사화 피복관 전해정련로 설계 및 제염 전략 ... 106
• 1. 보조 음극 전해정련로 ... 106
• 2. 회전형 드럼셀 전해정련로 ... 109
• 3. 사용후핵연료 피복관 제염 전략 ... 125
• 제4장 목표달성도 및 관련분야에의 기여도 ... 127
• 제5장 연구개발결과의 활용계획 ... 128
• 제6장 연구개발과정에서 수집한 해외과학기술정보 ... 129
• 제7장 연구시설.장비 현황 ... 130
• 제8장 참고문헌 ... 131
• 끝페이지 ... 135