Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT) (방사성폐기물학회지)

Korean Radioactive Waste Society (한국방사성폐기물학회)
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A Chemical Reaction Calculation and a Semi-Empirical Model for the Dynamic Simulation of an Electrolytic Reduction of Spent Oxide Fuels

산화물 사용후핵연료 전해환원 화학 반응 계산 및 동적 모사를 위한 반실험 모델

  • Received : 2009.12.15
  • Accepted : 2010.02.22
  • Published : 2010.03.30
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Abstract

Electrolytic reduction technology is essential for the purpose of adopting pyroprocessing into spent oxide fuel as an alternative option in a back-end fuel cycle. Spent fuel consists of various metal oxides, and each metal oxide releases an oxygen element depending on its chemical characteristic during the electrolytic reduction process. In the present work, an electrolytic reduction behavior was estimated for voloxidized spent fuel based on the assumption that each metal-oxygen system is independent and behaves as an ideal solid solution. The electrolytic reduction was considered as a combination of a Li recovery and chemical reactions between the metal oxides such as uranium oxide and the produced Li metal. The calculated result revealed that most of the metal oxides were reduced by the process. It was evaluated that a reduced fraction of lanthanide oxides increased with a decreasing $Li_2O$ concentration. However, most of the lanthanides were expected to be stable in their oxide forms. In addition, a semi-empirical model for describing $U_3O_8$ electrolytic reduction behavior was proposed by considering Li diffusion and a chemical reaction between $U_3O_8$ and Li. Experimental data was used to determine model parameters and, then, the model was applied to calculate the reduction yield with time and to estimate the required time for a 99.9% reduction.

고온 용융염 전해환원 공정은 후행핵연료 주기의 대안 공정인 파이로공정의 산화물 사용후핵연료의 확대를 위해 필수적인 공정이다. 사용후핵연료는 다성분 산화물로 이루어져 있으며 각 산화물은 전해환원 공정에서 화학적 특성에 따라 산소를 잃게 된다. 본 연구에서는 건식분말화 공정 이후 전해환원 반응기에 도입되는 사용후핵연료 조성을 기준으로 각 금속-산소 시스템을 독립적인 이상고용체로 가정하여 전해환원 반응거동을 계산하였다. 전해환원을 Li의 환원과 이어지는 Li과의 화학반응의 결합으로 산정하여 U을 비롯한 금속 환원 거동을 계산하였다. 계산결과 대부분의 산화물들은 전해환원 공정에 의해 금속으로 전환되는 것으로 예상되었다. 란타나이드 원소들의 경우 $Li_2O$의 농도가 낮아지면 금속 전환율이 높아지나 대부분 산화물로 존재하는 것으로 나타났다. 추가적으로 $U_3O_8$의 전해환원 거동에 대해 Li의 확산과 Li과의 화학반응을 고려하여 반실험적 모델이 제시되었다. 실험데이터를 활용하여 매개변수를 결정하였으며 시간에 대한 환원율 및 전류에 대한 99.9% 환원 시간을 계산하였다.

Keywords

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