Technetium (Tc) is a long-lived radioactive isotope, which exists as TcO4 - with high solubility under oxidative condition. The solubility of Tc is fundamental to assess the safety of radioactive waste repository in the case of a leakage of radioactive wastes. Cellulosic materials (paper, wood, cotton, etc.) contaminated by radionuclides are disposed of in low-level and intermediate-level radioactive waste repositories. Cellulose can be decomposed under anaerobic and alkaline conditions when cement pore water is saturated, and then isosaccharinic acid (ISA) is generated as a degradation product of cellulose. ISA forms complexations with radionuclides in solution and affects the solubilities of radionuclides. Therefore, the effect of ISA should be accurately evaluated to predict and assess the mobility of radionuclides in repository environments. In this study, batch tests were conducted to confirm the effect of ISA on the solubility of Rhenium(IV) Oxide. Herein, rhenium was used as a non-radioactive analog of Tc due to their similar chemical properties. Deionized water (DIW) and 0.1 M NaOH solution in pH 12.5 were used as background solutions, and ISA concentration was varied to 1~20 mM using Ca(ISA)2 and NaISA, respectively. The batch tests were conducted under both aerobic and anaerobic conditions. The whole batch tests under anaerobic conditions were performed in the glove box using oxygen purged DIW with a high purity nitrogen gas (99.9%) and low oxygen concentration (< 0.5 ppm). As a result, the rhenium concentration decreases as more ISA is dissolved in the solution, which shows the contrary effect of ISA on the solubility of other metals and radionuclides (e.g., Co, Th, Fe, Ni, etc.). It is assumed that the reducing capacity of ISA decreases the rhenium dissolution in the solution. Additional characterization of the oxidation state of rhenium oxide and the mechanism will be tested and presented.

This study investigated the densification behavior of rhenium alloys including W-25 wt.%Re and Re-2W-1Ta (pure Re) during sintering. The dilatometry experiments were carried out to obtain the in-situ shrinkage in H2 atmo-sphere. The measured data was analyzed through shrinkage, strain rate and relative density, and then symmetricallytreated to construct the linearized form of master sintering curve (MSC) and MSC as a well-known and straightforwardapproach to describe the densification behavior during sintering. The densification behaviors for each material were ana-lyzed in many respects including apparent activation energy, densification parameter, and densification ratio. MSC witha minimal set of preliminary experiments can make the densification behavior to be characterized and predicted as wellas provide guideline to sinter cycle design. Considering the results of linearized form and MSC, it was confirmed thatthe W-25 wt.%Re compared to Pure Re is more easily densified at the relatively low temperature.

리늄판의 미세경도를 압흔 하중 및 온도의 함수로 구하였다. 미세경도의 온도의존성은 상온에서 1000˚C까지의 범위에서 Vickers 압흔기가 내장된 고온 미세압흔기를 이용하여 연구되었다. 미세경도의 하중의존성은 Vickers와 Knoop 압흔기를 이용하여 검토되었다. 압흔 크기 영향은 표준화된 Meyers법칙에 위해 충분히 설명 되었다. 압흔도중 압흔기 아래에서의 가공경화 때문에 어닐링된 리늄판 경도값은 높은 압흔 하중에서 압련되 리늄판의 경도값에 접근하였다. 경도의 하중의존성으로부터 외삽하여 얻어진 하중 영에서의 경도값은 경도값이 다른 열활성을 나타내는 두 개의 다른 기구에 의해 제어됨을 제시하였다. 낮은 온도에서 활성화에너지는 0.02eV 였으며, 한편 높은 온도에서 활성화에너지는 0.15eV 였다. 이때 전이온도는 대략 250˚C 이었다.