Vaporization Behavior of Tritium Breeding Candidate Materials in Reducing Atmosphere at High Temperatures

聚变堆固体增殖材料的氚释放行为受扫气成分的影响很大。较低的氧势是获得较大解吸率所必需的，并使繁殖材料与不锈钢覆层之间具有良好的兼容性。为此，用质谱克努森渗出法研究了包括氧在内的气体物种及其分压与许多与石墨共存的孕育候选物质的平衡。此外，在石墨共存的还原气氛中，对育种材料的化学稳定性进行了热力学研究。研究结果总结如下：1.研究成果。根据Li_2O-ZrO_2体系中Li_2ZrO_3、Li_6Zr_2O_7和Li_8ZrO_6的分压数据，确定了它们的生成热。一般来说，Li_2O含量较少的复合氧化物在Li_2O-Mo_X(M=Al、Fe、Mo、Si、Sn、Ti和Zr)中更稳定。Li_2SnO_3在组成氧化物中的生成热大于Li_2SiO_3，其值似乎与IVB基团中原子序数的增加一致。相反，在IVA基团中，Li_2ZrO_3的生成热小于Li_2TiO_3。计算机模拟表明，在还原条件下，繁殖材料释放出的T_2O/T_2比值变小，导致解吸率较大。此外，育种材料与包层之间的反应被显著抑制。Li_2ZrO_3-石墨体系的氧分压比Li_2ZrO_3-铂体系的低8个数量级，这就是说，石墨的存在对降低氧分压非常有利。

Tritium release behavior from solid breeding materials in fusion reactors is very influenced by the composition of a sweep gas. Lower oxygen potential is essential for larger desorption rate and leads to good compatibility between the breeding materials and stainless steel claddings. For this reason, gas species including oxygen and their partial pressures in equilibrium with many breeding candidate materials existing with graphite were studied by a mass-spectrometric Knudsen effusion method. In addition, the chemical stability of the breeding materials was studied thermodynamically in the reducing atmosphere with the coexistence of graphite. The results are summarized as follows.1. Enthalpies of formation for Li_2ZrO_3, Li_6Zr_2O_7 and Li_8ZrO_6 in the Li_2O-ZrO_2 system were determined from the data of partial pressures over them. Generally, complex oxides with less Li_2O content are more stable in the Li_2O-MO_X(M=Al, Fe, Mo, Si, Sn, Ti and Zr).2. The enthalpy of formation for Li_2SnO_3 from constituent oxides is greater than that for Li_2SiO_3; it seems that the value increases in keeping with the atomic number in the IVB group. On the contrary, in the IVA group the enthalpy of formation for Li_2ZrO_3 is smaller than that for Li_2TiO_3.3. Computer simulation shows that under the reducing condition the ratio of T_2O/T_2 released from the breeding materials becomes small, leading to the large desorption rate. Furthermore, reactions between the breeding materials and the claddings are suppressued markedly.4. The oxygen partial pressure in the Li_2ZrO_3-graphite system is eight orders of magnitude lower than that in the Li_2ZrO_3-platinum system; that is, the presence of graphite is very useful for the reduction of the oxygen partial pressure.