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吹扫气组成的影响很大。较低的氧势对于较大的脱附速率是必要的，并且导致滋生材料与不锈钢覆层之间的良好相容性。为此，通过质谱克努森渗出法研究了与石墨一起存在的许多育种候选材料平衡的包括氧的气体物种及其分压。此外，在石墨共存的还原性气氛中，对孕育材料的化学稳定性进行了实验研究。研究结果如下：1.根据Li_2 O-ZrO_2体系中Li_2ZrO_3、Li_6Zr_2O_7和Li_8ZrO_6的分压数据，测定了它们的生成焓。Li_2 O-MO_X（M=Al，Fe，Mo，Si，Sn，Ti和Zr）复合氧化物中Li_2O含量越少，复合氧化物越稳定. Li_2SnO_3的生成焓比Li_2SiO_3的生成焓大，其值随IVB族原子序数的增加而增加。相反，在IVA族中，Li_2ZrO_3的生成焓小于Li_2TiO_3.3。计算机模拟结果表明，在还原条件下，增殖材料释放的T_2O/T_2比值变小，导致解吸速率增大。此外，育种材料与包层之间的反应被显著抑制. Li_2ZrO_3-石墨体系中的氧分压比Li_2ZrO_3-铂体系中的氧分压低8个数量级，即石墨的存在对氧分压的降低非常有利。

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.