Hydrogen Transportation Behavior and its Control on the Water-Metal Boundary Using Pure Tritium

为了讨论的详细机制氢从金属转移到水套water-metal边界,一系列的氚渗透实验已经完成在423 K,使用纯铁管道(4)10毫米x 75毫米^ 1 x 1毫米^ t)包含氚气体(1 kPa, 7.4 GBq,纯度> 90%)在监测化学物种的氚水套,加压到0.8 mpa的他或他平衡气体h_2 1%,通过离子净化室、水喷泉和氧化催化剂床。对纯铁管样品表面进行初步机械抛光处理。制备了在423K 0.8MPa-He水中生长20小时以上的氧化层样品。采用SEM、XRD等对样品表面进行了分析。氧化层由内细部和外多孔部组成，为磁铁矿（Fe_3O_4）而非赤铁矿（Fe_2O_3）。在此条件下，内细部氧化物的生长速度为0.06~0.07 μm/h。主要结果如下1。在本实验条件下，通过纯铁到水套的渗透量约为计算值的1/5。即使表面氧化层（细而多孔的磁铁矿）增大，氚对水的渗透速率也没有明显变化。然而，最初渗透氚的HT分数为30%，在> 1.4μm的细磁铁矿层生长后，渗透氚的HT分数急剧下降至1/50左右。结果表明，高温分数的降低与氧化层的生长有关。在423 K、0.8 MPa条件下，纯He和1% H_2的溶解氢量差异对渗透的种类和数量影响不明显。以上结果表明，纯铁中的氚会通过磁铁矿表面羟基物质的同位素交换反应转移到水中。另一方面，如果表面羟基密度小，氚在表面复合后会以氢气的形式渗透到水中。

In order to discuss detailed mechanism of hydrogen transferred from metal to water jacket at the water-metal boundary, a series of tritium permeation experiment has been performed at 423 K, using pure iron piping (4)10mm x 75mm^1 x 1mm^t) contained tritium gas (1 kPa, 7.4 GBq, >90% purity) under monitoring chemical species of tritium in the water jacket, which pressurized to 0.8MPa by He or 1%H_2 in He balance gases, by purging through ion chambers, water bubblers and oxidation catalyst bed. Surface of pure iron tube sample was mechanically polished initially. Also, samples with oxide layer, which grew in the water of 0.8MPa-He at 423K for more than 20 hours, were prepared. Sample surface was analyzed by SEM, XRD etc. The oxide layer consisted of inner fine part and outer porous part, and was magnetite (Fe_3O_4) not hematite (Fe_2O_3). The inner fine part of oxide grew 0.06~0.07 μm/h in the above condition. The main results are as follows1. The permeation amount through pure iron to water jacket was about 1/5 of the calculated value in this experimental condition.2. Even if surface oxide layer (fine and porous magnetite) grew, tritium permeation rate to water was not changed drastically.3. However, HT fraction of permeated tritium was 30% initially, then, it decreased drastically to about 1/50 after > 1.4μm of fine magnetite layer growth. It suggested the relation between the HT fraction decrease and oxide layer growth.4. Permeated species and amounts were not affected clearly by dissolved hydrogen amount difference between pure He and 1% H_2 in He balance purging under 0.8 MPa at 423 K.From the above results, it suggests that the tritium in pure iron would transfer to water by isotope exchange reaction through surface hydroxyl species of magnetite. On the other hand, if surface hydroxyl density is small, the tritium would permeate to water as hydrogen gas after surface recombination.