Optimization on producibility improvement and the recycling process of neutron multipliers for fusion applications
Optimization on producibility improvement and the recycling process of neutron multipliers for fusion applications
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DOI：
10.1007/s10853-019-04213-0
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发表时间：
2019-11
影响因子：
4.5
通讯作者：
Jae-Hwan Kim;M. Nakamichi
中科院分区：
文献类型：
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作者：
Jae-Hwan Kim;M. Nakamichi
铍和铍金属间化合物(铍)卵石被认为是国际热核实验堆(ITER)和示范聚变反应堆(DEMO)中的中子倍增器。采用等离子体烧结和旋转电极相结合的方法，成功地建立了一种制备铍系卵石的新工艺。然而，由于铍的脆性，其造粒产率约为70%，一般不能满足要求，而30%的碎片(指定为非球形)是作为副产品产生的。为了提高造粒率和考虑新的回收工艺，采用了一种新的基础实验步骤，以证实采用相同的等离子烧结和旋转电极工艺回收工艺的可行性。因为在这些材料中预计会形成氧化表面和中子引起的缺陷，所以这些缺陷应该在回收过程中消除。众所周知，等离子烧结工艺通过施加脉冲电流来去除粉末表面的杂质，而旋转电极法(REP)是一种在高于熔点的温度下使用电弧熔化的造粒工艺。因此，通过将鹅卵石碎块模拟为用过的鹅卵石，对回收工艺进行了可行性试验。在混合粉末和碎块的混合比例分别为1：1和2：1的情况下，以及由100%的碎块粉碎的粉末，即使发现了几个密度较低的区域，也可以成功地制备出等离子烧结棒材。不是所有的棒子都在重复试验中折断，这表明造粒结果具有相似的粒度分布和产量。对于100%碎屑生产的鹅卵石、碎屑和棒状鹅卵石的氧含量而言，等离子烧结对杂质清除的影响并不显著，而等离子烧结明显地导致氧作为杂质的显著还原。
Beryllium and beryllium intermetallic compound (beryllide) pebbles have been regarded as a neutron multiplier in an international thermonuclear experimental reactor (ITER), as well as a demonstration (DEMO) fusion reactor. A novel fabrication process of the beryllide pebbles has been successfully established by combining the plasma sintering and rotating electrode processes. However, owing to the brittleness of beryllides, their granulation yield is approximately 70%, which does not generally satisfy the requirement, whereas the fragments (designated to be not spherical) with 30% are generated as by-products. To improve the granulation yield and in considering a new recycling process, a novel step on fundamental experiments was adopted to confirm feasibility on the recycling process using the same plasma sintering and rotating electrode processes. Because the formation of oxidized surface and neutron-induced defects in these materials is anticipated, these defects should be eliminated during the recycling process. The plasma sintering process is known to remove impurities on powder surfaces by applying a pulse current, whereas the rotating electrode process (REP) is a granulation process that uses arc melting at a temperature higher than the melting point. Hence, a feasibility test on the recycling process was performed by applying this process with the fragments for the pebbles simulated as the used pebbles. In the case of mixture ratios of 1:1 and 2:1 for the mixed powders and fragments, respectively, and the powders pulverized by 100% fragments, the rods produced through plasma sintering were successfully fabricated even if several areas with low density are identified. Not all rods were broken during the REP, indicating granulation results with similar size distribution and yield. Regarding the oxygen contents of as-received pebbles, fragments, and rod and pebbles produced with 100% fragments, the plasma sintering effect on impurity cleaning is therefore not significant, whereas the REP evidently leads to remarkable reduction of oxygen as impurity.