The effect of Ar ion beam irradiation on mesocarbon microbead-densified graphite as the matrix of fuel elements in molten-salt nuclear reactors
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摘要: 为提高熔盐堆燃料元件基体石墨的致密性，采用准等静压工艺，对球形燃料元件A3-3基体石墨进行中间相炭微球（MCMB）固相增密，并对其进行了氩离子辐照性能研究。通过压汞测试研究了增密后基体石墨的进汞临界压强和平均孔径变化；利用氩离子辐照实验并结合纳米压痕技术和拉曼光谱分析，研究了固相增密前后基体石墨的离子辐照效应。结果表明，采用平均粒径为2、10和16 μm的MCMB对基体石墨A3-3增密后，基体石墨孔径由924 nm分别降至530、573和644 nm，MCMB以其自烧结同步收缩的特性，起到了填充孔隙和裂缝的作用，实现了对基体石墨的固相增密。MCMB增密剂粒径越接近基体石墨的孔径，增密后基体石墨的平均孔径越小，进汞临界压强越高，即增密效果越好。样品纳米压痕的测试表明高剂量离子辐照下（> 1 dpa），MDG2-15（粒径2 μm，质量百分数为15%的MCMB增密基体石墨）石墨比A3-3石墨的离子辐照硬化速率慢。拉曼光谱结果显示增密前后基体石墨在1.47 dpa剂量下，均发生非晶化，致密化调控前后基体石墨的离子辐照效应表现出一致性。Abstract: Mesocarbon microbeads (MCMBs) were added to the precursors of a traditional matrix A3-3 graphite to increase its density for use as the matrix of fuel elements to inhibit the impregnation of liquid fluoride salt in molten salt reactors. The physical properties of the densified graphite (MDG) obtained using MCMBs with different sizes were compared with those of the A3-3 graphite. Ar ion-beam irradiation by a 4 MV accelerator was used to obtain surface damage to ~1 μm depth in the specimens. Results show that the median pore sizes of the MDGs increase from 530 to 644 nm with the size of MCMBs increasing from 2 to 16 μm, but all are smaller than that of the A3-3 graphite (924 nm). The density is increased by adding MCMBs. The MDG prepared from MCMBs with a size of 2 μm has the highest resistance to irradiation hardening. Both the A3-3 graphite and the MDGs become amorphous at an Ar ion beam dose of 1.47 dpa.
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Key words:
- Molten salt reactor /
- Fuel element /
- Graphite matrix /
- Ion irradiation /
- Nanoindentation.
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