Thermal transient effects in fusion front wall/breeder blanket components

聚变反应堆内的高工作温度和核辐射会显著改变其部件的微观结构，进而改变材料特性和机械行为。为聚变反应堆选择的材料是专门为减少诱导辐射量而设计的，但了解这些材料在聚变等离子体的高温下会有什么表现也很重要。聚变反应堆中的等离子体可以达到数百万度的温度，并在运行期间使用聚焦磁场进行控制。然而，一旦失去这种保护，等离子体就有可能与壁面接触，导致短时间内温度急剧上升。热瞬变将在极短的时间内将反应堆材料加热到高于其所需的操作条件，但在操作过程中会多次加热。这可能会在部件中产生不希望看到的和不可预测的微结构演变。该项目将建立在布里斯托尔的工作基础上，该工作已经表明，即使是短期的高温(~750摄氏度)暴露也会导致用于结构支撑和冷却管的Eurofer-97不锈钢材料的微观结构显著退化[1]。这可能会影响机械性能和耐腐蚀性，进而导致部件寿命缩短。这个博士项目将研究非常短期的热漂移对聚变前壁、偏滤器和增殖包层材料的影响，并评估它们对材料微观结构和腐蚀行为的影响。学生将在布里斯托尔现有实验研究的基础上，使用定制设计的真空激光曝光台，使用二氧化碳激光将材料暴露在受控的热脉冲下，时间为1-10s。学生将调整这个实验台，以实现更快的冷却速度和更短的热峰，以更接近地模拟等离子体漂移的条件。然后，该系统将被用于研究聚变材料在重复的短期热暴露后的微观结构演变行为。该项目将调查在FW材料(例如，ODS钢)和/或增殖衬底(Eu97)靠近FW和界面接头处的大量(与反应堆相关的)热循环对FW材料(例如，ODS钢)和/或增殖体衬底(Eu97)的热演化和潜在影响。为了获得合适的循环速度(具有快速冷却速度)，可能需要投资一个新的钻机。但这样的试验台也可以用于其他聚变相关项目。热暴露的样品将使用扫描和透射电子显微镜、x射线衍射和层析成像进行表征，以观察材料微观结构随着热暴露的增加而发生的变化，并确定是否发生任何脆化或机械性能变化，如果在聚变反应堆中使用可能会导致问题。学生还将使用基于CALPHAD的建模将实验结果与相图的计算模拟进行比较。也可能有机会将热暴露与辐射和应力的影响相结合，并评估焊接件中的类似条件。

The high operating temperatures and nuclear radiation within a fusion reactor can significantly change the microstructure of its components, which in turn can change the material properties and mechanical behaviour. The materials chosen for fusion reactors have been specifically engineered to reduce the amount of induced radiation, but it is also important to understand how such materials will behave when exposed to the high temperatures of the fusion plasma. The plasma in a fusion reactor can reach temperatures of millions of degrees, and is kept controlled during operation using focused magnetic fields for containment. However, in the event of a loss of this containment it is possible for the plasma to contact with wall, leading to dramatic increases in temperature over short periods of time. The thermal transients will heat reactor materials above their desired operating conditions for very short spells but many times during operation. This could produce undesired and unpredicted microstructural evolution in components. This project would build on work at Bristol that has shown that even short periods high temperature (~750C) exposure can cause significant microstructural degradation of the Eurofer-97 stainless steel material used for structural support and cooling pipes [1]. This could affect mechanical properties and corrosion resistance, in turn leading to a shortening of component life. This PhD project will study the effect of very short-term thermal excursions on fusion front wall, divertor and breeder blanket materials and assess their effect on the microstructure and corrosion behaviour of the material.The student will build on existing experimental research at Bristol using a custom design vacuum laser exposure rig, that can expose materials to controlled thermal pulses for short (1-10s) thermal spikes using a CO2 laser. The student will adapt this experimental rig to enable faster cooling rates and shorter thermal spikes to more closely simulate the conditions of a plasma excursion. The system will then be used to study the microstructural evolution behaviour of fusion materials after repeated short-term thermal exposure. The project will investigate the thermal evolution and potential impacts from high numbers (reactor relevant) of thermal cycling above the desired operating temperatures on FW materials (e.g. ODS steel) and/or breeder substrate (Eu97) close to FW and interface joint. To getthe appropriate cycling rates (with fast cooling rates), investment in a new rig will likely by required. But such a rig could be used for other fusion relevant projects.Thermally exposed specimens will be characterised using scanning and transmission electron microscopy, x-ray diffraction and tomography to observe the change in the material microstructure with increasing heat exposure, and determine if any embrittlement or change in mechanical properties occur that might cause problems if used in a fusion reactor. The student will also compare experimental results to computational simulations of the phase diagram using CALPHAD-based modelling. There may also be opportunities to combine thermal exposures with the effects of irradiation and stress, and to assess similar conditions in weldments.