A new concept for compact radiation shielding: Reactive sintered tungsten borocarbides

迄今为止，由于二氧化碳排放导致的人为气候变化对人类的生存构成了最大的威胁。气候变暖的影响已经很明显了，极端天气增多，极地冰层融化，海平面上升。由于全球对电力的需求继续超过供应，化石燃料燃烧产生的二氧化碳排放大部分来自发电。可再生能源（风能、太阳能、水能）受到天气依赖性以及相关问题（如能源储存和土地利用）的限制。核聚变在使全球发电脱碳方面发挥着重要作用，但辐射屏蔽是一个限制因素。制造微型太阳是一部分，但必须存在能够承受实际聚变反应堆聚变条件的材料。w基合金和其他难熔金属是目前核聚变反应堆的解决方案，但发电核聚变反应堆的工程要求超过了现有材料的要求。该研究的目标是证明基于紧凑型球形托卡马克（cSTs）中硬质合金和反应烧结硼化物（cWC-RSB）概念的辐射屏蔽的可行性。cWC-RSBs可以弥合当前材料与发电cST工程要求之间的差距。cWCs-RSBs将重元素(W)和轻元素（C、B）结合在一起，并通过WC与延展性金属结合剂结合，获得了优异的辐射吸收性能。然而，迄今为止，由于Co（和Ni）金属作为粘结剂合金的使用，由于Co和Ni具有活化危险，因此阻止了使用cWCs作为辐射，因此cWCs从未在核反应堆中使用过。2014年，我发现不活化的FeCr合金适合作为cWC粘结剂合金，在研究cWC中添加硼后，RSB发展。与单独使用cwc相比，cWC-RSB复合屏蔽整体上具有更大的辐射衰减。第一个目标是评估候选屏蔽材料的热机械性能和安全情况，包括高温氧化和热冲击，以最坏的情况，如热屏蔽暴露在空气中。硅包覆cwc的实验数据表明，在900C-1200C的温度范围内，硅包覆cwc的氧化速率比钨包覆cwc的氧化速率延缓了4个数量级。我将评估cWC-RSBs在发电聚变反应堆预测的低温至失效（bbb1200c）温度下的性能。虽然自20世纪30年代以来存在大量关于cwc的热机械性能的数据，但考虑到rbs的新颖性，rbs的热机械性能在工业化之前众所周知是至关重要的，因此关于rbs的数据很少。rsb的新颖性意味着人们对其化学性质和制造途径知之甚少。目前的加工方法还没有完全优化致密，无裂纹的rsb。第二个目标是利用相图计算方法（CALPHAD）来预测最合适的成分和实验设计（DoE）方法来填补这些空白，以实现最有效的处理试验。这项研究表明，当当前解决方案存在明显的关键差距时，如何从现有材料和技术中获得新的解决方案。最近对基于WC和rsb的屏蔽概念的中子和伽马衰减的模拟显示出相当大的希望。然而，迄今为止，关于化学废物的辐射反应的数据很少，而关于rsb的数据则没有。为了实现第三个目标，我打算在目前的研究基础上，利用模拟cST来进行辐射实验和模拟cST内部条件范围的实验工作，包括离子轰击、带电粒子和二次辐射。模拟核聚变反应堆中cWC-RSB屏蔽材料的抗氧化性能数据表明，cWC-RSB材料在辐射衰减和安全性方面优于当前候选辐射屏蔽材料。

There has been no greater existential threat to humanity to date from anthropogenic climate change as a result of CO2 emissions. The effects are already apparent in terms of more extreme weather, loss of polar ice and rising sea levels. Power generation contributes to much of the CO2 emissions from fossil fuel burning as the worldwide demand for power continues to outstrip supply. Renewable energy (wind, solar, hydro) is limited by weather dependency, with associated issues such as energy storage and land use. Nuclear fusion has a significant role in decarbonizing global power generation but radiation shielding is a limiting factor. Creating miniature Suns is one part, but materials must exist that can withstand fusion conditions for practical fusion reactors. W-based alloys and other refractory metals are current solutions in fusion reactors, but the engineering requirements for power-generating fusion reactors exceed those in current materials. The goal of this fellowship will demonstrate the feasibility of radiation shielding based on the Cemented Tungsten Carbides and Reactive Sintered Borides (cWC-RSB) concept in Compact Spherical Tokamaks (cSTs). cWC-RSBs can bridge the gap between current materials and the engineering requirements for a power-generating cST. cWCs-RSBs have excellent radiation absorption properties by combining heavy (W) and light elements (C, B) with the strength and toughness by combining WC with a ductile metal binder. However, cWCs have never been used in nuclear reactors to date since the use of Co (and Ni) metal as a binder alloy prevented the use of cWCs as radiation due to Co and Ni being activation hazards. In 2014, I discovered that non-activating FeCr alloys are suitable as cWC binder alloys, with RSB development following on investigating boron additions in cWCs. Combined cWC-RSB shields have greater radiation attenuation overall, compared to cWCs alone. The first objective evaluates the thermo-mechanical properties and the safety case for shielding candidates, including high-temperature oxidization and thermal shock to in terms of worst-case scenarios, such as exposure of hot shielding to air. Experimental data on Si-coated cWCs showed that Si-coating retarded oxidization rate by 4 orders of magnitude relative to tungsten in the temperature range 900C-1200C. I will evaluate the properties of cWC-RSBs over cryogenic to failure (> 1200C) temperatures predicted for power-generating fusion reactors. While considerable data on the thermo-mechanical properties exist for cWCs since the 1930s, there is little on RSBs, given their novelty and it is crucial that thermo-mechanical properties of RSBs are well-known prior to industrialization.The novelty of RSBs means that very little is known about their chemistry and routes to fabrication. Current processing methods are not fully optimized for dense, crack-free RSBs. The second objective aims to fill these gaps using the calculation of phase diagram method (CALPHAD) for predicting the most suitable compositions and design of experiment (DoE) methodology for the most efficient processing trials. This research demonstrates how new solutions can be derived from existing materials and techniques when a critical gap in current solutions is apparent. Recent simulations of the neutron and gamma attenuation of WC- and RSB-based shielding concepts show considerable promise. However, there is little data on the radiation response of cWCs and none on RSBs to date. For this third objective, I intend to build on current research using simulated cSTs to inform radiation experiments and experimental work simulating the range of conditions inside a cST, including ion bombardment, charged particles, and secondary radiation. Data from cWC-RSB shields in a simulated fusion reactor alongside demonstrated oxidization resistance indicates that cWC-RSB materials exceed current radiation shielding candidates in terms of radiation attenuation and safety.