钍在核能中的长期潜力：原子能机构的分析
解读“核”
2021年8月，中国宣布建成第一座实验性钍基核反应堆。该反应堆建在中国北方的戈壁沙漠中，未来几年将对其进行测试。如果实验证明成功，北京计划建造另一座能够为10多万个家庭供电的反应堆。 中国并非唯一打算利用钍的特性的国家。过去，印度、日本、俄罗斯、英国、美国和其他国家都曾对研究钍在核能中的可能应用表现出热情。这种金属的吸引力在于它更加丰富和高效，可能成为主要核燃料的铀的替代品。
什么是钍？
钍是一种银色、略带放射性的金属，通常存在于火成岩和重矿砂中。它是以北欧神话中的雷神托尔命名的。在自然界中，它比铀含量上高出三至四倍，但在历史上很少用于工业或发电。这部分地是因为钍本身不是一种核燃料，但它可以用来创造核燃料。作为唯一天然存在的钍同位素，钍-232是一种可裂变材料，而不是易裂变材料，这意味着它需要高能中子进行裂变——原子核分裂，释放出用于发电的能量。然而，当受到辐照时，钍-232会发生一系列的核反应，最终形成铀-233这种可作为燃料在核反应堆燃烧的易裂变材料。
并非没有挑战
然而，存在着一些使钍的部署具有挑战性的经济和技术障碍。尽管这种金属很丰富，但目前提取的成本很高。
原子能机构铀资源专家Mark Mihalasky说，“作为稀土元素的一个主要来源的独居石矿也是钍的一个主要来源。如果不是目前对稀土元素的需求，就不会单单为了钍含量而开采独居石。钍是一种副产品，提取钍需要的方法比提取铀的成本要高。因此，就目前情况而言，能够以具有成本效益的方式从地下挖出的钍的数量并不像铀那样多。然而，如果对钍及其在核能中的应用有更高的需求，这种情况可能会改变。”
同样昂贵的是钍动力核装置的研究、开发和测试，因为缺乏关于钍的重要经验，而铀在核能中具有历史优势地位。原子能机构燃料工程和燃料循环设施技术负责人Anzhelika Khaperskaia说，“钍的另一个障碍是它可能难以处理。”作为一种能增殖但非易裂变材料，钍需要一个激励物，如铀或钚，来触发和维持链式反应。
原子能机构的一位科长Clément Hill总结说，“为了满足日益增长的能源需求和实现全球气候目标，世界正在寻找可持续和可靠的替代能源技术。钍可能成为其中之一。我们将继续进行研究，为那些有志于钍工作者提供可信和基于科学的成果。”
你想知道更多有关使用钍的挑战吗？
原子能机构的一本新出版物《钍基核能部署的近期和有发展前景的长远方案》全面总结了一个为期四年的原子能机构协调研究项目的成果，该项目侧重于发展钍基核能的可能性。该出版物审视了使用钍作为燃料的好处和挑战，并分析了其在从最常部署的水冷堆到熔盐堆等不同类型反应堆中的应用。
该出版物的作者之一Agarwal说，“许多国家认为钍既是可行又是非常有吸引力的发电和满足其日益增长的能源需求的方案，我们的研究项目有助于在国家实验室和研究机构之间分享使用钍的宝贵知识和经验，最终产生了这本出版物。”
What can thorium offer?
Thorium boasts several advantages over the conventional nuclear fuel, uranium-235. Thorium can generate more fissile material (uranium-233) than it consumes while fuelling a water-cooled or molten-salt reactor. According to estimates, the Earth's upper crust contains an average of 10.5 parts per million (ppm) of thorium, compared with about 3 ppm of uranium.
“Because of its abundance and its fissile material breeding capability, thorium could potentially offer a long-term solution to humanity’s energy needs,” Agarwal said.
Another advantage is that thorium-fuelled reactors could be much more environmentally friendly than their uranium counterparts. In addition to the fact that these reactors — and nuclear power in general — do not emit greenhouse gases in operation, they also produce less long-lived nuclear waste than present-day uranium-fuelled reactors.
Not without challenges
However, there are several economic and technical obstacles making the deployment of thorium challenging. Despite its abundance, the metal is currently expensive to extract.
“The mineral monazite, which is a major source of rare earth elements, is also a primary source of thorium,” said Mark Mihalasky, a Uranium Resources Specialist at the IAEA. “Without the current demand for rare earth elements, monazite would not be mined for its thorium content alone. Thorium is a by-product, and extraction of thorium requires methods that are costlier than for uranium. So, as it stands, the amount of thorium that can be pulled out of the ground in a cost-effective manner is not as great as for uranium. This, however, could change if there was a higher demand for thorium and its application in nuclear power.”
Equally expensive are research, development and testing of thorium-powered nuclear installations due to a lack of significant experience with thorium and uranium's historical pre-eminence in nuclear power. “Another hurdle for thorium is that it can be difficult to handle,” said Anzhelika Khaperskaia, Technical Lead on Fuel Engineering and Fuel Cycle Facilities at the IAEA. Being a fertile and not fissile material, it needs a driver, such as uranium or plutonium, to trigger and maintain a chain reaction.
“To meet growing energy demand and achieve global climate objectives, the world is looking for alternative sustainable and reliable energy technologies. Thorium may become one of those,” concluded Clément Hill, Section Head at the IAEA. “We will continue our research to deliver credible and science-based results for those interested in working with thorium.”