DESC0025084

Problem Statement: Liquid metal cooled nuclear reactors, or LMRs, are a type of reactor that uses molten metal, typically sodium, lead, or a lead-bismuth or other eutectic mixtures, as a coolant instead of water. The main reason for having a non-water coolant lies in the fact that moderation and cooling can be decoupled, since water is an excellent moderator compared to a liquid metal. In particular, in a reactor that operates with a fast spectrum, water cannot be used as a coolant, or it would simultaneously also moderate, or thermalize neutrons. In addition to designing the reactor with a fast spectrum, the liquid metal offers several advantages. Unlike water, it can operate at much higher temperatures, extracting more energy from the fuel and improving efficiency. Furthermore, by allowing the neutron population to have a large fraction of fast neutrons, fertile materials like Uranium-238 can be converted into fissile Plutonium-239, essentially creating new fuel within the reactor. This could significantly reduce reliance on mined uranium and create a more sustainable fuel cycle. One of the remaining technical challenge associated with LMRs is the inability to use conventional techniques to inspect reactors components that are submerged under liquid metal due to the opacity of the liquid, its electric conductivity, and the high operating temperatures (around 500 °C). As of today, there are no established and widely used methods for directly viewing or inspecting components submerged in liquid lead within operational LMRs. Proposed Solution: It is proposed to develop an under-lead viewing and inspection system for liquid-metal-cooled nuclear reactors based on ultrasonic techniques. High-temperature ultrasonic transducers will be utilized in a two-dimensional array to allow for full-matrix capture phased array focusing for three-dimensional image construction. The transducer array will be deployed in an insulated housing with active cooling. The proposed sensor system will be capable of performing viewing and also limited nondestructive evaluation of surface flaws such as corrosion and surface-breaking cracks. Phase I Objectives: The Phase I effort will be focused on demonstrating proof of concept for an under-lead viewing system by designing, fabricating, and testing an ultrasonic transducer operable at temperatures in excess of 500C and demonstrated in a liquid metal test bed developed by research partners in the Nuclear Engineering Department at Penn State University. During Phase I, a surrogate liquid metal such as Sn-Bi alloy will be used to avoid establishing time-consuming safety protocols required for handling of lead. The ultrasonic transducer design will be based on the literature available for high-temperature ultrasound applications and research on under-sodium viewing technologies, with the consultation of an expert in transducer design for harsh nuclear environments. Grid scanning with the prototype transducer will be utilized in conjunction with two-dimensional synthetic aperture focusing to generate an image of stainless steel targets in the molten metal during Phase I, and this will be matured to a two-dimensional phased array transducer with active focusing during Phase II. Commercial Applications & Other Benefits: The successful development of under-lead viewing and NDE techniques for LMRs with liquid lead coolant would be a significant breakthrough, unlocking the full potential benefits of wide-scale LMR deployment for the public. LMRs have the potential to contribute significantly to reducing greenhouse gas emissions compared to fossil fuel sources, offering a path toward environmental preservation and more sustainable future. Another benefit lies in LMRs offering the potential for more efficient fuel utilization and reduced waste generation compared to traditional reactors. However, maximizing these benefits hinges on reactor performance and longevity. Reliable NDE techniques would allow for optimizing fuel burnup cycles and extending component lifespans while maintaining safe operating conditions. This translates to a safer, more reliable, and more cost-effective nuclear energy source for the public. Successful development of under-lead viewing and NDE for LMRs would be a game-changer, paving the way for safer, more efficient, and cleaner nuclear power generation, ultimately benefiting the public in numerous ways.