Once this challenge is overcome, i.e. we have a positive gain factor, we can now start to mass deploy the nuclear fusion, and since nuclear
above ⬆ Power-plant Levels of Neutron Damage and Heat Flux Demand Innovations over State of the Art 9 Water-cooled W-monobloc ITER Divertor is highest TRL high-heat-flux component for fusion ever manufactured Capillary porous system maintains liquid tin surface on tungsten substrate with continuous material replenishment Retain favorable W properties (high Tmelt) while mitigating shortcomings (brittle) with fibers and functional grading State of the Art Self-healing Liquid Metal Surface Fiber-based and Functional Graded Surfaces Undergoing vacuum leak tests Challenges • Far from demonstrating tritium self-sufficiency in closed fusion system • Core units in fuel cycle not ready for continuous operation • Lack of integrated, tritium-capable test infrastructure at scale • No shared, architecture-agnostic design and data framework Continuous Tritium Processing and Approaches to Low Inventory Operation Remain to be Developed 10 Turn the plasma-facing wall from a survival challenge to a designed system Opportunities • Emerging international facilities focusing on sub-scale closed loop • Direct internal recycling concept for inner loop, smaller T plant • Increased scale and breadth of H&D testing of materials & systems • Tools for co-design of holistic blanket/tritium system Far Outer Fuel Cycle Technology is Mature The Opportunity is the Inner Cycles & Systems Optimization 11 Opportunity to validate closed-loop fuel handling at realistic scales for safe, self-sufficient fusion power plants Enables safer, more efficient fuel handling and is essential for achieving reliable, closed-loop fusion fuel cycles Opportunity to optimize the entire fuel cycle virtually, shortening development cycles and reducing risk and cost UNITY-2 Facility Hydrogen Permeators & Barriers Multi-loop Process Flow Challenges • Single-effect tests lack well-known synergistic physical effects • Materials, chemistry, MHD behavior are not yet understood or qualified • Design tools and data are insufficient to de-risk & down-select • The U.S. lacks integrated testbeds to replicate relevant blanket environmental conditions Blankets are the Energy Engine and Fuel Factory Yet No Functioning Blanket Has Ever Been Made 12 Blankets are fusion’s biggest
Achieving higher power densities in fusion reactors requires the development of as-yet-unknown materials or confinement concepts, due to the high heat fluxes which would occur at the plasma-facing components of the reactor. The first goal has been to reach what's called the break-even condition, which occurs when the amount of energy used to heat up the plasma is equal to the amount of energy that is produced by the fusion reaction. I will focus now on three specific areas where materials impact fusion reactor design: the plasma-facing region, where there is high heat flux and particles are impacting the metal structure; the plasma-diagnostic, heating, and magnet systems; and the structure of the blanket and first-wall region surrounding the plasma, which is the heart of the heat-extraction system. If you look at the sputtering behavior of various materials at fusion-relevant conditions (10-1,000 eV hydrogen ion energies), stainless steel is one of the worst possible plasma-facing materials.
Challenges include maintaining plasma stability, developing materials that can withstand extreme conditions, and achieving a net positive energy
There are dozens of unstated engineering problems that need to be solved before fusion can be commercially successful at scale.
“The energy of the fusion-generated neutrons poses serious challenges to the fusion power plant’s first wall and vacuum vessel, which means considerations need to be given to radiation damage, biological shielding, remote handling, and safety,” explained Ian Chapman, CEO of the United Kingdom Atomic Energy Authority. The IAEA is helping to address issues associated with fusion materials development and research by coordinating the drafting of guidelines for reference material testing techniques, and by bridging knowledge gaps in designing facilities for testing fusion reactor materials and components. “Technologies like the dual-beam ion facility installed in 2019 at the Ruđer Bošković Institute in Croatia with IAEA support can simulate the conditions that a material would be exposed to in a fusion reactor. Designing and building future fusion reactors will depend on the technical, technological and material results of ITER and other well-established multinational coordinated research and development activities, but the distance between us and a fusion-powered future continues to narrow every day.
[Skip to Content](https://kleinmanenergy.upenn.edu/research/publications/bringing-fusion-energy-to-the-grid-challenges-and-pathways/#content). [Download PDF](https://kleinmanenergy.upenn.edu/wp-content/uploads/2025/10/KC-Digest-81-Bringing-Fusion-Energy-to-the-Grid.pdf). ](https://kleinmanenergy.upenn.edu/wp-content/plugins/a3-lazy-load/assets/images/lazy_placeholder.gif)](https://kleinmanenergy.upenn.edu/wp-content/uploads/2025/09/Fig-3.jpg)[](https://kleinmanenergy.upenn.edu/wp-content/uploads/2025/10/Fig-4.jpg). This category has over $2.5 billion in funding and 15 startups, such as TAE Technologies, Helion, and General Fusion.](https://kleinmanenergy.upenn.edu/wp-content/plugins/a3-lazy-load/assets/images/lazy_placeholder.gif)](https://kleinmanenergy.upenn.edu/wp-content/uploads/2025/10/Table-1-4.jpg). Historically, facilities like the [UR-LLE National Laser Users’ Facility](https://www.lle.rochester.edu/about-the-laboratory-for-laser-energetics/nluf/) (NLUF) program, the [DIII-D National Fusion Facility](https://science.osti.gov/fes/Facilities/User-Facilities/DIII-D), and Princeton’s [National Spherical Torus Experiment](https://science.osti.gov/fes/Facilities/User-Facilities/NSTX-U) have enabled hundreds of users to conduct experiments not possible at their home institutions, diffusing knowledge while harnessing national scientific ingenuity (U.S. Department of Energy 2024). “Promoting Fusion Energy Leadership with U.S. Tritium Production Capacity.” [_https://fas.org/publication/fusion-energy-leadership-tritium-capacity/_](https://fas.org/publication/fusion-energy-leadership-tritium-capacity/). “Major Funding Milestone for World-First Prototype Fusion Plant.” [_https://www.gov.uk/government/news/25-billion-for-world-first-prototype-fusion-energy-plant_](https://www.gov.uk/government/news/25-billion-for-world-first-prototype-fusion-energy-plant). “U.S. Department of Energy Announces Selectees for $107 Million Fusion Innovation Research Engine Collaboratives, and Progress in Milestone Program Inspired by NASA.” _[https://www.energy.gov/articles/us-department-energy-announces-selectees-107-million-fusion-innovation-research-engine](https://www.energy.gov/articles/us-department-energy-announces-selectees-107-million-fusion-innovation-research-engine)_. [More…](https://kleinmanenergy.upenn.edu/research/publications/bringing-fusion-energy-to-the-grid-challenges-and-pathways/#addtoany "Show all").
Public sector efforts prioritize basic science, but fusion energy development requires an additional emphasis on technology and engineering research. Doing so may require significant public engagement, but little is known about public perception of fusion energy in the U.S. GAO developed four policy options that could help address these challenges or enhance the benefits of fusion energy. 34)** Implementation approaches: *Support facilities that address scientific and engineering challenges* *Support workforce development* *Assess sources of critical supplies and manufacturing capabilities* | * Could help fill critical research gaps on the path to fusion energy commercialization. GAO conducted a technology assessment on (1) the status, potential benefits, and limitations of fusion energy, (2) challenges that might affect the development or use of fusion energy, (3) policy options that might help enhance the benefits or mitigate challenges associated with fusion energy.