Isotope Production in Fusion Systems

TL;DR

This work demonstrates that fusion reactors can generate substantial economic value by co-producing high-value isotopes through neutron-driven transmutation in the blanket, potentially enabling deployment well before energy breakeven. It develops a comprehensive framework linking neutron physics, blanket feedstock burn, heat loading, and market-driven economics to define hybrid breakeven conditions and payback timelines. The authors derive scaling relations for transmutation in tokamaks and mirrors, examine neutron-wall loading non-uniformities, and explore neutron multiplication as a route to boost economic viability. Case studies on gold production and 99Mo radiopharmaceuticals illustrate how isotope value and market size can lower plasma-performance requirements and enable near-term, revenue-positive fusion concepts. The results advocate treating isotope production as a core capability of fusion energy, with significant practical implications for deployment strategies and blanket design.

Abstract

Fusion systems producing isotopes via neutron-driven transmutation can achieve economic viability well before reaching energy breakeven. Incorporating carefully selected feedstock materials within the blanket allows fusion systems to generate both electrical power and high-value isotopes, expanding the space of viable concepts, significantly enhancing the economic value of fusion energy, and supporting an accelerated path to adoption. We calculate the value of this co-generation and derive a new economic breakeven condition based on net present value. At lower plasma gain, $Q_{\mathrm{plas}}\lesssim1-3$, high-value transmutation, such as medical radioisotopes, enables pure transmuter fusion systems operating at only a few megawatts of fusion power: for example, a 3 megawatt system transmuting ${}^{102}\mathrm{Ru}\rightarrow{}^{99}\mathrm{Mo}$ could fulfill global ${}^{99}\mathrm{Mo}$ demand with $Q_{\mathrm{plas}}\ll1$. At higher gain $Q_{\mathrm{plas}}\gtrsim3$, it becomes viable to generate electricity in addition to isotopes. For example, co-production of electricity and gold, transmuted from mercury in a fusion blanket, can reduce the required plasma gain for viability from $Q_{\mathrm{plas}}\sim10-100$ to $Q_{\mathrm{plas}}\sim3-5$. We further highlight techniques to enhance transmutation including magnetic mirrors, asymmetric neutron wall loading, and neutron multiplication. Fusion neutron-driven transmutation therefore offers a revenue-positive pathway for deploying fusion energy at terawatt-scale, starting from smaller megawatt-scale machines for radioisotope production and then scaling up to co-producing electricity and gold in larger fusion power plants.

Figures (29)

• Figure 1: Threshold energy for $(\mathrm{n},\mathrm{2n})$ reactions versus proton number (Z) and neutron number (N). Red coloring above 14.1MeV indicates the $(\mathrm{n},\mathrm{2n})$ reaction is inaccessible at 14.1MeV. Data from Brown20181.
• Figure 2: Driving $(\mathrm{n},\mathrm{2n})$ reactions on ${}^{198}\mathrm{Hg}$ to produce stable gold ${}^{197}\mathrm{Au}$ using D-T neutrons Rutkowski2025, along with subsequent (n,t) reactions on ${}^{6}\mathrm{Li}$. Dashed lines indicate that fewer than 100% of the incoming products will undergo the incoming reaction.
• Figure 3: Net present value versus product price for a fusion power plant with 1GW$_\mathrm{th}$ power, $Q_\mathrm{plas} = 80$, and electricity price 50$/MWh. Solid curves: co-production of electricity and gold; dotted lines are electricity-only.
• Figure 4: Simplified blanket model layout.
• Figure 5: (a) $\Xi$ (\ref{['eq:Xiprefac']}) and $\eta_\mathrm{pro}$ (\ref{['eq:eta_prod', 'eq:eta_prod']}) versus $\Sigma l_b$ and (b) $\eta_\mathrm{pro}$ versus $\Xi$.