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Isotope Production in Muon-Catalyzed-Fusion Systems

J. F. Parisi, A. Rutkowski

TL;DR

Isotope Production in Muon-Catalyzed Fusion Systems demonstrates that μCF can serve as a high-flux neutron source for transmutation-based isotope production even when net energy breakeven is not achieved. The authors derive heat-neutron flux relationships, formulate a transmutation breakeven condition, and propose a concrete $^{225}$Ac production system using a spherical $^{226}$Ra blanket driven by a muon source, validated by OpenMC simulations. They show that with a steady-state muon rate of $10^{12}$ μ/s and ~$0.564$ kW of fusion power, ~20 mg/yr of $^{225}$Ac can be produced, and that higher muon production rates can enable additional isotope pathways. The work highlights that accelerating muon source development offers a practical route to large-scale, neutron-driven isotope supply ahead of energy production, potentially addressing critical shortages in valuable radioisotopes.

Abstract

Producing valuable isotopes with high-flux high-energy neutrons generated by muon-catalyzed fusion ($μ$CF) reactions could substantially improve the economic prospects for muon-catalyzed fusion. Because no external heating is required for $μ$CF, heat flux constraints are significantly relaxed compared with fusion systems requiring external heating. This could allow $μ$CF to attain much higher neutron flux without breaching material heat flux limits. If muon production rates can be increased, $μ$CF systems employing transmutation could be viable well before energy breakeven is possible. For $μ$CF systems transmuting valuable isotopes, the required number of catalyzed fusion events per muon and muon energy generation cost can be relaxed by several orders of magnitude relative to electricity-generating systems, making $μ$CF an attractive high-flux neutron source. We show an example $μ$CF system with a 10 gram ${}^{226}\mathrm{Ra}$ feedstock and a steady-state muon rate of $10^{12}$ muons / second - roughly half a kilowatt of fusion power - could produce 20 mg of ${}^{225}\mathrm{Ac}$ per year - comparable to 400 times global supply in 2024. As higher muon rate sources become available, many other radioisotope transmutation pathways become viable. These findings motivate the accelerated development of $μ$CF systems for neutron-driven isotope production far before net energy generation is possible.

Isotope Production in Muon-Catalyzed-Fusion Systems

TL;DR

Isotope Production in Muon-Catalyzed Fusion Systems demonstrates that μCF can serve as a high-flux neutron source for transmutation-based isotope production even when net energy breakeven is not achieved. The authors derive heat-neutron flux relationships, formulate a transmutation breakeven condition, and propose a concrete Ac production system using a spherical Ra blanket driven by a muon source, validated by OpenMC simulations. They show that with a steady-state muon rate of μ/s and ~ kW of fusion power, ~20 mg/yr of Ac can be produced, and that higher muon production rates can enable additional isotope pathways. The work highlights that accelerating muon source development offers a practical route to large-scale, neutron-driven isotope supply ahead of energy production, potentially addressing critical shortages in valuable radioisotopes.

Abstract

Producing valuable isotopes with high-flux high-energy neutrons generated by muon-catalyzed fusion (CF) reactions could substantially improve the economic prospects for muon-catalyzed fusion. Because no external heating is required for CF, heat flux constraints are significantly relaxed compared with fusion systems requiring external heating. This could allow CF to attain much higher neutron flux without breaching material heat flux limits. If muon production rates can be increased, CF systems employing transmutation could be viable well before energy breakeven is possible. For CF systems transmuting valuable isotopes, the required number of catalyzed fusion events per muon and muon energy generation cost can be relaxed by several orders of magnitude relative to electricity-generating systems, making CF an attractive high-flux neutron source. We show an example CF system with a 10 gram feedstock and a steady-state muon rate of muons / second - roughly half a kilowatt of fusion power - could produce 20 mg of per year - comparable to 400 times global supply in 2024. As higher muon rate sources become available, many other radioisotope transmutation pathways become viable. These findings motivate the accelerated development of CF systems for neutron-driven isotope production far before net energy generation is possible.

Paper Structure

This paper contains 7 sections, 48 equations, 3 figures, 1 table.

Table of Contents

  1. Introduction
  2. Heat and Neutron Fluxes in Muon-Catalyzed Fusion
  3. Transmutation Breakeven Condition
  4. A $\mu$CF System for $\ce{^225Ac}$ Production
  5. Discussion
  6. Acknowledgements
  7. Muon-catalyzed Fusion Cycle

Figures (3)

  • Figure 1: Heat flux and neutron wall loading versus neutron flux for a range of plasma gains, including a $\mu$CF system. We use $\eta_\mathrm{abs} = 0.90$.
  • Figure 2: (a) Required number of catalyzed fusion reactions per muon $N_\mathrm{fus,\mu}$ assuming $E_\mu$ = 3 GeV / muon (see \ref{['eq:N_mu_breakeven_elec', 'eq:N_mu_breakeven_transmuter']}) versus neutron transmutation fraction $\eta_\mathrm{pro}$. Vertical dashed lines are typical capture fractions for each isotope in a fusion transmutation blanket. (b) Breakeven $E_\mathrm{\mu}$ versus $\eta_\mathrm{pro}$ for each isotope. We use $\eta = 0.4$, $\eta_\mu = 0.8$, $\kappa = 1.1$, $\xi_\mathrm{circ} = 0.1$, $\xi_\mathrm{pro}$ = 0.1, $C_e = \$50$/MWh. We assumed $C_\mathrm{pro} = 1.4 \cdot 10^5$ $/kg for $\ce{^197Au}$, $C_\mathrm{pro} = 10^6$ $/kg for $\ce{^147Pm}$, $C_\mathrm{pro} = 5 \cdot 10^{11}$ $/kg for $\ce{^99Mo}$, and $C_\mathrm{pro} = 5 \cdot 10^{14}$ $/kg for $\ce{^225Ac}$.
  • Figure 3: $\ce{^225Ac}$ versus muon rate for a spherical $\mu$CF system with (a) High flux $2\cdot 10^{15}\ \mathrm{n\ cm^{-2}\ s^{-1}}$ and low flux $1.6\cdot 10^{12}\ \mathrm{n\ cm^{-2}\ s^{-1}}$ (with 10g $\ce{^226Ra}$ feedstock), (b) varying $\ce{^226Ra}$ feedstock mass (with $N_\mathrm{fus,\mu}$ = 200, high flux). (c) Blanket thickness $\Delta R$ (with 10g $\ce{^226Ra}$ feedstock), and (d) capture probability $\eta_\mathrm{pro}$ versus muon rate (with $N_\mathrm{fus,\mu}$ = 200, high flux). 2024 global production of $\ce{^225Ac}$ is reported at 3 Curies per year, or about 51 $\mu$g/yr Kraev2024PanTeraAc225.