Production of Nuclear Battery $β^{-}$ Emitters Driven by Fusion Neutrons

Abstract: Nuclear batteries require radioisotopes with specific combinations of half-life, decay mode, and radiation properties, yet most candidate fuels lack scalable production routes. We show how the future availability of deuterium-tritium (D-T) fusion neutrons could enable manufacturing nuclear battery radioisotopes at many orders of magnitude higher rate than at present. We assess the capability of 14 MeV D-T fusion neutrons to produce nuclear battery radioisotopes by simulating feedstock material irradiation with neutrons. Promising radioisotope candidates include ${}^{147}$Pm, ${}^{63}$Ni, ${}^{39}$Ar, and ${}^{137}$Cs. Some feedstocks allow a radioisotope to be produced at scale while also closing the tritium fuel cycle, resulting in hundreds to over one thousand kilograms of high specific activity radioisotope per gigawatt thermal year of D-T fusion irradiation. We perform OpenMC simulations of an enriched ${}^{148}$Nd blanket for a tokamak, demonstrating that tritium self-sufficient designs can produce over one ton of ${}^{147}$Pm per gigawatt thermal year, equivalent to $\sim$one billion Curies per year of ${}^{147}$Pm. Operation of such a blanket would represent an unprecedented increase of nuclear battery radioisotope production capability.

• The paper demonstrates that D-T fusion neutrons enable industrial-scale production of beta-emitting isotopes, notably 147Pm, for advanced nuclear batteries.
• It employs detailed simulations using OpenMC and ENDF/B-VIII.0 to validate irradiation performance and reactor blanket integration, ensuring efficient isotope yields.
• The economic analysis reveals that co-producing isotopes with fusion-generated electricity can boost reactor profitability by orders of magnitude compared to conventional methods.

Scalable Production of Nuclear Battery Beta Emitters via D-T Fusion Neutrons

Introduction and Motivation

Modern nuclear batteries leverage radioisotopic decay to provide long-duration electrical power, but their utility is sharply constrained by limited supplies of appropriate radioisotopes, particularly those suitable for betavoltaics. Existing inventory and production infrastructure, heavily reliant on fission reactor irradiation or legacy stockpiles, are inadequate for both current and projected commercial needs. This paper develops and quantitatively analyzes the case for a compelling solution: the use of high-flux, 14 MeV deuterium-tritium (D-T) fusion neutrons to produce high-specific-activity beta-emitting nuclear battery radioisotopes (NBRs) at industrial scales.

Technical Approach

The paper frames its analysis on two central observations concerning fusion neutrons:

• High-energy neutron-driven reactions: Threshold (n,2n), (n,p), (n,np), and (n,na) reactions become feasible at 14 MeV, unlocking access to radioisotope production channels that are energetically forbidden, or inefficient, with fission neutrons.
• Neutron economy and flux: Fusion reactors can dedicate a large fraction of source neutrons to transmutation processes without compromising reactor core function or tritium breeding, unlike tightly budgeted fission environments.

Feedstock irradiation simulations are performed with OpenMC and ENDF/B-VIII.0 libraries, modeling multi-centimeter slabs exposed to planar 14.1 MeV neutron sources. The analysis identifies key performance metrics such as neutron conversion fraction, annual isotope yield per gigawatt-thermal-year (GW-yr), and compatibility with a tritium self-sufficient fusion blanket.

Results: Pathways, Yields, and Blanket Integration

Radioisotope Candidate Survey

The study maps the full landscape of beta-emitting NBRs in the specific power versus half-life plane, emphasizing attributes best-suited to betavoltaics: low gamma co-emission and energy windows manageable for semiconductor junctions. Several isotopes are highlighted for their favorable decay properties and scalable production from abundant feedstocks, including:

• 147Pm (t₁/₂ = 2.62 y, Eβ,max = 225 keV): Exceptionally high neutron utilization (conversion fraction 52.1%) via 148Nd(n,2n) route, compatible with neutron multiplication and minimal gamma emission.
• 39Ar (t₁/₂ = 269 y, Eβ,max = 565 keV): High yield on 39K via (n,p), significant for radioluminescent and long-life battery applications.
• 63Ni (t₁/₂ = 100 y, Eβ,max = 67 keV): Produced from 63Cu (69.2% abundance) via (n,p), providing unmatched compatibility with silicon-based betavoltaics due to very low endpoint energy.
• 3H (tritium) and 14C: Both accessible via lithium or nitrogen blanket chemistry.

In contrast to their fission production, several of these NBRs lack practical thermal-neutron routes, positioning D-T fusion as a uniquely enabling technology.

Blanket Integration and Neutron Economy

The inclusion of transmutation-optimized materials into a D-T fusion reactor blanket is studied with coupled neutronics and depletion simulations. For 147Pm production with enriched 148Nd:

• Over one tonne of high-specific-activity 147Pm can be produced annually per GWth of fusion power, with battery energy yield ∼2.2 MW·yr GW⁻¹·yr⁻¹.
• Blanket configurations are identified where simultaneous tritium self-sufficiency (TBR ≥ 1.1) and radioisotope production are achievable, with 148Nd replacing part or all of conventional neutron multiplier materials.

For other feedstocks (e.g., 14N, 36S), blanket integration is more challenging due to limited neutron multiplication or moderation properties; their use would require careful volumetric partitioning.

Waste Classification and Processing

Online extraction schemes for product and contaminant isotopes are quantitatively modeled, demonstrating that with dual Pm and Sm extraction, residual blanket material can be reduced to Class A low-level waste within six years post-shutdown under present U.S. NRC guidelines.

Economic Analysis and Value per Neutron

A key claim is the substantial increase in value-per-fusion-neutron when co-producing NBRs alongside electricity in a commercial fusion facility. For 147Pm, the analysis suggests that the value per neutron, assuming current Pu-238 RTG pricing, can exceed the value per neutron from grid electricity by two orders of magnitude for mission durations up to decades. This premium arises from the combination of high production rates, high specific power, and the strategic value of portable/wireless power sources.

It is emphasized that this value calculation, while robust, applies price benchmarks from alpha-emitter RTGs to beta-emitting systems; real-world markets may further enhance or diminish this differential.

Implications for Nuclear Battery Deployment and Fusion Reactor Economics

This study projects a transformative effect for betavoltaic and related radioisotope-based batteries: commercial D-T fusion could unlock dramatic expansion in the scope and scale of portable and remote nuclear power sources. The ability to supply kilograms to tons per year of previously scarce isotopes would support deployment in space, defense, critical infrastructure, and low-maintenance distributed sensors. Furthermore, the economic model implies a potential redefinition of fusion plant revenue streams, wherein product streams beyond electricity (viz., high-value isotopes) become central to business cases.

On the theoretical side, the blanket engineering challenges and neutron economy considerations introduce a rich, multi-parameter optimization problem for future fusion system design. Further developments are likely in optimal material selection, isotope separation and extraction, and integration with advanced blanket and breeder technologies.

Conclusion

This paper quantitatively establishes that D-T fusion neutron sources enable orders-of-magnitude enhancement in the production of high-specific-activity, low-gamma beta-emitting radioisotopes crucial for advanced nuclear batteries. Of particular significance is the feasibility of co-producing 147Pm at scale in tritium self-sufficient fusion blankets—a capability unattainable via fission or charged-particle methods. The findings have substantial implications for nuclear battery technology commercialization and for the economics of future fusion power, paving the way for new multiproduct fusion reactor paradigms.