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Self-subsidizing Mercury Remediation with Fusion Reactors

J. F. Parisi, J. Azad

Abstract

Fusion reactors can permanently remediate mercury by using it as a neutron multiplier: each (n,2n) reaction reduces the neutron number towards ${}^{197}$Hg which quickly decays into stable gold, irreversibly removing it from the environment while generating substantial economic value. Fusion energy is therefore not merely environmentally benign, but anti-polluting through the continuous consumption of an environmental pollutant. The history of nuclear fission demonstrates that environmental concerns can be decisive obstacles to low-carbon power deployment, suggesting that integrated pollution remediation fundamentally improves the policy calculus for fusion energy. We show that at high neutron flux (achievable in muon-catalyzed and inertial confinement fusion), nuclear reactions make all mercury isotopes eligible for gold transmutation, incentivizing mercury recovery and valuing the world mercury extractable stock at ${\sim}\$200$ trillion, exceeding all in-ground gold reserves. Co-producing gold alongside electricity can triple a fusion plant's revenue, aligning economic incentives with complete, permanent mercury remediation.

Self-subsidizing Mercury Remediation with Fusion Reactors

Abstract

Fusion reactors can permanently remediate mercury by using it as a neutron multiplier: each (n,2n) reaction reduces the neutron number towards Hg which quickly decays into stable gold, irreversibly removing it from the environment while generating substantial economic value. Fusion energy is therefore not merely environmentally benign, but anti-polluting through the continuous consumption of an environmental pollutant. The history of nuclear fission demonstrates that environmental concerns can be decisive obstacles to low-carbon power deployment, suggesting that integrated pollution remediation fundamentally improves the policy calculus for fusion energy. We show that at high neutron flux (achievable in muon-catalyzed and inertial confinement fusion), nuclear reactions make all mercury isotopes eligible for gold transmutation, incentivizing mercury recovery and valuing the world mercury extractable stock at 200$ trillion, exceeding all in-ground gold reserves. Co-producing gold alongside electricity can triple a fusion plant's revenue, aligning economic incentives with complete, permanent mercury remediation.

Paper Structure

This paper contains 30 sections, 38 equations, 23 figures, 4 tables.

Table of Contents

  1. Isotope value table
  2. Derivation of the isotope value formula
  3. Single-step chain ($n=1$)
  4. NPV integral
  5. Multi-step chain through stable intermediates
  6. Physical interpretation
  7. Finite irradiation time
  8. Derivation of optimal flux
  9. Sensitivity and uncertainty
  10. Cross section
  11. Gold price
  12. Discount rate
  13. Isomer branching ratio
  14. Summary
  15. OpenMC validation
  16. ...and 15 more sections

Figures (23)

  • Figure 1: Schematic of a blanket geometry surrounding a D-T neutron source. Fusion neutrons radiate outward through the first wall into a liquid mercury layer, where successive (n,2n) reactions transmute Hg into Au. A tritium-breeding layer surrounds the Hg blanket to close the fuel cycle, enclosed by a radiation shield.
  • Figure 2: Left: single-step chain of mercury transmutation into gold. Right: multi-step chain example.
  • Figure 3: (a) Gold-production NPV $V_\mathrm{A}$ per kilogram of each stable Hg isotope as a function of neutron flux ($p_\mathrm{Au} = \$175$k/kg, $r = 5\%$, $T \to \infty$). At MCF fluxes, only ^198Hg is productive; at ICF fluxes, all isotopes become valuable. (b) Value per kilogram of mercury for natural mercury (dark red), 90%-enriched ^198Hg (orange), and the ^198Hg contribution alone (dashed blue). (c) Total transmutation value of world mercury extractable stock (1,500,000 tonnes) under the same scenarios, plus reference curves showing effects of finite plant life and discounting separately.
  • Figure 4: Availability of mercury and gold at increasing levels of resource definition. "Extractable stock" uses Sverdrup and Olafsdottir Sverdrup2020 for Hg (1,500,000 t) and Sverdrup and Ragnarsdottir Sverdrup2014 for Au (310,000 t); "Oceans" are dissolved inventories Lamborg2014; "Earth's crust" is the total mass in the top 10 km at average crustal abundances Rudnick2014. Mercury exceeds gold by 5 to 2,000$\times$ across all definitions.
  • Figure 5: Gold-production NPV per D-T source neutron ($\eta_\mathrm{pro} = 0.5$).
  • ...and 18 more figures