(616f) Catalytic Decomposition of Tritiated Ammonia As a By-Product of Nuclear Fusion

Nuclear fusion reactions power the Sun and stars where hydrogen atoms fuse to form helium and energy¹. The Sun’s gravitational force creates the right conditions for fusion, however making fusion happen on earth is difficult. There are many engineering challenges to successfully fuse hydrogen fuel including extreme temperatures, breeding the tritium for the deuterium-tritium fuel mixture, confining the hydrogen plasma and the vast amounts of energy that must be input to begin the fusion reactions. One additional challenge is the formation of 0.1-5% concentrations of tritiated ammonia² which could be stored as it has a relatively short half-life, however, it is more advantageous to decompose the ammonia into nitrogen and tritium and recycle the tritium into the reactor.

We investigated ruthenium-based catalysts for decomposition of small concentrations of tritiated ammonia. A design of experiment was utilized to optimize an ammonia decomposition catalyst formula previously reported by our group³. After optimization, we tested the catalyst for decomposition activity in concentrations of ammonia <5% balanced in both argon and hydrogen at atmospheric pressure and temperatures between 250-450°C. Chemical stability of the catalyst was determined by measuring the activity of the catalyst before and after exposure to low concentrations of oxygen, water vapor and carbon dioxide which are the primary products of fusion process impurities. Additionally, the catalyst was thermally cycled to see the effect on the activity. Finally, the catalysts were tested in isotopic ammonia to ascertain isotopic effects of the reaction. This work led to an understanding of decomposing tritiated ammonia that will be present in every magnetically confined fusion reactor.

1. Wilson, J.; et al. Fusion Technology. 2019, 75 (8), 802–809.
2. Gill, J. T.; et al. Fusion Technology. 2017, 14 (2P2A), 876–883.
3. McCullough, K.; et al. Materials (Basel). 2020, 13 (8), 1869.