A first-principles study of hydrogen surface coverage on δ-Pu (100), (111), and (110) surfaces.

Ryan Gotchy Mullen,Nir Goldman

doi:10.1063/5.0064515

Abstract

Hydriding corrosion of plutonium leads to surface cracking, pitting, and ultimately structural failure. Laboratory experiments demonstrate that hydriding begins on the surface or near the subsurface of plutonium. However, there has not yet been a systematic evaluation of hydrogen surface coverage on plutonium. In this work, we compute the surface energies of the low facet surfaces of face-centered cubic δ-Pu. The adsorption free energies of expected hydrogen structures at low and high coverage are presented along with the likely progression for filling sites as the H2 partial pressure increases. Implications for near-equilibrium pressure hydride nucleation and non-equilibrium millibar pressure hydriding are discussed.

Highlights

Plutonium’s unique material properties make it useful as a heat source in power plants and in radioisotope thermoelectric generators.[1]
Where ebPuulk is the energy of a plutonium atom in a defect-free fcc lattice, eH is the energy of a hydrogen atom in a gas-phase hydrogen molecule, and NP u and NH are the number of plutonium and hydrogen atoms in configuration i, respectively
We find that the adsorption energy of a single H atom at either site are indistinguishable, ∆Eh(1c1p11) = −2.69 eV versus ∆Ef(1c1c11) = −2.68 eV, consistent with previous results.[6]

Summary

Introduction

Plutonium’s unique material properties make it useful as a heat source in power plants and in radioisotope thermoelectric generators.[1]. Plutonium is highly reactive and will corrode if exposed to atmospheric gases, even in trace amounts. Hydriding in face-centered cubic (fcc) δ-Pu occurs if the hydrogen concentration exceeds a temperature-dependent solubility limit. As it incorporates hydrogen to form plutonium dihydride (PuH2), the plutonium lattice expands by approximately 60 volume %, causing cracks and fissures in the plutonium surface. PuH2 is pyrophoric, catalyzing rapid, violent exothermic oxidation. As a result, uncovering the mechanisms by which plutonium corrodes can improve safety regulations and eliminate toxic waste

Results

Discussion

Conclusion