Surprisingly Large Generation and Retention of Helium and Hydrogen in Pure Nickel Irradiated at High Temperatures and High Neutron Exposures

Abstract

Hydrogen and helium measurements in pure nickel irradiated to 100 dpa in HFIR at temperatures between 300 and 600°C show higher gas concentrations than predicted from fast-neutron reactions and the two-step 58Ni(n,γ)59Ni (n,p and n,α) reactions. This additional gas production suggests previously unidentified nuclear sources of helium and possibly hydrogen that assert themselves at very high neutron exposure. The elevated hydrogen measurements are especially surprising since it is generally accepted that hydrogen is very mobile in nickel at elevated temperatures and therefore is easily lost, never reaching large concentrations. However, it appears that relatively large hydrogen concentrations can be reached and retained for many years after irradiation at reactor-relevant temperatures. These new effects may have a significant impact on the performance of nickel-bearing alloys at high neutron fluences in both fission and fusion reactor irradiations.

The transport and fate of helium in nanostructured ferritic alloys at fusion relevant He/dpa ratios and dpa rates

“…The total dpa is also determined by the corresponding spectral averaged dpa cross-section. The pertinent cross-sections were used to compute He concentration, C f (appm), for pure Ni versus dpa for irradiations in the HFIR PTP spectrum [10].…”

Void nucleation, growth, and coalescence in irradiated metals

“…This is modeled for a Fe-Ni-Cr steel undergoing neutron bombardment according a two-step activation process, in analogy to the 58 Ni(n,γ) 59 Ni(n,α) reaction. Model transmutation rates are treated as free parameters and are fit to the experimental helium content in HFIR-irradiated nickel [34,35]. The parameters are γ, α, and δ for the rates of (respectively) 58 Ni(n,γ), 59 Ni(n,α), and the sum of all transmutations that consume 59 Ni.…”

Alloying of Steel and Graphite by Hydrogen in Nuclear Reactor

“…Kurchatov Institute at several experiments was determined that steel specimens irradiated at relatively low (100-140°C) temperatures in sealed Ar contained ampoules hydrogen content was many times higher relatively initial content but was independent on FNF ( concentrations in stainless steels irradiated in BWR type reactors ( Figure 3) and high generations of hydrogen and helium in nickel [5,6].…”