A Fusion Relevant Data-Driven Engineering Void Swelling Model for 9Cr Tempered Martensitic Steels

The UCSB database on cavity evolution in 9-12Cr tempered martensitic steels (TMS), includes the results for both dual heavy and helium ion (DII), and High Flux Isotope Reactor (HFIR) in situ helium injection (ISHI) neutron irradiations at 500°C. These results were combined with literature single ion and fission neutron irradiation data to derive a model for the void volume fraction, fv, as a function of displacements per atom (dpa) and transmutant helium concentrations in atomic parts per million (appm). The scientific foundation for the paper is described in a companion paper entitled “Cavity Evolution and Void Swelling in Dual Ion Irradiated Tempered Martensitic Steels”. Here, we show that fv(dpa, He/dpa) is described by the incubation dose, dpai, for the onset of void growth, and the post-incubation growth rate, fv’(%/dpa). Both dpai and fv’ decrease with increasing He/dpa at > ∼ 5. The dpai is also lower for the ISHI neutron irradiations at the same He/dpa. Single heavy ion and fission reactor neutron irradiations, with low He/dpa ratios, have a much larger dpai. Based on a combined analysis of DII, single ion, ISHI and fission neutron data, we further show that the post-incubation fv data analyzed here have a common empirical curve shape, with fv’ reaching up to ∼ 0.2%/dpa at very high dpa. We also show that fv’ can be predicted based on a physical model of defect partitioning between evolving sinks. At 500°C and fusion relevant He/dpa ≈ 10, the best-fit model predicts nominal swelling, S = fv/(1-fv), of ∼ 1.1, 4.9 and 16% at 50, 100 and 200 dpa, respectively. The physically motivated, data-driven model includes estimated uncertainties for both dpai and fv’.