Abstract: The current unavailability of high-flux test reactors requires that ion irradiation serve as a surrogate for investigating factors that lead to swelling resistance of improved alloys. Most current studies are directed toward lower swelling ferritic-martensitic alloys and their ODS variants. The credibility of using charged-particle simulation requires that the impact of all neutron-atypical features of ion irradiation be identified, understood, and minimized. Recently, significant attention has been directed toward operational concerns, especially ion-beam rastering, carbon contamination, and injected interstitials.

To demonstrate that ion irradiation is a credible tool, it is required that self-ion irradiation reproduce major aspects of neutron-induced swelling dependencies (compositional, fabricational, flux-spectral) observed in neutron tests.  Ion irradiation should also reproduce the swelling behavior (bilinear, steady-state after incubation), but should especially reproduce the well-established post-transient swelling rates of 1%/dpa for fcc iron-base and 0.2%/dpa for bcc iron-base alloys. Recently conducted studies indeed confirm this expectation.

While recent studies show very clearly the bilinear swelling behavior of ferritic-martensitic alloys with a post-transient swelling rate of 0.2%/dpa, most studies on austenitic alloys were conducted in the 1970s-1990s, but these studies did not show the expected 1%/dpa for fcc iron-base alloys. Also not observed in those earlier studies was a clear demonstration of the injected interstitial suppression effect. It is now recognized that the dose vs. depth calculations used in that early period were not correct, yielding artificially high dpa rates and significantly shortened ion ranges. This problem arose for use of energy deposition values calculated by using LSS theory, which did not include later recognized electron shell effects to produce mid-Z oscillations in energy deposition rates. One result of this change was to reverse the relative energy deposition rates for iron and nickel ions. The largest difference between LSS and current predictions arises for nickel ions onto high-nickel targets; unfortunately most of the early studies used nickel ions.

Many earlier studies, especially for simple metals and fcc iron-base alloys, have been re-examined in light of recently attained insights and current calculational practices. The results of this re-examination are very encouraging, attesting to the increased credibility in use of ion simulation for void swelling.

It is shown that dpa calculational codes (EDEP, BRICE, IONDOSE, early versions of TRIM) used in earlier studies overestimated energy deposition rates by ~20 to 35%,  leading to artificially high dpa levels and an incorrect visualization of swelling vs. dose. When earlier data sets are reevaluated using the SRIM code with modern descriptions of energy deposition, the 1%/dpa is routinely observed in fcc iron-base alloys. Also, injected-interstitial suppression of void nucleation, not clearly observed in these earlier studies, is equally strong in both bcc and fcc iron-base alloys, in contradiction to earlier theoretical predictions.

Finally, a number of studies using ion irradiation of ​“neutron-preconditioned” stainless steels with saturation void densities shows that the post-transient swelling rate is ~1%/dpa, independent of the ion irradiation temperature, calling into question some aspects of the ​“temperature shift” concept. When the void density is not saturated, the ion irradiation temperature controls the transient duration