*Article* **Effect of Irradiation on Corrosion Behavior of 316L Steel in Lead-Bismuth Eutectic with Different Oxygen Concentrations**

**Nariaki Okubo \*, Yuki Fujimura and Masakatsu Tomobe**

Nuclear Science and Engineering Center, Japan Atomic Energy Agency (JAEA), Tokai, Ibaraki 319-1195, Japan; fujimura.yuki@jaea.go.jp (Y.F.); tomobe.masakatsu@jaea.go.jp (M.T.)

**\*** Correspondence: okubo.nariaki@jaea.go.jp; Tel.: +81-29-282-6212

**Abstract:** In an accelerator-driven system (ADS), the beam window material of the spallation neutron target is heavily irradiated under severe conditions, in which the radiation damage and corrosion co-occur because of high-energy neutron and/or proton irradiation in the lead–bismuth flow. The materials used in ADSs must be compatible with the liquid metal (lead–bismuth eutectic (LBE)) to prevent issues such as liquid metal embrittlement (LME) and liquid metal corrosion (LMC). This study considers the LMC behavior after ion irradiation of 316L austenitic steel for self-ion irradiations followed by the corrosion tests in LBE with critical oxygen concentration. The 316L samples were irradiated by 10.5 MeV-Fe3+ ions at a temperature of 450 ◦C, up to 50 displacements per atom (dpa). After the corrosion test performed at 450 ◦C in LBE with low oxygen concentration, a surface of the nonirradiated area was not oxidized but appeared with locally corrosive morphology, Ni depletion, whereas an iron/chromium oxide layer fully covered the irradiated area. In the case of the corrosion surface with high oxygen concentration in LBE, the surface of the nonirradiated area was covered by an iron oxide layer only, whereas the irradiated area was covered by the duplex layers comprising iron and iron/chromium oxides. It is suggested that irradiation can enhance the oxide layer formation because of the enhancement of Fe and/or oxygen diffusion induced by the radiation defects in 316L steel.

**Keywords:** accelerator-driven system (ADS); liquid metal corrosion (LMC); lead–bismuth eutectic (LBE); self-ion irradiation; oxygen concentration in LBE; irradiation effect on corrosion behavior
