Mechanical Properties of Advanced Gas-Cooled Reactor Stainless Steel Cladding After Irradiation
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Mechanical Properties of Advanced Gas-Cooled Reactor Stainless Steel Cladding After Irradiation Claude Degueldre, James Fahy, Oleg Kolosov, Richard J. Wilbraham, Max Do¨beli, Nathalie Renevier, Jonathan Ball, and Stefan Ritter (Submitted December 12, 2017; in revised form February 11, 2018; published online April 9, 2018) The production of helium bubbles in advanced gas-cooled reactor (AGR) cladding could represent a significant hazard for both the mechanical stability and long-term storage of such materials. However, the high radioactivity of AGR cladding after operation presents a significant barrier to the scientific study of the mechanical properties of helium incorporation, said cladding typically being analyzed in industrial hot cells. An alternative non-active approach is to implant He2+ into unused AGR cladding material via an accelerator. Here, a feasibility study of such a process, using sequential implantations of helium in AGR cladding steel with decreasing energy is carried out to mimic the buildup of He (e.g., 50 appm) that would occur for in-reactor AGR clad in layers of the order of 10 lm in depth, is described. The implanted sample is subsequently analyzed by scanning electron microscopy, nanoindentation, atomic force and ultrasonic force microscopies. As expected, the irradiated zones were affected by implantation damage (< 1 dpa). Nonetheless, such zones undergo only nanoscopic swelling and a small hardness increase ( 10%), with no appreciable decrease in fracture strength. Thus, for this fluence and applied conditions, the integrity of the steel cladding is retained despite He2+ implantation. Keywords
atomic force microscopy, hardness, helium implantation, nanoindentation, stainless steel
1. Introduction Since the start of the 1970s, the UK has operated a fleet of nuclear reactors quite different to the light-water moderated reactors (LWR) typically found across the rest of the world. The advanced gas-cooled reactor (AGR) uses a graphite core and CO2 cooling with an annular in shape, slightly enriched (up to 3.5% U235) uranium dioxide-based fuel clad in stainless steel rather than Zircalloy. This cladding is rich in both nickel ( 25 wt.%) and chromium ( 20 wt.%) in order to withstand high gas temperatures (Ref 1). However, during in-reactor irradiation helium gas bubbles are generated by three different interaction routes with common elements within the steel. First, via neutron irradiation, nickel isotopes may undergo neutron capture. Among them, 58Ni (68% abundance in natural nickel) reacts with a neutron producing 59Ni that after a second neutron capture yields an alpha particle which becomes helium.
Claude Degueldre and Richard J. Wilbraham, Engineering Department, Lancaster University, Lancaster LA1 4YW, UK; James Fahy, Engineering Department, Lancaster University, Lancaster LA1 4YW, UK; and Jost Institute, University of Central Lancashire, Preston PR1 2HE, UK; Oleg Kolosov, Physics Department, Lancaster University, Lancaster LA1 4BA, UK; Max Do¨beli, Laborat
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