Effect of Surface Modification on Candidate Alloys for Canadian SCWR Fuel Cladding

Abstract

The Canadian Generation-IV supercritical water reactor (SCWR) requires peak cladding surface temperature of 800˚C for a core outlet temperature of 625˚C. Materials selection for high temperature fuel cladding is becoming one of the major challenging tasks. Austenitic stainless steels with excellent corrosion resistance are often susceptible to stress corrosion cracking upon SCW exposure. Low-Cr steels such as P91 exhibit good high-temperature mechanical properties, but the lack of sufficient Cr content makes this group of alloys corrode too fast. One possible solution is to use coatings or surface modification techniques to improve the surface resistance to corrosion. In this study, we investigated the effect of surface modification on commercial 316L stainless steel. Surface modification by mechanical deformation has marked improvement in corrosion resistance during SCW exposure. Possible mechanisms for such improvement are discussed.

Corrosion of engineering materials in a supercritical water cooled reactor: Characterization of oxide scales on Alloy 800H and stainless steel 316

“…Generally, Ni-based alloys develop a thinner oxide layer, as compared with stainless steels, under SCW conditions, however pitting has been observed in the vicinity of intermetallic precipitates [8].With a few exceptions, most studies of the corrosionof various materials in SCW, have been performedusing sealed capsules, static or refresh autoclaves [9]. Although widely used, these systems do not maintain a steady-state concentration of dissolved oxygen or other chemical species, environmental conditions being changed over the duration of the corrosion test.…”

“…TheCanadian SCWR [5][6][7] will operate at a pressure of 25 MPa, with a core inlet temperature of about 350°C and core outlet temperature of 625 °C . To achieve this, the peak fuel cladding temperature can be as high as 800°C [8].Supercritical water (SCW) poses some serious challenges towardsmaterialsselection,in terms of chemistry control strategies to minimize corrosion and corrosion product transport [9]. Austenitic stainless steels, Ni-based and Zr-based alloys are already widely used in the design of nuclear power plants and are regarded as possible candidate materials for the fuel cladding and other water bearing components in the proposed SCWR.…”

Alloy 800H under supercritical water conditions: a flow reactor study of corrosion and hydrogen evolution

“…The SCWR relies on the properties of supercritical water to increase thermal efficiency of the plant. A reference design for the SCWR will operate at a pressure of 25 MPa, with a core inlet temperature of about 350 °C and core outlet temperature of 625 °C, which are much greater than those of existing pressurized water reactors (PWRs) . To achieve this, the peak cladding temperature can be as high as 800 °C .…”

“…A reference design for the SCWR will operate at a pressure of 25 MPa, with a core inlet temperature of about 350 °C and core outlet temperature of 625 °C, which are much greater than those of existing pressurized water reactors (PWRs) . To achieve this, the peak cladding temperature can be as high as 800 °C . Therefore SCWR materials will be subject to higher levels of hydrostatic, thermochemical, and radiolytic stresses over a longer period than materials in currently operating reactors .…”