Resistance of Ferritic FeCrAl Alloys to Stress Corrosion Cracking for Light Water Reactor Fuel Cladding Applications

Abstract

Since 2011 the international nuclear materials community has been engaged in finding replacements for zirconium alloys fuel cladding for light water reactors (LWR). Iron-chromium-aluminum (FeCrAl) alloys are cladding candidates because they have high strength at high temperature and an extraordinary resistance to attack by superheated steam in the event of a loss of coolant accident. Since FeCrAl alloys have never been used in nuclear reactors, it is important to characterize their behavior in the entire fuel cycle. Stress corrosion cracking (SCC) studies were conducted for two FeCrAl alloys (APMT and C26M) in typical simulated boiling water reactor conditions at 288°C containing either dissolved hydrogen or oxygen. Crack propagation studies showed that both ferritic FeCrAl alloys were resistant to SCC at stress intensities below 40 MPa√m. Current results for FeCrAl confirm previous findings for Fe-Cr alloys showing that ferritic stainless alloys are generally much more resistant to high temperature water SCC than austenitic stainless steels.

Hydrogen Isotopes Permeation in Clean or Unoxidized FeCrAl Alloys: A Review

“…The FeCrAl alloys have excellent resistance to aqueous corrosion, [15,[37][38][39][40] superior resistance to oxidation in high temperature air [17,20,41] and steam, [10,40,[42][43][44][45] and better creep/mechanical properties expected at high temperatures. [10,46,47] The superior high-temperature oxidation resistance of FeCrAl reduces the generation of hydrogen and associated exothermic heat of reaction with coolant during severe accidents, [45,48,49] while the creep/mechanical properties enhance the cladding burst margin.…”

“…Additional development led to the use of FeCrAl in other commercial applications such as the automotive catalytic converters requiring superior oxidation resistance at high temperatures as well. Although this original FeCrAl alloy development was prior to the advent of nuclear reactor systems, the beneficial characteristics of FeCrAl made them desirable for nuclear applications mainly due to their ferritic nature, [15] their excellent mechanical properties and their unparalleled resistance to oxidation at 1000 °C or higher temperatures. [15][16][17][18][19] Within three decades of their discovery (to about 1960), the FeCrAl alloy system was well investigated with application limits well established for phase stability, workability, oxidation/corrosion resistance, and commercial viability.…”

“…Although this original FeCrAl alloy development was prior to the advent of nuclear reactor systems, the beneficial characteristics of FeCrAl made them desirable for nuclear applications mainly due to their ferritic nature, [15] their excellent mechanical properties and their unparalleled resistance to oxidation at 1000 °C or higher temperatures. [15][16][17][18][19] Within three decades of their discovery (to about 1960), the FeCrAl alloy system was well investigated with application limits well established for phase stability, workability, oxidation/corrosion resistance, and commercial viability. [20,21] A detailed investigation of the physical metallurgy of iron alloys containing 25 to 35 wt pct chromium and 3 to 8 wt pct aluminum, defining their limits for structural applications, was already well known prior to 1960.…”

“…[19] Also, the corrosion tests included LWR type environments (pH 10 to 7 at 563 K to 733 K and 10.3 to 22.1 MPa pressure, deionized water) and showed similar or better resistance to intergranular and stress corrosion cracking compared to the standard austenitic stainless steels, [19] and resistant in high temperature steam environment as well, [25,26] in support of the fuel cladding FeCrAl applications in LWRs. [15] In a detailed study of gas-cooled reactor designs for mobile applications [27] the use of Fe-25Cr-4Al was specified in one design as the cladding material with yttrium-hydride moderated fuel pins on the inside and coolant gas (air) on the outside of the cladding tubes, 0.25 mm wall thickness, under relatively high average nominal cladding temperature of about 1000 K in operation; a very thin layer of oxide facing the coolant air was also expected to provide hydrogen retention during the operation. Another early work on cladding application also discussed the development of a reactive element (yttrium)-added alloy (Fe-25Cr-4Al-1Y) that was suggested for its low-stress application of the fuel cladding tubes.…”

High‐temperature high‐pressure SCC testing of corrosion‐resistant alloys

“…Thus, most of the research works on SCC testing are performed at high temperatures but not at high pressure. [ 47–79 ]…”