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

Abstract

The US Department of Energy is working with fuel vendors to develop accident tolerant fuels (ATF) for the current fleet of light water reactors (LWRs). The ATF should be more resilient to loss of coolant accident scenarios and help extending the life of the operating LWRs. One of the proposed ATF concepts is to use iron-chromium-aluminum (FeCrAl) alloys for the cladding of the fuel. A concern in using ferritic FeCrAl is that this type of cladding may result in an increase in the concentration of tritium in the coolant. The objective of the current critical review is to collect and assess information from the literature regarding diffusion or permeation of hydrogen (H) and its isotopes deuterium (D) and Tritium (T) across industrial alloys (including FeCrAl) used or intended for the nuclear industry. Over a hundred years of data reviewed shows that the solubility of hydrogen in ferritic alloys is lower than in austenitic alloys but hydrogen permeates faster through a ferritic material than through austenitic materials. The tritium permeation rates in FeCrAl alloys are between those in austenitic stainless steels and in ferritic FeCr steels. The activation energy for hydrogen permeation is approximately 30 pct higher in the austenitic alloys compared with the ferritic (typically ∼ 50 kJ/mol in ferritic vs. ∼ 65 kJ/mol in the austenitic). None of the major elements in FeCrAl alloys react with hydrogen to form detrimental hydride phases. The effect of surface oxides on FeCrAl delaying hydrogen entrance into FeCrAl alloy is not part of this review.

Improved and Innovative Accident-Tolerant Nuclear Fuel Materials Considered for Retrofitting Light Water Reactors—A Review

“…For a cladding application, Zr alloys do not release tritium into the coolant because tritium and hydrogen become captured by the cladding itself, developing hydrides. FeCrAl alloys are more transparent to hydrogen (tritium) than Zr, and none of its elements (Fe, Cr or Al) react with H to form hydrides; therefore, it was anticipated that more tritium may be released into the coolant when a FeCrAl cladding is used [22,55]. It is argued that the formation of surface oxides on the walls of the FeCrAl cladding could be a barrier for tritium release into the coolant [22,26,56].…”

Recent Advances and Prospects in Design of Hydrogen Permeation Barrier Materials for Energy Applications—A Review

“…FeCrAl alloys are under consideration for these applications due to their inherent corrosion resistance, stress corrosion cracking resistance, radiation-induced swelling resistance, and high temperature oxidation resistance and hydrogen pick-up resistance. Handbook on the Material Properties of FeCrAl Alloys for Nuclear Power Production Applications [ 72 ] was published in 2018 by Field et al (ORNL report) and Garud et al [ 73 ] reviewed in 2022 hydrogen isotope permeation in clean and unoxidized FeCrAl alloys. Hydrogen permeation rates in ferritic steels are higher and hydrogen solubility is lower than in austenitic steels.…”

Numerical Simulation of Tritium Diffusion Behavior in FeCrAl Cladding

“…The FeCrAl alloy can form Cr 2 O 3 and α-Al 2 O 3 protective oxide films under high-temperature water vapor above 800 °C, which can alleviate or even avoid the problem of zirconium water reaction under LOCA conditions, and can greatly improve the safety margin of light water reactor. Therefore, the FeCrAl alloy is one of the candidate cladding materials for accident-tolerant fuel (Terrani et al, 2014;Rebak, 2020;Garud et al, 2022). FeCrAl usually contains 10-15 wt% Cr and 3-6 wt% Al.…”