The cladding material in a sodium fast reactor is exposed to intense radiation conditions, and also serves as a barrier between the coolant and the fuel rods. Therefore, the cladding material must be able to withstand the 600 dpa and 600 °C to 700 °C, as well as the corrosive environment created by the coolant.
High Entropy Alloys (HEAs) are alloys comprised of several approximately equimolar principle elements with a highly complex structure. They are favorable for use as a cladding material in sodium fast reactors because of their ability to withstand the intense radiation and temperature conditions. HEAs are also suspected to have advantageous corrosion resistant properties.
To determine the overall feasibility of HEAs as a cladding material, their performance must be tested in all intense conditions present in the cladding region. Therefore, electrochemical corrosion testing will be performed on the HEAs developed in the Environmental Degradation of Nuclear Materials Laboratory.
An electrochemical corrosion cell kit, the Flat Cell Kit manufactured by Ametek, was purchased. The Flat Cell Kit has capabilities adequate for lab use, including sparging and small working electrode size necessary. During testing, a voltage range is applied to the working electrode against a reference electrode, and the corresponding current is measured.
Thus far, stainless steel 310 (SS 310) has been used as a working electrode, and the data has been compared with literature to assure the repeatability and reproducability of the test method. A potentiodynamic polarization method is used, and an example polarization cure produced by this work is given. The active, passive, and transpassive regions are evident. The comparative data extracted from this plot is the resulting corrosion potential and current values, as well as the duration of the passivation region and the rate of reaction.
Electrochemical corrosion testing will be performed on lab-fabricated HEA coupons once a satisfactory fabrication method is developed. It is expected that the corrosion behavior of the HEAs will be similar or superior to that of SS 310.