Surface wettability and pool boiling Critical Heat Flux of Accident Tolerant Fuel cladding-FeCrAl alloys

Surface wettability analysis, including measurements of static (theta) advance (theta(A)), and receding (theta(r)) contact angles, and surface roughness, Ra, are effective parameters used in the literature to predict changes in the pool boiling Critical Heat Flux (CHF). The CHF is an important aspect of the thermal hydraulic performance that needs to be investigated for new Accident Tolerant Fuel (ATF) cladding materials, such as iron-chromium-aluminum alloys (FeCrAl). Surface wettability of FeCrAl samples oxidized under different simulated Light Water Reactor (LWR) water chemistry conditions was measured. These measurements were compared to as-machined and oxidized Zircaloy-4 (Zirc-4), the reference cladding material in LWRs, under the same conditions. Theoretical models were used to predict the pool boiling CHF using surface wettability measurements. Pool boiling experiments were conducted using the same samples to measure the CHF. The measured and predicted CHF data were compared for model validation. The obtained results showed no significant difference in the measured static contact angle and hence the predicted CHF between the as-machined samples of FeCrAl, 310 SS, and Zirc-4. The contact angles (static, advance, and receding angles) for corroded FeCrAl samples under different LWR water chemistry conditions are lower, and the measured surface roughness values are higher than Zirc-4 corroded under the same conditions. Existing models in the literature predicted higher pool boiling CHF of corroded FeCrAl compared to 310 stainless steel (SS), and Zirc-4. The measured pool boiling CHF for oxidized FeCrAl samples was higher than Zirc-4 samples. The measured and predicted CHF values are in good agreement. The CHF and the Departure from Nucleate Boiling Ratio (DNBR) were calculated using the Consortium for Advanced Simulation of Light Water Reactors (CASL) subchannel code COBRA-TF (CTF) for a one-eighth model of a 17 x 17 Pressurized Water Reactor (PWR) fuel assembly. The inlet conditions are consistent with typical PWR values except for the power, which was set 50% higher than is typical to represent possible accident conditions more accurately. The calculated distributions for the CHF and DNBR for oxidized FeCrAl showed significantly higher values throughout the fuel assembly octant compared to as machined Zirc-4 and as machined FeCrAl. These preliminary results show that oxidized FeCrAl may be able to withstand the proposed accident conditions without leading to a boiling crisis.