b'Selected Highlights: The temperatureCurrently, plans are being finalizing effects on the wettability of Zircaloy,for flow boiling tests in high pressure Chromium and FeCrAl using aconditions, including preliminary tran-first-of-a-kind apparatus developed tosient scenarios, such as loss of flow and enable contact angle measurements upreactivity-initiated accident conditions to pressurized water reactors (PWR)(e.g., an exponential power escalation).conditions, in a steam-saturatedProject 17-12688atmosphere. The results revealed that the intrinsic wettability of ChromiumTitle: is slightly higher than Zircaloy orAn Experimental and Analytical Investi-FeCrAl. However, at PWR conditionsgation into Critical Heat Flux Implica-all materials are super-hydrophilic, i.e.,tions for Accident Tolerant Fuel ConceptsFigure 2. Selected results from UW-ledtheir contact angle approaches zero. project: CHF data for ATF candidateFlow boiling tests at ambient pres- Investigators: A. Prinja, M. Chen, materials in pool boiling conditions as asure were performed using non- Blandford (now Kairos), Y. Lee (now function of static contact angle reportedSeoul National University, University in literature and compare to presentintrusive optical fiber and high-speedof New Mexico), N. Brown (Univer-study. All tests were performed withvideo diagnostics. Figure 3 presentssity of Tennessee-Knoxville), W. flat samples in the horizontal directionexamples of test results. The CHF on at atmospheric pressure. PredictedMarcum (Oregon State University),C. CHF plots based on the Kandlikar CHFuncoated Zircaloy and ChromiumJensen (Idaho National Laboratory), model with 20% uncertainty is shown. coated Zircaloy is approximatelyJohn Strumpell (Framatome), Raul the same (within a +/-10% uncer- Rebak (General Electric)tainty). Both PVD coated and spray coated Chromium were tested noSelected Highlights: Flow boiling major differences were observed.critical heat flux (CHF) experiments However, during the boiling crisis, theindicate that the thermomechanical Chromium coated surfaces are moreproperties of materials affect CHF oxidation resistant than bare Zircaloy.values for various claddings. The This property is beneficial, as it seemsdependence of flow boiling CHF to reduce the risk of melting.on cladding material is gradually The Westinghouse Advanced Loop Testreduced by increasing mass flux and/(WALT) loop was used to conductor inlet subcooling. Figure 4 presents tests in PWR conditions. The tests havea summary of mass flux and mate-revealed that there is no significantrial effects on CHF behavior. Beyond difference in CHF between Chromiumthe mass flux of 2000 kg/m2s and coated and bare Zirlo, even in thethe inlet subcooling of 30 , the CHF presence of CRUD. This suggest thatdifferences contributed by cladding the Chromium coating does not affectmaterials may be negligible. This thermal margins. However, whileimplies that the current CHF database these tests have been performed usingfor stainless steels and other commer-a direct heating technique, futurecial alloys could be applicable to experiments will be used using anaccident tolerant fuel (ATF) materials indirect heating, to verify that theunder certain conditions. The mecha-observed phenomena are not drivennism behind the CHF difference could by the heating solution. stem from two competing mecha-nisms: 1) the material-dominated 40 2020|AFC ACCOMPLISHMENTS'