April AMP_Digital

A D V A N C E D M A T E R I A L S & P R O C E S S E S | A P R I L 2 0 1 9 1 3 PROCESS TECHNOLOGY COLD SPRAY COATINGS PROTECT NUCLEAR REACTORS Researchers at the University of Wisconsin, Madison (UW-Madison) and Westinghouse Electric Company LLC developed a cold spray process for coating zirconium-alloy reactor fuel cladding tubes with the objective of im- proving accident tolerance and perfor- mance. In the cold spray process, the powder particles of the coating mate- rial are propelled at supersonic veloc- ities onto the surface of the substrate to form a coating. The powder particle temperature is low and the deposition occurs in solid state. Zirconium alloys have been suc- cessfully used as a fuel cladding mate- rial for nuclear fuel (approximately 12 to 17-ft-long tubes containing uranium- dioxide pellets) in light water reactors for many decades. Water coolant flows outside the tubes for cooling, but in the event of a loss-of-coolant accident, the zirconium-alloy tubes can heat up and oxidize severely in the surround- ing steam environment, a reaction that also leads to the production of hydro- gen. Oxidation-resistant coatings can protect the underlying zirconium-alloy cladding and mitigate hydrogen pro- duction in such high-temperature sce- narios. With such coatings, the reduced oxidation can lead to reduced hydrogen production and consequently less clad- ding embrittlement under normal reac- tor operating conditions. The UW-Madison/Westinghouse team successfully developed cold spray chromium coatings with superior coating micro- structure and coating- substrate adhesion for this application. As veri- fied through testing, the chromium coating pro- vides strong hydrother- mal corrosion resistance as well as high-tempera- ture oxidation resistance. The coatings have been subjected to oxidation and mechanical tests at temperatures up to 1300 o C in steam and air environments. The response of the coating-substrate system to radiation has been tested by ion irradiation in an accelerator and neutron irradiation in a test reactor. Technology transfer to the market is underway as cold spray coated, full- length tubes for lead test rod testing in a commercial reactor is scheduled this spring. The chromium cold spray coat- ing is now part of one of Westinghouse’s short-term products under its DOE acci- dent tolerant fuel (ATF) program. West- inghouse’s ATF, trademarked EnCore Fuel, is being introduced to market in two phases, the first using the chromi- um-coated cladding. For more information, contact Kumar Sridharan at kumar. sridharan@wisc.edu or Javier Romeroat romeroje @westinghouse.com. MAGNETIC MATERIALS FOR BETTER MOTORS In collaboration with the National Energy Tech- nology Laboratory, NASA Glenn Research Center, and North Carolina State University, a team of re- searchers from Carnegie Mellon University (CMU) is studying soft magnet- ic materials to make hard changes to motors. Through synthesiz- ing metal amorphous nanocomposite materials (MANCs), the scientists aim to make smaller motors that deliver com- parable power. MANCs provide an alter- native to silicon steels and due to their high resistivity, they don’t heat up as much and can therefore spin at much higher speeds. With help from their col- laborators, the CMU team is designing a 2.5-kW motor that weighs less than 2.5 kg. Most recently, they benchmarked it at 6000 rotations per minute and are looking to build bigger motors that will spin even faster. The design combines permanent magnets with the MANCs. These smaller, higher power mo- tors are well suited for aerospace, ve- hicle, and even vacuum cleaner appli- cations. To synthesize the MANC ma- terials, the team rapidly solidifies liq- uid metals at about a million degrees per second. Since they work at the lab scale, they look at 10-gram samples and screen them for magnetic proper- ties. Through various partnerships with research institutions and industry, they can take these MANCs and scale up the fabrication process for use in real-world applications. cmu.edu . Drawing of a motor rotor and stator. Gray represents where MANCs are used and blue symbolizes the permanent mag- nets. Courtesy of CMU. Watts Bar nuclear power plant. Courtesy of Tennessee Valley Authority and energy.gov.