Development of Basic Technology for FeCrAl-based LWR Cladding

Zirconium alloy cladding has good corrosion resistance in the operating environment of pressurized water reactor and boiling water reactor, but rapid oxidation reaction occurs when the loss-of-coolant accident occurs as in the Fukushima nuclear power plant accident. If the hydrogen generated by this oxidation reaction accumulates inside the containment, hydrogen explosion may occur. For this reason, the materials such as SiC, Mo and FeCrAl alloys, which are resistant to corrosion even in a high temperature steam environment, have been developed over the world. From the long-term point of view, it is necessary to study FeCrAl alloys that can replace existing zirconium cladding. FeCrAl alloys are known to have excellent oxidation resistance in a high temperature steam environment. They also have resistance to corrosion during primary water environment and to hydrogen embrittlement. But the optimized composition for light water reactor environments has not been determined yet. This study consists of three stages and stage 1 was being studied. The Fe14Cr4Al plate alloy was manufactured, and compared with APMT and Zr-Nb-Sn alloys by exposure at 1200 .deg. C in steam environment. The summary is as follows. 1. To fabricate the FeCrAl plate alloy, the ingot was casted by vacuum induction melting, homogenized at 1150 .deg. C for 2 hours and hot-rolled with a total thickness reduction rate of 92.5%, and annealed at 700 .deg. C for 1 hour. 2. Elongated grains were observed in the middle of two cross-sections perpendicular to the rolled surface. Further optimization of the manufacturing process is being carried out. 3. Polished Fe14Cr4Al and APMT specimens were exposed at 1200 .deg. C in steam environment for 371 and 250 seconds, respectively.