Surface Characterization of Candidate Materials for High Temperature Power Plants

Abstract

Introduction The decreasing supply of fossil fuel sources, coupled with the increasing concentration of green house gases has placed enormous pressure to maximize the efficiency of power generation (1). Increasing the outlet temperature of these power plants will result in an increase in Carnot efficiency (2). To increase their efficiency, coal fired power plants currently use both supercritical water (SCW) and ultrasupercritical water (USCW) with the most advanced designs allowing for a decrease of 58000 kg/hr in the coal fed to produce the same power as a conventional coal power plant (1). By employing a supercritical fluid as the coolant in nuclear reactors, the plant efficiency can be increased to 45%, compared to traditional reactors which currently operate at ~33% (3, 4). Experimental Experiments were conducted using the supercritical water loop (SCWL) facility at UNR. This unique facility allows for accelerated corrosion testing and mechanical behavior studies to be conducted. The primary loop environment that was used for these experiments contained deionized water held at a pressure of 27 MPa and temperatures ranging from room temperature up to 600°C. Materials studied include; austenitic steels (stainless steel 304 and Nitronic 50), and nickel based alloys (Inconel 625 and 718). Surface chemistry of the oxide layer was studied using, X-ray diffraction, X-ray photoelectron and Raman spectroscopies. Results Raman spectra for SS316 and I625 exposed to 600°C supercritical water is displayed in Figure 1. It can be observed that the oxide composition varies. Based on the Raman shift it can be observed that the largest features correspond to NiFe2O4 and Fe3O4, which formed on the surfaces of I625 and SS316 respectively (5-7). Further, the corrosion behavior of the candidate materials will be discussed with respect to surface chemistry. Figure 1: Raman spectra for alloys I625 and SS316 exposed to 600°C supercritical water. Acknowledgements: This study was supported by the Department of Energy (DOE) under contracts DE-NE0000454 and DE-NE0008236 and Nuclear Regulatory Commission (NRC) under awards NRC-38-10-949 and NRC-HQ-11-G-38-0039. D.R. is supported under a Fellowship program funded by NRC. Mr. Kenny Osborne and Ms. Nancy Hebron-Isreal serve as the program managers for the DOE and NRC awards, respectively.