Candidate Materials Evaluation for the Supercritical Water-Cooled Reactor

Participants: G. S. Was, PI, R. Zhou, Post-doctoral scholar; E. West, Graduate Student
SponsorU.S. Department of Energy, Nuclear Energy Research Initiative (NERI)

The supercritical-water-cooled reactor (SCWR) system is being evaluated as a Generation IV concept because it and builds on currently proven light water technology to provide for high thermal efficiency and plant simplification. Development, testing, and selection of suitable materials for cladding and internal components are central to the development of a SCWR. Supercritical water presents unique challenges to the long-term performance of engineering materials. Corrosion and stress corrosion cracking (SCC) in particular have been identified as critical problems because the temperature and the oxidative nature of supercritical water may accelerate the corrosion kinetics and induce stress corrosion cracking. In addition, the presence of radiation can influence corrosion and SCC both by altering the material microstructure and by accelerating corrosion and SCC due to the generation of oxygen and other free radicals via radiolysis. The existing database on the corrosion and stress corrosion cracking of materials in supercritical water is very sparse. Data on the behavior of irradiated alloys is non-existent.

The objective of the proposed research is to investigate degradation of materials in the supercritical water environment. First, representative alloys from the important classes of candidate materials will be studied for their corrosion and stress-corrosion cracking resistance in supercritical water. These will include ferritic-martensitic steels, austenitic stainless steels, and Ni-base alloys. Corrosion and SCC tests will be conducted at various temperatures and exposure times, as well as in various water chemistries. Second, emerging plasma surface modification and grain boundary engineering technologies will be applied to modify the near surface chemistry, microstructure, and stress-state of the alloys prior to corrosion testing. Third, the effect of irradiation on corrosion and stress-corrosion cracking of alloys in the as received and modified/engineered conditions will be examined by irradiating samples using high-energy protons and then exposing them to supercritical water. All these tests will be performed in close coordination with, and as a complement to, the Generation IV testing programs on radiolysis corrosion/SCC of neutron irradiated materials in supercritical water. The research program will be performed by the University of Wisconsin and the University of Michigan. Both these institutions have a proven infrastructure for successfully implementing all aspects of the proposed research. The research will have a strong educational component with several graduate and undergraduate students participating.