Neutronic and mechanical evaluation of rare earth doped and undoped nitride-based coatings for accident tolerant fuels

Abstract

As a part of the effort to develop accident-tolerant fuel (ATF) that would delay potential deleterious consequences of loss-of-coolant-accidents (LOCA), TiN and TiAlN coating application on nuclear fuel claddings were shown as a promising path to enhance corrosion resistance of nuclear fuel cladding. Recently, ytterbium doping was shown to contribute to improving TiAlN coating corrosion performance. However, overall cladding coating performance evaluation requires investigation of neutronic penalties and mechanical properties in addition to corrosion resistance. The current study is composed of two parts. First, the neutronic impact of adding monolithic TiN, monolithic TiAlN and 8-layer TiAlN/TiN coatings (with and without Yb dopants) to the exterior of conventional zirconium-alloy cladding was investigated. Second, an experimental investigation was performed through the deposition of select coating design architecture using cathodic arc physical vapor deposition process onto ZIRLO®1 sheets followed by mechanical testing to examine the adhesion and hardness of the coatings. Characterizations were performed using optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), electron probe microanalysis (EPMA), Raman spectroscopy and X-ray diffraction (XRD). It is concluded that to minimize the neutronic penalties, a limitation on the concentration of Yb-dopant is necessary. Mechanical testing showed that hardness decreased with increasing Yb content. The adhesion of the TiAlN coatings was not affected by doping but was affected by the cathode composition.