Nanoporous Tungsten for Improved Mechanical Performance and Safety in Nuclear Control Rod Cladding

Abstract

Driven by both the implications of the recent disaster in Fukushima as well as the coming maturity of fusion reactors in energy infrastructure, the nuclear industry is experiencing a renaissance not only in reactor design and fuel systems but also in safety. However, the combination of high temperature, high pressure, and radiation intensity of a reactor core poses a challenge to material selection for engineers, particularly related to nuclear cladding. For example, in a pressurized water reactor, the most prevalent reactor type currently in operation, control rod cladding can be subjected to temperatures over 500 • C, pressures at 15 MPa, and a neutron flux of 3.5 × 10 19 neutrons per cm 2 s. Thus, creep and cracking pose a threat to the cladding's functional integrity. As a result, high fracture toughness, low thermal expansion coefficient, and wear resistance become crucial metrics for the design and selection of nuclear cladding material for control rods. In response to these metrics, boron carbide (B4C) and Ag-In-Cd alloy have emerged as promising candidates for usage in control rod claddings. However, nanoporosity can impart significant mechanical advantages including higher fracture toughness, increased defect annihilation, and suppressed irradiation swelling. Density-modulated tungsten thin films with tunable nanoporosity can be manufactured through sputter coating. Consequently, density-modulated tungsten thin films have the potential to contribute to next-generation control rod cladding. Thus, the objective of this paper is to investigate the suitability of density-modulated tungsten thin films for nuclear control rod cladding through the analytical hierarchy process. Overall, conservative analytical hierarchy process analysis indicates that nanoporous tungsten is competitive with B4C for control rod cladding. As a result, our study may motivate current and future control rod cladding material development efforts focusing specifically on hybrid density-modulated tungsten thin film and B4C architectures for next-generation nuclear power plants.