FISSION AND FUSION WATER COOLING CIRCUITS: CHEMISTRY, CORROSION MITIGATION AND MATERIALS

The need to satisfy the world's ever-increasing demand for a low carbon, secure and affordable electricity and energy source is one of the greatest challenges of this century[1]. Nuclear fusion technology is aiming to join the family of non-greenhouse gas emitting electricity sources, currently consisting of renewables and nuclear fission power plants. For the realization of the first commercial fusion reactor, multiple challenges are yet to be solved, but the technological transfer from 60+ years operational experience of fission power plants, including materials research, cooling circuit optimisation and corrosion mitigation strategies, can be key to ensure the success of fusion reactors. This is especially the case as fusion reactors are expected to use similar coolants and structural materials as the current light water reactors fleet (LWRs). The challenges faced by materials in nuclear power plant cooling circuits are very unique. Materials need to maintain their mechanical properties intact for 40+ years (and even 60+ or 80+ years for current fission power plants) while operating at temperature, around 300°C for the current LWR fleet, up to 530°C for the UK's Advanced Gas cooled Reactors (AGRs) and up to 1000°C for future designs of Very High Temperature Reactors (VHTR), under neutron irradiation (up to 100 dpa) and in a corrosive environment. In the past, nuclear fission plants have exploited various coolants for research purposes or for commercial purposes (energy and electricity production): gases, liquid metals and molten salts, although water is by far the most common in current designs. The Generation IV roadmap for advanced reactors anticipates the use of liquid metals (lead & lead/bismuth eutectic or sodium), gases (helium), water and molten salts (mainly fluorides) as coolants [2]. Potential fusion reactor coolants are quite similar, with water, gases (helium) and liquid metals (lithium, lead/lithium) [3] under consideration. Notably, two types of innovative fission reactors are already in operation in the world: the high temperature gas (helium) cooled reactor-pebble bed module (HTR-PM) in China and the sodium fast reactors Beloyarsk Nuclear Power Station (BN-600 and BN-800) in Russia....