green slime said:
We are literally talking trillions of USD, man-centuries of research, and exotic materials.
Since 1954 through early 2021, the US has spent about $17.1 billion on fusion, or ~$34.1 billion adjusted for inflation. I believe ITER is included in the total funding, but one must peruse the cited references to figure out if that is the case.
http://large.stanford.edu/courses/2021/ph241/margraf1/
green slime said:
But if the technology is still decades away, is this really a good way to be spending these sums of money now?
Previous posts indicate a goal of 4 to 5 years. We'll see in 4 or 5 years.
As for exotic materials, same can be said for fission systems. Many are not so exotic, but the US, UK, EU and Japan, South Korea, and Russia and China, have spent considerable sums on variations of stainless steels and Ni-based alloys (and related alloys), a variety of ceramics, carbon-composites, graphite, and various reactive metal and refractory metal alloys for exotic fission systems, but also for fossil fuel systems. There is a huge array of Ni-based and Co-based alloys for aero-derivative combustion turbines.
Many of the alloys used in nuclear power systems (LWR, CANDU and Gas-cooled reactors) evolved for fossil fuel technology, e.g., austentic and ferritic/martensitic stainless steels. Each of the Gen-IV reactor designs requires some 'exotic' materials.
Ni-based alloys evolved from aerospace technology, e.g., Inconel for the X-plane program. Zirconium-based alloys (e.g., Zircaloys and their successors) are unique to the nuclear industry, although analogs of Zircaloys (Zircadynes) with natural levels of Hf still intact are used in certain applications in the chemical process industry. Similar, Nb, Ta, Mo, W and Re alloys have special applications in a variety of process industries other than nuclear power.
What is unique about nuclear applications is the presence of neutrons and gamma radiation in the operating environment. The radiation, in addition to temperature, affects the alloy microstructure over the course of years, or decades. Neutrons transmute elements (nuclei), sometimes in a beneficial way, but also in deleterious ways. Gammas influence the chemical potentials of atoms in an alloy, and this is an area that is not well-understood.