The other problem is that the thermal power density of ARC is about 1/40th that of a PWR reactor vessel. It's a much larger, much more massive/complex/expensive way to make heat.
Spilling a thousand tons of melted lithium (and beryllium?) would be disruptive enough that containment, safety systems, and armed guards would still be needed. Also, not spending to protect your $100B facility from harm might make your insurance company nervous. (You did find an insurer, didn't you?)
If it actually cost 100B to built then your never going to break even.
As to containment, the lack of high pressure steam makes much thinner walls completely viable. You still need shielding around the vessel, but not a completely redundant system capable of containing highly energetic steam explosions.
In terms of risks, sabotage at a nuclear reactor can be vastly more expensive than just the cost of equipment. Modern reactors are reasonably safe, but not if people where actually trying to break them. Especially when you consider what someone could do with access to the fuel. It’s not weapons grade, but dirty bombs are horrific.
You do still need a very strong structure to resist outward pressure. It's isn't steam pressure, it's magnetic pressure, from JxB forces in the magnets. For ARC, the stainless steel supports for the magnets weigh 5300 tonnes, and comprise 3/4 of the mass of the entire reactor. The energy stored in that magnetic field is (I think) larger than would be stored in the steam of a PWR of the same thermal power output.
The building housing an ARC will be very large. The reactor itself is 20 meters tall, and the entire top half of it has to be lifted off and moved aside when changing out the vacuum vessel. All that lifting and moving will have to be done remotely because of radiation from the activated vacuum vessel, which then will need yet another shielded area where it can be broken down for disposal and the debris from that cleaned up or at least contained.
> would be stored in the steam of a PWR of the same thermal power output.
Safety system don’t just need to handle normal operations. The energy in a fusion reactors magnetic fields is very well known, a fission reactor steam explosion or potentially hydrogen explosions can bet vastly more violent.
Using Fukushima as a baseline. ~1,000 kg of hydrogen * 142 MJ/kg is a lot of energy and that was vented outside the primary containment vessel before detonating.
Granted this is not an inherent requirement for fission, but good luck convincing regulators it’s unnecessary.
The ARC reactor uses 380 tonnes of TiH2 as a neutron shield for the magnets. This fully decomposes at the temperature of the molten salt, which could yield up to 15 tonnes of hydrogen.
> If it actually cost $100B to build then you're never going to break even.
IOW, we're never going to break even. You and I are paying now, and would in any case never get any of the revenue, if in fact any could be had.
But we are supporting the careers and research of plasma fluid dynamics physicists and their students, and a few of them might do other, actually useful, and anyway wholly unpredictable things, later. With a good measure of luck, none of those things will build up to any world-spanning catastrophes the way the steam engine did.
I give it 10% chance of being better than nuclear power in 30 years. That’s worth the investment even if the odds of a solid payoff are low, the upside is significant.
Lower risks should mean fewer NIMBY issues, which means wider adoption. Nuclear advocates miss that if fission played a larger role in energy generation it would also see more major incidents. Which then risks a backlash etc.
