But it is of course not only the price of buying a couple of those containers, you also need a facility to store them, you may have to move them around, you probably have to guard them, you have to monitor them, ...
Of course it isn't, but at least the CASTORS can be safely transported by train, and a processing facility is not orders of magnitude more expensive than the power plants themselves. If we could forgo the nimbyism, we already have a technical solution and a reasonable estimate of the cost now and in the next 100 years. It could easily be factored in the cost of electricity from nuclear and put in a fund for when it's needed.