One fairly obvious failure mode is that it has no checks on the other outputs.
So from my understanding, the AI is optimizing it's actions to produce a machine that outputs electricity and helium. Why does it produce a fusion reactor, not a battery and a leaking balloon?
A fusion reactor will in practice leak some amount of radiation into the environment. This could be a small negligible amount, or a large dangerous amount.
If the human knows about radiation and thinks of this, they can put a max radiation leaked into the goal. But this is pushing the work onto the humans.
From my understanding of your proposal, the AI is only thinking about a small part of the world. Say a warehouse that contains some robotic construction equipment, and that you hope will soon contain a fusion reactor, and that doesn't contain any humans.
The AI isn't predicting the consequences of it's actions over all space and time.
Thus the AI won't care if humans outside the warehouse die of radiation poisoning, because it's not imagining anything outside the warehouse.
So, you included radiation levels in your goal. Did you include toxic chemicals? Waste heat? Electromagnetic effects from those big electromagnets that could mess with all sorts of electronics. Bioweapons leaking out? I mean if it's designing a fusion reactor and any bio-nasties are being made, something has gone wrong. What about nanobots. Self replicating nanotech sure would be useful to construct the fusion reactor. Does the AI care if an odd nanobot slips out and grey goos the world? What about other AI. Does your AI care if it makes a "maximize fusion reactors" AI that fills the universe with fusion reactors.
Is this an alignment approach? How does it solve the problem of getting the AI to do good things and not bad things? Maybe this is splitting hairs, sorry.
It's definitely possible to build AI safely if it's temporally and spatially restricted, if the plans it optimizes are never directly used as they were modeled to be used but are instead run through processing steps that involve human and AI oversight, if it's never used on broad enough problems that oversight becomes challenging, and so on.
But I don't think of this as alignment per se, because there's still tremendous incentive to use AI for things that are temporally and spatially extended, that involve planning based on an accurate model of the world, that react faster than human oversight allows, that are complicated domains that humans struggle to understand.