Couldn’t we have a lead box lined with these radiation to electricity converters with a small amount of radioactive material in the center, and have an energy generating device that would last for thousands or even millions of years? Imagine putting the sun in a box lined with solar cells, but on a much smaller scale.
Is there a reason this wouldn’t work?
With betavoltaics it’s more a matter of physics than lack of engineering refinement. Even assuming 100% efficiency, you would need something like 250 gallons (1000 liters) of tritium gas at atmospheric pressure to power a 100 Watt lightbulb.
Nuclear reactors, however, absolutely should be supplying a larger fraction of our electrical grid. Traditional, large reactor facilities have such a high cost and long timescale for permitting/construction that it’s difficult to get newer, more modern reactors built in the US. There are some exciting developments in small, modular reactors that would sidestep these issues. I believe a few designs are in the process of being built for full scale testing.