There's a second big (huge, actually) problem with this idea. Strontium-90, with a half-life of just 28.8 years, does not exist in nature. It has to be manufactured in a nuclear reactor, then isolated from all the (also highly radioactive) by products. Hugely expensive both in dollar and energy terms, and would lead to incredible waste disposal issues.
It's cool technology, sure - but will never be more than a niche thing.
