Okay, complications. Sr-90 is fine, but I hadn't considered the decay chain. Sr-90 decays to Y-90, which has a half-life of 2.67d and by both beta and gamma emission at over 2MeV each! Y-90, then decays to Zr-90, which is stable fortunately.

But the point is that Y-90 may be too hazardous to be present. I haven't even considered the chemical factors. Y and Zr are transition metals, but will they come free of the ceramic when formed?

Further modelling is also necessary to determine the power generation from the ceramic taking into account the production of Y-90.