It's not equivalent to nuclear war with Ukraine in either the sense of relative risk (for the reasons I gave) nor in the sense in which the term "nuclear weapons" is actually used. Russia intelligence agents poisoned Alexander Litvinenko with radioactive polonium, but this was not called a nuclear attack because that's not what the term means.

One could argue, at most, that this would be equivalent to a radiological weapon ("dirty bomb"). But even then it wouldn't be correct because of the important difference between purposeful radiological dispersal and radiological dispersal as a side-effect of a legitimate military action.

There is a distinction between nuclear warfare and radiological warfare, which is what this would (arguably) be.