I don't think nuclear waste gets hot unless it's packed close enough ... otherwise it wouldn't be waste ... the stuff has to be refined again to allow criticality ... kinda guessing here but I know the waste from the power plants we have today is unsuitable for further use ... it's far more expensive to build breeder reactors from which the waste can be utilized ...
The lead lined nuclear water heater would need 1 foot 4 inches of lead ... heavy ... too heavy for wood-framed floors ... the problem is exposure time, water heaters are in our homes all the time, that's very bad ... and very close, distance from the source is also a mitigating factor ... and gamma radiation is a killer, strong enough to disassociate oxygen molecules and forming ozone right there in our homes ...
Terrorists are better off raiding hospitals, some really nasty stuff there ... plus for less than $100 at WalMart will get kill counts in the hundreds ... napalm costs the same as gasoline ... the radiological threat to way overblown unless we're talking nation-state terrorist activities ... and we all saw what Saudi Arabia can do with a handful of airplanes ...
Better is for us to insure our government isn't acting overseas in a way that makes folks overseas want to kill us ...