A strange meaning for "get rid of".
Ye of little imagination. Let's make the assumption that you wanted
to design a radioactive decay assisted domestic water heater for the
purpose of disposing of hot reactor byproducts and waste. Three
obvious problems appear immediately.
1. Pollutants in the water may be become radioactive.
2. Shielding is necessary to avoid exposure.
3. Heat build up must be regulated and controlled.
The first (hot dirt) can be solved by filtration. Considering the
junk found in domestic water, this might be a good idea even without
nuclear heating. Incidentally, nuclear heated water will be
essentially sterilized.
Shielding can best be accomplished by burying the water heater. This
is the method that Toshiba proposes for their domestic reactor. It's
also a common paradigm, where anything dangerous is made safe by
burying it. Polyethylene foam should work well for both shielding and
thermal insulation. The water in the heater will also provide
substantial shielding.
Heat build up is a big problem. Unlike with a chain reaction, there
is no easy way to regulate nuclear decay. It will decay, and
therefore generate heat, continuously and without much variation. Left
to itself, the water will simply get hotter and hotter, until it boils
away. Some method of removing the waste heat will be necessary and
can be done with conventional thermodynamic methods such as radiators
and heat pumps.
There are plenty of other technical problems that will need to be
solved. I'm sure they can be dealt with as they appear.
If the US embarks on a program to bury moderate half-life reactor and
fuel processing byproducts in domestic water heaters, there will
surely be a substantial reduction in domestic energy requirements,
nuclear waste disposal, and water borne pathogen problems. We have
successfully deployed fundamentally dangerous substances, such as
propane, natural gas, and fuel oil, gasoline, electric power, etc in
the home. We can surely do the same with nuclear power. After all,
it is energy and should not go to waste.