How is it planned to handle low level nuclear waste on Mars produced by the use of Kilowpower reactors?
Nothing is mentioned in the Wikipedia article about the resulting waste or spent fuel.
On earth storage of nuclear waste needs to contend with ground water contamination, earthquakes, political events and extreme climate change (flooding and glaciation).
All of these are generally simpler on Mars. Much of the water is frozen, though the salt content does mean there is potential for ground water flow well below 0 Celsius and that the flow will be highly corrosive. Storage would need to be chosen somewhere consistently frozen even with the added heat from the stored waste.
Mars appears to be less active tectonicly so quakes be less energetic than those on earth, generally meaning waste can be trusted to stay put and containment undamaged.
Politics is unpredictable but the current uninhabited nature of Mars would allow designation of a storage site before there is a resident population. Similarly it currently seems less likely that civilisation would fail and a forgotten waste site would cause a disaster for a martian disposal site.
The Mars climate is generally far more stable so it seems unlikely a glaciation or warming/flooding event would destroy a site*. The thinner atmosphere and minimal water movement minimizes erosion risk assuming solid rock is chosen as the site.
One additional risk for a Mars storage site would be asteroid impacts since the much thinner atmosphere means more and heavier strikes. First pass approximation is that strikes crater their own diameter, so even relatively shallow burial would protect waste against anything not already massively damaging to Mars and any people there.
*one unknown in this is that any future terraforming efforts, while unknowable in execution will certainly involve massive melting of water and reshaping of the landscape (and possibly a cometry bombardment) which voids all the above. On the scale of terraforming, needing to relocated all previous waste storage is relatively simple.
While there are risks in storing waste on mars it is possible that having made the fuel (and got it to Mars without crashing) it is safer there than it could be on Earth.