That is entirely impossible. Sodium Nitrate, or NaNO3, is nothing that contains higher elements that can have nuclear decay and hence produce radioactivity. Naturally occurring radioactive materials (NORM) are coal (as it contains uranium and thorium as well as potassium-40, lead-210 and radium-226. However, the actual radioactivity levels are not great), mineral sands (which contain titanium and zircon, sometimes monazite, a rare earth mineral containing thorium), Tantalum concentrate (which usually contains uranium and/or thorium, but hardly ever reaches critical levels), oil and gas produce (radium-226, lead-210), and Radon gas which sometimes occurs naturally in caves.

Now Radon is the best example that radioactivity does not directly have to do anything with heat! In Radon caves (which are sometimes used for healing purposes) the Radon gas cannot be smelled or felt, these caves are also rather cool.

You are mixing up some things here: heat is produced in a radioactive chain reaction (the H-Bomb for uncontrolled and the Atomic Plant for controlled chain reactions). These do not really happen in nature (at least not on Earth) as the amount of radioactive material needs to be really high - you might have heard that radio active material needs to be "enriched" in order to work as a fuel for Atomic Plants.

The intense heat in the Atacama Desert has a very simple reason: first of all the geographic location and - now this the real heat driver - the water absorbing nature of the sodium nitrate salt crystals. They literally draw all humidity out of the air (amongst other geographically reasons for the dryness of the area).

If the reason for the heat were radioactivity, the levels of radioactive decay furthermore would need to be so high that no human being would be able to survive even some place NEAR the Atacama ;-) So this is just popular myth by scientifically quite silly!