I have to assume your fear is that radioactive particles will set up a chain reaction and the resultant thermal output will heat up the earth.

You don't have to worry about such a possibility.

Spent control rods are quite dangerous and are kept in storage facilities designed to absorb and limit the contamination potential.

You have to remember that the entire planet is playing a game of checks and balances with atoms, particles, radioactive atoms and all are working to achieve ground state.

Nuclear radiation is eventually absorbed by atoms that can absorb the extra energy without becoming radioactive themselves. So even if all the control rods of all the nuclear reactors were dragged over the surface of the earth a balancing would eventually occur.

At first, all things that contact the rods would become extremely radioactive themselves and distort intelligent function, but eventually the atoms would reach ground state. In the process, thermal heat would be increased, but even that would find itself converted into different forms of energy and mass.

About forty years ago, scientists planted a tree in a box, watered it and weighed the amount of water they gave it. After five years the tree and dirt weighed several hundred pounds and yet only 100 pounds of water and dirt had been added to it. Where did the other 200 or so pounds come from? The answer? It pulled it from the air and from solar radiation itself.

I mention this because that is what will happen to radioactive materials. Radioactive atoms' nuclei energy will feed surrounding structures, first destructively but as time passes it will stabilize as mass.

Even the burnt out remains of a forest fire feeds the next generation of growth. Atoms are smart. They seek balance and once made radioactive will begin their quest returning to ground state. All thermal heat does not stay in the same form. Converting heat into mass is what the earth does all the time.

All of nature around you was fed by radiation. Radiation keeps you alive, even now. Radiation keeps things bound to the earth.

Addressing control rods, just like addressing any future increase in TSI, will involve helping to channel and convert such radiation into mass.

What is heat (outside of discussing thermal units)? Heat is only the perceived disparity of radiation rates. When we touch or come near something that oscillates faster than our own atomic oscillation, we perceive such disparity as heat.

It's all wave forms. Wave form energy is absorbed and the energy is distributed and follows atomic channels whereby it is demodulated.

Radioactive waste, even if 100 times more than exists now, would never pose a longterm threat to the earth's climate because of this balancing mechanism in place. We have probably a century to go before we should consider abandoning nuclear reactors if no progress on waste is made. By this time, hopefully, either more intelligent means of disposal or conversion of radioactivity into mass should already be achieved.

Solar energy, however, is so massive in scale it can rapidly overwhelm the earth's ability to balance.

That said, it's safe to say that evolution here on earth has adjusted to the existing solar output, and life on earth is just one method of putting this solar radiation to good use.

It's sort of an advanced concept. We hear about sunlight and plant growth but most never really understand the nitty-gritty of radiation being converted into mass and fueling growth.

It's the increases in TSI we must watch out for.