The reason that water is a good modulator/dampening agent for those radioactive spent fuel cores is that it absorbs neutrons. Now, I’m not sure where in the molecule those neutrons get absorbed, but I’d hazard a guess that it tends to be the hydrogen, whose atoms occupy a larger volume than the oxygen.
Now, 99+% of hydrogen is protium, H-1, to which adding a neutron produces deuterium, H-2, a completely stable, and useful, substance. But the other <1% is deuterium, to which adding a neutron produces radioactive tritium, H-3, (along with a vanishingly small quantity of tritium, which converts to He-4).
As the water continues to absorb neutrons, more and more H-2 is produced, and therefore more and more H-3 is produced.
Note that one of the primary characteristics of water is that it boils at 100 degrees Celsius (for normal composition water) – pure deuterium is a few degrees higher IIRC. Another characteristic is that it is absorbed by the soil, and will flow through cracks in a container to get there.
Given all this,
> To what actual extent is tritium produced and to what extent is it released to the environment?
> What is the possibility of the spent cores bringing the water to a boil – and perhaps boiling dry? Does this vary with time or with the amount of cores stored in a given storage unit?
> What is the possibility of an accident, or sabotage, causing the water to drain off? What would then happen to the cores?
These sorts of questions get stonewalled by major utilities, for reasons that should be obvious – any admission of possible danger whatsoever subjects them to a wide variety of possible penalties, ranging from lawsuit to NRC closure. On the other hand, much of the data prepared by anti-nuclear-plant protesters seems to be facile summaries of worst-case scenarios disguised as “what will happen sooner or later.” And while I’m not uninformed about this sort of thing, I don’t have the background in nuclear physics or engineering to possibly arrive at intelligent answers to those questions. And I live within 50 miles of a plant where Progress Energy is proposing to store twice as many cores.
Nor, may it be noted, do our elected representatives seem either able or interested in getting accurate answers to these questions.
I know I’m putting a fellow poster on the spot with this, and will understand if she declines to give answers that address those questions. However, I think they are questions that do deserve answers from somebody.