Nuclear reactors remain dangerous, even when shut down in hot weather
For Nuclear Power This Summer, It’s Too Darn Hot, Truth Out, 05 August 2012 By Gregg Levine, “……when it comes to nuclear power, as global temperatures continue to rise and water levels in rivers and lakes continue to drop, an even more disconcerting threat emerges.
When a coal plant is forced to shut down because of a lack of cool intake water, it can, in short order, basically get turned off. With no coal burning, the cooling needs of the facility quickly downgrade to zero.
A nuclear reactor, however, is never really “off.”
When a boiling water reactor or pressurized water reactor (BWR and PWR respectively, the two types that make up the total of the US commercial reactor fleet) is “shutdown” (be it in an orderly fashion or an abrupt “scram”), control rods are inserted amongst the fuel rods inside the reactor. The control rods absorb free neutrons, decreasing the number of heavy atoms getting hit and split in the fuel rods. It is that split, that fission, that provides the energy that heats the water in the reactor and produces the steam that drives the electricity-generating turbines. Generally, the more collisions, the more heat generated. An increase in heat means more steam to spin a turbine; fewer reactions means less heat, less steam and less electrical output. But it doesn’t mean no heat.
The water that drives the turbines also cools the fuel rods. It needs to circulate and somehow get cooled down when it is away from the reactor core. Even with control rods inserted, there are still reactions generating heat, and that heat needs to be extracted from the reactor or all kinds of trouble ensues–from too-high pressure breaching containment to melting the cladding on fuel rods, fires, and hydrogen explosions. This is why the term LOCA–a loss of coolant accident–is a scary one to nuclear watchdogs (and, theoretically, to nuclear regulators, too).
So, even when they are not producing electricity, nuclear reactors still need cooling. They still need a power source to make that cooling happen, and they still need a coolant, which, all across the United States and most of the rest of the world, means water. http://truth-out.org/news/item/10707-for-nuclear-power-this-summer-its-too-darn-hot