Reed water tube boiler straight tubes through which water and steam circulated more freely, it was considered by some contemporary writers on the subject such as Leslie S. Robertson as "behind" in its circulation because of the absence of down-comers. Whereas the Yarrow boilers fitted to the armoured cruiser of 1905 evaporated 11.664 pounds (5.291 kg) of water per pound (454 g) of coal at 100 degrees centigrade (212 degrees Fahrenheit) with natural draught, by the same measure a Reed boiler as fitted to the torpedo boat destroyer of 1896 evaporated 12 pounds (5.44 kg). An advantage of the Yarrow boiler was in weight:
Boiling water reactor safety systems the open pool slowly boils off, venting clean steam to the atmosphere. This makes it unnecessary to run mechanical systems to remove heat. Periodically, the pool must be refilled, a simple task for a fire truck. The (E)SBWR reactors provide three days' supply of water in the pool. Some older reactors also have IC systems, including Fukushima Dai-ichi reactor 1, however their water pools may not be as large. Under normal conditions, the IC system is not activated, but the top of the IC condenser is connected to the reactor's steam lines through an open valve. The IC automatically starts