Circulation, drop decay

Event II was the main plankton extinction and productivity crisis coimected to the rapid collapse of the surface-to-deep water carbon isotope gradient and drops in barium and carbonate accumulation rates. Curiously, there was a hundredfold increase in the concentration of foraminifera relative to total carbonate. It could be due to intensified deep circulation with winnowing of the fine fraction. Or possibly to better the preservation of the dissolution-prone planktonic forms through deepening of the CCD and/or lowered rates of in situ dissolution caused by decreased decay of organic carbon in sediment pore waters. There is support for this idea from the fact that coccoHths tend to be more dissolution-resistant than foraminifera, also from calcite dissolution above the calcite saturation horizon is driven mainly by titration by metabolic carbon dioxide derived from organic carbon decay at or near the sediment-water interface. 

The hot leg pipe outflow stops when the water level in the vessel has dropped below the hot leg nozzle, and pressure equilibrium between the containment and the reactor vessel is established. The sdphon breaker arrangement provides "containment" pressure also on the inside of the cold leg nozzle, and the large outflow from the reactor system stops - all by itself The core is cooled by reactor pool water in natural circulation, and the decay heat is absorbed in the pool. The pressure in the containment attains a peak of about 270 kPa after about 1 minute, and then decreases due to steam condensation on containment walls and structures. In about 2 hours, it is down to slightly above atmospheric pressure again. 

To enhance the passive decay heat removal capability by natural circulation, the pressure drop of the core has been limited below 0.2 MPa, and the difference of elevation between the core and heat exchangers has been enlarged, such as 38.7 m between the core and air cooler of IRACSs and 37.9 m between the core and the air cooler of DRAGS. The in-service inspection and repair capabilities are improved to... 

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