This system provides for the injection of water directly into the reactor core in three stages. In the first stage, injection from the accumulator takes place, see Fig. VI-4. In the second stage, water flows from the GDWP under gravity, providing core cooling for three days. In the third stage, water accumulated in the reactor cavity is pumped back to the GDWP, from which it eventually enters the core. The first and the second stages of ECCS are passively actuated and do not depend on any active component. The important components of the ECCS are the GDWP, which has been discussed in Section VI-1, and an advanced accumulator equipped with a fluidic device as shown in the right part of Fig. VI-4.

The FFCD consists of a vortex chamber with one outlet, a tall vertical stand pipe and a small tangential side connection with two inlets. With the incorporation of a fluidic flow control device (FFCD) at the bottom of the accumulators, the large amount of water which is flowing directly into the core in the early stage of a LOCA is reduced to a relatively small amount and continues to flow for a longer time into the core, removing the decay heat. The FFCD is a simple passive device which reduces flow automatically after some time because of an increase in the pressure drop due to the formation of vortex. This passive feature provides many safety benefits suc as design simplicity and high reliability, and cools the core for a longer time.