There are certain safety features and advantages in integral reactors related to decay heat removal due to their power range and compactness. They are, especially, beneficial if they are implemented with passive initiation as well as passive operation.

The benefits of these systems are

• Extension of the time available for operator action

• Possible reduction in redundancy requirements

• Use of intermediate circuit eases maintenance problems in the steam generators and turbine due to the absence of radioactivity

• Cost reduction due to a reduction in the number of system components

An intermediate circuit is necessary for heating applications to eliminate the possibility of radioactive leakage to the end user This protection is particularly effective if the intermediate pressure is higher than the primary pressure

Since a water/water heat exchanger can be more efficient than a steam generator, in terms of specific transfer capacity and m certain design conditions, an intermediate circuit can allow greater power in a given size of RPV or a reduction of operating pressure for the same power The choice is an optimization between space available and the relative costs of a larger internal steam generator compared with an intermediate circuit

Passive system initiators used in integral reactors are

• Rupture discs

• Non return or check valves

• Valves which operate on changes of pressure differential

• Systems constantly in operation in normal as well as accident conditions