Passive pressure pulse transducers (PPPT) are small heat exchangers with the primary and secondary sides enclosed in a small housing (see FIG. 4). In this design, the primary side is outside the heat exchanger tubes and the secondary side inside. The primary side is connected to the RPV without isolating elements, and thus forms part of the RPV. The pressure on the secondary side during standby condition is more or less atmospheric. The PPPTs were tested at the emergency condenser test facility at Julich in five different design variants.

The PPPTs function similarly to the emergency condensers: as long as the RPV water level is higher than the reference level, there is stratification on the primary and secondary sides and negligible heat loss. When the RPV water level drops below the reference level, the water level in the PPPTs drops accordingly until steam comes in contact with the heat exchanger tubes. In principle there is natural circulation on both the primary and secondary sides. The water inside the tubes is heated up by the steam and the condensed steam returns to the RPV. When the water inside the tubes evaporates, the pressure on the secondary side increases and would reach primary-side pressure after a longer period of time. A switching device is actuated once the secondary side reaches a pressure of 6 bar (gage) in order to obtain a shorter actuation time period.

Pressure differentials of several Pa on the primary side lead to pressure increases of several bar on the secondary side. This is a good example showing that passive devices are not necessarily connected by small driving or acting forces.

On the secondary side, forced or natural circulation should be prevented in order to obtain short actuation times. Otherwise the main secondary-side water inventory must be heated until a level of 6 bar (gage) is reached. In the last of the five design variants tested, nearly stratified conditions were achieved on the secondary side and the actuation time was only about 5 s.