**5.8. Seismic instrumentation and seismic EOPs**

In case of an earthquake, the reactor is shutdown either by reactor protection system due to malfunctions, or manually by the operator based on the criteria of CAV and response spectrum criteria for OBE exceedance. The OBE-exceedance criteria is set CAV=0,16gs and response spectrum in the amplified range less than 0,2g. The seismic instrumentation and the pre-earthquake preparedness and post-earthquake actions are defined via adaptation of the IAEA NS-G-1.6, US NRC Regulatory Guide and 1.12, 1.166 and 1.167 respectively. Selection of the OBE exceedance criteria at Paks NPP was based on the analysis of the frequency of expected events, probability and consequences of spurious signals.

It has to be noted that the implementation of the concept and methodology for OBEexceedance was not a simple copy-paste; it has been adapted to the conditions of Paks NPP. At Paks NPP, if the ggset measured at the base mat, the non-upgraded part of certain systems will be automatically isolated from the upgraded one by quick-closing valves. These system's parts do not have function during and after an earthquake and the separation will not disturb the operation either. In the same time, there is also a signal for control room. If an earthquake happens, there are two possible cases:


The seismic recording systems composed from tri-axial accelerometers that are installed at critical locations of structures and main components, provide information for the post-event evaluation of the plant condition.
