Criteria of Aseismic design of Nuclear power plants.
The aseismic design criteria of nuclear power plants require that damage to any item (structure, system, equipment or component) should not lead to any unacceptable consequence (i.e. release of radioactivity). Also interruptions in power generation on account of earthquakes are kept to a minimum. These objectives are achieved by using two levels of earthquake motion - one corresponding to a "maximum probable" event and the other a "maximum possible" event inferred from geological, geophysical and seismological information from the region- as the earthquake design basis. The maximum probable event fixes the Operating Basis earthquake (OBE) in the terminology of the United States Nuclear Regulatory Commission (USNRC), and the S1 level earrthquake ground motion in the terminology of the International Atomic Energy Agency (IAEA). The maximum possible event, which is more severe compared to the OBE, is the Safe Shutdown Earthquake (SSE) in the USNRC terminology and the S2 level motion in the IAEA terminology.
When the earthquake severity exceeds the OBE level the power plant should be able to reach a safe shut down without any damage to any of its critical parts - systems, equipments or components - which are required in achieving a safe shut down, and maintaining the safe shut down state until the plant is inspected, certified fit for operation and restarted its normal operation.
In the event of the most severe earthquake ground motion experienced at the plant site, the power plant should be able to reach the safe shut down state, and maintain it in that state (i.e. without any release of radioactivity, which could have any unacceptable consequence to public safety), even if the plant is damaged beyond repair. The highest level of earthquake severity corresponds to what is called the Safe Shutdown Earthquake (SSE) in engineering design.
Codes and guides have been developed on aseismic design, which lay down the procedures of fixing the various levels of aseismic design.
This page was updated on 12 Jan 2011