Operating basis earthquake

The respective nuclear organisation and regulatory commissions have criteria for the seismic design of nuclear power plants. The Operation Basis Earthquake (OBE) does consider the effect on a plant site during the operational life of the plant. Both local geology and seismology are related to specific characteristics of local subsurface materials. 

Earthquakes can cause local soil failure, surface ruptures and structural damage of nuclear power plants. The most significant earthquake effects on plants or their structural components result from the seismic waves which propagate outwards in all directions from the earthquake focus. These different types of waves can cause significant ground movements up to several hundred miles from the source. The movements depend upon the intensity, sequence, duration and the frequency content of the earthquake-induced 

When the history of ground shaking at a particular site or the response spectrum derived from this history is known, plants theoretical response can be calculated by various methods these are described later. 

The minimum acceptable acceleration for the OBE will be taken at least one-half of the Safe Shutdown Earthquake (SSE) acceleration. Sometimes OBE SSE have been permitted in some cases where SSE return period is such duration as not to be reasonably expected during the life of the nuclear power plant. If the vibratory ground acceleration of the site is equal to or greater tha n OBE acceleration, the US Federal Regulation makes it mandatory to shut the nuclear power plant for inspection. 

The recorded earthquake ground accelerations have no doubt similar properties to those of non-stationary random functions but owing to a lack of statistical properties related to such motions artificially generated accelerograms are used which are flexible for any duration. 

---

I Operating basis earthquake (OBE) test This is defined by an earthquake that may be expected to occur during the operating life of the object for which... 

Nuclear Island Cooling Water Building Normal Operating Pressure Net Positive Suction Head Nuclear Steam Supply System Operating Basis Earthquake Outer Neutron Control Assemblies Outer Pyrocarbon Peak Accelerograph Protective Action Guidelines Private Automatic Exchange... 

The Operating Basis Earthquake (OBE) maximum horizontal and vertical ground acceleration is less than or equal to 0.15g... 

The simultaneous occurrence of pipe break and either safe shutdown earthquake (SSE) or operating basis earthquake (QBE) as in Section 2.6, is considered too improbable to be incorporated in the plant design basis. This is reflected in the loading combinations for structures in Section 3.8. It is expected that the probabilistic risk assessment (PRA) will confirm the above, and additional revisions to load factors and load combinations may be made if they are supported by the results of probabilistic analyses. (Ref. 1) The current design is based on the following ... 

Seismic loads (E and Egg) are from the operating basis earthquake (QBE) and the safe shutdown earthquake (SSE), respectively. These seismic loads are inertial forces corresponding to maximum accelerations at floor elevations given for a range of site conditions. Seismic loads are determined based on analysis as described in Section 3.7. 

Steam Generator Tube Leak (Small) Control Rod Insertion Main Loop Overcooling Operating Basis Earthquake (OBE)... 

Safety Series No. 50-SG-Sl (Rev. 1), Earthquakes and Associated Topics in Relation to Nuclear Power Siting (1991). This Safety Guide also defines a second earthquake level (SL-1) which corresponds to an earthquake often denoted as operational basis earthquake (OBE) which can reasonably be expected to occur at the plant site during its operating hfe. It may also correspond to the inspection level earthquake after which the plant safety is reassessed to continue operation. 

SSE, The structures are designed and constructed in accordance with the seismic requirements for both the safety shutdown earthquake (SSE) and the operating basis earthquake (OBE). 

Various safety related systems and safety support systems are designed to appropriate safety class specifications depending on the functional importance. In addition, systems are seismically designed for two different intensities of earthquake. The operating basis earthquake (ODE) represents the intensity of earthquake for which the systems are designed to remain functional during and after the event. The safe shutdown earthquake (SSE) considers the maximum earthquake potential of the site and only those systems which are required to ... 

Generic Safety Issue (GSI) 119.3 in NUREG-0933 (Reference 1), addresses the question of assuring the public safety during seismic events in a more rational manner by eliminating the requirement to relate the Operating Basis Earthquake (OBE) to the magnitude of the Safe Shutdown Earthquake (SSE). 

Finally, the LPMS is qualified for the expected normal containment environment and is seismically qualified for an operating basis earthquake. Since the LPMS is important to the safe operation of the plant, limiting conditions for operation (LCD s) will be provided to the owner-operator in CESSAR-DC Chapter 16. The LCD s for the LPMS are included to ensure accurate monitoring of the NSSS for excessive vibration and/or debris during plant operation. 

The ALMS is qualified for the expected normal containment environment and is seismically qualified for an Operating Basis Earthquake. Finally, as identified within Regulatory Guide 1.97, the ALMS is supplied with power from non-vital buses X or Y. These buses are very reliable since they use batteries as a backup power source. 

Various structures, systems and equipment of the CHTR would be designed for high level and low probability seismic events such as an operating basis earthquake (OBE) and a safe shutdown earthquake (SSE). Seismic instrumentation is also foreseen. 

The Temelin NPP had an original seismic design basis value 0.06 g. In order to follow IAEA recommendation 1, the recommendation of the IAEA expert mission to Temelin in 1992, and the IAEA Safety Guides 50-SG-Sl and 50-SG-D15, the safe shutdown earthquake (SL2) and operational basis earthquake (SLI) values have been re-evaluated as follows ... 

The draft and subsequent revisions reflected the traditional philosophy that nuclear power plants should be designed against two levels of potential seismic events. Nuclear power plants are designed to continue to operate given earthquakes of moderate intensity and to safely withstand the effects of larger earthquakes. The operating basis earthquake (QBE) is the largest earthquake that... 

---