Development and Operation Experience of a Seismic Warning System for a Nuclear Power Plant

Abstract

Requirements for the seismic resistance of nuclear power plants (NPPs) considerably differ from those for of other industrial facilities due to the necessity of protecting not only the NPP itself, but also the environment from radiation hazard. According to special regulations, even if an NPP construction site is located in a region with low seismicity, the NPP design should be based on the maximum design earthquake and peak acceleration typical of the region. Note that seismic warning systems for NPPs differ fundamentally in design and operation principles from conventional seismic monitoring systems. Seismic warning systems are required to reliably detect seismic events threatening the operability of nuclear power plants, to promptly inform operators, and to prevent false alarms and unauthorized access to the system. Atomseismoizyskaniya LLC has developed a seismic warming system (SSZ-1M) and put it into trial operation at the reactor units of the Smolensk NPP in 2014–2015. The system comprises six seismic groups: two groups per each reactor unit. Each group consists of three independent seismic recording channels, the sensors of which are distributed around the reactor unit at a distance of up to 500 m from the latter. Each channel records three components of seismic signals; the acceleration vector is calculated and compared with a preset threshold. Signals exceeding the threshold are fed to a coincidence circuit that generates an alarm if two of the three signals exceed the threshold. This scheme excludes false alarms. The components of the system are characterized by high reliability and stability. The performance of the system channels has been officially certified. The system automatically performs continuous fault diagnosis. The programs responsible for system function and diagnostics are independent; the system units have individual equipment. To exclude the possibility of external impacts, the SSZ-1M warning system has no Internet connection. Special seismic signal simulators were developed to test the operability of the system when deployed.