The provision of reliable and safe operation of power Unit No.4 of Kalinin NPP, which is achieved by protecting the power Unit from design-basis accidents and beyond the design-basis accidents, occurring in the result of seismic influences (earthquakes), by reactor plant transferring into safe state in order to prevent an accident at the early stage.
Industrial seismic protection equipment (ISPE) is a completed part of the automated process control system (APCS) of power Unit No. 4 of Kalinin NPP, and jointly with the control and protection system (CPS) it performs automatic reactor shut-down at an earthquake which exceeds the level of design-basis value.
ISPE consists of two independent sets.
The composition of each set includes the following devices and units:
- Three channels for measurement of seismic influences, implemented on the base of three-component seismic sensors SD4;
- Three commutation units (BKK) for commutation and transfer of signals, coming from SD, to protection signals generation equipment (PSGE), to data display and logging hardware (DDLH) and to initial cause signaling equipment of typical software-hardware means (TPTS ICSE).
ISPE provides the following:
- Generation of discrete signals of emergency protection at exceeding of assigned emergency level of seismic influence threshold;
- Generation of discrete signals for start of registration (archiving of data) at exceeding of assigned preventive level of seismic influence;
- Generation of analogue signals on acceleration values by coordinates X, Y, Z, and general analogue signals corresponding to absolute value of seismic acceleration;
- Generation of discrete signals of SD good condition monitoring.
The range of analogue signals is (4-20) mA. The type of discrete signals: group of relay commutating contacts at current within the range up to 100 mA and supply voltage of 24 V.
Structural diagram of ISPE set:
Each ISPE channel performs diagnostics of intrinsic technical means. At failure of channel (at malfunction), at disconnection of electric supply the signal, equivalent to emergency protection signal, is generated.