Provision of reliable and safe operation of Beloyarsk NPP Unit 4, which is achieved by protecting the power Unit from design-basis 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.
ISPS is a completed part of automated process control system (APCS) of Beloyarsk NPP Unit 4, and jointly with control and protection system (CPS) it performs automatic reactor shut-down at an earthquake which exceeds the level of design-basis value.
ISPS consists of two independent sets.
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 transfer of signals, coming from SD, to initiating part of EP-PP (EP-PP IP);
ISPS provides the following:
- generation of discrete emergency protection signals at exceeding of assigned emergency level of seismic influence threshold to EP-PP IP;
- generation of discrete signals for start of registration (information archiving) at exceeding of assigned preventive level of seismic influence to EP-PP IP;
- generation of analogue signals on acceleration values by coordinates X, Y, Z, and general analogue signals corresponding to absolute value of seismic acceleration to EP-PP IP;
- generation of discrete signals of monitoring of SD good condition to EP-PP IP.
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 ISPS set:
Each ISPS 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.