The process parameters are not processed by the CPS, but by the Emergency Process Protection System (EPPS). The EPPS is a system of safety functions using process parameters to trip the reactor or reduce reactor power if abnormal process conditions in the reactor core protection, the main coolant system, the separator drum, the turbine generator, reinforced leaktight compartments and electric power supply. This system generates signals that are issued to the CPS in order to actuate the reactor protection features based on process parameters. Besides generating integrated signals for CPS, EPPS generates signals for actuating safety systems (ECCS, ACS, diesel-generators, etc.) and process safety-related systems of normal operation (components of the CPS cooling circuit, gas circuit, etc.). The same system is also involved in the control of process in the nuclear power plant. The EPPS:
The EPPS consists of the following 13 separate subsystems:
1) Emergency protection against fuel channel breaks: A FASS signal is generated in response to an increase in excess pressure in the reactor cavity to ~ 7.5 kPa (750 kgf/m2).
2) Emergency protection against pressure rise in ACS compartments: A FASS signal is generated due to a excess pressure rise in the ACS compartments to ~ 2 kPa (200 kgf/m2 ).
3) Emergency protection against out-of-range pressure in drum separators: An AZ-1 signal is generated in response to a excess pressure rise in separator drum of either loop to 7.26 MPa (74 kgf/cm2).
4) Emergency protection against out-of range levels in separators drum: An AZ-1 signal is generated in response to level gauge readings at the scale from -1200 mm to +400 mm given below:
5) Emergency protection against low flow in the MCC and MCP trip: An AZ-1 signal is generated due a multiple MCP trip in either loop, or due to a flow decrease in either loop to 1.39 m3/s (5000 m3/h) in two out of three operating MCPs, or one of two operating MCPs.
6) Emergency protection against low feedwater flow: An AZ-1 signal is generated if feedwater flow to either loop reduces to 50 percent of the current value, which corresponds to the current reactor power in range of 60 to 100 percent of the nominal power.
7) Emergency protection on load rejection and trip of turbine generators: An AZ-1 signal is generated in response to trip of both turbine generators, or the single operating turbine generator (i.e., closing of the stop valves or the main steam gate valve and of their bypasses) and load shedding by both turbine generators or by single operating turbine generator (i.e., drop of excess pressure downstream of the turbine stop-control valve below 1.27 MPa (13.0 kgf/cm2)).
8) Emergency protection against the loss of AC power supply: An AZ-1 signal is generated if power supply is lost.
9) Emergency protection against voiding of CPS channels: An AZ-1 signal is generated in response to:
10) Emergency protection against low levels in ECCS accumulators: An AZ-1 signal is generated in response to a level drop in the accumulators down to 4550 mm as indicated by the standard level gauges.
11) Emergency closing of throttling regulating valves of MCP: An AZ-4 signal is generated when valves close.
12) Protection on temperature rise at condensation trays of the ACS: Pumps and heat exchangers are activated if temperature in pools 1 to 4 rises to 35 oC, or if temperature of pool 5 rises to 50 oC.
13) FASS on pressure rise in the MCC compartments: A FASS signal is generated in response to pressure in the ACS compartments to ~ 2 kPa (200 kgf/m2 . This latter subsystem has been added to provide a redundant scram signal for loss of coolant accidents.
The EPPS includes appropriate process parameters sensors, three sets of data processing equipment for subsystem 1 through 12, three sets of data processing equipment for subsystem 13, and the appropriate connecting cables. Initiating of reactor protection and safety related systems is carried out through voting logic upon redundant parameter measurements. Every time a protection is actuated or disabled a light-sound signal appears on a special panel in the main control room. The signals are recorded in the TITAN monitoring system. Special engineered means prevent unauthorized access to the actuation/disabling means for protection and interlocks.