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2) Suppress the transient process of operation to avoid emergency shutdown of the unit and rebuild the unit in steady state operation.
3) Provide reactor operators with monitoring instruments that display all of the input and output parameters required for the control system and provide operators with the ability to manually operate on each system.
2. The nuclear island control system is designed around the two goals of nuclear power plant safety and availability.
1) The main function of the nuclear power plant instrument control system is to monitor the power plant parameters and the operating status of each system under normal operation, anticipated operational events and accident conditions, and provide all necessary information for the safe and effective operation of the operating personnel, either automatically or The operating parameters of the process system or equipment are maintained by the operating personnel's manual control within the limits defined by the operating conditions. Under abnormal operating conditions and accident conditions, automatic protection actions are triggered to protect the safety of personnel, reactors, and system equipment, and to avoid environmental pollution.
2) The design and manufacturing quality of nuclear power plants must ensure that no faults occur during normal operation and normal operation transients; the design of safety systems should minimize the effects of abnormal transients and events; the design of specially designed safety facilities should be able to minimize The effect of an imaginary accident on the inclusion of radioactive material.
3. Principles for the design of nuclear island instrumentation systems Nuclear power plant design must ensure the normal operation of the reactor under the premise of ensuring public health and safety without excessive risks. The safe operation of nuclear power requires back-end support, such as a powerful power supply, adequate cooling water, etc. Therefore, it is usually a multiple redundant standby mode. The design of the nuclear island instrumentation system must comply with the following principles:
1) Design according to the safety objective of the power plant to meet the defense requirements of the power plant in depth. In normal operation, when an abnormal condition occurs, the plant control system adjusts to restore the plant to normal operation; when an expected design transient event occurs, the protection system triggers the execution of the safety function; when the design basis accident occurs, the protection system comes Trigger execution of the security function.
2) The safety-critical instrument control system adopts a redundant design to meet a single failure criterion. At the same time, it is also used to improve the reliability of the system, to avoid the loss of its function of the instrument control system, affecting the operation and safety of the power plant. On the structure and components, a redundant subsystem performs its functions independently of Other subsystems, subsystem failures, and does not affect the normal operation of other subsystems. Internal signal exchanges between redundant subsystems must be electrically isolated or communicatively isolated.
3) Hierarchical organizational structure. Including the process system interface layer, automatic control and protection layer, operation and management information layer, the whole plant technology management;
4) Reduce the risk of common mode failures by diversifying the design of different instrumentation systems, structures and components. The overall structure of the instrumentation and control will be based on two different hardware and software platforms, respectively for the safety and non-safety instrument control system functions; the protection system uses a functional diversity design, a reasonable grouping of the protection variables, the trigger of each accident The event uses variables of different measurement principles as much as possible to prevent the influence of software common mode failures. In addition, system-level commands that manually trigger shutdown and special actions are retained. This command completely bypasses the digital protection system; the backup disk is at the workstation failure. Under the circumstances, the power plant can be maintained in normal operation for four hours, and when necessary, bring the power plant to a safe shutdown state.
5) Prioritization and handover of control ensure high security level of protection. The control commands from the emergency operation device have the same highest level of security as the automatic commands from the protection system.
4. Safety classification of nuclear island instrument control system According to the requirements of safety classification, the instrument control system can be divided into three parts: safety grade, safety related grade and non-safety grade. Safety-level systems play an important role in achieving or maintaining the safety of the power plant. It mainly includes reactor protection system, special safety facility logic system, safety function support system (parts of electrical and equipment cooling, important plant water, partial ventilation system), atmospheric side-by-side system, and post-accident monitoring system (PAMS). Security-level system requirements consist of redundant channels that require hardware isolation and electrical isolation between channels.
Safety-related systems function as complementary, supportive or indirect roles in achieving or maintaining the safety of nuclear power plants, and other functions that can contribute to the safety of the power plant, such as maintaining operating conditions, monitoring the availability of safety systems, and preventing the effects of internal hazards. , Radioactive release detection J/supervision, functions used after the accident to run, etc.
The non-safety level system includes various control systems, power plant computer information and control systems, and some special instrumentation control systems in addition to the above-mentioned safety level and safety related level in nuclear power plants.
5, nuclear island instrument control system structure instrumentation and control using digital distributed control system, the entire system is mainly divided into the following four levels:
1) Technical management of the whole plant: Complete the sharing of information among multiple units and contact with the outside world;
2) Operation and management information layer: complete tasks such as process control, process information and information management;
3) Automatic control and protection layer: complete system-level and equipment-level control and process monitoring;
4) Process System Interface Layer: Complete control and measurement of field equipment and process parameters.
Among them, the automatic control and protection layer includes a security level protection and control system, a security related level control system, and a non-security level control system.
The safety-level process instrumentation system and the safety-grade nuclear instrumentation system collect measurement information, perform calculations, and generate logic signals after comparing with the setting values. The protection system performs logical operations to generate reactor emergency shutdown drive signals and drive signals that specify the actions of the safety devices. The connection between the internals of the protection system is achieved through a security-grade data communication network. The communication network uses a fiber optic network to meet the mutual electrical isolation requirements. If the data communication between the high security level system and the low security level system is performed through the gateway, the data can generally only be transmitted from the high security level to the low security level, and not from the low security level to the high security level.
The safety-related control system is the instrument control system and equipment necessary to support the safe shutdown status during the mid-to-long term (manual operation) of the accident.
The main function of the non-safety level control system is to perform automatic control and supervision tasks under the normal operating conditions of the power station.
6. PWR Nuclear Nuclear System The main system nuclear island system mainly includes the primary loop system and some safety and auxiliary systems. The primary system of the primary loop includes the reactor coolant system (RCP), which includes chemical and volume control systems (RCV), boron and water recharge systems (REA), and residual heat removal system (RRA). The safety facilities include safety. Note system (RIS), containment sprinkler system (EAS), auxiliary water supply system (ASG) and containment isolation system (EIE).
The entire primary loop system is also called the nuclear steam supply system. The nuclear steam supply system has sufficient heat transfer capacity and can transfer heat generated during reactor power operation and at subcritical times (including shutdown and initial stage of power plant shutdown) to steam and power. Conversion system, and can transfer the heat generated during the second stage of shutdown and cold shutdown of the power plant to the residual heat removal system.
7, reactor control system 7.1 control system function is:
a) When the unit is operating in steady state, maintain the main operating parameters as close as possible to the optimum value required by the design of the nuclear power plant, so that the output power of the power plant is maintained within the required range;
b) Enable the nuclear steam supply system to adapt to various transient operating conditions of normal operation. According to the requirements of the power grid and the needs of operation, change the operating status of the system and maintain the operational flexibility;
c) In the event of transient operation or equipment failure, make the main parameters of the power plant within the allowable range, and minimize the action of the reactor protection system.
The reactor control system also performs the following functions:
1) To enable the nuclear power station to withstand:
Under possible helium restriction conditions, within the range of 15% FP to 100% FP, a step load variation of ±10% and a linear load change of 5%/min will not cause an emergency shutdown, steam discharge, and stabilization of the reactor. Pressure relief valve opens.
Dumping 100% of the external grid load without causing the reactor to shut down urgently will not cause the release valve or safety valve of the regulator or steam line to open.
As long as the condensing system and the condenser steam discharge valve are available, the turbine tripping will not cause the reactor to shut down.
2) During operation transients, control the temperature regulation rod set to keep the reactor coolant average temperature (Tavg) within the specified range.
7.2 The main control of PWR:
1) Reactive control and power distribution control The rapid change of the PWR is mainly achieved by changing the position of the control rod in the core. The slower reactivity change is achieved by adjusting the boron concentration in the water. After the fuel is loaded, the insertion of the control rod affects the power distribution. In addition, the temperature difference (power level) of the moderator core inlet and outlet moderator also affects the axial power distribution.
2) Power regulation Based on the turbine load and the average temperature of the reactor coolant, the position of the control rod in the core is manipulated to adjust the power of the reactor to match the output of the turbine unit.
3) The average temperature regulation system adjusts the temperature regulation rod to keep the average temperature of the primary circuit as close as possible to the set value determined by the load. In the steady state and transient process, assist power regulation bars to compensate for power losses.
4) One-loop system pressure control The regulator's heater (in the water zone) or sprayer (in the steam zone) is used to maintain the regulator pressure within the specified range.
5) The regulator water level controls the water volume in the reactor coolant system, ie the regulator water level is maintained by a chemical and volume control system (RCV).
6) The basic function of the steam generator water level control is to adjust the feedwater flow into the secondary side of the steam generator so that the water level of the steam generator is kept within the specified range under normal operating conditions.
7) Steam Emission Control The role of the steam discharge system is to discharge steam directly to the condenser after a sudden and drastic reduction in turbine load, thereby maintaining an artificial load on the steam generator to reduce the reactor coolant system. The transient changes.
8. Reactor protection system Reactor protection system is one of the important safety systems of nuclear power plants. It is very important to limit the development of nuclear power plant accidents, mitigate the consequences of accidents, ensure the safety of reactors and nuclear power plant equipment and personnel, and prevent the release of radioactive materials to the surrounding environment. effect. The function of the reactor protection system is to protect the integrity of the three major nuclear safety barriers (ie, fuel cladding, loop pressure boundary, and containment).
The reactor protection system includes an emergency shutdown system and a dedicated safety facility drive system to monitor the protection parameters determined by the safety analysis. When these parameters exceed a predetermined setting value, an emergency shutdown is triggered and a dedicated safety facility is activated. Safety of reactors is ensured through the control of shutdown breakers and safety drives.
1) The signal that triggers reactor shutdown is as follows:
a) nuclear power overpower shutdown;
b) core thermal power overpower shutdown;
c) reactor coolant system regulator pressure and water level shutdown;
d) reactor coolant system low-flow shutdown;
e) the steam generator water level shutdown;
0 Turbine tripped reactor shutdown;
g) A shutdown protection system (ATWT) signal triggers a shutdown;
h) Safety inject signal triggers shutdown;
i) The containment spray signal and the containment phase B isolation signal trigger the shutdown.
j) Manually shutdown.
2) The specific functions triggered by the dedicated safety facility drive system are:
a) emergency shutdown of the reactor (if the reactor emergency shutdown system fails to trigger an emergency shutdown);
b) security injection signal;
c) Phase I isolation of the containment vessel, whose function is to isolate all piping that is not necessary to protect the reactor to prevent the release of fission products outside the containment vessel;
d) Steam pipe (VVP) isolation to prevent continuous uncontrolled discharge of more than one steam generator to prevent RCP from uncontrolled cooling;
e) Isolate the main water supply pipeline (ARE) to prevent or mitigate excessive cooling of the RCP;
f) containment pressure high signal;
g) Start the auxiliary water supply system to discharge the core heat.
9. Nuclear power plant DCS system 9.1 Taking the example of a pressurized water reactor nuclear power plant introduced by Alpha Nuclear Energy of France (former Farmaton Nuclear Power Company), the design of its nuclear island control system is generally based on Siemens Teleperm XS (TXS) and TelepermXP (TXP). platform. All IE-level functions (safety levels, protection instrumentation functions) and partial safety-related levels (TXS in the post-accident instrument function and QDS equipment in the security display system) are completed in the TXS, and TXS is provided by the Famatong Nuclear Energy Corporation. Equipment supply control system. Other parts of the safety-related and non-safety functions are implemented in TXP. This part of the control function can be provided by the DCS supplier.
9.2 Safety-rated DCS systems include: Reactor Protection Control System (RPS), PACS and Core Control System (CCS).
Among them, the main functions of the reactor protection and control system are reactor protection, safety function-driven, post-accident detection and so on.
The priority actuator control system is primarily responsible for the control of the safety actuators, including priority management, actuator actuation, basic component protection, and actuator monitoring.
The core control system mainly monitors and controls the core section and exchanges data with the outside world.
10. Control room The entire nuclear power plant nuclear power station, including nuclear islands, conventional islands and some BOPs, adopts centralized monitoring and control to facilitate the operation personnel's monitoring, control and accident handling of the production process. Through the monitoring and control equipment installed in the main control room, the startup, shutdown, normal operation of the power plant and the handling of abnormal operating conditions or accident conditions can be realized. The security control system has four identical computerized workstations (OWPs), and one workstation is divided into a control part and an alarm part. Of the four workstations, two are the main operator stations during operation, the first and second loop operator stations, and the other two are used as standby and monitoring and processing auxiliary tasks. The hard-wired system is located between two lines of personnel workstations with a very small number of buttons to directly initiate control commands such as shutdown of the reactor, the provision of safety features, and the interpretation of turbines.
Although the computerized control system has a high degree of reliability, the possibility of completely losing the computer information and control system of the power station is also considered in the overall design. For this purpose, a spare disk is set in the main control room.
In the overall design, the unavailability of the main control room was considered and an emergency shutdown station was set up for this purpose. When the main control room is available, the function of the emergency shutdown station is locked; the emergency shutdown station is activated when the main control room becomes unavailable for some reason (eg, a fire).
The technical support center is located near the main control room and is the place where the expert group evaluates and diagnoses the condition of the power station. Under accident conditions, the technical support center has the same conditions of residency as the main control room. For a limited period of time, the technical support center can accommodate a certain number of technical experts and power plant managers to work at the same time. In the technical support center, there is a dedicated workstation (simplified operator workstation) for each unit. The staff of the technical support center are provided with the same information available in the main control room, except for the operating procedures. The workstation does not provide control functions.
1. The overall objective of the nuclear island control system 1) When the unit is operating in steady state, establish and maintain the power balance between the primary and secondary circuits.