Simulation Of Process Model And Control System

-The safe and efficient operation of a nuclear power plant is highly dependent upon the knowledge and skill of power plant operating personnel. There are many techniques and methodologies available in imparting knowledge to increase the skill sets of Nuclear power plant operators. The emerging technologies include Full Scope Replica Simulators (FSRS), 3-D Visualization and Virtual Reality for better understanding and to increase the reflexes and response of the operators. In the present scenario, Full Scope Replica Simulator (FSRS) is considered as one of the most adhered techniques in the Nuclear power plant training programmes. This paper discusses the Process Modeling and Simulation of Condensate extraction system and associated logics and controls, integration with main system, interconnection with the reactor sub systems etc. It also covers the significance of process simulator as a training tool, the design basis events considered for training purpose and adaptation of plant procedures for training. I Process Simulators For Training Purpose The Three Mile Island incident was the main triggering point of introduction of Simulators in the Nuclear power plant operator training programme. Generally simulators were used for analytical purpose for heat balance / thermal hydraulic and other design calculations since many decades. Other important uses of simulators have evolved over a period, based on the operational experience and more demanding training requirements. The technological advancement also has helped in improving the way of utilization of process simulators in the present scenario. Today the process simulators have taken a more important role in imparting comprehensive training to the plant operators. According to Atomic Energy Regulatory Board guidelines, the training simulator has to be installed and commissioned well in advance compared to the reference plant. II. Prototype Fast Breeder Reactor (Pfbr) Prototype Fast Breeder Reactor (PFBR) is a 500 MWe capacity, pool type reactor utilizing sodium as the main heat transport medium. The reactor core consists of fuel sub assemblies made up of (Uranium, Plutonium) Mixed Oxide Fuel. The heat transport system consists of primary sodium circuit, secondary sodium circuit and steam water system and electrical system. (Refer Fig-1 for details).The steam water system adopts a reheat and regenerative cycle using live steam for reheating. Figure -1 PFBR Flow Sheet III Operator Training Simulator For Pfbr A high fidelity full scope training simulator is being developed at IGCAR for training the operators. It is a training tool designed to replicate the steady state and dynamic conditions of the plant in response to operator actions. The training simulator covers various reactor sub systems like Neutronics system, Primary Sodium system, Secondary Sodium system, Electrical system, Steam Water System etc. The plant control room is replicated in all aspects so as to provide a smooth change over to the operators, after the completion of training to real plant environment. IV Hardware Architecture The Hardware architecture consists of Simulation Computers, Control Panels, Operator Information Consoles, Input/ Output systems, Instructor station, Simulation Network and Power Supply & Distribution system. (Refer Fig -2 for details). The Simulation Computer executes various Mathematical Models of the Sub-Systems in Real 2nd National Conference Mathematical Techniques: Emerging Paradigms for Electronics and IT Industries September 26-28, 2008 -126MATEIT-2008 Time. It takes Inputs from Control Panels, Console Panels through I/O Systems, processes them and responds by giving the information to I/O system for display on indicator/meters, recorders and raise alarms in real time. Control Panels are replica of the Plant Control Room Panels and made up of mosaic tiles with grid structure. Figure-2 Simulator Configuration Operator Consoles handle overall monitoring the most important and frequently used controls. Normally, Reactor startup, power raising, normal steady power operation and shutdown are carried from operator console. Instructor Station facilitates control and monitoring of Simulator Operations / Operator actions and conduct training sessions. The important commands like RUN, STEP, BACK TRACK, FREEZE, REPLAY, and SNAPSHOT are available on Instructor Station. All plant scenarios are loaded from here for conducting training for the operators. V Brief Description Of Condensate Extraction System And The Logics The Condensate Extraction System is a part of Steam Water System in PFBR (Prototype Fast Breeder Reactor) which produces superheated steam using once through steam generators (OTSG) to drive the Turbine Generator and produces 500 MWe power. The main function of Condensate Extraction System is to maintain the cycle flow and thermodynamic requirements of the system by supplying water from condenser hot well to deaerator. This is achieved through various stages of low pressure regenerative feed heating. The condensate from the hot-well of the Condenser is extracted using Condensate Extraction Pumps -3 Nos. and pumped to Deaerator through Condensate Polishing Unit, Gland Steam Condenser, Drain Coolers and Low Pressure Heaters. Steam cycle employs regenerative feed heating based on steam bleed from Intermediate Pressure and Low Pressure turbine extracts. Condensate drain from Low Pressure heaters is cascaded and sent to main Condenser. System parameters are measured and monitored using pressure, flow, and temperature and level transmitters located near the main components. (Refer Fig –3 for details). Figure -3 Condensate Extraction System During normal operation, only two pumps of 50 % capacity will be running, the third being a hot standby. The hot well level in the main condenser and deaerator water level is controlled automatically by operating the appropriate valves in the system. In case of very low level in the hot well, the condensate extraction pumps are tripped and very high level in LP heaters will isolate the respective heater and open the bypass valve. VI Simulation Of Process And Control System The process simulator is based on condensate extraction system along with logics and controls. It represents the hydraulic part of Steam Water System Simulator. The process simulator covers normal steady state condition and status under various plant operating conditions, related incidents and malfunctions etc. The process simulator takes the input signals from the interconnected steam water 2nd National Conference Mathematical Techniques: Emerging Paradigms for Electronics and IT Industries September 26-28, 2008 -127MATEIT-2008 system and accepts the plant stimuli through Human Machine Interface feature like Start/Stop signal of Condensate Extraction Pump, Close/Open signal of water side valves etc from the control panel and feed back signals from the processes. The training simulator is controlled from Instructor Station from where operator training programme is loaded. Various plant scenarios / operating conditions, connected to the system are loaded and the operator undergoing training is expected to respond to the incident by operating the components and devices using the controls knobs/switches available in the Control Panel. A. Design and Development of Process Simulator and Control Logics. Design and Development of Process Simulator is split into three stages namely, process modeling, control logic modeling and virtual panel modeling. Here the process model represents the actual condensate extraction system functioning, the logical model represents the interlocks and virtual panel represents control panel. Process Modeling Any model development requires thorough understanding of the processes, component functions, process status under various plant conditions etc. The main source of system knowledge is technical discussions, going through design and operation notes, consultation with experts will act as source of information and knowledge. Based on the process oriented knowledge, a simplified conceptual network model consisting of main components is modeled. After successful completion of testing the conceptual model, expansion of the process network is carried out. It is done by adding devices like pipes, valves, filters etc. For monitoring of input / output process parameters of each component like temperature, pressure, level, flow etc, transmitters are modeled and linked to appropriate components in the network. (Refer fig – 4 for details). Figure – 4 Simulated Process Model Modeling of condensate extraction system involves development of Condensate Extraction System and the associated networks like Heater Vent & Drain System, Condensate Cooling Water System etc. The components / devices considered are Main Condenser, Condensate Extraction Pumps, Condensate Cooling Water Pumps, Low Pressure Heaters, Heat exchangers, Connecting Pipes, Filters, Isolation and control valves etc. The components and device are modeled using component specifications and process parameters that are collected, based on design documents of condensate extraction system. The isometric pipe drawings of condensate extraction system and connected subsystems are referred for detailed design of the process model pertaining to pipe / valve/ filter / other components regarding location, elevation, diameter, length etc. The component and devices are designed using the data collected and the process networks are generated by connecting these components and devices with nodes as per the process flow sheets. Logic Modeling Development of logic modeling needs a good understanding of the component functioning and associated faults. Process and Instrumentation diagrams, logic diagram and operation notes are referred as sources of information. A simplified logic sheet is drawn and used as a base for generating the logic model. Logic models are developed using logic gates and related algorithms, representing the actual system logics 2nd National Conference Mathematical Techniques: Emerging Paradigms for Electronics and IT Industries September 26-28, 2008 -128MATEIT-2008 and controls. It covers controls and interlocks of various components and devices connected to the system. Figure -5 Condensate Extraction System Logic Model The logic model takes the input process signals from the process model of condensate extraction system, processes the signals as per the set points / thresholds and interlocks with other devices and components. The logic model then generates output signal and sends it for display on the Virtual Panel / Control Panel and automatic control of the process component and devices. Virtual Panel Modeling Virtual Panels are basically soft panels which represents the actual control room panels. All the alarm windows, indicating devices, meters and control switches and knobs are modeled as per the Control Room Panel drawings. The Virtual Panels are created using the built in instrument and display models. Generally the Virtual Panels are used during the development stage of training simulator for testing the process model and the control logics. Figure – 6 Virtual Panel for Monitoring At the later stage, the Virtual Panels will be replaced by the replica control room hardware panels. Operator training will be conducted using hardware control room panels only. The interface between the Process, Logic and the Virtual Panel are established by passing the input /output / feed back signals as depicted in (Refer fig – 6 for details). B. Integrated Testing of the Models Integrated testing of the process network models is carried out in three stages. In the first stage, integration of process model, logic model and virtual panel model is carried out. In the second stage, integration of the above with the main steam and water system is carried out. At the last stage, the model is integrated with all the reactor subsystems and tested. The input and output process signals are checked and compared with the actual process parameters. Figure-7 Display of Condensate Extraction System parameters Any deviation observed in the process simulator output parameter when compared to the actual process parameter is narrowed down by tuning the network components. 2nd National Conference Mathematical Techniques: Emerging Paradigms for Electronics and IT Industries September 26-28, 2008 -129MATEIT-2008 Following figure gives details of process parameters monitored during integrated testing of the simulator. PROCESS SIMULATOR AS A TRAINING TOOL The process simulators are best utilized as a training tool to impart specific process knowledge. Operators can be trained on plant procedures, initial conditions to be followed, system malfunctions, status of the system under various plant conditions etc. Simulation of malfunction here refers to failure/ malfunctions/ tripping of components like pumps, valves, control systems, sensors etc affecting the system by altering the normal operation of the system. Figure-8 System performance curve during pump failure Such incidents and events connected to condensate extraction system are simulated for training the plant operators. The list of transients include loss of steam supply to deaerator, tripping of condensate extraction pump, loss of vacuum in the condenser, turbine trip etc. An example of condensate extraction pump trip event and the system dynamics is shown in the figures. Figure 9 Window annunciation indication including CEP pump trip