The electrical energy is generated to bring some development to the world. The electrical energy lights the world during night time. People can do their work even during night time without any disturbance because the electrical energy replaces the sun during night time. The energy is neither be created nor be destroyed. The electrical energy is generated by converting other form of energy. Generally mechanical energy is converted in to electrical energy. The electrical energy is generated by different methods; say hydro thermal energy generation, diesel power generation, gas power generation, and nuclear power generation. The nuclear power generation is a complex form of power generation method because the leakage of nuclear radiation is one of the major disadvantages of using nuclear power. The nuclear reactor is protected by automatic cooling device. The ESBWR (Economic Simplified Boiler Water Reactor) is one of the commonly used reactors for power generation. The ESBWR has emergency core cooling system (ECCS). ESBWR is a passive system, which is used to cool the reactor without using pumps. The ESBWR passive system is the safety system for cooling. The emergency core cooling system automatically senses the temperature inside the reactor. If the unusual heat is generated the emergency core cooling system will start the cooling process. The ESBWR is the cheapest boiler system. The ESBWR provides natural circulation to drive the coolant flow. The ESBWR has a four sub system they are gravity driven cooling system, isolation condenser system, the standby liquid control system, and the automatic de pressurization system (ADS). The ESBWR system is installed in many nuclear power plants because of its reliable operation. This research paper will give a detailed working of subsystems of ECCS.
2. Emergency Core Cooling System
The emergency core cooling system (ECCS) is the safety system for the reactor. The Emergency core cooling system is operated to remove the residual heat from the reactor core. The over heat of reactor is due to the interruption between the core reactor and heat sink. Even the reactor coolant fails; the ECCS system removes the residual heat from the reactor. The ECCS prevents the reactor from the following damage.
- If coolant system losses its operation, the ECCS system is operated to remove the residual heat.
- If the multi stream line breaks (MLSB), the ECCS is operated to shut down the reactor.
- ECCS protects the reactor from the loss of chemical.
The ECCS system prevents reactor from fuel cladding damage. The ECCS system is divided into high pressure and low pressure system. The high pressure system is operated while the nuclear reactor is at high pressure. The low pressure system is operated while the reactor is at low pressure. The automatic depressurization is used to reduce the reactor pressure.
3. Gravity Driven Cooling System
The gravity cooling system is one of the safety systems of ECCS. The large number of depressurization valve is installed at the top and side of the reactor, which is called depressurization valve (DVPS). If the level I of safety is not operated within 50 seconds, then the depressurization valve is fired. The DVPS valve removes the pressure from the reactor core. The DVPS valve will increases the availability of water inside the reactor core in order to reduce the temperature of reactor. The automatic availability of water is increased to maintain the temperature inside the core. The availability of water is increased within the RPV to cool the core. The DVPS maintains the lower boiling point in the core. If the level 1 is not operated within 100seconds, then the GDCS (Gravity driven control system) valve is fired. The gravity driven control system is a large water tank. The gravity driven control system is directly connected to RPV so the pressure within the GDCS will be equalized with that of RPV. The water from gravity driven control system will flow in to RPV. The gravity driven control system is one of the reliable systems, which help to increase the availability of water during the nuclear reactor system failure. The safety is one of the important methods while operating nuclear power plant. The GDCS can ensure the safety for the operation of the nuclear power plant. The water inside the RPV is converted in to steam due to the excess of heat, and the heat is vented by the natural convection through the heat exchanger. This system of operation is called passive containment cooling system.
- Isolation Condenser
The isolation condenser is one of the safety methods used in ESBWR operated nuclear power plants. The isolation condenser is a passive system. The heat exchanger located near the pool of the water. The heat boils in to steam, then the heat exchanger removes the stem from the reactor; then it falls in to the reactor again due to the effect of gravity. This process is used to keep the cooling water inside the reactor, and by this process it is unnecessary to operate the power feed water pump. The water boils in to steam, and the steam water is vented in to the outside atmosphere. This makes unnecessary to operate mechanical system to remove heat. The pool should be refilled to keep the process continuous.
The isolation condenser is not allowed to operate in the normal conditions. The steam enters the isolation condenser. If the isolation condenser is operated, the valve is opened; then the water falls in to the reactor by gravity. The isolation condenser is a safety system, which is operated for keeping the continuous availability of water inside the reactor core. The isolation condenser is a backup system for core protection. The isolation condenser system is the cheapest protection system. The isolation condenser is operated only if the tank of the condenser is filled with the condensed water. This cycle continuous until the bottom valve is closed.
- The Standby Liquid Control System
The standby liquid control system (SLCS) is the last step to control the damage of the reactor. The SLCS is not commonly used because the ECCS system will prevent the core damage even if some components in the ECCS fail. If the complete ECCS failure occurs, then the SLCS system is used. The SLCS system has a tank, which consists of borated water. The borated water acts as a neutron observer. The SLCS system has battery operated pump, which allow the injection of the borated water in to the reactor core. If the reactor operation is out of control, then the borated water will shut down the reactor. The SLCS system is not operated until all systems are failed because the SLCS system could cause sufficient damage to the plant. In ESBWR uses a reactor water cleanup system to remove the boron. If the reactor is stabilized, then the borated water in the RPV can be filtered. The SLCS is operated only in the unusual situation. The SLCS has two explosive valves and heated storage tank. The SLCS is the slow method of reactor shut down. The SLCS system is used in ESBWR system. The SLCS is an active system because the boron in the reactor is injected by the pump. The ESBWR has a four protection system gravity driven control system, isolation condenser system, automatic de pressurization system, and the final stage of protection is standby liquid control system. Skilled technicians are required while operating SLCS system because the SLCS system can cause a sufficient amount of damage to the reactor core. The standby liquid control system has a powerful pump valve, which is used to inject the borated water in to the reactor core.
- Automatic Depressurization System (ADS)
The ADS is not a cooling system, but it is necessary for the reactor production. If the high pressure cooling system fails, then the ADS system is operated. The ADS system can be operated manually or automatically. The ADS is automatically operated, if it receives the auto start signal. The ADS releases pressure from the RPV. The ADS releases pressure in to the reactor through pipes. The ADS is the back up for the high pressure cooling system. The ADS has two channels called “Division 1” and “Division 2”. The ADS has a two solenoid air pilot valve. One solenoid air pilot valve is energized by the division 1 and other solenoid air pilot valve is energized by the “Division 2”. If the ADS system is operated, then the solenoid pilot valve is opened to apply pressure. Each division has two sub channels. Division 1 has a sub channel called “A” and “C” and division 2 has a sub channel called “B” and “D”. The ADS system has seven safety valve to de pressurize the reactor. The ADS allow the low pressure to flow in to the reactor. The time delay signal allows the HPCI to recover the water level. The ADS is used as a standby system. The ADS system is used when the reactor suffers from the low pressure. The automatic unit senses the pressure level in the reactor and it help to maintain the pressure level in the reactor. The operation and maintenance of ADS system is simple. The ADS system is one of the primary protection systems in ESBWR unit. The instrument nitrogen is used to open the ADS SRV unit by providing sufficient pressure. The ADS system is the primary system while the SLCS system is the secondary system. If all the ECCS system fails, the SLCS system is operated to cool the reactor. The nuclear reactor is protected by the sophisticated equipments. Many protection units are installed to protect the reactor core. The safe generation of nuclear energy is important. The out of safety will bring a lot of destruction to people and to the atmosphere.
- Protection and Control unit
The nuclear plant has various control system like pressure control, level control, flow control, temperature control, etc. Each control unit is programmed to operate only in the abnormal condition. The control unit can be operated manually, if the automatic system fails. The various control units will ensure the system protection from the core damage. The ADS system act as a backup for high pressure cooling system because to maintain the pressure of the reactor.
7.1 Function of I&C system
I&C is the control system, which controls pressure, temperature, level, and flow control. . To keep the parameters within the desired value, the accurate measurement about the parameters are necessary. The parameters can be of temperature, pressure, flow control, and level control. The parameters measurements are compared with the set point and from the deviated value. The parameters are measured by sensor unit. The data accusation is necessary to receive the entire signal from the parameters. The separation is provided between the safety system and the low class system. The physical isolation is provided between the safety system and the low class system. The electric isolation is provided between the safety system and the low class system. The signal connection is provided between the safety system and the low class system. All the instruments are needed to be grounded to avoid the electric and the noise interference. The measurement sensors are used to measure the parameters like voltage, current, pressure, and air pressure. The main control provided by I&C technique is temperature, pressure, flow, and level control. The measurement control is done by the sensor unit. The control can be done to increase the safety of the plant. The pressure control can be made by using the pressure transducer. The flow control can be done by the differential pressure transducer. The level control depends on the temperature load.
7.1.1 Pressure control
The reactor pressure control is used to maintain the pressure of the reactor. The control is done by controlling the heaters. The pressure control has a power relief valve to control the steam. The stem pressure is maintained at an equilibrium condition. The pressure is controlled by transducer, which converts the pressure in to the analog signal (4-20MA). Transducer will be measuring absolute or differential pressure. The differential pressure converts the pressure in to unease signal to measure the non absolute pressure.
7.1.2 Level Control
The steam level control maintains the water level, which depends on the turbine load. The steam level control has components like flow signal, feed water signal, programmed water level, pressure compensated, and clean flow signal. The pump is varied to maintain the pressure between the steam feed pump.
7.1.3 Flow control
The flow control is measured by the differential pressure transducer. The differential level transducer measures the pressure drop. The pressure drop is the square root of the flow. The pressure drop is converted in to linear signal. The other type of measurement is done by ultrasonic. The ultrasonic is used to measure the radioactivity. The temperature, pressure, level, flow, and temperature switches are the inexpensive mean of measurements.
The non renewable source of energy is mostly used for power generation in the world. The renewable source of energy has some disadvantage like environmental issue, depleting in nature, cost, maintenance, etc. Most of the country has shutdown their nuclear power station because of waste disposal, and safety issue. The nuclear power is the most reliable and the cheapest method for power generation. The nuclear fission reaction is used to convert mechanical energy in to the electrical power. The nuclear energy is the radioactive energy, which can destroy the entire environment. People affected by the radiation should be treated carefully because there is no treatment for removing radiation from their body. The installation of nuclear power is not a simple task. The nuclear power plant should be installed in a specific location like near the sea, proper place has been allotted for waste disposal, and the nuclear plant needs the highly skilled employees to operate the plant. There are many nuclear disaster occurred all around the world so advanced technologies has been developed to improve safety inside the nuclear plant. The ESBWR unit can ensure the safety for the nuclear power plant because it has lots of security unit like ABS system, SLCS system, ECCS system, and gravity driven cooling system. The instrumentation and the protection systems are used to monitor the parameters for the control. The safety system is used to keep the system away from the accident. This can avoid 99% of the nuclear accident. The safety system can improve the plant security in many ways. The people and the environmental safeties are assured in the ESBWR system of reactor unit. By ESBWR unit many countries are safely operating their nuclear power plant. Even the ECCS system fails; the SLCS system can be fired to solve the accident.
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