A Nuclear Power Station is a thermal power plant with Nuclear Reactors as the heat source. The heat generates steam that turns a steam turbine which is connected to an electric generator that produces electricity. Averagely, there are about 430 Nuclear Power Reactors operating in around 30 countries. Fuel, covering a small portion of the cost of production makes nuclear power stations to be considered as Base Load Stations.
Historical Background; Understanding Nuclear Power Stations
Electricity generation through Nuclear Reactors was for the first time generated in Tennessee, in the USA. Another nuclear reaction experiment was conducted in 1954, in the USA EBR-I station, near Arco, Idaho. By the year 1954,the first Nuclear Power Station to generate electricity for a power grid was started in Obninsk, (a Soviet City), and in October 1956, the first full scale Nuclear Power Plant was opened in Calder Hall, England.
Nuclear Stations Mode of Operation
To generate electrical energy, Heat is first produced (directly or indirectly) in a Nuclear Reactor by Fission. The Nuclear Reactor, being a light water reactor produces steam which is pressurized and fed into multiple steam turbines. The steam turbines expand and partially condense the steam with the remaining vapour channelled and condensed in a condenser connected to a cooling tower. The formed water is again pumped back to the Nuclear Reactor. All this process forms and completes a Water-Steam Cycle likened to the Rankine Cycle.
The successful processes and operations in the Nuclear Power Stations are made possible because of the following:
I. Nuclear Reactors
A Nuclear Reactor Device controls and initiates a Nuclear Chain Reaction. Nuclear Reactors are mostly used in Electric Energy Generation and Ship Propulsion.
In a Nuclear Power Station, Nuclear Reactors generate heat by Nuclear Fission. This generates steam that turns turbines to power ship propellers or electrical generators.
The process of Nuclear Fission is very radioactive; this makes the reactor core to be surrounded by protective materialsthat absorb radiations thus preventing the release of harmful radiations into the environment. Additionally, most reactors are surrounded by a Concrete Dome for protection against external impacts and internal casualties.
II. Steam Turbine
The Steam Turbine converts steam/vapor into Mechanical Energy.TheSteam Turbines are structured separately in the engine house away from the reactor building. It is structured to prevent debris (from operating turbine destruction) from being hurled towards the reactor.
Steam Turbines are installed separately in case of pressurized water reactors to ensure no passage of radioactive water in the initial stage. An Activity Meter tracks the outlet steam for detection of any available leaks that might be present in the steam generator. In opposition to this, boiling water reactors are passed through radioactive water in steam turbines, this makes the turbines part and parcel of the Control Area in the Nuclear Power Station.
III. Cooling System
The cooling system transfers heat from the reactors to another area where thermal energy harnessing is done to produce electricity. Again, the hot coolant provides heat for the boiler and pressurised steam from steam turbines.
IV. Feed-water pump
The Feed-Water System controls water levels in the Nuclear Reactor and steam generator. The Feed-Water Pump pumps water from the condensation unit, exerts more pressure and forces it through the steam generator (for pressurized water reactor) or into the reactors (in case of boiling water reactors).
V. Safety Valves
Safety Valves are used to prevent the reactor from exploding or bursting of pipes in case of any Emergency. They are designed in such a way that they can easily derive all the supplied flows with very small increase in pressure. If it’s the BWR, steam is projected into the Suppression Chamber for condensation. TheHeat Exchanger Chambers are then connected to the cooling circuit.
VI. Generator
Generators used here are High Power Rated. Their function is to generate Electrical Energy from Kinetic Energy in the turbines.
VII. Emergency Power Supply
A Nuclear Power Station requires up to two distinct offsite power stations that receive power from different transmission lines and are significantly separated from the Nuclear Power Station Switchyard. In some Nuclear Power Plants, turbine generators provide electricity for the station’s house loads. The power station service transformers keep the station online by tapping power from generator’s bus bars (output) before Step-Up by the Step-Up Transformer.
The Emergency Power Systems are important in maintaining safety in case of loss of offsite power and unit shut downs. Batteries ensure uninterruptible power supply to the Control Systems, Instrumentation and Valves. These batteries are charged by the Emergency Diesel Generators that provide AC current to also power AC systems for safe shut down of the reactor, Emergency Core Cooling and Used Fuel Pool-Cooling among other functions. The Emergency Diesel Generators are not used in backing up the Feed-Water Pumps, Circulating and Condensation Units and Reactor Coolant Pumps in Pressurized Water Reactors.
VIII. Personnel In a Nuclear Power Station
The people mostly found in the nuclear power station include; the Nuclear Engineers, Health Physicists, Reactor Operators, Emergency Personnel Teams and Inspectors from the Nuclear Regulatory Commission.
Apart from Managers and Professional i.e.Engineers, other workers in the nuclear power station should be from a Representative Trade or Labour Union.
Nuclear Power Station Economics
Nuclear power stations are a multi-billion dollar investment with extremely high capital costs. Comparison with other forms of power generation is based on Capital Financing, Construction Time scales, Cost Estimates on Nuclear Waste Storage and Recycling, and Decommissioning.
Again, other than Capital Costs and Construction Time Scales, it is vital to take into consideration measures that mitigate Global warming e.g. Carbon Emissions and Carbon Tax. For future efficiencies, Generation III Reactors, which are more improved and advanced reactor designs project an increased Fuel Efficiency of at least 17 percent And Low Capital Costs. Consequently, with Generation IV Reactors, Fuel Efficiency of up to 30000 per cent will be experienced and Nuclear Waste Eliminated.
Nuclear Power Station Economies also take into consideration the risk bearers for future uncertainties. In major occasions, Nuclear Stations were put up by the state or Regulated Electric Monopolies and the associated risks e.g. Fuel Prices, Operating Performance, Construction Costs etc. were borne by consumers. However, the emergence of Liberalization has led to various risks to be borne by suppliers and other operators.
For currently operating Nuclear Power Stations, there are increased requirements for Spent Fuel Management following the Fukushima 1 Nuclear Accidents In 2011. This plus unavailability of cheap gas and pulling out of Bankers and Potential Investors have proved to be a major problem for most nuclear projects.
Nuclear Stations’ Safety, Accidents and Attacks
Since 1970, there have been 5 Core Damage Accidents in different nuclear stations these include; Three Mile Island in 1979, Chernobyl in 1986 and Fukushima Daiichi that experienced three accidents in 2011. Since the inception of Generation II Reactors, the rate of accident happening has been estimated to be 1 after every eight years world-wide. To improve on safety and to curb accidents from happening, various measures have been taken including Advanced Reactor Designs and Nuclear Waste Management.
With regard to attacks,Nuclear Stations are vulnerable to attacks when military conflicts arise. Considering the last three decades, repeated attacks have been experienced in;
- Iran, in 1980, on the Al Tuwaitha Nuclear Complex.
- Iraq, in 1981, when the OsirakNuclear Research Centrewas completely destroyed by an Israeli air strike.
- Iran, between 1983 and 1988, when Iran’s BushehrNuclear Plantwas bombed six times by Iraq.
- SouthAfrica, in 1982. OnKoebergNuclear Power Plant, attacked by the armed Umkhonto we Sizwe while still under construction.
- Iraq, in 1991, when the USA bombed Pilot Facilities and Three Nuclear Reactorsin Iraq.
- Israel, in 1991, on DimonaNuclear Power, destroyed by Iraq scud missiles.
- Syria, in 2007, when Israel bombed a Nuclear Power Station still under construction.
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