2. Introduction Nuclear Reactor: A nuclear reactor is a device to initiate, and control, a sustained nuclear chain reaction. The most common use of nuclear reactor is for the generation of electrical power also termed as nuclear power.
3. Types of Nuclear Reactors 1. BWR-Boiling Water Reactor 2. PWR-Pressurized Water Reactor 3. PHWR-Pressurised Heavy Water Reactor 4. GCR-Gas Cooled Reactor 5. AGR-Advanced Gas-Cooled Reactor 6. LGR-Light Water Cooled - Graphite Moderated Reactor
4. BWR-Boiling Water Reactor In the boiling water reactor (BWR), the water which passes over the reactor core act as moderator and coolant. It is also the steam source for the turbine. The disadvantage of BWR is that any fuel leak might make the water radioactive and that radioactivity would reach the turbine and the rest of the loop. A typical operating pressure for BWR is about 70 atm at which the water boils at about 285C temperature. This operating temperature gives a efficiency of only 42% with a practical operating efficiency of around 32%, somewhat less than the Pressurized Water Reactor(PWR).
5. PWR-Pressurized Water Reactor In the pressurized water reactor (PWR), the water which passes over the reactor core act as moderator and coolant but does not flow to the turbine. It is sent in a pressurized primary loop. The primary loop water produces steam in the secondary loop which drives the turbine. The advantage PWR is that a fuel leak in the core would not pass any radioactive contaminants to the turbine and condenser. Another advantage is that the PWR can operate at higher pressure and temperature, about 160 atm and about 315C. This provides a higher efficiency than the boiling water reactor(BWR) , but PWR is more complicated and more costly to construct.
6. PHWR-Pressurised Heavy Water Reactor Pressurized Heavy Water Reactor (PHWR) is a Canadian design which is designed in Canada and subsequently exported to several countries (also known as CANDU). PHWR are heavy water cooled and moderated Pressurized Water reactors. Instead of using a single large pressure vessel as in a PWR, the fuel is contained in hundreds of pressure tubes. These reactors are fueled with natural uranium and are thermal neutron reactor designs. PHWRs can be refueled while at full power, which makes them very efficient in their use of uranium.
7. GCR-Gas Cooled Reactor Gas Cooled Reactor is also termed as Magnox reactor as the magnesium alloy is used to encase the fuel, natural uranium metal. These reactors are generally graphite moderated and CO2 cooled. The whole assembly is cooled by blowing carbon dioxide gas past the fuel cans, which are specially designed to enhance heat transfer. The hot gas then converts water to steam in a steam generator. They can have a high thermal efficiency compared with PWRs due to higher operating temperatures.
8. AGR-Advanced Gas-Cooled Reactor To improve the cost effectiveness of the gas cooled reactor, it was necessary to go to higher temperatures to achieve higher thermal efficiencies and higher power densities to reduce capital costs. This entailed increases in cooling gas pressure and changing from Magnox to stainless steel cladding and from uranium metal to uranium dioxide fuel. This in turn led to the need for an increase in the proportion of U235 in the fuel. The resulting design is known as the AGR-Advanced Gas-Cooled Reactor
9. LGR-Light Water Cooled - Graphite Moderated Reactor In this type of reactor heat is removed from the fuel by pumping water under pressure up through the channels where it is allowed to boil, steam generated here drives electrical turbo-generators. Many of the major components, including pumps and steam drums, are located within a concrete shield to protect operators against the radioactivity of the steam. The design of this type of reactor is known as the RBMK Reactor.