Types of Nuclear Reactors

IntroductionNuclear Reactor:

A nuclear reactor is a device to initiate, and control, a sustained nuclear chainreaction.

The most common use of nuclear reactor is for the generation of electricalpower also termed as nuclear power.

Types of Nuclear Reactors1. BWR-Boiling Water Reactor2. PWR-Pressurized Water Reactor3. PHWR-Pressurised Heavy Water Reactor4. GCR-Gas Cooled Reactor5. AGR-Advanced Gas-Cooled Reactor6. LGR-Light Water Cooled - Graphite Moderated Reactor

BWR-Boiling Water Reactor

In the boiling water reactor (BWR), the water which passes over the reactorcore 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 waterradioactive and that radioactivity would reach the turbine and the rest of theloop.

A typical operating pressure for BWR is about 70 atm at which the water boils atabout 285°C temperature. This operating temperature gives a efficiency of only42% with a practical operating efficiency of around 32%, somewhat less thanthe Pressurized Water Reactor(PWR).

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 ina pressurized primary loop. The primary loop water produces steam in thesecondary loop which drives the turbine.

The advantage PWR is that a fuel leak in the core would not pass any radioactivecontaminants to the turbine and condenser.

Another advantage is that the PWR can operate at higher pressure andtemperature, about 160 atm and about 315°C. This provides a higherefficiency than the boiling water reactor(BWR) , but PWR is more complicatedand more costly to construct.

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 (alsoknown 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 containedin hundreds of pressure tubes.

These reactors are fueled with natural uranium and are thermal neutronreactor designs. PHWRs can be refueled while at full power, which makes themvery efficient in their use of uranium.

GCR-Gas Cooled ReactorGas Cooled Reactor is also termed as Magnox reactor as the magnesium alloyis used to encase the fuel, natural uranium metal.

These reactors are generally graphite moderated and CO2 cooled. The wholeassembly is cooled by blowing carbon dioxide gas past the fuel cans, whichare specially designed to enhance heat transfer. The hot gas then convertswater to steam in a steam generator.

They can have a high thermal efficiency compared with PWRs due to higheroperating temperatures.

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 higherpower densities to reduce capital costs.

This entailed increases in cooling gas pressure and changing from Magnox tostainless steel cladding and from uranium metal to uranium dioxide fuel. This inturn 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

LGR-Light Water Cooled - Graphite Moderated Reactor

In this type of reactor heat is removed from the fuel by pumping waterunder pressure up through the channels where it is allowed to boil, steamgenerated here drives electrical turbo-generators.

Many of the major components, including pumps and steam drums, arelocated within a concrete shield to protect operators against theradioactivity of the steam.

The design of this type of reactor is known as the RBMK Reactor.