Nuclear Reactor Vessel

 

    You might wonder where all the energy is produced in a nuclear reactor and how massive amounts of energy are controlled and kept away from bursting open the entire facility.

    The reactor vessel is a pressure vessel (a closed container designed to hold gases and liquids at a higher pressure than the ambient pressure) in which the coolant and the nuclear core are held. It is a container designed in such a way that it allows full control over the most important reactions that take place in a nuclear power plant. In order to produce optimum quantities of energy, the core, coolant and other components must be kept at a certain temperature and pressure. The vessel is build in order to make things easier and safer.

    The types of nuclear power plants are not classified by type of vessel but by type of nuclear coolant. For more information visit http://aboutnuclearphysics.blogspot.com/2010/07/types-of-nuclear-reactors.html

    Of the main classes of reactor with a pressure vessel, the PWR is unique in that the pressure vessel suffers significant neutron irradiation (called fluence) during operation, and may become brittle over time as a result. In particular, the larger pressure vessel of the BWR is better shielded from the neutron flux, so although more expensive to manufacture in the first place because of this extra size, it has an advantage in not needing annealing to extend its life.

    Note: fluence is the flux integrated over time. For particles, it is defined as the total number of particles that intersect a unit area in a given amount of time. It is considered one of the fundamental units in dosimetry.

Nuclear Reactor

    

 Photo by http://mir-0.deviantart.com/

    A nuclear reactor is a facility in which nuclear chained reactions are initiated and controlled. There are various types of nuclear reactors, but the most common uses are for producing electric power and for ship propulsion. The concept is fairly simple; the heat from the nuclear reaction is used to heat up water, then the steam spins some turbines in order to generate electricity.

    The idea is that when a large fissile atomic nucleus, such as uranium 235 or plutonium 239 absorbs a neutron, the nucleus splits into two lighter nuclei, along with the emission of other neutrons and gamma radiation. These new neutrons are later absorbed by other large nuclei and the process is happening all over again. The problem is that some neutrons are too fast, and might burst out of the reactor or cause damage. These neutrons are dealt with filters called moderators which reduces the velocity of the neutrons that pass through. In today's nuclear reactors, as moderators, it is used: water (75% of the world's nuclear reactors), solid graphite (20% of the world's reactors) and heavy water (5% of the world's reactors). Of course, other materials have been proposed but these are only in experimental stages. 

    The core of the reactor (where the nuclear reactions take place) emits an enormous quantity of thermal energy (heat) and therefore needs to be cooled. What do they use in order to cool the reactor ? The answer might surprise you - WATER. It's as simple as that. Sometimes, in certain conditions and in certain types of reactors, they might use a gas or a liquid metal or molten salt. Whatever the coolant may be, it is circulated past the core in order to absorb the heat that is produced. The heat is carried away from the reactor and is then used to generate steam. 

    The key components common to most nuclear reactors are:

• Nuclear fuel
• Nuclear reactor core
• Neutron moderator
• Coolant
• Control rods
• Reactor vessel
• Boiler feedwater pump
• Steam generators
• Steam turbine
• Electrical generator
• Spent fuel pool
• Nuclear safety systems
• Containment building
• Control room