Radiation Shielding

    Of course, we can not talk about nuclear reactors without saying a thing or two about radiation shielding. In a reactor, the core especially, is covered lead. Lead is thought to be the most efficient shield against radiation (all types: neutron, alpha, beta, gamma and so on). The thickness of the lead shield is determined by the power of the reactor and also other factors.

    It is important to know that shielding is absolutely necessary mainly because some radiation types can penetrate deep into the human body and some can even alter the DNA. Some radiations can cause grave illnesses or even severe physical damages.

    The amount of damage radiation can cause is expressed in Siverds or Bequerrels (another unit of measurement is the Curie, but it is not Internationally recognized). The human body is naturally exposed to radiation absorbing about 250 mS (mili Sivert) per year (don't panic this is a normal thing). This amount of radiation comes from cosmic radiation, the Earth's radiation, the construction materials that your house is built from and so on. This is perfectly OK. The thing to worry about is when your body exceeds this amount. At that point (depending on the type and intensity of the radiation) illnesses and other disabilities will start to appear. Keep in mind that we do not react the same to the same quantity and intensity. It may take up to several years for effects to appear but maybe for others it may take up to a couple of months or even weeks.

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.