Schoolzone #1

NUCLEAR REACTORS


Here we present a brief and quite simplified description of a nuclear reactor's operation as part of a nuclear factory:

-What is a nuclear reactor?

It is the place, the shell where nuclear reactions take part under controlled conditions in order to obtain enough power (MWh) to move generators .It is pretty much as what a boiler is to thermoelectric factories...




-What does it contain ?

A nuclear reactor contains (usually) as a nuclear fuel Uranium-238 (or enhanced Uranium-238 i.e contains a bigger percentage of Uranium-235 which is highly fissionable).A reaction is caused when a neutron (the uncharged particle of a nucleus) collides with Uranium-235 and causes its fission into smaller nucleus (of atomic number from 56-140).So, one reaction results  to one or more neutrons ,2 new neuclei and a small amount of energy. A fraction of the new neutrons collides with Uranium 235 or 238 if their energy is high enough causing new circle of reactions and so goes on, the so called chain reactions.If we sum up the whole amount of energy emitted  by the fissions we are able to obtain about some thousands of megaWatts per hour (it depends on the amount of the fuel and its U-235 percentage).

-What is the nuclear reactor's core?

Uraniun is usually put as bars inside the reactor and more specifically inside a closed space inside the reactor called the core (see the pic below, the yellow box) .The core also contains liquid substances of small atomic mass such as light (H20) and heavy (D20 ) water as a "controller" to neutrons energy in order to succeed chain reactions.Both bars and core have proctetive cover.

-How do we "stop" the a nuclear reactor?

In order to slow down the chain process we need to restrict the neutrons.How? We put inside the core, bars that are made of an absorbent element that absorbs the neutrons and prevent their collisions with the fuel ( Cadmium -Cd) .These bars under normal conditions are kept outside the reactor and are used only when needed. In cases of emergency usually automatic systems activate their sinkage into the core.

-Where does the power go?

The energy produced is usually transfered into water ,boiling it or warming it up. The water turns into steam and steam motivates the generator. This is the circle in general. But IF all this energy has nowhere to go (like a possible accident) it is then  possible that it turns against the system itself melting the core down and allowing  its radiative elements to escape into the environment . Spilling water to freeze the meltdown can cause explosions in such high temperatures because of the rapid decomposition of water into hydrogen and oxygen.

-What is the worst case globally?

That i cannot know..Already people of Japan are evacuating cities, abandonning their homelands, we cannot really think about ourselves while being so far away.What i know is that it is maybe worse in the long run  for the radiative elements to escape into the ground than the atmosphere , as in the atmosphere these elements will be diluted and transfered attenuated with the wind .Being transfered in the ground will interfere with the food chain and sooner or later we will be all globaly affected. Lets not kid ourselves , nuclear factories are usually "safe " but  even one accident's consequences can be very severe and irreversible. The best solutions is "green energy".