Before considering the device and principle of operation of nuclear
power plants, let’s dwell in more detail on the device
the core – the part of the reactor that contains the nuclear fuel
fuel and a controlled fission chain reaction proceeds.
Nuclear fuel, which is in most cases di-
uranium oxide (UO 2 ) enriched in the fissile isotope – 235 U – from-
Prepared in the form of tablets (see Fig. 4.2). Fresh fuel pellets
can be held in the hand – in this form they do not represent radiation
These tablets are placed in a tube made of zirconium alloy (in domestic
In other reactors, an alloy Zr + 1% Nb is used). Zirconium is selected, in
first, due to the high melting point (1845 0 С), and secondly,
due to the fact that it has a small cross section for the capture of thermal neutrons
(that is, it almost does not react with neutrons “intended” for
uranium, for a chain reaction of fission). This tube of pills UO 2 HA
a fuel element is called – a fuel element (see Fig. 4.3).
Figure 4.3 – Fuel element
However, separate fuel rods are not loaded into the reactor. They are connected between
themselves into the so-called fuel assemblies (FA) (see Fig. 4.4).
Actually, the set of fuel assemblies (or rather, that part of them, which contains
nuclear fuel), and forms a core (see Figures 4.4, 4.5).
So, inside the fuel rods there are UO 2 pellets , in which a chain
fission reaction and a large amount of thermal energy is released
gii, and outside they are washed by a coolant (most often – water),
which continuously cools the cladding of the fuel elements. An important requirement
to fuel rods – tightness of cladding (if the zirconium cladding of a fuel rod
is leaky, then radioactive fission products representing
radiation hazard, can get into the coolant).
The terms “core”, “TVS”, “fuel rod” will be needed for adequate
understanding of the operation of a nuclear reactor and nuclear power plant as a whole.
Figure 4.2 – Tablets of uranium fuel