The core of a nuclear reactor

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

noisy danger.

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

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