In the PWR type of reactor, everything is done to contain the radioactivity. There are 3 successive barriers (like a Russian doll) to prevent any leakage of radioactivity into the environment:
- The first is the sleeving which surrounds the fuel. The uranium is packaged in the form of small pellets stacked in long tubes called fuel rods. These tubes, made of zircaloy (a highly resistant ally) form a first barrier;
- the second is the reactor vessel, in 20 cm thick stainless steel;
- the third is the containment structure in 1m thick concrete (a double structure in the more recent reactors), which contains the reactor vessel, the primary circuit, and the steam generator. This total construction constitutes the reactor building.
The reactors equipped with these safety provisions are designed so that, even in the case of a major accident (a run-away reactor if the chain reaction goes out of control), there would be
no leakage of radioactivity outside the reactor building. Such is the case for the majority of reactors in the world: the United States, Canada, Western Europe, Japan, etc.
In some countries of the ex-Soviet Union, a few reactors still exist which use different procedures (RBMK) and which are less safe.
It was the absence of a containment structure at Chernobyl in particular which resulted in such serious damage.
The international community, within the framework of the IAEA (International Atomic Energy Agency), is helping these countries to improve or gradually close down the reactors considered to be dangerous.
Safety is also ensured by command and control procedures. The operation of nuclear reactors is by remote control from a command room where technicians are permanently watching over the safety of the installations; the operators are trained on simulators and are capable of reacting to any situation and of implementing the actions detailed in the procedures. Current nuclear reactors are designed to operate for several decades.
Reactor safety is also dependent on maintenance: regular servicing is carried out each time the reactor is stopped to reload the core, and a full overall maintenance programme is carried out every ten years.
In France, the safety authority, the DGSNR (Direction G énérale à la S ûreté Nucléaire et à la Radioprotection), an independent organisation, issues the authorisation to continue
working for a further decade after the ten-year visit.
The oldest reactors in service in France are more than 30 years old. In the United States, certain reactors have obtained authorisation to continue working for a total period of 60 years.
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