Everything has been put in place to reduce the worldwide risks of nuclear energy as far as possible. User states are co-operating in this risk minimisation process. As with any industry, the nuclear industry has experienced a certain number of problems. But in the nuclear industry every incident, every anomaly must be declared.
Each case is analysed and corrective measures taken. An international scale exists according to which all incidents and accidents, even the most minor, are classified:
It is called the INES scale
(International Nuclear Event Scale).
The level 0 lists anomalies having no safety consequences.
From 1 to 3, incidents are listed, whilst from level 4 accidents are itemised.
The history of nuclear energy records two instances where subsequent analysis emphasised the role of successive barriers to contain radioactivity:
- in the United States, the accident at Three-Mile Island in 1979: the core of the reactor (PWR) melted although there was no incident outside of the site . The contamination was confined to the interior of the containment structure, which thus protected the population and the environment.
This accident was recorded at level 5 on the INES scale.
- in Ukraine, the 1986 accident at Chernobyl, where a reactor of type RBMK (without a containment structure)
exploded, resulting in appalling human suffering and major damage to equipment and the wider environment. It involved human error, the safety procedures having been flouted (automatic safety systems were blocked). The team lost control of the reactor and it ran wild, causing an explosion of steam inside the nuclear plant and a fire. The reactor core burnt for 10 days or so, before the fire was brought under control, discharging a significant quantity of radioactive products, into the atmosphere.
These products subsequently spread over hundreds of
km² reaching numerous countries. 32 people died in the 3 months following the accident and many others (several thousands) were seriously irradiated.
It was a major accident, classified level 7 on the INES scale.
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