They learned nothing from Chernobyl!

The Chernobyl disaster has profoundly transformed the global nuclear industry. Since the accident, safety has been integrated at all stages: design, operation, training, crisis management and sharing of feedback. Each area takes lessons learned from the accident to strengthen prevention and safety culture.

The International Atomic Energy Agency (IAEA) mandated the International Nuclear Safety Advisory Group (INSAG), established in 1985, to study the Chernobyl accident and make recommendations. The first two reports, INSAG-1 [1] and INSAG-7 [2], clarified the technical and human sequences at the origin of the accident and provided lessons learned. INSAG has published 28 reports, contributing to the establishment of an international safety doctrine and highlighting the importance of a strong safety culture that has become central to the sector.

Modifications have been made to the RBMKs (type of reactor at Chernobyl) to strengthen them.

• The positive void coefficient at the origin of the uncontrolled reaction has been reduced.
• The composition of the control bars was modified and their speed of insertion accelerated (their slowness had notably contributed to the accident).
• Protection systems have been added to prevent unstable operations.
• The operating rules prohibit certain hazardous configurations, such as those present during the accident.

These improvements have made it possible to increase the level of safety of RBMKs, despite a design that differs from Western standards.

The accident underscored the importance of the human factor. Operational errors and the absence or non-compliance of procedures contributed to the disaster [3]. This has led to the promotion of a “safety culture”, based on strictness and precision, transparency, and individual and managerial responsibility. Operators are better trained and encouraged to report any discrepancies without fear of sanctions. Crisis management doctrines have also been revised [6].

Transparency is overwhelmingly supported, breaking with the previous trend of silencing. Incidents must be promptly reported and analyzed, and the independence of the safety authorities strengthened. International bodies, including the World Association of Nuclear Operators (WANO) created after the accident [4], promote the sharing of experience and harmonizing of practices.

Finally, the integration of serious accidents marked the design of 3rd Generation reactors. Unlike previous reactors, these models integrate devices from the outset to manage extreme situations. On the EPR [7][8], systems make it possible to contain the corium and avoid breakthrough of the enclosure. Other devices limit the risk of hydrogen explosion and ensure heat removal, even in the event of a total loss of power supply.

In France, the fourth ten-yearly inspection of 900 and 1300 MW reactors (2nd generation) has increased safety in the face of serious accidents. It includes devices to stabilize corium, illustrating a convergence between the requirements applied to existing reactors and recent designs.