Chernobyl: 40 years on, an accident still at the heart of scientific interrogations

Editorial revision 2026

On April 26, 1986, the explosion of reactor No. 4 at the Chernobyl nuclear power plant in Ukraine caused one of the most severe industrial disasters ever recorded.

Forty years later, the accident remains a major case study for the scientific community. It has profoundly shaped the understanding of nuclear accidents, the dispersion of radioactive releases, and their long-term health and environmental effects.

Over the years, the radioactivity and the hazard posed by the radioactive releases have significantly decreased. Most fission products with short half-lives have disappeared. The activity of cesium-137, the main remaining radionuclide, has fallen to 40% of its initial level.

On the website laradioactivite.com, several articles revisit this major accident and shed light on its main aspects: the circumstances and causes of the accident, the nature and scale of the releases, as well as the formation and trajectory of the radioactive cloud across Europe, including France. Other content details the role of the main emitted radionuclides, notably iodine and cesium, and their evolution in the environment.

Our website also provides analyses of the consequences of the disaster, estimates of the number of victims, the environmental impact, as well as the reactor confinement systems implemented over time, from the first sarcophagus to the new confinement arch.

The current state of the accident site (affected by the ongoing war in Ukraine), as well as lessons learned at the international level, are also presented. This information is based on scientific reviews.

On the occasion of the 40th anniversary of the accident, these resources invite readers to revisit the established facts. They place the historic Chernobyl accident in a long-term perspective and provide insight into this disaster through the many scientific studies it has been the subject of, which have progressively contributed to a better understanding: observations, interpretations, and feedback from experience.