Freeman Dyson, in Princeton, New York, in April 2016.

Flames. With this spirit of independence that characterized him, the physicist Freeman Dyson passed away in February 2020, at the age of 96, for reasons other than the Covid-19 … This fertile scientist will have participated in major advances in quantum electrodynamics, where he contributed decisively to the success of the revolutionary approaches of Richard Phillips Feynman (1918-1988). His later activity as a theoretician in condensed matter physics and mathematics also aroused admiration for the incredible diversity and depth he exhibited. To be completely honest, let’s say that he was less happy when, late, he spoke about the climate, further from his areas of expertise …

Yet there was one of those side steps where Dyson truly demonstrated his genius. In the summer of 1956, he accepted the invitation to join a group of researchers for several weeks in an abandoned school in San Diego, to think about alternatives to the technological choices that were beginning to prevail in the developing civil nuclear industry. . With the means at hand and in an effervescence that had nothing to envy today’s start-ups, Dyson will be the spearhead of a collaboration that will lead to the invention of the Triga reactor, put on the market. three years later and still operated today. The essential characteristic of the Triga is its intrinsic safety: whatever happens to this reactor, a runaway reaction with core melt is structurally impossible. Unfortunately, its small size reserves it for peak activities, and today’s large power plants all still have to manage a risk of deviation with catastrophic consequences.

The genesis of the Triga is told by Dyson in his book The disturbers of the universe (1979, Payot, 1986). His pen is full of humor and mischief when he tells the story of this exceptional episode, but he also draws from it a deep reflection on the dynamics of research and innovation, the relevance of which remains intact forty years later. At the end of the 1970s when he wrote, the exhaustion of the enthusiasm and the initial post-war effort in the field of civilian nuclear power was palpable, with the cessation of several research and development programs, which inspires him this retrospective questioning: “Nuclear fission is no longer a promising playground, neither for young scientists nor for investors. What went wrong with civilian nuclear power? ”

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