ABSTRACT: The period of the Sixties sees the energy production in France, until there of thermal and hydraulic origin, relayed by other dies in a context of industrial and commercial redeployment. Engineers of the "Ponts" join the Commission of the Plan, in particular the Management ot the Forecast of the Ministry for the Economy, being diverted, apparently, from the technique to prefer searchs for operational studies of mathematical economy. Others leave the public sector to join the private sector. Two achievements, resting on a scientific base with tempting characteristics, are projected in a prospective vision of the regional development of the West of France. EL 4, power station of demonstration being used for the experimentation of a solution adopted in Canada, is built between 1961 and 1967 in a disinherited canton. Having a power of 70 megawatts, it must operate with a moderated reactor with heavy water and a cooling with carbonic gas. The experiment in the mounts of Arrée is established in the perimeter of the future regional park of America composing with several partners with the unexpected intrusion of "the street of Valois", direction of Architecture. Technical sophistication of old use of the force of the tides, generated by the intrusion of econometrics in the system of thought of Polytechnicians "X" and "Ponts et Chaussées", the slash of the dam-bridge of the Rance river beyond its strong cognitive pregnancy take on an iconic significance in a particular economic context. In the course of its completion, is inaugurated in November 1966 by the Général de Gaulle. An audacious structure, sophisticated, proud, attractive, monumental, inviting to an ambiguous contemplation on the background of a modification of the site morphology. Two imprints resulting from an architectural expression of an intense rationality : Subordination? Agression? Deterioration of two sites? The integration of these equipments had value of test. Which were the fields of transmission of these two production industries of electrical energy, tested in France, on an experimental basis, remained without continuation? What represented the fields of application of these two prototypes built in Brittany, estimated like "flattering gifts" for some, inappropriate to the territory for others or like missed occasions. Is the scientific creativity a guarantee of growth and economic success? Two challenges as regards civil engineering with innovating technical applications. A competence : the one of Robert Gibrat and other personalities. From a double point of view, the one of the historian of arts and architecture and the one of the historian of civil engineering, we propose to decipher these two buildings, from their genesis to their iconoclastic dimension.
