The French nuclear industry deals with technologies which will soon be thirty years old. If such technologies are not renewed they must last for another ten years- or more if the decision is taken to keep them working. There is a risk of technological obsolescence- something which is allowed for in other national and international projects. There is also the question of constant commercial demand- something also considered elsewhere in establishing contracts. Another problem is now beginning to emerge; the continuity and transmission of knowledge and experience concerning these plants. Personnel in the energy sector are being renewed. Most current employees are due to retire in the course of this decade. How is knowledge (both of maintenance and planning) to be transmitted to the new generations ? This knowledge includes written information but also knowhow and implicit working assumptions; expertise, experience, self-learning… In the United States the EPRI produced a technical dossier [EPRI 1]. The problem of knowledge of old technologies is therefore recent, but almost universal. As far as EDF knows, nobody is considering this subject in its entirety. Instead, each technology puts the emphasis on operation (and thus safety) according to a fixed timetable (ten-year visits, end of use). In this perspective the initial knowledge can be lost. It can happen, for example, that the need for renewal can oblige the agency to carry out a costly or difficult retro-engineering project so as to recover the original knowledge and technology. If we look ahead, the policy of long term development (notably extending the life of plants) requires us to consider the life-span of the different skills and knowledge required by each environment. So it is necessary to take into account the entire life cycle of a nuclear installation. We are working on organizing all this knowledge and building an innovating solution for easy acquisition, access and sharing knowledge and experiences. First we are creating an ontologybased common language for all involved and defining some applications on Intranet. Ontology, understood as an agreed vocabulary of common terms and meanings shared by a group of people, is a means for representing craft concepts upon which knowledge can be organised and classified. We shall present one of the first applications based on the Logic Diagrams Designer's ontology whose main goals are to keep in memory the craft knowledge about relay circuits schemas and to allow accessing and retrieval information. This choice of ontology as a basis provides an easy and relevant navigation, indexing and search of documents...