[en] The NEMO collaboration started the construction of the NEMO 3 detector heaving as objective reaching a 0.1 eV limit on mass of the Majorana type neutrino. The project has been accepted by IN2P3 in 1994 and the construction started in 1995, with the planned completion date 1998. The chosen project was similar to that of NEMO 2 up to a scale factor of about 10; it is this scale factor as well as a calorimetric enclosure of almost 4 π and measuring times of the order of several years that will permit reaching the necessary sensitivity. It is provided for studies of enriched simples of up to 10 kg in the emitting isotopes. NEMO 3 will allow investigation of the different processes ββ0ν, ββ0νm and ββ2ν up to lifetimes of 10²⁵, 10²³ and 10²² years. Such long lifetimes impose a severe selection on all the materials used in the construction of the detector to avoid that the expected signal be polluted from spurious signals induced by the own radioactivity of the detector. Also, a perfect knowledge of the radiation background of the laboratory and its effects on the detector is required. The paper gives a general layout of the NEMO 3 detector and presents the CENBG contribution to the construction of calorimetric wells, to the measurements of radioactive materials purity by γ spectroscopy and the computation by simulation of the effect of neutrons on the detector