[en] This document describes the method used to compute the activation of the structure components near the electron-positron converter of the Lure accelerator (Orsay). Activation comes from photon and neutron reactions on nuclei belonging to the concrete structure. Only radio-nuclides with a half-life greater than 200 days are considered penalizing for dismantling operations. The main photonuclear reactions produce the following nuclides: Na²², Cl³⁶, Mn⁵⁴, Nb⁹², Ba¹³³, Co⁵⁷ and Co⁶⁰. The main neutron reaction generate the following nuclides: H³, C¹⁴, Cl³⁶, K⁴⁰, Co⁶⁰, Ni⁶³, Zn⁶⁵, Se⁷⁹, Zr⁹³, Ag¹⁰⁸, Ag¹¹⁰, Ba¹³³, Cs¹³⁴, Eu¹⁵², Eu¹⁵⁴, Fe⁵⁵, Ca⁴¹, Na²², Mn⁵⁴, Cs¹³⁷, Nb⁹² and Ti²⁰⁴. The MCNPX code has been used to compute the values of the photon and neutron fluxes received by the structure components, the activation has been computed with the Cinder code from the flux values. The main contributors for radioactivity on long term basis appear to be Ca⁴¹ and Ni⁶³. Calculations have been compared with the measurement of activities of 3 concrete samples drilled out from the structure. The results of the comparison are given for Co⁶⁰, Cs¹³⁴, Eu¹⁵² and Eu¹⁵⁴. The computed values appear to be greater by a factor varying from 2 to 5 which is consistent with the method used that naturally overestimates the activation. These results are considered as satisfactory for performing waste zone labelling. (A.C.)