[en] The BiPo project is dedicated to the measurement of extremely low radioactive contaminations of SuperNEMO ββ source foils (²⁰⁸Tl < 2 μBq/kg and ²¹⁴Bi < 10 μBq/kg). A modular BiPo1 prototype with its 20 modules and its shielding test facility is running in the Modane Underground Laboratory since February, 2008. The goal of this prototype is to study the backgrounds and particularly the surface contamination of plastic scintillators. After 3 months, a preliminary upper limit on the sensitivity of a 12 m² BiPo detector in ²⁰⁸Tl contamination of selenium source foils can be extrapolated to: A(²⁰⁸Tl) < 7.5 μBq/kg (90% C.L.)