A high purity Fe15Cr alloy has been irradiated with 1 MeV electrons at 573 K to doses up to 0.7 dpa. Alpha' precipitates have been revealed by Atom Probe Tomography (APT). They were not associated with the irradiation induced defects confirming a radiation-enhanced mechanism. Comparison with literature shows that alpha' precipitation occurred after similar doses after neutron and electron irradiations but not under ion irradiation. Electron irradiation is more efficient to enhance alpha' precipitation. The same a Cr solubility limit as under neutron irradiation were found. alpha' Cr equilibrium composition at 573 K has been measured for the first time with APT.