The MetroFission project, a Joint Research Project within the European Metrology Research Program, aims at addressing a number of metrological problems involved in the design of proposed Generation IV nuclear reactors. As part of this project a secondary neutron fluence standard is being developed and tested at the neutron time-of-flight facility GELINA of the JRCs Institute for Reference Materials and Measurements. Such a secondary standard will help to arrive at the neutron cross section measurement uncertainties required for the design and safety assessment of new generation power plants and fuel cycles. Such a neutron fluence device contains targets for which the neutron induced cross section is considered to be a standard. A careful preparation and characterization of these samples is an essential part of the development of the secondary standard. In this framework a set of 235 U targets has been produced by vapour deposition of UF 4 on aluminium backings by IRMMs target preparation laboratory. These targets have been characterized for both their total mass and mass distribution over the sample area.