[en] The actinides (e.g. "2"3"6U and "xPu isotopes) are present in environmental samples at the ultra trace level since atmospheric tests of NWs (Nuclear Weapons) performed in the past, deliberate dumping of nuclear waste, nuclear fuel reprocessing, on a large scale and operation of NPPs (Nuclear Power Plants) on a small scale have led to the release of a wide range of radioactive nuclides in the environment. Their detection requires the most sensitive AMS (Accelerator Mass Spectrometry) techniques and at the Center for Isotopic Research on Cultural and Environmental heritage (CIRCE) in Caserta, Italy, an upgraded actinide AMS system, based on a 3-MV pelletron tandem accelerator, has been operated. In this paper the progress made in order to push the "2"3"6U mass sensitivity and "2"3"6U/"2"3"8U isotopic ratio down to the natural levels is reported. A uranium contamination mass of about 0.05 μg and a "2"3"6U/"2"3"8U isotopic ratio sensitivities at the level of 3.2 × 10"−"1"3 are presently achievable.