[en] The Idaho National Engineering Laboratory (INEL) is a participant in the nondestructive assay Performance Demonstration Program (PDP) as part of the U.S. TRU Waste Characterization Program. The PDP program was designed to help ensure compliance with the quality assurance objectives (QAO's) in the TRU Waste Characterization Program Plan. In June, 1996, cycle 1 of PDP program was completed at the Stored Waste Examination Pilot Plant (SWEPP) at INEL. The assay capability at INEL/SWEPP consists of a passive active neutron (PAN) radioassay system (for bulk fissile material assay) and a passive gamma spectrometry system (for isotopic mass ratio determination). The results from the two systems are combined to produce a single assay report which contains isotopic information (²³⁸Pu, ²³⁹Pu), density, total activity, alpha activity, TRU activity, TRU activity concentration, Pu equivalent Curies and fissile gram equivalent. The PDP cycle 1 tests were expected to test bias and precision of the assay systems under nearly ideal conditions; ie., non-interfering matrices and little or no source self shielding. The test consisted of two drums in which the source loading was not known by the site. One drum was essentially empty and the other was filled with ethafoam. As per PDP's instructions, the tests were to be conducted using the same procedures and equipment that normally would be used by SWEPP to assay real waste drums. This paper will discuss the lessons learned from these tests and INEL's plans to improve the capabilities of the SWEPP assay systems. 7 refs., 6 tabs