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Steam generator tube rupture (SGTR) incidents, such as those, which occurred in various operating pressurized, water reactors in the past, are serious operational concerns and remain among the most risk-dominant events. Although considerable efforts have been spent to understand tube degradation processes, develop improved modes of operation, and take preventative and corrective measures, SGTR incidents cannot be completely ruled out. Under certain conditions, high releases of radionuclides to the environment are possible during design basis accidents (DBA) and severe accidents. The severe accident codes' models for aerosol retention in the secondary side of a steam generator (SG) have not been assessed against any experimental data, which means that the uncertainties in the source term following an unisolated SGTR concurrent with a severe accident are not currently quantified.The accident management (AM) procedures aim at avoiding or minimizing the release of fission products from the SG. The enhanced retention of activity within the SG defines the effectiveness of the accident management actions for the specific hardware characteristics and accident conditions of concern. A sound database on aerosol retention due to natural processes in the SG is not available, nor is an assessment of the effect of management actions on these processes. Hence, the effectiveness of the AM in SGTR events is not presently known.To help reduce uncertainties relating to SGTR issues, an experimental project, ARTIST (AeRosol Trapping In a Steam generaTor), has been initiated at the Paul Scherrer Institut to address aerosol and droplet retention in the various parts of the SG. The test section is comprised of a scaled-down tube bundle, a full-size separator and a full-size dryer unit. The project will study phenomena at the separate effect and integral levels and address AM issues in seven distinct phases: Aerosol retention in 1) the broken tube under dry secondary side conditions, 2) the near field close to break under dry conditions, 3) the bundle farfield under dry conditions, 4) the separator and dryer under dry conditions, 5) the bundle section under wet conditions, 6) droplet retention in the separator and dryer sections and 7) the overall SG (integral tests). Prototypical test parameters are selected to cover the range of conditions expected in severe accident as well as DBA scenarios.This paper summarizes the relevant issues and introduces the ARTIST facility and the provisional test program which will run between 2003 and 2007.

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The European Commission-funded shared-cost action project PHEBEN2 brings together 13 partner organisations to understand the source term aspects of the integral Phebus FP experiments, to validate integral LWR severe accident codes against the test data, to develop and apply criteria regarding the strengths and weaknesses of the codes for plant applications, and to propose guidelines for their optimum use for this purpose. At the half-way point of the project, contributions to the final interpretation report of the first Phebus test FPT0 have been completed and work on the interpretation of the following test is proceeding. A detailed investigation by CFD and particle tracking appears to have identified the cause of the systematic underprediction of deposition in the steam generator tube of the Phebus circuit. Containment calculations using lumped-parameter codes have been supplemented by extensive CFD analyses, revealing complex circulation patterns within the relatively simple containment geometry of Phebus. Iodine chemistry studies have been made of both FPT0 and FPT1. Concerning criteria and code assessment for plant applications, a short list of safety-important phenomena explored in Phebus has been prepared, and partners have drafted a report analysing for each phenomenon its safety importance, the experimental data available, the modelling approach adopted in PSA codes, and the expected uncertainties. Jones et al. / Nuclear Engineering and Design 221 (2003) 225-240