ARTIST: introduction and first results

ARTIST (Aerosol Trapping In a Steam Generator) is an international project which investigates aerosol and droplet retention in a model steam generator under dry, wet and accident management conditions, respectively. The test section comprises a scaled steam generator tube bundle consisting of 270 tubes and 3 stages, one 1:1 separator unit, and one 1:1 dryer unit. As a prelude to the ARTIST project, four tests are conducted in the ARTIST bundle. These first tests address aerosol deposition phenomena on two different scales: near the tube break, where the gas velocities are sonic, and far away from the break, where the flow velocities are 3 orders of magnitude lower. With a dry bundle and the full flow representing the break stage conditions, there is strong evidence that the TiO2 aerosols used (AMMD 2-4 μm, 32 nm primary particles) disintegrate into much smaller particles because of the sonic conditions at the break, hence promoting particle escape from the secondary and lowering the overall decontamination factor (DF), which is found to be between 2.5 and 3. With a dry bundle and a small flow reproducing the far-field velocities, the overall bundle DF is of the order of 5, implying a DF of about 1.9 per stage. Extrapolating the results of the dry tests, it turns out that for steam generators with 9 or more stages, it is expected that substantial DFs could be achieved when the break is located near the tube sheet region. In addition, better decontamination is expected using more representative proxies of severe accident aerosols (sticky, multicomponent particles), a topic which is yet to be investigated. When the bundle is flooded, the DF is between 45 and 5740, depending on the mass flow rate, the steam content, and the water submergence. The presence of steam in the carrier gas and subsequent condensation inside the broken tube causes aerosol deposition and blockages near the break, leading to an increase in the primary pressure. This has implications for real plant conditions, as aerosol deposits inside the broken tube will cause more flow to be diverted to the intact tubes, with a corresponding reduction in the source term to the secondary. (authors)