AHMED: Facility to study hygroscopic aerosol behaviour in LWR containment conditions

AHMED (Aerosol and Heat Transfer Measurement Device) has been constructed to study thermal-hydraulic effects on aerosol behaviour in nuclear power station containment during a hypothetical severe reactor accident where the reactor core melts and releases radioactive aerosols into containment. In wet conditions steam condensation on particles, coupled with agglomeration, can provide much more effective particle growth mechanism than dry agglomeration alone. The growth is enhanced because the aerosol released from the core contains hygroscopic material which absorbs water under 100% relative humidity. Under favourable conditions particles may grow to sizes larger than 10 mu m. These particles will settle rapidly, after which a small fraction of micron-sized (or smaller) particles remains airborne. Our ability to model quantitatively the effect of steam condensation on particles depends strongly on both thermal-hydraulic and aerosol modelling. It is also important to have the capability to calculate aerosol behaviour in multicompartment volumes.