Experiments and computational models for aerosol behaviour in the containment

Abstract

Aerosols generated by condensation of volatile fission products during nuclear reactor core meltdown accidents represent a major fraction of the accidental airborne radioactivity. A comprehensive experimental research programme was performed at Battelle to investigate the transport and deposition behaviour of aerosols in the containment, in order to support the development of computer models which estimate the fission product behaviour in the containment and the source term for potential radionuclide releases to the environment. Important steps in the investigations were: (1) DEMONA experiments. The first large scale aerosol test series performed in the Battelle model containment (BMC) (total volume 640 m 3), using an open (quasi one-room) geometry and condensation aerosols from a plasma torch generator. (2) VANAM experiments. Advanced aerosol tests in the BMC, using a multi-room geometry, mixed hygroscopic/non hygroscopic condensation aerosols, a double injection period, and varying thermohydraulic conditions. One of the experiments was subject of the International Standard Problem ISP 37. (3) KAEVER experiments. A systematic investigation of aerosol materials and mixtures and the related deposition behaviour, using a simplified one-room test vessel (10 m 3 volume) and advanced instrumentation. Important computer codes developed and/or validated in connection with the experiments are FIPLOC and NAUA; aerosol codes CONTAIN, MELCOR and GOTHIC-MAEROS were also applied. Some important results from the investigations and code developments are: (1) significant local aerosol concentration differences can occur in a multi-room geometry; (2) concentration differences can be caused by atmospheric stratification; and (3) deposition is strongly affected by material hygroscopicity and atmospheric humidity. (4) Satisfactory prediction requires a consistent treatment of multi-room thermal hydraulics, aerosol transport and steam condensation on particles. (5) Prediction results can be affected by numerical stability and nodalization (user experience). This paper presents a number of results of the experimental investigations and the present state of code modelling, with special reference to the findings of ISP37.