Distribution and deposition behaviour of iodine species in multi-compartment reactor containments are subject to a strong interaction between thermal hydraulics and the structure surfaces. These processes distinctively influence the iodine concentration and the reactions in each individual compartment and hence the iodine source term.
The transport behaviour of molecular iodine (I2) was measured in three multi-compartment tests in the 60 m³ THAI facility. The steel vessel was subdivided into five compartments inter-connected by flow openings. In the first test phase the vessel atmosphere was stratified. Afterwards it was mixed by injecting steam and heating the vessel walls. Additionally helium was released. The distribution of iodine and helium in the vessel differed significantly because of I2 reactions with the surface. In test Iod-11 the relative humidity of the vessel atmosphere was high. In test Iod-12 additionally wall condensation occurred by a controlled cooling of the walls.
(The 60 m³ THAI vessel with a five-compartment configuration for the iodine transport tests)
In reactor containments the surfaces are coated with a decontamination paint. I2 reacts much faster with paint than with steel, but qualitatively the processes are comparable. The slower surface reactions in THAI tests offer the possibility to study their impact on the I2 transport for a long term under different flow conditions.
Data of tests Iod-11 and Iod-12 have been released by the German Ministry BMWi for the SARNET WP8 THAI Benchmark.
The main objective of the benchmark is twofold:
- Joint interpretation of tests Iod-11 and Iod-12,
- Benchmark of coupled thermal-hydraulic and iodine codes.
In detail the objectives are the investigation of the phenomena and the comparison of their modelling: iodine transport with gas and water flows, I2 adsorption on and desorption from a steel surface without and with wall condensation, I2 mass transfer between atmosphere and sump.
In the ongoing first step of the benchmark, Iod-11 is analysed by 8 different organisations using the codes ASTEC, MELCOR, COCOSYS and ECART. In a second step Iod-12 will be calculated.
Contact: Ari Auvinen, firstname.lastname@example.org