The CHIP programme aims at improving the assessment of iodine quantities (source term) released in the event of a core meltdown accident in a nuclear reactor. The “phenomenology line” is designed to reproduce the thermal-hydraulic and chemical conditions existing in the primary cooling system during a loss-of-coolant accident. The aim is to represent the homogeneous and heterogeneous chemical reactions occurring during the transport of iodine from the damaged reactor core to the reactor containment.
The experiment involving the phenomenology line will be performed over the 2008-2012 period and will help to:
Quantify the fraction of volatile iodine in the primary cooling system for chemical reaction systems representative of those existing in a reactor. The speciation of the aerosols generated in the CHIP facility will also be studied to provide important data on the molecular forms of iodine condensed in the primary cooling system;
Validate software developed by IRSN and used to simulate the behaviour and transport of iodine under accident conditions (SOPHAEROS model in the ASTEC software).
Experimental device and test conditions
The device is composed of:
Several generators to produce chemical species in vapour or gas form (I2, H2/H2O, Cs, B, Mo, Ag, In, Cd...);
A line designed to heat the different reagents to temperatures between 1,500 °C and 1,600 °C. This temperature level corresponds to those encountered in the upper part of a core undergoing melting;
A transport line made from the same material as that used for the primary cooling system, and including two types of sampling devices designed and developed by the VTT Research Institute:
High-temperature sampling between 500 °C and 900 °C to study hot-leg break conditions;
Low-temperature sampling at around 150 °C to study cold-leg break conditions.
The parameters studied are the temperature at the sampling points, the concentration ratios of the chemical reagents, and the hold time in the system. They are representative of the different ranges encountered under accident conditions in the primary cooling system of a pressurised water reactor. The pressure in the CHIP facility is that existing in a primary system with a large break, equivalent to an absolute pressure of about 2 bar.