4. DESCRIPTION OF TEST
Pressurized water reactors in use in Finland reactors have certain unique features which make them different from most other PWR designs. The 6 horizontal steam generators differ from the commonly used vertical steam generators. The fuel rods are arranged hexagonally, and the fuel bundles of 127 rods are in BWR-like channels. The lower plenum volume is large because of the fuel followers of the control rods. In particular, the ECC water is injected directly into the upper plenum and the downcomer of the reactor vessel.
The main measurements in the experiments are coolant and rod cladding temperatures with thermocouples at different radial and axial locations. System pressure, pressure difference along the test section (core simulator), coolant flow rates and heating power are also measured. The data acquisition system consists of measurement and control processor, digital voltmeter and desk-top computer. The maximum speed to scan all 96 data channels during an experiment is once per second. With this speed it takes 10 minutes to collect a maximum of 58,800 readouts.
Three different fuel rod simulator bundles have been used in experiments, two bundles with nine-step chopped cosine power distribution and one with uniform linear power.
The simulator rods have been compared with the VVER-440 fuel rods by performing reflood calculations using the FLOOD4 computer code developed at the INEL, USA.