Experiments ran as expected. The main objective of the experiments was to assure that natural circulation begins when core is heated despite of initially non-existent density differences. On the other hand the experiments were planned to prove that natural circulation is efficient enough to remove the heat from core even though vessel level decreases continuously andflow changes into two-phase flow. Experiments 1-4 were clearly for varying the position of the leak and radial distribution of the core power. Test number 5 was known to be difficult to perform already during the planning of the experiments. The purpose of this experiment was to investigate a situation, when the valves both in depressurizing and in level control system would not open. In this case the coolant flow path is only through the leakage. The objective was to find out a certain power level, which can generate a steam flow large enough to prevent the coolant flow back to the reactor vessel through a horizontal pipeline. The power control system in PACTEL is designed to operate up to 1 MW power level, so the power below 50 kW was expected to give difficulties. Table III describes the power variation used in the experiment.

TABLE III. TIME VARIATION OF POWER IN EXPERIMENT 5

The facility for SCRAM-system experiments consists of a scram tank, a blowdown tank, electric heaters, piping, valves and measurement instrumentation [9]. The main interest focused on the scram tank. Electric heaters located below the water level generate and maintain the steam volume and a layer of saturated water in the tank. After the scram signal the energy of the steam volume is used to move the control rods into the core. In the experiments orifices simulated the response of the control rods. High design pressure leading to a high steam temperature and high temperature differences in the facility during the system operation challenges the integrity of the whole scram system.

5. CONCLUSIONS

Lappeenranta University of Technology in co-operation with VTT Energy has carried out several experiments to investigate advanced light water reactor safety systems. The experiments studied passive safety injection system with PACTEL facility, long-term cooling of the WWER-640 reactor concept also with PACTEL and new SCRAM system of the SWR — 1000 reactor concept with separate test facility. Experiments have been successful and given useful information of different safety systems proposed for innovative reactor designs. Experiments have also proved that PACTEL integral test facility is flexible to use and to modify for various possible applications.