J. Vihavainen, J. Banati,

Lappeenranta University of Technology, Finland

H. Purhonen,

VTT Energy, Finland

Abstract. Several series of experiments has been carried out at Lappeenranta University of Technology (LTKK) in co-operation with VTT Energy in Finland to investigate systems to be used in advanced and innovative reactors. The integral and separate effects test facilities and the flexibility to use and modify existing instruments enables the variety of the possible applications. The main goal of the experimental work is to provide test data for validation of computer codes used for nuclear safety analysis. VTT Energy started the studies on Innovative Nuclear Power Plant designs by investigating the Core Make-up Tank (CMT) behaviour on the Parallel Channel Test Loop (PACTEL) facility. The main objective was to provide new and independent information about Passive Safety Injection System (PSIS) performance. The latest project on the PACTEL test facility in European Commission 4th Framework Programme “Assessment of Passive Safety Injection Systems of Advanced Light Water Reactors” involved 15 experiments in three series. The purpose of these experiments was to increase information about condensation and heat transfer processes in the CMT, thermal stratification of water in the CMT, and natural circulation flow through the PSIS lines. The PACTEL facility was modified for investigations of the WWER-640 emergency cooling system for reducing primary pressure in Loss-of-Coolant Accident by equalising the primary-system and containment pressures and removing the residual heat from the core by natural circulation to the emergency cooling pool. The results of the experiments have been used for computer code validation in low pressure and low power conditions. Another innovative experimental project is a hydraulic scram system for SWR-1000 power plant concept by Siemens-KWU. The system was studied in the series of separate effect experiments. The system uses pressurised water and steam as a driving force of the hydraulic scram system. 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.

1. INTRODUCTION

PACTEL (Parallel Channel Test Loop) [1] is a full height, medium-scale integral test facility (volumetrically scaled 1:305) designed to simulate the thermal-hydraulic phenomena characteristic of the Finnish Loviisa PWR. VTT Energy together with the Lappeenranta University of Technology run the facility. PACTEL has three primary coolant loops with pressurizer, primary coolant pumps and horizontal steam generators, high-pressure emergency core cooling system (ECCS), and low pressure ECCS with two accumulators. The peak operating pressures in the primary and secondary sides are 8 MPa and 4.6 MPa, respectively. The reactor vessel is simulated with a U-tube construction consisting of separate downcomer and core sections. The core comprises of 144 full length, electrically heated fuel rod simulators with a heated length of 2.42 meters. The maximum total core output is 1 MW, or 22% of scaled full power. The three coolant loops with double capacity steam generators model the six loops of the reference power plant. Each steam generator has 118 U-tubes with an average length of 2.8 m.

The passive safety injection experiments in Lappeenranta started already in 1992 with a series of five experiments. These experiments simulated hot leg SBLOCA’s. The PSIS included a CMT and two PBL’s. The second series included four cold leg SBLOCA experiments in 1993. These experiments used similar PSIS as in the first series. In 1996, a new project of passive safety injection experiments with a CMT and one PBL started. The new experiments are a part of the European Commission 4th Framework Programme Nuclear Fission Safety program. Within this new project, three series of five experiments were completed, project continued until September 1998.

The PACTEL facility was modified for investigations of the WWER-640 emergency cooling system for reducing primary pressure in Loss-of-Coolant Accident by equalising the primary — system and containment pressures and removing the residual heat from the core by natural circulation to the emergency cooling pool. The results of the experiments are not yet finally analysed but they are being used for computer code validation in low pressure and low power conditions.

Another innovative experimental project has been a hydraulic scram system for SWR-1000 power plant concept by Siemens-KWU. The system was studied in the series of seven separate effect experiments during December 1999. The project was a part of VTT’s Advanced Light Water Reactor (ALWR) technology programme. It was funded by Siemens, Teollisuuden Voima Oy (TVO), TEKES and VTT. The system uses pressurised water and steam as a driving force of the hydraulic scram system.