J. Vihavainen

Lappeenranta University of Technology

J. Tuunanen

VTT Energy

Finland

Abstract. VTT Energy in Finland and Lappeenranta University of Technology (LTKK) have run several experiments with the PACTEL (Parallel Channel Test Loop) facility to investigate the performance of Passive Safety Injection System (PSIS) of Advanced Light Water Reactors (ALWRs) in Small Break Loss-Of-Coolant Accident (SBLOCA) conditions. PACTEL is full-height medium scale (1:305) integral test facility originally designed to simulate thermal-hydraulic phenomena of the Finnish Loviisa PWR of WER-440 type. 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 Core Make-up Tank (CMT), two pressure balancing lines (PBL) and an injection line (IL). The second series included similar PSIS as in the first series. The European Commission 4th Framework Programme project “Assessment of Passive Safety Injection Systems of Advanced Light Water Reactors Reactors” involved experiments on the PACTEL test facility and computer simulations of selected experiments. The project involved 15 experiments in three series. The experiments provided 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 EC project included validation of three thermal-hydraulic computer codes. The APROS analyses were performed at LTKK. The analyses showed that the codes are capable of simulating the overall behaviour of the transients. The codes predicted accurately the core heat-up, which occurred when the primary coolant inventory was reduced so much that the core top became free of water. The detailed analyses of the calculation results showed that some models in the codes still needed improvement. Especially, further development of models for thermal stratification, condensation and natural circulation flow with small driving forces would be necessary for accurate simulation of the phenomena in the PSIS. The modelling of thermal stratification has already been improved and also tested with the APROS code. The new calculation results have showed significantly better behaviour in PSIS operation.

1. INTRODUCTION

PACTEL (Parallel Channel Test Loop) [1, 2] 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, two series of five experiments have been completed so far, and the third series is scheduled on September 1997. The project continues until September 1998. See Fig. 1 for a general view of PACTEL and Fig. 2 in the passive safety injection system in the fourth experiment series.

2. EXPERIMENTS WITH CMT AND TWO PBL’S

The main objective of the tests was the overall simulation of the PSIS behaviour. The experiments demonstrated the capability of PACTEL for the simulation of PSIS’s. The data did not provide very detailed information about phenomena in the CMT. The instrumentation of the CMT in the first test series was limited. The tests were partially aimed for investigation of possibilities to run passive safety injection tests on PACTEL. The experience gathered during this first series was then used in the specification of the test parameters and instrumentation of the second series.