Institute for Safety Research and Reactor Technology, Forschungszentrum Julich A. Schaffrath, F.-P. Weiss

Institute for Safety Research, Forschungszentrum Rossendorf Germany

Abstract. For the study of the effectiveness of passive safety systems a high pressure (up to 7 MPa) and high power (up to 4 MW) test facility — named NOKO — has been constructed and operated at the Forschungszentrum Julich. From 1996-1998 this facility was used for a project within the 4th FP of the EU "European BWR R&D Cluster for Innovative Passive Safety Systems". An overview and selected results are given for the tests with two bundles of the emergency condenser, with the building and plate condenser, with 4 different passive initiators, with a passive flooding system and with decay heat removal tests during shutdown. It has been decided to decrease substantially the safety research at the Forschungszentrum Julich; to maintain the experimental competence for two-phase flow the NOKO facility will be transferred to the Forschungszentrum Rossendorf by the end of the year 2000 up to the beginning of the year 2001. The facility will be named TOPFLOW; the main objectives of future tests will be oriented towards more generic research: investigation of steady state and transient two-phase flow phenomena especially transient two-phase flow patterns, the development of two-phase flow instrumentation, the generation of a data basis for Computati­onal Fluid Dynamic (CFD)-Code validation and testing of heat exchangers and safety systems. An overview will be given about the modifications and improvements related to the test facility and the planned tests.

1. INTRODUCTION

It is a good demonstration of safety culture if vendors, utilities and licensing authorities equally make an effort to increase the safety level of Nuclear Power Plants — existing and future ones. Recognising that design and main licensing requirements were developed in the sixties and seventies it is appropriate now to develop new solutions as well as new licensing requirements, evaluate the feasibility of these solutions and possibly test their effectiveness.

The goals for new safety systems are evident: effective, simpler, more reliable, cheaper and licensable. Without major efforts, it can be stated that passive safety systems proposed up to now are simpler and are expected to be more reliable. They also seem to be licensable if the remaining uncertainties with respect to requirements for redundancy and diversity have been solved. An assessment of the costs is complex and cannot be discussed here.

During recent years and still ongoing are efforts to experimentally study the effectiveness of passive safety systems and compare the results with code calculations; due to the different operating conditions (e. g. small driving forces) as compared with active systems, some models in computer codes have to be improved. Therefore, it was decided to plan, construct and operate a facility at Forschungszentrum Julich to study experimentally and analytically the effectiveness of the emergency condensers planned to be installed in the SWR 1000. This facility was named NOKO.

Due to the decision by the board of directors of the Forschungszentrum Jiilich to reduce substantially the safety research for Nuclear Power Plants at Jiilich and the decision to maintain the experimental competence for two-phase flow relevant to reactor safety it has been decided to transfer the NOKO facility from the Forschungszentrum Jiilich to the Forschungszentrum Rossendorf by the end of the year 2000/the beginning of the year 2001. This facility will be named TOPFLOW.