E. F. Hicken

Institute for Safety Research and Reactor Technology, Forschungszentrum Julich, Germany

H. Jaegers

Institute for Safety Research and Reactor Technology, Forschungszentrum Julich, Germany

Abstract. During shutdown the decay heat in commercial Boiling Water Reactors is removed from the core region by active and redundant pump/heat exchanger-systems which are, in addition, supported by emergency power. To study the capability of the newly developed emergency condensers to remove energy produced within the core region to a large water pool outside the Reactor Pressure Vessel by natural convection, a related test in the NOKO facility as performed. The pressure vessel in the NOKO facility has been flooded above the inlet line to the emergency condenser and heated up to about 100°C. The natural circulation resulted in a cool down of the water within the pressure vessel. With two specially designed grids equipped with up to 12 thermocouples the temperature fields in two cross sections were measured; no plume-effect was identified. The vertical temperature profile was measured with thermocouples. The test showed that decay heat could be removed some time after scram to an outside pool by natural convection processes; the time after scram depends on the emergency condenser heat exchange area.

1. INTRODUCTION

It is well known that also after scram decay heat in the range of 30 to 40 MW for a LWR with 1000-1300 MW(e) is produced within the reactor core. To avoid an evaporation of fluid active and redundant heat removal systems are mandatory; usually diesel generators are installed, in addition, to maintain the heat removal capability also in case of the Loss-Of — Outside-Power (LOOP).

The SWR 1000 is equipped with emergency condensers for the removal of decay heat mainly for transients without loss of coolant; for loss-of-coolant accidents these condensers will assist the decay heat removal for some time.

These emergency condensers do not need any power and no valves are needed to start the operation; they are “passive” by definition. Therefore, a test should be performed to evaluate the capability of these condensers to remove heat produced in the core region to the outside pool by natural convection and, in addition, at ambient pressure, as it will be during long term shutdown.

Although the removal of the decay heat cannot be expected from the beginning it would be beneficial if the decay heat could be removed after some time. This capability would then be diverse to the active heat removal systems.