Tomohisa Kurita

Primary-Side Two-Phase Flow and Heat Transfer Characteristics of a Horizontal-Tube PCCS Condenser

An experiment was performed using a horizontal condenser tube for the PCCS horizontal heat exchanger to confirm the performance and to estimate the thermal-hydraulic behavior in the tube thermally and visually. The PCCS, driven by the pressure difference between the drywell and wet-well, is a safety equipment to prevent the containment break for more than 1 day due to overpressurization at the containment spray failure situation. An annular flow, a wavy flow, a supercritical flow, a stratified flow and the liquid slug propagation are observed in the tube at the nominal condition. The flow regime transition, induced by the condensation, roughly agrees to the existing models. The observation also agrees with the condensate distribution in the tube circumference direction, which is suggested by the local thermal characteristics. (authors)

Heat Removal Capability of Core-Catcher With Natural Circulation

Toshiba has developed a core-catcher system. It is to be installed at the bottom of the lower drywell in order to stabilize a molten core flowing down from a reactor vessel. It consists of a round basin made up of inclined cooling channels arranged axisymmetrically, and the structure including risers, downcomers and a water chamber to get natural circulation of the flooding water. So it can cover entire pedestal floor and can work in passive manner.In order to confirm the heat removal capability of the core catcher with natural circulation, we have conducted full scaled tests in several conditions. Some important dimensionless numbers obtained from fundamental equations of the natural circulation are used for the tests.Using dimensionless number and to compare with several analysis, we can verify that the experiment is adequate to simulate the actual plant.Copyright

Heat Removal Capability of Core-Catcher in Consideration of Transformation of Cooling Channel

It is necessary to stabilize high temperature molten core in a severe accident for long time without electrical power. The core-catcher is to be installed at the bottom of the lower drywell in order to settle the molten core flowing down from a reactor vessel.Toshiba’s core-catcher system consists of a round basin made up of inclined cooling channels to get natural circulation of the flooding water. So it can cover all pedestal floor and can work in passive manner.We have been confirming an applicability of the core-catcher to actual plants. We have conducted full scaled tests with a unique cooling channel which has inclined rectangular flow section and changing the section area along flow direction in several conditions to evaluate the influence of the parameters on the natural circulation and heat removal capability. The test results showed good heat removal performance with nucleate boiling.However, we should consider a transformation of the cooling channel, for example, by the falling corium. So we calculate the assumed transformation of the cooling channel and conduct natural circulation tests with obstruction in the cooling channel. We confirm that natural circulation flow is stably continues and the cooling channel can remove prescribed heat, even if a flow area have got narrow locally.Copyright

Flow Characterization and Heat Transfer of Core-Catcher in Passive Safety System

A mitigation system which can keep core melt stable after a severe accident is necessary to a next generation BWR design. Toshiba has been developing a compact core catcher to be placed at the lower drywell in the containment vessel. The cooling water for the core catcher is supplied from the passive flooder and PCCS drain line. After the core catcher is flooded, the molten core would be cooled by both overflooding water and inclined cooling channels, in which water is boiling and natural circulation is established. So the core catcher can operate in passive manner and has no active component inside the containment.This paper summarizes flow dynamics and heat removal capability in an inclined cooling channel of core catcher when cooling water flows by the natural circulation.Copyright