Toshimi Tobimatsu

Measurement of Transient Flow Pattern by High Speed Scanning X-Ray Void Fraction Meter

In order to measure void distributions across pipe flow and to determine the transient flow pattern during blowdown from a high pressure water vessel to atmosphere, we have developed a high-speed scanning X-ray void fraction meter. The scanning X-ray beam is collimated by 8 hole-slits on a rotating disc. An X-ray beam scans across a pipe from top to bottom, according to the hole-slit movement. The maximum scanning frequency is 200 Hz. A void distribution curve can be obtained every 5.0 ms. Void signals are sent to a void distribution color display system that make it easy to recognize even a slug flow. Experimental results show that the system is very effective to determine how flow patterns change during blowdown.

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

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