Mitsuo Komuro

Experimental coupling efficiency of shaping mirrors matching a 168-GHz gyrotron output wave to the HE/sub 11/ mode

This paper presents an experiment in which the phase- and amplitude-flattened output of a 168 GHz gyrotron was converted into the HE/sub 11/ mode, the basic transmitting mode in corrugated waveguides, by means of an external matching box (MBOX) comprising two curved-surface mirrors. In estimating the coupling efficiency between the gyrotron output wave and the HE/sub 11/ mode, an improved method was proposed in which the reconstructed phase of the gyrotron output wave at four distances are averaged. From the phase reconstruction with averaging, it was found that 76% of the gyrotron output coupled into the HE/sub 11/ mode in a corrugated waveguide, while a coupling efficiency of 85% was calculated for an ideal gyrotron output. A detailed discussion on the MBOX performance as well as the accuracy of phase reconstruction shows that this low coupling efficiency is due to the nonideality of the actual gyrotron output and that designing the MBOX mirrors based on the actual measurement at the gyrotron window can improve the coupling efficiency.

Analysis on the Dynamic Load in a Water Pool during Air Discharge from Submerged Sparger

This paper presents a study of the applicability of the VOF (volume of fluid) method to estimation of dynamic load in a water pool induced by oscillation of bubbles that are ejected through sparger holes. We choose the VOF method to simulate this phenomenon, and the pressure of a bubble is given by entropy change in order to consider the compressible effect of the bubble and the effect of gas coming into the bubble. In calculation of the airflow rate passing through the holes, the effect of two-phase pressure drop is incorporated. in order to investigate applicability of this method, a simplified blowdown test is carried out. According to the numerical results, the pressure-rime history inside the sparger and that in a water pool are both generally reproduced well with analysis, except that the magnitude of first peak pressure in a water pool is overestimated. The most likely reason is that the bubble cloud has especially low void fraction at the early stage of bubble formation, anti mail bubbles around a major bubble work as a buffer, which is discussed, in detail, in this paper.

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

Analysis on the Dynamic Load in a Water Pool During Air Discharge From Submerged Sparger

This paper presents a study of the applicability of the VOF (Volume of Fluid) method to estimation of dynamic load in a water pool induced by oscillation of bubbles that are ejected through sparger holes. We choose the VOF method to simulate this phenomenon, and the pressure of a bubble is given by entropy change in order to consider the compressible effect of the bubble and the effect of gas coming into the bubble. In calculation of air flow rate passing through the holes, the effect of two-phase pressure drop is incorporated. In order to investigate applicability of this method, a simplified blowdown test is carried out. According to the numerical results, the pressure-time history inside the sparger and that in a water pool are both generally reproduced well with analysis except that the magnitude of first peak pressure in a water pool is overestimated. The most likely reason is that the bubble cloud has especially low void fraction at the early stage of bubble formation, and small bubbles around a major bubble work as a buffer, which is discussed in detail in this paper.Copyright