Hiromichi Adachi

Scale effects on countercurrent gas-liquid flow in a horizontal tube connected to an inclined riser

The scale effects of a flow path under countercurrent flow limitation (CCFL) (air/water or steam/saturated water) in a horizontal tube connected to an inclined riser have been studied. The studied geometry simulates that of a PWR hot leg. An analytical model with a two-fluid model was developed based on flow observation results in small scale experiments and then assessed with various scale experiments under various pressures to evaluate the scale effects. The assessments with small scale experiments revealed that the region controlling the flow limitation was shifted from the horizontal tube near the bend to the inclined riser part as the length of inclined riser increased. The degree of the shift became weaker for larger scale experiments under the assumption that the ratio of interfacial friction factor to wall-to-gas friction factor was maintained to be the same as that for small scale experiments. The degree of the shift was not affected by the change of pressure (0.3 MPa → 1.5 MPa).

SCTF-III test plan and recent SCTF-III test results☆

Abstract A test plan of the Slab Core Test Facility with Core-III (SCTF-III) has been clarified. The previous SCTF-III tests simulating PWRs with combined-injection-type ECCS indicated the following results on the thermal-hydraulics in the full-radius core: 1. (1) two-region separation and multidimensional thermal-hydraulics both before and after reflood initiation. 2. (2) practically no core cooling in the region far from the water downflow region before reflood initiation in spite of good core cooling in the water downflow region. 3. (3) good core cooling even in the two-phase upflow region after bottom reflood initiation. 4. (4) large fall-back flow rate in comparison with the prediction by a typical one-dimensional correlation.

Experimental study of two-dimensional thermal-hydraulic behavior in core during reflood phase of PWR LOCA.

Two-dimensional effects on the core cooling behavior during the reflood phase of a PWR-LOCA were experimentally studied by performing four tests with various radial core power profiles under the same total power and initial core stored energy conditions using the Slab Core Test Facility (SCTF). The heat transfer was enhanced and the cladding temperature was reduced for the higher and average power bundles in the steep radial power profile test especially at the upper elevation. The effect of radial power profile on the cladding temperature was quantitatively evaluated. For all tests with different radial power profiles, the collapsed water level in the upper plenum became higher in the hot leg side and the quench in the upper half of the core was delayed in the bundles corresponding to the outer bundles of a PWR core. The delay of the quench is considered to be caused by a flow stagnation trend in those bundles because the pressure in the outer bundles became higher than the pressure in the inner bundles ...

Coolability study on two-bundle scale flow blockage in the reflood process

Abstract A two-bundle scale channel flow blockage in the eight-bundle slab core test facility (SCTF) was examined for core cooling capability study in the reflood phase of a PWR-LOCA. The coplanar blockage with 60% blockage fraction resulted in promotion of quench for the elevation immediately above the blockage in relatively high reflood velocity tests. Conversely, this blockage led to delay of quench in low reflood velocity tests. Peak clad temperature, however, was not affected much by the existence of the blockage. These results are examined in comparison with the results of similar small scale test facilities. This examination revealed that the promotion of quench above the blockage was confined to a shorter length but the quench delay time was slightly longer for a large partial blockage than for a small blockage.

Characteritic of Low-Mass-Velocity Vertical Gas-Liquid Two-Phase Flow.

Low-mass-velocity two-phase flow in a vertical pipe shows lower void fraction than high-mass-velocity two-phase flow even though their qualities are the same. In order to clarify the flow characteristics of the low-mass-velocity two-phase flow, air, water two phase flow experiments were conducted under the froth or annular flow conditions. Experimental results show that wall shear stress is positive even though both gas and liquid superficial velocities are positive. Measured water film average velocity is negative under this condition. These results indicate that local flow reversal should exist along the channel wall. This local flow reversal gives rise to the low void fraction in low-mass-velocity two-phase flow. It is also clarified that the drift flux model can be applied to the low-mass-velocity two-phase flow with local flow reversal.

Verification study on alternative ECCS concepts for a PWR

Abstract An experimental study for alternative ECCSs for a PWR was performed with the ROSA-II facility. It was found through the tests that the combined injection of hot water into the upper plenum and cold water into the lower plenum accompanied by a low pressure coolant injection system in the hot legs is quite effective for core cooling through the whole period of a LOCA in the case of a cold leg break. The test results were compared with analytical results of the RELAP4J code. The code is found capable of estimating discharge flow behavior fairly well and can predict the overall fluid behavior in the tested method of the improved ECCSs. However, the calculated core heat transfer disagrees with the test data when the counter-cuurent flow of the two phases on the core is dominant.