Tadashi Narabayashi

Study on two-phase flow dynamics in steam injectors

Abstract A steam injector is a simple, compact, passive steam jet pump for water injection or the primary loop recirculation system. An analytical study has been conducted on a large-scale steam injector for a next-generation reactor, in order to check the feasibility of a large-scale steam injector for which a demonstration test was not able to be conducted at present. Visualized fundamental tests were conducted in order to develop separate two-phase flow models to be installed in the PHOENICS Code. The models were verified by using high-pressure steam test data, as well as the visualized data. Then the large-scale injectors analyses were conducted using the newly developed models. The analysis results showed that the large-scale steam injector could work in the high-pressure range and discharged over 12 MPa, even at the rated flow rate of 61 kg s −1 (220 ton h −1 ).

Study on two-phase flow dynamics in steam injectors. II. High-pressure tests using scale-models

Analytical and experimental studies have been conducted on large-scale steam injectors for a next-generation reactor. The steam injectors are simple, compact, passive steam jet pumps for a steam-injector-driven passive core injection system (SI-PCIS) or steam-injector-driven primary loop recirculation system (SI-PLR). In order to check the feasibility of such large-scale steam injectors we developed the separate-two-phase flow models installed in the PHOENICS Code, and scale-model tests were conducted for both SI-PCIS and SI-PLR. A 1/2 scale SI-PCIS model achieved a discharge pressure of almost 8 MPa with 7 MPa steam and 0.4 MPa water, and a 1/5 scale SI-PLR model attained a discharge pressure of 12.5 MPa with 3 MPa steam and 7 MPa water. Both results are in good agreement with the analysis, confirming the feasibility of both systems. The systems will help to simplify the next generation of BWRs.

Study on crack opening area and coolant leak rates on pipe cracks

Abstract This study was executed to support the establishment of Leak Before Break (LBB) standards for high energy piping, by examining crack opening shape on the pipe surface and crack opening area which may be used in the leak rate analysis. To decide crack opening shape, a bending test was conducted by using 8in schedule 80 carbon steel pipe with an artificially produced circumferential through-wall crack, and crack opening displacement (COD) at some points along the crack were measured by clip gages. Results indicated that the crack opening shape was nearly elliptical. When the crack opening area changes from the pipe inner surface to the outer surface, it is also necessary to clarify which part of the crack opening area may be used in the analysis. Therefore expansion and reduction slits leak tests were done. Those results showed that the middle crack opening area between the inner and outer surfaces may be used in the analysis. By using the above results, the analytical leak rate calculated from the Tada-Paris equation and Moodys critical flow model was in good agreement with the measured one obtained from the leak test.

Experimental study on leak flow model through fatigue crack in pipe

Abstract Fundamental tests were carried out, using a flat plate test specimen, and pipe tests, using 4 and 8 inch pipes. A fatigue crack was introduced in both a flat plate test specimen and a pipe test specimen by applying stress cycles. A new pressure loss model for the flow in the fatigue crack was examined. To determine leak flow model parameters, surface roughnesses were measured. The model was used to modify Moodys critical flow model and gave a good agreement with the test results. Leak flow tests, continuous leak test and clad plugging test, were conducted. It was confirmed that the leak rate was stable for at least an hour. The crack surface roughness and crack length did not change during that time. It was also confirmed that a clad in a crack was blown by the leak flow immediately. The results are useful to support the establishment of LBB standards for high energy piping.

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.

Instabilities in Parallel Channel of Forced-Convection Boiling Upflow System, (IV)

The steam generator for LMFBR is composed of multiple tubes with the different flow conditions from each other. Most of the computer codes developed to evaluate the stability analyze a representative tube on the basis of the assumption of the constant pressure drop between the feedwater header and the steam one as single channel. Although the method selecting the representative channel has never been investigated, it is one of the purposes of this paper to examine the approximate method to evaluate the stable boundary exactly. It is another purpose of this paper to research the mechanism of the limit cycle oscillation observed in 1 MW SG without the thermal insulated downcomer of Power Reactor and Nuclear Fuel Development Corp., so that the effect of boiling in downcomer on the flow instability is studied experimentally. The slug excursion instability, which does not belong to Boures classification of two-phase flow instability, is observed in our experimental apparatus. Then, this mechanism is studied u...

Evaluation of Flow-Induced Vibration for Fixed Type Guide Rods of Shroud Head and Steam Dryer in ABWR

For the purpose of shortening outage schedules, fixed type guide rods are expected to be used in the ABWR. Guide rods are the component for a shroud head and a steam dryer installation. However, guide rods are located near the main steam nozzle, therefore flow-induced vibration (FIV) is concern due to the high steam velocity. In the present study, tests of the 1/1.87-scale model and computational fluid dynamics (CFD) analysis for the 1/1.87-scale test and the actual ABWR model were conducted to prove the structural integrity of fixed type guide rods against FIV. As a result of CFD calculation, reduced damping was more than 5 and reduced velocity was approximately 1.44, so resonance did not occur fixed type guide rods. The maximum fluctuating stresses were conservatively evaluated as 8 MPa by the turbulence and 2 MPa by the Karman vortex shedding. Both values were below allowable limit. As noted above, the structural integrity against FIV was confirmed, so it is feasible to use the fixed type guide rods in the ABWR. (authors)

Heat transfer characteristics of fluid flow in an annulus with an inner rotating cylinder having a labyrinth structure

The convective heat transfer coefficient was experimentally investigated in an annulus with an inner rotating cylinder to estimate the thermal fatigue of the inner and outer cylinders on the rotating machine. The following three conclusions were obtained: (1) Within the range of the experimental conditions, the heat transfer coefficient did not depend on the axial flow rate; rather, it showed a larger dependence on the inner cylinder rotating speed. (2) The heat transfer coefficient at the top of the labyrinth was about three times as large as that at the bottom. (3) An empirical correlation equation considering the gap between the inner and outer cylinders is proposed, which predicts the heat transfer coefficient on the rotating machine within ±30 percent.

HEAT TRANSFER CHARACTERISTICS OF FLUID FLOW IN AN ANNULUS WITH AN INNER ROTATING CYLINDER HAVING A LABYRINTH STRUCTURE

The heat transfer coefficient of fluid flow was experimentally investigated in an annulus with an inner rotating cylinder to estimate thermal fatigue of the inner and outer cylinders on the rotating machine. Following three points were found in the study. (1) Within the range of the experimental conditions, the heat transfer coefficient did not depend on the axial flow rate, rather it had a large dependence on the inner cylinder rotating speed. (2) The heat transfer coefficient at the top of the labyrinth was about three times as larger as that at the bottom. (3) An empirical correlation equation considering the gap between the inner and outer cylinders was proposed, which predicted the heat transfer coefficient on the rotating machine within ±30%.

Effect of Non-Condensable Gas on Steam Injector

Next-generation reactor systems have been under development aiming at simplified system and improvement of safety and credibility. A steam injector has a function of a passive pump without large motor or turbo-machinery, and has been investigated as one of the most important component of the next-generation reactor. Its performance as a pump is depends on direct contact condensation phenomena between a supersonic steam and a sub-cooled water jet. Although non-condensable gases are well known for reducing heat transfer, the effect of the non-condensable gas on the condensation of supersonic steam on high-speed water jet has not been cleared. The present paper reports the results of an experimental study of condensation of supersonic steam around turbulent water jet with model steam injector made by transparent plastic. The visual observation carried out by using high-speed camera. The non-condensable gas effect on the pump performance and flow characteristics are clarified by the image processing technique for the jet shape and gas-liquid interface behavior.Copyright