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H.Tanab*; Miyake, Osamu*; M.hori*; Y.Ohmor*; Daigo, Y.*; Sato, Minoru*; T.Takah*
PNC TN943 81-02, 25 Pages, 1981/01
Analyses of leak propagation have been performed in order to support the selection of a design basis leak (DBL) for sodium-water reaction accidents in steam generators of the Japanese prototype fast breeder reactor, MONJU. For the purpose of estimating the possible maximum leak rate due to the failure propagation, a computer code, (LEAP) (Leak Enlargement and propagation), has been developed. This code analyzes the failure propagation process taking account of data from sodium-water reaction experiments throughout the world. This paper describes the model and structure of the LEAP code, a validation study, and results of the LEAP calculation for the MONJU steam generators and it has been concluded that the sodium-water reaction accidents can be terminated before the leak rate exceeds the DBL (one plus three DEG's) with the present detection system and safety devices.
Haga, K.*; M.Uotan*; Yamaguchi, K.*; M.hori*
PNC TN941 80-131, 11 Pages, 1980/08
The succeeding series of central-type blockage experiments were completed by the present one with 61-pin bundle test section. The interpretations of the present test results and those of our previous bundle configurations were summarized in the present paper. Concerning the single-phase flow, an empirical formula was derived to estimate the temperature rises behind various central-type blockages: τU
/d
= 35.3 (D/p)
, where τU/d is the dimensionless residence time and D/p is the Ring Parameter newly introduced here. This formula was validated to be effective within the region up to x
mockup scale (3.0<d<16.1 mm) and was also supported by the data of KfK and ORNL. It was guessed that the apparent peaking factor of temperature rises in the wake region that would be observed in case of bare bundle was about 1.5 and that the effect of three-dimensional distortion due to spacer wires was from 0.9 to 1.2. The estimation of peak temperature rise by the present formula and two kinds of constants led the conclusion that the central-type blockage will not cause local boiling without being detected by an in-core flow-meter. In case of sodium boiling two-phase flow, existence of a large boiling window could be identified through the experimental knowledge on oscillatory boiling and dry-out mechanism: the stable oscillatory behavior of a single bubble (or a cluster of bubbles) was never terminated untill the saturated region being widely built up enough to yeild the one-sided expansion of bubbly region and following clad melting. The oscillation improved the mass exchange between localized bubbly region and surrounding subcooled free stream region in compared with that under non-oscillatory conditions, and often relieved clads from melting.
Haga, K.*; M.Uotan*; Yamaguchi, K.*; M.hori*
PNC TN941 80-130, 10 Pages, 1980/08
Decay heat removal capability under boiling condition was investigated using an electrically heated 37-pin bundle test section. The flow was driven by natural circulation force of the out-of-pile sodium loop SIENA in O-arai Engineering Center, PNC. As the heater power was increased, the two-phase flow regime changed from bubbly flow to slug flow and then to annular or annular mist flow. In 15 runs, dry-out was not observed in the average exit quality region of less than 0.5. The results indicated the existance of a large "boiling window" for low flow rate and low power conditions.
M.hori*; Miyake, Osamu*
PNC TN941 80-91, 28 Pages, 1980/07
Simplified analytical methods applicable to the estimation of initial pressure spike in case of a large leak accident in LMFBR steam generators were devised as follows ; (1)Estimation of the initial water leak rate by the centered rarefaction wave method, (2)Estimation of the initial pressure spike by the one-dimensional compressible method with either the columnar bubble growth model or the spherical bubble growth model. These methods were compared with relevant experimental data or other more elaborate analyses and validated to be usable in simple geometry and limited time span cases. Application of these methods to an actual steam generator case was explained and demonstrated.
M.Uotan*; Haga, K.*; Kikuchi, Y.*; M.hori*
PNC TN941 78-141, 15 Pages, 1978/10
A series of out-of-pile experiments were conducted on local temperature rises due to non-heat generating blockages in 37-pin bundles. In the central blockage experiment, the central 24 subchannels of the bundle were blocked with a 5 mm thick stainless-steel plate at up-stream end of a grid spacer. The blocked area was 27% of the total flow area. In the edge blockage experiment, a stainless-steel plate blocked 39 subchannels of a 1/2 edge part of the cross-sectional area. In both cases of the central and the edge blockage, the pin surface temperature attained a local peak in the grid spacer behind the blockage and decreased with the distance from the blockage. The mass exchange rate and the coolant residence time in the wake rigions were evaluated from the observed temperature rises. The mass exchange rate per unit interface area behind the edge blockage agreed fairly well with that behind the central blockage. The dimensionless coolant residence time was found independent of Reynolds number except in the low number range, and the value obtained in the edge blockage experiment was about 2.4 times as much as that obtained in the central blockage experiment. when experimental results were extrapolated to the reactor condition, an edge blockage of more than 30% might cause local boiling in the wake region, while a central one would not cause local boiling in any blockage ratio less than 60 %. The temperature rises in the blocked grid spacer were also discussed.
Y.Ozaki*; Haga, K.*; Kikuchi, Y.*; T.Morik*; M.hori*
PNC TN941 78-140, 9 Pages, 1978/10
This paper deals with the measurement of acoustic noises with sodium boiling in an electrically heated 19-pin bundle which simulated an LMFBR fuel subassembly. The intensity of boiling acoustic noises measured with the waveguide method was much higher than the background noises such as mechanical and flow noises. A distinct peak, which was observed at approximately 10 kHz, may be attributed to the peculiarity of sodium boiling phenomena because this peak could easily be distinguished from the resonance peaks of the experimental system. The waveform of the boiling acoustic noises was similar to the burst type acoustic emission (AE). The propagation speed of acoustic noises agreed well with a prediction by the theory based on the assumption that the measured acoustic signals were transmitted on the pipe as surface waves (Rayleich waves) or Lamb waves.
Haga, K.*; Y.Daig*; T.Okou*; T.Kama*; Y.Kiku*; M.hori*
PNC TN941 77-39TR, 122 Pages, 1978/02
Out-of-Pile experiments were conducted to evaluate the thermal and hydrodynamic effects due to gas release into sodium flowing in a 37-Pin bundle, which consisted of a central gas-injector pin, seven electrically heated pins and other dummy pins. Each pin, except the gas-injector pin, was wrapped with a spacer wire. Argon was released transiently or continuously through a nozzle (0.3, 0.5, 0.8 mm in diameter) on the gas-injector pin into flowing sodium. The experimental conditions were as follows. Transient release experiments; [Gas plenum pressure : 29.6 - 75.9 bar] [Gas plenum volume : 70, 1,240 cm
] [Inlet sodium velocity : 1.95, 4.79 - 5.03m/s] [Heat flux : 36.4, 77.3 - 91.6W/cm
] [Inlet sodium temperature : 228 - 276
C] Continuous release experiments; [Gas plenum pressure : 6 - 64 bar] [Inlet sodium velocity : 0.45 - 5.07m/s] [Heat flux : 8.0 - 92.3W/cm] [Inlet sodium temperatures 238 - 290C] Pin surface temperatures increased by gas release. In the transient release experiments, the highest temperature rise was observed in the gas impingement area. Analyses of measured temperature rises by the transient heat transfer computer code SURFACE showed that the two-phase heat transfer coefficient after inception of gas release decreased to 1/20 - 3/20 of the sodium single-phase flow heat transfer coefficient. This two-phase heat transfer coefficient was similar to that obtained in the continuous release experiments. If the experimental results are extrapolated to reactor conditions, in which the heat flux is 200W/cm, the flow velocity is 5m/s, the temperature rise due to gas release is estimated to be less than 240C. The measured pressure pulses were less than 1/5 of initial gas plenum pressure in the transient release experiments. Neither damage nor deformation was observed in the pin bundle after the present experiments (total 14 transient experiments), and then the mechanical effect of FP gas release will be ...
M.Hishi*; M.hori*
PNC TN951 74-09, 77 Pages, 1974/11
For the purpose of studying pressure wave propagation in the secondary loop of the prototype Fast Reactor MONJU, we have taken up branches and bends for study and carried out experiments on pressure wave pro- pagation with respect to 2 kinds each of model specimens of branches and bends (Reduced scale of pipe diameter : About 1/12.5). The con- dotions for the experiments were as follows : ①Water was used as the medium for the pressure wave propagation. ② An input wave in which pulse rising time of pressure wave is about 1.5msec and wave height is 0.5kg/cm2-6.0kg/cm2 was used. The findings that we obtained as a result of the experiments include the following. ①We Studied in de- tail how the pressure wave propagates throughthe branch or bend parts, observing the wave form and height at the places near the branch part and near the bend part and have found that the results almost agree with the results obtained by the conventional one-dimensional, handling method. ②The e
