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M.Uotan*; Yamaguchi, K.*; Y.Ogino*; H.Inuji*
PNC TN941 80-132, 12 Pages, 1980/08
Out-of-pile experiments were carried out with the sodium test loop SIENA in O-arai Engineering Center of PNC, and the feasibility studies had been made on the local boiling detection by use of temperature and flow fluctuations. The studies showed that the temperature fluctuation transferred the information on local boiling toward the end of the bundle, but hardly to the outlet. In addition, it was proved that the anomaly detection method, which used the algorithm of whiteness test method to the residual time series data of autoregressive model, is an effective one for detecting anomaly such as local boiling.
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.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.
