Modeling of thermal hydraulic instabilities in single heated channel loop during startup transients

Citation
J. Paniagua et al., Modeling of thermal hydraulic instabilities in single heated channel loop during startup transients, NUCL ENG DE, 193(1-2), 1999, pp. 207-226
Citations number
35
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Nuclear Emgineering
Journal title
NUCLEAR ENGINEERING AND DESIGN
ISSN journal
0029-5493 → ACNP
Volume
193
Issue
1-2
Year of publication
1999
Pages
207 - 226
Database
ISI
SICI code
0029-5493(199909)193:1-2<207:MOTHII>2.0.ZU;2-7
Abstract
A thermal hydraulics computer code was developed to simulate the geysering instability in a natural circulation system starting from subcooled conditi ons and to assess the impact of the system pressure and channel inlet subco oling on the inception of instability. The formulation of thermal hydraulic s is inherently general and accounts for both single-phase liquid flow and nonhomogeneous, nonequilibrium two-phase flow. The computer code is based o n momentum integral method where the current practice of basing fluid prope rties on the system averaged pressure has been relaxed and the local proper ties are based on local pressures estimated using the shape of steady-state pressure distribution, thereby, improving the predictions while preserving the computation speed, one of the important strength of the integral metho ds. This is an important modeling feature since the local vapor generation rate depends on local saturation temperature The methodology has been valid ated with the experiments conducted to investigate the instabilities in a l ow pressure natural circulation loop at low powers and high inlet subcoolin gs. The numerical simulations predicted periodic channel flow reversal, whi ch is one of the feature of condensation-induced geysering. Basing local pr operties on local pressures instead of system. average pressure led to decr ease in the discrepancy in the prediction of the positive side amplitude fr om 40% to 6% and in the frequency from - 15% to 5%. In addition, it was obs erved that the start-up instability can be avoided by increasing system pre ssure or by decreasing channel inlet subcooling. This study showed that the integral method coupled with local pressure variation for the vapor genera tion model is suitable to predict startup or geysering transients. (C) 1999 Published by Elsevier Science S.A. All rights reserved.