Abstract
The behaviour of a parallel-channel natural circulation boiling water reactor under a low-pressure low-power startup condition has been studied numerically (using RELAP5) and compared with its scaled model. The parallel-channel RELAP5 model is an extension of a single-channel model developed and validated with experimental results. Existence of in-phase and out-of-phase flashing instabilities in the parallel-channel systems is investigated through simulations under equal and unequal power boundary conditions in the channels. The effect of flow resistance on Type-I oscillations is explored. For nonidentical condition in the channels, the flow fluctuations in the parallel-channel systems are found to be out-of-phase.
Highlights
A proper understanding of the system behavior and other important parameters during the startup of a natural circulation boiling water reactor (NCBWR) is of primary importance in thermal hydraulic safety analysis
Researchers in the recent past have reported and discussed various instabilities that occur in a natural circulation boiling system at low-pressure low-power startup conditions
In a previous work by Lakshmanan et al [8], RELAP5 models were developed for the natural circulation loop of a test facility and the prototype
Summary
A proper understanding of the system behavior and other important parameters during the startup of a natural circulation boiling water reactor (NCBWR) is of primary importance in thermal hydraulic safety analysis. Researchers in the recent past have reported and discussed various instabilities that occur in a natural circulation boiling system at low-pressure low-power startup conditions. An experimental study using a double-channel natural circulation loop was carried out, and the transport mechanism of various types of instability under startup conditions was discussed [5]. The RELAP5 code was used to predict the transients under low-pressure low-power natural circulation boiling system and the results are found to closely match with the experimental observations of a test facility [8, 11]. Numerical simulations of transients at low-pressure and low-power conditions in double-channel natural circulation boiling systems are performed using RELAP5/SCDAPSIM/MOD3.4 [12] code
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