Theoretical study on critical heat flux with non-uniform axial power distribution

Author(s):  
Wenxing Liu ◽  
Dawei Zhao ◽  
Yuanfeng Zan ◽  
Wanyu Xiong ◽  
Jun Huang
Author(s):  
Harish Pothukuchi ◽  
Prasad Patnaik ◽  
B.V.S.S.S Prasad

Abstract Study of thermal hydraulics of a hexagonal sub-assembly is essential to ensure safe operation of liquid metal cooled fast reactors. Identifying the dryout location in fuel sub-assembly (FSA) is a precursor to the determination of safe Critical Heat Flux (CHF) margins. In this study, a sub-channel analysis code coupled with a film thickness model is employed to predict the CHF location in a hexagonal sub-assembly. A simple post-CHF heat transfer model is proposed and validated against the experimental data. The nature of flow resistance changes and operating conditions would significantly influence the occurrence of CHF. To this end, the effect of blockage (0.0 ≤ b ≤ 0.3) and axial power distribution (APD) on CHF is systematically investigated in a hexagonal sub-assembly. It was observed that, the presence of blockage causes coolant flow maldistribution which results in an early occurrence of CHF for higher mass flux (G > 1500 kgm−2s−1) and lower inlet subcooling (ΔTsub ≤ 30 K) conditions for b = 0.3. Furthermore, a comparative study of uniform and sinusoidal heat flux distributions are performed. It was noticed that sinusoidal APD causes early occurrence of CHF compared to uniform APD.


Author(s):  
Audrius Jasiulevicius ◽  
Rafael Macian-Juan

This paper presents the assessment of TRACE (version v4.160) against the Critical Heat Flux (CHF) experiments in annular tubes performed at the Royal Institute of Technology (KTH) in Stockholm, Sweden. The experimental database includes data for coolant mass fluxes between 250 and 2500 kg/m2s and inlet subcoolings of 10 and 40 K at a pressure of 70 bar. The work presented in this paper supplements the calculations of single round tube experiments carried out earlier and provides a broader scope of validated geometries. In addition to the Biasi and CISE-GE CHF correlations available in the code, a number of experimental points at low flow conditions are available for the annular geometry experiments, which also permitted the assessment of the Biasi/Zuber CHF correlation used in TRACE v4.160 for low flow conditions. Experiments with different axial power distribution were simulated and the effects of the axial power profile and the coolant inlet subcooling on the TRACE predictions were investigated. The results of this work show that the Biasi/Zuber correlation provides good estimation of the CHF at 70 bar, and, for the same conditions, the simulation of the annular experiments resulted in the calculation of lower CHF values compared to single-tube experiments. The analysis of the performance of the standard TRACE CHF correlations shows that the CISE-GE correlation yields critical qualities (quality at CHF) closer to the experimental values at 70 bar than the Biasi correlation for annular flow conditions. Regarding the power profile, the results of the TRACE calculations seem to be very sensitive to its shape, since, depending on the profile, different accuracies in the predictions were noted while other system conditions remained constant. The inlet coolant subcooling was also an important factor in the accuracy of TRACE CHF predictions. Thus, an increase in the inlet subcooling led to a clear improvement in the estimation of the critical quality with both Biasi and CISE-GE correlations. To complement the work, three additional CHF correlations were implemented in TRACE v4.160, namely the Bowring, Tong W-3 and Levitan-Lantsman CHF models, in order to assess the applicability of these correlations to simulate the CHF in annular tubes. The improvement of CHF predictions for low coolant mass flows (up to 1500 kg/m2s) is noted when applying Bowring CHF correlation. However, the increase in the inlet subcooling increases the error in predicted critical quality with the Bowring correlation. The Levitan-Lantsman and Tong-W-3 correlations provide results similar to the Biasi model. Therefore, the most correct CHF predictions among the investigated correlations were obtained using CISE-GE model in the standard TRAC v4.160 code.


2020 ◽  
Vol 2020 ◽  
pp. 1-18
Author(s):  
Mengmeng Xi ◽  
Rong Cai ◽  
Xiao Chu ◽  
Fan Yang ◽  
Xu Ran ◽  
...  

With the wide application of sea-based reactors, the impact of ocean conditions on the safety performance of reactors has gradually attracted attention. In this paper, by establishing the thermal hydraulic transient analysis model and the critical heat flux (CHF) model of natural circulation system, the CHF characteristics in the rectangular channel of natural self-feedback conditions under ocean conditions are studied. The results show that the additional acceleration field generated by ocean conditions will affect the thermal hydraulic parameters of the natural circulation system, that is, the external macroscopic thermal hydraulic field. On the other hand, the boiling crisis mechanism will be affected, that is, the force on the bubble and the thickness of the liquid film. Within the parameters of the study, ocean conditions have a great impact on CHF of natural circulation, and the maximum degradation of CHF is about 45%. The obtained analysis results are significant to the improvement of design and safety operation of the reactor system.


1969 ◽  
Vol 91 (3) ◽  
pp. 355-361 ◽  
Author(s):  
S. Israel ◽  
J. Casterline ◽  
B. Matzner

Critical heat flux data were obtained for forced flow boiling in a 16-rod test section arranged in a square array. The tests were performed at 1000 psia and used a radial power distribution which represented the region about the hot corner in a BWR fuel assembly. The results are lower than data obtained in a 9-rod square array, having a uniform power distribution, based on the average bundle exit quality. These two sets of data are in fair agreement when compared on the basis of the highest subchannel exit quality. Comparisons of different sets of data show the effects of different rod spacers and bundle misalignment on the critical heat flux.


2012 ◽  
Vol 36 ◽  
pp. 21-31 ◽  
Author(s):  
D.X. Du ◽  
W.X. Tian ◽  
G.H. Su ◽  
S.Z. Qiu ◽  
Y.P. Huang ◽  
...  

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