Modeling Critical Flow Through Steam Generator Tube Cracks

2014 ◽  
Author(s):  
Andrew Oussoren ◽  
Jovica R. Riznic ◽  
Shripad Revankar
Keyword(s):  
Steam Generator ◽  
Critical Flow ◽  
Steam Generator Tube ◽  
Flow Rates ◽  
Flow Models ◽  
Modeling Techniques ◽  
Small Flow ◽  
Flow Through ◽  
Experimental Values ◽  
Similar Accuracy

Modeling of leakage rates through geometries representative of steam generator tube cracks is being investigated. These cracks are characterised by very small flow areas and low length to diameter ratios. Two sets of experiments were conducted by researchers at Purdue University measuring flow rates through several slits in 3.175 mm and 1.3 mm thick samples, with L/D ratios as low as 1.2. A pressure differential of 6.8 MPa was applied across the samples with varying degrees of subcooling. Flow rates through these samples were modeled using the thermal-hydraulic system codes RELAP and TRACE, using different nodalization techniques and both the Henry Fauske and Ransom Trapp critical flow models available in RELAP. Model results are compared to experimental values and modeling techniques are discussed. TRACE and RELAP were found to have similar accuracy in predicting flow rate trends, with higher accuracy at larger L/D. In general best results were achieved by modeling the crack as a junction component.

Assessment of Choking Flow Models in RELAP5 for Subcooled Choking Flow Through a Small Axial Crack of a Steam Generator Tube

2017 ◽  
Author(s):  
Mark A. Brown ◽  
Hung Nguyen ◽  
Shripad T. Revankar ◽  
Jovica Riznic
Keyword(s):  
Steam Generator ◽  
Nuclear Power ◽  
Large Scale ◽  
Maximum Flow ◽  
Channel Length ◽  
Steam Generator Tube ◽  
Flow Rates ◽  
Flow Models ◽  
Engineered Safeguards ◽  
Channel Lengths

Choking flow plays an integral part not only in the engineered safeguards of a nuclear power plant (NPP), but also to everyday operation. Current NPP steam generators operate on the leak-before-break approach. The ability to predict and estimate a leak rate through a steam generator tube crack is an important safety parameter. Knowledge of the maximum flow rate through a crack in the steam generator tube allows the coolant inventory to be designed accordingly while limiting losses during loss of coolant accidents. Here an assessment of the choking flow models in thermal-hydraulics code RELAP5/MOD3.3 is performed and its suitability to predict choking flow rates through small axial cracks of the steam generator tubes is evaluated based on previously collected experimental data. Three sets of the data were studied in this work which corresponds to steam generator tube crack sample 1, 2, and 3. Each sample has a wall thickness, channel length (L), of 1.285 mm to 1.3 mm. Exit areas of these samples are 5.22 mm2, 9.05 mm2, and 1.72 mm2 respectively. Samples 1 and 2 have the same flow channel length to hydraulics diameter ratio (L/D) of 2.9 whereas sample 3 has a L/D of 6.5. A pressure differential of 6.8 MPa was applied across the samples with a range of subcooling from 5 °C to 60 °C. Flow rates through these samples were modeled using the thermal-hydraulic system code RELAP5/MOD3.3. Simulation’s results are compared to experimental values and modeling techniques are discussed. It is found that both the Henry-Fauske (H-F) and Ransom-Trapp (R-T) models better predict choking mass flux for longer channels. As the channel length decreases both models’ predictions diverge from each other. While RELAP5/MOD3.3 has been shown to predict choking flow in large scale geometries, further investigation of data sets need to be done to determine if it is suited well for small channel lengths.

Assessment of Choking Flow Models in RELAP5 for Flashing Flow Through Small Cracks

2013 ◽  
Author(s):  
Shripad T. Revankar ◽  
Brian Wolf ◽  
Jovica R. Riznic ◽  
Ganesh Srinivasan
Keyword(s):  
Steam Generator ◽  
Mass Flux ◽  
Large Scale ◽  
Steam Generator Tube ◽  
Flow Models ◽  
Small Channel ◽  
Safety Parameter ◽  
Small Cracks ◽  
Flow Through ◽  
Channel Lengths

The estimation of leak rates through steam generator tube crack is an important safety parameter. An assessment of the choking flow models in thermal-hydraulics code RELAP5 is performed and its applicability to predict choking flow rates through steam generator tube cracks is addressed. A RELAP5 nodalization was created to model experimental data from literature. It is found that both the Henry-Fauske and Ransom-Trapp models better predict choking mass flux for longer channels. As the length of a channel decreases the both models’ predictions diverge from each other. While RELAP5 has been shown to predict choking flow in large scale geometries, it is not suited well for small channel lengths. In the case of a more conservative approach, where over prediction of mass flux through short channels is best, the Henry-Fauske model would be most appropriate.

CFD Predictions of Severe Accident Steam Generator Flows in a 1/7th Scale Pressurized Water Reactor

2002 ◽  
Author(s):  
Christopher Boyd ◽  
Kelly Hardesty
Keyword(s):  
Steam Generator ◽  
Natural Circulation ◽  
Severe Accident ◽  
Pressurized Water Reactor ◽  
Pressurized Water ◽  
Steam Generator Tube ◽  
Flow Phenomena ◽  
Experimental Values ◽  
High Degree ◽  
Side Flow

Computational Fluid Dynamics (CFD) is applied to steam generator inlet plenum mixing as part of a larger plan covering steam generator tube integrity. The technique is verified by comparing predicted results with severe accident natural circulation data [1] from a 1/7th scale Westinghouse facility. This exercise demonstrates that the technique can predict the natural circulation and mixing phenomena relevant to steam generator tube integrity issues. The model includes primary side flow paths for a single hot leg and steam generator. Qualitatively, the experimentally observed flow phenomena are predicted. The paths of the natural circulation flows and the relative flow proportions are correctly predicted. Quantitatively, comparisons are made with temperatures, mass flows, and other parameters. All predictions are generally within 10% of the experimental values. Overall, there is a high degree of confidence in the CFD technique for prediction of the relevant flow phenomena associated with this type of severe accident sequence.

Experimental Study of Entrance Effects on Laminar Gas Flow Through Silicon Orifices

2005 ◽  
Author(s):  
Aaron J. Knobloch ◽  
Joell R. Hibshman ◽  
George Wu ◽  
Rich Saia
Keyword(s):  
Flow Rate ◽  
Gas Flow ◽  
Flow Area ◽  
Fully Developed Flow ◽  
Flow Rates ◽  
Flow Models ◽  
Entry Length ◽  
Orifice Flow ◽  
Measured Flow ◽  
Flow Through

This study summarizes a fundamental investigation of flow through an array of silicon micromachined rectangular slots. The purpose of the study is to evaluate the effect of entrance pressure, flow area, orifice thickness, slot length, and slot width of the orifice on flow rate. These orifices were fabricated using a simple frontside through wafer DRIE process on a 385 μm thick wafer and wafer bonding to create thicker orifices. The dies were then packaged as part of a TO8 can and flow tested. To complement the results of this experimental work, two simple flow models were developed to predict the effect of geometrical and entrance conditions on the flow rate. These models were based on macroscale assumptions that were not necessarily true in the case of thin orifices. One relationship was based on Pouiselle flow which assumes fully developed flow conditions. Calculation of the entry length required for fully developed flow indicate that in the low Reynolds Number regime (32-550) evaluated, the entry flow development requires 2-8 times the thickness of the thickest orifices used for this study. Therefore, calculations of orifice flow based on a Pouiselle model are an overestimate of the actual measured flow rates. Another model examined typical orifice relationships using head loss at the entrance and exit of the slots did not accurately capture the particular flow rates since it overestimated the expansion or constriction losses. A series of experiments where the pressure was varied between 75 and 1000 Pa were performed. A comparison of the Pouiselle flow solution with experimental results was made which showed that the Pouiselle flow model overpredicts the flow rates and more specifically, the effect of width on the flow rates. The results of these tests were used to develop a transfer function which describes the dependence of flow rate on orifice width, thickness, length, and inlet pressure.

Applicability of Choking Flow Models for Subcooled Flashing Flow Through Tube Cracks

2011 ◽  
Author(s):  
Brian Wolf ◽  
Shripad T. Revankar ◽  
Jovica R. Riznic
Keyword(s):  
Mechanistic Model ◽  
Channel Length ◽  
Two Phase ◽  
Experimental Conditions ◽  
Flow Rates ◽  
Flow Models ◽  
Model Predictions ◽  
Flow Through ◽  
The Difference ◽  
Non Equilibrium

Recently there is some database available on choking flow through cracks relevant to steam generator (SG) tubes to model the critical flow. These data are used in assessing the key choking flow models. Based on this assessment a mechanistic choking model is developed. The model is used to predict the choking flow rates for various experimental conditions for subcooled flashing flow through narrow slits with L/D varying from small values (∼5) to large values (100). Results are presented on the effects of thermal and mechanical non-equilibrium on the choking flow for small L/D channels. A mechanistic model was developed to model two-phase choking flow through slits. A comparison of model results to experimental data shows that the homogeneous equilibrium based models markedly under predict choking flow rates in such geometries. As subcooling increases, and channel length decreases the non-equilibrium effects play a greater role in the choking phenomenon, therefore the difference in model predictions and experimental results increases.

Rotating Stall Induced in Vaneless Diffusers of Very Low Specific Speed Centrifugal Blowers

1985 ◽  
Vol 107 (2) ◽  
pp. 514-519 ◽  
Author(s):  
Y. Kinoshita ◽  
Y. Senoo
Keyword(s):  
Flow Analysis ◽  
Rotating Stall ◽  
Experimental Results ◽  
Flow Coefficient ◽  
Critical Flow ◽  
Flow Rates ◽  
Small Flow ◽  
Low Specific Speed ◽  
Specific Speed ◽  
Vaneless Diffusers

The limit of rotating stall was experimentally determined for three very small specific speed centrifugal blowers. The impellers were specially designed for stall-free at very small flow rates, so that the cause of rotating stall could be attributed to the vaneless diffusers. Experimental results demonstrated that the blowers did not stall until the flow coefficient was reduced to very small values, which had never been reported in the literature. The critical flow coefficient for rotating stall agreed very well with the prediction based on a flow analysis and a criterion for rotating stall in vaneless diffusers developed by the authors.

Model for Choking of Subcooled Flashing Flow Through a Steam Generator Tube Crack

2012 ◽  
Author(s):  
Brian Wolf ◽  
Shripad T. Revankar ◽  
Jovica R. Riznic
Keyword(s):  
Steam Generator ◽  
Mechanistic Model ◽  
Channel Length ◽  
Saturation Curve ◽  
Two Phase ◽  
Experimental Conditions ◽  
Flow Rates ◽  
Frictional Pressure Drop ◽  
Flow Through ◽  
Non Equilibrium

Recently there is some database available on choking flow through cracks relevant to steam generator (SG) tubes to model the critical flow. A one dimensional mechanistic model was developed to model two-phase choking flow through slits from conservation principles. The model takes into account channel entrance loss as well as frictional pressure drop for single-phase subcooled liquid. Flashing criteria are defined and temperature and pressure of the fluid are assumed to follow the saturation curve. The two-phase mixture was treated as a quasi-fluid with mixture properties and both homogenous equilibrium (HE) and homogeneous non-equilibrium models were considered. The models were compared with the choking flow rates for various experimental conditions for subcooled flashing flow through narrow slits with L/D varying from small values ( 5) to large values (100). Results are presented on the effects of thermal non-equilibrium on the choking flow for small L/D channels. A comparison of model results to experimental data shows that the HE based models grossly under predict choking flow rates in such geometries. As subcooling increases, and channel length decreases the non-equilibrium effects play a greater role in the choking phenomenon, therefore the difference in model predictions and experimental results increases for HE case.

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