Progress Report on Computational Analyses of Water-Based NSTF

Lv, Qiuping; Kraus, Adam; Hu, Rui; Bucknor, Matthew; Lisowski, Darius; Nunez, Daniel

doi:10.2172/1375451

Cited by 8 publications

(12 citation statements)

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“…The primary loop consists of the riser channels, water tank, and the piping network while the cavity is defined as the enclosure surrounded by the heater panel, the riser panel, and the unheated panels. A reference RELAP5 model for the primary loop NSTF has previously been developed by Lv et al (2017) temperature at approximately 30 • C throughout the simulation. For two-phase analysis, the activecooling component is removed where water is allowed to boil off and steam is discharged from the system to the environment.…”

Section: Primary Loop Modelmentioning

confidence: 99%

FY22 Progress on Computational Modeling of the Water-Based NSTF

Ooi¹,

Lv²,

Hu³

et al. 2022

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This report summarizes the system-level modeling effort by Argonne National Laboratory (Argonne) of the Natural convection Shutdown heat removal Test Facility (NSTF) in FY22. As an extension of the effort from FY21, this year's work focuses primarily on the two-phase modeling of the NSTF using RELAP5-3D, particularly with the inclusion of the cavity model.The results from simulations were used to compare against experimental data for benchmarking purposes of the RELAP5 deck. Additionally, RELAP5 was used as a predictive tool to guide planned test operations and identify expected system behaviors. In the first part of this report, details are provided of the cavity omitted model where heat flux is applied directly as a boundary condition to the risers. The general trend predicted by the RELAP5 model matches that from the experimental data when a single-phase natural circulation flow is first established, followed by an oscillatory two-phase period and finally a stable two-phase flow. However, the onset of oscillations is predicted early by the model due to the smaller thermal mixing region in the tank. However, by expanding the simulated thermal mixing region in the tank, the onset of oscillations predicted by the model is able to match that from the experiment. These oscillations where studied in depth and are deduced to be flashing-induced instability.The model was then modified to simulate an accident scenario case where a representative heat load based on the full-scale Framatome's 625 MW t SC-HTGR was applied directly to the riser channels. The simulated initial and boundary conditions were identical to those performed experimentally, facilitating direct comparisions between the predicted and experimental results. It was determined that the results showed some discrepancies remain, likely due to the overprediction of vapor generation rate by the computer model.In the second part of this report, the cavity model is re-introduced where it is observed that the RELAP5 prediction is now able to capture the major trends of the observed flow commonly observed during two-phase conditions. However, the onset of oscillations is once again predicted early by the model, possibly caused by the underprediction of heat loss from the heater and cavity. This is likely due to the omission of support structures in the cavity that can act as additional pathways for heat to escape to the environment. To overcome the underprediction of heat loss, part of the insulation surrounding the cavity side panels and the back of the heaters are removed to allow heat to escape directly to the environment, which then improves the RELAP5 prediction.Parametric studies are also performed to investigate the effects of heater power, tank inventory ii ANL-ART-257FY22 Progress on Computational Modeling of the Water-Based NSTF September 2022 level, and tank gas space pressure on flow behaviors, also in direct comparison to conditions tested experimentally. User option-61 in the RELAP5-3D input deck, which changes the heat transfer coefficient correla...

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Section: Primary Loop Modelmentioning

confidence: 99%

FY22 Progress on Computational Modeling of the Water-Based NSTF

Ooi¹,

Lv²,

Hu³

et al. 2022

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“…Since the amount of heat transfer by the internal air flow is small, RCCS is then the major contributor to the parasitic heat loss from the RPV in normal operational conditions. Nevertheless, air temperature variation in flowing direction might affect the panel temperature distribution, which was derived from previous experiences on natural convection shutdown heat removal test facility (NSTF), a scaled facility for the RCCS concept, on modeling the facility for predicting a heated plate temperature profile [9]. It led to the HC-HTGR performance analysis would include the influence of air flow in the cavity for more accurate prediction results, which will be elaborated more in Section 4.1.2.…”

Section: Lumped Parameter Analysis Modelmentioning

confidence: 99%

“…The primary objective of the system-level analysis is to gain a complete understanding of the complex flow and heat transfer phenomena expected, such that it will be used to investigate the integrated system behavior and performance and to conduct long-term cooling simulations. Previous analysis work of the water-based NSTF showed the promising capability of RELAP5 application to a natural circulation system in predicting various characteristics which correspond to different physical phenomena during the transients [9]. Therefore, RELAP5-3D [10] was utilized for preliminary system-level performance analysis for HC-HTGR RCCS.…”

Section: Preliminary System-level Performance Analysis Of Hc-htgr Rccsmentioning

confidence: 99%

Preliminary Design of Reactor Cavity Cooling System for a Horizontal Compact HTGR

Jeong¹,

Lisowski²,

Lv³

et al. 2022

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The Horizontal Compact High Temperature Gas Reactor (HC-HTGR) is being designed by a multi-disciplinary team of nuclear, mechanical, and structural engineers under the support of a DOE-NE Advanced Reactor Demonstration Program's Advanced Reactor award. The objective of this ARC-20 project is to deliver a conceptual design for the proposed MIGHTR in 3 years and support its commercialization as a safe and low-cost HTGR. Argonne National Laboratory (Argonne) is responsible for the design and analysis of the reactor cavity cooling system (RCCS) as a safety system for passive decay heat removal of the reactor concept. This report documents the preliminary design study of the RCCS for the HC-HTGR. It includes the establishment of the design requirements, a high-level design study by initial scoping calculations, and preliminary performance calculations of the HC-HTGR RCCS design.Design requirements for the HC-HTGR RCCS have been established to guide preliminary design activities and scoping performance calculations. Initial scoping calculations including estimation of the water inventory, estimation of HVAC thermal capability, and a parametric study on loop dimensions by standalone RCCS analysis. Based on scoping calculation results, a set of baseline dimensions of the HC-HTGR RCCS was derived.A water panel modeling approach was investigated to explore various potential design options for the water panel under consideration for the HC-HTGR RCCS using RELAP5-3D. A test case study was performed to assess the prediction capability of two modeling approaches. The results were compared with CFD simulations conducted in constant RPV temperature and heat flux boundary conditions. It confirms the capability of the RELAP5-3D modeling approach to include all important heat transfer mechanisms expected in the HC-HTGR RCCS operation conditions. Then, a reference RELAP5-3D model for the 1/8 th of a compartment of the preliminary design of the HC-HTGR RCCS was developed.A preliminary performance analysis was conducted to evaluate single-phase natural circulation performance with different top tank temperature values and panel conduction performance in various operation conditions. From single-phase natural circulation performance analysis, the system operation mode was investigated in normal operating and limiting design conditions. It showed operation mode in a subcooled state with a proper top tank water cooling system. Parasitic heat loss by both internal air flow and RCCS was estimated, showing it satisfies maintaining below target maximum heat loss of the HC-HTGR RCCS. From the panel conduction performance analysis, two candidate materials for the riser tube such as carbon steel and stainless steel were compared in the thermal performance of HC-HTGR RCCS. From a single water panel test compared with CFD simulation results, it was confirmed that the current capability of the RELAP5-3D modeling approach for the water panel predicts the thermal conduction of two different materials of the water panel. Then, system-level thermal p...

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“…Turbulent model is needed for a reasonable prediction of the flow field in the cavity, which is however limited in the current SAM multi-dimensional flow model. In this test, the turbulent viscosity from STAR-CCM+ 3-D simulation [14] is extracted and applied to SAM 2-D model. Figure 4-3 shows the profile of turbulent viscosity obtained from STAR-CCM+ simulation.…”

Section: Turbulent Viscosity From Star-ccm+ Simulationmentioning

confidence: 99%