Analysis of coupled two-phase natural circulation loops by developing HEM and DFM based numerical models

Boolean Dynamics of Biological Networks with Multiple Coupled Feedback Loops

Coupled positive feedback loops are frequently-occurring motifs in gene transcription regulatory networks and signaling pathways. So it's very important to investigate the function of coupled positive feedback loops. In this paper we establish mathematical models of coupled positive feedback loops. Through the bifurcation analysis, we prove that two coupled positive feedback loops can generate reversible and irreversible switch. And coupled positive feedback loops can strengthen bistable, enlarge signal and extend the signal reaction time. Coupled positive feedback loops play an important role in regulate biological behaviors.

The coupled natural circulation loops (NCLs) based passive systems have gained importance in nuclear industry due to their infinite grace time during severe accidents. However, the behavior of these systems is quite complex due to their regenerative feedback effects. In this connection, a numerical model to investigate the dynamics of single-phase coupled NCLs has been developed. The governing equations are solved using finite volume method. The model has additional features for wall conduction, fluid axial conduction, heater-cooler orientations, etc. Further, water-steam property subroutine is used for fluid properties instead of Boussinesq approximation. The model is validated against both single and coupled loop experimental facilities. It is then applied to investigate the transients of vertically coupled two identical NCLs. Results showed that Loop-1 flow is noted to be higher than Loop-2, the same is successfully explained based on temporal temperature profiles. A comparison of single and coupled NCLs revealed that their dynamics are different. The effects of aspect ratio, loop diameter, wall thickness, initial flow field on dynamics of coupled NCLs are investigated. Further, the flow is noted to be proportional to both loop diameter and aspect ratio. The influence of other parameters is also discussed to bring out their influence on dynamics of coupled NCLs.

Thermal-hydraulic phenomena for water cooled nuclear reactors

Fourier series-based modelling of the effects of thermal coupling on the transient dynamics of component loops in a coupled natural circulation loop

14 - Nuclear power plant systems

Influence of Passive Containment Cooling System on containment thermal hydraulic transients during a postulated severe accident

Reliability assessment of passive systems using artificial neural network based response surface methodology

Coupled positive and negative feedback loops form an essential building block of cellular signaling pathways, but the dynamics of such a system remain to be fully explored. Here, we systematically analyze a two-component circuit with interlinked positive and negative feedback loops, focusing on feedback-induced dynamics and their mechanisms. We show that feedbacks can induce monostability, oscillation, and excitability as well as the coexistence of two attractors (including that of two different stable steady states (called Type-I bistability) and that of both a stable steady state and a stable limit cycle (called Type-II bistability)). In particular for Type-II bistability, we find that feedback-controlled molecular noise can induce stochastic switching between two different attractors, and that the first passage time between them exhibits a multi-peak distribution. These investigations provide insights for understanding the biological functions of coupled positive and negative feedback circuits from the viewpoint of dynamics.

Safety is always the primary concern for designing and analyzing nuclear reactor systems. The requirements for the safety margin for advanced small modular reactor (SMR) systems are targeted even higher than the conventional commercial large-scale nuclear reactors incorporating the passive and inherent safety systems. The SMR systems are designed with the condensation passive containment cooling system (PCCS), which plays a critical role in removing reactor heat during a steam release accident case. However, the presence of non-condensable gas (NCG), like air, reduces the heat transfer performance. This physics phenomenon becomes multifactorial for nuclear reactor containment during a fuel failure accident case that releases hydrogen gas. Besides, the mixture component of steam-air-hydrogen varies in reactor accident cases, which needs simulation and validation keeping parameters of importance. Reviews showed that previous studies for SMR’s PCCS did not cover the condensation heat transfer (CHT) in the presence of multicomponent NCG mixture parametric computational fluid dynamics (CFD) simulation and validation, making a research gap in the SMR design safety. A comprehensive CHT parametric CFD study was performed for SMR PCCS to fill this research gap. This study used experimental data as simulation 3D physics domain inlet and outlet boundary conditions. However, the wall boundary conditions were constant temperature, curve-fit, and annular coolant for verifying the turbulence models. Parametric simulations were performed, verified, and optimized for steam-NCG mixtures. The multicomponent gases, multiphase mixtures, and fluid film condensation models were applied with associated turbulence models. The results of the parametric study were evaluated for realistic reactor conditions. Results showed that parametric study provided critical insight about the dependency of multicomponent gas mixture parameters that supports reactor safety design, analysis, and licensing.

A comparative economic assessment of a 200 MW nuclear heating reactor for seawater desalination by multi-effect distillation (MED)

Estimation of passive systems functional failure probabilities by the modified meta-IS algorithm

Safety assessment of passive safety systems in nuclear reactors using artificial neural networks

A Passive Gamma Emission Tomography system (PGET) [1] was developed for the IAEA Safeguards for verification of irradiated nuclear fuel assemblies (SFAs). In 2015-2016 PGET underwent significant re-design and its performance has been tested on multiple SFA types. The re-designed PGET features the functionality of traditional non-destructive assay systems commonly used for spent fuel verification: total neutron counting (Fork Detector, FDET), medium-resolution gamma spectrometry (Irradiated Item Attribute Tester, IRAT or Spent Fuel Attribute Tester, SFAT) and spent fuel assembly's lattice image (Digital Cherenkov Viewing Device, DCVD). Two <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sup> B neutron detectors and one-hundred-seventy-four collimated CdZnTe detectors are grouped in two arrays on a rotary baseplate inside a watertight stainless steel enclosure. A SFA is lowered through the center of the enclosure and held stationary to perform an underwater measurement. Detector arrays are then rotated on a baseplate in the horizontal plane around vertical axis of symmetry to obtain gamma sinogram and neutron count data simultaneously, typically in 3-5 min per assembly. Additionally, medium resolution spectra from all gamma detectors can be collected and recorded. Functional, technical and operational performance of the PGET was tested at four nuclear reactors on mockup, PWR, BWR and WWER-440 SFAs. Measurements have been performed on fuel with burnup in the range 5.7-58 GWd/tU and cooling times from 1.9 to 27 years. Lateral pin structure of the SFAs could be reconstructed for any tested fuel design in the above range of cooling times and burnups. Missing or replaced pins in all fuel types could be clearly visualized in the reconstructed images; spectrometric information ( <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">134</sup> Cs/ <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">137</sup> Cs peak ratio) and neutron counting rates were found to be consistent with declared fuel radiation history. This paper describes details of the PGET hardware and electronics and presents some results of performance evaluation.

A numerical and three-dimensional analysis of steady state rectangular natural circulation loop