NUMERICAL INVESTIGATION OF ON-POWER REFUELING IN A NATURAL CIRCULATION BOILING WATER REACTOR

ABSTRACT Most two-phase heat exchangers consist of multiple parallel boiling channels, and studies concerning multi-channel instabilities in boiling systems are of significant interest. The natural circulation boiling water reactor (NCBWR) considered in the present work is a pressure tube type boiling light water cooled and heavy water moderated reactor. The primary heat transport loop, comprising a number of parallel channels, is modeled by RELAP5/MOD3.4. The effects of on-power refueling on the flow rate and stability of the system are investigated. The conditions under which a sustainable flow rate can be maintained during on-power refueling are explored. It is observed that during on-power refueling, a near-stagnation condition or low-velocity reverse flow can occur, the possibility of reverse flow being higher at low pressures and low powers

Highlighting the Compound Risk of COVID-19 and Environmental Pollutants Using Geospatial Technology

The new COVID-19 coronavirus disease has emerged as a global threat and not just to human health but also the global economy. Due to the pandemic, most countries affected have therefore imposed periods of full or partial lockdowns to restrict community transmission. This has had the welcome but unexpected side effect that existing levels of atmospheric pollutants, particularly in cities, have temporarily declined. As found by several authors, air quality can inherently exacerbate the risks linked to respiratory diseases, including COVID-19. In this study, we explore patterns of air pollution for ten of the most affected countries in the world, in the context of the 2020 development of the COVID-19 pandemic. We find that the concentrations of some of the principal atmospheric pollutants were temporarily reduced during the extensive lockdowns in the spring. Secondly, we show that the seasonality of the atmospheric pollutants is not significantly affected by these temporary changes, indicating that observed variations in COVID-19 conditions are likely to be linked to air quality. On this background, we confirm that air pollution may be a good predictor for the local and national severity of COVID-19 infections.The authors acknowledge financial support from the Spanish Government, Grant RTI2018-354 094336-B-I00 (MCIU/AEI/FEDER, UE), the Spanish Carlos III Health Institute, COV 20/01213, and the Basque Government, Grant IT1207-19

Analysis of Instabilities, Nonlinear Oscillations and Startup Transients in Advanced Nuclear Reactors

Safety concerns for nuclear reactors necessitate analysis of instabilities that may occur during their startup or normal operation. Such analysis can be done exhaustively through computationally inexpensive reduced-order models using one-dimensional and lumped parameter approaches. While linear stability analysis gives information about the response of a dynamical system to small perturbations about its normal operating condition, analysis of nonlinear dynamics and bifurcations reveals the system behaviour in the presence of large perturbations. Transients occurring during the startup process involve large changes in system variables and have to be analysed accordingly. In this lecture, one-dimensional time-dependent mathematical modelling of boiling systems and supercritical fluid systems will be discussed along with lumped parameter modelling for linear and nonlinear stability analysis. Methods for analysis of linear and nonlinear oscillations and startup transients will be explained. Two advanced nuclear reactors — namely, the natural circulation boiling water reactor and the supercritical water-cooled reactor — will be considered for case studies. Mathematical modelling of these reactors — using the lumped parameter approach and the one-dimensional system code RELAP5/MOD3.4 — will be described. Using these models, the following studies will be discussed: linear stability analysis and parametric effects, nonlinear dynamics and bifurcations, startup transients and their time-series analysis

Concomitant Appearance of Pisa Syndrome and Striatal Hand in Parkinson’s Disease

Pisa syndrome is (PS) usually seen in patients receiving antipsychotic drugs and characterised by lateral flexion of trunk and axial dystonia. It is believed that antipsychotic drugs lead to dopamine blockage causing PS. We describe a Parkinson’s disease patient who was doing well with levodopa/carbidopa for 3 years and developed lateral flexion of trunk. His abnormal posture used to completely improve upon lying down position. He also had striatal hand deformity suggestive of focal dystonia

Design and development of a common synthetic strategy for a variety of 1-N-iminosugars

A new synthetic strategy has been developed for a general approach toward the synthesis of a variety of 1-N-iminosugar-type glycosidase inhibitors utilizing precursors developed by the PET-mediated cyclization of α-trimethylsilylmethylamine radical cation to a tethered π -functionality

Analysis of startup oscillations in natural circulation boiling systems

The aim of the present work is to get an insight of the phenomena behind the low-pressure low-power transients that occur during startup of a natural circulation boiling system. A RELAP5 model developed for a test facility and its prototype is used to record additional system parameters that were not included in the data obtained from experiments. The flow oscillations observed during experimental and numerical studies are analyzed and classified. It is inferred that the low amplitude oscillations are not condensation induced geysering instabilities, but a density wave instability supported by flashing. The similarity between the nature of startup transients observed in the test facility and the prototype is also examined. The effect of flashing is more pronounced in the prototype due to the strong variation of saturation temperature as the length scale is 4 times that of the model. The time series data obtained from experimental observations and numerical simulations are analyzed to identify the structural nature of flow oscillations. The power spectral density estimated using fast Fourier transform (FFT) algorithm illustrates the chaotic nature of the signals. The nonlinear time series analysis (TISEAN) package has been used for the estimation of Lyapunov exponent and the Poincaré section. The Poincaré section and the Lyapunov exponent confirm the chaotic nature of the flow oscillations.by S.P. Lakshmanan and Manmohan Pande

ANALYSIS OF COUPLED NEUTRONIC-THERMOHYDRAULIC INSTABILITIES IN SUPERCRITICAL WATER-COOLED REACTOR BY LUMPED PARAMETER MODELING

ABSTRACT The possibility of instabilities in future nuclear reactors cooled by supercritical water is a matter of concern due to sharp changes in thermodynamic properties of coolant within the core. In the present work, a lumped parameter dynamic model of supercritical water-cooled reactor has been developed for analysis of coupled neutronic-thermohydraulic instabilities. The coolant channel is divided into two nodes with a moving boundary between them. The heater wall dynamics is described by a lumped parameter energy balance. Point neutron kinetics with one group of delayed neutrons has been used to model the power dynamics. Simple non-dimensional equations of state have been obtained for evaluating thermodynamic properties. Stability analysis has been done for various values of parameters such as the reactor power, coolant mass flow rate and inlet temperature. Stability maps have been plotted in the parameter planes. Dynamic simulations have been performed in the time domain to study the nature of operating transients. The stability analysis with neutronics is found to be more conservative. Transient simulations without neutronics indicate a supercritical Hopf bifurcation and the existence of a stable limit cycles in the unstable region. However, simulations with coupled neutronics indicate a subcritical Hopf bifurcation and the existence of unstable limit cycles in the stable region. Therefore, the analysis with neutronics is more conservative and shows that the system can be unstable for large perturbations, even if it is stable for small perturbations

Numerical Investigation of Startup Instabilities in Parallel-Channel Natural Circulation Boiling Systems

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

A general strategy towards the synthesis of 1-N-iminosugar type glycosidase inhibitors: demonstration by the synthesis of D- as well as L-glucose type iminosugars (isofagomines)

Both enantiomers of isofagomine, the potent glycosidase inhibitor of a type 1-N-iminosugar have been synthesized by the intramolecular cyclization of the PET generated α-trimethylsilylmethylamine radical cation with the appropriate tethered acetylene moiety

Numerical investigations on power ramping procedure for a natural circulation boiling water reactor

Startup of a natural circulation boiling water reactor (NCBWR) is studied numerically, using a thermal-hydraulic system code RELAP5. A number of numerical experiments are carried out using various power ramps, and a suitable heat-up rate is identified to pressurize the reactor to the desired operating conditions in a reasonable time without considerable void generation in the core. It is observed that the occurrence of flashing in the riser section is unavoidable. Although flashing helps in steam production, the amplitude of flow oscillations induced by flashing is the event of concern, as in the case of the pressure tube type NCBWR studied here. Therefore, the feasibility of a complete single-phase startup is also examined and found not attractive. A new startup procedure, which completely bypasses the unstable two-phase region, is conceptualized, and the method to take the system to the operating condition without encountering flow oscillations is numerically investigated.by S.P. Lakshmanan and Manmohan Pandeyby S. P. Lakshmanan and Manmohan Pande