scholarly journals Problems of abnormal dynamics of thermal hydraulic processes in prospective reactors with supercritical parameters of light water coolant

2021 ◽  
Vol 21 (2) ◽  
pp. 3-16
Author(s):  
I. G. Sharayevsky ◽  
◽  
N. M. Fialko ◽  
A. V. Nosovskyi ◽  
L. B. Zimin ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Fuel Element ◽  
Nuclear Reactors ◽  
Physical Nature ◽  
Physical Sign ◽  
Water Coolant ◽  
Technical Problems ◽  
Light Water ◽  
Supercritical Parameters ◽  
Emergency Mode

A complex of scientific and technical problems directly related to the priority of ensuring the operational safety and reliability of the cores of promising power nuclear reactors with supercritical thermodynamic parameters of a light-water coolant is systematized. The problems of implementation of effective heat removal from the surface of fuel elements and ensuring reliable calculation of thermal and hydrodynamic processes in turbulent flows of a supercritical coolant are considered. The main attention in the consideration of thermohydraulic processes in the near-critical region is paid to the conditionality of the physical nature of these processes by the regularities of transformation of the thermophysical properties of the coolant with changes in its temperature. It is noted that these phenomena have not been sufficiently studied and that modern designers of nuclear reactors with supercritical parameters practically do not have physically substantiated adequate ideas about the physical nature of an emergency mode of deteriorated heat transfer, which can arise unpredictably on the surface of a fuel element even if it is continuously cooled by a coolant with supercritical parameters. It is only known that the main physical sign of the occurrence of this emergency mode is a significant deterioration in heat transfer, which becomes abnormally low, but the physical reasons for such a dangerous anomaly are currently unknown. Based on the analysis of the molecular kinetics data of the near-wall coolant layer, it was proposed to consider such facts of an emergency decrease in the heat transfer intensity due to the appearance of an unknown pseudo-film boiling regime on the fuel element surface. In this context, it is shown that under the conditions under study, macromolecular assemblies in the form of pseudo-vapor formations can appear on the heat exchange surface, as a result of which the heat transfer on the fuel element surface is disturbed. Using experimental data, it is shown that there is a rather deep physical analogy between heat transfer in a supercritical thermodynamic system and the subcooled boiling process at subcritical parameters of the coolant. The dynamics of changes in the characteristics of the experimental spectra of acoustic emission of pseudo-boiling with a sequential increase in the thermal load is analyzed and it is shown that these phenomena can, in principle, be used in promising systems for diagnostic monitoring of reactors with supercritical parameters for early detection of the initial phases of pseudo-boiling and prompt prevention of the occurrence of emergency modes of deteriorated heat transfer

scholarly journals Actual problems of the thermal hydraulic reliability ensuring of prospective nuclear reactors with supercritical parameters

2021 ◽  
Vol 20 ◽  
pp. 27-38
Author(s):  
I. G. Sharayevsky ◽  
◽  
N. M. Fialko ◽  
A. V. Nosovskyi ◽  
L. B. Zimin ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Thermodynamic Parameters ◽  
Experimental Studies ◽  
Heat Removal ◽  
Heat Transfer Process ◽  
Critical Area ◽  
Water Coolant ◽  
Operational Parameters ◽  
Reliable Determination ◽  
Light Water

There is a significant lack of reliable information on the physical characteristics of thermohydraulic processes in emergency heat transfer modes when cooling the surface of fuel rods with light water coolant with supercritical thermodynamic parameters, in particular, on the physics of heat transfer processes and hydromechanics in the critical area. It is shown that in these conditions there is physical uncertainty about the causes of deteriorating heat transfer, which limits the possibility of creating effective calculation techniques for reliable determination of the upper limit of safe forcing of the heat transfer process in the core. At present, the vast majority of theoretical and experimental studies of thermohydraulic processes in the near-critical area have been performed only for the socalled “normal” heat transfer, which corresponds to the heat removal conditions with mixed turbulent convection of superheated to “gas” state of light water coolant in its inertial mode. Attention is paid to the possible appearance of macromolecular ensembles on this surface in the form of pseudo-vapor formations, which are capable of causing an emergency mode of pseudo-film boiling. On the basis of the given experimental data of various authors existence of rather deep physical analogy between processes of heat exchange in supercritical thermodynamic system and unheated boiling at subcritical parameters of the heat carrier is proved. Existence of the pseudo-boiling process in the conditions of supercritical thermodynamic parameters makes it impossible to use in the thermohydraulic calculation the empirical dependences for “hot” gas for the range of active zones operational parameters.

scholarly journals Problem issues of cores thermal-hydraulic calculation for prospective water-cooled reactors with supercritical parameters

2020 ◽  
Vol 19 (4) ◽  
pp. 3-15
Author(s):  
І. G. Sharaevsky ◽  
◽  
N. М. Fіаlkо ◽  
А. V. Nоsоvskyi ◽  
L. B. Zimin ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Exchange ◽  
Exchange Process ◽  
Physical Nature ◽  
Heat Transfer Process ◽  
Hydraulic Calculation ◽  
Heated Wall ◽  
Complex Nature ◽  
Complex Flow ◽  
Supercritical Parameters

The fundamental thermophysical features of the heat exchange process between the heated wall of a vertical channel and the light-water coolant of supercritical parameters concerning the conditions of heat-generating assemblies channels and cores of perspective energy nuclear reactors are considered. The available methods and recommendations for determining the limits of thermal load are analyzed. It is a guarantee the absence of the characteristic dangerous mode possibility of deteriorated heat exchange in these conditions and corresponding sharp rise in the channels wall temperature, which threatens their destruction. The physical nature of the occurrence of degraded heat transfer regimes remains unclear, and the existing approaches to the implementation of thermohydraulic calculation in such conditions are not sufficiently justified. The complex nature of intercellular heat and mass transfer in the fuel assembly and the presence of individual thermohydraulic cells with reduced levels of heat transfer intensity indicate that the existing method of determining the area of degraded heat transfer in the reactor core channels with supercritical parameters of the coolant is significantly simplified. Insufficient data and research results have been revealed to create adequate methods of heat-hydraulic calculation, suitable for taking into account the peculiarities of the heat transfer process complex flow under conditions of supercritical parameters of the coolant. The application of such methods should be the basis for ensuring the safe operation of prospective reactors and minimizing potential losses of a different nature from accidents caused by the destruction of cores through unacceptable heat transfer modes. To this end, the main direction of further research is identified.

Modeling of Spacer Influence on Post-Dryout Heat Transfer in Heated Channels

2006 ◽  
Author(s):  
Henryk Anglart
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Phenomenological Model ◽  
Nuclear Reactors ◽  
Light Water Reactors ◽  
Transfer Enhancement ◽  
Light Water ◽  
Operational Conditions ◽  
Transfer Processes ◽  
Water Reactors

Post-dryout heat transfer plays an important role in safe and economical operations of Light Water Reactors (LWR). This type of heat transfer is avoided under normal operational conditions of nuclear reactors; however, it may occur in transient or accidential situations. To estimate the risk of clad damages due to increase of temperature associated with the occurrence of post-dryout, it is necessary to properly model heat transfer processes under such conditions. The influence of various parameters on heat transfer downstream of spacer has been investigated. It is concluded that heat transfer enhancement due to spacers is largely under-predicted for flows with relatively low quality. For such flows the effect of droplets impinging heated walls is significant and must properly be taken into account. The phenomenological model presented in this paper shows a superior accuracy over correlations and presents a potential to capture the phenomenon of rewetting that occurs downstream of spacers.

Mathematical simulation of heat transfer during fluid flow for a fuel element with a polyzonal finned shell

2017 ◽  
Vol 20 (4) ◽  
pp. 58-63
Author(s):  
K. Maksymenko-Sheiko ◽  
◽  
Yu. Litvinova ◽  
T. Sheyko ◽  
M. Khazhmuradov ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Fluid Flow ◽  
Fuel Element ◽  
Mathematical Simulation

Exploring the Use of Alumina Nanofluid as Emergency Coolant for Nuclear Fuel Bundle

2018 ◽  
Vol 11 (2) ◽  
Author(s):  
A. S. Chinchole ◽  
Arnab Dasgupta ◽  
P. P. Kulkarni ◽  
D. K. Chandraker ◽  
A. K. Nayak
Keyword(s):  
Heat Transfer ◽  
Nuclear Fuel ◽  
Nuclear Reactor ◽  
Cooling System ◽  
Nuclear Reactors ◽  
Electrical Heating ◽  
High Dose ◽  
Potential Candidate ◽  
Alumina Nanofluid ◽  
Core Cooling

Abstract Nanofluids are suspensions of nanosized particles in any base fluid that show significant enhancement of their heat transfer properties at modest nanoparticle concentrations. Due to enhanced thermal properties at low nanoparticle concentration, it is a potential candidate for utilization in nuclear heat transfer applications. In the last decade, there have been few studies which indicate possible advantages of using nanofluids as a coolant in nuclear reactors during normal as well as accidental conditions. In continuation with these studies, the utilization of nanofluids as a viable candidate for emergency core cooling in nuclear reactors is explored in this paper by carrying out experiments in a scaled facility. The experiments carried out mainly focus on quenching behavior of a simulated nuclear fuel rod bundle by using 1% Alumina nanofluid as a coolant in emergency core cooling system (ECCS). In addition, its performance is compared with water. In the experiments, nuclear decay heat (from 1.5% to 2.6% reactor full power) is simulated through electrical heating. The present experiments show that, from heat transfer point of view, alumina nanofluids have a definite advantage over water as coolant for ECCS. Additionally, to assess the suitability of using nanofluids in reactors, their stability was investigated in radiation field. Our tests showed good stability even after very high dose of radiation, indicating the feasibility of their possible use in nuclear reactor heat transfer systems.

Behaviour of CS and I In Zirconia Based Fuel

1998 ◽  
Vol 540 ◽  
Author(s):  
C. Degueldre ◽  
M. Pouchon ◽  
M. Doebli ◽  
G. Ledergerber
Keyword(s):  
Incident Energy ◽  
Nuclear Reactors ◽  
Fission Products ◽  
Concentration Profiles ◽  
Reactor Safety ◽  
Inert Matrix Fuel ◽  
Light Water ◽  
Inert Matrix ◽  
Stepwise Heating ◽  
Implantation Depth

AbstractA zirconia based ceramic is foreseen as an inert matrix fuel for burning excess plutonium in light water nuclear reactors. For reactor safety reasons the behaviour of volatile fission products such as cesium and iodine must be studied since a retention of fission products is favourable for licensing the studied inert matrix fuel. In this study, implantation of Cs and I was performed into polycrystalline (Zr0.85, Y0.15)O1.925 samples. The implantation depth was selected on the basis of the ability to observe by Rutherford backscattering spectroscopy (RBS) the behaviour of Cs and I after treatment. With a 1 MeV incident energy, the ions are implanted at a depth of 200 nm as predicted by TRIM. After implantations full quantification of I and Cs concentration profiles was performed by RBS. The implantation profiles are measured as a function of sample temperature during stepwise heating programs. It is interesting to observe retention of Cs and I at relatively high temperature (e.g. for 2 h, below 900 K for Cs and below 1400 K for I). This behaviour is likely to be due to the size and interactions of these species in the zirconia solid solution.

Modeling and Experiment on Physical and Chemical Liquid Deposition Processes for Rapid Tooling and Manufacturing

2000 ◽  
Author(s):  
Zongyan He ◽  
Jack G. Zhou
Keyword(s):  
Heat Transfer ◽  
Theoretical Models ◽  
Nucleation And Growth ◽  
Free Form ◽  
Technical Problems ◽  
Chemical Liquid Deposition ◽  
Deposition Processes ◽  
Physical And Chemical ◽  
Solid Free Form Fabrication ◽  
Liquid Deposition

Abstract A new solid free-form fabrication (SFF) technique, named Physical and Chemical Liquid Deposition (P/CLD), is introduced in this paper, and then several key technical problems are stated. In order to solve these problems, theoretical models to describe the nucleation and growth of deposits in PLD, the chemical dynamic process in CLD, and the heat transfer in P/LCD are studied. To determine the heat transfer parameters, some experiments are designed and experimental results are presented.

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