An analytical solution to a two-dimensional model of the rewetting of a hot dry rod

The model considers a hot dry rod of infinite length cooled by a film of liquid moving along its surface. The heat transfer coefficient is assumed to be constant on the wet side and zero on the dry side of the rewetting front, and the liquid film is assumed to move at constant speed. We derive an analytical formula relating the temperature difference in the rod, the temperature at the rewetting front, the wet side heat transfer coefficient, and the rewetting speed. The formula is thought to apply to the rewetting of a fuel rod during emergency cooling by flooding.     

Heat transfer during the rewetting of hot horizontal channels

The heat transfer in the rewetting of hot horizontal channels is investigated. The physical model assumes an inclined rewetting front advancing at a uniform velocity. Precursory cooling in the dry region is considered. Three-dimensional energy equations are solved numerically by a finite difference method. Further, the axial and circumferential temperature distributions are predicted. The influence of various parameters on the rewetting velocity is analyzed, as are the variations of the different heat transfer mechanisms, convection to the fluid and conduction in the three-dimensions, as a function of time.     

Calculations on the rewetting of hot surfaces

Previous theoretical and experimental work has shown that the rate of advance of a quench front over a hot surface is a function of the initial temperature, the thickness and the physical properties of the hot surface, and the cooling water flow conditions. The heat conduction problem, which determines the quench rate, is solved accurately by an analytic method which requires a computer. The results, based on a constant heat transfer coefficient in the wetted region, can be applied to most conditions of practical interest, and are applied to determining the quenching heat transfer coefficient and the sputtering temperature from previous experimental results at high pressures, with cooling water near its saturation temperature.     

On the process of rewetting a hot surface by a falling liquid film

A two-dimensional transient heat conduction model for rewetting a hot surface by a falling liquid film predicts that for stainless steel, Inconel or Zircaloy only a wall thickness of some 0.020 in. takes part in the rewetting process in steam at 100–1000 psia. The rewetting rate is nearly independent of heat flux and thermal conductivity, but increases with pressure and decreases with volumetric heat capacity.     

Experimental studies on rewetting of hot vertical annular channel

Studies on the rewetting behaviour of hot vertical annular channels are of interest in the context of emergency core cooling in nuclear reactors following LOCA. Experimental studies were carried out to study the rewetting behaviour of a hot vertical annular channel, with hot inner tube, for bottom flooding and top flow rewetting conditions. The length of the inner tube of the test section was 3030 mm for bottom flooding rewetting experiments and 2630 mm for top flow rewetting experiments. The tube was made of stainless steel. Experiments were conducted for water flow rates in the annulus upto 7 lpm (11.7×10⁻⁵ m³ s⁻¹). The initial surface temperature of the inner tube was varied from 200 to 500°C. The experimental studies show that for a given initial surface temperature of the tube, the rewetting velocity increases with an increase in flow rate of water and it decreases with an increase in the initial surface temperature for a given water flow rate. For a given water flow rate and initial surface temperature, the rewetting velocity is higher in the case of rewetting under bottom flooding conditions as compared to that in the case of rewetting under top flow conditions. These conclusions agree with the conclusions reported in the earlier literature. Using the experimental data of the present work, correlations for bottom flooding and top flow rewetting velocities are developed.     

An analysis of rewetting of a nuclear fuel rod in water reactor emergency core cooling

An exact solution of the quasi-steady two-dimensional conduction equation for the rewetting of a nuclear fuel rod in water reactor emergency core cooling is obtained for a cylindrical rod geometry. The analysis adopts the conventional model of two heat transfer regions: zero heat transfer coefficient over the dry surface and a constant heat transfer coefficient over the wetted surface. Both the wet front velocity and the temperature distribution in the rod are computed. The present solution is valid over the whole range of Biot number.     

An analytical solution to fuel-and-cladding model of the rewetting of a nuclear fuel rod

An exact solution of the quasi-steady two-dimensional conduction equation for the rewetting of a nuclear fuel rod in water reactor emergency core cooling is obtained for a fuel-and-cladding model. A method of solving non-separable differential equations is presented, which is used in the present analysis. The recently developed theorem of orthogonality of piecewise continuous eigenfunctions is also used to handle the composite rod in the present model. The present analysis reveals that the wet front velocity increases with the increase of the gap resistance between the fuel and the cladding, and approaches a limiting value, which is equal to the wet front velocity of the tube of cladding alone, as the gap resistance becomes infinite. For convenience in practical application, the results of the present analysis are correlated in simple expressions.     

Evaluation of heat-transfer coefficient at direct-contact condensation of cold water and steam

The estimation of the heat transfer coefficient at the direct-contact condensation of cold water and steam is a very hard task since the phenoma are essentially undsteady and the interface motion is so complicated that an exact estimation of its area is almost impossible. The present study shows the heat transfer coefficient evaluated experimentally by assuming simple interface shapes for complicated surfaces and estimated those through comparison of the numerical analyses to the data of experiments related to the loss of coolant accidents of light water reactors.At chugging, the heat transfer coefficient reached up to 2 × 10⁶W/(m^{2 K}). At condensation oscillation, it ranged between 10⁵–10⁶ W/(m² K). At a jet region of cold water injected into the steam flow in a pipe or the stationary steam in a vessel, the value was around 2 × 10⁵W/(m²K), and at the surface of stratified flow, it was between 3 × 10³–3 × 10⁴W/(m²K).     

An experimental study on rewetting phenomena in transient conditions of bwrs

It is known that rod temperature rise after boiling transition (BT) is not excursive and that the peak cladding temperature (PCT) is suppressed by rewetting to return to nucleate boiling, even if BT occurs under severe conditions exceeding abnormal operational transients for a BWR. The purpose of this study is to develop and verify the rewetting correlation. The rewetting correlation was developed based on single rod data, as a function of quality, mass flux, pressure and heat flux. The transient thermal-hydraulic code used in the BWR design analysis (SCAT) with this rewetting correlation was compared with transient rod temperature result after the occurence of BT obtianed by the 8×8 and 4×4 rod bundle. It is concluded that the transient code with the developed rewetting correlation predicts the PCT conservatively, and the rewetting time well.     

相对转换系数法在核材料识别与分析中的应用

针对核武器和核保障核查中大体积多层结构的复杂源项的测量特点,建立了一套相对转换系数法,通过γ能谱分析,可得到核材料的丰度、相对质量及储存时间等信息,并完成了初步的实验验证。     

The effect of precursory cooling on rewetting of a slab

The Dua and Tien (1976) model for the rewetting of a slab with precursory cooling is solved exactly by separation of variables. The solution for the rewetting velocity is found to agree very well with a Wiener Hopf technique solution to this model by the author. Rewetting rates predicted by the approximate solution of Dua and Tien are found to agree with the present solution for small Peclet numbers, while underpredicting them for large Peclet numbers. Theoretical quench front velocities compare favorably with experimental data for copper quenched by liquid nitrogen. Precursory cooling is shown to be able to greatly increase the rewetting velocity, in particular for cases of high flow rates, while neglecting it in modelling may result in much too low quench velocities, as compared to experimental measurements.     

An analysis of containment responses during a station blackout accident

An analysis of the responses of the containment during a station blackout accident is performed for the APR1400 nuclear power plant using MELCOR 2.1. The analysis results show that the containment failure occurs at about 84.14 h. Prior to the failure of the reactor vessel, the containment pressure increases slowly. Then, a rapid increase of the containment pressure occurs when a large amount of hot molten corium is discharged from the reactor pressure vessel to the cavity. The molten corium concrete interaction (MCCI) is arrested when water is flooded over a molten corium in the cavity. The boiling of water in the cavity causes a fast increase in the containment pressure. During the early phase of the accident, a large amount of steam is condensed inside the containment due to the presence of the heat structures. This results in a mitigation of a containment pressure increase. During the late phase, the containment pressure increases gradually due to the addition of steam and gases from an MCCI and water evaporation. It was found that two-thirds of the total mass of steam and gases in the containment is from an MCCI and one-third of the mass is from water evaporation.     

Sub-channel analysis of CANDU–SCWR and review of heat-transfer correlations

The paper presents the results of sub-channel analysis of CANDU–SCWR based on a wide review of heat transfer correlations. According to comparison with experiment data at different heat flux, Bishop Correlation is selected in SUBCHAN code to analyze CANDU–SCWR fuel channel. By detailed calculation of 43 fuel rods fuel channel in CANDU–SCWR, the paper gets the conclusion that the mass flux redistribution and reduction of heat-transfer coefficient at supercritical condition caused by the steep change of coolant density will limit the power of fuel channel in CANDU–SCWR.     

Experimental investigation of the rewetting process in a freon-113 vapour environment

An experimental facility to simulate two-phase high-pressure flow phenomena using low-pressure Freon-113 has been built, commissioned, and employed to investigate the rewetting process of hot surfaces in a Freon-113 environment at pressures up to 5.43 bar. The experimental results and the correlations derived show good agreement with previous results using water and confirm the feasibility of simulating rewetting phenomena in water by the use of Freon.     

A general one-dimensional model for conduction-controlled rewetting of a surface

A computer-oriented analytical method for predicting the rewetting rate of a hot dry wall is proposed. The wall, which is modeled as a thin flat plate with internal heat generation, receives a variable heat flux from one side while it is cooled from the other side. The model accounts for the large variations of the heat transfer coefficient near the wet front and for the temperature dependence of the thermal and physical properties of the wall. The one-dimensional heat-conduction equation is solved by dividing the quenching zone into small segments of arbitrary temperature increment and constant properties and heat transfer coefficient. A trial-and-error method is developed to predict the velocity of the wet front, the length of the quenching zone and the temperature profile. The one-dimensional models of other authors can be obtained as particular cases of the present model.