Critical Water Level Research Articles

Mechanisms of Water Retention Dynamics in Intertidal Sandy Flats and Beaches

In this paper we describe and clarify the mechanisms of water retention dynamics in intertidal sandy flats and beaches. This was done by performing field observations, laboratory experiments and theoretical analyses, which developed in an interactive manner. The combined results demonstrate that the difference in the water retention dynamics for sandy flats and beaches arises from the difference in pore water migrations that take place around air entry suctions for both types of the soils. Furthermore, it is found that for a given sandy soil, there exists a critical ground water level above which the degree of saturation does not decline. Two quantitative index are proposed for assessing and creating such water retention fields. The results obtained can directly apply to the design and management of artificial sandy flats.

Validation study of the Monte Carlo code MVP for analysis of two-region TCA critical experiments with PWR-type MOX fuels

A series of critical experiments containing PWR-type MOX fuels conducted at the TCA facility of Japan Atomic Energy Research Institute have been analyzed. The cores were composed of a central 4.91 wt% plutonium enriched mixed-oxide (PuO 2–UO 2) 10 × 10 test lattice with water-to-fuel volume ratio of 2.40 or 2.96, surrounded by 2.6 wt% enriched UO 2 driver lattice with water-to-fuel volume ratio of 1.50 with a water gap in-between. The fissile plutonium content was 91.4 wt%. The critical water level, the power distribution in the test region, and the neutron activation distribution of Au-wire were measured for six different cores of which two contain soluble boron of 309.4 and 554.0 ppm, one contains four equidistant water holes in the central test lattice and one contains cross water gap at the core center. Calculation of corresponding effective multiplication factor, the fission reaction-rate distribution in the test region, and the capture reaction-rate distribution of Au have been performed using a continuous-energy Monte Carlo code MVP with two nuclear data sets based on JENDL-3.2 and JENDL-3.3. The calculated results agreed to the measurements within a maximum difference of 0.27% for the effective multiplication factors, 3.0% for the power distributions, 5.9% for the thermal activation distributions throughout the whole region, and 4.3% for the epithermal activation distributions in the core region.

A benchmark on the calculation of kinetic parameters based on reactivity effect experiments in the CROCUS reactor

Measurements in the CROCUS reactor at EPFL, Lausanne, are reported for the critical water level and the inverse reactor period for several different sets of delayed supercritical conditions. The experimental configurations were also calculated by four different calculation methods. For each of the supercritical configurations, the absolute reactivity value has been determined in two different ways, viz.: (i) through direct comparison of the multiplication factor obtained employing a given calculation method with the corresponding value for the critical case (calculated reactivity: ρ calc); (ii) by application of the inhour equation using the kinetic parameters obtained for the critical configuration and the measured inverse reactor period (measured reactivity: ρ meas). The calculated multiplication factors for the reference critical configuration, as well as ρ calc for the supercritical cases, are found to be in good agreement. However, the values of ρ meas produced by two of the applied calculation methods differ appreciably from the corresponding ρ calc values, clearly indicating deficiencies in the kinetic parameters obtained from these methods.

Synoptic features associated with critical water level rises in the Río de la Plata

AbstractThis study aims to describe the synoptic features that caused the water level in the Río de la Plata estuary to rise above critical levels between December 1989 and December 1998. Floods in the estuary can seriously affect the land beside the river from Punta Indio (35.22°S,57.17°W) to the Paraná delta, including the lowlands of Buenos Aires City.Surface pressure patterns associated with floods in the Río de la Plata estuary were obtained by using Quartimax rotated T‐mode Principal Component Analysis (PCA) of 1000 hPa geopotential heights. The PCA patterns and 1000 hPa composite and anomaly fields show two main causes for overflows in the Río de la Plata estuary. First, the presence of a surface anticyclone, located south of Buenos Aires province and over northern Patagonia; and, second, cyclogenesis over northeastern Argentina or over Uruguay. The two synoptic features are often present simultaneously.Two representative points were selected in the area under study: one over the continent at the Aeroparque meteorological station (34.34°S,58.25°W) and another over the ocean between 36°S,56°W and 36°S,50°W. Predominant 1000 hPa wind directions associated with overflows were SE at the former location and SSW at the latter.Based on the analysis of the obtained fields, the relationship between the estuary overflow and blocking situations and/or positive pressure anomalies over southern South America and adjacent seas was studied. The zonal circulation index (I), used to detect blocking actions, was found to be useful for identifying synoptic situations related to the estuary swelling. The probability of water level rises in the Río de la Plata with a blocking or I > 0 at 70°W is 0.48, 0.72, 0.78 and 0.73, for summer, autumn, winter and spring, respectively. When I > 0 is observed over the Atlantic at 40°W the probability of flooding is 0.16 for the whole year, but it decreases to 0.028 in autumn, winter and spring.These results and weather charts from different numerical prediction models show that alerts of possible Río de la Plata estuary overflow can be released five days in advance. Copyright © 2005 Royal Meteorological Society

Near-infrared spectroscopy for soil water determination in small soil volumes

Critical soil water levels for soil microscale processes are difficult to determine because of variability in large soil volumes and lack of techniques for logging soil water contents in small soil volumes. This study tested nearinfrared (NIR) spectroscopy for soil water content determination. Five soil horizons with a range in soil texture, soil organic carbon, carbonates, pH and horizon depth, were tested at air-dry, field capacity and 0.1 MPa tension water content. Volumetric soil water content, determined using the standard method of oven-drying and soil bulk density, was compared to NIR absorbance in various combinations and wavelengths. The NIR spectra obtained with the probe in direct contact with the soil gave better results than when the probe was separated from the soil with a glass slide. The most reliable validation results were obtained using a multivariate partial least squares regression of the full spectrum with an r2 of 0.95 and RMSE of prediction of 6.4%. Smoothing and derivatives of the spectra did not improve the validation results. The relationships for absorbance at single wavelength segments, ratios, differences and area under the curve around the 1940 nm peak were good (r2 values near 0.85 ) but poorer than the results using the full spectra. The high correlation coefficients obtained with the wide variety of soils utilized in this study suggest that NIR absorbance is a practical method for determining volumetric soil water content for small soil volumes. Key words: Near-infrared spectroscopy, soil water, Near-infrared absorbance

Measurements and Analyses of Reactivity Effect of Fission Product Nuclides in Epithermal Energy Range

Experimental data usable for evaluating cross sections of main fission product elements (Rh, Cs, Nd, Sm, Eu and Gd) in the epithermal energy range were measured. A cadmium-covered vessel containing a pure water or an aqueous solution of a fission product element was inserted at the center of TCA (Tank-type Critical Assembly) core. Reactivity effects were obtained by the difference in the critical water levels between a pure water and an aqueous solution in the vessel. The measured reactivity was more than 1 φ and it was greater than the experimental uncertainties. Since the adjoint thermal flux below the cadmium-cutoff energy are largely depressed in the vessel, the reactivity effects in epithermal energy range could be measured. The analyses for the experiments were performed using the SRAC code system and neutron transport calculation code TWOTRAN. The exact Perturbation theory was applied to calculate the reactivity effects of fission product elements. The calculated reactivity effects using JENDL-3.2 and ENDF/B-IV cross-section libraries were compared against the measured values. The analyses using JENDL-3.2 gave reasonable results for these measurements.

Stomatal and Cuticular Transpiration of Greenhouse Tomato Plants in Response to High Solution Electrical Conductivity and Low Soil Water Content

`Capello' tomato plants (Lycopersicon esculentum Mill.) were grown in a greenhouse in peat-based substrate (70% sphagnum peat and 309'. perlite, by volume) and supplied with nutrient solutions of high (4.5 mS·cm-1) or low (2.3 mS·cm-1) electrical conductivity (EC) under high (95% ± 5%) or low (55% ± 8% of capillary capacity) soil water conditions. Three weeks after treatments started, stomatal transpiration (TRst) and cuticular transpiration (TRcu) rates were measured by three methods: 1) analyzing TRst and TRcu from a water retention curve obtained by drying excised leaves in air under a photosynthetic photon flux (PPF) of 400 μmol·m-1·s-1, 2) analyzing TRst and TRcu from a transpiration decline curve obtained by measuring transpiration rates after cutting the leaf from the stem of the dehydrated plant in the gas-exchange system, and 3) measuring transpiration rates under light and in dark respectively using the gas-exchange method. TRst and TRcu were decreased by high EC and/or low soil water content. For method 1, the transpiration decline curve shows two distinct phases: the initial steep slope that indicates TRst and the gently sloped section that indicates TRcu. Both slopes were lower for high EC and/or water-stressed plants compared to the control (low EC and high soil water content). The tangent lines of these two phases of the curve intersect at one point (t, w). The value oft that indicates the time for stomatal closure was longer and the value of w that indicates the critical tissue water level for stomatal closure was lower for high EC and/or water-stressed plants. In method 2, the initial rate of total transpiration was higher in high EC and/or water-stressed plants. Leaf wax content increased, especially under high EC stress. This suggests that increased deposition of wax prevents water loss from the cuticle. A delay in complete stomatal closure, complete closure at lower RWC, and reduced TRcu or an increase in wax deposit were adaptations to water and salinity stresses in tomato plants under our controlled environmental conditions.

Rainfall Thresholds for the Initiation of Debris Flows at La Honda, California

In order to study the relation between heavy rainfall, shallow pore pressures, and slope stability in hillslopes susceptible to debris flows, we have been observing debris flows and measuring rainfall and hillslope pore pressures in a 10-km 2 study area in the central Santa Cruz Mountains near La Honda, California. A simple numerical model, based on the physical analogy of a leaky barrel, can simulate significant features of the interaction between rainfall and shallow-hillslope pore pressures. In the model, the barrel is filled at a rate equal to the rainfall intensity and drained at a rate equal to the product of the water level retained in the barrel, Z, times the drainage coefficient, k d . If the retained rainfall exceeds a critical water level, Z c , the slope becomes unstable. Thus, the threshold for the intensity and duration of storm rainfall required to initiate debris flows is determined by the k d and Z c values of the most susceptible slopes in the study area. Although comparisons of leaky-barrel-model simulations with piezometer measurements indicate reasonable agreement, the k d values of individual piezometers in the study area vary widely because of spatial variations in soil properties and slope geometry. The spatial distribution of rainfall, in contrast, is fairly uniform over a scale of a few square kilometers. Thus, rather than attempt to model an actual slope in any detail, the leaky-barrel model may be used to compare the relative hydrologic effects of storms by plotting the maximum response level, Z max , against the drainage coefficient, k d . Values of Z max versus k d can then be compared for storms that triggered debris flows versus storms that failed to trigger debris flows. Using this technique, we can backcalculate k d and Z c values for the most susceptible slopes in the study area. These threshold values are k d = 0.85/hr and Z c = 8.5 mm. This leaky-barrel-model threshold is consistent with, but slightly higher than, an earlier, purely empirical, threshold. We can also relate the number of debris flows triggered by a storm to the time and amount by which the leaky-barrel-model response exceeded the threshold during the storm.

Reactivity Effect of Borated Stainless Steel Plate in Single and Coupled Cores Composed of Low-Enriched UO2Rods

For the criticality safety designs of the storage pools which store large number of spent fuels, neutron poison materials are useful for increasing capacity of the storage pool by minimizing the spacing between the fuel assemblies. Since few experimental data exist for examining the validation of calculation methods which evaluate the nuclear criticality safety of fuel storage using the borated SUS (B-SUS) plates, critical experiments with B-SUS plates in the water region of single and coupled cores were performed at the Tank-type Critical Assembly (TCA). The systematic data on the reactivity effect of B-SUS plate as a function of the thickness, the boron content and the position of B-SUS plates in the water region were obtained using the critical water level method. The interacting effect between the two cores was also measured to clarify the nuclear characteristics of the coupled two core system which is the simplest system among multiple unit system. Criticality calculations with the combination of a Monte Carlo code, KENO-IV, and the MGCL-137 neutron cross section library in JACS were carried out, and these calculations reproduced the reactivity effect of B-SUS plate within ±0.6%δK/K.

Reactivity Effect of Borated Stainless Steel Plate in Single and Coupled Cores Composed of Low-Enriched UO2 Rods.

For the criticality safety designs of the storage pools which store large number of spent fuels, neutron poison materials are useful for increasing capacity of the storage pool by minimizing the spacing between the fuel assemblies. Since few experimental data exist for examining the validation of calculation methods which evaluate the nuclear criticality safety of fuel storage using the borated SUS (B-SUS) plates, critical experiments with B-SUS plates in the water region of single and coupled cores were performed at the Tank-type Critical Assembly (TCA). The systematic data on the reactivity effect of B-SUS plate as a function of the thickness, the boron content and the position of B-SUS plates in the water region were obtained using the critical water level method. The interacting effect between the two cores was also measured to clarify the nuclear characteristics of the coupled two core system which is the simplest system among multiple unit system. Criticality calculations with the combination of a Monte Carlo code, KENO-IV, and the MGCL-137 neutron cross section library in JACS were carried out, and these calculations reproduced the reactivity effect of B-SUS plate within ±0.6%δK/K.

Evaluation of Critical Bucklings of Light-Water Moderated Low Enriched UO2Cores by the Variable Loading Method

Abstract Horizontal extrapolated distances Xh and critical bucklings B2 C for light-water moderated low enriched UO2 cores were evaluated using the variable loading method. A set of critical height (water levels) of the cores having various horizontal dimensions was used in this method. Errors of the present method were smaller than the previous ones by the flux shape method in which the horizontal extrapolated distance was determined from the horizontal power distribution. The presently obtained Xh and B2 C reproduced well the change in the critical water level for the whole range of the horizontal core size, while the previous ones could be used only for a limited range. Moreover, the effective multiplication factors obtained through the cell calculation of the SRAC code by using the presently evaluated critical bucklings agreed much better with the rigorous ones by the continuous energy Monte Carlo calculation using a full core model, than those by using the previous values. Therefore, it was concluded that the variable loading method can give more accurate values for Xh and B2 C than the flux shape method for the cores investigated.

Evaluation of Critical Bucklings of Light-Water Moderated Low Enriched UO2 Cores by the Variable Loading Method.

Abstract Horizontal extrapolated distances Xh and critical bucklings B2 C for light-water moderated low enriched UO2 cores were evaluated using the variable loading method. A set of critical height (water levels) of the cores having various horizontal dimensions was used in this method. Errors of the present method were smaller than the previous ones by the flux shape method in which the horizontal extrapolated distance was determined from the horizontal power distribution. The presently obtained Xh and B2 C reproduced well the change in the critical water level for the whole range of the horizontal core size, while the previous ones could be used only for a limited range. Moreover, the effective multiplication factors obtained through the cell calculation of the SRAC code by using the presently evaluated critical bucklings agreed much better with the rigorous ones by the continuous energy Monte Carlo calculation using a full core model, than those by using the previous values. Therefore, it was concluded that the variable loading method can give more accurate values for Xh and B2 C than the flux shape method for the cores investigated.

Axial Dependence of Partial Void Reactivity in a Light Water-Cooled, Heavy Water-Moderated, Pressure-Tube Reactor

The effect on reactivity of changes in the coolant levels in the pressure tubes of a pressure-tube heavy water reactor is experimentally studied to clarify the effect of an axial coolant void fraction distribution. The coolant void fraction distribution is simulated by stepwise changes in the coolant levels in the Deuterium Critical Assembly (DCA). The reactivity is measured for a 25.0-cm-pitch square-lattice core with a positive coolant void reactivity. The reactivity changes resulting from changes in the coolant levels are measured as changes in the critical heavy water levels. The axial distribution of the thermal neutron flux is also measured by the copper activation method.In these measurements, the critical heavy water levels show a sinuous curve having a maximum and a minimum, and a positive reactivity larger than those of both the 0% and the 100% void uniform cores is introduced at certain coolant levels by stepwise changes in the coolant levels.An experimental analysis is performed with the coupled WIMS-ATR/CITATION code system, whose analytical method was established through DCA critical experiments. Agreement between experiment and analysis is fairly good. Furthermore, the peculiar reactivity behavior resulting from changes in the coolant levels is analyzed using a simplified model to take note of typical reactor physics parameters. It is clarified that this anomalous phenomenon is caused by the combined effect of the flattened S curve change in the thermal neutron absorption and the even flatter S curve change in the neutron leakage caused by the changes in the coolant levels. Useful information is obtained regarding reactivity behavior with an axial coolant void fraction distribution.

A study on criticality of coupled fast-thermal core HERBE at RB reactor

The coupled fast-thermal core HERBE at the RB zero power heavy water reactor in Vinča was designed with the aim to improve experimental possibilities in fast neutron fields. The requirements for minimum modifications in the RB construction and application of available fuel restricted design flexibility of the coupled system. Thus the following core is considered optimal in the sense of the foregoing constraints: the central fast core of natural uranium is surrounded by neutron filter zone (cadmium and natural uranium) and converter zone (enriched uranium fuel, without moderator). The coupling region is heavy water. Thermal core is formed of RB heavy water 80% enriched uranium lattice with 12 cm pitch. The criticality of the system is obtained by adjusting moderator level. The critical heavy water levels were measured for normal reactor operation and some simulated accidental conditions. These data were analyzed by computer code package for the design of thermal and coupled fast-thermal reactors recently developed in IBK Nuclear Engineering Laboratory. Good agreement between computations and experimental data was achieved.

Prediction of the water level At the onset of dryout for a multitube one-through boiler.

Experiments were made on a critical water level under which the dryout of the heating surface occurred near the exit of the water tubes of a multitube one-through boiler. The special feature of this boiler is that the feed water rate is quite low. Based on a theoretical relation the critical water level was related to the quality, the void fraction and the slip ratio. The slip ratio was determined by the measured value of the critical water level. A correlation of the slip ratio was proposed in order to determine the water level. The correlation is expressed as a function of density ratio and Froude number, and may cover a wide range of the mass velocity including the high velocity covered in the former literatures.

Boiling Heat-Transfer Performance at Critical Water Level in a Porous Bed

Boiling Heat-Transfer Performance at Critical Water Level in a Porous Bed

Boiling heat transfer in porous bed with water injection and critical water level.

An Experimental study has been conduced to determine the influence of the saturated-water injection into packed bed on boiling heat transfer or a upward facing surface covered with the bed. Three kinds of the particles of alumina, glass, and steel balls were utilized as the testing porous beds. Injection of the saturated water was found to increase the heat-transfer performances over the range of injection rate investigated. It was also observed that there might be a critical water level for which a maximum boiling heat-transfer coefficient takes place at a given ΔTs.

Optimal control of a dam under seasonal electricity prices

This study concerns the optimal control of a hydroelectric dam under seasonal electricity prices: high in winter, low in summer. The goal is to maximize the expected discounted infinite-horizon return through a policy that determines the amount of electricity to be produced in each time period, depending on the water level at the beginning of the period under consideration. The prices are assumed to be deterministic, and the flows into the reservoir are seasonal, stochastic, but independent from one period to another. The electric power generated is proportional to the amount of water flow through the turbines. There exist seepage and evaporation losses. It is shown that in the simplest price structure, the optimal policy is entirely determined by a single critical water level in each period of time, at which one starts producing. An example shows that the discretization of the reservoir levels can destroy this property. A method is proposed to avoid this difficulty. Another way of defining a policy is through goal-levels. This approach is shown to give higher returns than the standard approach.

Water as a melting point depressant for acrylic polymers

Water is known to strongly depress the melting point of polyacrylonitrile (PAN) and acrylic copolymers. A scanning calorimetric technique has been developed that utilizes this melting point depression in probing the structure of acrylic fibers. In this report the melting and crystallization of PAN and acrylonitrile-vinyl acetate copolymers is studied as a function of water content. Addition of water continually depresses the polymer melting point until a critical water level is reached where the molten polymer separates from the water and no further reduction in the melting point is observed. Both the minimum melting point and the critical amount of water required for phase separation decreases as the level of vinyl acetate comonomer is increased. The latter relationships are examined in terms of the acrylic polymer morphology and the possibility that the water molecules become associated with the nitrile group during the melting process.

Future Water‐level Declines in Deep Sandstone Wells in Chicago Region

AbstractFuture water‐level declines in deep sandstone wells penetrating the Cambrian‐Ordovician Aquifer, the most highly developed aquifer for large ground‐water supplies in the Chicago region, are considered. The Cambrian‐Ordovician Aquifer is encountered at an average depth of about 500 feet below the land surface at Chicago; it has an average thickness of 1000 feet and is composed chiefly of sandstones and dolomites. Recharge is received from overlying glacial deposits in areas averaging 47 miles west of Chicago and from leakage through a shale confining bed.Geohydrologic conditions are simulated by a model aquifer, i. e., a semi‐infinite rectilinear strip of sandstones and dolomites 84 miles wide and 1000 feet thick. The model aquifer is bounded by a recharge boundary 47 miles west of Chicago and by two intersecting barrier boundaries 37 miles east and 60 miles south of Chicago, and is overlain by a confining bed consisting mostly of shale averaging 200 feet thick. The hydraulic properties of the model aquifer and its confining bed, the image‐well theory, and appropriate ground‐water formulas are used to construct a mathematical model which provides a means of evaluating the practical sustained yield of the aquifer and predicting future water‐level declines. Records of past pumpage and water levels establish the validity of this mechanism as a model of the response of the aquifer to heavy pumping.Pumpage from deep sandstone wells concentrated in six pumping centers has increased from 200,000 gallons per day (gpd) in 1864 to 96.5 millions of gallons per day (mgd) in 1961. As a result of heavy pumping, water levels in deep sandstone wells declined more than 650 feet at Chicago between 1864 and 1961.The maximum amount of water that can be continually withdrawn from existing pumping centers without creating critical water levels or exceeding recharge is estimated to be about 46 mgd. Withdrawals from the Cambrian‐Ordovician Aquifer have exceeded the practical sustained yield since 1959. It is estimated that about 65 mgd could be obtained by shifting one existing pumping center toward the west and by adding 2 new pumping centers north and northwest of Chicago.Unless lake water is made available to those areas with short supply a pumpage increase from 96.5 mgd in 1961 to 243 mgd in 2010 can be expected. Using this pumpage increase and taking into consideration dewatering of portions of upper units of the aquifer, declines in nonpumping water levels that may be expected between 1963 and 2010 at existing pumping centers were computed by using the mathematical model.Pumping water levels in most pumping centers will be at critical stages a few feet above the top of the lowermost and most productive unit of the aquifer by 2010.