Computer Code Predictions Research Articles

Decay heat uncertainty for BWR used fuel due to modeling and nuclear data uncertainties

Characterization of the energy released from radionuclide decay in nuclear fuel discharged from reactors is essential for the design, safety, and licensing analyses of used nuclear fuel storage, transportation, and repository systems. There are a limited number of decay heat measurements available for commercial used fuel applications. Because decay heat measurements can be expensive or impractical for covering the multitude of existing fuel designs, operating conditions, and specific application purposes, decay heat estimation relies heavily on computer code prediction. Uncertainty evaluation for calculated decay heat is an important aspect when assessing code prediction and a key factor supporting decision making for used fuel applications. While previous studies have largely focused on uncertainties in code predictions due to nuclear data uncertainties, this study discusses uncertainties in calculated decay heat due to uncertainties in assembly modeling parameters as well as in nuclear data. Capabilities in the SCALE nuclear analysis code system were used to quantify the effect on calculated decay heat of uncertainties in nuclear data and selected manufacturing and operation parameters for a typical boiling water reactor (BWR) fuel assembly. The BWR fuel assembly used as the reference case for this study was selected from a set of assemblies for which high-quality decay heat measurements are available, to assess the significance of the results through comparison with calculated and measured decay heat data.

Determination of electronic stopping powers of 0.05–1 MeV/u 131Xe ions in C-, Ni- and Au-absorbers with calorimetric low temperature detectors

A new experimental system for precise determination of electronic stopping powers of heavy ions has been set up at the accelerator laboratory of the University of Jyväskylä. The new setup, combining an established B-ToF system and an array of calorimetric low temperature detectors (CLTDs), has been used for the determination of electronic stopping powers of 0.05–1MeV/u 131Xe ions in carbon, nickel and gold. Thereby advantage of the improved linearity and energy resolution of CLTDs as compared to the previously used ionization detector was taken to reduce energy calibration errors and to increase sensitivity for the energy loss determination, in particular at very low energies. The total uncertainties of 3–4% for C- and Ni-targets, and 5–7% for Au-targets, respectively, are dominated by the target properties, i.e. thickness determination and inhomogeneities. The results are compared to data from literature and to predictions of different theoretical computer codes. In the high energy part of the examined energy range the results are in good agreement with previously published data, while new stopping power data for very heavy ions in different Z2-materials have been obtained at lower energies. Moreover, unexpectedly strong channeling effects for the transmission of the 131Xe ions in thin, partly polycrystalline nickel and gold target foils have been observed and investigated.

Energy loss of 132Xe-ions in thin foils

The energy loss of 132Xe-ions in C, Al, Ni, Ag, Lu, Au, Pb and Th foils was measured in the energy range from 0.1 to 5 MeV/u using the TOF-E method. The results are compared with previously published data and with the predictions of several computer codes. They include theoretical codes: PASS, CASP, semi-empirical programs: SRIM, LET and the Hubert table predictions.

Exposure to galactic cosmic radiation and solar energetic particles

Several investigations of the radiation field at aircraft altitudes have been undertaken during solar cycle 23 which occurred in the period 1993-2003. The radiation field is produced by the passage of galactic cosmic rays and their nuclear reaction products as well as solar energetic particles through the Earth's atmosphere. Galactic cosmic rays reach a maximum intensity when the sun is least active and are at minimum intensity during solar maximum period. During solar maximum an increased number of coronal mass ejections and solar flares produce high energy solar particles which can also penetrate down to aircraft altitudes. It is found that the very complicated field resulting from these processes varies with altitude, latitude and stage of solar cycle. By employing several active and passive detectors, the whole range of radiation types and energies were encompassed. In-flight data was obtained with the co-operation of many airlines and NASA. The EURADOS Aircraft Crew in-flight data base was used for comparison with the predictions of various computer codes. A brief outline of some recent studies of exposure to radiation in Earth orbit will conclude this contribution.

Cosmic ray measurements at aircraft altitudes and comparison with predictions of computer codes

Extensive measurements of dose exposure of aircrew have been carried out in recent years using passive detectors on subsonic and supersonic air routes by DIAS (Dublin Institute for Advanced Studies). Studies were based on measurement of LET spectra using nuclear recoils produced in CR-39 nuclear track detectors by high energy neutrons and protons. The detectors were calibrated using energetic heavy ions. Data obtained were compared with the predictions of the EPCARD and CARI-6 codes. Good agreement has been found between the experimental and theoretical values.

Irradiation Behavior and Thermodynamic Properties of Metallic Fuel

Applicability of metallic U-Pu-Zr fuel to commercial fast reactors is being studied in Japan. This requires evaluation of the integrity of the metallic fuel to be used under severe irradiation conditions of commercial reactors, such as higher coolant temperature and higher burnup. When the high temperature application of the metallic fuel is considered, one of the fuel design limits is elimination of fuel centerline melting. The author presents review on some thermal properties of the fuel alloys for fuel temperature estimation. Another design limit is elimination of liquefaction at the fuel-cladding interface during normal reactor operation. The experiments and analyses to determine the liquefaction condition are summarized, where thermodynamic assessments of the relevant alloy systems play an important role as well as in estimation of the fuel alloy properties. The computer code prediction of the irradiation behavior up to a peak burnup ~20at% is also presented This suggests that appropriate estimations of cladding wastage by rare-earth elements and accumulation of non-gaseous fission products are important for the analysis of the metallic fuel performance up to such a high burnup.

Nonequilibrium boundary-layer effects on the aerodynamic heating of hypersonic waverider vehicles

The aerodynamic heating of hypersonic waverider vehicle configurations is examined in the high-altitude hypersonic flight regime where nonequilibrium dissociation-recombination in the boundary-layer and finite surface catalysis effects are both important. Analytical treatment of these effects is given for highly cooled surfaces in three important heating regions: 1) the nose, 2) the swept-wing leading-edge attachment line, and 3) the windward body center line. Relationships for the relative nonequilibrium effects are developed for each region that enable both computer code-prediction validation and cost-effective parametric engineering studies.

Non-equilibrium boundary layer effects on the aerodynamic heating of hypersonic vehicles

The aerodynamic heating of a generic lifting hypersonic vehicle configuration is examined in that high altitude hypersonic flight regime where non-equilibrium dissociation/recombination in the boundary layer and finite surface catalysis effects are both important. Analytical treatment of these effects is given for highly-cooled surfaces in three important heating regions: the nose, the swept wing leading edge attachment line and the windward body centerline. Relationships for the relative non-equilibrium effects are developed for each region that enable both computer code-prediction validation and cost-effective parametric engineering studies.

The results of postirradiation examinations of VVER-1000 and VVER-440 fuel rods

The paper presents the results of postirradiation examination of the fuel rods having different fuel-cladding gaps, pellet densities, pellet inner diameters and so on. The fuel rods were irradiated in the material science reactor (MR) of the Kurchatov Institute of Atomic Energy and at 4 unit of the Novo-Voronezh nuclear powerplant. Some data on fission gas release and rod geometry and compared with computer code predictions.

A 10-stage reconnection demonstration launcher

A small-scale, 10-stage cylindrical reconnection launcher has been designed, fabricated, and tested. Ten-gram projectiles are accelerated from rest to 317 m/s through the 0.44-m launcher assembly with a projectile kinetic energy to capacitor stored energy efficiency of 9%. Comparison of test results and computer code predictions are presented. Results of these studies have substantiated launcher scaling at small size and have provided a useful test bed for launcher components and diagnostics. >

Ground Distribution Patterns of Selected Radioactive, Chemical, and Physical Contaminants from Dispersion of U Mill Tailings

Ground concentrations of 226Ra and total alpha activity as a function of soil depth and distance from an acidic U mill tailings pile were measured, as well as soil pH, sulfate, chloride, and conductivity. Contamination decreased with increasing soil depth and distance from the source. Most of the measured parameters were indistinguishable from background after a distance of 3.3 km from the tailings impoundment. The highest concentrations of all contaminants were contained in the particles less than 0.045 mm in diameter at the soil surface (0-0.6 cm). This fraction represents only 4% to 10% of the total soil mass. Surface soil particles greater than 2.0 mm contained higher concentrations of all contaminants than the intermediate-size (0.045-2.0 mm) fraction. Aggregate formation of the greater than 2.0-mm fraction from small particles or preferential erosion and transport of the tailings sand fractions were proposed as possible explanations. The significant correlations between various measurements were soil 226Ra vs. total alpha activity, sulfate concentration, and conductivity. The latter two parameters are indicative of sulfuric acid leached tailings. The sulfate concentration appeared to be a sensitive and easily measured indicator of tailings contamination and migration into the soil profile. Furthermore, sulfate may be used to delineate acidic U tailings from other sources of contamination (U ore dust, yellowcake, naturally elevated U and Ra) in the environment. Actual site measurements for surface 226Ra concentration were approximately twice the MILDOS computer code prediction.

AN EXPERIMENTAL AND NUMERICAL INVESTIGATION OF TURBULENT RECIRCULATING FLOW IN A CAVITY WITH AN INLET WALL JET

Abstract Recirculating turbulent flow within a cavity with an inlet wall jet was examined. In steady water flow profiles were constructed with measurements taken with a Laser Dopplcr Anemometer system mounted on a traversing mechanism for two different inlet velocities. The results are presented in terms of mean velocities and turbulent kinetic energy distributions. Comparisons are then made with results obtained using a finite difference computational scheme based on the k-e turbulence model. In general, good agreement was obtained between the computer code predictions and the experimental data. However, the agreement between measurements and the code predictions was much better for the mean velocity field as compared to the turbulent kinetic energy field.

Evaluation of kinetic parameters appropriate for modeling urethane foam insulation performance

Computer codes which model the pyrolysis of thermal insulators for in-depth temperature response are particularly sensitive to the kinetic parameters used in the code. The parameter values, which are evaluated from thermogravimetric analysis (TG), are, in turn, sensitive to the heating and gas flow rates in the TG sample environment as well as the composition of the gas. In this study, the effects of these experimental variables on computer code predictions and their correlations with experimental data are demonstrated. The insulators are urethane foams and were subjected to simulated and actual instantaneous fire test conditions. The Charring Material Ablation computer code was used to model insulator performance.

The Brine Migration Test - A Nuclear Waste Repository Simulation Experiment at the Asse Salt Mine - Federal Republic of Germany

ABSTRACTA joint US/FRG nuclear waste repository simulation experiment was performed at the Asse Salt Mine in the Federal Republic of Germany (FRG). The High Level Waste (HLW) disposal in boreholes was simulated by the simultaneous emplacement of electrical heaters and cobalt-60 sources at four individual test sites located in a special underground test room at the 800 m-level.In order to resolve the issues of rock mass/waste package interaction the temperature field, brine migration into the heater boreholes, borehole gas pressure and composition, and rock mass stresses and displacements were monitored during the test. In order to validate computer code predictions the acquired data were compared to calculational results. Corrosion specimens remained in the heater boreholes during the course of the experiment and were afterwards examined.

E-Guns and depressed collectors for two-stage free electron lasers

An e -gun, depressed collector, and guide-field solenoid have been designed and tested for operation at a maximum of 400 kV and 38 A in order to simulate key components of a typical low-voltage free electron laser (FEL). Detailed beam-energy-spread analyses and computer simulations are presented for the e -gun and the drift regions. The results of experiments with the depressed collector show beam-current-recovery efficiencies of over 90 percent for e -beam voltages from 160 to 400 keV. We have also set up and confirmed computer-code predictions that a space-charge depression in the collector (which is essential for efficient collection) forms at a collector-voltage setting of 1 percent of the beam voltage. These results demonstrate the validity of substantially increasing the efficiency of systems by using depressed collectors to recover the bulk of the energy which is left in the e -beam after it leaves the laser resonator. The recovery-efficiency parameter (recovered current/cathode-emission current) is shown to be a function of the relativistic-orbit parameter ( B/\beta\gamma ) and reaches a maximum of 94 percent. These results imply that FEL system efficiencies can be achieved which are an order of magnitude higher per stage than would be possible without the use of depressed collection.

The bi-directional amplifier in the constant intensity approximation and its application to KrF lasers

Bi-directional and folded laser amplifiers are analysed in the constant intensity approximation. Simple analytical expressions are developed for gain, output intensity and extraction efficiency. The analysis is applied to electron-beam pumped KrF lasers and expressions for saturation intensity, small-signal gain coefficient and intrinsic efficiency in terms of gas composition and pump power per unit volume are given. The problem of fluorine burn-up in KrF lasers is discussed. Under certain conditions the analysis is shown to be equally applicable to oscillators and comparison is made with previous experimental results and computer code predictions.

Development of Analytical and Experimental Techniques for Determining Store Airload Distributions

A semiempirical computer code has been developed for the prediction of the distribution of static aerodynamic loads acting on a store both in the free stream and in the interference flow field of an aircraft. The code is applicable to a wide range of configuration s for subsonic through supersonic Mach numbers and angles of attack to approximately 45 deg. Wind tunnel tests were conducted using a 1/4-scale pressure model, a 1/4scale force model divided into four segments, and a three-segment 1/20-scale force model of the same configuration. Integrated pressure data, segmented force data, and previously obtained single balance data agreed well, and computer code predictions correlated well with the experimental data.

Performance of an annular resonator with a polarizer in the annular leg

Experiments were performed on a CO(2) laser with an annular resonator. The objective of these experiments was to control the polarization in an annular laser and to verify computer code predictions. A Mylar pellicle was placed in the annular leg, and its angular orientation with respect to the optical axis was varied. The pellicle had different transmittances for horizontal and vertical polarizations and also had stress-induced birefringence. At small angles of incidence in the pellicle, the birefringence dominated, and the output had a complicated nature. However, at large angles of incidence, the transmittance difference forced the laser into a well-defined mode for which the near field was horizontally polarized at the top and bottom and the two sides and vertically polarized at intermediate locations. The experimental results were in good agreement with the computer code calculations.

Analytic Calculation of Late-Time Source-Region EMP Fields below the Earth's Surface

An analytic technique is presented for calculating late-time source-region EMP fields in the earth. The radial electric field is found to result from the near-cancellation of two competing effects. Despite the sensitivity suggested by this circumstance, the present results are in reasonable agreement with LEMP-SUBL computer code predictions. Results are also obtained for a layered earth.

Calculational Modeling of Explosive Fracture and Permeability Enhancement

With its underground explosion computer codes SOC and TENSOR, the Lawrence Livermore Laboratory is developing a capability for computer code prediction of fracture intensity and permeability enhancement far from a free face. Because the codes calculate fracture and not permeability, one must relate experimental measurements to a calculable parameter for fracture. High-explosive experiments in a coal outcrop and a multiple-charge experiment in a coal seam were designed to provide the needed data. Fracture intensity observed around the explosion centers is shown to be related to a calculated damage parameter εf. This parameter is actually the total failure-induced deviatoric strain. Intrinsic permeability, determined from hydraulic conductivity and calculated from results from slug tests in wells near the explosion, correlates at least qualitatively with the calculated residual tensile-fracture porosity, πf. An important observation is that no tensile failure occurs for some distance from the explosion-formed cavity when spherical charges are employed, whereas, tensile failure occurs near the cavity wall when cylindrical charges are used.