摘要：Two different numerical proceudres are suggested for evaluating a previous analytic result for the scalar flux for the penil beam problem with screened Rutherford scattering. The first of these is an asymptotic evaluation of a divergent integral, and the second is based upon an asymptotic expansion method due to Moliere. Both are relatively simple algorithms, and comparisons with each other and with benchmark Monte Carlo are given to establish the accuracy of each.
摘要：To meet the needs for neutron capture theraopy (NCT) irradiations, a high-intensity, hgihquality fission converter-based epithermal neutron beam has been designed for the MITR-II research reactor. This epithermal neutron beam, capable of delivering treatments in a few minutes with negligible background contamination from fast neutrons and photons, will be installed in the present thermal column and hohlraum of the 5-MW MITR-II resarch reactor.
摘要：The radial distribution of capture rate and effective cross section in fuel rods of radii R, forming a light water reactor (LWR) lattice, is derived with routine cell calculations. Any internal radial subrange (r_1,r_2) is treated through the assessment of absorption in the two corresponding annual abosrbers (r_1,R) and (r_2,R). The lattice of the latter absorbers, whose pitch is eactaly the riginal LWR lattice pitch, is equivalenced to a lattice of solid cylindrical rods. Thus, for example, to obtain a tenfold radial distribution, ten routine cell calculations are requried.
摘要：Experimental determination of the resonance neutron absorption in a heavy water solution of 2.57 g/e ~237Np is presented. Experimental samples were irradiated in the MAKET critical plant. Prior to irradiation, ~237Np was radiochemically purified to remove ~233Pa. The experimental samples were prepared by evaporating two aliquot samples taken from the irradiated solution. The nuclide composition of the samples was analyzed using a GC-2518 Ge detector, a 1510 module, and an S-100 pltate to emulate a multichannel analyzer in an IBM personal computer. The spectrometric resolution was 1.8 keV at the 1332-keV line.
摘要：In the DUPIC fuel cylce, spent pressurized water reactor (PWR) fuel is refabricated as a DUPIC fuel by a dry process. Because the spent PWR fuel composition dpends on the initial enrichment and burnup conditions of PWR fuel, the composition heterogeneity on core performance, an adjustment of DUPIC fuel composition was studied. The composition adjustment was made in two steps: mixing two spent PWR fuel composition was studied. The composition adjustment was madei n two steps: mixing two spent PWR fuels.
摘要：An extended version of the cascade-exciton model (CEM) of nuclear reactions is applied to analyze nucleon-induced fission cross sections for ~209Bi and ~208Pb nuclei in the 45 - to 500-MeV energy range. The available data on linear momentum transfer are analyzed as well. The resuts are compared with analytical approximations resulting from a comparative critical analysis of all available experimental data. Systematic discrepancies between calculations and experimental data are revealed. A modification of the CEM is proposed, which signficantly improves the model predictions for projectile energies above 100 MeV.
摘要：A dynamic model of natural circulation boiling water reactors (BWRs) is analyzed using a bifurcation code and numerical simulations. The two fundamental bifurcation types relevant to BWRs, the supercritical and the subcritical Hopf bifurcations, are first studied in natural circulation systems without nuclear feedback. The effect of nodalization approximation in the rsier on stability and bifurcation characteristics of the system is determined. The strong effect of the nuclear-thermohydraulic interaction on the nonlinear characteristics of a natural circulation BWR is then explored in a parametric study.
摘要：A parameter estimation method based on Bayes' theorem is applied t the parameters of the neutron optential for ~209Bi. The potential parameters at a certain energy are determined according to an assumption that parameters vary gradually with the incident neutron enerigies, and its is demosntrated that the method can be used as an efficient tool for investigating the energy dependence of the optical potential parameters.
摘要：The neutron slowing-down-time method for nondestructive assay of light water reactor spent fuel has been under development for many years. Results for a newly optimized design of a lead solowing-down-time spectrometer for spent-nuclear-fuel assay are presented. Monte Carlo analyses wee performed to optimize the design of the assay device, determine its main parameters, investigate the effects of the spent-fuel assembly and the detector impurities on its performance, determine the fission signatues of the fissile isotopes in spent-fuel elements, and simulate the assay signal as a function of the solwing-down tiem, assuming threshold fission chambers for the assay detectors. The assay signals from the threshold detectors were analyzed to predict the unknown masses of the fissile isotopes in a typical spent commercial light water reactor fuel element. The broadened resolution of the system caused by the presence of the spent fuel inside the spectrometer pile was found sufficient to separate the signatures of the U and Pu fissiles in spent fuel.
摘要：New ways to calculate the direction cosines and polarization vectors for Monte Carlo photon scattering are developed and presented. The new approach for direction cosines is mroe physical, easier to understand, straightforward to implement, and-for simulatins involving polarized photons--slightly faster than the traditional approach. The polarization vector after scatter is also presented.
摘要：Mechanical quadratures that allow systemawtic improvement and solution convergence are derived for application of the discrete ordinates method to the Boltzmann transport equation. The quadrature directions are arranged on n latitudinal levels, are uniformly distrbuted over the unit sphere, and have positive weights. Both a uniform and equal-weight quadrature set UE_n and a uniform and Gauss-weight quadrature set UG_n are derived. These quadratures have the advantage over the standard level-symmetric LQ_c quadrature sets in that the weights are positive for all orders, and the solution may be systematically converged by increasing the order of the quadrature set.
摘要：Space-dependent nuclear characteristics, measured by critical experiments on large-size fast breeder reactor (FBR) cores, were reviewed and interpreted. It was observed that radial neutron flux distributions were signficantly distorted by perturbations, control rod reactivity interaction effects were large, and the point kinetics was not valid. These physical behaviors are enhanced as the spatial neutronic decoupling increases. To obtain stable and benign nuclear characteristics and to make the kinetics as close to the point kinetics as possible, it is necessary to reduce the spatial decouping. This is an important issue that must be taken into account in the nuclear design for large FBR cores.
摘要：It is well knonw thawt after one of the spatial harmonics of a boiling water reacotr (BWR) is driven toward limit-cycle oscillations with a decawy ratio very clsoe to 1, the nonlienar behavior of the system starts to manifest itself, and a series of resonance appears at frequencies that are multiples of the characteristic oscillationf requency (commonly called harmonic frequencies). Several suxh resonances have been clearly identified during measurements in BWRs. during which the system is in the unstable, limit-cycle oscillations regime. The ability to identify three and possibly four of these harmonic resonace peaks in the neturon spectra of Ringhals-1 is reported. For the measurements to be analyzed, there resonances are due to the limit-cycle oscillations not of the fundamental but of the first spatial harmonic of the neutron flux.
摘要：A dimensionally adaptive, automatic swtiching algorithm is presented that has been developed for the RELAP5/PANBOX coupled thermal-hydraulics and neutron kinetics code system to swtich between three-dimensional (3-D), one-dimensional (1-D), and point neutorn kientics models during a transient calculation. The switching criteria from higher-to lower-dimensioanl models are based on the time evolution of the flux shape, while the switching criteria from lower-dimensional models to the 3-D model are based on error estimates and reactivity criteria.
摘要：Neutron time-of-flight experiments have long been used to determine resonance parameters. Those resonance paraemters have then been used in calculations of integral quantities such as Maxwellian averages or resonance integrals, and results of those calcualtions in turn have been used as a criterion for acceptability of the resonance analysis.
摘要：A dimensionally adaptive, automatic switching algoithm has been developed for the RELAP5/PANBOX coupled thermal-hydraulics and neutron kinetics systems to switch between three-dimensional (3-D), one-dimensional (1-D), and point neutron kinetics models during a transient calculation. The 3-D, 1-D, and point neutron kinetics models are developed and analyzed. The basis of this development is the consistent and stable nodal expansion method. Thue 1-D and point neutron kinetics models are dervied in a unified manner from the 3-D model using the adiabatic approximation. The operator formulation of perturbation/sensitivity theory is consistently used to determine the reactivity for the point-kinetics model. Furthermore, the new features of the coupled RELAP5/panbox code are described. This provides the basis underlying the dimensionally adaptive algorithm.
摘要：At this, experiemntal transmission data are analyzed with codes like REFIT or SAMMY, which use the free gas model to fit the form of the resonances. The use of the resonance paraemters issued from such analysis for further reconstruction of the cross section with codes like NJOY can result in nonnegligible errors in the cross sections as well as in the reaction rates.
摘要：The effect of low-energy neturons on activation cross-section measurements was analyzed carefully and proved by the measured neutorn spectra of T(d,n)~4He and D(d,n)~3He reactions. The ~58Ni(n,p)~58m+gCo and ~64Zn(,p)~64Cu reactions were used to confirm this analysis, and their cross sections were measured accurately. In addition, their evaluated excitawtion functions are given.
摘要：The verification of calculated neutron fluence onto the VVER-440/230 pressure vessel is a very timely task, especially considering that some of these reactorshave been operating for the major part of the reactor design lifetime. Since the induced activity from the neutorn irradiation onto the elements is a simple response of neutron flux, the neutron fluence verification usually is done using the measured activity of radionuclides produced during reactor operation.
摘要：Work performed in part for an American Nuclear Society Standards committee Subgroup (ANS 19.9) to assess the stawtus of delay8ed neutron data is summarized. Recent measurements of delayed neutron emission conducted at Texas A&M University are also described. During the last 10 yr, there have been advances in nuclear data libraries (e.g., improved fission product yields) that make it possible to quantitatively predict delayed neutron emission from basic data.