摘要:

AbstractA simplified approach is described for selection of the constitutive relations for the interphase exchange terms in the two-fluid code, THERMIT, The approach used distinguishes between pre- and post-critical heat flux conditions. Interfacial mass, energy, and momentum exchange terms are selected and tested against one-dimensional measurements for a wide range of mass flow rate, pressure, and void fraction conditions. It is concluded that the simplified regime-map approach leads to accurate predictions for light water reactor applications, excluding depressurization events.

ISSN:0029-5639    

DOI:10.13182/NSE82-A20276

出版商:Taylor&Francis    

年代:1982

数据来源: Taylor

摘要:

AbstractThe wall heat transfer coefficient for the forced convective two-phase flow of sodium is theoretically derived by using the momentum-heat transfer analogy and a logarithmic law for the velocity distribution in the liquid film. Only one constant in this logarithmic form needs to be empirically determined. The relationship between the film average temperature and the interfacial liquid-vapor temperature is also derived. The results from the suggested correlation are in excellent agreement with the Zeigarnick and Litvinov data over a broad range of parameters. The predictions are also in agreement with the high heat transfer coefficient observed in some General Electric Company experiments. The proposed correlation is found to result in a higher heat transfer coefficient for sodium than do the previously advanced correlations.

ISSN:0029-5639    

DOI:10.13182/NSE82-A20277

出版商:Taylor&Francis    

年代:1982

数据来源: Taylor

摘要:

AbstractWe report the basis for new estimates of“free-in-air”kermas resulting from the nuclear explosions at Hiroshima and Nagasaki for ground ranges out to 2 km. The results are substantially different from previously accepted values known as T65D, particularly for Hiroshima.The methodology used in our study is different from that of T65D. To obtain prompt neutron and gamma-ray kermas, calculated leakage spectra were utilized that had been generated by modern weapons design codes. These leakage spectra were used as sources in radiation transport calculations performed with extensively validated modern transport codes. We have further cross-checked our calculational results in one and two dimensions, and by using very different solution techniques. For delayed gamma rays, we used a formalism based on the results of atmospheric testing.Our results have been compared with Japanesein situmeasurements of neutron activation and of gamma-ray kerma, and found to show good agreement with them. We have explained the major differences between the T65D values and our own, as well as between neutron kermas inferred from thein situactivations and our kerma values.These new results merit confidence. However, improvements in these estimates can occur when additional work is done. One application of practical importance to radiological protection standards has already been made.

ISSN:0029-5639    

DOI:10.13182/NSE82-A20278

出版商:Taylor&Francis    

年代:1982

数据来源: Taylor

摘要:

AbstractAs a contribution to a required review of the American National Standard for Nuclear Criticality Safety in Operations with Fissionable Materials Outside Reactors, limits for homogeneous235U systems have been recalculated to confirm their subcriticality or, where there were doubts, to propose more restrictive values. In addition, other limits were calculated to propose for inclusion in the Standard, namely limits for solutions of235UO2(NO3)2and limits for solutions of both UO2F2and UO2NO3)2that allow credit for the presence of238U. Limits were also calculated for uranium oxides. The same three methods of calculation were used as in similar work done recently for plutonium systems. The validity of each was established by extensive correlations with pertinent critical experiments.

ISSN:0029-5639    

DOI:10.13182/NSE82-A20279

出版商:Taylor&Francis    

年代:1982

数据来源: Taylor

摘要:

AbstractAs a contribution to the required quinquennial review of the American National Standard for Nuclear Criticality Safety in Operations with Fissionable Materials Outside Reactors (ANSI N16.1-1975/ANS-8.1), limits for homogeneous233U systems have been recalculated to confirm their subcriticality or, where there were doubts, to propose more restrictive values. In addition, other limits were calculated to be proposed for inclusion, namely, limits for aqueous solutions of UO2(NO3)2and limits for uranium oxides. The same three methods of calculation were used as in similar work done recently for plutonium and235U systems. The validity of each was established by correlation with the results of pertinent critical experiments.

ISSN:0029-5639    

DOI:10.13182/NSE82-A20280

出版商:Taylor&Francis    

年代:1982

数据来源: Taylor

摘要:

AbstractA new experimental method has been used to determine the isomeric ratio (IR) in neutron capture of241Am in a differential experiment. Thin241Am samples have been activated with subthermal monoenergetic neutrons of 14.75 meV and quasi-monoenergetic neutrons of∼30 keV. The decay of the242Am nuclei produced has been determined by observing the emitted beta spectrum in a mini-orange spectrometer. The measurements have been performed relative to gold. The ratio R1=σγ(241Am→242gAm)/σγ(Au) was found to be R1= 5.79±0.33 at 14.75 meV and R1= 2.73±0.16 at∼30 keV. The corresponding IRs,σγ(241Am→242gAm)/σγ(Am), are 0.92.±0.06 at 14.75 meV and 0.65±0.05 at∼30 keV.Detailed theoretical calculations of the total capture cross section, the IR, and the capture gamma-ray spectra were performed in the energy range from 1 to 1000 keV taking advantage of recently available information on the discrete level scheme of242Am. With the present knowledge on the level scheme of242Am, it seems to be difficult to reproduce the strong energy dependence of IR as indicated by the experimental results.

ISSN:0029-5639    

DOI:10.13182/NSE82-6

出版商:Taylor&Francis    

年代:1982

数据来源: Taylor

摘要:

AbstractThe133Cs(n,γ) cross section was measured at the Oak Ridge Electron Linear Accelerator from 2.66 to 600 keV with 3 to 4% uncertainty. Individual resonance parameters were determined by least-squares adjustment to fit the yield data below 6 keV and the average cross section was derived up to 600 keV.

ISSN:0029-5639    

DOI:10.13182/NSE82-A20282

出版商:Taylor&Francis    

年代:1982

数据来源: Taylor

摘要:

AbstractA major obstacle in obtaining adjusted cross sections from integral experiments is the expensive and time-consuming evaluation of sensitivities and modeling corrections. The principal contribution of this paper is the development of a state-of-the-art Monte Carlo method that evaluates sensitivities particularly efficiently and that uses“point”nuclear data and three-dimensional combinatorial geometry to eliminate modeling errors. This method enables adjustment procedures to be applied more reliably and generally than previously possible. Theoretical advances include the way the sensitivity estimator is chosen and evaluated. Also the adjustment procedure takes into account all the Monte Carlo statistical errors, and iteration is used to cope with nonlinearities. The methods developed are successfully applied to an analysis of the Winfrith Iron Benchmark Experiment.

ISSN:0029-5639    

DOI:10.13182/NSE82-A20283

出版商:Taylor&Francis    

年代:1982

数据来源: Taylor

摘要:

AbstractAn analysis of spectral effects that arise from solving the k-,α-,γ-, andδ-eigenvalue formulations of the neutron transport equation is presented. Hierarchies of neutron spectra softness are established and expressed in terms of spatial-dependent local indices that are defined for both the core and the reflector of nuclear system configurations. Conclusions regarding the general behavior of the spectrum-dependent integral spectral indices and initial conversion ratios given by the k-,α-,γ-, andδ-eigenvalue equations are also presented. Spectral effects in the core and in the reflector are distinguished by defining separate integral spectral indices for the core and for the reflector.It is shown that the relationship between the spectra given by the k-,α-,γ-, andδ-eigenvalue equations and the spectrum in a corresponding critical configuration depends on the specific physical process that causes deviation from criticality. Nevertheless, some general recommendations are offered regarding the use of a particular eigenvalue equation for specific applications. All conclusions are supported by numerical experiments performed for an idealized thermal system.

ISSN:0029-5639    

DOI:10.13182/NSE82-A20284

出版商:Taylor&Francis    

年代:1982

数据来源: Taylor

摘要:

AbstractThe concept of aleakage importancefunction is introduced and analyzed for physical systems governed by the Boltzmann transport equation. The homogeneous equation with inhomogeneous boundary conditions satisfied by the importance function is derived by using adjoint operators. A standard discrete ordinates transport code is used to solve this equation, and some important numerical aspects are highlighted. Idealized nuclear systems are analyzed to illustrate that the leakage importance function gives a measure of the relative importance of each source particle in phase space in contributing to the leakage, and that the leakage importance function provides insight regarding the specific physical process that leads to leakage.

ISSN:0029-5639    

DOI:10.13182/NSE82-A20285

出版商:Taylor&Francis    

年代:1982

数据来源: Taylor