摘要:

AbstractDifferential cross sections for neutron elastic and inelastic scattering from the actinide nuclei232Th,233U,235U,238U,239Pu, and242Pu have been measured at incident energies ranging from 0.6 to 3.4 MeV using a multiangle time-of-flight spectrometer. The energy resolution of the spectrometer was high enough to experimentally resolve the elastic and first inelastic groups for232Th,233U,238U, and242Pu at all energies. Cross sections for groups of states have been obtained for235U and239Pu. Comparison of these measurements with evaluations in the latest evaluated data files shows substantial discrepancies, particularly at high energies. The present results for232Th,235U,238U, and239Pu have been combined with total cross-section measurements and low-energy scattering properties in an analysis based on the coupled-channel and compound-nucleus formalisms. Optical potential parameters and nuclear deformations have been derived and are discussed.

ISSN:0029-5639    

DOI:10.13182/NSE82-A21439

出版商:Taylor&Francis    

年代:1982

数据来源: Taylor

摘要:

AbstractWe have measured the fission cross-section ratio232Th:235U as a function of neutron energy from 0.7 to 30 MeV using ionization fission chambers, the threshold cross-section method, and the time-of-flight technique at the Lawrence Livermore National Laboratory 100-MeV electron linear accelerator. The measured cross-section ratio, averaged over the neutron energy interval from 1.75 to 4.00 MeV, was 0.1086±0.0024.

ISSN:0029-5639    

DOI:10.13182/NSE82-A21440

出版商:Taylor&Francis    

年代:1982

数据来源: Taylor

摘要:

AbstractThe99Tc(n,γ) average cross section was measured at the Oak Ridge Electron Linear Accelerator from 2.65 to 2000 keV with an estimated uncertainty ranging from 4.0 to 4.9%. Individual resonance parameters were fitted by least-squares adjustment to the capture yield data from 2.65 to 5.08 keV. The average cross-section data agree with the ENDF/B-V (Mod 1) evaluation above 900 keV and lie within±15% of the JENDL-1 evaluation below 700 keV.

ISSN:0029-5639    

DOI:10.13182/NSE82-A21441

出版商:Taylor&Francis    

年代:1982

数据来源: Taylor

摘要:

AbstractThe 48.6-min isomeric state at 0.396 MeV in111Cd can be excited by the neutron reactions110Cd(n,γ)111mCd,111Cd(n,′)111mCd, and112Cd(n, 2n)111mCd. When natural cadmium is bombarded with fast neutrons, the influence of these reactions on the activation response varies according to the nature of the neutron spectrum. For a predominantly low-energy spectrum, the nonthreshold reaction110Cd(n,γ)111mCd dominates, while for a relatively hard spectrum, the threshold reactions111Cd(n,n′)111mCd and112Cd(n,2n)111mCd are the most influential This situation offers interesting possibilities for utilization of elemental cadmium samples as neutron activation dosimeters in reactor applications. Accordingly, the elemental differential cross section for111mCd excitation has been measured for cadmium over the energy range 0.135 to 10.01 MeV using activation techniques, and the response of this excitation function has been investigated for a standard fission-neutron spectrum. Some implications of these results for dosimetry applications are examined.

ISSN:0029-5639    

DOI:10.13182/NSE82-A21442

出版商:Taylor&Francis    

年代:1982

数据来源: Taylor

摘要:

AbstractThe multigroup diffusion equation is solved for the pulsed problem and the time-dependent energy spectra are obtained using the eigenfunction expansion method. It is shown that complete spectral equilibrium can be obtained beyond 2000 ns in a 40-cm cube (B2∼0.015 cm−2) of natural uranium. This time is found to increase with increasing assembly size. The earlier exponential decays observed in a pulsed uranium system are traced to the establishment of the pseudo-equilibrium condition due to the trapping of neutrons in certain energy groups. It is shown that such a pseudo-decay corresponds to the establishment of the first higher mode of decay and the time range in which it is established is a function of B2.

ISSN:0029-5639    

DOI:10.13182/NSE82-A21443

出版商:Taylor&Francis    

年代:1982

数据来源: Taylor

摘要:

AbstractA two-dimensional finite difference method is presented to calculate the effective thermal conductivity of sphere-pac fuel in its initial configuration. This method employs an approach using progressive unit cells for the various size fractions of the fuel The effects of temperature and fill gas pressure are also incorporated into the calculation. Comparison between computed and experimental values indicates that the model agrees with measured data to within 20%.

ISSN:0029-5639    

DOI:10.13182/NSE82-A21444

出版商:Taylor&Francis    

年代:1982

数据来源: Taylor

摘要:

AbstractAn approximate method for calculating the interference of neutron streaming between different regions (drawers) in fast critical assemblies is described by applying the well-known Benoist formula to super cell problems. The interference effect on the diffusion coefficient was numerically evaluated and the results are compared with those obtained by Yoshida’s method. Sodium void worths in control rod positions (control rod follower channel) relative to the sodium-filled channel are calculated on the basis of diffusion theory with the interference effect and compared with the results obtained from transport calculations. The comparison reveals that the inclusion of the interference effect improves the calculational accuracy remarkably.

ISSN:0029-5639    

DOI:10.13182/NSE82-A21445

出版商:Taylor&Francis    

年代:1982

数据来源: Taylor

摘要:

AbstractAn expression for ion beam deposition rate, which also includes energy loss to collective modes of the target plasma, quantum mechanical value of the impact parameter, and close collision corrections to the Coulomb logarithm, has been used in numerical calculations of the ion beam-pellet interaction. A comparison of the results with those obtained using the unmodified stopping power expression is presented. It is found that the integrated effect of the modifications considered for the energy deposition is such as to decrease the penetration range during the entire ion beam-pellet interaction below that provided by the unmodified energy deposition approach; it leads to the enhancement of the heating rate and, consequently, to different thermonuclear yield ratios.

ISSN:0029-5639    

DOI:10.13182/NSE82-A21446

出版商:Taylor&Francis    

年代:1982

数据来源: Taylor

摘要:

AbstractKalman filter methodology has been applied to an in-pile liquid-metal fast breeder reactor simulation experiment to obtain estimates of the fuel-clad thermal gap conductance. A transient lumped parameter model of the experiment is developed. An optimal estimate of the state vector chosen to characterize the experiment is obtained through the use of the Kalman filter. From this estimate, the fuel-clad thermal gap conductance is calculated as a function of time into the test and axial position along the length of the fuel pin.

ISSN:0029-5639    

DOI:10.13182/NSE82-A21447

出版商:Taylor&Francis    

年代:1982

数据来源: Taylor

摘要:

AbstractAn analytical method is presented to estimate the effective thermal conductivity of sphere-pac fuel during restructuring. This method is based on a unit cell model in which a sintering model is used to describe the extent of restructuring occurring between the fuel particles. As a result of sintering, a“neck”is formed between the fuel spheres. The effective conductivity of the sphere-pac bed can then be evaluated in terms of restructuring, i.e., as a function of temperature and necking between the fuel spheres. The effects of other relevant parameters such as the gas pressure in the sphere-pac pin and fission gas release are also included in the model Furthermore, a thermal conductivity criterion is used to determine the matching conductivity boundary, which is defined as the outer radial boundary where fuel restructuring is completed.Fuel restructuring is of particular importance in sphere-pac fuel because of its controlling effect on the temperature distribution. By knowing the effective conductivity, the temperature distribution of the fuel, both in its initial configuration and during restructuring, can be determined. Using the model, the temperature distribution as well as the extent of restructuring can be calculated. This model can be incorporated into computer codes to predict the overall thermal and mechanical performance of sphere-pac fuel pins.

ISSN:0029-5639    

DOI:10.13182/NSE82-A21448

出版商:Taylor&Francis    

年代:1982

数据来源: Taylor