摘要:

A direct, iterative method has been developed for the numerical solution of the transient few-group neutron diffusion and delayed precursor equations in three-dimensional, hex-z geometry. The method is shown to be numerically stable, and truncation errors are of order h2. The results of numerical experiments as well as comparison with space-time experimental results indicate that the method is accurate and that three-dimensional calculations can be performed at“reasonable”computing costs. The method is incorporated as a JOSHUA module at the Savannah River Laboratory.

ISSN:0029-5639    

DOI:10.13182/NSE59-289

出版商:Taylor&Francis    

年代:1976

数据来源: Taylor

摘要:

Experimental data that test the validity of a numerical solution of the transient few-group neutron diffusion and delayed precursor equations in two-dimensional hexagonal geometry are presented. The experiments involve free fall insertion of235U-bearing rods into an off-center location of a large critical, heavy-water-moderated lattice. The resulting transient flux tilts are strongly influenced by delayed neutron holdback. The calculated flux tilts agree with the measured flux tilts within the small uncertainty of the measurements. The data and input to the calculations are presented in sufficient detail to allow other methods of solution to be tested.

ISSN:0029-5639    

DOI:10.13182/NSE76-A26832

出版商:Taylor&Francis    

年代:1976

数据来源: Taylor

摘要:

A step-wise tensor transformation technique is presented for the transformation of the single energy group transport equation to an arbitrary spatial coordinate system. Both gradient and divergence forms of the equation are given, and the same method is applied to the derivation of the diffusion approximation. We demonstrate that using an orthogonal representation of the propagation vector will simplify the divergence form of the equation. The application of this technique is in the representation of the transport equation in coordinate systems other than the usual rectangular, cylindrical, and spherical ones. Its use is demonstrated by transforming the transport equation to a toroidal coordinate system consisting of nested circular toroids.

ISSN:0029-5639    

DOI:10.13182/NSE76-A26833

出版商:Taylor&Francis    

年代:1976

数据来源: Taylor

摘要:

A new representation of scattering kernels particularly appropriate for highly anisotropic scattering is investigated. It is found that the partial-range orthogonal function representation developed here can conveniently avoid the traditional problem of“negative fluxes”while retaining a high directional accuracy for even extreme cases of anisotropy.

ISSN:0029-5639    

DOI:10.13182/NSE76-6

出版商:Taylor&Francis    

年代:1976

数据来源: Taylor

摘要:

The coarse-mesh rebalance method is adopted in Monte Carlo schemes for aiming at accelerating the convergence of a source iteration process to obtain the eigenvalue of a nuclear reactor system. At every completion of the Monte Carlo game for one batch of neutron histories, the scaling factor for the neutron flux is calculated to achieve the neutron balance in each coarse-mesh zone. This rebalance factor is multiplied to the weight of each fission neutron in the coarse-mesh zone for playing the next Monte Carlo game. The numerical examples have shown that the present rebalance method gives a new usable sampling technique to get a better estimate of the number of neutrons lost or produced in each coarse-mesh zone by modifying the value obtained directly from the normal Monte Carlo calculation.

ISSN:0029-5639    

DOI:10.13182/NSE76-A26835

出版商:Taylor&Francis    

年代:1976

数据来源: Taylor

摘要:

Uranium fueled thermal-reactor lattice benchmarks, as well as some other experimental assemblies, were analyzed with ENDF/B-IV data and calculational techniques based on integral transport and SN methods together with Monte Carlo calculations in the resolved resonance region. Only a relatively small overprediction of the238U resonance events—∼3 to 4%—remains when the present version of the ENDF/B data is used. It accounts for a considerable part of the∼1% underprediction of criticality. Uranium-235 resonance absorption was found to be influenced noticeably by shielding due to the238U resonances. For both235U epithermal and238U fast fissions, the agreement between calculation and experiment, although relatively good, showed greater fluctuations than in the case of the238U capture. Calculated temperature variations of material buckling with temperature were greater than in the measurements, especially near room temperature, but the discrepancies were smaller in the critical than in the exponential assemblies.

ISSN:0029-5639    

DOI:10.13182/NSE76-A26836

出版商:Taylor&Francis    

年代:1976

数据来源: Taylor

摘要:

An experiment was performed with a mock-up of the core of the Fast Flux Test Facility (FFTF) reactor to evaluate three reactivity measurement methods for application to liquid-metal fast breeder reactors (LMFBR): modified source multiplication measurements with the low-level flux monitor for refueling (∼35 dollars subcritical) of FFTF, noise analysis to 35 dollars subcritical, and inverse kinetics rod drop to∼12 dollars subcritical. To investigate the spatial dependence of these measurement methods and to resolve discrepancies previously reported, detectors were placed in the core, reflector, and radial shield, and experimental data were collected with the reactivity at near delayed criticality to∼35 dollars subcritical. Conclusions from this experiment are the following. Low-level flux monitors in the shield of the FFTF will be adequate for reactivity surveillance during refueling, using the modified source multiplication method calibrated near critical by an inverse kinetics rod drop measurement. The break frequency noise analysis method to−35 dollars with in-core detectors, the modified source multiplication method to−35 dollars, and inverse kinetics rod drop method to -12 dollars with detectors at all locations (corrected for changes in nuclear parameters), yielded the same reactivities within<5%. From reactor physics considerations, breakfrequency noise analysis with in-core detectors is best for monitoring reactivity down to full shutdown since it requires only a simple correction with reactivity that depends on global parameters of the system rather than a correction that depends on the value of the flux at a point or on the inherent source intensity, such as are required for the modified source multiplication method. However, for simple point kinetics interpretation of the results, the measurements must be made only with in-core detectors.

ISSN:0029-5639    

DOI:10.13182/NSE76-A26837

出版商:Taylor&Francis    

年代:1976

数据来源: Taylor

摘要:

A minicomputer-based system for reactor surveillance was developed and demonstrated on-line. The state of the reactor is characterized by the system from an analysis of noise signals, and a surveillance algorithm statistically describes normal behavior from this characterization. Hyperellipsoids are constructed from this description to enclose normal regions of behavior in the multidimensional measurement space, which represents all possible reactor states. When measurements outside normal regions are detected, the status of the reactor is suspect. Tests at the High Flux Isotope Reactor demonstrate that the algorithm can sense changes in reactor conditions that the plant instrumentation cannot detect.

ISSN:0029-5639    

DOI:10.13182/NSE76-A26838

出版商:Taylor&Francis    

年代:1976

数据来源: Taylor

摘要:

Neutron capture cross sections for238U,237Np,232Th,197Au,193Ir,191Ir,187Re,185Re,186W,181Ta, and114Cd relative to the235U fission cross sections have been determined for neutron energies from 120 keV to 2.9 MeV by the measurement of the activation products. Neutrons were produced by the3H(H,n)3He reaction on tritium gas targets on the Los Alamos Scientific Laboratory vertical Van de Graaff accelerator. Metal foils were exposed at selected angles and distances from the neutron source to achieve a selection of neutron energies. Neutron fluxes were measured with235U fission detectors placed at various angles for different proton energies. Scattering corrections were applied to the experimental results through the use of Monte Carlo computer simulation techniques. Corrections were also calculated for the purely geometrical effects on energy resolution due to finite source and sample width and thickness.

ISSN:0029-5639    

DOI:10.13182/NSE76-A26839

出版商:Taylor&Francis    

年代:1976

数据来源: Taylor

摘要:

A consistent compound nucleus theory of (n, 2n) and (n, 3n) neutron emission was applied to238U to obtain the energy spectra of the second and third secondary neutrons. The evaluation was based on inelastic level excitation and evaporation data for238U,237U, and236U. The238U and236U data were retrieved from ENDF/B-IV files; the237U data were evaluated in the Soreq Nuclear Research Center using experimental information and statistical reaction theory codes. At reaction energies E0just above the (n, 2n) threshold energy B2, the energy E of the second inelastic neutron has a spectrum of (E0−B2−E); above the (n, 3n) threshold, B3, the third neutron energy has a spectrum of (E0−B2−E)3. At energies E0, high above the thresholds, the second and third neutron spectra approach the evaporation form. A secondary neutron spectrum for any given reaction energy E0is approximated by a composite formwhere i = 2, 3 for the second and third neutrons, respectively. The temperatures Tiand blending coefficientsβiwere evaluated for several energies in the range from threshold up to 15 MeV.

ISSN:0029-5639    

DOI:10.13182/NSE76-A26840

出版商:Taylor&Francis    

年代:1976

数据来源: Taylor