摘要:

The transfer matrix method is used to determine the eigenvalues and eigenfunctions needed to obtain the response of nuclear power reactor internals to dynamic excitations. Transfer matrices and delta matrices are developed for a particular closed-cycle pressurized-water-reactor (PWR) configuration. Two cases are studied, 1) where the internals are rigidly supported near the bottom by the vessel walls and 2) where the vessel elastically supports the internals requiring that the combined structure be analyzed. The analysis takes into consideration structures with different cross sections and masses that are connected in series and/or parallel. Results obtained with a digital computer are shown.The method and the results obtained in this paper can be used for a complete reactor dynamical analysis of most PWR internals, since their structures are similar in design.

ISSN:0029-5639    

DOI:10.13182/NSE65-A20233

出版商:Taylor&Francis    

年代:1965

数据来源: Taylor

摘要:

Thermal-neutron doses can be simply and inexpensively measured over many orders of magnitude of integrated flux by a count of induced-fission-damage tracks in a solid with uranium impurities. Examples are given of the use of a single ordinary glass to measure neutron flux from 3×1014to 4×1018nvt and of the use of glass to measure the spatial variation of neutron flux. Other materials, either glassy or crystalline, allow a wide range of fluxes to be measured.

ISSN:0029-5639    

DOI:10.13182/NSE65-A20234

出版商:Taylor&Francis    

年代:1965

数据来源: Taylor

摘要:

A series of experimental and theoretical investigations on neutron spectra in lattice cells has been started at the reactor R1. This report gives the results from the work on the first three cells.The cells consisted of uranium tubes surrounded by D2O. They were placed in the central vertical channel of the reactor. The neutron spectra from lead scatterers in the center of the tubes were measured with a fast chopper in the energy region from 0.01 to 100 eV.The beam spectrum from the lead piece was expected to correspond to the angular flux integrated over all angles. This was tested in an accessory experiment which gave some correction factors for the tube measurements.For the calculations the THERMOS code has been used. The energy region ranged from 0.00025 to 3.06 eV. Three scattering models for deuterium have been used—the free-gas model (D mass 3.595), the effective-width model, and the Nelkin model.With all three models the THERMOS code reproduced the thermal spectra within a few percent. The effective-width model and the Nelkin model also gave reasonable agreement in the epithermal region. The free-gas model, however, gave too high a ratio between the epithermal and the thermal neutron densities.The computation time required for a 20-space, 30-energy-group calculation on an IBM-7090 computer was about 4 min.

ISSN:0029-5639    

DOI:10.13182/NSE65-A20235

出版商:Taylor&Francis    

年代:1965

数据来源: Taylor

摘要:

Numerical comparisons have been made between exact and approximate solutions to the two-group space-time diffusion equations. Two slab cores were studied, one 240-cm thick and the other 60-cm thick. Prompt critical bursts and limited ramp insertions of reactivity were simulated by imposing perturbations on the fission cross sections throughout the first quarter of the core. Feedback effects were neglected. Results were obtained using the conventional point kinetics equation, the adiabatic approximation and the space-time synthesis method. For one situation, two nodal methods were also examined. Comparisons with the exact space-time solutions suggest that, when the point kinetics equations are expected on qualitative grounds to be a poor approximation, the actual quantitative errors can be extremely large. Of the other approximations tested the space-time synthesis method gave the most accurate results.

ISSN:0029-5639    

DOI:10.13182/NSE65-A20236

出版商:Taylor&Francis    

年代:1965

数据来源: Taylor

摘要:

A numerical experiment of the transient neutron behavior following a source burst has been performed. The time-dependent Boltzmann equation (in the diffusion approximation without delayed neutrons) was propagated in time until asymptotic conditions were reached. The explicit time, space and energy solution was programed for the IBM-7094. Space-independent calculations of defined effective multiplication factors, neutron lifetimes and decay constants were performed for hydrogenous and graphite-moderated U235or Pu239systems.Seventy-three velocity groups were employed to detail spectral changes that occur in the approach to equilibrium. About 20µsec and 150µsec, respectively, were required for the energy modes to decay in the hydrogenous and graphite systems considered. The initial response of a cadmium detector is shown to be similar in multiplying and nonmultiplying assemblies and indicates the neutron slowing-down time to the cadmium resonance. No further structure in the cadmium-detector response due to the regenerative process was noted. The space-dependent properties of bare and reflected one-dimensional slabs were also briefly studied.

ISSN:0029-5639    

DOI:10.13182/NSE65-A20237

出版商:Taylor&Francis    

年代:1965

数据来源: Taylor

摘要:

The concept of a transfer function for a nuclear system is extended to include spatial effects. The general equation is derived using the time-dependent Fermi age and diffusion theories for a single-region, isotropic, homogeneous medium. The fluctuations of the thermal-neutron density at any point in the assembly is related to the variation of the fast-neutron source.The general transfer function equation is specialized for several cases, including the case of a point source in a cylindrical medium. Theoretical curves are calculated for multiplying and non-multiplying media and compared with the commonly used lumped-parameter transfer function.The results indicate, in general, that the lumped-parameter model predicts the correct behavior of the nuclear system only if the output detector is carefully positioned at a specific distance from the source. If the detector is located elsewhere, the lumped-parameter model is not capable of accurate results.The theoretical equations were used to calculate the spatially dependent transfer function between two detectors (the cross-transfer function) that were located within light- and heavy-water subcritical assemblies, simulating some experimental measurements. A comparison of the experimental and theoretical transfer functions indicate that the Fermi age, diffusion theory model might be quite adequate in describing the kinetics of a nuclear system.

ISSN:0029-5639    

DOI:10.13182/NSE65-A20238

出版商:Taylor&Francis    

年代:1965

数据来源: Taylor

摘要:

The complementary nature of pulsed-neutron and reactor-noise techniques in the investigation of reactor dynamic parameters is illuminated by considering the response of a reactor to two types of forcing functions. One of these forcing functions is the impulse function employed in pulsed-neutron studies, while the other is derivable from the inherent randomness of the nuclear events taking place in the reactor. Both the prompt-neutron density following a burst of neutrons into a reactor system and the spectral density of the reactor noise can be expressed in terms of the prompt-neutron decay constant,α. This, in turn, is related to the ratioβ/ℓand the reactivity of the system.Either technique can be used to measureα; however, in practice, each is limited according to a‘figure of merit’for a given experimental situation. Measurements made on both subcritical and critical assemblies in the Critical Mass Laboratory at Hanford illustrate the complementary feature of these two techniques and their usefulness in verifying each other’s experimental results.

ISSN:0029-5639    

DOI:10.13182/NSE65-A20239

出版商:Taylor&Francis    

年代:1965

数据来源: Taylor

摘要:

A general procedure for solving the space-energy-angle-dependent neutron transport equation is presented. A complete set of eigenfunctions of the transport equation is found under the assumptions of plane symmetry, constant cross sections, and stationary nuclei. The eigenfunctions are shown to be orthogonal with a proper weight function. The slowing-down problem in a hydrogen medium is treated in detail. An analytical solution of this problem is compared with the results of a Monte Carlo experiment.

ISSN:0029-5639    

DOI:10.13182/NSE65-A20240

出版商:Taylor&Francis    

年代:1965

数据来源: Taylor

摘要:

In this paper the normal-mode-expansion method is applied to the Boltzmann equation in plane geometry. The simple, isotropic, separable kernel is used. With such a kernel the energy-dependent thermalization theory is described in terms of singular integral equations in a way quite similar to that in the one-velocity approximation. In particular, the solutions of the Milne problem and of the two adjacent half-spaces problem allow the boundary conditions for the asymptotic neutron distribution to be determined.

ISSN:0029-5639    

DOI:10.13182/NSE65-A20241

出版商:Taylor&Francis    

年代:1965

数据来源: Taylor

摘要:

It is possible to derive a correction to the mean chord length used in the Wigner Rational Approximation whichgives a better estimate of the escape probabilitypreserves the equivalence relationship for each resonancepreserves the value of the resonance integral.Various methods of achieving objectives 1 and 2 have been discussed previously. It is shown in this paper that employing criterion 3 dictates an averaging procedure similar to earlier ones but involving different weighting points. A table of weighting points is given.

ISSN:0029-5639    

DOI:10.13182/NSE65-A20242

出版商:Taylor&Francis    

年代:1965

数据来源: Taylor