摘要:

AbstractFor large perturbations the usual assumption in power reactor stability that the flux variationsδnare small in comparison with the steady-state flux leveln0is not valid. Due to the product term of excess reactivity and neutron flux, harmonics are generated in the flux. The stability under such conditions can be discussed by extracting the fundamental flux component and obtaining a quasi frequency response as the ratio of fundamental incremental flux component to excess reactivity as a function of frequency and amplitude of perturbation. This approach is applied to two Argonne power reactors, the Experimental Boiling Water Reactor (EBWR) and the Experimental Breeder Reactor (EBR-I), where experimental frequency responses have been obtained and a peak has been observed. It is found that for both reactors the stability decreases as the amplitude of perturbation increases.

ISSN:0029-5639    

DOI:10.13182/NSE59-A25637

出版商:Taylor&Francis    

年代:1959

数据来源: Taylor

摘要:

AbstractIn order to determine the relative merits of the various rare earths as reactor control materials, a series of relative worth measurements was made in the Dresden Critical Assembly at Vallecitos Atomic Laboratory. Combinations of the oxides of five rare earths with highest thermal cross sections (dysprosium, erbium, europium, gadolinium, and samarium) were compared with cadmium and 2 per cent boron steel. Dy2O3, Gd2O3, and Sm2O3, separately and in combination, were found to be roughly equivalent in worth. Eu2O3was found to be the strongest absorber. Er2O3was found to be much less effective than the other materials studied.

ISSN:0029-5639    

DOI:10.13182/NSE59-A25638

出版商:Taylor&Francis    

年代:1959

数据来源: Taylor

摘要:

AbstractThe adsorption of simulated fission products on slurries of ThO2−UO3mixtures has been studied. Experiments were performed using tracer techniques employing slurries which had been previously pumped in order that the condition of the slurry as well as concentration of the fission products, temperature, and pressure might simulate reactor conditions. Results of some preliminary experiments designed to remove fission products by the use of eluting agents are also reported.

ISSN:0029-5639    

DOI:10.13182/NSE59-A25639

出版商:Taylor&Francis    

年代:1959

数据来源: Taylor

摘要:

AbstractThe various conventions and definitions of thermal and resonance flux are discussed. Measurements of the thermal neutron cross sections, resonance integrals, and reactor cross sections of the following nuclides are critically reviewed: Th232, Th233, Pa233, U233, U234, U235, U236, U238, U239, Np239, Pu239, Pu240, Pu241, and Pu242.

ISSN:0029-5639    

DOI:10.13182/NSE59-A25640

出版商:Taylor&Francis    

年代:1959

数据来源: Taylor

摘要:

AbstractEpithermal nonabsorption probabilities for neutron absorbers are important parameters in the evaluation of control rod worths. In this article, the average epithermal nonabsorption probability () for hafnium slabs is calculated by two different methods: (1) Within the framework of a specific two-dimensional, three-energy-group calculational scheme, an empirical value ofis determined which gives agreement with experimental rod worths. (2) Based on available microscopic cross-section data for the hafnium isotopes, the value ofis calculated and compared with the empirical value obtained above. The values ofobtained by these different methods for 0.1 in. and 0.2 in. thick slabs agree to within 10 per cent, thus verifying the physical reasonableness of the empirical probabilities.

ISSN:0029-5639    

DOI:10.13182/NSE59-A25641

出版商:Taylor&Francis    

年代:1959

数据来源: Taylor

摘要:

AbstractIn a low-enrichment reactor at sufficiently high temperature that the Pu239absorption cross section departs appreciably from 1/υ, plutonium build-up increases the sensitivity of the calculated thermal cross sections to the thermalization techniques used. Thermal neutron spectra are compared for two thermalization models in a heterogeneous lattice of a low-enrichment water-moderated reactor. Using blackness theory, equivalent homogeneous, monoenergetic cross sections for the lattice are computed at closely spaced energy intervals over the thermal energy range. The energy distribution of the thermal neutron flux is then obtained using both the Wigner-Wilkins and the Wilkins thermalization equations. Calculations are made with the fuel elements assumed to contain only U235and U238yielding almost pure 1/υabsorption, and also for the case of appreciable Pu239present in addition to the uranium resulting in a significant departure from 1/υabsorption. Sensitivity of the calculated spectrum to the effective mass of the hydrogen is tested by allowing wide variations of theξσsvalues for water at low energies in several applications of the Wilkins equation. Variations in the thermal neutron spectra, resulting from the choice of the thermalization equation (Wigner-Wilkins or Wilkins), from changingξσs, or as a result of plutonium build-up, are evaluated in terms of isotopic cross sections averaged over the spectrum in each case.

ISSN:0029-5639    

DOI:10.13182/NSE59-A25642

出版商:Taylor&Francis    

年代:1959

数据来源: Taylor

摘要:

AbstractThe reactivity worth of cylindrical control rods of small cross section inserted in a cylindrical reactor is evaluated by means of a variational method. Both one-group and two-group diffusion theory are used and simple formulae are developed for a single eccentric and a concentric array of control rods. The results obtained are illustrated by means of a numerical example and compared to the results derived from other methods available in the literature.

ISSN:0029-5639    

DOI:10.13182/NSE59-A25643

出版商:Taylor&Francis    

年代:1959

数据来源: Taylor

摘要:

AbstractPermissible void volume in photon shields is calculated in terms of shield thickness, photon energy, and permissible leakage factor. Several graphical aids for lead are presented. A simple method of void evaluation is included which may form the basis for an engineering acceptance test.

ISSN:0029-5639    

DOI:10.13182/NSE59-A25644

出版商:Taylor&Francis    

年代:1959

数据来源: Taylor

摘要:

AbstractA two-group albedo theory is developed which seems to be valid for the calculation of temperature coefficients of nuclear reactors characterized by the PSR. Measurements of over-all coefficient for the PSR are in qualitative agreement with results calculated by the theory. Analysis under the present theory singles out the temperature variation of the ratio of the age to the thermal neutron diffusion length of the reflector as the primary contributor to a low temperature positive coefficient effect. The advantage of representing the criticality factor,k, by the two-group albedo theory is well illustrated by the endeavor of calculating the temperature coefficient. Under normal two-group multiregion treatment the criticality factor never explicitly appears and therefore it is impossible to obtain an explicit form of the variation ofkwith system parameters. The dissection of the nonleakage probability in the present theory is not unique, but it does lead to easy physical interpretation.

ISSN:0029-5639    

DOI:10.13182/NSE59-A25645

出版商:Taylor&Francis    

年代:1959

数据来源: Taylor

摘要:

AbstractAfter a high-flux thermal nuclear reactor is shut down, the concentration of fission product xenon may rise for many hours as a result of the decay of fission product iodine into Xe135. This results in reactor poisoning and may, with consequent loss of efficiency, postpone the time at which the reactor may be restarted. This poisoning may be minimized by carefully controlling the rate at which the neutron flux is decreased during the shut-down operation. The determination of optimal control in this situation leads to some nonclassical problems in the calculus of variations. The aim of this paper is to show how they can be treated by the functional equation technique of dynamic programming. The methods we present rely upon the use of high-speed digital computers with large memories. The method automatically produces a valuable parameter study and results in stable designs.

ISSN:0029-5639    

DOI:10.13182/NSE59-A25646

出版商:Taylor&Francis    

年代:1959

数据来源: Taylor