摘要:

AbstractReactivity worth measurements are reported for various metal plates in a quasi-homogeneous subcritical assembly of enriched uranium and beryllium oxide. Worths of nickel, iron, cobalt, gold, Hastelloy R-235 and René41 were measured in this system using the pulsed-neutron method. Equivalences were determined between these absorber materials and the fueled-core material. The results indicate that the prompt lifetime of this system is relatively insensitive to massive localized absorbers.

ISSN:0029-5639    

DOI:10.13182/NSE65-A20031

出版商:Taylor&Francis    

年代:1965

数据来源: Taylor

摘要:

AbstractThe slowing-down spectra in several natural-uranium heavy-water reactor cores and in a U235light-water reactor have been intercompared using activation techniques. The main features of the spectra agree with multigroup diffusion theory calculations but there are additional effects not included in the theory which can be correlated with uranium resonances.

ISSN:0029-5639    

DOI:10.13182/NSE65-A20032

出版商:Taylor&Francis    

年代:1965

数据来源: Taylor

摘要:

AbstractThe thermalization of a pulse of fast neutrons in a large, homogeneous water assembly is investigated numerically. The effect of chemical binding is studied by comparing the results obtained with the free-hydrogen gas and the Nelkin kernels. It is found that chemical binding has an observable effect on some of the quantities of interest in a pulsed-neutron experiment. Two definitions of mean slowing-down time are considered and their relationship examined. Comparisons are made to several experimental measurements and earlier calculations.

ISSN:0029-5639    

DOI:10.13182/NSE65-A20033

出版商:Taylor&Francis    

年代:1965

数据来源: Taylor

摘要:

AbstractA neutron-exposure unit for radiation-damage studies is derived which is proportional to gross-displacement production with little dependence on the reactor spectra or displacement model selected. The unit is applied to the analysis of irradiation-induced changes in nil-ductility temperature in steel. Data from a graphite reactor and from the core of a water-moderated test reactor were statistically distinct as originally reported. Through the application of this unit, these results could be reconciled to constitute a single body of data.

ISSN:0029-5639    

DOI:10.13182/NSE65-A20034

出版商:Taylor&Francis    

年代:1965

数据来源: Taylor

摘要:

AbstractTo assess diffusion's importance, the temperature distribution in a cylindrical reactor is derived for a coolant with uniform properties and velocity, taking into account both radial and axial diffusion, for a cosine-J0power distribution. The fractional temperature rise of the coolant is found to bewhereE(z) = [sin(z) + sin(Z)]/2 sin(Z),z=πx/2′,xis the axial distance from the core center, -Hand′are the core half-height and extrapolated half-height, -H≤x≤H;Fn= 1/J0(Pn)·[(Pn/2.405P)2-10,J1(Pn) = 0,P= R/R′= core radius/extrapolated radius,ρ= r/R,r= radial distance from axis, 0≤r≤R;an= =βnH/Z, 2Aβn+ 1 =[1 + 4αβ(Pn/R)2]½,A= axial diffusivity/u,B= radial diffusivity/u, u= coolant axial velocity, andThe expression is evaluated for a variety of values for all the parameters, and the results are discussed analytically and presented in tables and graphs. The effect is dependent upon the relative size of the diffusion eddies in comparison with the dimensions of the reactor. The eddy diffusivity is proportional to the size of the particles in the bed and is about ten times larger axially than radially. A small core with large fuel particles will be affected by eddy diffusion, thereby reducing hot spots, but a large core with small particles will not. For a core 8 ft in diameter cooled by sodium flowing at 2 ft/sec, the effect is perceptible with 2-in. particles, but not with 0.2-in. particles.

ISSN:0029-5639    

DOI:10.13182/NSE65-A20035

出版商:Taylor&Francis    

年代:1965

数据来源: Taylor

摘要:

AbstractA more precise value of the half-life of U235, for alpha emission, has been determined from an analysis of the alpha spectrum of natural uranium. The alpha spectrum was measured using solid-state detectors and the half-life obtained by a comparison of the intensity of the resolved portion of the U235alpha spectrum with the intensities of the U234and U238alpha groups. The value obtained wasT1/2= (6.92±0.09)×108years.

ISSN:0029-5639    

DOI:10.13182/NSE65-A20036

出版商:Taylor&Francis    

年代:1965

数据来源: Taylor

摘要:

Asymptotic neutron spectra have been measured in the center and from the surface of three U235hydrogen-moderated multiplying assembliesusingthe pulsedelectron Linac mechanical-chopper technique. Two of the assemblies were watermoderated while the third was homogeneous and paraffin-moderated. The sizes and the hydrogen-to-U235ratios were made different so that absorption, leakage, and scattering were varied. The measured spectra were compared with diffusion theory spectrum calculations based on Nelkin’s scattering kernel for water and Goldman’s scattering kernel for polyethylene (for the paraffin-moderated assembly). Corngold’s formulation was used in the epithermal energy range. The agreement with theoretical predictions of the scalar spectrum was satisfactory when measured values of the asymptotic time-decay constant were used to calculate the spectrum.

ISSN:0029-5639    

DOI:10.13182/NSE65-A20037

出版商:Taylor&Francis    

年代:1965

数据来源: Taylor

摘要:

AbstractPulsed-neutron experiments have been performed in a borehole model to determine the effects of tool position, borehole fluid, and source-detector spacing on pulsed-neutron/thermal-neutron logging. Neutron-time distributions were measured with various combinations of the above parameters in a sand model of 32.5% porosity filled with fresh water or salt water with 230 g/liter NaCl. Neutron lifetimes determined from the distributions indicate the degree of validity of the assertion that undesirable borehole effects are largely eliminated by this logging method. A numerical computer code (CUNLAP) has been developed to solve the time-dependent, three-group diffusion equations which apply to borehole geometry. Results of test calculations are presented and compared to the experiments in a semiquantitative way. The numerical results are also compared to those of an analytical, fundamental-mode calculation. It is shown that the latter approach is inappropriate for the type of measurement and size of system used in experiments of this nature.

ISSN:0029-5639    

DOI:10.13182/NSE65-A20038

出版商:Taylor&Francis    

年代:1965

数据来源: Taylor

摘要:

AbstractAn asymptotic velocity of (18.79±0.32)×103cm/sec is reported for the propagation of a TRIGA reactor neutron pulse through a 4 ft×4 ft×5.8 ft graphite thermal column. Interpretation in terms of a proposed theory yieldsDv= (2.34±0.02)×105cm2/sec for 1.60 g/cm3graphite.The propagation velocity was found to be independent of reactivity inserted in the range covered by experiment (to 2.90 dollars). Also, the pulse shape was preserved with an amplitude attenuation length equal to that for the steady-state thermal flux. These results are attributed to the fact that the neutron lifetime in the column was shorter than the pulse width and period. Calculations are presented for the reverse situation where the pulse shape is distorted.Pulse measurements with a Boral curtain lowered into the column are used to test the theory for situations where the slowing-down density is important.

ISSN:0029-5639    

DOI:10.13182/NSE65-A20039

出版商:Taylor&Francis    

年代:1965

数据来源: Taylor

摘要:

AbstractFluctuations of the neutron populations in various phase-space regions in a reactor have been examined by development of a three-step analysis. First, the usual transport equation, or an approximation to it, is used to compute the probability that a neutron injected at a certain location in the reactor gives rise to a chain-related descendant neutron in each of a number of differential volume elements in phase space. Second, these conditional probabilities are used to compute product densities, probabilities that nuclear reactions of a certain class are induced in various time intervals by neutrons in each of a number of differential volume elements. Finally, the product densities are used to compute local population moments, parameters arising in the Rossi alpha experiment, auto- and cross-correlation functions, and other quantities of interest in fluctuation studies. The analysis, as applied to various reactor geometries, shows that the usual point-reactor analysis of reactor neutron fluctuations can lead to substantial error in predicting fluctuation magnitudes in startup studies and in determination of some reactor parameters from fluctuation experiments.

ISSN:0029-5639    

DOI:10.13182/NSE65-A20040

出版商:Taylor&Francis    

年代:1965

数据来源: Taylor