摘要:

AbstractThe fission-product release of spherical monogranular UC2particles is studied by postirradiation annealing of neutron-activated samples and by exposing samples to a steady rate of photofission. The release of the several fission products studied appears to follow the kinetics and temperature-dependence of an activated diffusional process. The anomalous fast release of a portion of the Xe133in annealing experiments may be interpreted as being due to release of attached or trapped xenon atoms by a process not following Fick's law.Analysis of the data obtained gives the following diffusion coefficients for krypton, tellurium, iodine, xenon and barium in UC2(in cm2/sec):The diffusion coefficient for xenon in UC2shows agreement with the diffusion coefficient for xenon in UO2. A negative activation entropy (‒13 eu) for diffusion is indicated.

ISSN:0029-5639    

DOI:10.13182/NSE65-A21008

出版商:Taylor&Francis    

年代:1965

数据来源: Taylor

摘要:

AbstractHeat transfer in flat-plate UO2fuel elements has been studied theoretically. Particular attention has been focused on internal-radiation heat transfer. Local radiant-heat fluxes have been calculated and the relative importance of radiation compared to conduction has been established. The results show that even at elevated temperatures single crystal UO2is transparent enough, and internal radiation contributes significantly to high-temperature heat transfer. The presence of scattering at the grain boundaries in polycrystalline UO2increases the extinction coefficient considerably. Because of this, radiant heat transfer was found to be unimportant compared to conduction.

ISSN:0029-5639    

DOI:10.13182/NSE65-A21009

出版商:Taylor&Francis    

年代:1965

数据来源: Taylor

摘要:

AbstractThe thermal neutron-capture cross section of 1.0-year Ru106has been determined from the yield of 22-min Rh107formed in reactor irradiations. The average of four measurements is 0.146 barns. The experimental error is about±7% but when systematic errors are included, largely in gamma-ray abundances from Ru106and Rh107decay, the uncertainty is about 30%. Cadmium-ratio measurements were made and the resonance-capture integral, including the 1/υpart, was found to be 2.0±0.6 barns for an effective cadmium cutoff of 0.54 eV. These results are relative to a cobalt thermal neutron-capture cross section of 37.5 barns and total resonance integral of 72.7 barns. It has been assumed that neutron capture by Rh106, Ru107and Rh107is negligible, that the cross section of Ru106in the thermal region has a 1/υdependence and that the neutron spectrum is 1/Ein the resonance region.

ISSN:0029-5639    

DOI:10.13182/NSE65-A21010

出版商:Taylor&Francis    

年代:1965

数据来源: Taylor

摘要:

AbstractThe absorption spectra for single crystal and polyerystalline UO2have been measured between 0.6 and 15μm at room temperature. The spectrum for UO2resembles that of a typical semiconductor, opaque in the visible but transparent over a large portion of the infrared. An absorption edge is located at approximately 0.6μm (2.0 eV). A large optical window extends from 3 to 13μm.The absorption coefficient for single crystal UO2has been determined between 1.5 and 15μm. A maximum value of 57 cm-1was measured at 1.70μm with minimum values of 6 cm-1at 2.75 and 8μm. The absorption coefficient of polyerystalline UO2at wavelengths less than 8μm is estimated to be ten times larger than for single crystal UO2.

ISSN:0029-5639    

DOI:10.13182/NSE65-A21011

出版商:Taylor&Francis    

年代:1965

数据来源: Taylor

摘要:

AbstractThe electrical conductivity of an 0.085 cm-thick layer of flame-sprayed alumina was examined as a function of temperature and of the specific power of an operating nuclear reactor. It was determined that the electrical conductivity of the alumina can be expressed asThe first term on the right is the normal expression for ionic conductivity as a function of temperature. The second term accounts for the impurity conduction in the insulator and the third term assumes an ionized material in which Rutherford scattering plays a dominant role in the mobility of the electron-hole pairs created by photon interactions in the alumina. The assumption of electronic conductivity, a temperature-dependent mobility varying asT3/2, and a density of charge carriers proportional to the reactor specific powerPis seen to hold over a temperature range up to 1300°K and up to reactor specific powers to 6 kW liter. An extrapolation of the results to higher specific powers shows the conductivity of Al2O3adequate for nuclear thermionic systems.

ISSN:0029-5639    

DOI:10.13182/NSE65-A21012

出版商:Taylor&Francis    

年代:1965

数据来源: Taylor

摘要:

AbstractTwo different reactions have been found to occur simultaneously when graphite is exposed to air which has been ozonized by a high-voltage silent discharge. One is the formation of a lamellar compound with nitrogen pentoxide which is always present in ozonized air. The second reaction is a rapid volatilization because of oxidation, which has also been traced to nitrogen pentoxide rather than to the much less reactive ozone.The lamellar compound has been characterized as an acceptor-type compound in which every two molecules of pentoxide constitute one electron acceptor. Equilibrium concentrations which are established in a few hours in ozonized air amount to about 10wt% of pentoxide at 25°C, and 0.1wt% at 150°C. The oxidation reaction has been studied both in ozonized air and in N2O5. A much slower oxidation occurs in ozonized oxygen which can, however, be considerably accelerated if the graphite is first converted to a lamellar N2O5compound.Pre-irradiation of the graphite causes only minor changes in the rates of compound formation and oxidation.The reactions may constitute hazards to reactors operating at low temperatures.

ISSN:0029-5639    

DOI:10.13182/NSE65-A21013

出版商:Taylor&Francis    

年代:1965

数据来源: Taylor

摘要:

AbstractIn the work previously reported, the solution to the problem of minimizing boiling reactor noise through external control was based on the work of the late Norbert Wiener. There are, however, serious drawbacks in applying Wiener theory. The mathematical sophistication and algebraic complexity greatly increase as more realistic and complex models are assumed for the reactor. Physical intuition is lost among the numerous digital calculations required for complex systems. In this paper a new graphical technique is used to determine an optimum reactor control system that will minimize boiling reactor noise. This technique practically eliminates these serious drawbacks and permits a considerable physical insight into the basic structural properties of optimum control systems to minimize reactor noise. Contrary to previous results, it was found that a reactor control system independent of reactor power level except for a gain constant could be designed that would minimize boiling noise at all power levels. This, in effect, eliminates the need for a complex adaptive control system to account for the dependency of the optimum reactor control system on reactor power level. Simulation studies verified these findings.

ISSN:0029-5639    

DOI:10.13182/NSE65-A21014

出版商:Taylor&Francis    

年代:1965

数据来源: Taylor

摘要:

AbstractThe integral neutron-transport equation is solved for the space-dependent mono-energetic neutron density in a unit cell. By using step functions to represent the spatial dependence of the collision probabilities, one may rearrange the integro-differential transport equation in a special way such that the left-hand side contains only the leakage term and the term describing the total collision probability for the homogeneous medium of one region,k′, of the original problem. The Green's-function technique is then used to convert the integro-differential equation to an integral equation. Thus, although the resulting equation may be applied to a heterogeneous cell, the kernel of the equation depends only on the total collision probability in the particular regionk′. Numerical results are presented for a two-region unit cell in slab geometry and compared with published results of DSN,PNdouble-PNand variational calculations. For unit cells that are of the order of two mean free paths or less in thickness, the zeroth-order spherical harmonic approximation for this method yields results comparable to very high order DSN,PNand double-PNcalculations. Further, once the Green's function has been computed, additional cell calculations can be performed with relatively little additional computational effort.

ISSN:0029-5639    

DOI:10.13182/NSE65-A21015

出版商:Taylor&Francis    

年代:1965

数据来源: Taylor

摘要:

AbstractA diffusion theory for the asymptotic transport scalar flux is derived from the monoenergetic transport equation in slab geometry. By allowing the scalar flux to be discontinuous at a material property and/or an external-source discontinuity, the theory is able to predict exact asymptotic transport-theory behavior for two standard halfspace problems. A supplementary diffusion-like theory is developed to treat the non-asymptotic flux. The total (asymptotic plus non-asymptotic) formalism yields a continuous scalar flux distribution and gives exact transport -theory leakage from a halfspace with a spatially-constant source. Numerous numerical comparisons indicate that the theory proposed here is significantly more accurate than classical (P1) diffusion theory. The complexity of both the asymptotic and non-asymptotic formalisms is comparable with that of theP1method. Finally, the entire formalism is generalized to three dimensions in rectilinear- and curvilinear-coordinate systems.

ISSN:0029-5639    

DOI:10.13182/NSE65-A21016

出版商:Taylor&Francis    

年代:1965

数据来源: Taylor

摘要:

AbstractAn analytical study has been made of the general problem of heat-transfer to liquid metals flowing between parallel plates. All the results are for the conditions of uniform heat fluxes and fully-established temperature and velocity profiles. Both unilateral and bilateral heat-transfer situations have been considered. In the former, three different methods of determining the velocity profiles were compared; and for each of these, three different types of profile curves for the eddy diffusivity of momentum,ϵM, were compared. The three different methods of determining the velocity profiles showed remarkably good agreement.In the case of bilateral heat transfer, the fraction of total heat transfer to the fluid from any one plate,ξ, was varied from zero to unity. It was found that the heat-transfer coefficient for any one plate is a sensitive function ofξfor that plate. Aboveξ= 0.31, the coefficients are positive; below it, they are negative. Atξ= 0.31, the coefficient is infinite, because at this condition the difference between wall and bulk temperatures is zero.Asξapproaches 0.50, from either above or below, the shape of theεMprofile in the vicinity of the center of the channel has less and less effect on the heat-transfer coefficient. Whenξ= 0.50, the effect is negligible for all practical purposes.There are no adequate experimental data available with which to test the calculated Nusselt numbers, but indications are that the recommended relationships are reasonably correct.

ISSN:0029-5639    

DOI:10.13182/NSE65-A21017

出版商:Taylor&Francis    

年代:1965

数据来源: Taylor