摘要:

AbstractAn exact formulation is presented for the release of metallic fission products. Such radioactive atoms are created through fission processes inside the kernel of fuel particles. They can diffuse through the coating of a fuel particle and the surrounding charcoal matrix into the structural graphite of the reactor core. Some atoms traverse this graphite along internal surfaces and finally enter the coolant gas. To find the number of radioactive atoms released into the coolant gas, the diffusion equation in one space dimension is solved numerically taking into account as driving forces both the gradient of the chemical potential and that of the temperature field. The chemical potential is determined respectively by the Langmuir and Freundlich adsorption isotherms for small and large concentrations of metal atoms adsorbed at the highly active internal surfaces of charcoal and graphite. As an example, a parameter study of the release is presented for the most danagerous radioactive metallic isotope,90Sr. The calculation of the release rate from a single fuel particle shows that the coating does not act as an effective diffusion barrier in this case. It is found that the structural graphite governs the release by virtue of its good adsorptive properties and its low diffusion constant. The results for the concentration profile, the mass current (or flux), and the release of90Sr are highly sensitive to experimental information on diffusion and adsorption coefficients, in part because of the temperature-activated nature of adsorption and diffusion processes. Since the experimental variables are known with limited accuracy only, a parameter study of the90Sr release is carried out, that is centered around the best available empirical values for diffusion and adsorption coefficients.

ISSN:0029-5639    

DOI:10.13182/NSE68-A21086

出版商:Taylor&Francis    

年代:1968

数据来源: Taylor

摘要:

AbstractThe cosorption of water and carbon dioxide by molecular sieves is a potential method of removing these contaminants from the helium coolant of a nuclear gas cooled reactor. This system was experimentally investigated by both differential- and deep-bed tests at a temperature of 25°C; at pressures of 1 to 30 atm for differential tests and 10 to 30 atm for deep-bed tests; with gas flow rates of 0.0010 to 0.0138 g/(cm2sec); and with inlet water or carbon dioxide concentrations of 3.4×10−8to 9.3×10−7g moles/cm3. These tests showed that the system could be described by the rate limiting step of intracrystalline diffusion with diffusion coefficients at 25°C of 1.92×10−10cm2/sec for water and 3.11×10−10cm2/sec for CO2. Sorbed CO2was found to be irreversibly replaced by sorbed water, and the CO2loading was dependent on water concentration.Differential equations were derived to describe the system of the cosorption of two interacting fluid species with Freundlich-type isotherms in a flowing fluid by a fixed bed of solids in which the sorption rate is controlled by intracrystalline diffusion. The set of differential equations was solved by a finite difference method for the case of water and carbon dioxide cosorption by molecular sieves.Generalized breakthrough curves for both water and CO2were determined, and their use for design purposes is demonstrated.

ISSN:0029-5639    

DOI:10.13182/NSE68-A21087

出版商:Taylor&Francis    

年代:1968

数据来源: Taylor

摘要:

AbstractThe Karlsruhe rotating crystal time-of-flight spectrometer was used to measure the slow neutron scattering law of graphite in a range of energy transfer of 7 to 180 meV and momentum transfer of 1.5 to 16Å−1. The graphite samples were heated to a temperature of 533°K, thereby increasing the probability of scattering with high energy transfer.The experimental data are corrected for multiple scattering in the sample using the incoherent approximation. The corrected data are in good agreement with calculated scattering law values. Large discrepancies between theory and previous experimental results are thus satisfactorily explained.The coherent nature of inelastic scattering in graphite is apparent in the data, especially in the region of lower energy and momentum transfers. The possibility of using the experimental results in this region directly to test and eventually to correct lattice model parameters is discussed. It is suggested that further measurements in this region with higher energy resolution might yield useful information.A phonon frequency distribution is extrapolated from the data and used to calculate several integral quantities. The values obtained are compared with previous results, both theoretical and experimental.

ISSN:0029-5639    

DOI:10.13182/NSE68-A21088

出版商:Taylor&Francis    

年代:1968

数据来源: Taylor

摘要:

AbstractAccurate critical parameters have been obtained for bare, nearly homogeneous assemblies of enriched uranium and graphite having C/U atom ratios in the range 960 to 23 000. Among the quantities measured werekeff, critical bucklings, extrapolation distances, spectral indices, and neutron lifetimes. Particular attention was paid to the problem of neutrons returning from the surroundings.

ISSN:0029-5639    

DOI:10.13182/NSE68-A21089

出版商:Taylor&Francis    

年代:1968

数据来源: Taylor

摘要:

AbstractAnalysis of the nearly homogeneous enriched uranium-graphite critical assemblies described in the preceding paper by Phelps and Weinstock are reported in this paper. These assemblies are characterized mainly by their high leakage rate, and two methods are used for estimating the leakage: 1) the conventionalB1approximation method and 2) the moments method using Monte Carlo calculations for the moments of the slowing down distribution. It is found that theB1approximation describes the leakage effects quite accurately. Most of the cross sections used in the calculations are from the recent evaluated nuclear data file (ENDF/B). Results of calculations forkeff, neutron lifetimes, and foil activation ratios are generally in excellent agreement with the measurements.

ISSN:0029-5639    

DOI:10.13182/NSE68-A21090

出版商:Taylor&Francis    

年代:1968

数据来源: Taylor

摘要:

AbstractA group of 11 aqueous critical experiments fueled by233U and235U and performed by Gwin and Magnuson have been analyzed to serve as integral tests of nuclear data important in reactor design. Measured eignvalues were corrected for various effects including the presence of the aluminum container, departures from sphericity, delayed-neutron importance, and room return. Eigenvalues were calculated in simplifiedP-3 approximation using 60 energy groups, and determinations were made of the eigenvalue uncertainties (±0.1%) associated with this treatment. Within the eigenvalue uncertainties (±0.25%) resulting from fuel inventories, it was concluded that fissile nuclide and H(n,γ) cross sections were adequate to match calculations and experiments but that there was evidence of erroneous nuclear data important in determining neutron leakage. In particular, a substantially harder233U fission neutron spectrum seems to be indicated.

ISSN:0029-5639    

DOI:10.13182/NSE68-A21091

出版商:Taylor&Francis    

年代:1968

数据来源: Taylor

摘要:

AbstractThe pulsed-neutron method has been used with ice cylinders in the buckling range from 0.039 to 0.739 cm−2over temperatures between−5 and−85°C. The purpose was to determine whether there would be early establishment of an asymptotic neutron spectrum and, since this proved to be so, to measure the neutron diffusion parameters. The neutron decay data were analyzed by using a nonlinear least-squares fitting method with two exponential modes. The resulting diffusion parameters are compared with those found by other workers for H2O at various temperatures, and the effect of the solid-liquid phase transition on the diffusion coefficient and diffusion cooling coefficient is discussed.

ISSN:0029-5639    

DOI:10.13182/NSE68-A21092

出版商:Taylor&Francis    

年代:1968

数据来源: Taylor

摘要:

AbstractIn a previous publication by Benoist, a simple and general formulation of the streaming effect in lattices was established which defines the diffusion coefficients by a suitable weighting of the mean-free-paths of the various media; this formulation introduced special types of collision probabilities initially calculated by an iteration technique. However, it appeared better to work with a closed formulation as the series of angular correlation terms evidenced a very slow convergence, especially for large channels. This approach requires the solution of the Boltzmann equation with particular types of sources.This solution is shown to be equivalent to the treatment of a cell in terms of some fictitious reaction. rates which are defined. The problem is essentially analogous to the calculation of the thermal utilization factor, an analogy that has been exploited as far as possible. Finally, by an adjustment on the corresponding void channel system, the treatment of fueled channels is made and a new method is proposed for the direct treatment of the latter case. The new expressions obtained for the diffusion coefficients are very simple and the numerical results obtained with them agree very well with reference calculations made by a variational method which is also exposed. Various auxiliary corrections are studied, and, finally, formulae for practical utilization are given in the Appendix.

ISSN:0029-5639    

DOI:10.13182/NSE68-3

出版商:Taylor&Francis    

年代:1968

数据来源: Taylor

摘要:

AbstractA discussion is given of the use of the indirect variational method for generating the trial functions needed to compute a variational estimate of a homogeneous functional of the solution to an eigenvalue equation. It is shown that one use of the method leads to no difficulties, whereas another use gives meaningless results. In this latter instance, the method of weighted residuals can be used to generate the necessary trial functions. With the trial functions known, the variational estimate of the functional of interest follows by quadrature.

ISSN:0029-5639    

DOI:10.13182/NSE68-A21094

出版商:Taylor&Francis    

年代:1968

数据来源: Taylor

摘要:

AbstractThis work tests the accuracies of some common approximate methods for calculating spatially dependent neutron slowing down distributions. According to each procedure, an analytic expression for the detailed distribution of neutrons from a plane monoenergetic source in hydrogen is obtained and compared with accurate analytic solutions. Most of the latter are derived here and appear to have other far reaching potential applications. In particular, the exact value and first two lethargy derivatives of the collided angular flux at source lethargy are found in terms of elementary functions of position and angle. These results are used to show that an expression derived by McInerney for the spatial distribution of the scalar flux has, at any given position, only first-order accuracy in powers of lethargy, even though the zeroth and second spatial moments are exact at all lethargies. While theB-1 andP-1 approximations produce poor results at small lethargies, they are accurate at large values; for the errors are due primarily to high-order spatial Fourier components, and these rapidly decay with increasing lethargy. At any lethargy, a Tauberian theorem facilitates calculating the spatial derivative of the scalar flux at the source plane. This quantity is used to trace the lethargy dependence of some peculiarities of the entire spatial distributions given by theB-1 andP-1 approximations. At asymptotically large lethargies, these spatial distributions are obtained explicitly and shown to agree with a well-known accurate expression.

ISSN:0029-5639    

DOI:10.13182/NSE68-A21095

出版商:Taylor&Francis    

年代:1968

数据来源: Taylor