摘要:

AbstractTemperature differences which will exist across the diameters of the Experimental Gas-Cooled Reactor (EGCR) fuel elements will cause the elements to bow. Since the elements are restrained at their midpoints as well as at the ends, the bowing will be accompanied by bending stresses and, as these stresses relax at the relatively high element temperatures, the bowing deflections will increase. A theoretical analysis was developed for predicting the time-dependent bowing behavior of an element subjected to a linearly distributed temperature difference across the diameter. The element behavior was considered to be a combination of creep and elastic bending.The analysis shows that, in every case, the maximum limiting deflection that an element will approach is approximately 2.63 times the initial bowing deflection, or 78% of the maximum deflection the element would have if its midpoint behaved as a plastic hinge. Although the time-dependent bowing will lead to increased temperature gradients, the analysis indicates that the additional deflection produced by the increase will be small compared to the deflection that caused the increase, and, consequently, the elements will be thermally stable.

ISSN:0029-5639    

DOI:10.13182/NSE64-A28902

出版商:Taylor&Francis    

年代:1964

数据来源: Taylor

摘要:

AbstractA method has been developed for predicting the effect of an air/ground interface on the fast-neutron flux or dose at large distances from a point isotropic source of neutrons in air. The method yields numerical values for functionsf(HS)andf(HD)that may be used to express the fast-neutron intensity as a function of source heightHS, receiver heightHD, and source-receiver separation distanceR, in terms of the corresponding infinite air intensityI(R). ThusI(HS,HD,R) = f(HS)f(HD)I(R).The method is called the“First-Last Collision Model”because it is based on the influence of the ground upon the distribution of“first”collisions of neutrons about the source and of“last”collisions about the receiver. Generalized numerical results have been computed, and means have been developed for applying these results to specific cases* Comparisons of these results with those derived from Monte Carlo calculations, and from experiments performed at the ORNL Tower Shielding Facility and the Nevada Test Site indicate that the first-last collision model predicts the fraction of the infinite air intensity within 5 per cent in almost all cases.

ISSN:0029-5639    

DOI:10.13182/NSE64-A28903

出版商:Taylor&Francis    

年代:1964

数据来源: Taylor

摘要:

AbstractThe power spectral density of the neutron density of a reactor is frequency dependent and related to the reactor transfer function and the power spectral density of the input disturbance. For a critical reactor, a power-spectral-density measurement can be used to evaluate the ratio (β/) whereβis the effective delayed-neutron fraction andlthe effective neutron lifetime. For subcritical operation, an evaluation of the reactor shutdown margin can be obtained by determining the quantitywherek, the effective reproduction constant, can be determined if the effective neutron lifetime and effective delayed neutron fraction are known.The output power spectral density of the University of Florida Training Reactor, operating in the subcritical region, has been measured using a plutonium/beryllium source to provide the input disturbance. The data are then fitted by a least-squares method to a theoretical model to obtain the quantity

ISSN:0029-5639    

DOI:10.13182/NSE64-A28904

出版商:Taylor&Francis    

年代:1964

数据来源: Taylor

摘要:

AbstractDiffusion is an important mechanism in the transport and deposition of very small particles from gas streams to the surfaces of a conduit. Based on the heat/mass analogy, an analytical model has been formulated for the deposition of the precursor (i.e., the fission product that first enters the gas stream) and for its first and second daughter products from laminar, and turbulent gas streams under steady-state conditions. The model is strictly applicable to deposition in the isothermal regions; axial temperature gradients have been found to alter the deposition pattern. Activity deposited on the surfaces of a conduit has been correlated with this model both for the molecular and larger size particles (0.004μ) assuming a perfect-sink condition at the wall surface. There is experimental evidence that wall surfaces do not always act as a perfect sink for the colliding particles; effects of an imperfect-retention scheme have been included in the analysis by introducing a factor for the effectiveness of the wall surfaces in retaining the particles. No rational evaluation of this factor is known. However, activity deposited on such surfaces can be correlated with the model developed if a suitable value is chosen for this factor.

ISSN:0029-5639    

DOI:10.13182/NSE64-A28905

出版商:Taylor&Francis    

年代:1964

数据来源: Taylor

摘要:

AbstractA calculational model for the Doppler reactivity feedback in a thermal, low-enrichment oxide core with non-uniform temperature distribution is derived on the basis of the UO2resonance integral varying as the square root of the absolute temperature. An analytical solution of the prompt-approximation, space-independent neutron kinetic equation, with the Doppler feedback written as a function of the fission energy, is obtained and application made to the self-limiting power-excursion tests conducted in the SPERT I oxide core. Comparison of the experimental and calculated Doppler effects, peak powers, burst energies and burst shapes is made for various published values of the UO2resonance integral temperature coefficient, which acts as a scaling factor in the calculations. The values used cover a spread of about 20% of the mean value, and excellent agreement with experiment is obtained for the smallest values of the coefficient. Systematic agreement is obtained between the calculated and experimental Doppler effects over the entire experimental range of adiabatic fuel-temperature rises attained in the short-period SPERT tests. This agreement implies the validity of a square-root temperature dependence for the Doppler effect in a thermal oxide core, in contrast with a logarithmic or aT1/2dependence, for which similar calculations give results which differ significantly from the experimental data.

ISSN:0029-5639    

DOI:10.13182/NSE64-A28906

出版商:Taylor&Francis    

年代:1964

数据来源: Taylor

摘要:

AbstractBy use of a certain“addition”formula, the flux due to an eccentric point source in a spherical reactor is expressed as a single infinite series of known tabulated functions. The change in buckling due to a small point sink is examined together with the shape of such a sink.

ISSN:0029-5639    

DOI:10.13182/NSE64-A28907

出版商:Taylor&Francis    

年代:1964

数据来源: Taylor

摘要:

AbstractSome diffusion parameters of water are computed with various thermal-neutron scattering laws. It is found that the diffusion cooling coefficient, in particular, is reasonably sensitive to the scattering law, but that the diffusion cooling coefficients predicted by the Radkowsky and Nelkin kernels are in fortuitious agreement. The coefficients computed for the Nelkin kernel, when treated in a manner consistent with the way in which experimental data are treated, are in reasonable agreement with the results of a recent experiment.

ISSN:0029-5639    

DOI:10.13182/NSE64-A28908

出版商:Taylor&Francis    

年代:1964

数据来源: Taylor

摘要:

AbstractA variational principle for resonance capture in heterogeneous reactors has been developed. The functional becomes the exact resonance integral when the flux is exact, and in general the functional also has the convenient form of an explicit resonance integral multiplied by a correction factor. A reasonable trial function for the adjoint is selected, which allows explicit, interpretable expressions to be derived for the correction factor when trial functions corresponding to the various currently used approximations are inserted. When solutions of Chernick-Rothenstein type equations are used for trial functions, the correction factor is unity. The inexactness in these equations is detectable only with higher-order approximations to the adjoint function. The correction factor for other approximations then furnishes a measure of the error as compared to exact solutions of C-R equations as a standard. Several applications are discussed.

ISSN:0029-5639    

DOI:10.13182/NSE64-A28909

出版商:Taylor&Francis    

年代:1964

数据来源: Taylor

摘要:

AbstractA new method for measuring neutron thermalizaton parameters that was proposed on theoretical grounds is tested experimentally for H2O. The characteristic thermalization parameters in the present formulation arewhereare Laguerre polynomials of order unity and degreeiandTis the temperature of the system expressed in energy units. The present experimental results for H2O can be described using one parameter. The result isγ11= (0.210±0.026)cm-1for 23 C. The value of this parameter as derived from diffusion-cooling measurements lies in the range of 0.4cm-1to 0.8cm-1. A possible explanation for this discrepancy is given. The value ofγ11as calculated on the basis of Nelkin's model is about four times higher than the present result.

ISSN:0029-5639    

DOI:10.13182/NSE64-A28910

出版商:Taylor&Francis    

年代:1964

数据来源: Taylor

摘要:

AbstractDiscrete-ordinates methods for the solution of the mono-energetic transport equation in infinite slab and infinite cylindrical geometry are considered. A numerical method for each geometry is defined, and successive over-relaxation schemes for accelerating the convergence of iterative solutions to each approximate equation system are illustrated. Numerical evidence is given to show that the successive overrelaxation schemes have a considerably higherrate of convergencethan the standard Gauss-Jacobi iterative schemes. For the method for cylinders, the evidence shows also that the use of the acceleration technique results in a factor of at least 2.0 improvement in the actual time required to solve a range of problems to given accuracy.

ISSN:0029-5639    

DOI:10.13182/NSE64-A28911

出版商:Taylor&Francis    

年代:1964

数据来源: Taylor