摘要:

AbstractA detailed evaluation of theRmatrix resonance parameters describing the interaction of neutrons with235U has been performed up to 500 eV using the most recent high-resolution measurements of the235U neutron cross sections. The availability of235U spin-separated neutron cross-section data, in conjunction with the use of theΔ3statistics of Metha and Dyson, has made possible a detailed study of the statistical distribution of the resonance parameters and their average values. The presentRmatrix resonance parameters have been converted into equivalent sets of Adler-Adler parameters and multipole momentum space expansion parameters. Extensive validation of this evaluation has been performed by comparing self-shielded fission rates computed with theseRmatrix parameters with the measurements of Czirr; a test of the ENDF/B unresolved resonance formalism for the calculation of235U self-shielding factors is also presented.

ISSN:0029-5639    

DOI:10.13182/NSE91-A23840

出版商:Taylor&Francis    

年代:1991

数据来源: Taylor

摘要:

AbstractPairing corrections in particle-hole (exciton) state-density formulas used in precompound nuclear reaction theories are, strictly speaking, dependent on the nuclear excitation energy U and the exciton number n. A general formula for (U, n)-dependent pairing corrections was derived earlier for the exciton state-density formula for a system of one kind of fermion. A similar derivation is made for a system of two kinds of fermions, a system in which neutrons and protons occupy different sets of single-particle states. It is shown that the constant-pairing-energy correction used in standard state-density formulas, such as U0in Gilbert and Cameron, is a limiting case of the present general (U, n)-dependent results. Spin cutoff factors are calculated using the same pairing theory and parameterized into an explicit (U, n)-dependent function, thereby defining the exciton level-density formula for two kinds of fermions. The results show that the ratios in the exciton level densities in the one- and two-fermion approaches vary with both U and n, thus, most likely leading to differences in calculated compound-to-precompound ratios. However, the differences in the spin cutoff factors in the two cases are found to be rather small.

ISSN:0029-5639    

DOI:10.13182/NSE91-A23841

出版商:Taylor&Francis    

年代:1991

数据来源: Taylor

摘要:

AbstractBest-estimate calculations of realistic source terms are presented that reduce uncertainties in predicting volatile fission product release from the UO2fuel over the temperature range from 770 to 2500 K. The proposed method of correlation includes such fuel morphology effects as equiaxed fuel grain growth and fuel/cladding interaction. The method correlates the product of fuel release rate and equiaxed grain size with the inverse fuel temperature to yield a bulk mass transfer correlation. It is found that fewer and slower releases are predicted utilizing the bulk mass transfer correlation than with the steam oxidation model and the U.S. Nuclear Regulatory Commission’s NUREG-0956 correlation. Computational modules are developed to perform the thermal-hydraulic and fission product calculations needed to analyze the severe fuel damage tests. The predictions utilizing the bulk mass transfer correlations overall follow the experimental time-release histories during the heatup, power hold, and cooldown phases of the transients. Good agreements are achieved for the integral releases both in timing and in magnitude. The proposed bulk mass transfer correlations can be applied to both current and advanced light water reactor fuels.

ISSN:0029-5639    

DOI:10.13182/NSE91-A23842

出版商:Taylor&Francis    

年代:1991

数据来源: Taylor

摘要:

AbstractThe effect of elevated temperature on the limits of the various modes of combustion of hydrogen-air-steam mixtures is reviewed. The modes include spontaneous combustion, diffusion flames, deflagrations, and detonations. The existing data on high-temperature hydrogen combustion are reviewed, areas where uncertainties exist are identified, and the importance of these uncertainties are discussed with respect to reactor safety for four different accident scenarios.

ISSN:0029-5639    

DOI:10.13182/NSE91-A23843

出版商:Taylor&Francis    

年代:1991

数据来源: Taylor

摘要:

AbstractThe PNtheory is shown to be an asymptotic limit of transport theory for an optically thick planar-geometry system with small absorption and highly anisotropic scattering. The asymptotic analysis shows that the solution in the interior of the system is described by the standard PNequations for which initial, boundary, and interface conditions are determined by asymptotic initial, boundary layer, and interface layer calculations. The asymptotic initial, (reflecting) boundary, and interface conditions for the PNequations agree with conventional formulations. However, at a boundary having a prescribed incident flux, the asymptotic boundary layer analysis yields PNboundary conditions that differ from previous formulations. Numerical transport and PNresults are presented to substantiate this asymptotic theory.

ISSN:0029-5639    

DOI:10.13182/NSE91-A23844

出版商:Taylor&Francis    

年代:1991

数据来源: Taylor

摘要:

AbstractThe PNtheory has been shown to be an asymptotic limit of transport theory for problems in optically thick planar-geometry media with low absorption rates and highly anisotropic scattering. Transport problems that lie outside the asymptotic regime of validity of PNtheory are considered. Such problems occur in media that are either optically thin, or contain isotropic or mildly anisotropic scattering, or are not weakly absorbing. For such problems, the accuracy of numerical solutions of the PNequations obtained using the asymptotic boundary conditions is demonstrated. These numerical solutions are compared with others obtained using various familiar boundary conditions. Solutions obtained using the asymptotic boundary conditions are always competitive with, and often superior to, solutions obtained using these other boundary conditions.

ISSN:0029-5639    

DOI:10.13182/NSE91-A23845

出版商:Taylor&Francis    

年代:1991

数据来源: Taylor

摘要:

AbstractA common practice in Monte Carlo radiation transport codes is to start each random walk a specified number of steps up the random number sequence from the previous one. This is called the stride in the random number sequence between source particles. It is used for correlated sampling or to provide tree-structured random numbers. A new random number generator algorithm for the major Monte Carlo code MCNP has been written to allow adjustment of the random number stride. This random number generator is machine portable. The effects of varying the stride for several sample problems are examined.

ISSN:0029-5639    

DOI:10.13182/NSE91-A23846

出版商:Taylor&Francis    

年代:1991

数据来源: Taylor

摘要:

AbstractRecently obtained experimental total beta-ray spectra for 77 radionuclides created during fission of235U are compared with predicted total beta-ray spectra based on beta-ray transition energies and intensities of individual components currently available in the Evaluated Nuclear Structure Data File (ENSDF). In addition, experimental average beta-ray energiesfor 100 radionuclides are compared with evaluated/theoreticalfrom four compilations, namely, (a) a 1982 compilation, (b) the 1989 and current ENSDF, (c) a 1988 compilation by the Japanese Nuclear Data Committee, and (d) predictions using the microscopic theory of Klapdor and Metzinger. None of these evaluations/predictions is superior in reproducing the experimental data. A comparison of the experimentalwith the total available beta decay energies Qβindicates that the approximation≍Qβ/3 somewhat overestimateson the average; however, the ratio R =/Qβvaries between 0.11 and 0.46, and there is no discernible trend in R compared with Qβor2 s. Lastly, the intensities of possible ground-state decay transitions were estimated for 47 radionuclides and compared with similar data in ENSDF. In 14 cases, a nonzero ENSDF value is supported by the experimental data, and in 8 cases a zero value in ENSDF is supported by the lack of experimental data suggesting a high-energy ground state beta-ray transition. Of the remaining 25 radionuclides, the experimental data for 9 cases suggest that increases are needed in the ENSDF, and for 16 radionuclides the data indicate the need for smaller values of the ground-state transition intensities from those given in the ENSDF, being zero for 4 nuclides (80,81Ga,84As, and145Cs).

ISSN:0029-5639    

DOI:10.13182/NSE91-A23847

出版商:Taylor&Francis    

年代:1991

数据来源: Taylor

摘要:

AbstractThe heuristic search method for generation and optimization of pressurized water reactor (PWR) fuel reload configurations is developed and implemented in a research prototype. This is used to test the method on a sequence of typical PWR reload problems. Applying the method to a problem of reload with burnable poisons (BPs) helps avoid decoupling the fuel configuration problem from the reactivity control BP problem. Thus, better and physically transparent solutions are obtained. In another example, an attempt to achieve the flattest possible power distribution demonstrates the flexibility of the method. Finally, the potential of developing the method into a practical software tool for routine use by fuel-management engineers in industry is demonstrated.

ISSN:0029-5639    

DOI:10.13182/NSE91-A23848

出版商:Taylor&Francis    

年代:1991

数据来源: Taylor

ISSN:0029-5639    

DOI:10.13182/NSE91-A23849

出版商:Taylor&Francis    

年代:1991

数据来源: Taylor