摘要:

AbstractA methodology for the assessment of uncertainties about reliability of nuclear reactor systems described by Markov models is developed, and the uncertainties about the failure probability of the shutdown system of the Clinch River Breeder Reactor (CRBR) are assessed.Failure and repair rates and all other inputs of reliability analysis are taken as random variables with known probability distribution functions (pdf's). The pdf of reliability is calculated by both a Monte Carlo simulation and a Taylor series expansion approximation. Three techniques are developed to reduce the computational effort: (a) ordering of system states, (b) merging of Markov processes, and (c) judicious choice of time steps.A Markov model has been used for reliability analysis under uncertainty of the shut down system of the CRBR. It accounts for common-cause failures, interdependences between unavailability of the system and occurrence of transients, and inspection and maintenance procedures that depend on the state of the system and that include possibility of human errors. Under these conditions, the failure probability of the shutdown system differs significantly from that computed without common-cause failures, human errors, and input uncertainties.

ISSN:0029-5639    

DOI:10.13182/NSE80-A18703

出版商:Taylor&Francis    

年代:1980

数据来源: Taylor

摘要:

AbstractData on the heat transfer and the pressure drop in sodium under forced convection boiling are presented. It is shown that in annular-dispersed flow, a difference between wall and saturation temperatures is small, being within 1 to 5°C. It is also shown that in two-phase alkali-metal flow with heat input friction losses are smaller than in adiabatic flow. This is associated with a“push aside”effect on the main stream of the vapor flowing from the interface.The heat transfer and friction loss data indicate that the phase change takes place by evaporation from a liquid film surface, without vapor bubble generation at the wall. The experiments showed that, even in the presence of artificial cavities, the incipient super-heat is statistical in nature. The efficiency of the double-reentrant-angle-type cavities and of inert gas injection as a means of stabilizing forced convection boiling of the alkali metal was proven.

ISSN:0029-5639    

DOI:10.13182/NSE80-A18704

出版商:Taylor&Francis    

年代:1980

数据来源: Taylor

摘要:

AbstractGraphite rods and vitreous silica blocks were exposed to the neutrons generated in a spallation source having a large flux component in the 100-MeV region. The electrical conductivity of the former and the dilatation of the latter were measured. The ratio of the damage rate in silica to that in graphite exceeded that reported for fission neutrons, and this is attributed to the scattering cross sections of carbon falling more in the neutron high-energy region than do those of silicon and oxygen. Within our knowledge of the fluxes and their spectra and the yield functions, no great enhancement of the damage rate is found as compared to that which would be calculated from simple isotropic scattering.

ISSN:0029-5639    

DOI:10.13182/NSE80-A18705

出版商:Taylor&Francis    

年代:1980

数据来源: Taylor

摘要:

AbstractMonte Carlo calculations have been performed for neutrons reflecting between two Type 04 concrete plane-parallel interfaces. A new 23-group albedo data base (SAIL) was used in conjunction with the MORSE code to calculate the neutron spectrum at each reflection. It was found that, after thermalization, for the same order of reflection, the number of neutrons in the cavity is dependent on the initial energy of the neutrons. Typical results are presented along with a brief history of the motivations for these calculations.

ISSN:0029-5639    

DOI:10.13182/NSE80-A18706

出版商:Taylor&Francis    

年代:1980

数据来源: Taylor

摘要:

AbstractAbsolute cumulative yields have been determined for 49 fission products representing 36 mass chains created during thermal-neutron fission of239Pu, including 3 mass chains for which no prior data exist. Using Ge(Li) spectroscopy, spectra were obtained of gamma rays from decay of fission products between 1550 s and 31 days after a 100-s irradiation. Data were obtained for all fission products simultaneously. Gamma rays were assigned to the responsible fission products by matching gamma-ray energies and half-lives. Gamma-ray data associated with decay of135I and140Ba-140La, in particular, were thoroughly studied; uncertainties were obtained for the two largest intensity gamma rays from decay of135I that are smaller than previously evaluated uncertainties.Fission product yields were obtained from the data by first determining the appropriate gamma-ray activity as of the end of the irradiation, then correcting for detector efficiency and gamma-ray branching ratio, and, finally, dividing by the number of fissions created in the sample. The number of fissions was determined by direct comparison of gamma rays emanating from fission products created during a careful irradiation of a well-calibrated239Pu-loaded fission chamber.The resulting fission product yields are compared with previous measurements and with recommended yields given in two recent (and independent) evaluations. The present results are significantly larger for mass chains 101 and 105, somewhat smaller for mass chains 87 and 151, and in reasonable agreement with the remaining mass chains. Uncertainties assigned to the present results range between 2.5 and 25%, and are smaller than or comparable to uncertainties assigned to previous experimental (or evaluated) yields for 14 mass chains.

ISSN:0029-5639    

DOI:10.13182/NSE80-A18707

出版商:Taylor&Francis    

年代:1980

数据来源: Taylor

摘要:

AbstractThe transfer matrix method is used to solve the Milne problem for a half space for neutrons interacting with a moderator at temperature T. Two different scattering models are considered. They are (a) the free monatomic gas of arbitrary molecular mass with constant cross sections in the center-of-mass system, and (b) the Nelkin kernel for water. Both models permit an additional 1/v absorption cross section. We have obtained accurate numerical values for the diffusion length, the extrapolated end point, the critical absorption strength, and the boundary heating for a variety of values of the parameters. Comparison is made both with other calculations and with experiments.

ISSN:0029-5639    

DOI:10.13182/NSE80-A18708

出版商:Taylor&Francis    

年代:1980

数据来源: Taylor

摘要:

AbstractSufficient conditions are provided in terms of transition kernels under which one game results in a lower variance than another game when both estimate the same quantity. By defining the efficiency of a Monte Carlo game by the inverse of the product of the variance and the number of collisions per history and the computing time per collision, and by using a special approximation, called the separation assumption, for the evaluation of integrals occurring in the analysis, it is shown in a simplified situation that the expected leakage probability method in reaction rate and leakage estimations, although reducing the variance, is less efficient than the analog game with an expectation estimator. The efficiency of a game with survival biasing and Russian roulette is examined, and a simple method is presented for the determination of a quasi-optimum value of the Russian roulette parameter.

ISSN:0029-5639    

DOI:10.13182/NSE80-A18709

出版商:Taylor&Francis    

年代:1980

数据来源: Taylor

摘要:

AbstractThe order of convergence, as the spatial cell widths tend to zero, is derived for six numerical methods that have been proposed for the slab geometry, multigroup, discrete-ordinates neutron transport equations. Our results, which in two cases differ from earlier experimental results, are illustrated by means of a simple test problem.

ISSN:0029-5639    

DOI:10.13182/NSE80-3

出版商:Taylor&Francis    

年代:1980

数据来源: Taylor

摘要:

AbstractThe readiness of supervised protective systems for nuclear reactors is analyzed by the use of a four-state Markov process. The supervisions are short and reveal the capability of the system to initiate the protection action. When this capability—defined as the probability of initiating the protection action—is found to be below an acceptable level, the reactor is shut down. The analysis interrelates the probability level of readiness with the desired readiness of the protection system and its rate of supervision.

ISSN:0029-5639    

DOI:10.13182/NSE80-A18711

出版商:Taylor&Francis    

年代:1980

数据来源: Taylor

摘要:

AbstractCross-section sensitivities calculated with one- and two-dimensional models of a fusion reactor shielding experiment are compared. The effectiveness of the two-dimensional calculation in accurately modeling the experiment and detector configurations is demonstrated. At the same time, the validity of a one-dimensional sensitivity study is also demonstrated.

ISSN:0029-5639    

DOI:10.13182/NSE80-A18712

出版商:Taylor&Francis    

年代:1980

数据来源: Taylor