摘要:

AbstractConditions for the reduction of the time-independent neutron transport equation to an energy-independent (one-group) equation are discussed. It is shown that a meaningful reduction is equivalent to angular flux separability into a product of an energy spectrum and a spatial and angular function. It is proven that such a separability in a finite system is possible if and only if the total cross section is energy independent, provided some auxiliary conditions are met. The physical situations in which these conditions are satisfied and the similarity to the so-called first fundamental theorem of reactor theory are discussed.

ISSN:0029-5639    

DOI:10.13182/NSE78-A27303

出版商:Taylor&Francis    

年代:1978

数据来源: Taylor

摘要:

AbstractThe integral transport equation for the flux density in the interior of an infinite homogeneous cylinder is reduced to a matrix eigenvalue problem for the critical cylinder and a set of linear algebraic equations for the driven case with surface in-currents. The matrix elements are identified as moments of modified Bessel functions and are easily computed.A connection is made with classical diffusion theory via a related matrix eigenvalue problem, from which the diffusion coefficient and extrapolation endpoint can be computed. Analytic properties of the matrix elements are used to obtain approximate solutions for (optically) dense and transparent cylinders. Numerical results are given for the American Nuclear Society benchmark black rod problem, and the fact that only small matrices are required for a large range of problems is demonstrated.

ISSN:0029-5639    

DOI:10.13182/NSE78-A27304

出版商:Taylor&Francis    

年代:1978

数据来源: Taylor

摘要:

AbstractNeutrons and prompt gamma rays emitted by excited fission fragments have been studied using an angular momentum dependent statistical model. The computer program MAMI written for this purpose is described briefly. The difficulties in choosing suitable emission strengths are discussed in more detail. Some results are given, related to the influence of spin on competition between neutron and gamma-ray emission, on total average gamma-ray energy, on average neutron multiplicity, and on average neutron kinetic energy.

ISSN:0029-5639    

DOI:10.13182/NSE78-A27305

出版商:Taylor&Francis    

年代:1978

数据来源: Taylor

摘要:

AbstractA method is developed for calculating effective neutron cross sections in the resolved resonance groups of homogeneous mixtures of cylindrical cells in regular reactor lattices. A rigorous treatment of the nucleonic and neutronic problems provides accurate numerical solutions with detailed dependence in energy and space for both Doppler-broadened cross sections and self-shielded neutron fluxes.The common simplifying approximations are not introduced, so that the method is used as a reference to analyze some of the detailed self-shielding effects that are commonly ignored or approximated in applications ranging from homogeneous mixtures of different resonant nuclides to cylindrical cells with nonuniform temperatures and concentrations within the fuel.

ISSN:0029-5639    

DOI:10.13182/NSE78-A27306

出版商:Taylor&Francis    

年代:1978

数据来源: Taylor

摘要:

AbstractTwo unusual aspects of safety component operation—abnormal environmental conditions and aging—are combined analytically. The result is implemented in a computer code to quantify a safety system figure-of-merit. In conjunction with a probabilistic approach employing a specified risk criterion, the analytical method has been applied to a reactor protection system to determine a desired component-qualified age. The effect of a preventive renewal program as a substitute for or complement to an age qualification program is also discussed. Substantial economic benefits should be realized from the implementation of the analytical method.

ISSN:0029-5639    

DOI:10.13182/NSE78-A27307

出版商:Taylor&Francis    

年代:1978

数据来源: Taylor

摘要:

AbstractWe investigate the growth of Rayleigh-Taylor instabilities following the deceleration of fuel by a less dense coolant using the method of generalized coordinates, which allows us to study the nonlinear, late-time aspects of the problem as well as the possibility of fuel freezing at the interface. We consider liquid coolant in contact with three possible states of fuel—pure liquid, pure solid, and liquid fuel freezing at the interface—and treat several acceleration mechanisms. Assuming the instability starts at a planar interface as a velocity perturbation proportional to the interfacial velocity, we find that when the fuel is completely frozen or freezing at the interface, instabilities will not grow unless the initial interfacial relative velocity satisfies a relationship of the formwhereυ0is the initial relative velocity,ρfthe density of the fuel, Y0the yield strength of the frozen fuel,λthe wavelength of the instability, and L a characteristic length. The specific form of C depends on the acceleration mechanism and when freezing begins. For the case of UO2and sodium, we follow the growth of the fastest growing wavelength instability for different acceleration mechanisms and determine the impulse needed for instabilities to grow when freezing is occurring at the interface.

ISSN:0029-5639    

DOI:10.13182/NSE78-A27308

出版商:Taylor&Francis    

年代:1978

数据来源: Taylor

摘要:

AbstractA sensitivity theory based on reactor physics experience was successfully developed for a reactor thermal-hydraulics problem. The new theory is derived for the case of nonlinear transient heat and mass transfer in a typical reactor subassembly. Suitable adjoint equations for heat and fluid flow are presented along with methods for deriving the sources and boundary and final conditions for these equations. Expressions for the sensitivity of any integral temperature response to problem input data are also presented. The theory is applied to a sample problem describing the steady-state thermal-hydraulic conditions in a Clinch River Breeder Reactor fuel channel. For this case, sensitivity coefficients are derived for several thermal response functions (i.e., peak clad and peak fuel temperature) for all physical input data (i.e., the heat transfer coefficient, thermal conductivities, etc.). A typical uncertainty analysis for peak clad and peak fuel temperature was also performed using uncertainty information about the physical data. Conclusions are drawn about the applicability of this approach to more general problems, and the procedures for its implementation in conjunction with large safety or thermal-hydraulics codes are outlined. The method is also compared with currently used response surface techniques.

ISSN:0029-5639    

DOI:10.13182/NSE78-A27309

出版商:Taylor&Francis    

年代:1978

数据来源: Taylor

摘要:

AbstractRecent studies have shown that available theoretical models for critical two-phase flows in simple nozzles are not able to predict observed data. To achieve agreement, it is customary to multiply the computed mass flow rates by empirically determined factors. In this paper, a two-dimensional theory is used to show that the deficiencies are associated with geometric effects not accounted for in the earlier models. The theory presented here is applied to both equilibrium and nonequilibrium situations with considerable success and supplies a rational basis for the use of break flow multipliers.

ISSN:0029-5639    

DOI:10.13182/NSE78-A27310

出版商:Taylor&Francis    

年代:1978

数据来源: Taylor

摘要:

AbstractThree-group diffusion theory has been applied to a computation of the231Pa mass required to sustain a fast-neutron chain reaction. The method was tested by preliminary calculation of several235U-238U systems and of a single239Pu-240Pu system. The best agreement between predictions and measurements was found for high-enrichment235U-238U systems. In the case of231Pa, where many of the necessary data do not exist, use was made of the characteristics of237Np as a substitute. The predicted critical radius for231Pa is 22.67±1.81 cm, and the corresponding critical mass is 750±180 kg.

ISSN:0029-5639    

DOI:10.13182/NSE78-A27311

出版商:Taylor&Francis    

年代:1978

数据来源: Taylor

摘要:

AbstractA new method is proposed to unfold a neutron spectrum from measured activities with a guess shape for the spectrum. This method minimizes the weighted sum of the deviations from the guess shape and the measured activities and optimizes the scaling factor of the spectrum at the same time. Unlike most conventional methods, it does not need iterations, but instead directly obtains an unfolded spectrum by solving a positive definite matrix, whose size is equal to the number of the measured activities. Both analytical and numerical comparisons with some conventional methods are also presented.

ISSN:0029-5639    

DOI:10.13182/NSE78-A27312

出版商:Taylor&Francis    

年代:1978

数据来源: Taylor