摘要:

AbstractA multigrid acceleration scheme for the one-dimensional slab geometry SNequations with anisotropic scattering and linear discontinuous spatial differencing is developed. The high-frequency relaxation iteration consists of three steps: a standard source iteration, independent two-cell block inversions centered about each spatial cell edge, and an averaging of the iterates from the previous two steps. Because the linear discontinuous differencing scheme is a finite element method, fine-to-coarse projection and coarse-to-fine interpolation are straightforward. Although standard linear discontinuous differencing is derived under the assumption of spatially constant cross sections within each cell, the scheme is generalized to allow for a linear spatial variation of the cross section in each cell. This linear variation is required to obtain accurate coarse-grid equations when homogenizing two fine-grid cells with different cross sections into a single coarse-grid cell. This multigrid method is very effective in terms of the spectral radius of the total iteration process, but the computational cost of the block inversions in the second step of the high-frequency relaxation is quite high. However, in optically thick problems with highly anisotropic scattering, this multigrid method is more economical than diffusion synthetic acceleration. Because the block inversions are independent for each cell edge, parallel processing might significantly reduce the cost of the scheme.

ISSN:0029-5639    

DOI:10.13182/NSE89-A23628

出版商:Taylor&Francis    

年代:1989

数据来源: Taylor

摘要:

AbstractA computational test problem for the MAEROS aerosol model is used to illustrate the application of uncertainty/sensitivity analysis techniques based on Latin hypercube sampling and regression analysis to aggregation problems. The test problem involves a five-component aerosol in the containment of a pressurized water reactor. The following topics are investigated:Cray 1-S CPU time requirements to implement and solve the system of differential equations on which MAEROS is basedeffects on computational time and representational accuracy due to the use of different overall section boundaries and numbers of sections and componentsbehavior of the aerosol and the variables that influence this behavior.The analysis provides information in each of the indicated areas in a reasonably straightforward and efficient manner. The same analysis approach could be productively employed in similar investigations for other models. Furthermore, due to the extensive use of MAEROS and other aerosol models in the analysis of reactor accidents, the results obtained in the analysis are also of considerable interest.

ISSN:0029-5639    

DOI:10.13182/NSE89-A23629

出版商:Taylor&Francis    

年代:1989

数据来源: Taylor

摘要:

AbstractA knowledge-based production system was developed for generating optimal fuel reload configurations. The system was based on a heuristic search method and implemented in Common Lisp programming language. The knowledge base embodied the reactor physics, reactor operations, and a general approach to fuel management strategy. The data base included a description of the physical system involved, i.e., the core geometry and fuel storage. The fifth cycle of the Three Mile Island Unit 1 pressurized water reactor was chosen as a test case. Application of the system to the test case revealed a self-learning process by which a relatively large number of“near-optimal”configurations were discovered. Several selected solutions were subjected to detailed analysis and demonstrated excellent performance. To summarize, applicability of the proposed heuristic search method in the domain of nuclear fuel management was proved unequivocally.

ISSN:0029-5639    

DOI:10.13182/NSE89-A23630

出版商:Taylor&Francis    

年代:1989

数据来源: Taylor

摘要:

AbstractA new approach to the solution of burnup equations is developed that takes into account the dependence of the reaction constants on time as well as nonlinear and feedback effects. With the help of the transition probabilities for the simplified problem, the burnup differential equation is reduced to the equivalent integral equation, which is solved by iterations. The solution is made easy to understand with the help of diagrams constructed following the suggested rules. It is strictly proved that any nuclide transmutation network can be broken into independent depletion chains if the burnup equations are linear in concentrations. The theory is illustrated by examples of the time dependence of reaction constants.

ISSN:0029-5639    

DOI:10.13182/NSE89-A23631

出版商:Taylor&Francis    

年代:1989

数据来源: Taylor

摘要:

AbstractA general review of investigations of gamma-ray buildup factors is presented. Gamma-ray buildup factors for a point isotropic source in stratified spherical shields have been calculated using the one-dimensional gamma-ray transport code BIGGI-4T. The behavior of the buildup factor for stratified shields with respect to the behavior for the component materials differs between spherical and slab geometry. In addition to a material change effect, the buildup factor for a point isotropic source in stratified spherical shields suffers a density variation effect, which is much more prominent for configurations of heavier density followed by lighter density. The density variation effect can be eliminated by using a specially adjusted calculation of the stratified shields. It has also been found that energy absorption buildup factors in Goldstein and Wilkins’data have relatively large uncertainties.

ISSN:0029-5639    

DOI:10.13182/NSE88-68

出版商:Taylor&Francis    

年代:1989

数据来源: Taylor

摘要:

AbstractThe U.S. Nuclear Regulatory Commission pressurized thermal shock (PTS) study had previously identified small-break loss-of-coolant accidents (SBLOCAs) as a risk dominant accident scenario due to (numerically calculated) primary loop flow stagnation at high pressure. The objectives of the present effort were twofold: first, to develop a physically based understanding of controlling thermal-hydraulic phenomena producing such PTS SBLOCA stagnation scenarios and second, to use these insights in developing a simple (computationally efficient)“mapping”tool to quantify the occurrence and thermal behavior of such high-pressure flow stagnation regimes. Review of the previous [transient reactor analysis code (TRAC)] calculations revealed that inaccurate modeling of vapor condensation erroneously produced the flow stagnation and hence overly conservative (rapid) vessel cooldown rates. Using a corrected version of this code, our new calculations now exhibit flow circulation. However, parametric analysis of less likely (more equipment failure—power-operated relief valves/high-pressure injection pumps) scenarios revealed that flow stagnation was indeed possible but could only occur at lower pressures. This simple mapping procedure has been favorably benchmarked against the (TRAC) system calculations. This tool is therefore useful for screening possible risk dominant SBLOCA scenarios in various pressurized water reactor designs.

ISSN:0029-5639    

DOI:10.13182/NSE89-A23633

出版商:Taylor&Francis    

年代:1989

数据来源: Taylor

摘要:

AbstractA methodology is developed to assess distortions generated by scaling laws. This requires distinction between distortions inherent in a given scaling scheme [scaling law distortions (SLDs)] and the actual distortions (ADs) existing between prototypical behavior and the transposed behavior of a model. To develop the methodology, additional scaling concepts including“reference”and“resultant”similarity parameters and“required”and“assumed”’conditions are defined. These parameters distinguish between conditions that are directly controllable and thus can be unequivocally determined by a scaling procedure and those that must rely to varying degrees on implied assumptions.In an illustrative example, it is shown that assessments of alternate scaling schemes can produce different conclusions when based on the results of an AD analysis as compared to an analysis of SLDs alone. The RELAP5 code is used to evaluate both prototypical and model behavior.

ISSN:0029-5639    

DOI:10.13182/NSE89-A23634

出版商:Taylor&Francis    

年代:1989

数据来源: Taylor

摘要:

AbstractThe time-dependent slowing down of neutrons in noncapturing media depends in an important way on how the energy-dependent mean-free-time between scatterings behaves as E→0. For example, if the mean-free-time decreases, i.e.,ν∑sincreases, as any positive power of E, the integrated density of neutrons does not remain constant in time. This anomalous behavior is discussed, noting both analogies in other physical processes and early references to the phenomenon of“non-conservation.”The analysis uses some unfamiliar solutions for slowing down in hydrogen, when the cross section has power-law variation; however, the general discussion is not limited to the equal mass case.

ISSN:0029-5639    

DOI:10.13182/NSE89-A23635

出版商:Taylor&Francis    

年代:1989

数据来源: Taylor