Neutronics methods for the dynamic analysis of source-driven subcritical multiplying systems.

摘要

Certain advantageous characteristics of accelerator-driven sub-critical nuclear systems have spurred recent investigations into potential applications of this technology. Accelerator-driven sub-critical nuclear systems are highly insusceptible to super-critical excursion type transients. However, there are other types of behavior which may cause difficulties, such as large power or temperature swings and oscillatory behavior. These types of transients are highly dependent on feedback effects. Proper accounting of these feedback effects requires significant computational expense in the form of thermal hydraulic and isotope decay/buildup calculations. Thus, computationally efficient dynamic analysis methods are required to ensure system safety and to optimize performance.;In this work, general characteristics of accelerator-driven systems, in certain regions of parameter space, were identified that can greatly simplify the dynamic analysis process. A theoretical review of the standard point kinetics approach to dynamic analysis of accelerator-driven sub-critical nuclear systems was performed and potential problems were found. Two new computational methods for dynamic analysis which avoid these potential problems were developed and presented.;Subsequent numerical analyses have mapped the sub-critical parameter space over which certain advantageous properties of accelerator-driven systems become manifest. Also, simple numerical studies have shown that the potential problems in applying standard point kinetics to accelerator-driven systems, identified in the theoretical analyses, are evident at levels of sub-criticality equivalent to those of contemporary system designs. More robust numerical analyses, however, have shown that due to more subtle effects these potential problems do not manifest themselves until much lower levels of sub-criticality, beyond the region of current system designs. At and below certain system-specific levels of sub-criticality, the new methods of dynamic analysis developed in this work can yield significant improvements in accuracy.;Finally, it was recognized that it may be of interest to track transients which take accelerator-driven systems between the regions of sub-critical parameter space where their advantageous system characteristics are, and are not, evident. A computationally efficient strategy for following these types of transients is developed and presented.