A Progress Update on Selected AREVA NP Advanced BWR Methodologies

摘要

This article presents an overview of select advances in AREVA NP methods Analytical Fuel Rod Model - The analytical fuel rod model relies heavily on first-principles closed-form solutions instead of ever finer nodalization and higher dimensions of standard numerical methods such as finite differences or finite elements This analytical fuel rod model takes full account of the complications that made numerical analysis necessary, e g. variation of pellet thermal conductivity with temperature and burnup, and the radial dependence of fission power deposition in pellets. The model also calculates thermo-mechanical parameters such as clad stress and strain, fission gas release, pellet sintering and swelling, and pellet-clad gap size and thermal resistance There is no claim of improved accuracy compared with high order numerical solutions, but the remarkable speed and robustness of analytical solutions offer the potential of explicit modeling of every rod in a fuel bundle and for online core monitoring applications following the example of XEDOR~(™) which guides power maneuvering to protect the fuel from stress corrosion cracking failures. The model is suited for innovative fuel designs such as doped pellets. Transient and Accident Simulation - AREVA NP's BWR evaluation model, AURORA-B, is an advanced transient and accident simulator that is under review by the USNRC for licensing applications AURORA-B includes S-RELAP5, a two fluid thermal hydraulic code comprehensively reviewed by international safety authorities for BWR and PWR applications; R0DEX4, a best estimate fuel performance code used to evaluate the local thermal-mechanical behavior of fuel rods during postulated transients and accidents, and MB2-K, a neutron kinetics extension of the steady state core simulator MICR0BURN-B2 Recent advancements have been made in all three areas of the evaluation model including the extension of R0DEX4 to accommodate analysis of chromium-doped fuel to increase resistance to pellet-clad interaction (PCI). Chromium doping will impact thermo-mechanical properties such as gap width, gap conductance, and thermal conductivity The evaluation of transients and accidents with chromium-doped fuel supports AREVA NP's continued emphasis on increased fuel reliability and performance A selection of events will be presented with respect to the impacts of chromium-doped fuel. The analytical domains will include transients as well as control rod drop and loss of coolant accidents ATWSi Post Dryout Treatment - AREVA NP will report on advances in simulating severe power and flow oscillations associated with hypothetical anticipated transients with failure to scram. Previous publications presented AREVA NP tests where a full scale electrically heated bundle operated at natural circulation was allowed to reach an unstable state and the reactivity based power oscillations to grow to severe amplitudes well past the onset of inlet flow reversal The experimental data including extensive cyclical dryout and rewetting were used in the development and benchmarking of new models and codes The dryout and rewetting with ultimate failure to rewet are modeled using physically-based post-CHF dynamic models. These models have been extensively benchmarked and have been helpful in advancing the basic understanding of the so-called boiling curve and its limitations XEDOR and ATRIUM are trademarks of AREVA NP in the USA or other countries.