Nuclear Technology / Volume 179 / Number 3 / September 2012 / Pages 339-359
Technical Paper / Fission Reactors/Nuclear Plant Operations and Control
Local space and energy impact densities of various types of loose parts have been generated within a representative steam generator inlet plenum. This work expands upon previous experimental research to identify important mechanisms that govern accumulated loose part damage to steam generator tube sheets. As a result, a computational model for estimating loose part impact damage, including damage to steam generator tube ends from multiple impacts, was previously created. Damage effects were determined to be local effects that depended only on single impacts and impact overlaps in a small region of interest. It was found that the damage could be directly related to local impact density on the steam generator tube sheet.
In this work, three-dimensional flow fields were generated, first for a previously used 1:8 scale experimental inlet plenum and then for a 1:1 scale Westinghouse type D steam generator. Monte Carlo simulations were carried out as a function of coolant temperature, coolant inlet velocity, loose part type, shape, mass, density, initial starting location, and initial kinetic energy. No a priori knowledge was assumed for the initial starting location and initial kinetic energy of the parts. Comparisons were performed between previous scaled experimental results and scaled computational simulation results to assess the validity of predictions from the scaled simulation. Combined, both this work and previous work could allow for the assessment of impact damage rates on steam generator tube sheets via simulation.
The most-energetic impacts are not localized to any particular region on the tube sheet. The general progression of the spatial distribution of all impact locations as a function of initial kinetic energy accurately depicts the progression for the highest-energy impacts. As the initial kinetic energy increases and as the starting location moves toward the inlet plenum, there is an increase in the number of higher-energy impacts. The higher-initial kinetic energy impacts lead to higher-energy first impacts on the tube sheet. Beyond the first impact, the energy distribution is invariant to initial kinetic energy and initial start location. The invariance seen in the energy distribution does not hold the same for the spatial distribution. The effects of the initial kinetic energy and initial start location ripple into the second and third impacts. Beyond the third impacts little to no change can be discerned and the invariance due to initial kinetic energy and initial start locations is valid. Ultimately, with these types of analyses, reactor facilities will be able to better judge whether a system necessarily needs to shut down due to safety concerns about loose parts damage before a scheduled outage.