Full-scale Reactor System Research Articles

Utilizing Sensitivity and Correlation Coefficients from MCNP and Whisper to Guide Microreactor Experiment Design

When designing experiments for full-scale reactor systems, the Monte Carlo N-Particle® and Whisper codes can be used to create neutronic models and compare the similarity of two nuclear systems via correlation coefficients for , the effective multiplication factor. This paper applies this framework to a conceptual heat pipe yttrium-hydride-moderated microreactor system and experiments, but the method can be applied generally to any nuclear reactor design. The framework is intended as a supplement to other neutronics/thermal/multiphysics analyses and provides an objective method to measure the neutronic similarity of two systems. By analyzing the shared nuclear data uncertainty, as well as sensitivity to nuclear data over all neutron energies, highly informative experiments can be designed to aid in the development of microreactor and other advanced reactor technologies and systems.

CFD predictions of standby liquid control system mixing in lower plenum of a BWR

During an anticipated transient without scram (ATWS) scenario in certain boiling water reactor (BWR) systems, a standby liquid control system (SLCS) is used to inject a sodium pentaborate solution into the reactor system in order to quickly shut down (scram) the reactor without the use of the control rods. Some BWR designs utilize a SLCS that injects through a set of nozzles on a vertical pipe in the peripheral region of the lower plenum of the reactor vessel. During the scenario, system water levels are reduced and natural circulation flow rates down through the jet pump nozzles and up into the core are a small fraction of the rated system flow. It is during this period that the SLCS flows are considered. This work outlines some initial scoping studies completed by the staff at the Nuclear Regulatory Commission (NRC).An attempt at benchmarking the computational fluid dynamics (CFD) approach using a set of available test data from a small facility is outlined. Due to our lack of information related to specific details of the facility geometry along with the limited data available from the test, the benchmark exercise produced only a qualitative basis for selecting turbulence models and mesh density.A CFD model simulating a full-scale reactor system is developed for the lower plenum of a representative BWR/4 design and SLCS flows and mixing are studied under a range of flow conditions. The full-scale BWR simulation builds upon the lessons learned from the benchmark exercise. One challenge for this work is the large size of the domain and the relatively small size of the geometric details such as flow passages and gaps. The geometry is simplified to make meshing feasible by eliminating some of the small features. The model includes the lower plenum, control rod drive tubes, basic support structures, and SLCS piping. A series of simulations are completed and modeling choices are discussed in light of best practice guidance. The predictions shed light on the applicability of previous test programs and provide a clearer understanding of the lower plenum flows and mixing.

Versatility and application of anaerobic ammonium-oxidizing bacteria

With the unique cell compartmentalization and the ability to simultaneously oxidize ammonium and reduce nitrite into nitrogen gas, anaerobic ammonium-oxidizing (anammox) bacteria have challenged our recognitions of microorganism. The research conducted on these bacteria has been extended from bench-scale tryouts to full-scale reactor systems. This review addresses the recently discovered versatile properties of anammox bacteria and the applications and obstacles of implementing the anammox process in ammonia-rich wastewater treatment. We also discuss the merits and drawbacks of traditional and anammox-based processes for nitrogen removal and suggest areas for improvement.