CASL

A new 3D CRUD model, known as "MAMBA" (for “MPO Advanced Model for Boron Analysis”), is being developed by the Crud Group within the MPO focus area of CASL. The 3D MAMBA v2.0 computer code was released to CASL on Feb. 28, 2012 and is capable of being run in “stand-alone” mode or in coupled mode with a thermal hydraulics computational fluid dynamics model (e.g., STAR-CCM+) and/or a neutron transport capability (e.g., DeCart). Fully coupled simulations using the MAMBA/STAR-CCM+ /DeCart framework have been recently reported for a single pin and a 4x4 subassembly. Recent enhancements to MAMBA include coupling it to the micro-scale Boron Deposition Model (BDM) being developed by Mike Short (MIT) and the integration of new thermodynamics models being developed by Ted Besmann (ORNL), Dongwon Shin (ORNL), and David Anderson (LANL).

In this study, MAMBA was run in “stand-alone” mode with specific coolant conditions and heater rod fluxes used in the single-rod autoclave experimental apparatus at Westinghouse (the “Walt Loop”) and initial validation of MAMBA against several of the Walt Loop experimental data sets has been performed. The cladding temperature computed by MAMBA was compared to the measured values in the Walt Loop experiment as a function of heater rod flux and crud thickness. Good overall agreement is observed between the cladding temperatures computed by MAMBA and the Walt Loop data sets. Some preliminary sensitivity studies were also performed for a few key parameters in MAMBA such as the chimney density, crud porosity and the rate of nickel ferrite deposition/ growth inside the pores of the crud.

Additional initial comparisons were made between the boiling model predictions (i.e., the mass evaporation rate) between MAMBA and an industry standard model (known as BOA v3.0, developed by EPRI). The mass evaporation rate was computed as a function of crud thickness and power level. The mass evaporation rates computed by MAMBA were compared to those computed by two different boiling models used in BOA (IDEP=1 and IDEP=4). The MAMBA results without lithium tetraborate precipitation are in reasonably good agreement with the IDEP=1 results . However, significant differences are observed between MAMBA and IDEP=4 . In MAMBA, the precipitation of lithium tetraborate significantly affects the mass evaporation rate which for this case often lies in-between BOA’s IDEP=1 and IDEP=4 results. The results of this analysis are being used by EPRI to help guide the development of improved boiling models in future releases of BOA.