Scientific tools

The following tools are operated by SACRE:

“ANSYS Fluent software contains the broad physical modeling capabilities needed to model flow, turbulence, heat transfer, and reactions for industrial applications ranging from air flow over an aircraft wing to combustion in a furnace, from bubble columns to oil platforms, from blood flow to semiconductor manufacturing, and from clean room design to wastewater treatment plants. Special models that give the software the ability to model in-cylinder combustion, aeroacoustics, turbomachinery, and multiphase systems have served to broaden its reach.” (ANSYS, 2014).
At SACRE, the Fluent CFD code has been used in the past 15 years for research as well as education purposes. A significant part of the work was devoted to the implementation of models inside the code through User Defined Functions (UDF’s). For example, a UDF was developed and validated to model turbulent velocity fluctuations that aerosol particles experience as they are transported in a turbulent field. Recently, a model to predict vapor condensation in the presence of noncondensing gases was also incorporated in Fluent and successfully validated.

(Accident Source Term Evaluation Code)

The aim of the ASTEC code is to simulate an entire severe accident sequence from the initiating event through to fission product release out of the containment. The applications are:

• Source term determination studies.
• Probabilistic safety assessment level 2 studies.
• Accident management studies.
• Physical analyses of experiments to improve the understanding of the phenomenology.

The code has the following requirements: sufficient validation to cover the main physical phenomena; account for safety systems and procedures; user-friendly to easily perform sensitivity analyses; fast running code.

(Large Atomic/Molecular Massively Parrallel Simulator)

The Large Atomic/Molecular Massively Parallel Simulator (LAMMPS) is a Discrete Element Method (DEM) code developed at Sandia National Laboratories. The code is widely used and provides a framework for carrying out particle simulations interacting under a diverse variety of forces. The code has been used at SACRE to model pebble flows and resulting dust generation inside pebble-bed reactors.

(Methods for Estimation of Leakages and COnsequences of Releases)

MELCOR is a fully integrated, engineering-level computer code that models the progression of severe accidents in light water reactor nuclear power plants. MELCOR is being developed at Sandia National Laboratories (SNL) for the U.S. Nuclear Regulatory Commission (NRC) as a second-generation plant risk assessment tool and the successor to the Source Term Code Package. A broad spectrum of severe accident phenomena in both boiling and pressurized water reactors is treated in MELCOR in a unified framework. These include thermal-hydraulic response in the reactor coolant system, reactor cavity, containment, and confinement buildings; core heatup, degradation, and relocation; core-concrete attack; hydrogen production, transport, and combustion; fission product release and transport behavior. Current uses of MELCOR include estimation of severe accident source terms and their sensitivities and uncertainties in a variety of applications.

In the SACRE group MELCOR is used for full plant severe accident calculations (TMI-II, Fukushima, ...) and model assessment using single effect tests or integrated experiments (QUENCH, PARAMETER, ...).

The SCDAP/RELAP5 code has been developed for best-estimate transient simulation of light water reactor coolant systems during a severe accident. The code models the coupled behavior of the reactor coolant system, core, fission product released during a severe accident transient as well as large and small break loss-of-coolant accidents, operational transients such as anticipated transient without SCRAM, loss of offsite power, loss of feedwater, and loss of flow. A generic modeling approach is used that permits as much of a particular system to be modeled as necessary. Control system and secondary system components are included to permit modeling of plant controls, turbines, condensers, and secondary feedwater conditioning systems.

In the SACRE group SCDAP/RELAP5 is used for core degradation calculations and model assessment using single effect tests or integrated experiments (QUENCH, PARAMETER, ...) in addition to the MELCOR calculations.

(Symbolic Nuclear Analysis Package)

The Symbolic Nuclear Analysis Package (SNAP) consists of a suite of integrated applications designed to simplify the process of performing engineering analysis. SNAP is built on the Common Application Framework for Engineering Analysis (CAFEAN) which provides a highly flexible framework for creating and editing input for engineering analysis codes as well as extensive functionality for submitting, monitoring, and interacting with the codes. SNAP currently includes support the CONTAIN, COBRA, FRAPCON-3, MELCOR, PARCS, RELAP5 and TRACE analysis codes. Each code is supported by a separate plug-in.

(SPECtral Unstructured eLements Object-Oriented System)

The Spectral unstructured ELements Object-Oriented System (SpecuLOOS) is a computational toolbox written in C++ and developed at the EPFL. SpecuLOOS is a spectral and mortar element analysis software for the numerical solution of partial differential equations and in particular incompressible unsteady fluid flow problems. The code has been extensively used to perform Large Eddy Simulations (LES) of particulate flows inside closed cavities which model nuclear containment.