ARMI FFTF Model

This repository contains a pin-detailed full core description of the Fast Flux Test Facility (FFTF) reactor in the form of input files for the open-source nuclear reactor analysis framework, ARMI.

The FFTF was a 400 MWt liquid-metal cooled fast-neutron reactor in Washington state that achieved criticality in 1980 and operated from 1982 to 1992. During startup, tests were performed determining the critical control rod positions and measuring control rod worths, excess reactivity, shutdown margin, and the isothermal reactivity coefficient.

A full description of the core and benchmark results was published by Bess, et. al¹. We have translated the information in that public document into ARMI input files. You can use them to validate your nuclear analysis codes or to perform any other analysis based on FFTF.

The input files contain a pin-detailed description of fuel and absorber assemblies and homogenized descriptions of others. ARMI automatically homogenizes the pin-detailed parts and agreement with the published homogenized compositions has been verified.

The control rods are in their defined critical positions (but can be moved with the ARMI framework).

TerraPower uses this model plus a set of physics modules to perform weekly Continuous Integration testing of ARMI and the physics tools using MC2-3 for cross sections and DIF3D/VARIANT for global flux. VARIANT P3/P3 mode or similar is recommended for reaching accurate results.

We hope that by providing these ARMI inputs and the digital FFTF-at-your-fingertips in a software-accessible form, the limited labor dedicated to nuclear analysis can focus more efficiently on pushing the envelope in nuclear technology development and deployment.

Interacting with this model

To use these inputs, first install ARMI, and also go through the optional wxPython and Paraview sections.

View the core map

For a quick demo, run:

(armi-venv) $ python -m armi grids FFTF-blueprints.yaml

to pull up the graphical GUI editor for the core map.

Run a dummy case and view the output database

Now run a quick ARMI main loop (even though no physics plugins are active) to get a output database:

(armi-venv) $ python -m armi run FFTF.yaml

This will print lots of text and produce a binary output file called FFTF.h5. Convert this to a VTK file for visualization with:

(armi-venv) $ python -m armi vis-file FFTF.h5

Now open up your Paraview or VisIT program to view the model in 3D. Check out some of the number density parameters to see the core loading and control rod positions.

Explore the data model

Then, we recommend going through ARMI's Hands-on at the ARMI Terminal tutorial but swap out the input files used there for these FFTF inputs to get started.

More resources

You can learn more about the ARMI input format in this input tutorial

Doing real analysis

To run physics calculations, you will need some ARMI plugins that bring in physics capabilities. The DRAGON plugin can compute microscopic cross sections for this model in ISOTXS format. More physics capabilities will become available as more people build ARMI plugins to other codes.

Credits

• Mohamed Elsawi initially created the FFTF input deck
• Jacob Hader moved the CRs to the critical position and made several other enhancements

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1. John Bess, et. al, "Evaluation of the Initial Isothermal Physics Measurements at the Fast Flux Test Facility, a Prototypic Liquid Metal Fast Breeder Reactor", INL/EXT-09-16524 (March 2010) https://digital.library.unt.edu/ark:/67531/metadc1013078/↩