GUI Integrated Shutdown Dose Rate and Inventory Calculations

Fornax is a GUI driven activation solver that tracks the population of isotopes created through neutron activation and decay processes. Fornax provides users with the capability to use the Rigorous Two-Step (R2S) method with either the Attila deterministic solver or MCNP^® through the Attila4MC^TM based workflow. With the Attila deterministic workflow, users can run neutron flux and activation calculations on the tetrahedral mesh and produce gamma sources at desired decay time steps with an appropriate neutron flux strength. The gamma activation sources are generated in every tetrahedral element of activated region(s), providing unrivaled spatial precision. The activation gamma calculations can then be run on the same tetrahedral mesh, making for a streamlined, simple, and accurate workflow.

Users have the flexibility to choose which regions to burn and optionally to output additional reports such as radioactive isotope inventories and activity data. The Attila4MC workflow with MCNP performs cell-wise activation calculations on the tetrahedral mesh, generating cell-wise activation gamma sources for MCNP. This entire workflow, through visualization, is GUI integrated.

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Fornax Features

Decay chains specified in a single XML file
Users can modify or add decay chain data for their applications
User specifies which CAD/mesh regions to activate
Creates a unique activation source in each tetrahedral element, providing a high spatial resolution
Eliminates the need for a user defined activation “grid”
Provides unrivaled solution precision
Fine resolution, body-fitted activation mesh
No spatial homogenization
Intuitive post processing visualization of calculated inventories
Optional output of region-wise activities for waste categorization

Activation and Depletion

Performed as a 2-step process (R2S):

Step One:
Calculate neutron flux field and activation source at desired timesteps

Run through regular Attila neutron calculation and Fornax/ASG
Activation gamma source can be created at every timestep

Step Two:
Compute activation dose rate field

Regular Attila gamma calculation using activation gamma source file

Generic Tokamak Case Study

Attila calculations performed using SFSW-FENDL31d-FG cross sections and SFSW-Fornax-r2 dataset
~1.2 million tetrahedral mesh elements
Neutron flux calculation performed with 53 neutron groups
2.0E+20 n/s over 1 day, and cooling time of 30 days after final “shot”
Activation calculation time 20 minutes
Gamma shut down dose rate (SDDR) calculation performed with 42 gamma groups, 1 hr 20 minutes run time
Activity inventory report produced for concrete walls

FNG Activation Benchmark

Benchmark¹ to validate accuracy of dose-rate calculations after shut-down in representative ITER shielding conditions (ITER Task T-426)

Neutron flux and activation calculations performed using SFSW-FENDL31d-FG cross sections and SFSW-Fornax-r2 dataset
~220k tetrahedral mesh elements, 3.5 cm mesh for fine spatial resolution
Neutron calculation performed with 175 neutron groups, calculation time ~5 hrs
Activation calculation time 13 minutes
Shut down gamma calculations performed with Transpire94g cross section, 20-30 minutes depending on timestep