fgrSCIANTIXRIA

Description

This class is designed for use in RIA simulations, specifically after a restart. The intended workflow is for the user to apply the 'SCIANTIX' fission gas release model during the base irradiation phase and then switch to 'SCIANTIXRIA' for the restart or RIA simulation.

In this class, the SCIANTIX module itself is not actively called. Instead, the SCIANTIX fields - representing grain and grain boundary gas concentrations - computed during the base irradiation are read from the initial restart time folder.

During each iteration, the 'SCIANTIXRIA' class checks whether a given fuel cell has exceeded certain conditions:

• The burnup or temperature threshold for HBS, if HBS release is activated. In this case the grain and grain boundary gases are vented (added to the release fraction) and the intra- and inter-granular swelling fields are set to 0.
• A damage threshold where the 'damage' field is typically calculated using the 'damageModel' class in the constitutive law behavior. In this case, only the inter-granular gases are release and the corresponding swelling is set to 0

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Options

The fgrSCIANTIXRIA model requires the user to specify a few additional parameters in the fgrOptions sub-dictionary located inside the solverDict.

Parameters in fgrOptions:

relax	Relaxation factor applied to inter/intra-gaseous swelling and fgr fraction. It can improve convergence when dealing with strongly coupled simulations. It is set to 1 by default.
releaseHBS	Switch to activate HBS release model. It is set to true by default.
buReleaseThresholdHBS	Burnup HBS release threshold in MWd/t. It is set to 80000 by default.
temperatureReleaseThresholdHBS	Temperature HBS release threshold in K. It is set to 1000 by default.
damageReleaseThreshold	Damage release threshold in fraction. It is set to 0.85 by default.

Note

To minimize the creation of multiple volumetric fields (such as volScalarFields or volVectorFields), SCIANTIX fields are, by default, defined as standard fields (scalarFields or vectorFields). This is achieved using a template function located in globalFields.H.

Typically, these fields are read from a regIOObject named SCIANTIXfields, which is saved at each write time step. At the top of this dictionary, a summary of the current fission gas release (FGR) is included. If a specific field is missing from the dictionary, it is initialized with a default value. However, if an IOObject corresponding to one of these fields exists in the initial time step folder, the field is read from that file. This approach can be helpful when performing advanced operations, such as using OpenFOAM’s mapping routines.

In certain scenarios, adding fields to the registry is necessary for specific tasks, such as visualization in ParaFoam, probing, or mapping. This behavior is controlled by the addToRegistry keyword in the FGR options dictionary, enabling users to specify whether fields should be registered as volumetric fields.

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Usage

Here is an example of (part of) the solverDict file to be used to activate the SCIANTIXRIA class.

fgr     SCIANTIXRIA;

fgrOptions
{
    //- relax is 1 by default
    relax  1;

    // Switch to activate HBS release model
    releaseHBS true;

    // Bu HBS release threshold in MWd/t
    buReleaseThresholdHBS 80000;

    // Temperature HBS release threshold in K
    temperatureReleaseThresholdHBS 1000;

    // Damage release threshold in fraction
    damageReleaseThreshold 0.85;
}

//... other physics subdictionaries

materials
{
    fuel
    {
        type UO2;

        //... other material specific options

        rGrain 5e-6;

    }
    //... remaining material subdictionaries
}

There is no need to set the SCIANTIX input file for this class as SCIANTIX code is not actually called.