2.2. The Blueprints Input File

The blueprints input defines the dimensions of structures in the reactor, as well as their material makeup. In a typical case, pin dimensions, isotopic composition, control definitions, coolant type, etc. are defined here. The specifics of each assembly type are then overlayed, possibly including enrichment distributions and other material modifications.

Note

See the blueprints module for implementation and more detail.

This input file is formatted using YAML, which allows text-based change tracking for design control. ARMI does not have a blueprints-editing GUI yet, but may in the future.

Note

You can point many ARMI runs to the same Blueprints input file using full paths in loadingFile setting.

ARMI adds an !include YAML tag, which can be used to include the contents of an external YAML file in any part of a blueprints file. The can be useful for sharing core or assembly pin layouts amongst multiple cases. For example:

grids:
    core: !include path/to/core_grid.yaml

would have the effect of copy-pasting the contents of path/to/core_grid.yaml into the main blueprints file. The rules that ARMI uses to handle things like indentation of the included text are usually rather intuitive, but sometimes it can be useful to witness the behavior first-hand. The expand-bp command can be used to do a dry run for testing inputs with !includes.

ARMI models are built hierarchically, first by defining components, and then by larger and larger collections of the levels of the reactor.

2.2.1. Blueprint sections

The blueprints input file has several sections that corresponds to different levels of the reactor hierarchy. You will generally build inputs “bottoms up”, first by defining elementary pieces (like pins) and then collecting them into the core and reactor.

The ARMI data model is represented schematically below, and the blueprints are defined accordingly:

../../_images/armi_reactor_objects.png

Figure 1. The primary data containers in ARMI

blocks:

Defines Component inputs for a Block.

asssemblies:

Defines vertical stacks of blocks used to define the axial profile of an Assembly.

systems:

Reactor-level structures like the core, the spent fuel pool, pumps, the head, etc.

grids:

Lattice definitions for the core map or pin maps

nuclide flags:

Special setting: Specifies nuclide modeling options, whether a nuclide is being modeled for cross sections and/or depletion. For instance, it allows you to ignore nuclides above Curium for depletion speed. This also allows you to expand elements to a subset of nuclides. For example, you can choose to expand Oxygen to just Oxygen-16 and neglect Oxygen-17 and 18.

custom isotopics:

Special setting: defines user-specified isotopic compositions.

Warning

YAML is not order specific; however, one of the techniques used to limit the size of the input includes using YAML anchors to resuse block and component definitions. YAML anchors (e.g. &block_name) must be defined before their corresponding alias (e.g. *block_name) used.

2.2.2. Blocks and Components

Blocks and components are defined together in the blueprints input.

We will start with a component, and then define the whole blocks: input. The structure will be something like:

blocks:
    block name 1:
        component name 1:
            ...
        component name 2:
    block name 2:
        component name 1:
            ...
        component name 2:
            ...

Note

You can also define components at the top level of the blueprints file under the components: top level section, but bringing anything defined there into the reactor model must currently be done programatically. We are currently developing additional input capabilities to use these more flexibly.

Associated with this is a component groups: section which can collect different free components with different volume fractions. This also is not fully implemented yet.

2.2.2.1. Defining a Component

The Components section defines the pin (if modeling a pin-type reactor) and assembly in-plane dimensions (axial dimensions are defined in the Assemblies input) and the material makeups of each Component. Blocks are defined here as collections of geometric components that have specific temperatures, dimensions, material properties, and isotopic compositions.

An component may be defined as:

fuel:
    shape: Circle
    material: UZr
    Tinput: 20.0
    Thot: 450.0
    mult: 169
    id: 0.0
    od: 0.757

Here we have provided the following information:

Component name

The component name (fuel) is specified at the top. Some physics kernels interpret names specially, so pay attention to any naming conventions. As a general rule, you can expect that people will be doing regex on your name, so you should not use any of these characters in your component names: . ^ $ * + ? { } [ ] \ | ( ) :.

shape

The shape will be extruded to the length specified in the assemblies input section below. ARMI contains a variety of built-in simple shapes, and plugins can define their own design-specific/proprietary shapes.

material

The material links the component to a certain set of thermo-physical properties (e.g. temperature-dependent thermal expansion coefficients, density, thermal conductivity, etc., which are used in the various physics kernels. Natural isotopic composition is determined from this material specification as well (unless custom isotopics are supplied). The entry here should either be a class name of a valid material (UZr) or a module:className pair for specifying specific material (e.g. armi.materials.uZr:UZr). Materials are handled through the material library.

Tinput

The temperature (in C) that corresponds to the input dimensions given here. This facilitates automatic thermal expansion.

Thot

The temperature (in C) that the component dimensions will be thermal expanded to (using material properties based on the material input). To disable automatic thermal expansion, set Tinput and Thot both to the same value

Note

The T/H modules of ARMI will update the hot temperature when coupling is activated.

mult

Multiplicity specifies how many duplicates of this component exist in this block. If you want 169 pins per assembly, this would be 169. This does not explicitly describe the location of the pins. Note that many fast-neutron systems only need volume fractions, not precise spatial locations, at least for pre-conceptual/simple studies.

id

Inner diameter (in cm). Each shape has different required input dimension keys. For annulus, set id to non-zero.

od

Outer diameter (in cm).

2.2.2.2. Component Types

Each component has a variety of dimensions to define the shape and composition. All dimensions are in cm. The following is a list of included component shapes and their dimension inputs. Again, additional/custom components with arbitrary dimensions may be provided by the user via plugins.

Component list

Component Name

Dimensions

Component

ShapedComponent

Circle

od, id, mult, modArea

Hexagon

op, ip, mult, modArea

Rectangle

lengthOuter, lengthInner, widthOuter, widthInner, mult, modArea

SolidRectangle

lengthOuter, widthOuter, mult, modArea

Square

widthOuter, widthInner, mult, modArea

Triangle

base, height, mult, modArea

HoledHexagon

op, holeOD, nHoles, mult, modArea

HexHoledCircle

od, holeOP, mult, modArea

HoledRectangle

holeOD, lengthOuter, widthOuter, mult, modArea

HoledSquare

holeOD, widthOuter, mult, modArea

Helix

od, axialPitch, helixDiameter, mult, id, modArea

Sphere

od, id, mult, modArea

Cube

lengthOuter, lengthInner, widthOuter, widthInner, heightOuter, heightInner, mult, modArea

RadialSegment

inner_radius, outer_radius, height, mult, inner_theta, outer_theta

DifferentialRadialSegment

inner_radius, radius_differential, inner_axial, height, inner_theta, azimuthal_differential, mult

NullComponent

UnshapedComponent

modArea

UnshapedVolumetricComponent

op, volume

ZeroMassComponent

op, volume

PositiveOrNegativeVolumeComponent

op, volume

DerivedShape

modArea

When a DerivedShape is specified as the final component in a block, its area is inferred from the difference between the area of the block and the sum of the areas comprised by the other components in the block. This is useful for complex shapes like coolant surrounding a lattice of pins.

2.2.2.4. Pin lattices

Pin lattices may be explicitly defined in the block/component input in conjunction with the grids input section. A block may assigned a grid name, and then each component may be assigned one or more grid specifiers.

For example, the following input section specifies that fuel pins will occupy all grid positions marked with a 1 and cladding components will occupy all grid positions marked with either a 1 or a 2. This situation may be desirable when some burnable poison pins use the same cladding as the fuel pins.

blocks:
    fuel: &block_fuel
        grid name: fuelgrid
        fuel:
            flags: fuel test
            shape: Circle
            material: UZr
            Tinput: 25.0
            Thot: 600.0
            id: 0.0
            mult: 169.0
            od: 0.86602
            latticeIDs: [1]
        clad:
            shape: Circle
            material: HT9
            Tinput: 25.0
            Thot: 470.0
            id: 1.0
            mult: fuel.mult
            od: 1.09
            latticeIDs: [1,2]

Note

A grid with the name fuelgrid must be defined as well in the grid input section.

2.2.3. Flags and naming

All objects in the ARMI Reactor Model possess a set of armi.reactor.flags.Flags, which can be used to affect the way that the various physics kernels treat each object. Most flags are named after common reactor components, like FUEL, or CLAD, and are used to declare what something is in the reactor model. Various physics or other framework operations can then be parameterized to target specific types of things. For instance, the fuel handling code can infer that blocks with the GRID_PLATE flag should be considered stationary and not move them with the rest of the block stack in an assembly.

Historically, flags have also been used to describe directly what should be done with an object in the reactor model. For instance, an object with the DEPLETABLE flag set will participate in isotopic depletion analysis, whereas objects without the DEPLETION flag set will not. This has led to a lot of confusion, as the meaning of various flags is buried deep within the code, and can conflict from place to place. We are trying to align around a what something is interpretation, and bind those to specific behaviors with settings. For more details, see armi.reactor.flags.

The set of specific flags that should be set on an object can be specified in one of two ways for each object defined in the blueprints. The most precise way is to use include a flags: entry for the object blueprint in question. In the example above, the fuel component sets the FUEL and TEST flags. When specifying flags in this way, the value specified must be completely and unambiguously convertible into valid Flags. If it cannot, it will lead to an error when constructing the object.

If flags: is empty, or not specified, then the name of the object blueprint will be used to infer as many flags as possible. In the above example, the clad component will get the CLAD flag from its name.

Note

Additional flags may be specified from plugins, but this should be done with care; see the armi.reactor.flags module and armi.plugins.ArmiPlugin.defineFlags() plugin hook for more details.

2.2.4. Assemblies

Once components and blocks are defined, Assemblies can be created as extruded stacks of blocks from bottom to top. The assemblies use YAML anchors to refer to the blocks defined in the previous section.

Note

We aren’t happy with the use of anchors to refer to blocks, and plan to change it (back) to just using the block names directly. However, the use of anchors for input to be applied to multiple assemblies (e.g. heights) is quite nice.

A complete definition of an inner-core assembly may be seen below:

assemblies:
    heights: &standard_heights [10.05, 20.10, 30.15, 20.10, 20.10, 30.15]
    axial mesh points: &standard_axial_mesh_points [1, 2, 3, 4, 5, 6]
    inner core:
        specifier: IC
        blocks: &inner_core_blocks [*block_shield, *block_fuel, *block_fuel, *block_fuel, *block_fuel, *block_plenum]
        height: *standard_heights
        axial mesh points: *standard_axial_mesh_points
        hotChannelFactors: TWRPclad
        material modifications:
            U235_wt_frac: ['', '', 0.001, 0.002, 0.03, '']
            ZR_wt_frac: ['', '', 0.1, 0.1, 0.1, 0.1]
        nozzleType: Inner
        xs types: [A, B, C, D, E, F]

Note

While component dimensions are entered as cold dimensions, axial heights must be entered as hot dimensions. The reason for this is that each component with different material will thermally expand at different rates. In the axial dimension, this is problematic because after a change in temperature each component in the same block will have a different height. The solution is to pre-expand each component axially and enter hot axial block heights. After the reactor is created, further temperature changes will cause dimension changes only in 2 dimensions (radially). Mass is always conserved, but if temperature deviates significantly from hot axial heights, density may deviate as well.

For many cases, a shared height and axial mesh point definition is sufficient. These can be included globally as shown above and linked with anchors, or specified explicitly.

specifier

The Geometry Assembly Specifier, which is a two-letter ID, such as “IC” (for inner core), “SH” (for shield), etc. correspond with labels in the geometry input file that is created by the GUI hex dragger.

xs types

The cross-section type is a single capital letter that identifies which cross section (XS) set will be applied to this block. Each cross section set must be defined for at least one block with fissile fuel. When the lattice physics code executes in ARMI, it determines the representative blocks from each cross section type and burnup group and runs it to create the cross section set for all blocks of the same type and in the same burnup group. Generally, it is best to set blocks that have much different compositions to have separate cross section types. The tradeoff is that the more XS types you define, the more CPU time the case will take to run.

axial mesh points

Blocks will be broken up into this many uniform mesh points in the deterministic neutronics solvers (e.g. DIF3D). This allows you to define large blocks that have multiple flux points within them. You have to keep the neutronic mesh somewhat uniform in order to maintain numerical stability of the solvers. It is important to note that the axial mesh must be uniform throughout the core for many physics kernels, so be sure all block interfaces are consistent among all assemblies in the core. Blocks deplete and get most state variables on the block mesh defined by the height specification. Provisions for multiple meshes for different physics are being planned.

hotChannelFactors

A label to define which set of hot channel factors (HCFs) get applied to this block in the thermal/hydraulic calculations. There are various valid sets included with ARMI.

nozzleType

This is a string that identifies what type of inlet nozzle an assembly has. This parameter could be used in an implementation of a thermal-hydraulics solver with flow orificing to apply different pressure loss coefficients and/or flow rates to different types of assemblies.

material modifications

These are a variety of modifications that are made to the materials in blocks in these locations. It may include the fuel enrichment (mass frac.), poison enrichment (mass frac.), zirconium mass frac, and any additional options required to fully define the material loaded in the component. The material definitions in the material library define valid modifications for them.

Material Name

Available Modifications

B4C

B10_wt_frac, theoretical_density, TD_frac

FuelMaterial

class1_custom_isotopics, class2_custom_isotopics, class1_wt_frac, customIsotopics

Lithium

LI_wt_frac, LI6_wt_frac

Sulfur

sulfur_density_frac, TD_frac

ThU

U233_wt_frac

Thorium

class1_custom_isotopics, class2_custom_isotopics, class1_wt_frac, customIsotopics

ThoriumOxide

TD_frac

ThoriumOxide

TD_frac

UThZr

U235_wt_frac, ZR_wt_frac

UZr

U235_wt_frac, ZR_wt_frac

Uranium

U235_wt_frac, TD_frac

UraniumOxide

U235_wt_frac, TD_frac

UraniumOxide

U235_wt_frac, TD_frac

The class 1/class 2 modifications in fuel materials are used to identify mixtures of custom isotopics labels for input scenarios where a varying blend of a high-reactivity feed with a low-reactivity feed. This is often useful for closed fuel cycles. For example, you can define any fuel material as being made of LWR-derived TRU plus depleted uranium at various weight fractions. Note that this input style only adjusts the heavy metal.

To enable the application of different values for the same material modification type on different components within a block, the user may specify material modifications by component. This is useful, for instance, when two pins within an assembly made of the same base material have different fuel enrichments. This is done using the by component attribute to the material modifications as in:

blocks:
    fuel: &block_fuel
        fuel1: &component_fuel_fuel1
            shape: Hexagon
            material: UZr
            Tinput: 600.0
            Thot: 600.0
            ip: 0.0
            mult: 1
            op: 10.0
        fuel2: &component_fuel_fuel2
            shape: Hexagon
            material: UZr
            Tinput: 600.0
            Thot: 600.0
            ip: 0.0
            mult: 1
            op: 10.0
assemblies:
    fuel a: &assembly_a
        specifier: IC
        blocks: [*block_fuel]
        height: [1.0]
        axial mesh points: [1]
        xs types: [A]
        material modifications:
            by component:
                fuel1:
                    U235_wt_frac: [0.20]
                fuel2:
                    Zr_wt_frac: [0.02]
            U235_wt_frac: [0.30]

Material modifications specified on the material modifications level are referred to as “block default” values and apply to all components on the block not associated with a by-component value. This example would apply an enrichment of 20% to the fuel1 component and an enrichment of 30% to all other components in the block that accept the U235_wt_frac material modification.

All by-component material modifications override any block default material modifications of the same type. In addition, any by-component entries omitted for a given axial block will revert to the block default (or material class default, if no block default value is provided and a material class default exists) value:

blocks:
    fuel: &block_fuel
        fuel1: &component_fuel_fuel1
            shape: Hexagon
            material: UZr
            Tinput: 600.0
            Thot: 600.0
            ip: 0.0
            mult: 1
            op: 10.0
        fuel2: &component_fuel_fuel2
            shape: Hexagon
            material: UZr
            Tinput: 600.0
            Thot: 600.0
            ip: 0.0
            mult: 1
            op: 10.0
assemblies:
    fuel a: &assembly_a
        specifier: IC
        blocks: [*block_fuel, *block_fuel]
        height: [0.5, 0.5]
        axial mesh points: [1, 1]
        xs types: [A, A]
        material modifications:
            by component:
                fuel1:
                    U235_wt_frac: [0.20, ''] # <-- the U235_wt_frac for the second block will go to the block defaul value
                fuel2: # the U235_wt_frac for fuel2 component in both axial blocks will go to the block default values
                    Zr_wt_frac: [0.02, ''] # <-- the Zr_wt_frac for the second block will go to the material class default because there is no block default value
            U235_wt_frac: [0.30, 0.30]

The first block listed is defined at the bottom of the core. This is typically a grid plate or some other structure.

2.2.5. Systems

Once assemblies are defined they can be grouped together into the Core, the spent fuel pool (SFP), etc.

A complete reactor structure with a core and a SFP may be seen below:

systems:
    core:
        grid name: core
        origin:
            x: 0.0
            y: 10.1
            z: 1.1
    Spent Fuel Pool:
        type: sfp
        grid name: sfp
        origin:
            x: 1000.0
            y: 12.1
            z: 1.1

The origin defines the point of origin in global space in units of cm. This allows you to define the relative position of the various structures. The grid name inputs are string mappings to the grid definitions described below.

2.2.5.1. Plugin Behavior

The armi.plugins.ArmiPlugin.defineSystemBuilders() method can be provided by plugins to control how ARMI converts the systems section into Composites to be modeled. By default, the type field is used to determine what object is created. The default armi.reactor.ReactorPlugin provides the following mapping:

type Value

Builds

core (default)

Core

sfp

SpentFuelPool

Plugins are able to provide a superset (e.g., include core and sfp) and new mappings of values to builders.

2.2.6. Grids

Grids are described inside a blueprint file using lattice map or grid contents fields to define arrangements in Hex, Cartesian, or R-Z-Theta. The optional lattice pitch entry allows you to specify spacing between objects that is different from tight packing. This input is required in mixed geometry cases, for example if Hexagonal assemblies are to be loaded into a Cartesian arrangement. The contents of a grid may defined using one of the following:

lattice map:

A ASCII map representing the grid contents

grid contents:

a direct YAML representation of the contents

Example grid definitions are shown below:

grids:
    control:
        geom: hex
        symmetry: full
        lattice map: |
           - - - - - - - - - 1 1 1 1 1 1 1 1 1 4
            - - - - - - - - 1 1 1 1 1 1 1 1 1 1 1
             - - - - - - - 1 8 1 1 1 1 1 1 1 1 1 1
              - - - - - - 1 1 1 1 1 1 1 1 1 1 1 1 1
               - - - - - 1 1 1 1 1 1 1 1 1 1 1 1 1 1
                - - - - 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
                 - - - 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
                  - - 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
                   - 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
                    7 1 1 1 1 1 1 1 1 0 1 1 1 1 1 1 1 1 1
                     1 1 1 1 1 1 1 1 2 1 1 1 1 1 1 1 1 1
                      1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
                       1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
                        1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
                         1 1 1 1 1 1 1 1 1 1 1 1 1 1
                          1 1 1 1 1 1 1 1 1 3 1 1 1
                           1 1 1 1 1 1 1 1 1 1 1 1
                            1 6 1 1 1 1 1 1 1 1 1
                             1 1 1 1 1 1 1 1 1 1
sfp:
    symmetry: full
    geom: cartesian
    lattice pitch:
        x: 50.0
        y: 50.0
    grid contents:
        [0,0]: MC
        [1,0]: MC
        [0,1]: MC
        [1,1]: MC

Tip

We have gone through some effort to allow both pin and core grid definitions to share this input and it may improve in the future.

2.2.7. Custom Isotopics

In some cases (such as benchmarking a previous reactor), the default mass fractions from the material library are not what you want to model. In these cases, you may override the isotopic composition provided by the material library in this section. There are three ways to specify the isotopics: mass fractions (sum to 1.0), number densities (in atoms/barn-cm), or number fractions (sum to 1.0). For example:

custom isotopics:
    LABEL1:
        input format: mass fractions
        density: 7.79213903298633
        C: 0.000664847887388523
        CR: 0.182466356404319
        CU: 0.00323253628006144
        FE: 0.705266053783901
        MN: 0.0171714161260001
        MO: 0.00233843050046998
        NI: 0.0831976890804466
        SI: 0.00566266993741259

See the List of Nuclides for all valid entries. Note that ARMI will expand elemental nuclides to their natural isotopics in most cases (to correspond with the nuclear data library).

The (mass) density input is invalid when specifying number densities; the code will present an error message.

2.2.8. Advanced topics

2.2.8.1. Overlapping shapes

Solids of different compositions in contact with each other present complications during thermal expansion. The ARMI Framework does not perform calculations to see exactly how such scenarios will behave mechanically; it instead focuses on conserving mass. To do this, users should input a zero-dimension component linking the 2 solid components made of the special Void material. This gap will allow the 2 components to thermally expand independently while keeping track of the overlapping area.

It is important to keep track of the areas when a DerivedShape is included in a block design because ARMI calculates the derived area by taking the full area of the block and subtracting the total area of the non-DerivedShapes. If area between thermally-expanding solids was not accounted for, this would non-physically add or subtract coolant into these gaps. To model overlapping components heterogeneously, it is suggested to use a block converter.

Additionally, it should be noted that assigning mult: fuel.mult will be ever-so-slightly slower than just defining the actual value. This is because ARMI needs to find the sibling component and get the siblings mult. If you are concerned about performance at that level and don’t expect mult to change much in your case, you can replace the constant link (i.e. it does not change over time) with a YAML anchor and alias.

2.2.8.2. Component area modifications

In some scenarios, it is desired to have one component’s area be subtracted or added to another. For example, the area of the skids in a skid duct design needs to be subtracted from the interstitial coolant. The mechanism to handle this involves adding a parameter to the component to be modified after all the required ones in the form of <componentName>.add or <componentName>.sub. The component to be added or subtracted must be defined before the component that is being modified. This allows fairly complicated configurations to be modeled without explicitly defining new components.

blocks:
    rect with 100 holes:
        holes:
            shape: Cicle
            material: Sodium
            Tinput: 600
            Thot: 600
            mult: 100
            od: 0.05
        square of steel:
            shape: Square
            material: Iron
            Tinput: 25.0
            Thot: 600.0
            widthOuter: 3.0
            modArea: holes.sub      # "holes" is the name of the other component

2.2.8.3. Putting it all together to make a Block

Here is a complete fuel block definition:

blocks:
    fuel: &block_fuel
        bond:
            shape: Circle
            material: Sodium
            Tinput: 450.0
            Thot: 450.0
            id: fuel.od
            mult: fuel.mult
            od: cladding.id
        clad:
            shape: Circle
            material: HT9
            Tinput: 25.0
            Thot: 450.0
            id: 0.905
            mult: fuel.mult
            od: 1.045
        coolant:
            shape: DerivedShape
            material: Sodium
            Tinput: 450.0
            Thot: 450.0
        duct:
            shape: Hexagon
            material: HT9
            Tinput: 25.0
            Thot: 450.0
            ip: 15.2
            mult: 1.0
            op: 16.2
        fuel:
            shape: Circle
            material: UZr
            Tinput: 25.0
            Thot: 600.0
            id: 0.0
            isotopics: LABEL1
            mult: 169.0
            od: 0.757
        intercoolant:
            shape: Hexagon
            material: Sodium
            Tinput: 450.0
            Thot: 450.0
            ip: duct.op
            mult: 1.0
            op: 16.79
        wire:
            shape: Helix
            material: HT9
            Tinput: 25.0
            Thot: 450.0
            axialPitch: 30.0
            helixDiameter: 1.145
            id: 0.0
            mult: fuel.mult
            od: 0.1

2.2.8.4. Making blocks with unshaped components

Sometimes you will want to make a homogenous block, which is a mixture of multiple materials, and will not want to define an exact shape for each of the components in the block. In this case unshaped components can be used, but ARMI still requires there to be at least one component with shape to define the pitch of the block.

In the example below, the block is a rectangular pitch so one of the components is defined as a rectangle to indicate this. Its outer dimensions determine the pitch of the block. The inner dimensions can be whatever is necessary to preserve the area fraction. Note that rectangular blocks have pitch defined by two numbers, since they may not be a square. In this case the rectangle component is half the area fraction and the other two components are one quarter:

blocks:
    fuel:
        clad:
            shape: Rectangle
            material: HT9
            Tinput: 25.0
            Thot: 25.0
            lengthOuter: 3.0
            lengthInner: 2.4
            widthOuter: 2.0
            widthInner: 1.25
            mult:1.0
        fuel:
            shape: UnshapedComponent
            material: UZr
            Tinput: 25.0
            Thot: 25.0
            area = 1.5
        coolant:
            shape: UnshapedComponent
            material: Sodium
            Tinput: 25.0
            Thot: 25.0
            area = 1.5

Warning

When using this method avoid thermal expansion by setting TInput=THot, or your pitch component dimensions might change, thus changing your pitch.

Alternatively, a void (empty) component with zero area can be added for defining the pitch, and then all three components can be defined as unshaped. The downside, is there are now four components, but only three that have actual area and composition:

blocks:
    fuel:
        clad:
            shape: UnshapedComponent
            material: HT9
            Tinput: 25.0
            Thot: 25.0
            area: 3.0
        fuel:
            shape: UnshapedComponent
            material: UZr
            Tinput: 25.0
            Thot: 25.0
            area = 1.5
        coolant:
            shape: UnshapedComponent
            material: Sodium
            Tinput: 25.0
            Thot: 25.0
            area = 1.5
        PitchDefiningComponent:
            shape: Rectangle
            material: Void
            lengthOuter: 3.0
            lengthInner: 3.0
            widthOuter: 2.0
            widthInner: 2.0
            mult:1.0

This can similarly be done for hex geometry and and a hexagon with Outer Pitch (op).

Warning

The rest of the input described below are scheduled to be moved into the settings input file, since their nature is that of a setting.

2.2.9. Nuclide Flags

The nuclide flags setting allows the user to choose which nuclides they would like to consider in the problem, and whether or not each nuclide should transmute and decay. For example, sometimes you may not want to deplete trace elements in structural materials, but in other analysis you might. If the nuclide should deplete, it must have burn: true. If it is to be included in the problem at all, it must be have xs: true All nuclides that will be produced via transmutation/decay must also have burn: true, so if you add Thorium, make sure to add all other actinides in its chain. You can use the expandTo: section to list a subset of natural nuclides to expand into. If you leave this section out, a default set of nuclide flags will be applied to your problem. Remember this section when you start changing which nuclides are modeled and which ones deplete.:

# this is a YAML comment
nuclide flags:
    AL: {burn: false, xs: true}
    AM241: {burn: true, xs: true}
    C: &carbon_flags {burn: false, xs: true}    # an anchor to "carbon_flags"
    CA: *carbon_flags
    CL: *carbon_flags
    CO: *carbon_flags                           # the alias back to "carbon_flags"
    CR: *carbon_flags
    CU: *carbon_flags
    FE: *carbon_flags
    H: {burn: false, xs: true}
    MN: {burn: false, xs: true}
    MO: {burn: false, xs: true}
    N: {burn: false, xs: true}
    NA: {burn: false, xs: true}
    NI: {burn: false, xs: true}
    O: {burn: false, xs: true, expandTo: ["O16", "O17"]}
    P: {burn: false, xs: true}
    PU238: {burn: true, xs: true}
    PU239: {burn: true, xs: true}
    PU240: {burn: true, xs: true}
    PU241: {burn: true, xs: true}
    PU242: {burn: true, xs: true}
    S: {burn: false, xs: true}
    SI: {burn: false, xs: true}
    U234: {burn: false, xs: true}
    U235: {burn: true, xs: true}
    U236: {burn: true, xs: true}
    U238: {burn: true, xs: true}

The code will crash if materials used in Blocks and Components contain nuclides not defined in nuclide flags. A failure can also occur if the burn chain is missing a nuclide.

Tip

We plan to upgrade the default behavior of this to inherit from all defined materials in a problem to reduce the user-input burden.