# UPuZr Creep Update

Calculates the secondary thermal and irradiation creep for UPuZr fast metal fuel. This material must be run in conjunction with ComputeMultipleInelasticStress.

## Description

UPuZrCreepUpdate is used to model the thermal and irradiation creep behavior of U-Pu-Zr fast reactor fuel. If porosity and porosity_material are both defined an error will result. The user has the choice of not supplying any porosity, supplying a variable for porosity, or coupling to a material that calculates the porosity.

A model for combined secondary thermal creep and irradiation creep for U-Pu-Zr fast reactor fuel is available, with the creep rate modeled as a function of time, fuel porosity, effective stress, and fission rate. The constitutive relation is taken from Kutty et al. (2010) and is given as (1) where is the creep rate (1/s), is the effective (Mises) stress (MPa), is the temperature (K), is the porosity, is the volumetric fission rate (fissions/-s), are the activation energies (cal/mol), is the universial gas constant (1.987 cal/mol-K) and are material constants given as = , = , and = .

The first term in Eq. 1 represents diffusional thermal creep and is applicable to low stress and low temperature conditions. The second term represents thermal dislocation or power-law creep and is applicable to high stress and high temperature conditions. The third term represents the irradiation creep as it depends upon the fission rate. The activation energies for the thermal creep terms ( and ) are given as cal/mol.

These U and Pu alloys have a phase change temperature of 923.15 K. Above this temperature, the creep rate equation changes to (2) where is and is 28500 cal/mol.

## Example Input Syntax


[./creep]
type = UPuZrCreepUpdate
block = 1
temperature = temp
fission_rate = fission_rate
[../]
(test/tests/tensor_mechanics/upuzr_creep/upuzr_creep_rz.i)

UPuZrCreepUpdate must be run in conjunction with the inelastic strain return mapping stress calculator as shown below:


type = ComputeMultipleInelasticStress
tangent_operator = elastic
inelastic_models = 'creep'
block = 1
[../]
(test/tests/tensor_mechanics/upuzr_creep/upuzr_creep_rz.i)

## Input Parameters

• temperatureCoupled temperature

C++ Type:std::vector

Description:Coupled temperature

### Required Parameters

• relative_tolerance1e-08Relative convergence tolerance for Newton iteration

Default:1e-08

C++ Type:double

Description:Relative convergence tolerance for Newton iteration

• max_inelastic_increment0.0001The maximum inelastic strain increment allowed in a time step

Default:0.0001

C++ Type:double

Description:The maximum inelastic strain increment allowed in a time step

• fission_rateCoupled fission rate

C++ Type:std::vector

Description:Coupled fission rate

• base_nameOptional parameter that defines a prefix for all material properties related to this stress update model. This allows for multiple models of the same type to be used without naming conflicts.

C++ Type:std::string

Description:Optional parameter that defines a prefix for all material properties related to this stress update model. This allows for multiple models of the same type to be used without naming conflicts.

• max_its30Maximum number of Newton iterations

Default:30

C++ Type:unsigned int

Description:Maximum number of Newton iterations

• acceptable_multiplier10Factor applied to relative and absolute tolerance for acceptable convergence if iterations are no longer making progress

Default:10

C++ Type:double

Description:Factor applied to relative and absolute tolerance for acceptable convergence if iterations are no longer making progress

• use_material_fission_rateFalseFlag to use the material 'fission_rate_material' instead of variable fission rate

Default:False

C++ Type:bool

Description:Flag to use the material 'fission_rate_material' instead of variable fission rate

• gamma_transition923Gamma phase transition temperature.

Default:923

C++ Type:double

Description:Gamma phase transition temperature.

• absolute_tolerance1e-11Absolute convergence tolerance for Newton iteration

Default:1e-11

C++ Type:double

Description:Absolute convergence tolerance for Newton iteration

• boundaryThe list of boundary IDs from the mesh where this boundary condition applies

C++ Type:std::vector

Description:The list of boundary IDs from the mesh where this boundary condition applies

• fission_rate_materialfission_rate_materialFission rate material property name

Default:fission_rate_material

C++ Type:MaterialPropertyName

Description:Fission rate material property name

• porosity0Porosity material property name

Default:0

C++ Type:MaterialPropertyName

Description:Porosity material property name

• blockThe list of block ids (SubdomainID) that this object will be applied

C++ Type:std::vector

Description:The list of block ids (SubdomainID) that this object will be applied

### Optional Parameters

• effective_inelastic_strain_nameeffective_creep_strainName of the material property that stores the effective inelastic strain

Default:effective_creep_strain

C++ Type:std::string

Description:Name of the material property that stores the effective inelastic strain

• enableTrueSet the enabled status of the MooseObject.

Default:True

C++ Type:bool

Description:Set the enabled status of the MooseObject.

• use_displaced_meshFalseWhether or not this object should use the displaced mesh for computation. Note that in the case this is true but no displacements are provided in the Mesh block the undisplaced mesh will still be used.

Default:False

C++ Type:bool

Description:Whether or not this object should use the displaced mesh for computation. Note that in the case this is true but no displacements are provided in the Mesh block the undisplaced mesh will still be used.

• control_tagsAdds user-defined labels for accessing object parameters via control logic.

C++ Type:std::vector

Description:Adds user-defined labels for accessing object parameters via control logic.

• seed0The seed for the master random number generator

Default:0

C++ Type:unsigned int

Description:The seed for the master random number generator

• implicitTrueDetermines whether this object is calculated using an implicit or explicit form

Default:True

C++ Type:bool

Description:Determines whether this object is calculated using an implicit or explicit form

• constant_onNONEWhen ELEMENT, MOOSE will only call computeQpProperties() for the 0th quadrature point, and then copy that value to the other qps.When SUBDOMAIN, MOOSE will only call computeSubdomainProperties() for the 0th quadrature point, and then copy that value to the other qps. Evaluations on element qps will be skipped

Default:NONE

C++ Type:MooseEnum

Description:When ELEMENT, MOOSE will only call computeQpProperties() for the 0th quadrature point, and then copy that value to the other qps.When SUBDOMAIN, MOOSE will only call computeSubdomainProperties() for the 0th quadrature point, and then copy that value to the other qps. Evaluations on element qps will be skipped

• internal_solve_output_onon_errorWhen to output internal Newton solve information

Default:on_error

C++ Type:MooseEnum

Description:When to output internal Newton solve information

• internal_solve_full_iteration_historyFalseSet true to output full internal Newton iteration history at times determined by internal_solve_output_on. If false, only a summary is output.

Default:False

C++ Type:bool

Description:Set true to output full internal Newton iteration history at times determined by internal_solve_output_on. If false, only a summary is output.

### Debug Parameters

• output_propertiesList of material properties, from this material, to output (outputs must also be defined to an output type)

C++ Type:std::vector

Description:List of material properties, from this material, to output (outputs must also be defined to an output type)

• outputsnone Vector of output names were you would like to restrict the output of variables(s) associated with this object

Default:none

C++ Type:std::vector

Description:Vector of output names were you would like to restrict the output of variables(s) associated with this object