UCOFGR

Fission gas release model for UCO

Description

Fission gas release represents the amount of fission gas that is released by the UCO kernel into the void volume of the TRISO particle (kernel and buffer porosities and buffer-inner pyrolytic carbon (IPyC) gap).

The functional relationships are partly derived from experimental data on UO and assumed valid for UCO due to lack of relevant UCO data.

Automatic differentiation is available using ADUCOFGR.

Validity Range

Burnup: assumed valid at all burnups (via fission rate density).

Temperature: assumed valid at all temperatures.

Fission Gas Release

The fission gas release (FGR), (mol), includes contributions from both direct recoil release and diffusive release:

(1) where (dimensionless) and (dimensionless) are the release fractions of fission gas by direct recoil and diffusion, respectively, and (mol) is the amount of fission gas produced in the kernel.

Direct Recoil

Direct kinetic release of fission gases from the kernel to the buffer is accounted for by geometrical considerations using a formulation taken from PARFUME (Miller et al., 2018). The fission gas mixture is assumed to be composed entirely of krypton (Kr) and xenon (Xe), the fission fragment ranges of which are derived from compiled experimental data. The fractional yields of Kr and Xe taken from PARFUME for use in the formulation (18.5 and 81.5%, respectively) are consistent with measured values in the open literature (Blades et al., 1956) (20.4 and 79.6%, respectively). The recoil fraction is therefore given by:

where (dimensionless) is the release fraction of species due to recoil.

The maximum release fraction of species due to recoil can be estimated by assuming that (1) the fission rate density is spatially uniform throughout the kernel and (2) all fission fragments are born with momentum oriented in the outward radial direction. The maximum fraction is then given by the ratio of (1) the volume of a spherical shell of thickness and outer radius to (2) the volume of the kernel with radius . Here, the shell thickness is the mean range of fission fragment in the kernel. Accounting for the isotropic distribution of initial fission fragment directions reduces potential recoil release by a factor of 75% (Olander, 1976). The resulting release fraction of species due to recoil is described by:

The mean range of fission fragment in UCO, , can be estimated from the weighted average of the mean ranges of fission fragment in pure uranium (U), carbon (C), and oxygen (O):

where (dimensionless) and (dimensionless) are the initial O to U and C to U ratios, respectively, and (kg/m) is the density of the kernel. The mean ion ranges of species in target material , , are taken from the literature (Littmark and Ziegler, 1980) using nominal ion energies of 107 MeV and 72 MeV for Kr and Xe, respectively (Morris et al., 2004). The values are summarized in Table 1 below.

Table 1: Mean ion ranges of Kr and Xe in pure U, C, and O (Littmark and Ziegler, 1980).

Target material UCO
(mg/cm)11.73.13.3
(mg/cm)8.32.22.3

Booth Model

Diffusive release through kernel grains to the grain boundaries and subsequent transport through the interconnected porosity is estimated by the Booth equivalent sphere diffusion model (Booth, 1957).

The Booth release fraction for both short-lived () and long-lived () fission products is given by:

where (m) is the radius of the diffusing sphere (i.e., the average grain radius), (m/s) is the diffusivity of the fission gas in the grain, (s) is the time, , and .

The release of the fission products from the fuel kernel, during accident condition/isothermal heating tests, is approximated by solving the diffusion equation without source/sink terms (Verfondern, 2012). Thus, the Booth release fraction becomes (Booth, 1957):

(2)

Note that the adjustment for low flux is an approximation in the code. Once the fast neutron flux is less than or equal to the preset cut-off flux (via cutoff_neutron_flux), the fractional release is computed according to Eq. (2).

The unperturbed diffusion coefficient, (m/s), formulated for UO fuel by Turnbull et al. (1982), is given as:

where (m/s) for are the diffusion coefficients of the mechanisms controlling diffusion at different temperature ranges.

Diffusion coefficients used in PARFUME

Legacy TRISO fuel development programs have predominantly focused on UO fuel; consequently, most UCO kernel properties currently used in PARFUME are derived from experimental data on UO and assumed valid for UCO, due to lack of relevant UCO data. Following diffusion coefficients taken from PARFUME are implemented in BISON.

  1. At the highest temperatures, diffusion proceeds through cation lattice by means of thermally activated vacancies:

where R=1.9872 cal k mol and (K) is the temperature of the kernel.

  1. At intermediate temperatures, diffusion is driven by means of vacancies produced by the irradiation process:

where (m) is the atomic jump distance, () is the cation vacancy jump rate, () is the rate of defect production per atom, and Z (dimensionless) is the number of sites around a point defect from which recombination is inevitable. They are given by:

and

where K (10 defects/fission) is the damage rate and (FIMA) is the burnup. Note that PARFUME lists the atomic jump distance for UO as 3.0x m while it is listed as 3.87x m in Perriot et al. (2015).

  1. Finally, at lower temperatures, a term proportional to the fission rate density, (fission/m-s), is used to agree with experimental results reported by Turnbull et al. (1982):

Diffusion coefficients computed by LANL's lower length scale models

Alternatively, BISON provides an option (use_diffusion_coefficients_from_LLS = true) to use diffusion coefficients for UCO fuel that were calculated from LANL's cluster dynamics code Centipede. The diffusion coefficients are fitted to exponential functions that can be used in BISON. The fitted equations for the , and terms are,

and

Effective diffusivity

BISON provides an option to use the effective diffusivity by setting use_effective_diffusivity = true. The effective diffusivity is described as

where () is the trapping rate, (s) is the resolution rate, and (ms) is the unperturbed diffusivity.

The trapping and resolution parameters are given by: and where m is the length of a fission fragment track, m is the radius of influence of a fission fragment, and is the fission rate density. The bubble radius and bubble density, and respectively, are given as (White and Tucker, 1983) and

Fission Gas Production

The amount of fission gas produced by the kernel, (mol), during a time interval (s), is calculated as:

where (dimensionless) is the combined fractional fission yield of krypton and xenon atoms per fission, (m) is the volume of the kernel, and (6.022x10 at/mol) is Avogadro's number.

The fission yield of {Kr+Xe} is equal to (Miller et al., 2018):

The fission yields come from TRISOUtils in BISON. Currently, this number is constant but it may be updated in the future.

Example Input Syntax

[Materials<<<{"href": "../../syntax/Materials/index.html"}>>>]
  [fission_gas_release]
    type = UCOFGR<<<{"description": "Fission gas release model for UCO", "href": "UCOFGR.html"}>>>
    block<<<{"description": "The list of blocks (ids or names) that this object will be applied"}>>> = '1'
    average_grain_radius<<<{"description": "Average grain radius (m)"}>>> = 10e-6
    triso_geometry<<<{"description": "TRISOGeometry user object name"}>>> = particle_geometry
    temperature<<<{"description": "Coupled temperature (K)"}>>> = temp
    fast_neutron_flux<<<{"description": "The fast neutron flux (neutrons/m^2/s) material property"}>>> = 1e15
    cutoff_neutron_flux<<<{"description": "The cutoff fast neutron flux for enabling the Booth fractional release calculations during accident simulation conditions."}>>> = 0.0
  []
[]
(test/tests/triso/UCOFGR/UCOFGR.i)

BISON provides an option (release_all = True) to allow 100% of the fission gas to be released in the void volume.

Input Parameters

  • C_UCarbon to uranium ratio

    C++ Type:double

    Unit:(no unit assumed)

    Controllable:No

    Description:Carbon to uranium ratio

  • O_UOxygen to uranium ratio

    C++ Type:double

    Unit:(no unit assumed)

    Controllable:No

    Description:Oxygen to uranium ratio

  • average_grain_radiusAverage grain radius (m)

    C++ Type:double

    Unit:(no unit assumed)

    Controllable:No

    Description:Average grain radius (m)

  • temperatureCoupled temperature (K)

    C++ Type:std::vector<VariableName>

    Unit:(no unit assumed)

    Controllable:No

    Description:Coupled temperature (K)

  • triso_geometryTRISOGeometry user object name

    C++ Type:UserObjectName

    Controllable:No

    Description:TRISOGeometry user object name

Required Parameters

  • Nterms100Selected first N terms in the infinite summation.

    Default:100

    C++ Type:unsigned int

    Controllable:No

    Description:Selected first N terms in the infinite summation.

  • blockThe list of blocks (ids or names) that this object will be applied

    C++ Type:std::vector<SubdomainName>

    Controllable:No

    Description:The list of blocks (ids or names) that this object will be applied

  • boundaryThe list of boundaries (ids or names) from the mesh where this object applies

    C++ Type:std::vector<BoundaryName>

    Controllable:No

    Description:The list of boundaries (ids or names) from the mesh where this object applies

  • computeTrueWhen false, MOOSE will not call compute methods on this material. The user must call computeProperties() after retrieving the MaterialBase via MaterialBasePropertyInterface::getMaterialBase(). Non-computed MaterialBases are not sorted for dependencies.

    Default:True

    C++ Type:bool

    Controllable:No

    Description:When false, MOOSE will not call compute methods on this material. The user must call computeProperties() after retrieving the MaterialBase via MaterialBasePropertyInterface::getMaterialBase(). Non-computed MaterialBases are not sorted for dependencies.

  • 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 computeQpProperties() 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

    Options:NONE, ELEMENT, SUBDOMAIN

    Controllable:No

    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 computeQpProperties() for the 0th quadrature point, and then copy that value to the other qps. Evaluations on element qps will be skipped

  • cutoff_neutron_flux0The cutoff fast neutron flux for enabling the Booth fractional release calculations during accident simulation conditions.

    Default:0

    C++ Type:double

    Unit:(no unit assumed)

    Controllable:No

    Description:The cutoff fast neutron flux for enabling the Booth fractional release calculations during accident simulation conditions.

  • declare_suffixAn optional suffix parameter that can be appended to any declared properties. The suffix will be prepended with a '_' character.

    C++ Type:MaterialPropertyName

    Unit:(no unit assumed)

    Controllable:No

    Description:An optional suffix parameter that can be appended to any declared properties. The suffix will be prepended with a '_' character.

  • fast_neutron_fluxfast_neutron_fluxThe fast neutron flux (neutrons/m^2/s) material property

    Default:fast_neutron_flux

    C++ Type:MaterialPropertyName

    Unit:(no unit assumed)

    Controllable:No

    Description:The fast neutron flux (neutrons/m^2/s) material property

  • fission_ratefission_rateFission rate density material name (fission/m^3-s)

    Default:fission_rate

    C++ Type:MaterialPropertyName

    Unit:(no unit assumed)

    Controllable:No

    Description:Fission rate density material name (fission/m^3-s)

  • radioactive_decay_constant0Radioactive decay constant

    Default:0

    C++ Type:double

    Unit:(no unit assumed)

    Controllable:No

    Description:Radioactive decay constant

  • release_allFalseWhether to release all fission gas produced.

    Default:False

    C++ Type:bool

    Controllable:No

    Description:Whether to release all fission gas produced.

  • use_diffusion_coefficients_from_LLSFalseWhether to use diffusion coefficients that are computed by lower length scale models.

    Default:False

    C++ Type:bool

    Controllable:No

    Description:Whether to use diffusion coefficients that are computed by lower length scale models.

  • use_effective_diffusivityFalseWhether to use effective diffusion coefficients that consider trapping and resolution rates.

    Default:False

    C++ Type:bool

    Controllable:No

    Description:Whether to use effective diffusion coefficients that consider trapping and resolution rates.

Optional Parameters

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

    C++ Type:std::vector<std::string>

    Controllable:No

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

  • enableTrueSet the enabled status of the MooseObject.

    Default:True

    C++ Type:bool

    Controllable:Yes

    Description:Set the enabled status of the MooseObject.

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

    Default:True

    C++ Type:bool

    Controllable:No

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

  • seed0The seed for the master random number generator

    Default:0

    C++ Type:unsigned int

    Controllable:No

    Description:The seed for the master random number generator

  • 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

    Controllable:No

    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.

Advanced Parameters

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

    C++ Type:std::vector<std::string>

    Controllable:No

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

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

    Default:none

    C++ Type:std::vector<OutputName>

    Controllable:No

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

Outputs Parameters

  • prop_getter_suffixAn optional suffix parameter that can be appended to any attempt to retrieve/get material properties. The suffix will be prepended with a '_' character.

    C++ Type:MaterialPropertyName

    Unit:(no unit assumed)

    Controllable:No

    Description:An optional suffix parameter that can be appended to any attempt to retrieve/get material properties. The suffix will be prepended with a '_' character.

  • use_interpolated_stateFalseFor the old and older state use projected material properties interpolated at the quadrature points. To set up projection use the ProjectedStatefulMaterialStorageAction.

    Default:False

    C++ Type:bool

    Controllable:No

    Description:For the old and older state use projected material properties interpolated at the quadrature points. To set up projection use the ProjectedStatefulMaterialStorageAction.

Material Property Retrieval Parameters

Input Files

References

  1. A. T. Blades, W. H. Fleming, and H. G. Thode. The ratio of xenon to krypton in U235 fission. Canadian Journal of Chemistry, 34(3):233–237, 1956. URL: https://doi.org/10.1139/v56-035, doi:10.1139/v56-035.[BibTeX]
  2. A.H. Booth. A method of calculating gas diffusion from UO$_2$ fuel and its application to the X-2-f loop test. Technical Report AECL-496, Atomic Energy of Canada Ltd., 1957.[BibTeX]
  3. U. Littmark and J.F. Ziegler. Handbook of Range Distributions for Energetic Ions in All Elements. Technical Report, Pergamon Press, 1980.[BibTeX]
  4. G.K. Miller, D.A. Petti, J.T. Maki, D.L. Knudson, and W.F. Skerjanc. PARFUME Theory and Model Basis Report. Report INL/EXT-08-14497 (Rev.1), Idaho National Laboratory, September 2018.[BibTeX]
  5. R. N. Morris, D. A. Petti, D. A. Powers, B. E. Boyack, and M. B. Rubin. TRISO-coated particle fuel phenomenon identification and ranking tables (PIRTs) for fission product transport due to manufacturing, operations, and accidents. Technical Report NUREG/CR-6844, Nuclear Regulatory Commission, 2004.[BibTeX]
  6. D. R. Olander. Fundamental aspects of nuclear reactor fuel elements. Technical Information Center, Energy Research and Development Administration, 1976.[BibTeX]
  7. R. Perriot, X. Y. Lui, C. R. Stanek, and D. A. Andersson. Diffusion of Zr, Ru, Ce, Y, La, Sr, and Ba fission products in UO2. Journal of Nuclear Materials, 459:90–96, 2015. URL: https://doi.org/10.1016/j.jnucmat.2015.01.001.[BibTeX]
  8. J.A. Turnbull, C.A. Friskney, J.R. Findlay, F.A. Johnson, and A.J. Walter. The diffusion coefficients of gaseous and volatile species during the irradiation of uranium dioxide. Journal of Nuclear Materials, 107(2):168–184, 1982. doi:10.1016/0022-3115(82)90419-6.[BibTeX]
  9. K. Verfondern. 3.24 - TRISO fuel performance modeling and simulation. In Rudy J.M. Konings, editor, Comprehensive Nuclear Materials, pages 755–788. Elsevier, Oxford, 2012. doi:10.1016/B978-0-08-056033-5.00076-8.[BibTeX]
  10. R.J. White and M.O. Tucker. A new fission-gas release model. Journal of Nuclear Materials, 118(1):1–38, 1983. doi:10.1016/0022-3115(83)90176-9.[BibTeX]