JOYO Experiments

Overview

Two uranium–plutonium UN fuel pins with different He-gap widths were irradiated at a linear heating rate 75 kW/m to 4.3% FIMA in the experimental fast reactor JOYO MK-II, and nondestructive and destructive post irradiation examinations were carried out. The UN pellets were loaded into 15Cr-20Ni stainless steel cladding tubes, irradiated in a fast-test reactor, JOYO, and destructively examined after reaching a burnup of 4.3% FIMA (fraction of initial metal atom). Pin geometry, irradiation conditions, fuel swelling, fission-gas release, and microstructural data were published in Tanaka et al. (2004).

Test Description

The JOYO test consisted of two helium-bonded MN pins (L413 and L414) that were irradiated in the experimental fast reactor JOYO to investigate the role of gap size on pin swelling. Subsequently, nondestructive and destructive post irradiation examinations were carried out in hot cells. In particular, fission gas and swelling behavior during irradiation were investigated in detail (Tanaka et al., 2004). These two pins are listed as assessment cases in BISON for MN fuel. The L413 and L414 pins had the same rod design and similar irradiation condition with only the gap size and a slightly different position in the test reactor varying between the two.

Rod Design Specifications

The fuel was solid cylindrical pellets of MN positioned between insulator and reflective pellets in 15Cr-20Ni stainless steel cladding tubes. Table 1 lists the rod design specifications specifying if the value comes from a direct measurement or was unknown and had to be estimated or calculated.

Table 1: SP-1 Rod Geometry

Parameter	Value	Units	Source
Bonding	He		Tanaka et al. (2004)
Pin length	1486	mm	Unknown, fixed as in JOYO-B14 (Maeda et al., 2011; Ikusawa et al., 2017)
Clad material	15Cr-20Ni SS		Tanaka et al. (2004)
Clad OD	8.50	mm	Tanaka et al. (2004)
Clad ID	7.60	mm	Tanaka et al. (2004)
Clad thickness	0.45	mm	Tanaka et al. (2004)
Diametral gap - L413	0.32	mm	Tanaka et al. (2004)
Diametral gap - L414	0.17	mm	Tanaka et al. (2004)
Smear density - L413	77.8	%TD	Tanaka et al. (2004)
Smear density - L414	82.2	%TD	Tanaka et al. (2004)
Pellet diameter - L413	7.28	mm	Tanaka et al. (2004)
Pellet diameter - L414	7.43	mm	Tanaka et al. (2004)
Pellet height	~8	mm	Tanaka et al. (2004)
Fuel stack - L413	200.1	mm	Tanaka et al. (2004)
Fuel stack - L414	198.8	mm	Tanaka et al. (2004)
Bulk density - L413	84.8	%TD	Tanaka et al. (2004)
Bulk density - L414	86.0	%TD	Tanaka et al. (2004)
Fuel Composition
Pu/(U+Pu)	18.6	wt%	Tanaka et al. (2004)
U235-enrichment	19.39	wt%	Tanaka et al. (2004)
N/M ratio - L413	1.00	-	Tanaka et al. (2004)
N/M ratio - L414	1.01	-	Tanaka et al. (2004)
Top/bottom plug	4.8	mm	Unknown, fixed as in MTR-SNAP50
Bottom gap under pellet	375	mm	Estimated based on Fig. 4 in Tanaka et al. (2004)
Plenum height - L413	901.3	mm	Calculated (Pin length-Fuel stack-2*Top/bottom plug-Bottom gap under pellet)
Plenum height - L414	902.6	mm	Calculated (Pin length-Fuel stack-2*Top/bottom plug-Bottom gap under pellet)
Fill gas pressure	0.1	MPa	Unknown, fixed equal to what is used in JOYO-B14 (Maeda et al., 2011; Ikusawa et al., 2017)

Note that due to the currently limited information about the insulator and reflective pellets used in this experiment, they are currently not modeled in the BISON assessment cases.

Operating Conditions and Irradiation History

The actual power history for specific JOYO MK-II experiments is still being determined. Therefore, a simplified power history containing an initial ramp to power and hold for a given amount of time with a final power down is being used. The average burnup of the fuel at the end of the simulation is used as a check that the power history is reasonable. The parameters for the irradiation and temperature history are detailed in Table 2. Using an average linear heating rate of 70 kW/m, the final burnup reached in the BISON simulations is around 4.5 % FIMA (4.7 % FIMA for L413, and 4.4 % FIMA for L414).

The exact temperature history is also still being determined. In the meantime, the initial temperature is fixed to 298 K, and the temperature ramps up to the desired profile for the irradiation time before ramping down at the end of the simulation.

Table 2: SP-1 Operating Conditions

Parameter	Value	Units	Source
Fast neutron flux	$var element = document.getElementById("moose-equation-2916156b-9991-4f4d-88cb-2edf23c21e51");katex.render("3.2\\times 10^{15}", element, {displayMode:false,throwOnError:false});$	n cm $var element = document.getElementById("moose-equation-21ba0b34-054e-4dc1-9d94-57c6f2aee250");katex.render("^{-2}", element, {displayMode:false,throwOnError:false});$ s $var element = document.getElementById("moose-equation-cb1dd801-ac95-40af-b717-ac975ba44efe");katex.render("^{-1}", element, {displayMode:false,throwOnError:false});$	Aoyama et al. (2004)
Max linear heating rate	75	kW/m	Tanaka et al. (2004)
Average linear heating rate	70	kW/m	Tanaka et al. (2004)
Burnup	~4.3	% FIMA	Tanaka et al. (2004)
Irradiation duration	276	Equivalent full power days	Tanaka et al. (2004)
Inlet temperature	643.15	K	Nomoto et al. (1980) and Aoyama et al. (2004)
Outlet temperature	773.15	K	Aoyama et al. (2004)
Average cladding temperature	900	K	Estimated

Note that since the burnup [Material] block does not currently account for fuel enrichment, the full effect of the fuel enrichment in Pu and U-235 on burnup is not yet accounted for. This will need to be updated. Similarly, Tanaka et al. (2004) provides the linear heating rate as a function of burnup, which varies from 75 kW/m to below 65 kW/m. Currently, the linear heating rate is assumed to be fixed at 70 kW/m. This could also be updated once the burnup is updated.

Model Description

The L413 and L414 pins are modeled in BISON using a base input file titled JOYO_Pin_base.i (either with the full input file or using the action to create the necessary blocks), a file titled JOYO_Pin_options.i containing the information common to the three pins (e.g., rod design, irradiation conditions, etc.), and files containing the information specific to each pin, titled JOYO_Pin_options_L413.i, and JOYO_Pin_options_L414.i.

The specifications and conditions for all three pins are described below. Note that only the pins are being modeled, not the L4C4 compartment or the PFB090 fuel assembly.

Temperature Profile

Since the exact temperature profile on the surface of the cladding is unknown, it is assumed to follow a second degree polynomial $var element = document.getElementById("moose-equation-f84681c1-f2ec-4400-8e2d-42da6bb7420c");katex.render("T(x) = ax^2 + bx + c", element, {displayMode:false,throwOnError:false});$ with $var element = document.getElementById("moose-equation-cd1e5738-6e4e-4c86-84e3-80f49d87951a");katex.render("x", element, {displayMode:false,throwOnError:false});$ being the position along the cladding, and $var element = document.getElementById("moose-equation-9a3bd086-b14f-432b-8837-b40a7c139744");katex.render("a", element, {displayMode:false,throwOnError:false});$ , $var element = document.getElementById("moose-equation-9b4d2fee-9e79-4e77-b3c4-f3d2ec617712");katex.render("b", element, {displayMode:false,throwOnError:false});$ , and $var element = document.getElementById("moose-equation-fab8a36a-7147-40d0-bf50-51871625ae9b");katex.render("c", element, {displayMode:false,throwOnError:false});$ constants defined to reproduce the provided inlet, outlet, and average temperatures in Kelvins provided in Table 2, as shown in Figure 1. To define the temperature profile, the average cladding temperature is estimated as provided in Table 2.

Figure 1: Temperature profile used to model L413 and L414 with informed inlet and outlet temperatures.

Power Profile

The exact power profile for these tests is still unknown. For now, as for the modelization of the JOYO MK-II Core, the FFTF power profile shown in Figure 2 is being used (Karahan, 2009).

Figure 2: Power peaking factors for FFTF and used for MK-II cores (Karahan, 2009).

Pressure Profile

The coolant pressure is unknown for now. The coolant is made out of sodium, and the pressure is assumed to be equal to 15.1 MPa.

Geometry and Mesh

The 2D-RZ mesh for the assessment case is generated with the internal smeared pellet meshing capability in BISON FuelRPinMeshGenerator.

All of the dimensions and meshing details are contained in the [Mesh] block.

Material and Behavioral Models

The following material and behavioral models for the MN fuel were used:

MNElasticityTensor: Computes Young's modulus and Poisson's ratio for MN fuel
MNThermalExpansionEigenstrain: Computes an eigenstrain due to thermal expansion for MN fuel
MNCreepUpdate: Creep mechanical properties and deformation behavior for MN fuel
MNThermal: Calculates the thermal conductivity and specific heat for MN fuel
MNThermalExpansionEigenstrain: Calculates thermal expansion coefficient and isotropic expansion for MN fuel
MNVolumetricSwellingEigenstrain: Computes swelling due to solid and gaseous fission products for MN fuel

The following material and behavioral models are used for the 15Cr-20Ni stainless steel cladding. Note that due to the current lack of property data on 15Cr-20Ni stainless, the properties of SS316 are currently used:

SS316ElasticityTensor: Temperature-dependent Young's modulus and constant Poisson's ratio ( $var element = document.getElementById("moose-equation-207c9c40-9648-4273-9d73-2aaaa46fed93");katex.render("\\nu=0.31", element, {displayMode:false,throwOnError:false});$ )
SS316ThermalExpansionEigenstrain: Eigenstrain due to thermal expansion for Stainless Steel 316 using a function that describes the mean thermal expansion as a function of temperature
SS316CreepUpdate: Steady state creep as sum of thermal and irradiation creep following Altenbach and Gorash (2013) and Garner and Porter (1988)
SS316Thermal: Thermophysical material properties
To compute the density of SS316, a DerivativeParsedMaterial provides $var element = document.getElementById("moose-equation-2e5d6505-2a21-4e23-8bbf-7554c9bcabba");katex.render("\\rho=-4.454\\times 10^{-5}T^2-0.4297T+8089.4", element, {displayMode:false,throwOnError:false});$ in kg/m $var element = document.getElementById("moose-equation-4de4c397-7eda-44eb-b457-304d6bc1e665");katex.render("^3", element, {displayMode:false,throwOnError:false});$ , which is valid for T in Kelvin for 298.15 K $var element = document.getElementById("moose-equation-dac186db-ddce-4a09-a2d5-13bd7db718f4");katex.render("\\le", element, {displayMode:false,throwOnError:false});$ T $var element = document.getElementById("moose-equation-056bbcaf-1d0f-43a7-aca9-36fa86913522");katex.render("\\le", element, {displayMode:false,throwOnError:false});$ 1573.15 K (Mills, 2002)).

Note that thermal and mechanical contacts are modeled using mortar contact.

Input files

The input files for these assessment cases are located at bison/assessment/nitride/JOYO/J4C4/analysis.

To run the assessment cases, the input files and option files need to be combined into one by listing them in the command. For example, to run the assessment case for pin L413, one should list JOYO_Pin_options_L413.i JOYO_Pin_options.i JOYO_Pin_base.i, or JOYO_Pin_options_L413.i JOYO_Pin_options.i JOYO_Pin_base_action.i to use the action.

Results Comparison

The post-irradiation examinations (PIE) of the JOYO - L413 and JOYO - L414 pins provide the measurements listed in Table 3 and Table 4, respectively (Tanaka et al., 2004). The profilometry results provided in Tanaka et al. (2004) are reproduced in figure Figure 3. The profilometry data shown in figure Figure 3 is available in csv files titled JOYO_L413_profilometry_data_A-C.csv, JOYO_L413_profilometry_data_B-D.csv, JOYO_L413_profilometry_data_Average.csv, and JOYO_L414_profilometry_data_A-C.csv, JOYO_L414_profilometry_data_B-D.csv, JOYO_L414_profilometry_data_Average.csv.

Table 3: PIE data for JOYO - L413

Quantity	Measurements	Units	Source
FGR Xe	Unknown
FGR Kr	Unknown
FGR total	3.3	%	Tanaka et al. (2004)
Fuel swelling $var element = document.getElementById("moose-equation-baca4cc8-b23a-4ed4-89c5-05e4849feefd");katex.render("\\Delta", element, {displayMode:false,throwOnError:false});$ V/V $var element = document.getElementById("moose-equation-612ea834-6f6e-4ac4-89bc-f58e80c203af");katex.render("_0", element, {displayMode:false,throwOnError:false});$	7.4	%	Tanaka et al. (2004)
Max cladding strain $var element = document.getElementById("moose-equation-ee4829ad-eed9-4f3b-ba83-30446213a088");katex.render("\\Delta", element, {displayMode:false,throwOnError:false});$ D/D $var element = document.getElementById("moose-equation-2e82c6bf-0806-4cc0-b817-f7087c91623c");katex.render("_0", element, {displayMode:false,throwOnError:false});$	0.17	%	Tanaka et al. (2004)
Fuel density decrease	5.8	%	Tanaka et al. (2004)
Change in cladding length	Unknown
Open porosity	4.2	%	Tanaka et al. (2004)
Closed porosity	16.8	%	Tanaka et al. (2004)

Table 4: PIE data for JOYO - L414

Quantity	Measurements	Units	Source
FGR Xe	Unknown
FGR Kr	Unknown
FGR total	5.2	%	Tanaka et al. (2004)
Fuel swelling $var element = document.getElementById("moose-equation-4a497b06-ee17-43e0-ad14-b02d468bb61e");katex.render("\\Delta", element, {displayMode:false,throwOnError:false});$ V/V $var element = document.getElementById("moose-equation-fb080591-7962-46a0-b65d-5b4b8b5a9503");katex.render("_0", element, {displayMode:false,throwOnError:false});$	6.7	%	Tanaka et al. (2004)
Max cladding strain $var element = document.getElementById("moose-equation-b5063a02-774c-4b4c-a869-7e38913a95aa");katex.render("\\Delta", element, {displayMode:false,throwOnError:false});$ D/D $var element = document.getElementById("moose-equation-1cb3ca67-273c-4cf8-91b0-d6cf9c38b6b5");katex.render("_0", element, {displayMode:false,throwOnError:false});$	0.51	%	Tanaka et al. (2004)
Fuel density decrease	5.4	%	Tanaka et al. (2004)
Change in cladding length	Unknown
Open porosity	4.1	%	Tanaka et al. (2004)
Closed porosity	15.3	%	Tanaka et al. (2004)

Figure 3: Profilometry Results for L413 and L414 (Tanaka et al., 2004). A, B, C, and D are points on the outer diameter of the cladding positioned at 0, 90, 180, and 270 degrees, respectively.

The radial distribution of the area fraction of pores and the measured Xe content is also provided in Tanaka et al. (2004) for L414.

Discussion

The BISON simulation results have not yet been compared to the post-experiment examinations data.

References

Holm Altenbach and Yevgen Gorash. High-temperature inelastic behavior of the austenitic steel aisi type 316. In Advanced Materials Modelling for Structures, pages 17–30. Springer, 2013.

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Takafumi Aoyama, Takashi Sekine, and Shiro Tabuchi. Characterization of neutron field in the experimental fast reactor joyo for fuel and structural material irradiation test. Nuclear Engineering and Design, 228:21–34, 3 2004. doi:10.1016/J.NUCENGDES.2003.06.003.

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Aydin Karahan. Modeling of thermo-mechanical and irradiation behavior of metallic and oxide fuels for sodium fast reactors. PhD thesis, Massachusetts Institute of Technology, Jun 2009. URL: https://tinyurl.com/y72vqvbn.

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Overview
Test Description
Model Description
Input files
Results Comparison
Discussion
References