AGR-1

note:More Information Available

Material presented here is a subset of information in Hales et al. (2021). See the JNM paper for more information.

AGR-1 Assessment Cases

AGR-1 is the first of a series of irradiation tests sponsored by DOE's Advanced Gas Reactor program. The experiment involved six capsules with three stacks of four compacts in each for a total of 72 compacts. Each compact consisted of TRISO particles in a matrix. Details of AGR-1 can be found in Collin et al. (2015). Many of the compacts were analyzed with Bison. Results were compared to results from PARFUME and to experimental data (PIE). The general analysis procedure followed with Bison matches that in Collin et al. (2015).

The mesh for the simulation was generated internally using TRISO1DFiveLayerMeshGenerator. Second order elements were used. Biasing was used to concentrate elements at the kernel/buffer interface.

Surface temperature, power level, fast neutron flux, and experiment duration were extracted from a data file prepared by the Advanced Gas Reactor program and placed in separate data files, one for each compact. Using a script, each compact in a list was run one at a time, reading data from the appropriate data file, with results subsequently placed in plots using a Python script.

The analysis is done in several sections: irradiation test, silver; irradiation test, cesium and strontium with no failed particles; irradiation test, cesium and strontium with failed particles; safety test, silver, cesium and strontium with no failed particles; irradiation test, silver with the effect of microstructure on the Ag diffusion coefficient in the silicon carbide (SiC) layer accounted for; safety test, silver, cesium, and strontium with no failed particles; safety test, silver, cesium, and strontium with failed particles; safety test, krypton with failed particles. A subset of results is given below. In all cases, it is assumed that any fission product that diffuses outside the particle will diffuse outside the compact. This is a valid assumption given the large diffusion coefficients associated with the matrix material.

The release fraction is the quantity of interest. It is defined as the ratio of the amount of a fission product released to the total amount produced: $var element = document.getElementById("moose-equation-0de1c0f9-1275-4f88-8d9c-f37480b9b64e");katex.render(" f=r/p", element, {displayMode:true,throwOnError:false});$

In some cases, particles in the compact failed. Failed particles are assumed to have a high diffusion coefficient in the SiC layer (10 $var element = document.getElementById("moose-equation-105c0de1-78f3-4f26-b174-cccd83102a5f");katex.render("^{-6}", element, {displayMode:false,throwOnError:false});$ m $var element = document.getElementById("moose-equation-d87c2ac4-7fd7-4a79-94d1-169195bbb225");katex.render("^2", element, {displayMode:false,throwOnError:false});$ /s). The number of failed particles in each compact was determined in post-irradiation examination. For compacts with failed particles, the release fraction is: $var element = document.getElementById("moose-equation-d76364fa-199f-44a5-90b6-35e6c102adc2");katex.render(" f_{net} = \\frac{f_i(n-n_f) + f_fn_f}{n}", element, {displayMode:true,throwOnError:false});$ where $var element = document.getElementById("moose-equation-3c0a9d9a-ded8-488a-8255-f7b2a7b8b01c");katex.render("f_{net}", element, {displayMode:false,throwOnError:false});$ is the overall release fraction, $var element = document.getElementById("moose-equation-32b547bc-2703-4a2a-bd21-d08d36179cd2");katex.render("f_i", element, {displayMode:false,throwOnError:false});$ is the release fraction from the intact particle, $var element = document.getElementById("moose-equation-e02e1742-228d-41b2-bd03-c87eac2f7cdb");katex.render("f_f", element, {displayMode:false,throwOnError:false});$ is the release fraction from the failed particle, $var element = document.getElementById("moose-equation-95a3a562-3df7-4397-93df-569ad8940c74");katex.render("n", element, {displayMode:false,throwOnError:false});$ is the total number of particles in the compact, and $var element = document.getElementById("moose-equation-3858e347-fee5-40fc-a848-dd634accdbe4");katex.render("n_f", element, {displayMode:false,throwOnError:false});$ is the number of failed particles in the compact.

The compacts can be differenciated according to the variant: B - baseline, V1 - variant 1, V2 - variant 2, and V3 - variant 3 (Demkowicz, 2015; Collin, 2015).

It was necessary to include the effect of uranium contamination in order to obtain reasonable results for the fractional release of krypton. Uranium contamination is trace amounts of uranium found outside the kernel. This uranium is picked up at the exterior of the SiC or in the outer pyrolytic carbon (OPyC) during manufacturing. For modeling purposes, we assume the uranium contamination is uniformly distributed in the OPyC layer. Although this additional fission product generation is more significant for Krypton, it is added for a species (Ag, Cs, Kr, and Sr). The values are provided in Skerjanc (2020) and Hales et al. (2022); they are different for UO2 and UCO kernels.

Irradiation Test, Silver Release, No Failed Particles

The release fraction for eighteen compacts as computed by Bison and PARFUME and as measured experimentally is shown in Figure 1. It can be seen that Bison and PARFUME results are very similar. Note: there is no PARFUME or CORRECTED_PIE data for compacts: 4-1-1 and 4-4-2 (Demkowicz et al., 2015; Demkowicz, 2015).

Figure 1: Comparison of measured and computed silver release fractions for eighteen compacts.

An multiscale modeling effort to account for the effect of microstructure on the Ag diffusion coefficient in the SiC layer improves the predictions for most compacts. Since Ag diffuses faster along the SiC grain boundary than in the bulk, the microstructure of the SiC layer affects Ag release. This effect has been quantified in Jiang et al. (2021) and Simon et al. (2022) using the microstructure data published in Gerczak et al. (2016) and the improved results are shown in Figure 2.

Figure 2: Comparison of measured and computed silver release fractions for seventeen compacts, with Bison accounting for microstructural effects on Ag diffusion in SiC.

Recently, the irradiation-enhance diffusivity has been quantified at the lower lengthscale, and a new temperature, microstructure, and irradiation-dependent effective Ag diffusivity has been developed (Aagesen et al., 2022). The Ag release predictions accounting for irradiation-enhanced diffusivity are shown in Figure 3.

Figure 3: Comparison of measured and computed silver release fractions for seventeen compacts, with Bison accounting for microstructural and irradiation effects on Ag diffusion in SiC.

Irradiation Test, Silver Release, Failed Particles

The release fraction of silver for three compacts with failed particles as computed by Bison and PARFUME and as measured experimentally is shown in Figure 4 (Demkowicz et al., 2015).

Figure 4: Comparison of measured and computed silver release fractions for three compacts with failed particles. The numbers $var element = document.getElementById("moose-equation-aa2ccfb6-2f0b-405a-b5b4-e8e8edf64a7d");katex.render("xf", element, {displayMode:false,throwOnError:false});$ provide the number of failed particles for each compact.

Irradiation Test, Cesium and Strontium Release, No Failed Particles

The release fraction of cesium and strontium for six compacts as computed by Bison and PARFUME and as measured experimentally is shown in Figure 5 and Figure 6. These six compacts had no failed particles (Hales et al., 2021; Collin et al., 2015; Demkowicz et al., 2015).

Figure 5: Comparison of measured and computed cesium release fractions for six compacts.

Figure 6: Comparison of measured and computed strontium release fractions for six compacts.

Irradiation Test, Cesium and Strontium Release, Failed Particles

The release fraction of cesium and strontium for three compacts with failed particles as computed by Bison and PARFUME and as measured experimentally is shown in Figure 7, Figure 8. Failed particles result in very little additional strontium release due to the fact that little strontium diffuses outside the fuel kernel (Hales et al., 2021; Collin et al., 2015; Demkowicz et al., 2015).

Figure 7: Comparison of measured and computed cesium release fractions for three compacts with failed particles. The numbers $var element = document.getElementById("moose-equation-d9df02c5-6773-49b5-9f52-e4e2af28ad09");katex.render("xf", element, {displayMode:false,throwOnError:false});$ provide the number of failed particles for each compact.

Figure 8: Comparison of measured and computed strontium release fractions for three compacts with failed particles. The numbers $var element = document.getElementById("moose-equation-428d8146-c191-4c50-9388-d7a565bb2c81");katex.render("xf", element, {displayMode:false,throwOnError:false});$ provide the number of failed particles for each compact.

Safety Test, Silver, Cesium and Stronium Release, No Failed Particles

The release fraction of silver, cesium and strontium for six compacts with no failed particles as computed by Bison and PARFUME and as measured experimentally is shown in Figure 9, Figure 10, and Figure 11 respectively. Experimental measurement and PARFUME results are taken from Collin et al. (2016), Collin (2014), and NDMAS (2023).

Figure 9: Comparison of measured and computed silver release fractions for six compacts with intact particles.

Figure 10: Comparison of measured and computed cesium release fractions for six compacts with intact particles.

Figure 11: Comparison of measured and computed strontium release fractions for six compacts with intact particles.

Safety Test, Silver, Cesium and Stronium Release, Failed Particles

The release fraction of silver, cesium and strontium for nine compacts with failed particles as computed by Bison and PARFUME and as measured experimentally is shown in Figure 12, Figure 13, and Figure 14 respectively (NDMAS, 2023).

Figure 12: Comparison of measured and computed silver release fractions for nine compacts with failed particles. The numbers $var element = document.getElementById("moose-equation-44d226aa-a22e-4c1f-8e50-b7471967c9fb");katex.render("xf", element, {displayMode:false,throwOnError:false});$ provide the number of failed particles for each compact.

Figure 13: Comparison of measured and computed cesium release fractions for nine compacts with failed particles. The numbers $var element = document.getElementById("moose-equation-a27268c8-8283-43df-bebf-93d8543e38bc");katex.render("xf", element, {displayMode:false,throwOnError:false});$ provide the number of failed particles for each compact.

Figure 14: Comparison of measured and computed strontium release fractions for nine compacts with failed particles. The numbers $var element = document.getElementById("moose-equation-6790dec3-397c-4210-816d-013ecf3063a2");katex.render("xf", element, {displayMode:false,throwOnError:false});$ provide the number of failed particles for each compact.

Safety Test, Krypton Release, No Failed Particles

The release fraction of krypton for two compacts with no failed particles as computed by Bison and as measured experimentally is shown in Figure 15 (Demkowicz, 2015; NDMAS, 2023).

Figure 15: Comparison of measured and computed krypton release fractions for two compacts with no failed particles.

Safety Test, Krypton Release, Failed Particles

The release fraction of krypton for seven compacts with failed particles as computed by Bison and PARFUME and as measured experimentally is shown in Figure 16 (Demkowicz, 2015; Demkowicz et al., 2020; NDMAS, 2023). Note: For compact 6-4-1, there is no PARFUME data.

Figure 16: Comparison of measured and computed krypton release fractions for seven compacts with failed particles. The numbers $var element = document.getElementById("moose-equation-16124978-a1ad-489d-a5b1-64d8b6f70b2b");katex.render("xf", element, {displayMode:false,throwOnError:false});$ provide the number of failed particles for each compact.

Summary

The AGR-1 experiment provided data on silver, cesium, and strontium diffusion in TRISO fuel. Bison's predictions of that diffusion compare favorably with predictions from PARFUME. Improved diffusion coefficients would improve comparisons to experimental data.

References

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@techreport{INLRPT-22-02769,
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    institution = "Idaho National Laboratory",
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@TECHREPORT{INLEXT-14-31976,
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    year = "2014",
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}

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@TECHREPORT{INLEXT-10-18097,
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@article{COLLIN2015426,
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}

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}

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@TECHREPORT{INLEXT-20-60147-Rev000,
    author = "Demkowicz, Paul A and Collin, Blaise P. and Ueta, Shohei and Aihara, Jun and Kim, young Min",
    title = "{G}eneration {IV} {B}enchmarking of {TRISO} {F}uel {P}erformance {M}odels {U}nder {A}ccident {C}onditions {F}inal {R}eport",
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    url = "https://www.osti.gov/biblio/1821122",
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}

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@TECHREPORT{INLEXT-21-64633,
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    title = "Atomistic and mesoscale simulations to determine effective diffusion coefficient of fission products in {SiC}",
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    institution = "Idaho National Laboratory"
}

P.-C.A. Simon, L. K. Aagesen, C. Jiang, W. Jiang, and J.-H. Ke. Mechanistic calculation of the effective silver diffusion coefficient in polycrystalline silicon carbide: application to silver release in AGR-1 TRISO particles. Journal of Nuclear Materials, 563:153669, 2022. doi:10.1016/j.jnucmat.2022.153669.

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@TechReport{rpt:skerjanc:2020,
    author = "Skerjanc, William F.",
    institution = "Idaho National Laboratory",
    number = "INL/EXT 20 59448 (Rev.0)",
    title = "Comparison of Fission Product Release Predictions Using {PARFUME} With Results From the {AGR}-2 Irradiation Experiment",
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    year = "2020"
}

Idaho National Laboratory's NDMAS. Nuclear Data Management and Analysis System database - PIE safety test compact. https://esas.inl.gov/links/resources/report?uri=, 2023.

@MISC{SAS-AGR-web-page,
    author = "{N}ational {L}aboratory's {NDMAS}, Idaho",
    title = "{N}uclear {D}ata {M}anagement and {A}nalysis {S}ystem database - {PIE} Safety Test Compact",
    year = "2023",
    howpublished = "https://esas.inl.gov/links/resources/report?uri=\%2Freports\%2Freports\%2Fd5a75911-dc5e-4949-b6a8-98c21c694d3d\&page=vi3520"
}

AGR - 1 Assessment Cases
Summary
References