Comparison of silver, cesium, and strontium release predictions using PARFUME with results from the AGR-1 irradiation experiment

Abstract

The PARFUME (PARticle FUel ModEl) code was used to predict the release of fission products silver, cesium, and strontium from tristructural isotropic coated fuel particles and compacts during the first irradiation experiment (AGR-1) of the Advanced Gas Reactor Fuel Development and Qualification program. The PARFUME model for the AGR-1 experiment used the fuel compact volume average temperature for each of the 620 days of irradiation to calculate the release of silver, cesium, and strontium from a representative particle for a select number of AGR-1 compacts. Post-irradiation examination measurements provided data on release of these fission products from fuel compacts and fuel particles, and retention of silver in the compacts outside of the silicon carbide (SiC) layer. PARFUME-predicted fractional release of silver, cesium, and strontium was determined and compared to the PIE measurements. For silver, comparisons show a trend of over-prediction at low burnup and under-prediction at high burnup. PARFUME has limitations in the modeling of the temporal and spatial distributions of the temperature and burnup across the compacts, which affects the accuracy of its predictions. Nevertheless, the comparisons on silver release lie in the same order of magnitude. Results show an overall over-prediction of the fractional release of cesium by PARFUME. For particles with failed SiC layers, the over-prediction is by a factor of up to 3, corresponding to a potential over-estimation of the diffusivity in uranium oxycarbide (UCO) by a factor of up to 250. For intact particles, whose release is much lower, the over-prediction is by a factor of up to 100, which could be attributed to an overestimated diffusivity in SiC by about 40% on average. The release of strontium from intact particles is also over-predicted by PARFUME, which also points towards an overestimated diffusivity of strontium in either SiC or UCO, or possibly both. The measured strontium fractional release from intact particles varied considerably from compact to compact, making it difficult to assess the effective over-estimation of the diffusivities. Furthermore, the release of strontium from particles with failed SiC is difficult to observe experimentally due to the release from intact particles, preventing any conclusions to be made on the accuracy or validity of the PARFUME predictions and the modeled diffusivity of strontium in UCO.

Fission product inventory and burnup evaluation of the AGR-2 irradiation by gamma spectrometry

“…Destructive examination [14] and safety testing [15] are in progress on the AGR-2 compacts, and will provide additional information on silver retention. In addition, the silver retention of the fuel compacts has been compared to fuel performance models [16].…”

Fission Product Transport in TRISO Particles and Pebbles

“…The first of these, AGR-1, included PIE to characterize the release of silver, cesium, and strontium. The details of AGR-1 are documented elsewhere (see [13] and the references therein). AGR-2 was similar [42].…”

“…To compare experimentally measured release fractions of silver, we follow the approach in [13]. In particular, we analyzed the 17 compacts listed in Table 3 of that work and plotted the results in a manner similar to its Note that the calculation of silver release in this section (and of cesium and strontium) relies on effective fission yields and does not consider decay.…”

BISON TRISO Modeling Advancements and Validation to AGR-1 Data

“…where R is the universal gas constant. Values of D 0 and Q for silver, cesium, and strontium are given in Table 3.5 [34,35].…”

“…The first of these, AGR-1, included post-irradiation examination (PIE) of the release of silver, cesium, and strontium. The details of AGR-1 are documented elsewhere (see [34] and the references therein), so only a brief orientation is given here. The analysis procedure is as follows.…”