Physics Assessment of the Impact of Modified End Pellets on Axial Power Peaking for Advanced/Nonconventional Uranium-Based Fuels in Pressure Tube Heavy Water Reactors
Bibliographic record
Abstract
Abstract Axial power peaking is a phenomenon with safety implications for pressure tube heavy water reactors (PT-HWRs). Since PT-HWRs use shorter (∼50 cm) bundles, there are small axial gaps, which expose the ends of the fuel elements to more neutron flux, and therefore results in higher power density levels occurring in the ends of the fuel elements. Power peaking has the potential to cause fuel damage and failure, if the local linear element rating (LER) exceeds 57 kW/m, and may be of greater concern for advanced, higher burnup fuels. Earlier studies have been done using three-dimensional mcnp models of a PT-HWR fuel bundle with slightly enriched uranium; they demonstrated that ThO2 could be used to reduce axial power peaking in fresh fuel. This result was achieved by replacing some of the UO2 with ThO2 in the last 3 cm of fuel pellets at each end of a fuel bundle. This study extends the previous work by performing 3D neutronics and burnup calculations using serpent, to evaluate how power peaking changes with burnup. In addition, alternative dilution materials (such as depleted UO2, ZrO2, and MgO) were also evaluated. It was found that axial power peaking can be significantly reduced by using the ThO2 dilution material for fresh fuel, while ZrO2 or MgO are even more effective at higher burnup levels. Dilution materials have little impact (less than 2%) on the exit burnup of the fuel.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".