Accurate Predictions of Volatile Plutonium Thermodynamic Properties
Bibliographic record
Abstract
The ability to predict the nature and amounts of plutonium emissions in industrial accidents, such as in solvent fires at PUREX nuclear reprocessing facilities, is a key concern of nuclear safety agencies. In accident conditions and in the presence of oxygen and water vapor, plutonium is expected to form the three major volatile species PuO 2, PuO 3, and PuO 2 (OH) 2, for which the thermodynamic data necessary for predictions (enthalpies of formation and heat capacities) presently show either large uncertainties or are lacking. In this work we aim to alleviate such shortcomings by obtaining the aforementioned data via relativistic correlated electronic structure calculations employing the multi-state complete active space with second-order perturbation theory (MS-CASPT2) with a state-interaction RASSI spin–orbit coupling approach, which is able to describe the multireference character of the ground-state wave functions of PuO 3 and PuO 2 (OH 2 ). We benchmark this approach by comparing it to relativistic coupled cluster calculations for the ground, ionized, and excited states of PuO 2 . Our results allow us to predict enthalpies of formation Δ f H ⊖ (298.15 K) of PuO 2, PuO 3, and PuO 2 (OH) 2 to be −449.5 ± 8.8, −553.2 ± 27.5, and −1012.6 ± 38.1 kJ mol –1, respectively, which confirm the predominance of plutonium dioxide but also reveal the existence of plutonium trioxide in the gaseous phase under oxidative conditions, though the partial pressures of PuO 3 and PuO 2 (OH) 2 are nonetheless always rather low under a wet atmosphere. Our calculations also permit us to reassess prior results for PuO 2, establishing that the ground state of the PuO 2 molecule is mainly of 5 Σ g + character, as well as to confirm the experimental value for the adiabatic ionization energy of PuO 2 .
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.001 |
| 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 | 0.001 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.001 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 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 source (direct Gemma or distilled Codex), 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".