Assessment of DRACCAR predictive capabilities during bundle reflood under low-power conditions: A systematic uncertainty and sensitivity analysis
Year: 2026
Type: article
Abstract: Accurately predicting the thermal evolution of fuel rods during a Loss-of-Coolant Accident (LOCA) is essential for nuclear safety assessments, yet nonlinear coupling among reflood phenomena remains a major source of predictive uncertainty. This work performs a systematic uncertainty propagation and sensitivity analysis using DRACCAR, applied to two low-power, low-injection-velocity tests (9178, 9271) from the OECD/NEA RBHT Phase II benchmark. By propagating uncertainties in thirteen thermal–hydraulic closure laws and five experimental boundary conditions, the methodology quantifies the resulting uncertainty bands on the local maximum cladding temperature and quench time evaluated at each instrumented thermocouple location, and identifies, via Partial Rank Correlation Coefficients, the closures most responsible for experimental discrepancies. These demanding conditions are exploited as a diagnostic framework to identify which closure laws control the predictive response of the code. Results show that this discrepancy is primarily driven by three closures: post-CHF interfacial friction, steam-droplet interfacial heat transfer, and steam-to-wall convection. Increasing interfacial coupling systematically reduces the error, whereas intensifying steam-to-wall convection amplifies it, suggesting that enhanced steam-to-wall heat transfer disproportionately heats the steam core without cooling the cladding at the limiting axial locations. Rod power emerges as the single most influential parameter, with a PRCC reaching 0.90 against the cladding temperature error metric despite its narrow experimental uncertainty range. These results indicate that, beyond refining the dominant closure laws identified here, the extreme sensitivity to rod power reflects an intrinsic difficulty of resolving the multiphase flow finely under very-low-power conditions.
Source: Nuclear Engineering and Design
Authors: J.E. Luna Valencia, T. Glantz
Institution: Autorité de sûreté nucléaire et de radioprotection
Language: English
Subfield: Nuclear Energy and Engineering
Field: Energy
Domain: Physical Sciences
Open Access status: hybrid
Estimated APC paid: $2,710
OpenAlex ID: W7212294502