Tightly Coupled Adjoint-Based Perturbation Theory for Dynamics and Heat Transfer Multiphysics for Nuclear Transients

Nuclear engineering uncertainty quantification for modeling and simulation has historically focused on first-order perturbation theory–based approaches to rapidly generate sensitivity and similarity coefficients for the effective multiplication factor to assess the accuracy of nuclear data, guide criticality experiment design, and propagate uncertainty effects. This work extends these efforts from the steady-state to the transient regime with the Coupled Adjoint Perturbation Theory for dynAmIcs and heat traNsfer (CAPTAIN) framework. Building on previous verification work of the CAPTAIN methodology using single physics, this work couples the reactor dynamics and heat conduction to verify the accuracy of the CAPTAIN framework on a tightly coupled transient with temperature feedback for the reactivity insertion, effective delayed neutron fraction, temperature reactivity coefficient, decay constant, change in temperature, density, specific heat capacity, and power density. Tightly coupled power, delayed neutron precursor, and temperature sensitivity coefficients are generated for all of these inputs with respect to time. The sensitivity and similarity coefficients computed using CAPTAIN can be leveraged to rapidly quantify uncertainty for coupled multiphysics nuclear transients, guide experiment design to target largest uncertainties, calibrate uncertain nuclear data and physics parameters, and increase confidence in nuclear data for performing transient simulations.