PSO-Based Adaptive NMPC for Uranium Extraction-Scrubbing Operation in Spent Nuclear Fuel Treatment Process

TL;DR

The paper tackles adaptive control of the nonlinear, high-dimensional uranium extraction-scrubbing step in PUREX, using NMPC coupled with NMHE and solved online via an enhanced PSO in a software-in-the-loop setting with the validated PAREX simulator. By leveraging PAREX as a black-box predictor and estimator, the approach accommodates limited online measurements and hard process constraints while handling disturbances. The key contributions include a PSO-augmented NMPC/MHE framework with constraint-handling extensions, a controller-selector to reduce computation, and SIL validation that demonstrates effective setpoint tracking and constraint satisfaction. The work advances practical adaptive control for nuclear chemical processes, offering a scalable, derivative-free optimization pathway feasible for complex, real-time operation. The results highlight potential gains in safety, reliability, and efficiency of PUREX solvent management and waste minimization through robust online control.

Abstract

This paper addresses the particularities of adaptive optimal control of the uranium extraction-scrubbing operation in the PUREX process. The process dynamics are nonlinear, high dimensional, and have limited online measurements. In addition, analysis and developments are based on a qualified simulation program called PAREX, which was validated with laboratory and industrial data. The control objective is to stabilize the process at a desired solvent saturation level, guaranteeing constraints and handling disturbances. The developed control strategy relies on optimization-based methods for computing control inputs and estimates, i.e., Nonlinear Model Predictive Control (NMPC) and Nonlinear Moving Horizon Estimation (NMHE). The designs of these two associated algorithms are tailored for this process's particular dynamics and are implemented through an enhanced Particle Swarm Optimization (PSO) to guarantee constraint satisfaction. Software-in-the-loop simulations using PAREX show that the designed control scheme effectively satisfies control objectives and guarantees constraints during operation.

Figures (8)

• Figure 1: Extraction - fission products (FP) scrubbing step (vo2023).
• Figure 2: Steady state relationship of feed solution flow rates and uranium concentrations.
• Figure 3: Proposed MPC-MHE control strategy using the PAREX simulator in the loop.
• Figure 4: Particle swarm re-initialization to guarantee constraints at $t=4$ h in case (I), Sec. \ref{['sec:case_studies']}.
• Figure 5: Simulation results for nominal PSO-based NMPC with $\bS=\bR=0.001/u_\text{set} \bI$.