A Kolmogorov-Arnold Surrogate Model for Chemical Equilibria: Application to Solid Solutions

TL;DR

This paper introduces a Kolmogorov-Arnold neural network surrogate model that significantly improves accuracy and efficiency over traditional models for simulating chemical equilibria in geochemical systems, aiding in nuclear waste disposal safety.

Contribution

It is the first to apply Kolmogorov-Arnold networks to co-precipitation with radionuclide incorporation in complex solid solutions, demonstrating superior performance over multilayer perceptrons.

Findings

Outperforms multilayer perceptrons with 62% and 59% error reduction.

Maintains median prediction errors near 1e-3 for complex solid solutions.

Enables faster reactive transport simulations for nuclear waste safety assessment.

Abstract

The computational cost of geochemical solvers is a challenging matter. For reactive transport simulations, where chemical calculations are performed up to billions of times, it is crucial to reduce the total computational time. Existing publications have explored various machine-learning approaches to determine the most effective data-driven surrogate model. In particular, multilayer perceptrons are widely employed due to their ability to recognize nonlinear relationships. In this work, we focus on the recent Kolmogorov-Arnold networks, where learnable spline-based functions replace classical fixed activation functions. This architecture has achieved higher accuracy with fewer trainable parameters and has become increasingly popular for solving partial differential equations. First, we train a surrogate model based on an existing cement system benchmark. Then, we move to an application case for the geological disposal of nuclear waste, i.e., the determination of radionuclide-bearing solids solubilities. To the best of our knowledge, this work is the first to investigate co-precipitation with radionuclide incorporation using data-driven surrogate models, considering increasing levels of thermodynamic complexity from simple mechanical mixtures to non-ideal solid solutions of binary (Ba,Ra)SO$_4$ and ternary (Sr,Ba,Ra)SO$_4$ systems. On the cement benchmark, we demonstrate that the Kolmogorov-Arnold architecture outperforms multilayer perceptrons in both absolute and relative error metrics, reducing them by 62% and 59%, respectively. On the binary and ternary radium solid solution models, Kolmogorov-Arnold networks maintain median prediction errors near $1\times10^{-3}$. This is the first step toward employing surrogate models to speed up reactive transport simulations and optimize the safety assessment of deep geological waste repositories.