Novel Neutron Noise Unfolding Methods and Applications for Anomaly Detection in 2D HTTR Core

This paper introduces new neutron noise unfolding method based on Green’s function called the greedy method. Neutron noise unfolding methods are the methods used to determine the magnitude, location, energy, and frequency of neutron noise sources. The challenge of neutron noise unfolding is that neutron noise is not known at all positions and neutron energy. It is only known at the detector positions. The greedy method iterates Green’s function to find the Green’s function matrix and the local minimum of the residual. This results in several valid solutions to the noise sources. The correct solution is the one that requires the least number of Green’s function combinations to minimize the residual. The method is compared with the scanning method, which is the standard method. The scanning method minimizes the ratio of neutron noise and the Green’s function at two different detector locations. This is done iteratively for all combinations of two detectors. Both methods are applied to unfold noise sources in 2D HTTR core. The noise sources are defined as absorber of variable strength (AVS) type noise sources. The results indicate that the scanning method shows satisfactory results but is limited to only one AVS-type source. For the greedy method, the results show that the greedy method is able to unfold multiple neutron noise sources simultaneously.

Recommended citation: Ardiansyah, H., & Kozłowski, T. (2026). Novel Neutron Noise Unfolding Methods and Applications for Anomaly Detection in 2D HTTR Core. Proceeding of PHYSOR 2026. The International Conference on Physics of Reactors (PHYSOR) 2026. https://doi.org/10.5281/ZENODO.20803920