Development and dual validation on a transient inspired by KRUSTY of the sNDM diffusion method for easy, MC-based, core analysis. (January 2023)

• Record Type: Journal Article
• Authors: Nuttin, A.; Capellan, N.; David, S.; Doligez, X.; Méplan, O.
• Is Part Of: Annals of nuclear energy. Volume 180(2023)
• Publication Date: 2023-01
• Subjects: Spatial kinetics -- Diffusion theory -- Finite volume method -- MCNP neutron tallies -- Lumped thermal model -- Heat pipe cooled reactor; Nuclear energy -- Periodicals; Nuclear engineering -- Periodicals; 621.4805
• DOI: 10.1016/j.anucene.2022.109469
• Languages: English
• ISSNs: 0306-4549

Abstract

Highlights: NDM is a simple well-validated finite difference method for diffusion calculations. sNDM has been developed as a finite volume extension to cores with few large cells. In addition to usual diffusion data, MCNP provides sNDM with essential corrections. Adjusted node positions and surface factors from MCNP allow sNDM accurate currents. sNDM is validated on a KRUSTY-like lumped thermal transient against point kinetics. Abstract: Successfully validated on a typical CANDU LOCA and fruitfully applied to safety assessment studies of high conversion water-cooled cores, the Nodal Drift Method (NDM) has recently been generalized. The so-called "super NDM" (sNDM) methodological product offers an even simpler way to core analysis, basically by feeding the diffusion approximation with specific adjustments from Monte Carlo calculations. The test case chosen for validation has been inspired by the KRUSTY experiment of a fast small UMo core driven by its radial BeO reflector, and is defined by a MCNP model of a few cells. The selected heat-up transient consists in a slow reactivity insertion, from nominal steady-state, of 120 pcm in 600 s. Fuel power and average temperature increase from about 2200 W and 1000 K up to 2500 W and 1100 K at the new equilibrium reached one hour later. Using an axisymmetric structured mesh, large nodal volumes and appropriate MCNP tallies, sNDM manages to reproduce the exact same initial equilibrium as its Monte Carlo reference. Lightly completed for reactivity insertion and thermal feedback, sNDM is doubly validated by comparison to both known-valid point kinetics over the whole transient and MCNP neutron balance for two remarkable states. Such a simplifying and promising approach, making full use of MC-based diffusion, is methodologically discussed. Further development effort and small core design applications are finally proposed.